Contents lists available atScienceDirect
Physics
Letters
B
www.elsevier.com/locate/physletb
Search
for
heavy
resonances
decaying
into
a
vector
boson
and
a
Higgs
boson
in
final
states
with
charged
leptons,
neutrinos,
and
b
quarks
.
The
CMS
Collaboration
CERN,Switzerland
a
r
t
i
c
l
e
i
n
f
o
a
b
s
t
r
a
c
t
Articlehistory:
Received25October2016
Receivedinrevisedform28December2016 Accepted15February2017
Availableonline22February2017 Editor:M.Doser
Keywords:
CMS Physics B2G Diboson VH Semileptonic
AsearchforheavyresonancesdecayingtoaHiggsbosonandavectorbosonispresented.Theanalysis isperformedusingdatasamplescollectedin2015bytheCMSexperimentattheLHCinproton–proton collisionsatacenter-of-massenergyof13 TeV,correspondingtointegratedluminositiesof2.2–2.5 fb−1.
Thesearchisperformedinchannelsinwhichthevectorbosondecaysintoleptonicfinalstates(Z→
νν
, W→ν
,andZ→,with=e,μ
),whiletheHiggsbosondecaystocollimatedbquarkpairsdetected asasinglemassivejet.Thediscriminatingpowerofajetmassrequirementandabjettaggingalgorithm are exploited to suppress the standard model backgrounds. The event yields observed in data are consistentwiththebackgroundexpectation.Inthecontextofatheoreticalmodel withaheavyvector triplet,aresonancewithmassless than2 TeVisexcludedat95%confidencelevel.Theresultsarealso interpreted in terms of limits on the parameters of the model, improving on the reach of previous searches.©2017TheAuthor.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3.
1. Introduction
Thediscovery ofa HiggsbosonH attheCERN LHC[1–3] sug-geststhatthestandardmodel(SM)mechanismthatconnects elec-troweak (EW) symmetry breaking to the generation of particle massesislargelycorrect.However,therelativelylightvalueofthe HiggsbosonmassmH
=
125.
09±
0.
21(stat)±
0.
11(syst) GeV[4–7]leaves the hierarchy problem unsolved [8], pointing to phenom-enabeyond theSM, which could be unveiled by searches atthe LHC. Manytheories that incorporatephenomena beyond the SM postulate the existence of new heavy resonances coupled to the SMbosons.Amongthem,weaklycoupledspin-1Z [9,10]andW models[11]orstronglycoupledCompositeHiggs[12–14],and Lit-tleHiggsmodels[15–17]havebeenwidelydiscussed.
A large number of models are generalized in the heavy vec-tor triplet (HVT) framework [18], which introduces one neutral (Z)andtwoelectricallycharged(W) heavyresonances.The HVT modelisparametrizedintermsofthreeparameters:thestrength
gVofanewinteraction;thecouplingcHbetweentheheavyvector
bosons, the Higgs boson, and longitudinally polarized SM vector bosons;andthecouplingcF betweentheHVTbosonsandtheSM
fermions.In the HVTscenario, model Bwith parameters gV
=
3,cH
=
0.
976,andcF=
1.
024 [18] is used asthe benchmark.WithE-mailaddress:cms-publication-committee-chair@cern.ch.
these values, the couplings of the heavy resonances to fermions and to SM bosons are similar, yielding a sizable branching frac-tionfortheheavyresonancedecayintoaSMvectorbosonW orZ (genericallylabeledasV)andaHiggsboson[18].
Bounds fromprevious searches [19–22] requirethe massesof theseresonancestobeabove1 TeV intheHVTframework.Inthis mass region, the two bosons produced in the resonance decay would have large Lorentz boosts in the laboratory frame. When decaying, each boson would generatea pair of collimated parti-cles, a distinctive signature, which can be well identified in the CMS experiment. Because of the large predicted branching frac-tion,thedecayofhigh-momentumHiggsbosonstobb finalstates isconsidered.TheHiggsbosonisreconstructedasoneunresolved jet, taggedascontaining atleastone bottom quark. Backgrounds from single quark and gluon jets are reduced by a jet mass re-quirement.Inordertodiscriminateagainstthelargemultijet back-ground,thesearchisfocusedontheleptonicdecaysofthevector bosons(Z
→
νν
,W→
ν
,andZ→
,with
=
e,
μ
).The main SM backgroundprocess is the productionof vector bosons withadditional hadronic jets (V
+
jets). The estimation of this background is based on events in signal-depleted jet mass sidebands,withatransferfunction,derivedfromsimulation,from thesidebandstothesignal-enrichedregion.Topquark production alsoaccountsforasizablecontributiontothebackgroundin1fi-nalstates,andisdetermined fromsimulationnormalizedtodata indedicatedcontrolregions.Dibosonproductionprocesses,
includ-http://dx.doi.org/10.1016/j.physletb.2017.02.040
ingpairsofvectorbosons(VV)andtheSMproductionofaHiggs bosonandvectorboson(VH),representminorcontributionstothe overall background and are estimated from simulation. A signal wouldproduce a localized excess above a smoothly falling back-groundin the distribution ofthe kinematic variablemVH, whose
definitionandrelationshipto theresonancemassmX dependson
thefinalstate.ResultsareinterpretedinthecontextofHVT mod-elsinthebenchmarkscenario B[18].
2. Dataandsimulatedsamples
Thedatasamplesanalyzedinthisstudywerecollectedwiththe CMSdetector inproton–protoncollisions at a center-of-mass en-ergyof13 TeVduring 2015.Thesamplescorrespondtointegrated luminosities of2.2–2.5 fb−1, depending on thefinal state consid-ered.
Simulatedsignaleventsaregeneratedatleadingorder(LO) ac-cordingtothe HVTmodel B [18] withtheMadGraph5_amc@nlo v5.2.2.2 matrix element generator [23]. The Higgs boson is re-quiredtodecayintoabb pair,andthevectorbosonintoleptons. Acontributionfromvectorbosondecaysinto
τ
leptonsisalso in-cludedthroughsubsequentdecaystoe orμ
thatsatisfytheevent selection. DifferentmX hypotheses inthe range 800to 4000 GeVareconsidered,assuming aresonancewidthnarrowenough (0.1% oftheresonancemass)tobenegligiblewithrespecttothe exper-imental resolution.Thisapproximation isvalidina large fraction oftheHVTparameterspace,andwillbediscussedinSection8.
The analysis utilizes a set of simulated samples to character-izethemainSM backgroundprocesses.SamplesofV
+
jets events are produced withMadGraph5_amc@nlo andnormalized to the next-to-next-to-leading-order(NNLO)crosssection, computed us-ing fewz v3.1 [24]. The V boson pT spectra are corrected to ac-count fornext-to-leading-order (NLO) QCDandEW contributions [25].TopquarkpairproductionissimulatedwiththeNLOpowheg v2generator[26–28]andrescaledtothecrosssectionvalue com-puted with Top++
v2.0 [29] at NNLO. Minor SM backgrounds, such asVV and VH production, andsingle top quark (t+
X) pro-ductionin s-channel,t-channel, andintW associatedproduction, aresimulatedatNLOwithMadGraph5_amc@nlo.Multijet produc-tionissimulatedatleadingorderwiththesamegenerator.Partonshoweringandhadronizationprocessesaresimulatedby interfacing theeventgenerators to pythia8.205 [30,31]withthe CUETP8M1 [32,33] tune. The NNPDF 3.0 [34] partondistribution functions(PDFs)areusedtomodelthemomentumdistributionof thecollidingpartonsinsidetheprotons.Generatedevents, includ-ing additionalproton–proton interactions within the samebunch crossing (pileup) at the level observed during 2015 data taking, areprocessedthroughafulldetectorsimulationbasedonGeant4 [35]andreconstructedwiththesamealgorithmsusedfordata.
3. CMSdetector
The central feature ofthe CMS detector is a superconducting solenoidof6 minternaldiameter.Withinthesolenoidvolumeare a silicon pixel andstrip tracker, a lead tungstate crystal electro-magnetic calorimeter(ECAL), anda brass and scintillator hadron calorimeter (HCAL), each composed of a barrel and two endcap sections.Forwardcalorimetersextendthepseudorapidity[36] cov-erage provided by the barrel and endcap detectors. Muons are measured ingas-ionizationdetectors embeddedin thesteel flux-returnyokeoutsidethesolenoid.
Thesilicontrackermeasureschargedparticleswithinthe pseu-dorapidity range
|
η
|
<
2.
5. It consists of 1440 silicon pixel and 15 148 silicon strip detector modules andis located in the 3.8 Tfield ofthe solenoid. For nonisolatedparticles of transverse mo-mentum 1
<
pT<
10GeV and|
η
|
<
1.
4,the trackresolutions aretypically1.5%inpTand25–90(45–150) μminthetransverse
(lon-gitudinal) impactparameter [37]. The ECALprovides coverage up to
|
η
|
<
3.
0. The dielectron mass resolution for Z→
ee decays when both electrons are in the ECAL barrelis 1.9%, and is 2.9% when both electrons are in the endcaps. The HCAL covers the range of|
η
|
<
3.
0, which is extended to|
η
|
<
5.
2 through for-wardcalorimetry.Muonsaremeasuredinthepseudorapidityrange|
η
|
<
2.
4, with detection planes made using three technologies: drift tubes, cathodestrip chambers, andresistive-platechambers. Combiningmuontrackswithmatchingtracksmeasuredinthe sil-icon trackerresults in a pT resolution of 2–10% for muonswith0
.
1<
pT<
1TeV[38].Thefirstlevel(L1)oftheCMStriggersystem,composedof cus-tom hardware processors,uses informationfromthecalorimeters andmuondetectorstoselectthemostinterestingeventsinafixed timeintervaloflessthan4 μs.Thehigh-leveltrigger(HLT) proces-sorfarmfurtherdecreases theeventratefromaround 100 kHzto about1 kHz,beforedatastorage.
AdetaileddescriptionoftheCMSdetector,togetherwitha def-inition of thecoordinatesystemused andtherelevant kinematic variables,canbefoundinRef.[36].
4. Eventreconstruction
In CMS, a global event reconstruction is performed using a particle-flow(PF)algorithm[39,40],whichusesanoptimized com-bination of information from the various elements of the CMS detectorto reconstructandidentify individual particles produced ineach collision.The algorithmidentifieseach reconstructed par-ticleeitherasanelectron,amuon,aphoton,achargedhadron,or aneutralhadron.
ThePFcandidatesareclusteredintojetsusingtheanti-kT
algo-rithm[41]withadistanceparameterR
=
0.
4 (AK4jets)orR=
0.
8 (AK8 jets). In order to suppress the contamination from pileup, charged particles not originating from the primary vertex, taken to be the one with the highest sum of p2T over its constituent
tracks,are discarded.The residualcontaminationremovedis pro-portional to theeventenergy densityandthe jet area estimated usingtheFastJetpackage[42,43].Jetenergycorrections,extracted fromsimulation anddata inmultijet,
γ
+
jets, andZ+
jetsevents, are applied as functionsof the transversemomentum and pseu-dorapidity tocorrectthe jetresponse andtoaccount forresidual differences between data and simulation. The jet energy resolu-tion amounts typically to 5% at 1 TeV [44]. Jets are required to pass an identification criterion, based on the jet composition in termsofthedifferentclassesofPFcandidates,inordertoremove spurious jets arising from detector noise. The pruning algorithm [45],which is designedto remove contributions from soft radia-tionandadditionalinteractions,isappliedtoAK8jets.Thepruned jet mass mj isdefinedas theinvariant mass associatedwith thefour-momentumoftheprunedjet,aftertheapplicationofthejet energycorrections[44].TheAK8jetsaresplitintotwosubjets us-ingthesoftdropalgorithm[46,47].
The combinedsecondaryvertexalgorithm [48]is usedforthe identificationofjetsthatoriginatefrombquarks(btagging). The algorithm uses thetracks andsecondary vertices associatedwith AK4jetsorAK8subjetsasinputstoaneural networktoproduce a discriminator withvaluesbetween 0and1,with highervalues indicatingahigherbquarkjetprobability.Thelooseandthetight operatingpointsareabout85and50%efficient,respectively,forb jetswithpTofabout100 GeV,withafalse-positive ratefor
The missing transverse momentum vector p
missT is defined as the projection of the negative vectorial sum of the momenta of allPFcandidatesonto theplane perpendiculartothe beams,and itsmagnitudeis referredto as EmissT . Themissinghadronic activ-ityHmissT isdefinedasthemagnitudeofthenegativevectorialsum ofthe transversemomentaofallAK4jetswith pT>
20GeV.Cor-rectionsforthe Emiss
T detectorresponseandresolutionarederived
from
γ
+
jets andZ+
jetsevents,andapplied to simulatedevents [49].Electronsare reconstructed in thefiducial region
|
η
|
<
2.
5 by matching the energy deposits in the ECAL with tracks recon-structedinthetracker[50].Theelectronidentificationisbasedon thedistributionofenergydepositedalong theelectrontrajectory, thedirectionandmomentumofthetrackintheinnertracker,and itscompatibilitywiththeprimary vertexoftheevent. Additional requirements are applied to remove electrons produced by pho-tonconversions.Electronsarefurtherrequiredtobeisolatedfrom other activityin thedetector. The electronisolation parameteris definedasthesumoftransversemomentaofallthePFcandidates (excludingtheelectronitself)withinR
=
(
η
)
2+
(φ)
2<
0.
3aroundtheelectron direction,after thecontributionsfrompileup andotherreconstructedelectronsareremoved.Photonsare recon-structedasenergyclustersintheECAL,andaredistinguishedfrom jetsandelectronsusinginformationthatincludesisolationandthe transverseshapeoftheECALenergydeposit.
Muons are reconstructed within the acceptance of the CMS muon systems,
|
η
|
<
2.
4, using the information from both the muonspectrometerandthesilicontracker[38].Muon candidates are identified via selection criteriabased on the compatibilityof tracks reconstructed from silicon tracker information only with tracksreconstructedfromthecombinationofthehitsinboththe trackerandmuon detector.Additional requirementsare basedon the compatibility of the trajectory with the primary vertex, and onthenumberofhitsobservedinthetrackerandmuonsystems. Themuonisolationiscomputedfromreconstructed trackswithin aconeR
<
0.
3 aroundthe muon direction, ignoring the muon itself.Hadronically decaying
τ
leptons are reconstructed combining oneorthreehadronicchargedPFcandidateswithuptotwo neu-tralpions,the latteralsoreconstructed bythe PFalgorithmfrom thephotonsarisingfromtheπ
0→
γ γ
decay[51].5. Eventselection
Theset ofcriteria usedto identifythe Higgs bosoncandidate is the same for each event category. The highest-pT AK8 jet in
the event is required to have pT
>
200GeV and|
η
|
<
2.
5. Theprunedjet massmj must satisfy 105
<
mj<
135GeV.The region65
<
mj<
105GeV is not used, to avoid overlaps with searchestargetingresonantVV finalstates.Inordertodiscriminateagainst the copious vector boson production in association with light-flavoredjets,eventsareclassifiedaccordingtothenumberof sub-jets(1 or 2)passingtheloosebtaggingselection;thosefailingthis requirementarediscarded.
Events are divided into categories depending on the number (0,1,or 2)andflavor (e or
μ
) ofthe reconstructedcharged lep-tons, and the presence of either 1 or 2 b-tagged subjets in the AK8jet.The twocategories withno chargedleptons are referred tocollectivelyasthezero-lepton(0)channel.Similarly,the single-lepton (1
) and double-lepton (2
) channels each comprise four categories.Intotal,10exclusivecategoriesaredefined.
Inthe0
channel,candidatesignaleventsareexpectedtohave a large EmissT due to the boosted Z boson decaying into a pair of neutrinos, which escape undetected. Data are collected using triggers that require Emiss
T or HmissT greater than 90 GeV, without
including muons in the EmissT or HmissT computation. A stringent selection is appliedto the reconstructed Emiss
T , whichis required
to begreater than 200 GeV,to ensurethat the triggerisfully ef-ficient. The copious multijet production is greatly suppressed by imposing requirementsonthe minimumazimuthal angular sepa-rationsbetweenjetsandthemissingtransversemomentumvector,
φ (
jet,
pmissT
)
. All the AK8 and AK4jets in the eventmustsat-isfy
φ (
jet,
pmissT
)
>
0.
5.TheHiggsbosonjetcandidatemustfulfillthe tighter requirement
φ (
jet,
pmissT
)
>
2 and additionalcriteriadesignedtoremoveeventsarisingfromdetectornoise.Events con-tainingisolatedleptonswithpT
>
10GeV,hadronically-decayingτ
leptons with pT
>
18GeV,andphotons with pT>
15GeV arere-movedinordertoreduce thecontributionofotherSM processes. The tt backgroundcontributionisreducedby removing eventsin which any AK4 jet, excluding the Higgs boson jet candidate, is b tagged using the looseoperating point. Because of the lack of visibledecayproductsfromtheZ boson,reconstructionofthe res-onance mass is not directly viable. Instead, the Higgs boson jet momentumandthep
missT areusedtocomputethetransversemassmTVH
=
2EmissT EjetT
[
1−
cosφ (
jet,
pmissT)
]
.Thisvariableisutilized asanestimatorofmXforthe0channel.
Events in the 1
channel are collected requiring one lepton to be reconstructed online. The pT threshold at trigger level is
105 GeV for electrons and45 GeV for muons. Offline, events are accepted if there is exactly one reconstructed electron or muon with pT larger than 135 GeV or 55 GeV, respectively, passing
re-strictive selection criteria. Events with additional leptons pass-ing looserselections, orhadronically decaying
τ
leptons, are dis-carded. Inthe single-electronchannel, multijetbackground is re-ducedbyrequiring EmissT>
80GeV.Azimuthalangularseparationsφ (,
pmissT)
<
2 andφ (
jet,
pmissT)
>
2 are required to select a back-to-back topology.As for the 0selection, eventswith addi-tionalb-taggedAK4jetsarevetoed.Thefour-momentumoftheW bosoncandidateis quantifiedusinga kinematicreconstruction of theneutrinomomentum.Thecomponentsoftheneutrino momen-tuminthetransverseplane areassumedtobeequalto pmissT .By constrainingtheinvariantmassofthechargedleptonandneutrino tobeequaltotheW bosonmass,aquadraticequationisderived for the longitudinal component of the neutrino momentum, pνz. The reconstructed pνz is chosen to be the real solution with the lower magnitude or, where both the solutions are complex, the real partwiththe lowestvalue. If theW boson has a transverse momentumgreaterthan200 GeV,itisusedtoconstructthe reso-nancecandidatemassmVH,otherwisetheeventisdiscarded.
The2
channelacceptseventscollectedwiththesametriggers asinthe1
channel.Anadditionalisolatedelectronormuonwith
pT
>
20GeV,withthesameflavorastheleadingoneandoppositecharge, isrequiredtobe reconstructedandidentified.Inorder to increasethesignalefficiency,alooseridentificationrequirementis appliedtobothelectrons,andoneofthetwomuonsisallowedto be identifiedonlyinthetracker.Iftheisolation conesofthetwo muonsoverlap,thecontributionofoneissubtractedfromthe iso-lationcalculationoftheotherineachcase.TheZ bosoncandidates are retained only if the dilepton invariant mass lies between 70 and110 GeV.ThetransversemomentumoftheZ bosoncandidate isrequiredtobeatleast200 GeV,otherwisetheeventisremoved. Additionally,theseparationin
η
andφ
betweentheZ boson candi-dateandtheHiggsbosonjetisrequiredtosatisfy|
η
(
Z,
jet)
|
<
5 andφ (
Z,
jet)
>
2.
5.Sincethett contributionissmall,novetoon additional b-taggedAK4 jetsis applied. The resonance candidate massmVHisdefinedastheinvariantmassoftheZ bosonandtheAK8jet.
cat-egoriesforaresonancemassmX
=
1TeV,decreasingtoabout10%formX
=
4TeV. Thisreduction isdue tothe degradationof trackreconstructionandbtaggingperformancesatverylarge pT,andto
thesmalleranglebetweenthetwobquarks,whichtendtobe re-constructedinonesinglesubjet.Thelossofefficiencyisrecovered by the 1b-tagged subjetcategories, which providean additional 10%signalefficiencyatmX
=
1TeV,and20%atmX=
4TeV.6. Estimatedandobservedbackground
Themainsourceofbackgroundeventsoriginatesfromthe pro-duction of a vector boson in association with jets, and the sub-sequent decay of the vector boson into one of the considered leptonic final states.This backgroundisrelevant both when gen-uinebjetsareidentifiedandwhenajetoriginatingfromalighter quarkoragluonismisidentifiedasoriginatingfromabquark.In the1
and2
channels,themaincontributionsareduetoW
→
ν
andZ→
processes,respectively.Inthe0
channelZ
→
νν
and W→
ν
processesaccount forapproximately60% and40% ofthe V+
jets background, respectively. In the lattercase, the lepton is either emitted outside the detector acceptance, or is not recon-structed and identified. A sizable background originates from b jetsandW bosonsfromdecaysofpair-producedtopquarks.Minor contributionscomefromt+
X,VV,VH,andmultijetprocesses.Thenormalizationofthetopquarkbackground(tt andt
+
X)is determinedintopquarkenrichedcontrolregionswherethe simu-latedmj andmVHdistributionsarealsocheckedagainstdata.Fourtop quark control regions are defined, depending on the number ofreconstructedleptons(0or1)andthenumberofb-tagged sub-jets(1or2).Thetopquarkcontrolregionsaredefinedbyinverting thebtaggingvetoontheAK4jetsintheevent,andbyapplyinga tightbtaggingselectiontoobtaina tt samplewithhigherpurity. Data are found to be in agreement with the shape of the sim-ulated mj andmVH distributions. Multiplicative scale factors are
[image:4.612.303.553.118.173.2]derived for each region fromthe difference in normalization be-tween data andsimulation, after subtracting the contribution of the other backgrounds fromthe data. These factors, reported in Table 1,areappliedtocorrectthenormalizationofthett andt
+
X background.Inthe dileptonchannel,dueto thesmallnumberof events,thett normalizationandshapearetakenfromsimulation.The contribution of the dominant V
+
jets background is esti-matedthroughaprocedurebasedondata.Signal-depletedsamples aredefined,containingeventsthatpassallselectionsdescribedin Section5apartfromtherequirementontheprunedjetmass.Twomj sidebands (SB) are considered, andused to predict the
back-groundcontributions inthesignal region(SR).Thelower and up-persidebandsaccepteventsfallingintheranges30
<
mj<
65GeVand mj
>
135GeV, respectively. Analytic functions are fitted tothedistributionsofmj foundinsimulation,consideringseparately
V
+
jets, tt andt+
X,andallSM dibosonproductionprocesses.Themj spectrumin V
+
jets events consistsof a smoothly fallingdis-tribution,whiledibosonsamplespresentoneortwopeaks corre-spondingtotheW/Z andHiggsbosonmasses.Topquarksamples haveinsteadone peakinthemjspectrumforhadronically
decay-ing W bosons and one for the top quark itself, in eventswhere thehadronicW bosonortopquarkisreconstructedwithinthe se-lectedAK8jet.
The shape and normalization of the mj distribution for the
mainV
+
jets backgroundisextractedfromafit ofthesumofall contributingprocesses to the SBdata,after fixing the shape and normalizationofthesubdominantbackgrounds.ThefitstothemjdistributionsareshowninFig. 1.Thenormalizationofthediboson processesisderivedfromsimulation,whilethetopquark normal-izationistakenfromthecontrolregionswiththeexceptionofthe dileptonchannels.Theprocedureisrepeatedselectingan
alterna-Table 1
Scalefactorsderivedforthenormalizationoftheestimatedtt andt+X backgrounds fromsimulation,for differenteventcategories.Electronand muoncategoriesare merged.Uncertaintiesduetothelimitedsizeoftheeventsamples(stat)andthe uncertaintyinthebtaggingefficiency(syst)arereportedseparately.
Category Scale factor Stat Syst
1 b tag 1 0.82 ±0.03 ±0.04
0 0.85 ±0.06 ±0.04
2 b tag 1 0.83 ±0.07 ±0.04
0 0.54 ±0.13 ±0.02
tivefunctiontomodelthemjdistributionforthemainbackground.
Thedifferencebetweentheresultsobtainedwiththemainandthe alternativefunctionisconsidered asasystematicuncertainty.The number of expectedandobserved events in theSR are reported separately foreach category inTable 2. Adeficit of2
.
4 standard deviationsisobservedinthe1μ
,2btagcategory.The shape of the V
+
jets background distribution in the mVHvariableisobtainedviaatransferfunctiondeterminedfrom simu-lationas:
α
(
mVH)
=
NsimSR ,V+jets
(
mVH)
NsimSB ,V+jets
(
mVH)
(1)
where NsimSR,V+jets
(
mVH)
,NSBsim,V+jets(
mVH)
aretwo-parameterprob-ability densityfunctionsdetermined fromthemVH spectrainthe
SRandtheSBofthesimulatedV
+
jets sample,respectively.The ra-tioα
(
mVH)
accountsforthe correlationsandthesmallkinematicdifferencesinvolvedintheinterpolationfromthesidebandstothe SR, andislargelyindependentoftheshape uncertaintiesandthe assumptions onthe overall cross section. The shape of the main backgroundisextractedfromdatainthemj sidebands,after
mul-tiplying theobtaineddistributionbythe
α
(
mVH)
ratio.Theoverallpredictedbackground distributioninthe SR, NSRpred
(
mVH)
,isgivenbythefollowingrelation:
NSRpred
(
mVH)
=
NSBobs,V+jets(
mVH)
α
(
mVH)
+
Nsim,ttSR(
mVH)
+
Nsim,VVSR(
mVH)
(2)where Nobs,VSB +jets
(
mVH)
istheprobabilitydistributionfunctionob-tained from a fit to datain the mj sidebands of the sumof the
background components, and Nsim,ttSR
(
mVH)
and NSRsim,VV(
mVH)
arethe tt and dibosoncomponents, respectively,fixed tothe shapes andnormalizationsderived fromthesimulatedsamplesand con-trol regions. The observed data inthe SR are inagreement with thepredictedbackground,asshowninFig. 2.
Thevalidityandrobustnessofthismethodistestedondataby splitting thelower mj sidebandin twoandpredicting shape and
normalization of the intermediate sideband from the lower and upper sidebands. The number of events and distributions found in dataare compatiblewiththeprediction within thesystematic uncertainties.
The shape ofthereconstructed signal massdistribution is ex-tracted from the simulated signal samples. The signal shape is parametrized separately for each channel with a Gaussian peak and a powerlaw to modelthe lower tails. The resolutionof the reconstructedmVH isgivenbythewidthoftheGaussian corefor
the1
and2
channelsandbytheRMSofthemT
VHdistributionin
the 0
channel,andisfound tobe 10–16%,8–5%, 5–3%ofmX in
Fig. 1.PrunedjetmassdistributionoftheleadingAK8jetinthe0(upper),1(middle),and2(lower)categories,andseparatelyforthe1(top)and2(bottom)b-tagged subjetselections.Theshadedbandrepresentstheuncertaintyfromthefittodataintheprunedjetmasssidebands.Theobserveddataareindicatedbyblackmarkers.The dashedverticallinesseparatethelower(LSB)andupper(HSB)sidebands,theW andZ bosonsmassregion(VR),andthesignalregion(SR).Thebottompanelsreportthe pullsineachbin,(Ndata−Nbkg)/σ,whereσisthePoissonuncertaintyindata.TheerrorbarsrepresentthenormalizedPoissonerrorsonthedata.(Forinterpretationofthe
Fig. 2.ResonancecandidatemassmVHdistributionsinthe0(upper),1(middle),and2(lower)categories,andseparatelyforthe1(top)and2(bottom)b-taggedsubjet
selections.Theexpectedbackgroundeventsareshownwiththefilledarea,andtheshadedbandrepresentsthetotalbackgrounduncertainty.Theobserveddataareindicated byblackmarkers,andthepotentialcontributionofaresonancewithmX=2000GeV producedinthecontextoftheHVTmodelBwithgV=3 isshownwithasolidred
line.Thebottompanelsreportthepullsineachbin,(Ndata−Nbkg)/σ,whereσisthePoissonuncertaintyindata.TheerrorbarsrepresentthenormalizedPoissonerrors
Table 2
Expectedandobservednumbersofeventsinthesignalregion,foralleventcategories.Threeseparatesourcesof uncer-taintyintheexpectednumbersarereported:statisticaluncertaintyfromthefitprocedure(fit),theshapeofthetopquark anddibosonbackgrounddistributions(tt,VV),andthedifferencebetweenthenominalandalternativefunctionchoicefor thefit(alt.function).
Category Events Uncertainties
Observed Expected Fit tt, VV Alt. function
1 b tag 0 47 49.5 ±8.5 ±0.4 ±6.9
1e 57 73 ±23 ±1 ±6
1μ 119 123 ±8 ±1 ±5
2e 7 4.8 ±1.1 ±0.1 ±1.0
2μ 19 13.2 ±1.8 ±0.1 ±0.8
2 b tag 0 6 8.0 ±1.3 ±0.2 ±1.2
1e 7 8.7 ±1.0 ±0.3 ±0.5
1μ 14 29.5 ±3.4 ±1.0 ±0.9
2e 2 1.1 ±0.5 ±0.1 ±0.1
2μ 1 1.9 ±0.7 <0.1 ±0.3
7.Systematicuncertainties
The sensitivity of this analysis is limited by statistical rather thansystematicuncertainties.
The systematicuncertainty in the V
+
jets background yield is dominatedbythestatisticaluncertaintyassociatedwiththe num-ber ofdata events inthe mj sideband.Minor contributions arisefromthepropagationoftheuncertaintiesintheshapeofthe func-tionmodelingthemj distributionsofthe tt andVV backgrounds.
The tt and t
+
X normalization uncertainty,in the 0and1
cat-egories, originatesfrom thelimited numberof eventsin the top quark controlregions. The dibosonnormalizationuncertainty de-pends on the propagation of the theoretical uncertainties in the relevantphasespace,andisestimatedtobe20%.Giventherather largescalefactorobservedinthe0
,2btagtt controlregion,the topquark normalizationuncertaintyinthe 2
category is conser-vativelytakentobe50%.
The uncertainties in the V
+
jets background shape are esti-mated fromthe covariancematrix of the fit to data of the mVHdistributioninthesidebandregionsandfromtheuncertaintiesin themodelingofthe
α
(
mVH)
ratio,whichdependsonthenumberofdataandsimulationevents,respectively.
Othersourcesofuncertaintyaffectboththenormalizationand shapeofthe simulatedsignal andthesubdominant backgrounds. Theuncertaintiesinthetriggerefficiencyandtheelectron,muon, and
τ
leptonreconstruction,identification, andisolation are eval-uated through specific studies ofevents withdilepton massesin theregion of the Z peak, andamount to a 6–8% uncertaintyfor thecategorieswithchargedleptons, and3% inthe 0categories. Inthe1
and2
categories,theleptonenergyscaleandresolution arepropagatedtothesignalshape,andtheresultinguncertainties inthemeanandthewidthofthesignalmodelareestimatedtobe aslargeas16%and10%,respectively,dependingonthelepton fla-vorandsignalmass.Thejetenergyscaleandresolution[44]affect both shape and selection efficiencies. The jet energy corrections, propagatedtothejetmass,arealsotakenintoaccount,andare re-sponsiblefora5%variation inthe background,andavariationof 1–3%,depending onthemasshypothesis,inthenumberofsignal events.Thejet energyresolutionaccountsforan additional2–3% uncertainty. The effects are propagated to the mVH distributions
andconsidered asuncertainties in thesubdominant backgrounds andsignalsamples.Asaresult,inthesignalsamplea0.3% uncer-taintyisassignedtothemeanofthesignalshape,and1.0%tothe width.
Theefficiency forsignal eventsto enter theSR jet mass win-dowisevaluated withherwig[52,53]asanalternativeshowering algorithm.The7% differenceobservedwithrespecttothe default pythiashoweringistakentobethesystematicuncertainty.
Uncertainties on the b tagging efficiency [48] represent the largest source of normalization uncertainty for samples that are not normalizedtodata.Forthesignal efficiency,these uncertain-tiesintheyieldofbetween4–15%and8–30%,dependingonmVH,
are estimated in the 1 and2 b-tagged subjet categories, respec-tively;forbackgroundevents,respectiveuncertaintiesof5and12% arefoundinthetwocases.Anadditional10%btagginguncertainty isassigned tothe tt background toaccount forthe extrapolation fromthetopquarkcontrolregiontotheSR.
The factorization and renormalization scale uncertainties as-sociated withthe event generators are estimated by varying the corresponding scales up anddown by a factor of 2, andare re-sponsiblefora5%normalizationvariationintheestimateddiboson background. The effectof thesescale uncertainties is propagated to the tt and VV backgrounddistributions, and thedifference in the mVH distribution parameters is takenas an additional shape
uncertainty.Theeffectonthesignalshape modelingisnegligible, and the resulting normalizationuncertainty is 4–12%, depending onmVH.
Additional systematicuncertaintiesaffecting thenormalization ofbackgroundsandsignalfrompileupcontributions(3and0.5%), integratedluminosity(2.7%)[54],EmissT scaleandresolution(1%in the 0
channel),andthe choice of PDFs[55] (3% foracceptance, and4–18%forsignalnormalization)arealsoincludedinthe anal-ysis.
8. Resultsandinterpretation
Results are obtainedfrom a combined signal and background fit to the unbinned mVH distribution, based on a profile
likeli-hood. Systematic uncertainties are treated as nuisance parame-tersand areprofiled inthe statisticalinterpretation [56–59].The background-onlyhypothesisistestedagainsttheX
→
VH signalin thetencategories.Theasymptoticmodified frequentistmethodis usedtodeterminelimitsat95%confidencelevel(CL)onthe contri-butionfromsignal.Limitsarederivedontheproductofthecross sectionforaheavyvectorbosonX andthebranchingfractionsfor thedecaysX→
VH andH→
bb,denotedσ
(
X)
B
(
X→
VH)
B
(
H→
bb)
.NospecificassumptionismadeonB
(
H→
bb)
,sincethis de-caychannelhasnotyetbeenmeasured.The0and2
categories are combined to provide upper limitsfor the casewhere X is a heavyspin-1vectorsingletZ,inthenarrow-widthapproximation. Similarlythe1
categoriesare combinedtoprovidelimitsforthe casewhereX is a heavyW.Theexclusionlimitsare reportedin Fig. 3.These limitsareverified withthemodified frequentist CLs
Fig. 3.Observedandexpected95%CLupperlimitsonσ(Z)B(Z→ZH)B(H→bb)
(top)andσ(W)B(W→WH)B(H→bb)(bottom)asafunctionoftheresonance massforasinglenarrowspin-1resonance,includingallstatisticalandsystematic uncertainties.Theinner greenandouteryellowbandsrepresentthe±1 and±2 standard deviationuncertaintiesonthe expectedlimit.The redsolidcurve cor-respondstothe crosssectionspredictedbythe HVTmodel B with gV=3.(For
interpretationofthereferencestocolorinthisfigurelegend,thereaderisreferred tothewebversionofthisarticle.)
The result of this study is primarily interpreted in the con-text of a simplified model with a triplet of heavy vector bosons (V±,V0)[18].Thepredictions ofthebenchmark model Bare
su-perimposedon the exclusion limitsin Fig. 3. All the 0
, 1
, and 2
channelsarecombinedtoputstringentexclusionlimitsonthe HVTmodel,scenario B, assuming theZ andW crosssectionsas predictedby themodel.Therearenormalizationincreasescaused by eventmigrationbetweenthe leptonic channels, whichare es-timated to be 5–10% in the 0
channel, due to mis-assignedW events,and lessthan 1% in the 1
channel, due to mis-assigned Zevents.Fig. 4presentstheexclusionlimitsasafunction ofthe heavy tripletmass.AresonancewithmX2
.
0TeV isexcluded at95%CLintheHVTmodel B.
TheexclusionlimitshowninFig. 4canbeinterpretedasalimit inthe
gVcH,
g2cF/
gVplaneoftheHVTparameters,whereg rep-resentstheelectroweakcouplingconstant.Theexcluded regionof the parameter space for narrow resonances relative to the com-bination of all the considered channels is shown in Fig. 5. The fraction of the parameter space where the natural width of the resonances is larger than the typical experimental resolution of 5%,andthusthenarrowwidthapproximation isnotvalid,isalso indicated in Fig. 5. The exclusion ofthe parameter space signifi-cantlyimprovesonthereachof
√
s=
8TeV searchesinthe1[22] andall-hadronicchannels[20].Thesensitivityisequivalentwithin the statistical and systematic uncertainties to the corresponding
√
s
=
13TeV searchfromATLAS[60].Fig. 4.Observedandexpected95%CLupperlimitwiththe±1 and±2 standard deviationuncertaintybandsonσ(X)B(X→VH)B(H→bb)intheHVTmodel B benchmarkscenariowithgV=3 asafunctionoftheresonancemass,forthe
[image:8.612.323.528.66.219.2]combi-nationofalltheconsideredchannels.(Forinterpretationofthecolorsinthisfigure, thereaderisreferredtothewebversionofthisarticle.)
Fig. 5.ObservedexclusionintheHVTparameterplanegVcH,g2cF/gVforthree
differentresonancemasses(1.5,2.0,and2.5 TeV).TheparametergVrepresentsthe
couplingstrengthofthenewinteraction,cHthecouplingbetweentheHVTbosons
and theHiggsboson andlongitudinally polarizedSMvector bosons,andcF the
couplingbetweentheheavyvectorbosonsandtheSMfermions.Thebenchmark scenario BwithgV=3 isrepresentedbytheredpoint.Thegrayshadedarea
cor-respondstotheregionwheretheresonancenaturalwidthispredictedtobelarger thanthetypicalexperimentalresolution(5%),andthusthenarrow-width approx-imationbreaksdown.(Forinterpretationofthereferencestocolorinthisfigure legend,thereaderisreferredtothewebversionofthisarticle.)
9. Summary
A search for a heavy resonance with mass between 800 and 4000 GeV, decaying into a vector boson and a Higgs boson, has been described.The datasampleswere collected by theCMS ex-periment at
√
s=
13TeV during 2015, and correspond to inte-gratedluminositiesof2.2–2.5 fb−1,dependingonthechannel.The final statesexplored includetheleptonicdecaymodesofthe vec-torboson,eventswithzero(Z→
νν
), exactlyone(W→
ν
),and two (Z→
) charged leptons, with
=
e,
μ
. Higgs bosons are reconstructedfromtheirdecaystobb pairs.Dependingonthe res-onance mass,upperlimits inthe range10–200 fb areset on the productofthecrosssectionforanarrowspin-1resonanceandthe branchingfractionsforthedecayoftheresonanceintoaHiggsand avectorboson,andforthedecayoftheHiggsbosonintoapairof b quarks.Resonanceswithmasseslower than2 TeV areexcluded withintheheavyvectortripletmodelinthebenchmarkscenario B with gV=
3.Theseresultsrepresentasignificantreductioninthe [image:8.612.328.525.283.431.2]Acknowledgements
WecongratulateourcolleaguesintheCERNaccelerator depart-ments for the excellent performance of the LHC and thank the technicalandadministrativestaffs atCERN andatother CMS in-stitutes for their contributions to the success of the CMS effort. Inaddition,wegratefullyacknowledgethecomputingcentersand personneloftheWorldwideLHCComputingGridfordeliveringso effectivelythecomputinginfrastructure essential toour analyses. Finally, we acknowledge the enduring support for the construc-tionandoperationofthe LHCandtheCMSdetectorprovided by thefollowingfundingagencies:BMWFWandFWF(Austria);FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MOST, and NSFC (China); COLCIEN-CIAS(Colombia);MSESandCSF(Croatia);RPF(Cyprus);SENESCYT (Ecuador); MoER, ERC IUT, and ERDF (Estonia); Academy of Fin-land,MEC,andHIP(Finland);CEAandCNRS/IN2P3(France);BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hun-gary);DAEandDST (India);IPM(Iran);SFI(Ireland);INFN (Italy); MSIPandNRF (RepublicofKorea);LAS(Lithuania);MOE andUM (Malaysia); BUAP,CINVESTAV, CONACYT, LNS, SEP, and UASLP-FAI (Mexico); MBIE (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland);FCT (Portugal);JINR (Dubna); MON, RosAtom,RAS, and RFBR (Russia); MESTD (Serbia); SEIDI and CPAN (Spain); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter, IPST, STAR, and NSTDA(Thailand); TUBITAK and TAEK(Turkey); NASU andSFFR(Ukraine);STFC(UnitedKingdom);DOEandNSF(USA).
Individuals have received support from the Marie-Curie pro-gram and the European Research Council and EPLANET (Euro-pean Union); the Leventis Foundation; the Alfred P. Sloan Foun-dation; the Alexander von Humboldt Foundation; the Belgian Federal Science Policy Office; the Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technolo-gie (IWT-Belgium); the Ministry of Education, Youth and Sports (MEYS)of the CzechRepublic; the Councilof Science and Indus-trial Research, India; the HOMING PLUS program of the Foun-dation for Polish Science, cofinanced from European Union, Re-gional Development Fund, the Mobility Plus program of the Ministry of Science and Higher Education, the National Sci-ence Center (Poland), contracts Harmonia 2014/14/M/ST2/00428, Opus 2013/11/B/ST2/04202, 2014/13/B/ST2/02543 and 2014/15/B/ST2/03998,Sonata-bis2012/07/E/ST2/01406; theThalis andAristeiaprograms cofinancedbyEU-ESFandtheGreekNSRF; the National Priorities Research Program by Qatar National Re-search Fund;the ProgramaClarín-COFUND del Principado de As-turias;theRachadapisekSompotFundforPostdoctoralFellowship, Chulalongkorn University and the Chulalongkorn Academic into Its 2nd Century Project Advancement Project (Thailand); andthe WelchFoundation,contractC-1845.
References
[1] ATLASCollaboration,Observationofanewparticleinthesearchforthe Stan-dardModelHiggsbosonwiththeATLASdetectorattheLHC,Phys.Lett.B716 (2012)1,http://dx.doi.org/10.1016/j.physletb.2012.08.020,arXiv:1207.7214. [2] CMSCollaboration, Observationofanewbosonat amassof125GeVwith
theCMSexperimentattheLHC,Phys.Lett.B716(2012)30,http://dx.doi.org/ 10.1016/j.physletb.2012.08.021,arXiv:1207.7235.
[3] CMSCollaboration,Observationofanewbosonwithmassnear125 GeVin ppcollisionsat√s=7 and 8 TeV,J.HighEnergyPhys.06(2013)081,http:// dx.doi.org/10.1007/JHEP06(2013)081,arXiv:1303.4571.
[4] G.Aad,etal.,ATLAS,MeasurementoftheHiggsbosonmassfromtheH→γ γ
and H→Z Z∗→4channelsinpp collisionsatcenter-of-massenergiesof 7and8TeVwiththeATLASdetector,Phys.Rev.D90(2014)052004,http:// dx.doi.org/10.1103/PhysRevD.90.052004,arXiv:1406.3827.
[5] CMSCollaboration,PrecisedeterminationofthemassoftheHiggsbosonand testsofcompatibilityofitscouplingswiththestandardmodelpredictions us-ingproton collisionsat 7and8TeV, Eur.Phys.J. C75(2015)212,http:// dx.doi.org/10.1140/epjc/s10052-015-3351-7,arXiv:1412.8662.
[6] CMSCollaboration,Evidence forthe directdecayofthe125GeVHiggs bo-sontofermions,Nat.Phys.10(2014)557,http://dx.doi.org/10.1038/nphys3005, arXiv:1401.6527.
[7] ATLAS and CMS Collaborations, Combined measurement of the Higgs bo-son mass in pp collisions at √s=7 and 8 TeV withthe ATLAS and CMS experiments, Phys. Rev. Lett. 114 (2015) 191803, http://dx.doi.org/10.1103/ PhysRevLett.114.191803,arXiv:1503.07589.
[8] R.Barbieri,G.F. Giudice,Upper bounds onsupersymmetricparticle masses, Nucl.Phys.B306(1988)63,http://dx.doi.org/10.1016/0550-3213(88)90171-X. [9] V.D.Barger,W.-Y.Keung,E.Ma,Agaugemodelwithlight W and Z bosons,
Phys.Rev.D22(1980)727,http://dx.doi.org/10.1103/PhysRevD.22.727. [10] E.Salvioni,G.Villadoro,F.Zwirner,MinimalZ models:presentboundsand
earlyLHC reach,J.HighEnergyPhys.09(2009)068,http://dx.doi.org/10.1088/ 1126-6708/2009/11/068,arXiv:0909.1320.
[11] C.Grojean,E.Salvioni,R.Torre,Aweakly constrainedW at theearlyLHC, J. HighEnergyPhys.07(2011)002,http://dx.doi.org/10.1007/JHEP07(2011)002, arXiv:1103.2761.
[12] R.Contino,D.Pappadopulo,D.Marzocca,R.Rattazzi,Ontheeffectof reso-nancesincompositeHiggs phenomenology,J.HighEnergyPhys.10(2011)081,
http://dx.doi.org/10.1007/JHEP10(2011)081.
[13] D.Marzocca,M.Serone,J.Shu,GeneralcompositeHiggsmodels,J.HighEnergy Phys.08(2012)13,http://dx.doi.org/10.1007/JHEP08(2012)013.
[14] B.Bellazzini,C.Csaki, J.Serra,CompositeHiggses,Eur.Phys. J.C74(2014) 2766,http://dx.doi.org/10.1140/epjc/s10052-014-2766-x,arXiv:1401.2457. [15] T.Han,H.E.Logan,B.McElrath,L.-T.Wang,PhenomenologyofthelittleHiggs
model, Phys. Rev. D 67 (2003) 095004, http://dx.doi.org/10.1103/PhysRevD. 67.095004,arXiv:hep-ph/0301040.
[16] M.Schmaltz,D.Tucker-Smith,LittleHiggs theories,Annu.Rev.Nucl.Part.Sci. 55(2005)229,http://dx.doi.org/10.1146/annurev.nucl.55.090704.151502. [17] M.Perelstein,LittleHiggsmodelsandtheirphenomenology,Prog.Part.Nucl.
Phys. 58 (2007)247,http://dx.doi.org/10.1016/j.ppnp.2006.04.001, arXiv:hep-ph/0512128.
[18] D.Pappadopulo,A.Thamm,R.Torre,A.Wulzer,Heavyvectortriplets:bridging theoryanddata,J.HighEnergyPhys.09(2014)60,http://dx.doi.org/10.1007/ JHEP09(2014)060,arXiv:1402.4431.
[19] CMSCollaboration,SearchforapseudoscalarbosondecayingintoaZboson andthe125GeVHiggsbosonin+−bb finalstates,Phys.Lett.B748(2015) 221,http://dx.doi.org/10.1016/j.physletb.2015.07.010,arXiv:1504.04710. [20] CMSCollaboration,SearchforamassiveresonancedecayingintoaHiggs
bo-son andaWorZbosoninhadronicfinalstatesinproton–protoncollisions at √s=8 TeV,J.HighEnergyPhys.02(2016)145,http://dx.doi.org/10.1007/ JHEP02(2016)145,arXiv:1506.01443.
[21] CMSCollaboration,Searchfornarrowhigh-massresonancesinproton–proton collisionsat√s=8 TeV decayingtoaZandaHiggsboson,Phys.Lett.B748 (2015)255,http://dx.doi.org/10.1016/j.physletb.2015.07.011,arXiv:1502.04994. [22] CMSCollaboration,SearchformassiveWHresonancesdecayingintotheνbb finalstateat√s=8 TeV,Eur.Phys.J.C76(2016)1,http://dx.doi.org/10.1140/ epjc/s10052-016-4067-z,arXiv:1601.06431.
[23] J.Alwall,R.Frederix,S.Frixione,V.Hirschi,F.Maltoni,O.Mattelaer,H.-S.Shao, T.Stelzer,P.Torrielli,M.Zaro,Theautomatedcomputationoftree-leveland next-to-leading orderdifferentialcross sections,and theirmatching to par-tonshowersimulations,J.HighEnergyPhys.07(2014)079,http://dx.doi.org/ 10.1007/JHEP07(2014)079,arXiv:1405.0301.
[24] Y.Li,F.Petriello,CombiningQCDandelectroweakcorrectionstodilepton pro-ductioninFEWZ, Phys.Rev.D86 (2012)094034, http://dx.doi.org/10.1103/ PhysRevD.86.094034,arXiv:1208.5967.
[25] S. Kallweit, J.M. Lindert, S. Pozzorini, M. Schönherr, P. Maierhöfer, NLO QCD+EWpredictionsforV+jetsincludingoff-shellvector-bosondecaysand multijetmerging,J.HighEnergyPhys.04(2016)021,http://dx.doi.org/10.1007/ JHEP04(2016)021,arXiv:1511.08692.
[26] P.Nason,AnewmethodforcombiningNLOQCD withshowerMonteCarlo algorithms, J. High Energy Phys. 11 (2004) 040, http://dx.doi.org/10.1088/ 1126-6708/2004/11/040,arXiv:hep-ph/0409146.
[27] S.Frixione,P.Nason,C.Oleari,MatchingNLOQCDcomputationswithParton Showersimulations:thePOWHEGmethod,J.HighEnergyPhys.11(2007)070,
http://dx.doi.org/10.1088/1126-6708/2007/11/070,arXiv:0709.2092.
[28] S.Alioli, P. Nason, C.Oleari,E. Re,A general framework for implementing NLOcalculationsinshowerMonteCarloprograms:thePOWHEGBOX,J. High EnergyPhys.06(2010)043,http://dx.doi.org/10.1007/JHEP06(2010)043,arXiv: 1002.2581.
[29] M.Czakon,A.Mitov,Top++:aprogramforthe calculationofthe top-pair cross-sectionat hadroncolliders,Comput.Phys.Commun.185(2014)2930,
http://dx.doi.org/10.1016/j.cpc.2014.06.021,arXiv:1112.5675.
[31] T. Sjöstrand,S. Mrenna, P.Skands,PYTHIA 6.4physics and manual,J. High EnergyPhys.05(2006)026,http://dx.doi.org/10.1088/1126-6708/2006/05/026, arXiv:hep-ph/0603175.
[32] P.Skands,S.Carrazza,J.Rojo,TuningPYTHIA8.1:theMonash2013Tune,Eur. Phys. J.C74 (2014)3024,http://dx.doi.org/10.1140/epjc/s10052-014-3024-y, arXiv:1404.5630.
[33] CMS Collaboration, Event generator tunes obtained from underlying event and multiparton scattering measurements, Eur. Phys. J. C 76 (2016) 155,
http://dx.doi.org/10.1140/epjc/s10052-016-3988-x,arXiv:1512.00815. [34] R.D.Ball,etal., NNPDF,Partondistributionsfor theLHCRun II,J. High
En-ergy Phys. 04 (2015) 040,http://dx.doi.org/10.1007/JHEP04(2015)040, arXiv: 1410.8849.
[35] S.Agostinelli, et al., GEANT4, GEANT4—a simulation toolkit,Nucl. Instrum. MethodsA506(2003)250,http://dx.doi.org/10.1016/S0168-9002(03)01368-8. [36] CMSCollaboration,TheCMSexperimentattheCERNLHC,J.Instrum.3(2008)
S08004,http://dx.doi.org/10.1088/1748-0221/3/08/S08004.
[37] CMSCollaboration,Descriptionandperformanceoftrackandprimary-vertex reconstruction with the CMS tracker,J. Instrum. 9 (2014) P10009, http:// dx.doi.org/10.1088/1748-0221/9/10/P10009,arXiv:1405.6569.
[38] CMSCollaboration,PerformanceofCMSmuonreconstructioninppcollision eventsat √s=7 TeV,J.Instrum.7(2012)P10002,http://dx.doi.org/10.1088/ 1748-0221/7/10/P10002,arXiv:1206.4071.
[39] CMSCollaboration,Particle-FlowEventReconstructioninCMSandPerformance forJets,Taus,andEmiss
T ,CMSPhysicsAnalysisSummaryCMS-PAS-PFT-09-001,
CERN,2009,http://cdsweb.cern.ch/record/1194487.
[40] CMSCollaboration,Commissioningofthe Particle-FlowEventwiththeFirst LHCCollisionsRecordedintheCMSDetector,CMSPhysicsAnalysisSummary CMS-PAS-PFT-10-001,CERN,2010,http://cdsweb.cern.ch/record/1247373. [41] M.Cacciari,G.P.Salam,G.Soyez,Theanti-ktjetclusteringalgorithm,J.High
EnergyPhys.04(2008)063,http://dx.doi.org/10.1088/1126-6708/2008/04/063, arXiv:0802.1189.
[42] M.Cacciari,G.P.Salam,G.Soyez,FastJetusermanual,Eur.Phys.J.C72(2012) 1896,http://dx.doi.org/10.1140/epjc/s10052-012-1896-2,arXiv:1111.6097. [43] M.Cacciari, G.P.Salam, G. Soyez, The catchment areaof jets, J. High
En-ergy Phys. 04 (2008) 005, http://dx.doi.org/10.1088/1126-6708/2008/04/005, arXiv:0802.1188.
[44]CMSCollaboration,JetenergyscaleandresolutionintheCMSexperimentin ppcollisionsat8TeV,arXiv:1607.03663,J.Inst.(2016),submittedfor publica-tion.
[45] S.D.Ellis,C.K. Vermilion,J.R. Walsh,Recombination algorithmsand jet sub-structure:pruningasatoolforheavyparticlesearches,Phys.Rev.D81(2010) 094023,http://dx.doi.org/10.1103/PhysRevD.81.094023,arXiv:0912.0033. [46] M.Dasgupta,A.Fregoso,S.Marzani,G.P.Salam,Towardsanunderstandingof
jetsubstructure,J.HighEnergyPhys.09(2013)029,http://dx.doi.org/10.1007/ JHEP09(2013)029,arXiv:1307.0007.
[47] A.J.Larkoski,S.Marzani,G.Soyez,J.Thaler,Softdrop,J.HighEnergyPhys.05 (2014)146,http://dx.doi.org/10.1007/JHEP05(2014)146,arXiv:1402.2657. [48] CMSCollaboration,IdentificationofbQuarkJetsattheCMSExperimentinthe
LHCRun2,CMSPhysicsAnalysisSummaryCMS-PAS-BTV-15-001,CERN,2016,
http://cds.cern.ch/record/2138504.
[49] CMSCollaboration,PerformanceofMissingEnergyReconstructionin13TeVpp CollisionDataUsingtheCMSDetector,CMSPhysicsAnalysisSummary CMS-PAS-JME-16-004,CERN,2016,http://cds.cern.ch/record/1479660.
[50] CMSCollaboration,Performanceofelectronreconstructionandselectionwith the CMS detector in proton–proton collisions at √s=8TeV, J. Instrum. 10 (2015) P06005, http://dx.doi.org/10.1088/1748-0221/10/06/P06005, arXiv: 1502.02701.
[51] CMS Collaboration, Reconstruction and identificationofτ lepton decays to hadrons and ντ at CMS, J. Instrum. 11 (2016) P01019, http://dx.doi.org/ 10.1088/1748-0221/11/01/P01019,arXiv:1510.07488.
[52] J.Bellm,etal.,Herwig7.0/Herwig++3.0releasenote,Eur.Phys.J.C76(2016) 196,http://dx.doi.org/10.1140/epjc/s10052-016-4018-8,arXiv:1512.01178. [53] M. Bähr, S. Gieseke, M.A. Gigg, D. Grellscheid, K. Hamilton, O.
Latunde-Dada, S. Plätzer, P. Richardson, M.H. Seymour, A. Sherstnev, B.R. Webber, Herwig++physicsandmanual,Eur.Phys.J.C58(2008)639,http://dx.doi.org/ 10.1140/epjc/s10052-008-0798-9,arXiv:0803.0883.
[54] CMS Collaboration,CMSLuminosityMeasurementforthe 2015DataTaking Period, CMS Physics Analysis SummaryCMS-PAS-LUM-15-001, CERN, 2015,
http://cds.cern.ch/record/2138682.
[55] J. Butterworth, et al., PDF4LHC recommendations for LHC Run II, J. Phys. G43 (2016) 23001,http://dx.doi.org/10.1088/0954-3899/43/2/023001, arXiv: 1510.03865.
[56] T. Junk, Confidence level computation for combining searches with small statistics,Nucl.Instrum.MethodsA434(1999)435,http://dx.doi.org/10.1016/ S0168-9002(99)00498-2,arXiv:hep-ex/9902006.
[57] A.L.Read,Presentationofsearchresults:theC Lstechnique,J.Phys.G28(2002)
2693,http://dx.doi.org/10.1088/0954-3899/28/10/313.
[58] CMS and ATLAS Collaborations, Procedure for the LHC HiggsBosonSearch Combination inSummer 2011, Technical report CMS-NOTE-2011-005, ATL-PHYS-PUB-2011-11,CERN,2011,https://cds.cern.ch/record/1379837. [59] G.Cowan,K.Cranmer,E.Gross,O.Vitells,Asymptoticformulaefor
likelihood-basedtestsofnewphysics,Eur.Phys.J.C71(2011)1554,http://dx.doi.org/ 10.1140/epjc/s10052-011-1554-0, arXiv:1007.1727, http://dx.doi.org/10.1140/ epjc/s10052-013-2501-z.
[60] ATLASCollaboration,SearchfornewresonancesdecayingtoaW orZ boson andaHiggsbosoninthe+−bb¯,νbb¯,andνν¯bb¯channelswithppcollisions at√s=13 TeV withtheATLASdetector,Phys.Lett.B765(2016)32,http:// dx.doi.org/10.1016/j.physletb.2016.11.045,arXiv:1607.05621.
TheCMSCollaboration
V. Khachatryan,
A.M. Sirunyan,
A. Tumasyan
YerevanPhysicsInstitute,Yerevan,Armenia
W. Adam,
E. Asilar,
T. Bergauer,
J. Brandstetter,
E. Brondolin,
M. Dragicevic,
J. Erö,
M. Flechl,
M. Friedl,
R. Frühwirth
1,
V.M. Ghete,
C. Hartl,
N. Hörmann,
J. Hrubec,
M. Jeitler
1,
A. König,
I. Krätschmer,
D. Liko,
T. Matsushita,
I. Mikulec,
D. Rabady,
N. Rad,
B. Rahbaran,
H. Rohringer,
J. Schieck
1,
J. Strauss,
W. Waltenberger,
C.-E. Wulz
1InstitutfürHochenergiephysik,Wien,Austria
O. Dvornikov,
V. Makarenko,
V. Zykunov
InstituteforNuclearProblems,Minsk,Belarus
V. Mossolov,
N. Shumeiko,
J. Suarez Gonzalez
NationalCentreforParticleandHighEnergyPhysics,Minsk,Belarus
S. Alderweireldt,
E.A. De Wolf,
X. Janssen,
J. Lauwers,
M. Van De Klundert,
H. Van Haevermaet,
P. Van Mechelen,
N. Van Remortel,
A. Van Spilbeeck
S. Abu Zeid,
F. Blekman,
J. D’Hondt,
N. Daci,
I. De Bruyn,
K. Deroover,
N. Heracleous,
S. Lowette,
S. Moortgat,
L. Moreels,
A. Olbrechts,
Q. Python,
S. Tavernier,
W. Van Doninck,
P. Van Mulders,
I. Van Parijs
VrijeUniversiteitBrussel,Brussel,Belgium
H. Brun,
B. Clerbaux,
G. De Lentdecker,
H. Delannoy,
G. Fasanella,
L. Favart,
R. Goldouzian,
A. Grebenyuk,
G. Karapostoli,
T. Lenzi,
A. Léonard,
J. Luetic,
T. Maerschalk,
A. Marinov,
A. Randle-conde,
T. Seva,
C. Vander Velde,
P. Vanlaer,
R. Yonamine,
F. Zenoni,
F. Zhang
2UniversitéLibredeBruxelles,Bruxelles,Belgium
A. Cimmino,
T. Cornelis,
D. Dobur,
A. Fagot,
G. Garcia,
M. Gul,
D. Poyraz,
S. Salva,
R. Schöfbeck,
A. Sharma,
M. Tytgat,
W. Van Driessche,
E. Yazgan,
N. Zaganidis
GhentUniversity,Ghent,Belgium
H. Bakhshiansohi,
C. Beluffi
3,
O. Bondu,
S. Brochet,
G. Bruno,
A. Caudron,
S. De Visscher,
C. Delaere,
M. Delcourt,
B. Francois,
A. Giammanco,
A. Jafari,
P. Jez,
M. Komm,
V. Lemaitre,
A. Magitteri,
A. Mertens,
M. Musich,
C. Nuttens,
K. Piotrzkowski,
L. Quertenmont,
M. Selvaggi,
M. Vidal Marono,
S. Wertz
UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium
N. Beliy
UniversitédeMons,Mons,Belgium
W.L. Aldá Júnior,
F.L. Alves,
G.A. Alves,
L. Brito,
C. Hensel,
A. Moraes,
M.E. Pol,
P. Rebello Teles
CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil
E. Belchior Batista Das Chagas,
W. Carvalho,
J. Chinellato
4,
A. Custódio,
E.M. Da Costa,
G.G. Da Silveira
5,
D. De Jesus Damiao,
C. De Oliveira Martins,
S. Fonseca De Souza,
L.M. Huertas Guativa,
H. Malbouisson,
D. Matos Figueiredo,
C. Mora Herrera,
L. Mundim,
H. Nogima,
W.L. Prado Da Silva,
A. Santoro,
A. Sznajder,
E.J. Tonelli Manganote
4,
A. Vilela Pereira
UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil
S. Ahuja
a,
C.A. Bernardes
b,
S. Dogra
a,
T.R. Fernandez Perez Tomei
a,
E.M. Gregores
b,
P.G. Mercadante
b,
C.S. Moon
a,
S.F. Novaes
a,
Sandra S. Padula
a,
D. Romero Abad
b,
J.C. Ruiz Vargas
aUniversidadeEstadualPaulista,SãoPaulo,Brazil bUniversidadeFederaldoABC,SãoPaulo,Brazil
A. Aleksandrov,
R. Hadjiiska,
P. Iaydjiev,
M. Rodozov,
S. Stoykova,
G. Sultanov,
M. Vutova
InstituteforNuclearResearchandNuclearEnergy,Sofia,Bulgaria
A. Dimitrov,
I. Glushkov,
L. Litov,
B. Pavlov,
P. Petkov
UniversityofSofia,Sofia,Bulgaria
W. Fang
6BeihangUniversity,Beijing,China
M. Ahmad,
J.G. Bian,
G.M. Chen,
H.S. Chen,
M. Chen,
Y. Chen
7,
T. Cheng,
C.H. Jiang,
D. Leggat,
Z. Liu,
F. Romeo,
S.M. Shaheen,
A. Spiezia,
J. Tao,
C. Wang,
Z. Wang,
H. Zhang,
J. Zhao
InstituteofHighEnergyPhysics,Beijing,China
Y. Ban,
G. Chen,
Q. Li,
S. Liu,
Y. Mao,
S.J. Qian,
D. Wang,
Z. Xu
C. Avila,
A. Cabrera,
L.F. Chaparro Sierra,
C. Florez,
J.P. Gomez,
C.F. González Hernández,
J.D. Ruiz Alvarez,
J.C. Sanabria
UniversidaddeLosAndes,Bogota,Colombia
N. Godinovic,
D. Lelas,
I. Puljak,
P.M. Ribeiro Cipriano,
T. Sculac
UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia
Z. Antunovic,
M. Kovac
UniversityofSplit,FacultyofScience,Split,Croatia
V. Brigljevic,
D. Ferencek,
K. Kadija,
S. Micanovic,
L. Sudic,
T. Susa
InstituteRudjerBoskovic,Zagreb,Croatia
A. Attikis,
G. Mavromanolakis,
J. Mousa,
C. Nicolaou,
F. Ptochos,
P.A. Razis,
H. Rykaczewski,
D. Tsiakkouri
UniversityofCyprus,Nicosia,Cyprus
M. Finger
8,
M. Finger Jr.
8CharlesUniversity,Prague,Czechia
E. Carrera Jarrin
UniversidadSanFranciscodeQuito,Quito,Ecuador
E. El-khateeb
9,
S. Elgammal
10,
A. Mohamed
11AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt
B. Calpas,
M. Kadastik,
M. Murumaa,
L. Perrini,
M. Raidal,
A. Tiko,
C. Veelken
NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia
P. Eerola,
J. Pekkanen,
M. Voutilainen
DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland
J. Härkönen,
T. Järvinen,
V. Karimäki,
R. Kinnunen,
T. Lampén,
K. Lassila-Perini,
S. Lehti,
T. Lindén,
P. Luukka,
J. Tuominiemi,
E. Tuovinen,
L. Wendland
HelsinkiInstituteofPhysics,Helsinki,Finland
J. Talvitie,
T. Tuuva
LappeenrantaUniversityofTechnology,Lappeenranta,Finland
M. Besancon,
F. Couderc,
M. Dejardin,
D. Denegri,
B. Fabbro,
J.L. Faure,
C. Favaro,
F. Ferri,
S. Ganjour,
S. Ghosh,
A. Givernaud,
P. Gras,
G. Hamel de Monchenault,
P. Jarry,
I. Kucher,
E. Locci,
M. Machet,
J. Malcles,
J. Rander,
A. Rosowsky,
M. Titov,
A. Zghiche
IRFU,CEA,UniversitéParis-Saclay,Gif-sur-Yvette,France
A. Abdulsalam,
I. Antropov,
S. Baffioni,
F. Beaudette,
P. Busson,
L. Cadamuro,
E. Chapon,
C. Charlot,
O. Davignon,
R. Granier de Cassagnac,
M. Jo,
S. Lisniak,
P. Miné,
M. Nguyen,
C. Ochando,
G. Ortona,
P. Paganini,
P. Pigard,
S. Regnard,
R. Salerno,
Y. Sirois,
T. Strebler,
Y. Yilmaz,
A. Zabi
LaboratoireLeprince-Ringuet,EcolePolytechnique,IN2P3-CNRS,Palaiseau,France
J.-L. Agram
12,
J. Andrea,
A. Aubin,
D. Bloch,
J.-M. Brom,
M. Buttignol,
E.C. Chabert,
N. Chanon,
C. Collard,
E. Conte
12,
X. Coubez,
J.-C. Fontaine
12,
D. Gelé,
U. Goerlach,
A.-C. Le Bihan,
K. Skovpen,
P. Van Hove
S. Gadrat
CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France
S. Beauceron,
C. Bernet,
G. Boudoul,
E. Bouvier,
C.A. Carrillo Montoya,
R. Chierici,
D. Contardo,
B. Courbon,
P. Depasse,
H. El Mamouni,
J. Fan,
J. Fay,
S. Gascon,
M. Gouzevitch,
G. Grenier,
B. Ille,
F. Lagarde,
I.B. Laktineh,
M. Lethuillier,
L. Mirabito,
A.L. Pequegnot,
S. Perries,
A. Popov
13,
D. Sabes,
V. Sordini,
M. Vander Donckt,
P. Verdier,
S. Viret
UniversitédeLyon,UniversitéClaudeBernardLyon1,CNRS-IN2P3,InstitutdePhysiqueNucléairedeLyon,Villeurbanne,France
A. Khvedelidze
8GeorgianTechnicalUniversity,Tbilisi,Georgia
Z. Tsamalaidze
8TbilisiStateUniversity,Tbilisi,Georgia
C. Autermann,
S. Beranek,
L. Feld,
A. Heister,
M.K. Kiesel,
K. Klein,
M. Lipinski,
A. Ostapchuk,
M. Preuten,
F. Raupach,
S. Schael,
C. Schomakers,
J. Schulz,
T. Verlage,
H. Weber,
V. Zhukov
13RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany
A. Albert,
M. Brodski,
E. Dietz-Laursonn,
D. Duchardt,
M. Endres,
M. Erdmann,
S. Erdweg,
T. Esch,
R. Fischer,
A. Güth,
M. Hamer,
T. Hebbeker,
C. Heidemann,
K. Hoepfner,
S. Knutzen,
M. Merschmeyer,
A. Meyer,
P. Millet,
S. Mukherjee,
M. Olschewski,
K. Padeken,
T. Pook,
M. Radziej,
H. Reithler,
M. Rieger,
F. Scheuch,
L. Sonnenschein,
D. Teyssier,
S. Thüer
RWTHAachenUniversity,III.PhysikalischesInstitutA,Aachen,Germany
V. Cherepanov,
G. Flügge,
F. Hoehle,
B. Kargoll,
T. Kress,
A. Künsken,
J. Lingemann,
T. Müller,
A. Nehrkorn,
A. Nowack,
I.M. Nugent,
C. Pistone,
O. Pooth,
A. Stahl
14RWTHAachenUniversity,III.PhysikalischesInstitutB,Aachen,Germany
M. Aldaya Martin,
T. Arndt,
C. Asawatangtrakuldee,
K. Beernaert,
O. Behnke,
U. Behrens,
A.A. Bin Anuar,
K. Borras
15,
A. Campbell,
P. Connor,
C. Contreras-Campana,
F. Costanza,
C. Diez Pardos,
G. Dolinska,
G. Eckerlin,
D. Eckstein,
T. Eichhorn,
E. Eren,
E. Gallo
16,
J. Garay Garcia,
A. Geiser,
A. Gizhko,
J.M. Grados Luyando,
P. Gunnellini,
A. Harb,
J. Hauk,
M. Hempel
17,
H. Jung,
A. Kalogeropoulos,
O. Karacheban
17,
M. Kasemann,
J. Keaveney,
C. Kleinwort,
I. Korol,
D. Krücker,
W. Lange,
A. Lelek,
J. Leonard,
K. Lipka,
A. Lobanov,
W. Lohmann
17,
R. Mankel,
I.-A. Melzer-Pellmann,
A.B. Meyer,
G. Mittag,
J. Mnich,
A. Mussgiller,
E. Ntomari,
D. Pitzl,
R. Placakyte,
A. Raspereza,
B. Roland,
M.Ö. Sahin,
P. Saxena,
T. Schoerner-Sadenius,
C. Seitz,
S. Spannagel,
N. Stefaniuk,
G.P. Van Onsem,
R. Walsh,
C. Wissing
DeutschesElektronen-Synchrotron,Hamburg,Germany
V. Blobel,
M. Centis Vignali,
A.R. Draeger,
T. Dreyer,
E. Garutti,
D. Gonzalez,
J. Haller,
M. Hoffmann,
A. Junkes,
R. Klanner,
R. Kogler,
N. Kovalchuk,
T. Lapsien,
T. Lenz,
I. Marchesini,
D. Marconi,
M. Meyer,
M. Niedziela,
D. Nowatschin,
F. Pantaleo
14,
T. Peiffer,
A. Perieanu,
J. Poehlsen,
C. Sander,
C. Scharf,
P. Schleper,
A. Schmidt,
S. Schumann,
J. Schwandt,
H. Stadie,
G. Steinbrück,
F.M. Stober,
M. Stöver,
H. Tholen,
D. Troendle,
E. Usai,
L. Vanelderen,
A. Vanhoefer,
B. Vormwald
UniversityofHamburg,Hamburg,Germany