Physics Letters B 800 (2020) 135069
Contents lists available atScienceDirect
Physics
Letters
B
www.elsevier.com/locate/physletb
Searches
for
lepton-flavour-violating
decays
of
the
Higgs
boson
in
√
s
=
13 TeV pp collisions
with
the
ATLAS
detector
.TheATLASCollaboration
a r t i c l e i n f o a b s t ra c t
Articlehistory: Received13July2019
Receivedinrevisedform27August2019 Accepted13September2019
Availableonline4November2019 Editor:M.Doser
This Letter presents directsearches forlepton flavour violationin Higgs bosondecays, H→eτ and
H→μτ,performed with the ATLASdetector at the LHC. The searches are based on adata sample
of proton–proton collisions ata centre-of-mass energy √s=13 TeV, corresponding to an integrated
luminosityof36.1 fb−1.NosignificantexcessisobservedabovetheexpectedbackgroundfromStandard
Model processes. The observed (median expected) 95% confidence-level upper limits onthe
lepton-flavour-violatingbranchingratiosare0.47% (0.34−+00..1310%)and0.28% (0.37+−00..1410%)forH→eτandH→μτ, respectively.
©2019TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense
(http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3.
1. Introduction
The search for processes beyond the Standard Model (SM) is one of the main goals of the Large Hadron Collider (LHC) pro-gramme at CERN. A possible sign of such processes is lepton flavour violation (LFV) in decays of the Higgs boson [1,2]. Many beyond-SMtheories predict LFV decaysof the Higgsboson, such assupersymmetry [3,4], other modelswithmore thanone Higgs doublet [5,6], composite Higgs models [7], models with flavour symmetries [8] or warped extra dimensions [9–11] models and others [12,13].
In this Letter, searches for LFV decays of the Higgs boson,
H→eτ andH→μτ,attheLHCwiththeATLASexperimentare presented.Studiesare basedonproton–proton(pp)collisiondata recordedin 2015–2016 at a centre-of-mass energy √s=13 TeV. Thedatasetcorrespondstoanintegratedluminosityof36.1 fb−1.
PreviousATLASsearches [14,15] placedanupperlimitof1.04% (1.43%)onthe H→eτ (H→μτ)branchingratio(B)witha95% confidencelevel(CL)usingRun 1datacollectedat√s=8 TeV, cor-respondingtoanintegratedluminosityof20.3 fb−1.TheCMS Col-laborationrecentlyprovided95%CLupperlimitsonthese branch-ingratiosof0.61%and0.25%,respectively,usingdatacollectedat √
s=13 TeV,withanintegratedluminosityof35.9 fb−1 [16]. Thesearchespresentedhereinvolvebothleptonic(τ→ νν¯1)
andhadronic(τ→hadrons+ν)decaysof τ-leptons,denoted τ and τhad respectively. The dilepton final state τ only consid-erspairsofdifferent-flavourleptons.Same-flavourleptonpairsare
E-mailaddress:atlas.publications@cern.ch.
1 Unlessexplicitly mentionedotherwise, leptons(denotedbyor )referto
electronsormuons.
rejected due to the large lepton pair-production Drell-Yan back-ground.Twochannelsareconsideredforeachofthetwosearches:
eτμ and eτhad for the H→eτ search, μτe and μτhad for the
H→μτ search. The analysisisdesignedsuch that anypotential LFVsignal overlapbetweenthe H→eτ and H→μτ searchesis negligible.Manymethodsarereusedfromthemeasurementofthe Higgsbosoncross-sectionintheH→τ τ finalstate [17].
The ATLAS detector2 is described in Refs. [18–20]. It
con-sists of an inner tracking detector covering the range |η|<2.5, surrounded by a superconducting solenoid providing a 2T ax-ialmagneticfield,high-granularityelectromagnetic(|η|<3.2)and hadroniccalorimeters (|η|<4.9), anda muon spectrometer(MS) which coversthe range|η|<2.7 and includes fasttrigger cham-bers(|η|<2.4)andsuperconductingtoroidalmagnets.
2. Simulationsamples
SamplesofMonteCarlo(MC)simulatedeventsareusedto op-timizetheeventselection,andtomodelthesignal andseveralof the background processes. The samples were produced with the ATLAS simulationinfrastructure [21] usingthefull detector simu-lationperformedbythe Geant4 [22] toolkit.TheHiggsbosonmass wassettomH=125 GeV [23].The fourleadingHiggsboson pro-ductionmechanismsareconsidered:thegluon–gluonfusion(ggF), vector-boson fusion (VBF) and two associated production modes
2 ATLASuses aright-handedcoordinatesystemwith itsoriginat thenominal
interactionpointinthecentreofthedetectorandthez-axisalongthebeampipe. Theazimuthalangleφrunsaroundthebeampipe,thepseudorapidityisdefinedin termsofthepolarangleθasη≡ −ln tan(θ/2).Angulardistanceintheη–φspace isdefinedas R≡( η)2+ ( φ)2.
https://doi.org/10.1016/j.physletb.2019.135069
0370-2693/©2019TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3.
Table 1
Generatorsusedtodescribethesignalandbackgroundprocesses,partondistributionfunction(PDF)setsforthehardprocess,and modelsusedfor partonshowering, hadronizationandtheunderlyingevent(UEPS).Theordersofthetotalcross-sectionsusedtonormalizetheeventsarealsogiven.MoredetailsaregiveninRef. [17].
Process Generator PDF UEPS Cross-section order
ggF Powheg-Box v2 [26–30] NNLOPS [31] PDF4LHC15 [32] NNLO Pythia 8.212 [25] N3LO QCD + NLO EW [33–36]
VBF Powheg-Box v2 MiNLO [30] PDF4LHC15 NLO Pythia 8.212 ∼NNLO QCD + NLO EW [37–39]
W H, Z H Powheg-Box v2 MiNLO PDF4LHC15 NLO Pythia 8.212 NNLO QCD + NLO EW [40–42]
W/Z+jets Sherpa 2.2.1 [43] NNPDF30NNLO [44] Sherpa 2.2.1 [45] NNLO [46,47]
V V/Vγ∗ Sherpa 2.2.1 NNPDF30NNLO Sherpa 2.2.1 NNLO
tt¯ Powheg-Box v2 [26–28,48] CT10 [49] Pythia 6.428 [50] NNLO+NNLL [51]
Single t Powheg-Box v1 [52,53] CT10 Pythia 6.428 NLO [54–56]
(W H , Z H ),whiletheothersgivenegligiblecontributions andare ignored.Thecross-sectionsofallHiggsbosonproductionprocesses werenormalizedtotheSM predictions [24].TheLFVHiggsboson decaysaswell asthe H→τ τ andH→W W background decays weremodelledwithPythia 8 [25].Otherbackgroundprocesses in-volve electroweak productionof W/Z bosons via VBF, Drell–Yan productionof W/Z inassociation withjet(s) as well asdiboson, single top-quarkandtop-quarkpair(t¯t)production.TheMC gen-eratorsusedfortheSM H→τ τ cross-sectionmeasurement [17] werealsoemployedhereforallbackgroundcomponents.The gen-eratorsandpartonshower modelsusedtosimulatedifferent pro-cessesaresummarizedinTable1.
3. Objectreconstruction
The correct identification of H→ τ events requires recon-struction of severaldifferent objects (electrons, muons, and jets, includingthoseinitiatedbyhadronicdecaysof τ-leptons)andthe missing transverse momentum pmiss
T , whose magnitude is called
EmissT .
Electrons are reconstructed by matching tracks in the in-ner detector to clusteredenergy deposits in the electromagnetic calorimeter [57]. Loose likelihood-based identification [58], pT> 15 GeV and fiducial volume requirements (|η|<2.47, excluding thetransitionregionbetweenthebarrelandtheendcap calorime-ters 1.37<|η|<1.52) are applied.Medium identification, corre-sponding to an efficiencyof 87% at pT=20 GeV, is imposed for thebaselineelectronselection.
Muonsare identified by tracks reconstructed inthe inner de-tectorandmatchedto tracksintheMS. Looseidentification [59],
pT>10 GeV and |η|<2.5 requirements are applied. Medium identification(efficiencyof96.1%formuonswith pT>20 GeV) is imposedforthebaselinemuonselection.
Isolation criteriaexploiting calorimeter and track-based infor-mation are applied to both electrons and muons. The gradient working point is used, featuring an efficiency of 90% (99%) ob-tainedforleptonswithpT>25 GeV (60 GeV)originatingfromthe
Z→ process [58,59].
Jetsare reconstructed using the anti-kt algorithm [60] as im-plemented by the FastJet [61] package.The algorithm is applied to topologicalclustersof calorimetercells [62] with aradius pa-rameter R=0.4. Only jets with pT>20 GeV and |η|<4.5 are considered.Jetsfromother pp interactionsinthesameand neigh-bouringbunch crossings(pile-up)are suppressedusingjet vertex tagger(JVT) algorithms [63,64]. Jetscontaining b-hadrons (b-jets) areidentified by theMV2c20algorithm [65,66] in thecentral re-gion (|η|<2.4). A working point corresponding to 85% average efficiencydetermined forb-jets int¯t simulatedeventsis chosen, rejectionfactorsare2.8and28againstc-jetsandlight-flavourjets respectively.
The reconstruction of the object formed by the visible prod-uctsofthe τhad decay(τhad-vis)beginsfromjetsreconstructedby
the anti-kt jet algorithm with a radius parameter R=0.4. Infor-mation fromtheinnerdetectortracksassociatedwiththeenergy deposits in the calorimeteris incorporatedin the reconstruction. Only τhad-vis candidates with pT>20 GeV and|η|<2.5 are con-sidered.3 One or three associated tracks with an absolute total
charge |q|=1 are required. An identification algorithm [67,68] based on boosted decisiontrees (BDT) [69–71] is used to reject τhad-vis candidates arising from misidentification of jets or from decays of hadrons with b- or c-quark content. Unless otherwise indicated, atightidentification(ID)workingpoint isusedforthe τhad-vis, corresponding to an efficiency of 60% (45%) for 1-prong (3-prong)candidates.Jetscorresponding toidentified τhad-vis can-didates are removed from the jet collection. The τhad-vis candi-dates withonetrackoverlappingwithanelectroncandidatewith high ID score,as determined by a multivariate (MVA) approach, are rejected. Leptonic τ-decays are reconstructed as electrons or muons.
Events considered in the analysis are triggered with single-electron or single-muon triggers. The pT thresholds depend on theisolationrequirementanddata-takingperiod [72,73].The low-est trigger thresholds correspond to 25−27 GeV (electrons) and 21−27 GeV (muons).
4. Eventselectionandcategorization
Events selected in the τ channel contain exactly one elec-tronandonemuonofopposite-sign(OS)charges.Similarlyinthe τhad channel, alepton anda τhad-vis ofOScharges arerequired, andevents withmorethan one baselinelepton are rejected. The selection criteriaaresummarizedinTable2fortheanalysis cate-goriesaswell asthecontrolregions(CRs),whicharedescribedin Section5.
Intheτ channel,1 and2denotetheleadingand sublead-ing lepton in pT,respectively. Events wheretheleading lepton is anelectron(muon)areusedinthesearchforH→eτμ (H→μτe). A requirement on the dilepton invariant mass, equal to the in-variantmassoftheleptonandthevisible τ-decayproducts,mvis, reducesbackgroundswithtopquarks,andthecriterionappliedto the track-to-cluster pT ratioofthe electronreducesthe Z→μμ background wherea muon deposits a large amountof energyin theelectromagneticcalorimeterandismisidentifiedasanelectron in the μτe channel. The contribution fromthe H→τ τ decayis reducedbytheasymmetricpT selectionofthetwoleptons.
In the τhad channel, the criterion based on the azimuthal separations of lepton–EmissT and τhad-vis–EmissT ,
i=,τhad-viscos φ (i,E
miss
T ), reduces the W + jets background whereas therequirementon| η(, τhad-vis)|reducesbackgrounds withmisidentified τhad-viscandidates.
Forbothchannelsofeachsearch,ab-vetorequirementreduces the single-top-quarkandt¯t backgrounds.Eventsare further
The ATLAS Collaboration / Physics Letters B 800 (2020) 135069 3
Table 2
Baselineeventselectionandfurthercategorizationfortheτ andτhadchannels.Thesamecriteriaarealso
usedforthecontrolregion(CR)definitionsintheτ channel(Section5),butonerequirementofthebaseline selectionisinvertedtoachieveorthogonaleventselection.ThereisnoCRintheτhadchannel.
Selection τ τhad
Baseline
exactly 1e and 1μ, OS exactly 1and 1τhad-vis, OS
p1 T >45 GeV pT>27.3 GeV p2 T >15 GeV p τhad-vis T >25 GeV,|ητhad-vis| <2.4
30 GeV<mvis<150 GeV
i=,τhad-vis
cos φ(i,Emiss T ) >−0.35
pe
T(track)/peT(cluster) <1.2 (μτeonly) | η(,τhad-vis)| <2
b-veto (for jets with pT>25 GeV and|η| <2.4)
VBF Baseline ≥2 jets, pj1 T>40 GeV, p j2 T>30 GeV | η(j1,j2)| >3, m(j1,j2) >400 GeV − pτhad-vis T >45 GeV Non-VBF
Baseline plus fail VBF categorization mT(1,EmissT ) >50 GeV − mT(2,EmissT ) <40 GeV − | φ(2,EmissT )| <1.0 − pτT/p 1 T >0.5 −
Top-quark CR inverted b-veto:
VBF and non-VBF ≥1 b-tagged jet (pT>25 GeV and|η| <2.4)
Z→τ τCR inverted p1
T requirement:
VBF and non-VBF 35 GeV<p1
T <45 GeV
gorizedintoVBF(withafocusontheVBFproductionoftheHiggs boson)andnon-VBFcategories. TheVBFselectionisbasedonthe kinematics ofthe two jets withthe highest pT,where j1 andj2 denotetheleadingandsubleadingjetinpT,respectively.The vari-ablesm(j1,j2) and η(j1,j2) stand forthe invariant mass and η separationofthesetwojets.Thenon-VBFcategorycontainsevents failingtheVBFselection.Inthedileptonchannel,additional selec-tioncriteriaareappliedtofurtherrejectbackgroundeventsinthis category.ThesecriteriaarealsolistedinTable2,wheremT stands forthe transversemass4 ofthetwo objectslisted inparentheses, and pτT represents the magnitude of the vector sum of p2
T and
EmissT .Therequirementon pτT/p1
T reducesthebackgroundarising fromjetsmisidentifiedasleptons.TheVBFandnon-VBFcategories ineachoftheτ andτhad channelsgiveriseto foursignal re-gionsineachsearch.
TheanalysisexploitsBDTalgorithmstoenhancethesignal sep-arationfrom thebackground inthe individual searches,channels andcategories.Thecomponentsofthefour-momentaofthe analy-sisobjectsaswellasderivedeventvariables(e.g.invariantmasses andangular separations) are the input variables ofthe BDT dis-criminant. Correlations between these input variables have been carefullychecked,highly correlatedvariables have beenremoved and the remaining ones are ranked according to their discrimi-nation power [74,75]. The list of variables isthen optimized, re-movingthelowest-rankedvariableswithmarginalcontributionto the sensitivity. The final list of variables is presented in Table 3 foreachchannelandcategory.TheinvariantmassoftheHiggs bo-sonreconstructedundertheH→ τ decayhypothesisexhibitsthe highestsignal-to-backgroundseparationpowerandithelpsto dis-tinguishLFVsignalfromH→τ τ andH→W W backgrounds.For theτ channeltheinvariantmassisreconstructedwiththeMMC algorithm [76] and isdenoted bymMMC; forthe τhad channel it isreconstructedwiththe collinearapproximation [76] andis de-notedbymcoll.The analysisCRsare used tovalidate the levelof
4 Thetransversemassoftwoobjectsisdefinedasm
T=
2pT 1pT 2(1−cos φ),
wherepT iaretheindividualtransversemomentaand φistheanglebetweenthe
twoobjectsintheazimuthalplane.
agreement between data and simulated distributions of the BDT scoreandinputvariables,aswellastheircorrelations.
5. Backgroundmodelling
Themostsignificantbackgroundsinthesearcharefromevents with Z→τ τ decaysorwith(singleorpair-produced)topquarks, especiallyintheτ channel,aswellasfromeventswith misiden-tified objects, which are estimatedusing data-driven (d.d.) tech-niques.Therelativecontributionfrommisidentified objectstothe total background yield is 5–25% in the τ channel and 25–45% in the τhad channel, depending on the search andthe analysis category. The shapes of distributions fromthe Z→τ τ and top-quark (single-top-quark and tt)¯ processes are modelled by sim-ulation in both the τ and τhad decay channels. In the τ channel,the relativecontributionsof Z→τ τ andtop-quark pro-duction processes are20–35% and20–55%, respectively; the top-quark background dominates in the VBF category. In the τhad channel, the top-quark background fraction is 1–10%, while the
Z →τ τ process contributes to 45–55% of the total background. The individual contributionsare listed inTables 4and 5. Smaller backgroundcomponentsare alsomodelledby simulationandare grouped together: Z →μμ, diboson production, H→τ τ and
H→W W .
GoodmodellingofthebackgroundisdemonstratedinFig.1for a selectionof importantBDT input variables.Detailsof the back-groundestimationtechniquesaregivenbelow.
5.1. τchannel
TwosetsofCRs,asdefinedinTable2,areusedtoconstrainthe normalizationof Z→τ τ andtop-quarkbackgroundcomponents. These CRs inherit their definitions from the corresponding anal-ysiscategory but invertone requirementto ensure orthogonality with the nominal selection. The normalization factors are deter-mined during the statistical analysis by fitting the event yields in all signal andcontrol regions simultaneously. Foreach search, separate Z →τ τ normalizationfactors are usedfor theVBF and non-VBF categories. In the case of the top-quark background, in
Table 3
BDTinputvariablesusedintheanalysis.Foreachchannelandcategory,usedinputvariablesaremarkedwithHR (indicatingthefivevariableswiththehighestrank)orabullet.Analogousvariablesbetweenthetwochannelsare listedonthesameline.
τ τhad
Variable VBF non-VBF Variable VBF non-VBF
mMMC HR HR mcoll HR HR p1 T • • p T • HR p2 T HR HR p τhad-vis T • HR R(1, 2) HR • R(,τhad-vis) • • mT(1,EmissT ) • HR mT(,EmissT ) HR •
mT(2,EmissT ) HR • mT(τhad-vis,EmissT ) HR HR
φ(1,EmissT ) • • φ(,E miss
T ) HR •
φ(2,EmissT ) HR φ(τhad-vis,EmissT ) •
m(j1,j2) • m(j1,j2) • η(j1,j2) HR η(j1,j2) • pτ T/p 1 T HR i=,τhad-vis cos φ(i,Emiss T ) • • EmissT HR • mvis HR η(,τhad-vis) • η • ητhad-vis • φ • φτhad-vis • φ(Emiss T ) • Table 4
Eventyieldsandpredictionsasdeterminedbythebackground-onlyfitindifferentsignalregionsoftheH→eτ analy-sis.Uncertaintiesincludeboththestatisticalandsystematiccontributions.“Other”containsdiboson,Z→ ,H→τ τ
andH→W W backgroundprocesses.Fortheeτhad channelthe“ Z→ee (d.d.)”componentcorrespondstoelectrons
misidentifiedasτhad-vis.Thiscontributionissummedwith“Other”sincetherearefeweventsintheVBFcategory.The
uncertaintyofthetotalbackgroundincludesallcorrelationsbetweenchannels.Thenormalizationsoftop-quark(τ channelonly)and Z→τ τ backgroundcomponentsaredeterminedbythefit,whiletheexpectedsignaleventyields aregivenforB(H→eτ)=1%.
eτμnon-VBF eτμVBF eτhadnon-VBF eτhadVBF
Signal 379±31 19.8±2.7 1180±110 25±4 Z→τ τ 2470±230 221±34 73 800±1900 290±40 Top-quark 1640±140 490±40 1580±190 56±12 Mis-identified 1330±250 73±33 74 400±1600 140±50 Z→ee (d.d.) 15 900±1800 82±13 Other 1700±80 220±15 2960±200 Total background 7130±100 1003±33 168 700±1000 570±40 Data 7128 992 168 883 572 Table 5
Eventyieldsandpredictionsasdetermined bythe background-onlyfit indifferentsignalregionsofthe H→μτ
analysis.Uncertaintiesincludeboththestatisticalandsystematiccontributions.“Other”containsdiboson,Z→ ,H→ τ τ and H→W W backgroundprocesses.Theuncertaintyofthetotalbackgroundincludesallcorrelationsbetween channels.Thenormalizationsoftop-quark(τchannelonly)andZ→τ τ backgroundcomponentsaredeterminedby thefit,whiletheexpectedsignaleventyieldsaregivenforB(H→μτ)=1%.
μτenon-VBF μτeVBF μτhadnon-VBF μτhadVBF
Signal 287±23 14.6±1.9 1200±120 25±5 Z→τ τ 1860±130 144±26 96 100±2000 274±33 Top quark 1260±130 390±34 1620±210 51±10 Misidentified 1340±210 41±21 63 900±1600 149±33 Other 1180±140 168±18 23 000±1000 104±15 Total background 5640±100 743±29 184 500±1200 580±30 Data 5664 723 184 508 583
whichleadingjetsareproducedatalowerorderofthe perturba-tiveexpansionofthescatteringprocess,acombinednormalization factoracrossthetwocategoriesisusedintheτ channel.
Top-quark CRs are almost exclusively composed of top-quark backgrounds:thepurityis95%acrossbothsearchesandcategories,
with tt process¯ accounting for more than 90% of the top-quark
backgrounds.The Z→τ τ CRsachieved apurity of ∼80% inthe non-VBFcategories, whilea lower purityof ∼60%is observed in
theVBFcategories.Thecontributionsofallotherbackground com-ponents are normalized to their SM predictions when the likeli-hoodfit(Section7)isapplied.
The shape and normalization of diboson and Z→μμ back-grounddistributions are validatedwithdata indedicatedregions where their contributions are enhanced. The latter process only contributessizeablyinthe μτe channel,whereitrepresentsupto 10%ofthetotalbackground.
The ATLAS Collaboration / Physics Letters B 800 (2020) 135069 5
Fig. 1. Distributions ofrepresentativekinematicquantitiesfordifferentsearches,channelsandcategories,beforethe fitasdescribedinSection7isapplied.Toprow: transversemassmT(1,EmissT )(eτμnon-VBF),collinearmassmcoll(eτhadnon-VBF)andmMMC(eτμVBF).Bottomrow:mMMC(μτenon-VBF),muonpT(μτhadnon-VBF)and
mcoll(μτhadVBF).Entrieswithvaluesthatwouldexceedthex-axisrangeareincludedinthelastbinofeachdistribution.Thesizeofthecombinedstatistical,experimental
andtheoreticaluncertaintiesinthebackgroundisindicatedbythehatchedbands.TheH→eτ(H→μτ)signaloverlaidintop(bottom)plotsassumesB(H→ τ)=1% andisenhancedbyafactor10.Inthedata/backgroundpredictionratioplots,pointsoutsidethedisplayedy-axisrangeareshownbyarrows.
AnothersourceofbackgroundcomesfromW+jets, top-quark andmulti-jetevents,wherejetsaremisidentifiedasleptons.This background is estimated directly from OS data events where an invertedisolation requirementis imposed onthe subleading lep-ton [17]. Normalization factors are applied to correct forthe in-vertedisolationrequirement.Thenormalizationfactorsarederived inadedicatedregionwheretheleptonsarerequiredtohave same-sign (SS) charges. Additional corrections are made by reweight-ing the MC distributions of φ (1,ETmiss) and φ (2,EmissT ) to dataintheSSregion,whichimprovesthemodellingofazimuthal angles between leptons and the EmissT direction as well as the modelling of mT(2,EmissT ). A similar improvement is observed in the nominal OS region. In most of the cases, the misidenti-fiedjet mimics the lepton of lower pT, 2, while the fractionof events where both leptons are misidentified varies between 2% to 8% across categories. The systematic uncertainties of the es-timation of the misidentified lepton background include contri-butions from closure tests in SS and OS regions enriched with misidentified leptons, from the correctionsmade to the φ dis-tributions, andfrom the composition ofthe misidentified lepton background.
5.2. τhadchannel
The main background contributions come from the Z →τ τ process andevents whereeither a jet oran electron is misiden-tifiedas τhad-vis.TheshapeoftheZ→τ τ backgrounddistribution is modelled by simulation, and the corresponding normalization factors are determined from the simultaneous fit of the event yieldsinallsignalandcontrolregions.The Z→τ τ normalization factorsarefullycorrelatedwiththoseoftheτ channel,ineach VBF and non-VBF category. Top-quark production represents less than 1% of thetotal background inthe τhad channel and is de-terminedbysimulation,includingitsnormalization,whichiskept fixedinthefit.
The main contributions to jets misidentified as τhad-vis come frommulti-jeteventsandW -bosonproductioninassociationwith jets, anda fake-factormethod is used to estimate the contribu-tionofeachcomponentseparately.Afakefactorisdefinedasthe ratioofthe numberofeventswherethe highest-pT jetis identi-fied asa tight τhad-vis candidate to the numberof events where the highest-pT jet failsto satisfy this τ-ID criterion but satisfies a loosercriterion. The procedure,including systematic uncertain-ties,isdescribedinRef. [17].Sinceadifferent τ-IDworkingpoint
isconsideredinthisanalysis,fakefactorsarere-derivedasa func-tionof pTandtrackmultiplicityofthe τhad-vis candidate.
Electrons misidentified as τhad-vis,denoted by “ Z→ee (d.d.)” inthefollowingfigures andtables, representanother background component in the eτhad channel, with a contribution about five timessmallerthan thatofjetsmisidentifiedas τhad-vis.Whilethe rate of electrons misidentified as 3-prong τhad-vis makes a neg-ligible contribution and is modelled by simulation, the rate of electrons misidentified as 1-prong τhad-vis is determined with a fake-factormethod.Thistime,thefakefactorisdefinedastheratio ofthenumberofeventswithtight τ-ID tothenumberofevents withanti-identified τhad-vis (sucha candidate satisfies all criteria but the requirement on the high electron ID score is inverted). Thesefakefactorsarederived ina dedicated Z→ee enriched re-gion definedby |mvis−mZ|<5 GeV, mT(,EmissT )<40 GeV, and
mT(τhad-vis,EmissT )<60 GeV, where the τhad-vis candidate satis-fiesthe medium τ-ID(corresponding toan efficiencyof55% and 40%for1-prong and3-prongcandidates,respectively)butnotthe tight τ-IDcriterion toavoidoverlapwiththeτhad signal region. Thesefakefactorsare appliedtosignal-like eventswiththe anti-identified τhad-vis todeterminethebackgroundcontributioninthe categoriesoftheanalysis.Thesystematicuncertaintiesincludethe statistical uncertainty of the fake factors and account for looser τ-IDinthe Z→ee enrichedregionaswell asforthesubtraction ofthenotmisidentifiedcomponentsinthisregion.
6. Systematicuncertainties
Thesystematicuncertainties affectthe normalizationofsignal andbackground,and/ortheshapeoftheircorrespondingfinal dis-criminant distributions. Each source of systematic uncertainty is considered to be uncorrelated withthe other sources. The effect ofeachsystematicuncertaintyisfullyconsideredineachcategory, including control regions. Correlations of each systematic uncer-tainty are maintained across processes, channels, categories and regions.The sizeofthesystematicuncertainties andtheir impact onthefittedbranching ratioarediscussedinSection 7.Themain sourcesofsystematicuncertaintiesarerelatedtotheestimationof thebackgroundsoriginatingfrommis-identifiedleptons/jetsandto thejetenergyscaleuncertainties.
Experimental uncertainties include those originating fromthe reconstruction,identification,taggingandtriggeringefficiencies of allphysicsobjectsaswellastheirmomentumscaleandresolution. Theseinclude effectsfromleptons [57–59], τhad-vis [68],jets [63, 64,77] and EmissT [78].Uncertaintiesaffectingthekinematicsofthe physicsobjectsarepropagatedtotheBDTinputvariables.The cor-respondingshapeandnormalizationvariationsoftheBDT discrim-inantareconsideredinthestatisticalanalysis.Uncertaintiesofthe luminositymeasurement [79],pile-upmodellinganduncertainties specific tomis-identified backgroundestimationtechniques men-tionedinSection5areincluded.
The procedures to estimate the uncertainty of the Higgs bo-son productioncross-sectionsfollowtherecommendationsofthe LHC Higgs Cross-Section Working Group [80]. Theoretical uncer-tainties affectingthe ggF signal originate fromnine sources [24]. Twosources account for yielduncertainties, which are evaluated by an overall variation of all relevant scales and are correlated acrossall bins ofthe BDT discriminantdistribution [81]. Another twosourcesaccountformigrationuncertaintiesofzerotoonejet andonetoatleasttwojetsintheevent [81–83],twoforHiggs bo-son pTshapeuncertainties,oneforthetreatmentofthetop-quark mass inthe loop corrections, andtwo forthe acceptance uncer-tainties ofggF productioninthe VBF phase spacefromselecting exactly two and at least three jets, respectively [84,85]. For VBF and W H , Z H productioncross-sections, the uncertainties dueto
missinghigher-orderQCDcorrectionsareestimatedbyvaryingthe factorizationandrenormalizationscalesupanddownbyfactorsof two around thenominalscale. Forallsignal samples,PDF uncer-tainties areestimatedusing30eigenvectorvariationsandtwo αs variationsusingthedefaultPDFsetPDF4LHC15[32].Uncertainties related to the simulation of the underlying event, hadronization and parton shower are estimated by comparing the acceptances whenusingPythia 8.212 [25] orHerwig 7.0.3 [86,87].
Thesourcesofmodellinguncertaintiesconsideredforthe Z→
τ τ process are the same asin Ref. [17] and their effect on the eventmigrationsbetweencategoriesandontheshapeoftheBDT discriminant are considered, since the overall normalizations are determined from data in the statistical analysis. These system-atic uncertaintiesincludevariations ofPDF sets,factorizationand renormalization scales, CKKW matching [88], resummation scale andpartonshowermodelling.Theotherbackgroundprocessesare eithernormalizedusingdata(processeswithtop-quarksand mis-identifiedleptonsand τhad-viscandidates)ortheircross-section un-certainties havenegligibleimpact andthereforeare notincluded. The shape uncertainties of thesebackgrounds originate from ex-perimentaluncertaintiesonly.
7. Statisticalanalysis
The searches for H→eτ and H→μτ are treated indepen-dently.Foreachsearch,theanalysisexploitsthefoursignalregions andthetwocontrolregionsspecifiedinTable2.TheBDTscore dis-tributionsofallsignalregionsareanalysedtotestthepresenceof a signal, simultaneously withthe eventyields in control regions, which are included to constrain the normalizations of the ma-jorbackgroundsestimatedfromsimulation.Thestatisticalanalysis usesabinnedlikelihoodfunctionL(μ,θ ),constructedasaproduct ofPoissonprobabilitytermsoverallbinsconsideredinthesearch. Thisfunctiondependsontheparameter μ,definedasthe branch-ingratioB(H→ τ),andasetofnuisanceparametersθ that en-codetheeffectofsystematicuncertaintiesinthesignaland back-groundexpectations.Allnuisanceparametersare implementedin thelikelihoodfunctionasGaussianorlog-normalconstraints.The normalization factors ofthe single-top-quark andt¯t backgrounds
intheτ channelandofthe Z→τ τ backgroundcomponentare unconstrainedparametersofthefit.Estimatesoftheparametersof interestarecalculatedwiththeprofile-likelihood-ratioteststatistic ˜
qμ [89],andtheupperlimitsonthebranching ratiosarederived byusingqμ and˜ theCLSmethod [90].
The discriminantdistributionsafterthefitineachchannelare shown in Figs. 2 and 3. Good agreement between data and the background expectation is observed. The event yields after the background-onlyfitaresummarizedinTables4and5.Inthe non-VBF category, the yields in the τhad channel are larger than in theτ channelduetothelooserselectioncriteriadefinedforthe formerchannel(Section4).Table6showsasummaryofthe uncer-taintiesofB(H→ τ).Theuncertaintiesassociatedwith misiden-tified leptons and τhad-vis candidatedandthose relatedtothe jet energyscaleandresolutionexhibitthehighestimpactonthe best-fitbranchingratiosinbothsearches.Thecombinedimpactfromall systematicuncertaintiesandthedatastatisticsrangesfrom0.17% to0.19%.
8. Results
The best-fit branching ratios and upper limits are computed while assuming B(H→μτ)=0 for the H→eτ search and B(H→eτ)=0 fortheH→μτ search.Thebest-fitvaluesofthe LFV Higgs boson branching ratios are equal to (0.15+−0.180.17)% and (−0.22±0.19)% forthe H→eτ andH→μτ search,respectively.
The ATLAS Collaboration / Physics Letters B 800 (2020) 135069 7
Fig. 2. Distributions oftheBDTscoreafterthebackground+signalfitineachsignalregionoftheeτsearch,withtheLFVsignaloverlaid,normalizedwithB(H→eτ)=1% andenhancedbyafactor10 forvisibility.ThetopandbottomplotsdisplayeτμandeτhadBDTscoresrespectively,theleft(right)columncorrespondstothenon-VBF(VBF)
category.Thesizeofthecombinedstatistical,experimentalandtheoreticaluncertaintiesofthebackgroundisindicatedbythehatchedbands.Thebinningisshownasin thestatisticalanalysis.
Table 6
Summaryofthesystematicuncertaintiesandtheirimpactonthebest-fitvalueofBintheH→eτandH→μτsearches.The measuredvaluesareobtainedbythefittodata,whiletheexpectedvaluesaredeterminedbythefittoabackground-onlysample.
Source of uncertainty Impact onB(H→eτ)[%] Impact onB(H→μτ)[%]
Measured Expected Measured Expected
Electron +0.05/−0.05 +0.06/−0.06 +0.03/−0.03 +0.02/−0.02 Muon +0.04/−0.04 +0.04/−0.04 +0.10/−0.10 +0.08/−0.10 τhad-vis +0.02/−0.02 +0.02/−0.02 +0.04/−0.04 +0.04/−0.05 Jet +0.09/−0.08 +0.09/−0.09 +0.11/−0.12 +0.11/−0.12 Emiss T +0.02/−0.02 +0.02/−0.03 +0.05/−0.08 +0.03/−0.05 b-tag +0.02/−0.03 +0.03/−0.03 +0.01/−0.01 +0.01/−0.01 Mis-ID backg. (τ) +0.08/−0.07 +0.09/−0.08 +0.07/−0.07 +0.07/−0.07 Mis-ID backg. (τhad) +0.12/−0.11 +0.11/−0.12 +0.11/−0.11 +0.10/−0.10
Pile-up modelling +0.02/−0.01 +0.01/−0.01 +0.05/−0.03 +0.08/−0.06
Luminosity <0.01 <0.01 <0.01 <0.01
Background norm. +0.05/−0.04 +0.05/−0.03 +0.04/−0.02 +0.05/−0.03 Theor. uncert. (backg.) +0.04/−0.03 +0.04/−0.03 +0.08/−0.07 +0.09/−0.09 Theor. uncert. (signal) +0.01/−0.01 +0.01/−0.01 +0.04/−0.02 +0.02/−0.02 MC statistics +0.04/−0.04 +0.03/−0.03 +0.04/−0.04 +0.05/−0.04 Full systematic +0.17/−0.16 +0.17/−0.17 +0.18/−0.18 +0.19/−0.20 Data statistics +0.07/−0.07 +0.07/−0.07 +0.07/−0.07 +0.08/−0.08 Total +0.18/−0.17 +0.18/−0.18 +0.19/−0.19 +0.20/−0.21
Fig. 3. Distributions oftheBDTscoreafterthebackground+signalfitineachsignalregionoftheμτ search,withtheLFVsignaloverlaid,normalizedwithB(H→μτ)=1% andenhancedbyafactor10 forvisibility.ThetopandbottomplotsdisplayμτeandμτhadBDTscoresrespectively,theleft(right)columncorrespondstothenon-VBF(VBF)
category.Thesizeofthecombinedstatistical,experimentalandtheoreticaluncertaintiesofthebackgroundisindicatedbythehatchedbands.Thebinningisshownasin thestatisticalanalysis.Inthedata/backgroundpredictionratioplots,pointsoutsidethedisplayedy-axisrangeareshownbyarrows.
In the absence of a significant excess, upper limits on the LFV branching ratios are set for a Higgs boson with mH =125 GeV. The observed (median expected) 95% CL upper limits are 0.47% (0.34+−0.130.10%)and0.28% (0.37−+0.140.10%)fortheH→eτ andH→μτ searches,respectively.Theselimitsaresignificantlylowerthanthe correspondingRun 1limitsofRefs. [14,15].Thebreakdownof con-tributionsfromdifferentsignalregionsisshowninFig.4.
The branching ratio of the LFV Higgs boson decay is related tothenon-diagonalYukawacouplingmatrixelements [91] bythe formula |Yτ|2+ |Yτ|2= 8π mH B(H→ τ) 1−B(H→ τ) H(SM),
where H(SM)=4.07 MeV [92] standsfortheHiggsbosonwidth as predicted by the Standard Model. Thus, the observed lim-its on the branching ratio correspond to the following limits onthe couplingmatrix elements:|Yτe|2+ |Yeτ|2<0.0020,and
|Yτμ|2+ |Yμτ|2<0.0015.Fig.5showsthelimitsonthe individ-ualcouplingmatrixelementsYτandYτ togetherwiththelimits
fromtheATLASRun 1analysisandfrom τ→ γ searches [91,93].
9. Conclusions
Direct searches forthe decays H→eτ and H→μτ are per-formed with proton–protoncollisions recorded by theATLAS de-tector at the LHC corresponding to an integrated luminosity of 36.1 fb−1 ata centre-of-mass energyof √s=13 TeV. No signifi-cantexcessisobservedabovetheexpectedbackgroundfrom Stan-dardModelprocesses.Theobserved(expected)upperlimitsat95% confidencelevelonthe branchingratiosof H→eτ andH→μτ are 0.47% (0.34+−0.130.10%)and0.28% (0.37+−0.140.10%),respectively.These limitsaremorestringentbyafactorof2(5)thanthe correspond-ing limitsforthe H→eτ (H→μτ) decaydeterminedbyATLAS at√s=8 TeV.
Acknowledgements
We thank CERN forthe very successful operation ofthe LHC, as well asthe supportstaff fromour institutions withoutwhom ATLAScouldnotbeoperatedefficiently.
WeacknowledgethesupportofANPCyT,Argentina;YerPhI, Ar-menia; ARC, Australia; BMWFW and FWF, Austria; ANAS,
Azer-The ATLAS Collaboration / Physics Letters B 800 (2020) 135069 9
Fig. 4. Upper limitsat95%CLontheLFVbranchingratiosoftheHiggsboson,H→eτ(left)andH→μτ (right),indicatedbysolidanddashedlines.Best-fitvaluesofthe branchingratios(μˆ)arealsogiven,in%.ThelimitsarecomputedwhileassumingthateitherB(H→μτ)=0 (left)orB(H→eτ)=0 (right).First,theresultsofthefitsare shown,whenonlythedataofanindividualchannelorofanindividualcategoryareused;inthesecasesthesignalandcontrolregionsfromallotherchannels/categories areremovedfromthefit.Theseresultsarefinallycomparedwiththefullfitdisplayedinthelastrow.
Fig. 5. Upper limitsontheabsolutevalueofthecouplingsYτ andYτ togetherwiththelimitsfromtheATLASRun 1analysis(lightgreyline)andthemoststringent indirectlimitsfromτ→ γ searches(darkpurpleregion).Alsoindicatedarelimitscorrespondingtodifferentbranchingratios(0.01%,0.1%,1%,10% and50%)andthe naturalnesslimit(denotedn.l.)|Yτ Yτ|mτm
v2 [91] wherev isthevacuumexpectationvalueoftheHiggsfield.
baijan;SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI,Canada; CERN; CONICYT,Chile; CAS, MOSTandNSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic;DNRFandDNSRC,Denmark;IN2P3-CNRS,CEA-DRF/IRFU, France; SRNSFG, Georgia; BMBF, HGF, andMPG, Germany; GSRT, Greece;RGC,HongKong SAR,China;ISFandBenoziyo Center, Is-rael; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands;RCN, Norway;MNiSW andNCN, Poland;FCT, Portu-gal;MNE/IFA,Romania;MESofRussiaandNRCKI,Russian Feder-ation;JINR;MESTD,Serbia;MSSR,Slovakia;ARRSandMIZŠ, Slove-nia; DST/NRF, South Africa; MINECO, Spain;SRC and Wallenberg Foundation,Sweden;SERI,SNSF andCantonsofBernandGeneva, Switzerland;MOST,Taiwan; TAEK,Turkey;STFC,UnitedKingdom; DOE and NSF, United States of America. In addition, individual groupsandmembershavereceivedsupportfromBCKDF,CANARIE, CRCandComputeCanada,Canada;COST,ERC,ERDF,Horizon2020, andMarieSkłodowska-Curie Actions,European Union; Investisse-mentsd’AvenirLabexandIdex,ANR,France;DFGandAvH Foun-dation,Germany;Herakleitos,ThalesandAristeiaprogrammes co-financed by EU-ESF and the Greek NSRF, Greece; BSF-NSF and GIF,Israel;CERCAProgrammeGeneralitatdeCatalunya,Spain;The RoyalSocietyandLeverhulmeTrust,UnitedKingdom.
The crucial computingsupport from all WLCG partnersis ac-knowledged gratefully, in particular from CERN, the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Swe-den),CC-IN2P3(France),KIT/GridKA(Germany),INFN-CNAF(Italy), NL-T1(Netherlands),PIC(Spain),ASGC(Taiwan),RAL(UK)andBNL (USA),theTier-2facilitiesworldwideandlargenon-WLCGresource providers.Majorcontributorsofcomputingresourcesare listedin Ref. [94].
References
[1]ATLASCollaboration,Observationofanewparticleinthesearchforthe Stan-dardModelHiggsbosonwiththeATLASdetectorattheLHC,Phys.Lett.B716 (2012)1,arXiv:1207.7214 [hep-ex].
[2]CMSCollaboration,Observationofanewbosonatamassof125GeVwith theCMSexperimentattheLHC,Phys.Lett.B716(2012)30,arXiv:1207.7235 [hep-ex].
[3]M.Arana-Catania,E.Arganda,M.J.Herrero,Non-decouplingSUSYinLFVHiggs decays:awindowtonewphysicsattheLHC,J.HighEnergyPhys.1309(2013) 160,Erratum:J.HighEnergyPhys.1510(2015)192,arXiv:1304.3371 [hep-ph].
[4]A.Arhrib,Y.Cheng,O.C.Kong,Comprehensiveanalysisonleptonflavor violat-ingHiggsbosontoμ∓τ±decayinsupersymmetrywithout R parity, Phys.Rev. D87(2013)015025,arXiv:1210.8241 [hep-ph].
[5]J.Bjorken,S.Weinberg,Mechanismfornonconservationofmuonnumber,Phys. Rev.Lett.38(1977)622.
[6]J.L.Diaz-Cruz,J.Toscano,LeptonflavorviolatingdecaysofHiggsbosonsbeyond thestandardmodel,Phys.Rev.D62(2000)116005.
[7]K.Agashe,R.Contino,CompositeHiggs-mediatedflavor-changingneutral cur-rent,Phys.Rev.D80(2009)075016,arXiv:0906.1542 [hep-ph].
[8]H.Ishimori,etal.,Non-Abeliandiscretesymmetriesinparticlephysics,Prog. Theor.Phys.Suppl.183(2010)1,arXiv:1003.3552 [hep-th].
[9]G.Perez,L.Randall,Naturalneutrinomassesandmixingsfromwarped geom-etry,J.HighEnergyPhys.01(2009)077,arXiv:0805.4652 [hep-ph].
[10]A.Azatov,M.Toharia,L.Zhu,Higgsmediatedflavorchangingneutralcurrent inwarpedextradimensions,Phys.Rev.D80(2009)035016,arXiv:0906.1990 [hep-ph].
[11]M.E.Albrecht,M.Blanke,A.J.Buras,B.Duling,K.Gemmler,Electroweakand flavourstructureofawarpedextradimensionwithcustodialprotection,J.High EnergyPhys.09(2009)064,arXiv:0903.2415 [hep-ph].
[12]A.Goudelis,O.Lebedev,J.-h.Park,Higgs-inducedleptonflavorviolation,Phys. Lett.B707(2012)369,arXiv:1111.1715 [hep-ph].
[13]D.McKeen, M.Pospelov,A.Ritz,ModifiedHiggsbranchingratiosversusCP and leptonflavorviolation,Phys. Rev.D86(2012)113004,arXiv:1208.4597 [hep-ph].
[14]ATLASCollaboration,Searchforlepton-flavour-violating H→μτdecaysofthe HiggsbosonwiththeATLASdetector,J.HighEnergyPhys.11(2015)211,arXiv: 1508.03372 [hep-ex].
[15]ATLAS Collaboration, Searchfor lepton-flavour-violatingdecaysofthe Higgs and Z bosons withtheATLAS detector,Eur.Phys.J.C77(2017)70,arXiv: 1604.07730 [hep-ex].
[16]CMSCollaboration,SearchforleptonflavourviolatingdecaysoftheHiggs bo-sontoμτand eτinproton–protoncollisionsat√s=13 TeV,J.HighEnergy Phys.06(2018)001,arXiv:1712.07173 [hep-ex].
[17]ATLASCollaboration,Cross-sectionmeasurementsoftheHiggsbosondecaying toapairoftauleptonsinproton–protoncollisionsat√s=13 TeV withthe ATLASDetector,Phys.Rev.D99(2019)072001,arXiv:1811.08856 [hep-ex].
[18]ATLASCollaboration,TheATLASexperimentattheCERNlargehadroncollider, J.Instrum.3(2008)S08003.
[19] ATLASCollaboration,ATLASInsertableB-LayerTechnicalDesignReport, ATLAS-TDR-19,https://cds.cern.ch/record/1291633,2010;
ATLAS Insertable B-Layer Technical Design Report Addendum, ATLAS-TDR-19-ADD-1,https://cds.cern.ch/record/1451888,2012.
[20]B.Abbott,etal.,ProductionandintegrationoftheATLASinsertableB-Layer,J. Instrum.13(2018)T05008,arXiv:1803.00844 [physics.ins-det].
[21]ATLAS Collaboration,TheATLAS simulationinfrastructure,Eur.Phys.J. C70 (2010)823,arXiv:1005.4568 [physics.ins-det].
[22]S.Agostinelli,etal.,GEANT4Collaboration,GEANT4—asimulationtoolkit,Nucl. Instrum.Methods,Sect.A506(2003)250.
[23]ATLAS andCMSCollaborations, Combinedmeasurementofthe Higgsboson massin pp collisions at√s=7 and8 TeV withtheATLASandCMS experi-ments,Phys.Rev.Lett.114(2015)191803,arXiv:1503.07589 [hep-ex].
[24]D.deFlorian,etal.,LHCHiggsCrossSectionWorkingGroup,HandbookofLHC Higgscrosssections:4.DecipheringthenatureoftheHiggssector,arXiv:1610. 07922 [hep-ph],2017.
[25]T.Sjöstrand,etal.,AnintroductiontoPYTHIA8.2,Comput.Phys.Commun.191 (2015)159,arXiv:1410.3012 [hep-ph].
[26]P.Nason,AnewmethodforcombiningNLOQCDwithshowerMonteCarlo algorithms,J.HighEnergyPhys.11(2004)040,arXiv:hep-ph/0409146.
[27]S.Frixione,P.Nason,C.Oleari,MatchingNLOQCDcomputationswithparton showersimulations:thePOWHEGmethod,J.HighEnergyPhys.11(2007)070, arXiv:0709.2092 [hep-ph].
[28]S.Alioli,P.Nason,C.Oleari,E.Re,AgeneralframeworkforimplementingNLO calculationsinshowerMonteCarloprograms:thePOWHEGBOX,J.High En-ergyPhys.06(2010)043,arXiv:1002.2581 [hep-ph].
[29]E.Bagnaschi,G.Degrassi,P.Slavich,A.Vicini,Higgsproductionviagluonfusion inthePOWHEGapproachintheSMandintheMSSM,J.HighEnergyPhys.02 (2012)088,arXiv:1111.2854 [hep-ph].
[30]K.Hamilton,P.Nason,G.Zanderigh,Finitequark-masseffectsintheNNLOPS POWHEG+MiNLOHiggsgenerator,J.HighEnergyPhys.05(2015)140,arXiv: 1501.04637 [hep-ph].
[31]K.Hamilton,P.Nason,E.Re,G.Zanderighi,NNLOPSsimulationofHiggsboson production,J.HighEnergyPhys.10(2013)222,arXiv:1309.0017 [hep-ph].
[32]J.Butterworth,etal.,PDF4LHCrecommendationsforLHCRunII,J.Phys.G43 (2016)023001,arXiv:1510.03865 [hep-ph].
[33]C.Anastasiou,C.Duhr,F.Dulat,F.Herzog,B.Mistlberger,Higgsboson gluon-fusionproductioninQCDatthreeloops,Phys.Rev.Lett.114(2015)212001, arXiv:1503.06056 [hep-ph].
[34]C.Anastasiou,etal.,HighprecisiondeterminationofthegluonfusionHiggs bosoncross-sectionattheLHC,J.HighEnergyPhys.05(2016)058,arXiv:1602. 00695 [hep-ph].
[35]S. Actis,G. Passarino,C.Sturm, S. Uccirati,NLOelectroweak corrections to Higgsbosonproductionathadroncolliders,Phys.Lett.B670(2008)12,arXiv: 0809.1301 [hep-ph].
[36]C.Anastasiou,R.Boughezal,F.Petriello,MixedQCD-electroweakcorrectionsto Higgsbosonproductioningluonfusion,J.HighEnergyPhys.04(2009)003, arXiv:0811.3458 [hep-ph].
[37]M.Ciccolini,A.Denner,S.Dittmaier,Strongandelectroweakcorrectionstothe productionofaHiggsboson+2jetsviaweakinteractionsatthelargehadron collider,Phys.Rev.Lett.99(2007)161803,arXiv:0707.0381 [hep-ph].
[38]M.Ciccolini,A.Denner,S.Dittmaier,ElectroweakandQCDcorrectionstoHiggs productionviavector-bosonfusionattheLHC,Phys.Rev.D77(2008)013002, arXiv:0710.4749 [hep-ph].
[39]P.Bolzoni,F.Maltoni,S.-O.Moch,M.Zaro,Higgsbosonproductionvia vector-boson fusion at next-to-next-to-leading orderin QCD,Phys. Rev. Lett.105 (2010)011801,arXiv:1003.4451 [hep-ph].
[40]O. Brein, A. Djouadi, R. Harlander, NNLO QCD corrections to the Higgs-strahlungprocessesat hadroncolliders,Phys.Lett.B579(2004)149,arXiv: hep-ph/0307206.
[41]L. Altenkamp, S. Dittmaier, R.V. Harlander, H. Rzehak, T.J.E. Zirke, Gluon-inducedHiggs-strahlungatnext-to-leadingorderQCD,J.HighEnergyPhys.02 (2013)078,arXiv:1211.5015 [hep-ph].
[42]A.Denner,S.Dittmaier,S.Kallweit,A.Mück,Electroweakcorrectionsto Higgs-strahlungoffW/Zbosonsatthe Tevatronand theLHCwith Hawk,J.High EnergyPhys.03(2012)075,arXiv:1112.5142 [hep-ph].
[43]T.Gleisberg,etal.,EventgenerationwithSHERPA1.1,J.HighEnergyPhys.02 (2009)007,arXiv:0811.4622 [hep-ph].
[44]R.D.Ball,etal.,PartondistributionsfortheLHCRunII,J.HighEnergyPhys.04 (2015)040,arXiv:1410.8849 [hep-ph].
[45]S.Schumann,F.Krauss,ApartonshoweralgorithmbasedonCatani-Seymour dipolefactorisation,J.HighEnergyPhys.03(2008)038,arXiv:0709.1027 [hep -ph].
[46]K.Melnikov,F.Petriello,Electroweakgaugebosonproductionathadron collid-ersthroughO(α2
s),Phys.Rev.D74(2006)114017,arXiv:hep-ph/0609070.
[47]C.Anastasiou,L.J.Dixon,K.Melnikov,F.Petriello,HighprecisionQCDathadron colliders:electroweakgaugebosonrapiditydistributionsatNNLO,Phys.Rev.D 69(2004)094008,arXiv:hep-ph/0312266 [hep-ph].
[48]S.Alioli,S.-O.Moch,P.Uwer,Hadronictop-quarkpair-productionwithonejet andpartonshowering, J.HighEnergy Phys.01(2012)137,arXiv:1110.5251 [hep-ph].
[49]H.-L.Lai,etal.,Newpartondistributionsforcolliderphysics,Phys.Rev.D82 (2010)074024,arXiv:1007.2241 [hep-ph].
[50]T.Sjöstrand, S.Mrenna, P.Z.Skands,PYTHIA6.4physicsandmanual,J.High EnergyPhys.05(2006)026,arXiv:hep-ph/0603175.
[51]M.Czakon, A.Mitov, Top++: aprogramfor the calculation ofthe top-pair cross-sectionat hadroncolliders,Comput.Phys.Commun.185(2014)2930, arXiv:1112.5675 [hep-ph].
[52]S.Alioli,P.Nason,C.Oleari,E.Re,NLOsingle-topproductionmatched with showerinPOWHEG:s- andt-channelcontributions, J.HighEnergyPhys.09 (2009)111,arXiv:0907.4076 [hep-ph].
[53]E.Re,Single-topWt-channelproductionmatchedwithpartonshowersusing thePOWHEGmethod,Eur.Phys.J.C71(2011)1547,arXiv:1009.2450 [hep-ph].
[54]M.Aliev,etal.,HATHOR- HAdronicTopandHeavyquarkscrOsssection calcu-latoR,Comput.Phys.Commun.182(2011)1034,arXiv:1007.1327 [hep-ph].
[55]P.Kant,et al.,HATHORforsingletop-quarkproduction:updatedpredictions anduncertaintyestimatesforsingletop-quarkproductioninhadronic colli-sions,Comput.Phys.Commun.191(2015)74,arXiv:1406.4403 [hep-ph].
[56]N.Kidonakis,Two-loopsoftanomalousdimensionsforsingletopquark asso-ciatedproductionwitha W− or H−,Phys.Rev.D82(2010)054018,arXiv: 1005.4451 [hep-ph].
[57]ATLASCollaboration,ElectronandphotonenergycalibrationwiththeATLAS detector using2015–2016LHC proton–proton collisiondata, J. Instrum. 14 (2019)P03017,arXiv:1812.03848 [hep-ex].
[58]ATLASCollaboration,Electron reconstructionandidentificationinthe ATLAS experimentusingthe2015and2016LHCproton–protoncollisiondataat√s=
13 TeV,arXiv:1902.04655 [hep-ex],2019.
[59]ATLASCollaboration,MuonreconstructionperformanceoftheATLASdetector inproton–protoncollisiondataat√s=13 TeV,Eur.Phys.J.C76(2016)292, arXiv:1603.05598 [hep-ex].
[60]M.Cacciari,G.P.Salam,G.Soyez,Theanti-ktjetclusteringalgorithm,J.High
EnergyPhys.04(2008)063,arXiv:0802.1189 [hep-ph].
[61]M.Cacciari,G.P.Salam,G.Soyez,FastJetusermanual,Eur.Phys.J.C72(2012) 1896,arXiv:1111.6097 [hep-ph].
[62]ATLASCollaboration,TopologicalcellclusteringintheATLAScalorimetersand itsperformanceinLHCRun1,Eur.Phys.J.C77(2017)490,arXiv:1603.02934 [hep-ex].
[63] ATLASCollaboration,Taggingandsuppressionofpileupjetswiththe ATLAS detector,ATLAS-CONF-2014-018,https://cds.cern.ch/record/1700870,2014. [64]ATLASCollaboration,Identificationandrejectionofpile-upjetsathigh
pseu-dorapidity with the ATLAS detector, Eur. Phys. J. C 77 (2017) 580, arXiv: 1705.02211 [hep-ex],Erratum:Eur.Phys.J.C77(2017)712.
[65]ATLASCollaboration,Performanceof b-jet identificationintheATLAS experi-ment,J.Instrum.11(2016)P04008,arXiv:1512.01094 [hep-ex].
The ATLAS Collaboration / Physics Letters B 800 (2020) 135069 11
[66] ATLASCollaboration,OptimisationoftheATLASb-taggingperformanceforthe 2016 LHC Run, ATL-PHYS-PUB-2016-012, https://cds.cern.ch/record/2160731, 2016.
[67] ATLASCollaboration,Reconstruction, energycalibration,andidentificationof hadronicallydecayingtauleptonsintheATLASexperimentforRun-2ofthe LHC,ATL-PHYS-PUB-2015-045,https://cds.cern.ch/record/2064383,2015. [68] ATLASCollaboration,Measurementofthetauleptonreconstructionand
iden-tificationperformanceintheATLASexperimentusing pp collisionsat√s=
13 TeV,ATLAS-CONF-2017-029,https://cds.cern.ch/record/2261772,2017. [69]L.Breiman,J.Friedman,R.Olshen,C.Stone,ClassificationandRegressionTrees,
Chapman&Hall,1984,358pp.
[70]Y.Freund,R.E.Schapire,Adecision-theoreticgeneralizationofon-linelearning andanapplicationtoboosting,J.Comput.Syst.Sci.(ISSN 0022-0000)55(1997) 119.
[71]J.Friedman,Stochasticgradientboosting,Comput.Stat.DataAnal.38(2002) 367.
[72]ATLASCollaboration, PerformanceoftheATLAS triggersystemin2015,Eur. Phys.J.C77(2017)317,arXiv:1611.09661 [hep-ex].
[73] ATLASCollaboration, Triggermenu in2016,ATL-DAQ-PUB-2017-001,https:// cds.cern.ch/record/2242069,2017.
[74]A.Hoecker,etal.,TMVA- ToolkitforMultivariateDataAnalysis,arXiv:physics/ 0703039 [physics.data-an],2007.
[75] T.Chen,C.Guestrin,XGBoost:ascalabletreeboostingsystem,in:Proceedings ofthe 22ndACMSIGKDDInternationalConferenceon KnowledgeDiscovery andDataMining,2016,https://dl.acm.org/citation.cfm?doid=2939672.2939785. [76]A.Elagin,P.Murat,A.Pranko,A.Safonov,Anewmassreconstructiontechnique forresonancesdecayingtoτ τ,Nucl.Instrum.Methods,Sect.A654(2011)481, arXiv:1012.4686 [hep-ex].
[77]ATLASCollaboration,Jetenergyscalemeasurementsandtheirsystematic un-certaintiesinproton–protoncollisionsat√s=13 TeV withtheATLASdetector, Phys.Rev.D96(2017)072002,arXiv:1703.09665 [hep-ex].
[78]ATLAS Collaboration, Performance of missingtransverse momentum recon-structionwith the ATLAS detector usingproton–proton collisions at √s=
13 TeV,Eur.Phys.J.C78(2018)903,arXiv:1802.08168 [hep-ex].
[79] ATLASCollaboration,Luminositydeterminationinpp collisionsat√s=13 TeV usingtheATLASdetectorattheLHC,ATLAS-CONF-2019-021,https://cds.cern. ch/record/2677054,2019.
[80]S.Dittmaier,etal.,LHCHiggsCrossSectionWorkingGroup,HandbookofLHC Higgscrosssections:1.Inclusiveobservables,arXiv:1101.0593 [hep-ph],2011.
[81]W.Stewart,F.J.Tackmann,J.R.Walsh,S.Zuberi,Jet pT resummationinHiggs
production atNNLL+NNLO,Phys.Rev.D89(2014)054001,arXiv:1307.1808 [hep-ph].
[82]X.Liu,F.Petriello,ReducingtheoreticaluncertaintiesforexclusiveHiggs-boson plusone-jetproductionattheLHC,Phys.Rev.D87(2013)094027,arXiv:1303. 4405 [hep-ph].
[83]R. Boughezal,X. Liu, F.Petriello, F.J. Tackmann, J.R. Walsh, Combining re-summed Higgspredictionsacross jet bins,Phys. Rev.D89 (2014)074044, arXiv:1312.4535 [hep-ph].
[84]I.W. Stewart,F.J.Tackmann, Theoryuncertaintiesfor Higgs massand other searchesusingjetbins,Phys.Rev.D85(2012)034011,arXiv:1107.2117 [hep -ph].
[85]S. Gangal,F.J.Tackmann, Next-to-leading-orderuncertaintiesinHiggs+2jets fromgluonfusion,Phys.Rev.D87(2013)093008,arXiv:1302.5437 [hep-ph].
[86]M.Bähr,etal.,Herwig++physicsandmanual,Eur.Phys.J.C58(2008)639, arXiv:0803.0883 [hep-ph].
[87]J.Bellm,etal.,Herwig7.0/Herwig++3.0releasenote,Eur.Phys.J.C76(2016) 196,arXiv:1512.01178 [hep-ph].
[88]L.Lönnblad,S.Prestel,Matching tree-levelmatrix elementswithinterleaved showers,J.HighEnergyPhys.03(2012)019,arXiv:1109.4829 [hep-ph].
[89]G.Cowan,K.Cranmer,E.Gross,O.Vitells,Asymptoticformulaefor likelihood-based testsofnewphysics,Eur.Phys.J. C71(2011) 1554,arXiv:1007.1727 [physics.data-an],Erratum:Eur.Phys.J.C73(2013)2501.
[90]A.L. Read,Presentation ofsearch results:the C LS technique, J.Phys. G 28
(2002)2693.
[91]R.Harnik,J.Kopp,J.Zupan,FlavorviolatingHiggsdecays,J.HighEnergyPhys. 03(2013)026,arXiv:1209.1397 [hep-ph].
[92]LHCHiggsCrossSection WorkingGroup,HandbookofLHCHiggscross sec-tions:3.Higgsproperties,arXiv:1307.1347 [hep-ph],2013.
[93]B. Aubert,etal., BaBarCollaboration,Searches forleptonflavorviolationin the decaysτ±→e±γ andτ±→μ±γ,Phys.Rev.Lett.104(2010)021802, arXiv:0908.2381 [hep-ex].
[94] ATLAS Collaboration, ATLAS computing acknowledgements, ATL-GEN-PUB-2016-002,https://cds.cern.ch/record/2202407.
TheATLASCollaboration
G. Aad101,B. Abbott128, D.C. Abbott102,A. Abed Abud70a,70b,K. Abeling53, D.K. Abhayasinghe93, S.H. Abidi167, O.S. AbouZeid40,N.L. Abraham156,H. Abramowicz161,H. Abreu160,Y. Abulaiti6, B.S. Acharya66a,66b,m, B. Achkar53, S. Adachi163,L. Adam99,C. Adam Bourdarios5, L. Adamczyk83a, L. Adamek167, J. Adelman121,M. Adersberger114,A. Adiguzel12c,ag,S. Adorni54, T. Adye144,
A.A. Affolder146,Y. Afik160, C. Agapopoulou132, M.N. Agaras38,A. Aggarwal119, C. Agheorghiesei27c, J.A. Aguilar-Saavedra140f,140a,af, F. Ahmadov79,W.S. Ahmed103, X. Ai15a,G. Aielli73a,73b,S. Akatsuka85, T.P.A. Åkesson96, E. Akilli54, A.V. Akimov110,K. Al Khoury132, G.L. Alberghi23b,23a, J. Albert176,
M.J. Alconada Verzini88,S. Alderweireldt36, M. Aleksa36, I.N. Aleksandrov79,C. Alexa27b,
D. Alexandre19,T. Alexopoulos10, A. Alfonsi120,M. Alhroob128,B. Ali142, G. Alimonti68a,J. Alison37, S.P. Alkire148,C. Allaire132, B.M.M. Allbrooke156,B.W. Allen131,P.P. Allport21,A. Aloisio69a,69b,
A. Alonso40, F. Alonso88,C. Alpigiani148, A.A. Alshehri57,M. Alvarez Estevez98, D. Álvarez Piqueras174, M.G. Alviggi69a,69b, Y. Amaral Coutinho80b, A. Ambler103,L. Ambroz135,C. Amelung26,D. Amidei105, S.P. Amor Dos Santos140a,S. Amoroso46, C.S. Amrouche54,F. An78, C. Anastopoulos149,N. Andari145, T. Andeen11, C.F. Anders61b,J.K. Anders20, A. Andreazza68a,68b,V. Andrei61a,C.R. Anelli176,
S. Angelidakis38,A. Angerami39, A.V. Anisenkov122b,122a, A. Annovi71a,C. Antel61a,M.T. Anthony149, M. Antonelli51, D.J.A. Antrim171, F. Anulli72a,M. Aoki81, J.A. Aparisi Pozo174,L. Aperio Bella36, G. Arabidze106, J.P. Araque140a,V. Araujo Ferraz80b,R. Araujo Pereira80b,C. Arcangeletti51, A.T.H. Arce49, F.A. Arduh88,J-F. Arguin109,S. Argyropoulos77, J.-H. Arling46, A.J. Armbruster36, A. Armstrong171, O. Arnaez167, H. Arnold120, A. Artamonov111,∗,G. Artoni135, S. Artz99,S. Asai163, N. Asbah59,E.M. Asimakopoulou172,L. Asquith156, K. Assamagan29, R. Astalos28a, R.J. Atkin33a,
M. Atkinson173, N.B. Atlay19,H. Atmani132,K. Augsten142,G. Avolio36,R. Avramidou60a,M.K. Ayoub15a, A.M. Azoulay168b, G. Azuelos109,av,H. Bachacou145, K. Bachas67a,67b,M. Backes135, F. Backman45a,45b, P. Bagnaia72a,72b,M. Bahmani84,H. Bahrasemani152,A.J. Bailey174,V.R. Bailey173, J.T. Baines144, M. Bajic40,C. Bakalis10, O.K. Baker183, P.J. Bakker120, D. Bakshi Gupta8,S. Balaji157,
E.M. Baldin122b,122a,P. Balek180,F. Balli145, W.K. Balunas135, J. Balz99, E. Banas84, A. Bandyopadhyay24, Sw. Banerjee181,i, A.A.E. Bannoura182,L. Barak161, W.M. Barbe38,E.L. Barberio104, D. Barberis55b,55a,
M. Barbero101,T. Barillari115, M-S. Barisits36, J. Barkeloo131, T. Barklow153,R. Barnea160, S.L. Barnes60c, B.M. Barnett144,R.M. Barnett18,Z. Barnovska-Blenessy60a, A. Baroncelli60a,G. Barone29, A.J. Barr135, L. Barranco Navarro45a,45b,F. Barreiro98, J. Barreiro Guimarães da Costa15a,S. Barsov138,
R. Bartoldus153, G. Bartolini101,A.E. Barton89,P. Bartos28a,A. Basalaev46,A. Bassalat132,ao, R.L. Bates57, S. Batlamous35e,J.R. Batley32,B. Batool151,M. Battaglia146, M. Bauce72a,72b, F. Bauer145,K.T. Bauer171, H.S. Bawa31,k, J.B. Beacham49,T. Beau136,P.H. Beauchemin170, F. Becherer52, P. Bechtle24, H.C. Beck53, H.P. Beck20,q,K. Becker52, M. Becker99,C. Becot46,A. Beddall12d,A.J. Beddall12a,V.A. Bednyakov79, M. Bedognetti120, C.P. Bee155,T.A. Beermann76, M. Begalli80b, M. Begel29, A. Behera155,J.K. Behr46, F. Beisiegel24, A.S. Bell94,G. Bella161, L. Bellagamba23b,A. Bellerive34,P. Bellos9,
K. Beloborodov122b,122a, K. Belotskiy112,N.L. Belyaev112, D. Benchekroun35a,N. Benekos10,
Y. Benhammou161,D.P. Benjamin6, M. Benoit54,J.R. Bensinger26, S. Bentvelsen120,L. Beresford135, M. Beretta51, D. Berge46,E. Bergeaas Kuutmann172,N. Berger5, B. Bergmann142, L.J. Bergsten26, J. Beringer18,S. Berlendis7,N.R. Bernard102, G. Bernardi136,C. Bernius153, T. Berry93, P. Berta99, C. Bertella15a,I.A. Bertram89, O. Bessidskaia Bylund182,N. Besson145, A. Bethani100, S. Bethke115, A. Betti24, A.J. Bevan92,J. Beyer115, R. Bi139,R.M. Bianchi139,O. Biebel114,D. Biedermann19, R. Bielski36,K. Bierwagen99,N.V. Biesuz71a,71b,M. Biglietti74a,T.R.V. Billoud109, M. Bindi53,
A. Bingul12d,C. Bini72a,72b,S. Biondi23b,23a,M. Birman180, T. Bisanz53,J.P. Biswal161,D. Biswas181,i, A. Bitadze100,C. Bittrich48, K. Bjørke134,K.M. Black25,T. Blazek28a,I. Bloch46,C. Blocker26,A. Blue57, U. Blumenschein92,G.J. Bobbink120, V.S. Bobrovnikov122b,122a, S.S. Bocchetta96,A. Bocci49,
D. Boerner46, D. Bogavac14,A.G. Bogdanchikov122b,122a,C. Bohm45a,V. Boisvert93, P. Bokan53,172, T. Bold83a,A.S. Boldyrev113,A.E. Bolz61b,M. Bomben136,M. Bona92, J.S. Bonilla131, M. Boonekamp145, H.M. Borecka-Bielska90,A. Borisov123,G. Borissov89,J. Bortfeldt36,D. Bortoletto135,V. Bortolotto73a,73b, D. Boscherini23b,M. Bosman14, J.D. Bossio Sola103, K. Bouaouda35a,J. Boudreau139,
E.V. Bouhova-Thacker89,D. Boumediene38,S.K. Boutle57,A. Boveia126,J. Boyd36,D. Boye33b,ap, I.R. Boyko79,A.J. Bozson93, J. Bracinik21, N. Brahimi101, G. Brandt182,O. Brandt32,F. Braren46, U. Bratzler164,B. Brau102, J.E. Brau131,W.D. Breaden Madden57, K. Brendlinger46,L. Brenner46, R. Brenner172,S. Bressler180,B. Brickwedde99,D.L. Briglin21,D. Britton57,D. Britzger115, I. Brock24, R. Brock106,G. Brooijmans39,W.K. Brooks147b,E. Brost121,J.H Broughton21,
P.A. Bruckman de Renstrom84,D. Bruncko28b,A. Bruni23b,G. Bruni23b,L.S. Bruni120,S. Bruno73a,73b, B.H. Brunt32, M. Bruschi23b,N. Bruscino139,P. Bryant37,L. Bryngemark96,T. Buanes17, Q. Buat36, P. Buchholz151,A.G. Buckley57,I.A. Budagov79, M.K. Bugge134,F. Bührer52, O. Bulekov112, T.J. Burch121, S. Burdin90, C.D. Burgard120, A.M. Burger129,B. Burghgrave8, K. Burka83a,J.T.P. Burr46,
J.C. Burzynski102,V. Büscher99,E. Buschmann53,P.J. Bussey57, J.M. Butler25,C.M. Buttar57,
J.M. Butterworth94, P. Butti36, W. Buttinger36,A. Buzatu158,A.R. Buzykaev122b,122a, G. Cabras23b,23a, S. Cabrera Urbán174,D. Caforio56,H. Cai173, V.M.M. Cairo153, O. Cakir4a, N. Calace36, P. Calafiura18, A. Calandri101,G. Calderini136, P. Calfayan65,G. Callea57, L.P. Caloba80b,S. Calvente Lopez98,
D. Calvet38, S. Calvet38,T.P. Calvet155,M. Calvetti71a,71b, R. Camacho Toro136, S. Camarda36,
D. Camarero Munoz98, P. Camarri73a,73b, D. Cameron134,R. Caminal Armadans102,C. Camincher36, S. Campana36, M. Campanelli94,A. Camplani40, A. Campoverde151,V. Canale69a,69b,A. Canesse103, M. Cano Bret60c,J. Cantero129,T. Cao161,Y. Cao173,M.D.M. Capeans Garrido36, M. Capua41b,41a, R. Cardarelli73a, F.C. Cardillo149,G. Carducci41b,41a, I. Carli143, T. Carli36, G. Carlino69a, B.T. Carlson139, L. Carminati68a,68b,R.M.D. Carney45a,45b,S. Caron119, E. Carquin147b,S. Carrá46,J.W.S. Carter167, M.P. Casado14,d, A.F. Casha167, D.W. Casper171, R. Castelijn120,F.L. Castillo174,V. Castillo Gimenez174, N.F. Castro140a,140e, A. Catinaccio36,J.R. Catmore134, A. Cattai36, J. Caudron24, V. Cavaliere29,
E. Cavallaro14,M. Cavalli-Sforza14,V. Cavasinni71a,71b,E. Celebi12b, F. Ceradini74a,74b,
L. Cerda Alberich174,K. Cerny130, A.S. Cerqueira80a, A. Cerri156, L. Cerrito73a,73b,F. Cerutti18,
A. Cervelli23b,23a,S.A. Cetin12b,Z. Chadi35a, D. Chakraborty121,S.K. Chan59,W.S. Chan120,W.Y. Chan90, J.D. Chapman32, B. Chargeishvili159b,D.G. Charlton21,T.P. Charman92, C.C. Chau34, S. Che126,
A. Chegwidden106,S. Chekanov6, S.V. Chekulaev168a, G.A. Chelkov79,au, M.A. Chelstowska36, B. Chen78, C. Chen60a,C.H. Chen78, H. Chen29,J. Chen60a,J. Chen39, S. Chen137, S.J. Chen15c,X. Chen15b,at,
Y. Chen82,Y-H. Chen46, H.C. Cheng63a,H.J. Cheng15a,15d, A. Cheplakov79, E. Cheremushkina123,
The ATLAS Collaboration / Physics Letters B 800 (2020) 135069 13 G. Chiarelli71a,G. Chiodini67a, A.S. Chisholm36,21,A. Chitan27b,I. Chiu163,Y.H. Chiu176,M.V. Chizhov79, K. Choi65,A.R. Chomont72a,72b,S. Chouridou162, Y.S. Chow120,M.C. Chu63a, X. Chu15a, J. Chudoba141, A.J. Chuinard103,J.J. Chwastowski84,L. Chytka130,K.M. Ciesla84,D. Cinca47, V. Cindro91,I.A. Cioar˘a27b, A. Ciocio18,F. Cirotto69a,69b, Z.H. Citron180, M. Citterio68a, D.A. Ciubotaru27b, B.M. Ciungu167,
A. Clark54,M.R. Clark39, P.J. Clark50,C. Clement45a,45b,Y. Coadou101, M. Cobal66a,66c,A. Coccaro55b, J. Cochran78, H. Cohen161,A.E.C. Coimbra36, L. Colasurdo119,B. Cole39, A.P. Colijn120,J. Collot58, P. Conde Muiño140a,e,E. Coniavitis52, S.H. Connell33b, I.A. Connelly57, S. Constantinescu27b, F. Conventi69a,aw, A.M. Cooper-Sarkar135,F. Cormier175,K.J.R. Cormier167,L.D. Corpe94,
M. Corradi72a,72b,E.E. Corrigan96,F. Corriveau103,ab,A. Cortes-Gonzalez36,M.J. Costa174, F. Costanza5, D. Costanzo149,G. Cowan93,J.W. Cowley32,J. Crane100, K. Cranmer124, S.J. Crawley57, R.A. Creager137, S. Crépé-Renaudin58, F. Crescioli136, M. Cristinziani24,V. Croft120,G. Crosetti41b,41a,A. Cueto5,
T. Cuhadar Donszelmann149, A.R. Cukierman153, S. Czekierda84,P. Czodrowski36,
M.J. Da Cunha Sargedas De Sousa60b, J.V. Da Fonseca Pinto80b,C. Da Via100,W. Dabrowski83a,
T. Dado28a,S. Dahbi35e, T. Dai105,C. Dallapiccola102, M. Dam40,G. D’amen23b,23a, V. D’Amico74a,74b, J. Damp99, J.R. Dandoy137, M.F. Daneri30, N.P. Dang181, N.D Dann100,M. Danninger175, V. Dao36, G. Darbo55b,O. Dartsi5,A. Dattagupta131,T. Daubney46,S. D’Auria68a,68b, W. Davey24,C. David46, T. Davidek143,D.R. Davis49,I. Dawson149, K. De8,R. De Asmundis69a, M. De Beurs120,
S. De Castro23b,23a,S. De Cecco72a,72b,N. De Groot119, P. de Jong120, H. De la Torre106,A. De Maria15c, D. De Pedis72a, A. De Salvo72a,U. De Sanctis73a,73b, M. De Santis73a,73b,A. De Santo156,
K. De Vasconcelos Corga101, J.B. De Vivie De Regie132,C. Debenedetti146,D.V. Dedovich79,
A.M. Deiana42, M. Del Gaudio41b,41a, J. Del Peso98, Y. Delabat Diaz46, D. Delgove132, F. Deliot145,p, C.M. Delitzsch7,M. Della Pietra69a,69b, D. Della Volpe54, A. Dell’Acqua36,L. Dell’Asta73a,73b,
M. Delmastro5,C. Delporte132, P.A. Delsart58, D.A. DeMarco167, S. Demers183, M. Demichev79, G. Demontigny109,S.P. Denisov123, D. Denysiuk120, L. D’Eramo136,D. Derendarz84,J.E. Derkaoui35d, F. Derue136,P. Dervan90,K. Desch24,C. Deterre46, K. Dette167,C. Deutsch24,M.R. Devesa30,
P.O. Deviveiros36,A. Dewhurst144, F.A. Di Bello54,A. Di Ciaccio73a,73b,L. Di Ciaccio5,
W.K. Di Clemente137, C. Di Donato69a,69b,A. Di Girolamo36,G. Di Gregorio71a,71b, B. Di Micco74a,74b, R. Di Nardo102,K.F. Di Petrillo59,R. Di Sipio167, D. Di Valentino34,C. Diaconu101,F.A. Dias40,
T. Dias Do Vale140a,M.A. Diaz147a,J. Dickinson18,E.B. Diehl105, J. Dietrich19, S. Díez Cornell46,
A. Dimitrievska18,W. Ding15b, J. Dingfelder24, F. Dittus36,F. Djama101,T. Djobava159b,J.I. Djuvsland17, M.A.B. Do Vale80c,M. Dobre27b, D. Dodsworth26, C. Doglioni96, J. Dolejsi143,Z. Dolezal143,
M. Donadelli80d,B. Dong60c, J. Donini38,A. D’onofrio92, M. D’Onofrio90,J. Dopke144, A. Doria69a, M.T. Dova88,A.T. Doyle57, E. Drechsler152, E. Dreyer152,T. Dreyer53,A.S. Drobac170,Y. Duan60b, F. Dubinin110, M. Dubovsky28a,A. Dubreuil54,E. Duchovni180,G. Duckeck114,A. Ducourthial136, O.A. Ducu109, D. Duda115,A. Dudarev36,A.C. Dudder99,E.M. Duffield18, L. Duflot132,M. Dührssen36, C. Dülsen182,M. Dumancic180,A.E. Dumitriu27b,A.K. Duncan57,M. Dunford61a,A. Duperrin101, H. Duran Yildiz4a,M. Düren56, A. Durglishvili159b,D. Duschinger48,B. Dutta46,D. Duvnjak1, G.I. Dyckes137, M. Dyndal36,S. Dysch100,B.S. Dziedzic84,K.M. Ecker115,R.C. Edgar105,
M.G. Eggleston49,T. Eifert36,G. Eigen17,K. Einsweiler18,T. Ekelof172,H. El Jarrari35e,M. El Kacimi35c, R. El Kosseifi101, V. Ellajosyula172,M. Ellert172,F. Ellinghaus182,A.A. Elliot92,N. Ellis36,J. Elmsheuser29, M. Elsing36, D. Emeliyanov144,A. Emerman39, Y. Enari163, M.B. Epland49, J. Erdmann47,A. Ereditato20, M. Errenst36,M. Escalier132, C. Escobar174,O. Estrada Pastor174,E. Etzion161, H. Evans65,A. Ezhilov138, F. Fabbri57, L. Fabbri23b,23a, V. Fabiani119,G. Facini94,R.M. Faisca Rodrigues Pereira140a,
R.M. Fakhrutdinov123, S. Falciano72a,P.J. Falke5,S. Falke5, J. Faltova143, Y. Fang15a, Y. Fang15a, G. Fanourakis44,M. Fanti68a,68b,M. Faraj66a,66c,A. Farbin8,A. Farilla74a, E.M. Farina70a,70b,
T. Farooque106,S. Farrell18,S.M. Farrington50, P. Farthouat36, F. Fassi35e,P. Fassnacht36,D. Fassouliotis9, M. Faucci Giannelli50, W.J. Fawcett32,L. Fayard132,O.L. Fedin138,n,W. Fedorko175,M. Feickert42,
L. Feligioni101,A. Fell149,C. Feng60b, E.J. Feng36,M. Feng49,M.J. Fenton57,A.B. Fenyuk123, J. Ferrando46,A. Ferrante173, A. Ferrari172,P. Ferrari120, R. Ferrari70a, D.E. Ferreira de Lima61b, A. Ferrer174, D. Ferrere54, C. Ferretti105, F. Fiedler99,A. Filipˇciˇc91,F. Filthaut119,K.D. Finelli25, M.C.N. Fiolhais140a, L. Fiorini174,F. Fischer114, W.C. Fisher106,I. Fleck151, P. Fleischmann105,
