Measurement of W boson angular distributions in events with high transverse momentum jets at √s=8 TeV using the ATLAS detector

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Citation for this paper:

Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Abeloos, B.; … &

Zwalinski, L. (2017). Measurement of W boson angular distributions in events with high transverse momentum jets at √s=8 TeV using the ATLAS detector. Physics

Letters B, 765, 132-153. DOI: 10.1016/j.physletb.2016.12.005

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Measurement of W boson angular distributions in events with high transverse momentum jets at √s=8 TeV using the ATLAS detector

M. Aaboud et al. (ATLAS Collaboration) 2017

Creative Commons Attribution License. http://creativecommons.org/licenses/by/4.0/

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Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Measurement

of

W boson

angular

distributions

in

events

with

high

transverse

momentum

jets

at

√

s

=

8 TeV using

the

ATLAS

detector

.TheATLAS Collaboration

a rt i c l e i nf o a b s t ra c t

Articlehistory:

Received23September2016

Receivedinrevisedform30November2016 Accepted2December2016

Availableonline6December2016 Editor: W.-D.Schlatter

TheW bosonangulardistributionineventswithhightransversemomentumjetsismeasuredusingdata collectedbytheATLASexperimentfromproton–protoncollisionsatacentre-of-massenergy√s=8 TeV attheLargeHadronCollider,correspondingtoan integratedluminosityof20.3 fb−1.Thefocusison thecontributionsto W+jets processes fromrealW emission,which isachievedby studyingevents whereamuonisobservedclosetoahightransversemomentumjet.Atsmallangularseparations,these contributionsare expectedtobelarge.Varioustheoreticalmodelsofthisprocessare comparedtothe dataintermsoftheabsolutecross-sectionandtheangulardistributionsofthemuonfromtheleptonic

W decay.

1. Introduction

Precision measurements of Standard Model processes at the LargeHadronCollider(LHC)arecrucialforprobingthe fundamen-talstructure ofthestrongand electroweakinteractions. Thedata sample corresponding to an integrated luminosity of 20.3 fb−1 collected by theATLAS experimentfrom proton–proton (pp) col-lisions ata centre-of-massenergy √s=8 TeV at the LHCallows detailed study ofperturbative quantumchromodynamics (pertur-bativeQCD, pQCD)and realandvirtual electroweak(EW) correc-tionsthatimpactmeasurementsofW+jets production.

Athigh energies,realemission ofweakbosons indijet events can contribute signiﬁcantly to inclusive W +jets measurements

[1–5].Inleading-order (LO) calculationsof W+1-jet production, theW bosonisbalancedbytherecoilhadronicjet,oftenreferred toasback-to-back production.Atnext-to-leadingorder(NLO),QCD and EW corrections to W+1-jet processes appear, both as real and virtual contributions. In the case of real W boson emission froman initial- or ﬁnal-statequark, these contributions scale as Oαln2pT,j/mW

,where α isthe gaugecouplingofthe uniﬁed EWtheory, pT,j is thetransverse momentumof thejet and mW is the W boson mass, and havea collinear enhancement in the distribution of the angular distance between the W boson and the closest jet. The collinear enhancement arises from collinear and infrareddivergences which wouldbe present in the limit of

_E-mail_address:_{atlas.publications@cern.ch}_.

vanishing W boson mass, but which are regulated by its ﬁnite mass.Theprocedurestocorrectlyaccountforcollinearparton radi-ation,suchasmasslessgluonemission,arewellknownandledto theintroductionof(Sudakov)partonshoweringoftheinitial- and ﬁnal-state partonsin Monte Carlo generators for QCD as well as quantumelectrodynamics (QED)contributions.An analogous pro-cedure is available for the emission of real W bosons [6]. The effectofrealW bosonemissioncanbeprobedbyisolatingevents forwhichthecancellation betweenrealand virtualcorrections is incomplete, forexample by studyingthe region of smallangular separationbetween ajet andthe W boson.Thisregionalso con-tainsLO contributionsfrom W+2-jets, as well as corrections to thatprocess,whichmustbeincludedforaccuratepredictions.

DuetothiscomplexmixtureofW+1-jetand W+2-jet pro-cesses,andtherelevantQCDandEWcorrectionstoboth, compar-isons of measurements to predictions using multiple approaches for estimating those corrections are crucial. Comparisons of the measured angularspectra of the muon fromthe W boson with ﬁxed-order predictions at NLO and next-to-next-to-leading-order (NNLO)andwithprogramswith electroweakpartonshowershelp inunderstandingtheaccuracyofthesepredictions.

The measurements presented here focus on events that con-tain amuonand ajetwith transversemomentum pT>500 GeV.

Inthiskinematicregime,contributionstoW+jets processesfrom realW bosonemissionareenhancedintheregionofsmallangular separationbetween the W boson decayproducts and the closest jet.Theangularseparationisdeﬁnedasthedistancebetween the http://dx.doi.org/10.1016/j.physletb.2016.12.005

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muon and the closest jet, R(μ,jet)=(φ)2_{+ (}_η₎2_,1 here-afterreferred to as R.Measurements ofthisangularseparation thus provideprecision testsofpQCD and electroweakpredictions for the rate and pattern of real W boson emission. Real W bo-sonemission,alsotermedcollinearW production,isthedominant processforeventswithR<2.4,andthusR<2.4 isreferredto asthecollinearregion.Thesigniﬁcanceofthishigher-order contri-butionatsmallR isshowninRef.[5].ForeventswithR>2.4, the W bosonisbalancedbya hadronicrecoilthat mayconsistof oneormorejets.

These measurements of the R distribution probe a new re-gionofphasespacethat hasnot beenexplicitlystudiedindetail. MeasurementsofW+jets productionbyboththeATLASandCMS experiments oftenremove portionsof thecollinear regionby re-quiring that thelepton (e or μ) is separatedfromany jet by an angulardistanceofR>0.5[7,8].Byrelaxingthisrequirementto R>0.2 andfocusing on the distribution ofangular separation between themuonandtheclosestjetineventswithatleastone very high pT jet(pT>500 GeV),it ispossibletoexplicitlytarget

realW emissionwiththismeasurement.

Collinear W production may constitute an important back-ground in searches for beyond the Standard Model physics that involve Lorentz-boosted top quarks [9], either in rare topologies or at high energies. If the W decay products are collinear with one of the jets, the structure of that jet can begin to resemble that ofthethree-prongedstructureofaboosted topquark.While the rate forcollinear W production is suppressedrelative to di-jetproductionwithnoW emission,hadronic W decayscancause a large increase in the measured jet mass. The result is that W emission from quarks atvery high pT can yield single jetswith

deﬁnite substructure thatresemble the boostedtop-quarksignals beingsearchedfor.

2. The ATLAS detector

TheATLASdetector[10,11]providesnearlyfullsolidangle cov-eragearoundthe pp collisionpointattheLHC.

The inner detector (ID)comprises a silicon pixeltracker clos-esttothebeamline,a microstripsilicontracker,and astraw-tube transition-radiationtrackeratradiiupto108 cm. Athinsolenoid surrounding the tracker provides a 2 T axial magnetic ﬁeld en-ablingthemeasurementofcharged-particlemomenta.Theoverall ID acceptancespansthefull azimuthalrangein φ,and therange |η|<2.5 forparticlesoriginatingnearthenominalLHCinteraction region[12].

The electromagnetic(EM)and hadronic calorimeters are com-posedofmultiplesubdetectors spanning|η|<4.9.TheEM barrel calorimeterusesaliquid-argon(LAr)activemedium,togetherwith lead absorbers,and covers|η|<1.45.Intheregion|η|<1.7,the hadronic calorimeter isconstructedfromsteelabsorberand scin-tillatortilesand isseparatedintobarrel(|η|<1.0)and extended-barrel (0.8<|η|<1.7) sections. The endcap (1.375<|η|<3.2) and forward(3.1<|η|<4.9) regions are instrumented with LAr calorimetersforEMaswellashadronicenergymeasurements.

A muon spectrometer with three large air-core toroid magnet systemssurroundsthecalorimeters.Themuonspectrometer mea-sures the momentum of muonsfrom their tracks, which are re-constructedwiththreelayersofhigh-precisiontrackingchambers.

1 _ATLAS_uses_a_right-handed_coordinate_system_with_its_origin_at_the_nominal in-teractionpoint(IP)inthecentreofthedetectorandthez-axisalongthebeampipe. Thex-axispointsfromtheIPtothecentreoftheLHCring,andthe y-axispoints upward.Cylindricalcoordinates(r,φ)areusedinthetransverseplane,φbeingthe azimuthalanglearoundthez-axis.Thepseudorapidityisdeﬁnedintermsofthe polarangleθasη= −ln tan(θ/2).

These chambers provide coverage in the range |η|<2.7, while dedicatedfastchambersallowtriggeringintheregion|η|<2.4.

Athree-leveltrigger systemisusedto record eventsfor anal-ysis. The different parts of the trigger system are referred to as the Level-1 trigger, theLevel-2 trigger, and the Event Filter[13]. The Level-1 triggeris implemented inhardware and usesa sub-set of detectorinformation to reduce the event rate to a design value of atmost 75 kHz. The Level-1 trigger isfollowed by two software-based triggers, the Level-2 trigger and the Event Filter, whichtogetherreducetheeventratetoafewhundredHz.

3. Data and simulated samples

Themeasurement presentedhereis basedon theentire2012 pp dataset ata centre-of-massenergy of√s=8 TeV.Events are requiredto meet baseline quality criteria during stable LHC run-ningperiods.Thesedataqualitycriteriaprimarilyrejectdatawith signiﬁcantcontaminationfromdetectornoiseorissuesinthe read-out [14] basedupon individualassessments foreachsubdetector. The resulting dataset corresponds to an integratedluminosity of 20.3 fb−1. The absolute luminosity scale is derived from beam-separationscansperformedinNovember2012.Theuncertaintyin theintegratedluminosityis±1.9%[15].

Simulatedevents fromMonte Carlo (MC) generators are used forcalculatingthesignal eﬃciencyand estimating backgroundin thesignalregion.TheeventsaresimulatedusingaGEANT4-based

[16] full detectorsimulation[17]. Inaddition tothe hardscatter, each event is overlaid with a numberof additional pp collisions (pile-up) extracted from the distribution of the average number of pp interactions per bunchcrossing μ observed in data.These additionalpp collisionsaregeneratedwithPYTHIA v8.160[18] us-ingtheATLAS A2setoftuned parameters(A2tune)[19]and the MSTW2008LOpartondistributionfunction(PDF)set[20].

Events containing W +jets are generated with ALPGEN 2.14

[21], which implements MLM matching [22] of the matrix ele-mentcalculationwithpartonshowering.TheW bosonisproduced as partofthematrixelementcalculations,allowing simulationof bothcollinearandback-to-backW+jets production.Inthelatter, the W bosonisbalanced by thehadronic recoilsystem. The ma-trixelements provided by ALPGEN are configuredto allow up to fivepartonsinthefinalstate inadditiontothe W boson, includ-ing heavy-flavour production as well. The generatoris interfaced withPYTHIA v6.427[23]forpartonshoweringandfragmentation. TheCTEQ6L1 PDFset [24]is used.A K -factorisapplied tothese samples to correct the normalisation to a NNLO pQCD inclusive cross-sectioncalculatedwithFEWZ[25]andtheMSTW2008NNLO PDFset.AsampleofeventsisalsogeneratedwithPYTHIA v8.210 andusingtheCT10NLOPDFset[26]inwhichW bosonradiation canbeproducedviaaweakpartonshower.

DijeteventsaregeneratedwithPYTHIA v8.165. Top-quarkpair production is simulated with POWHEG-r2129 [27–30] interfaced with PYTHIA v6.426with theP2011C [31]tune forparton show-ering and fragmentation. Diboson production is simulated with MC@NLO v4.07[32].Additionalsamplesofdibosonproductionare generated using SHERPA v1.43 [33] and these are used to esti-matetheoretical uncertaintiesinthe dibosonbackground estima-tion.TheabovesamplesareallgeneratedusingtheCT10NLOPDF set.Events containing Z+jets aregenerated with ALPGEN using the same conﬁgurationas the W+jets simulation above. Single top-quarkproduction is a negligible backgroundfor thisanalysis andisnotincluded.

Allsamples arenormalised totheir calculated inclusive cross-sections.However,fortheW+jets,dijets,tt and¯ Z+jets samples, thereisanadditionalcorrectionappliedtothenormalisation, de-rivedfromthecomparisonofdataandMonteCarlosimulationsin

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thesignalregionandcontrolregions.The processofderiving this correctionisexplainedindetailinSection4.

4. Object and event selections

4.1.Baselineeventselection

Thetopology ofcollinear W production involvestwo back-to-backhigh-pT jets, oneofwhichemitsa nearby W boson.Events

arerequiredtocontainatleastonejetwith pT>500 GeV,asthis

is found to be suﬃcient to probe the kinematic region of inter-est.The probability ofa collinear W emissionfromsuch a jetis estimatedbyPYTHIA v8.210tobe0.15%.Overhalfofthe produc-tionof W+jets in thephasespace probedinthismeasurement isinthecollinearregion.Arequirement forasecond high-pT jet

isnot applied.Althoughboth jetsinitially recoilfromeach other andhavesimilar pT,thejetthatemitsthecollinearW bosoncan

loseasigniﬁcantamountofenergytothemuonandneutrino, nei-therofwhicharereconstructedaspartofthejetenergy.Requiring asecond high-pT jet wouldimposean implicitmaximumonthe

energycarriedbytheW bosonanditsdecayproducts.

The analysis focuses on the leptonic decays of W bosons to muonsin orderto ensure a high reconstruction purity, and thus events are required to have exactly one muon. Events that con-tain an electron are rejected, which reduces the background by removingmixed-flavourdileptonic(electronplusmuon)t¯t decays. ControlregionsareusedtoestablishthenormalisationofMC sim-ulationsofseveralbackgroundprocesses.Theseregionsaredefined by invertingvarious selection criteria used inthe final measure-ment.

Toreject non-collisionbackground[34],eventsarerequiredto contain at least one primary vertex consistent with the beam-interactionregion,reconstructedfromatleasttwotrackseachwith ptrack_T >400 MeV.Theprimaryhard-scattervertexisdefinedasthe vertexwith thehighest (p_Ttrack)2.Torejectrareevents contam-inatedby spurious signals inthe detector,all anti-kt [35,36] jets withradiusparameter R=0.4 and pjet_T >20 GeV (seebelow)are requiredtosatisfytheloosestjet-qualityrequirementsdiscussedin Ref.[34].Thesecriteria aredesigned to rejectnon-collision back-ground and significant transient noise in the calorimeters while maintaining an efficiency for good-quality events greater than 99.8% with as high a rejection of contaminated events as possi-ble.Inparticular,thisselectionisveryefficientinrejectingevents thatcontainfakejetsduetocalorimeternoise.

4.2.Triggerselection

Eventsusedinthisanalysisareselectedbyrequiringthatthey passatleastone oftwo single-muontriggers[37].The ﬁrst trig-ger requiresan isolatedmuon with pT>24 GeV and thesecond

triggerrequiresamuonwith pT>36 GeV withnoisolation

crite-riaapplied.The track-basedisolation usedin thetrigger requires thatthescalarsumofthe pT ofalltrackswithinaconeofradius

R=0.2 aroundthemuonislessthan12%ofthemuonpT.

4.3.Objectreconstruction

Muonsare reconstructed by combining tracks in the ID with tracksin themuon spectrometer [38]. Theyare requiredto have pT>25 GeV and|η|<2.4.Toreducecontaminationfrom

semilep-tonicb-decays,in-ﬂightpionandkaondecaysandcosmicmuons, their longitudinal impact parameter with respect to the primary vertexz0mustsatisfy|z0|sinθ <0.5 mm andtheirtransverse

im-pactparameterwithrespecttotheprimaryvertexd0 mustsatisfy

|d0|/σ(d0)<3.Theselectedoﬄinereconstructedmuonmustalso

matchtheonlinemuonthatpassedthetrigger.

Jetsarebuiltusingtheanti-kt algorithmwitha radius param-eterof R=0.4 fromlocallycalibratedthree-dimensional topolog-ical energy clusters [39]. The resulting jets are required to have pT>100 GeV and|η|<2.1.

Thenumberofb-taggedjetsforagiveneventiscalculated us-ing theMV1 tagger[40]on jetsbuiltusingthe anti-kt algorithm with R=0.4.Thejetsconsideredforb-tagginghavepT>25 GeV

and are reconstructed within |η|<2.1. The MV1 tagger is con-ﬁgured to have a b-tagging eﬃciency of 70% in semileptonic t¯t events.

Electronsare reconstructedfromacombination ofa calorime-ter energy cluster and a matched ID track [41,42]. They must meet a set of identiﬁcation criteria (the so-called medium crite-riaofRef. [41]). Theyarealsorequiredto have pT>20 GeV and

|η|<2.47,excludingthetransitionregionbetweenthebarreland theendcapcalorimeters(1.37<|η|<1.52).Toreducethe contam-inationfromsemileptonicb-decaysandmisidentiﬁcation,thesame impactparameterrequirementsusedformuonsareappliedalong withanisolationrequirement.Thisisolationistrack-basedand re-quiresthatthescalarsumofthepTofalltracksinaconeofradius

R=0.2 aroundtheelectronbelessthan15%oftheelectronpT.

4.4. Measurementselection

ToselecttheW+jets signal,eventsarerequiredtocontainat leastone jet with pT>500 GeV, exactlyone muon, nob-tagged

jets, a primary vertex and no electrons. Any additional jetswith pT>100 GeV are included in the analysis. The leading jet,

de-ﬁned as the jet with the highest pT, is not necessarily the one

closest to the muon. The R distance is always measured with respecttotheclosestjet.Themuonisrequiredtobeisolated us-ing both track-basedand calorimeter-based isolation criteria. The track isolationrequiresthatthescalarsumofthe pT ofalltracks

ina coneofradius R=0.2 aroundthemuon beless than 10% ofthemuon pT.Thecalorimeter isolationrequiresthatthescalar

sumofthe pTinallcalorimetercellsinaconeofradiusR=0.2

aroundthemuonbelessthan40%ofthemuon pT.Applyingthese

isolation criteria significantly reduces the background from dijet events, where muonsmostly originate from heavy-flavour or in-flightdecaysandarenon-isolated.Theb-tagvetoalsoreducesthe backgroundfrom t¯t,whichgeneratestwob-quarksintheirdecay, byover80%,whileonly10%oftheW+jets signalisrejected. Re-quirements onmissing transversemomentum were not found to improvethesignalselectionorbackgroundrejection.Theefficiency of theisolation requirement was studied both insimulated sam-ples andin situusingdataeventscontaining high-pT topquarks,

and the results from the two studies were in agreement. How-ever,intheextremelycollinearregion,wherethedistancebetween themuon and theclosestjet isR<0.2,thelimitedsizeofthe eventsampledidnotallowthesameconclusion.Asaresult,events where R<0.2 arealso excluded.Thiscauses approximately2% oftheW+jets signaltoberejected.

4.5. Controlregiondeﬁnitionsandbackgroundestimation

For the ﬁnal state with at leastone high-pT jet and a single

muon, thedominantbackgroundprocessesthat contributeto the signalregionaredijets,tt and¯ Z+jets.Inaddition,thereisasmall background contribution from diboson production. These are all modelledusingthesimulatedsamplesdescribedinSection 3.

Foreachofthethreemainbackgroundprocesses,acontrol re-gionutilisinganeventselectiondifferentfromthesignalregionis deﬁnedsuchthatmostoftheeventsinthiscontrolregionarefrom

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Fig. 1. ComparisonsbetweendataandthepredicteddistributionfromMCsimulationsoftheangularseparationbetweenthemuonandtheclosestjetinControlRegion 1(left),ControlRegion2(right)andControlRegion3(bottom).Thelowerpanelsshowtheratioofdatatothepredicteddistribution.Theerrorbarscorrespondtothe statisticaluncertaintyandtheshadederrorbandcorrespondstothesystematicuncertainties.Thedijet,tt and¯ Z+jets backgroundshavebeenscaledaccordingtotheir respectivecontrolregions.TheW+jets signalhasbeenscaledby0.71.

thechosenbackground.ControlRegion1isenrichedindijets,with a 93%purityofdijetevents, byapplyingtheinverseofthesignal regionisolationselection.Ituseseventsthatpassthemuontrigger without an isolation requirement and requiresthe muon tohave pT>38 GeV,as eventswithanon-isolatedmuonoflower pT are

mostly rejectedby thetrigger,together witha distanceR>0.2 betweenthemuonandtheclosestjet.ControlRegion2isenriched in t¯t, with 91% of events originating from tt production,¯ by re-quiringatleasttwob-taggedjets.ControlRegion3isenrichedin Z+jets, which constitute 94% of eventsin thisregion, by using eventswithexactlytwomuons,withbothmuonspassingthe sig-nalregionisolation.Itisfurtherrequiredthatthedimuoninvariant mass in ControlRegion 3 satisﬁes 60 GeV<mμμ<120 GeV. In thiscase,themuonwiththehigherpTischosentodeﬁneR.

Using data from these control regions and the signal region, a scale factor is derived for each main background process and theW+jets signaltocorrectthenormalisationoftheMCsample to that observed in data. To ensure the scale factor is not af-fectedbycontaminationfromotherbackgroundsandtheW+jets signal, it isnecessary to subtractthe MC predictionfor the

con-tamination from the control region data. As there is a circular dependency in using scaled MC predictions to derive new scal-ings, an iterative approach is applied. First, the scale factors are derived with thecontamination subtracted usingtheuncorrected normalisations.Thenthenormalisationsareupdatedwiththescale factor corrections and theprocedure to derive them isrepeated. Sincethecontamination ineach oftheregionsisquitesmall, the scale factorsconverge very rapidly. The dijet sample isscaled by 1.134±0.054,thet¯t sampleisscaledby0.861±0.061,theZ+jets sample is scaled by 0.705±0.052 and the W+jets sample is scaled by 0.711±0.016.These uncertainties inthe scale factors areduetothestatistical uncertaintyofthe dataandMC samples and arepart oftheoverall uncertaintiesinthe measurement de-tailedinSection6.However,theuncertaintyintheW+jets scale factorhasnoeffecton theresultsofthe measurement.Afterthe scalefactors areapplied,the MCpredictions and observed distri-butionsofthedistancebetween themuonand theclosest jetfor eachcontrolregionareshowninFig. 1.Thesystematic uncertain-tiesshowninFig. 1correspondtothosedescribedinSection6.

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Table 1

Thesystematicuncertaintiesinthecross-section measurement.Multipleindependentcomponents havebeen combinedintogroupsofsystematicuncertainties.

Systematic Source 0.2< R<2.4 R>2.4 Inclusive Scaling of dijets to data 0.4% 0.1% 0.3% Scaling of t¯t to data 0.6% 0.2% 0.5% Scaling of Z+jets to data 0.6% 0.3% 0.5% Jet energy scale 4.6% 5.8% 5.0%

b-tagging eﬃciency 3.7% 1.2% 2.9%

Data/MC disagreement for dijets 0.9% 0.6% 0.8% Data/MC disagreement for t¯t 1.2% 0.4% 1.0% Data/MC disagreement for Z+jets 0.6% 1.5% 0.9% Diboson background estimate 2.2% 0.1% 1.5% Unfolding dependence on prior 1.1% 1.8% 1.3% Muon momentum scale and resolution 0.0% 0.1% 0.1% Muon reconstruction eﬃciency 0.4% 0.4% 0.4% Muon trigger eﬃciency 2.0% 1.9% 1.9% Jet energy resolution 0.6% 0.8% 0.6% MC background statistical 2.4% 1.8% 2.3% MC response statistical 1.7% 2.2% 1.9% Total systematic (excluding luminosity) 7.6% 7.4% 7.3%

Luminosity 1.9% 2.0% 2.0%

Data statistical 2.7% 3.6% 2.2% 5. Deﬁnition of observable and correction for detector effects

The estimatedbackground is subtracted from the datain the signalregionandtheresultantdistributionofthedistanceR be-tweenthemuonandtheclosestjet isunfolded usingan iterative Bayesian technique [43] to correct for detector effects including both theefficiency ofthe selection criteria and the resolution of the angular separation between the muon and the nearest jet, where the former effect is dominant. This technique is imple-mentedwithin theRooUnfold framework [44].Aresponse matrix derived from MC simulation is used to correct the distribution fromdetector-level to particle-level. The particle-level prediction fromMCsimulationisusedasaninitialpriorduringthefirst iter-ationoftheunfolding.Subsequentiterationsusetheprevious iter-ation’sunfoldeddistributionasanewprior.Asingleiterationstep isused,asthiswasfoundtobetheoptimalchoicethatminimised thecombination ofstatistical fluctuation and thebias introduced bythepriorofunfoldedresults.

Thedetectorresponseand thecombinedefficiencyofthe trig-ger, reconstruction and the analysis selection for the W+jets signal isobtainedfrom MC simulation.The fiducialselection ap-plied to MC simulation is similar to the kinematic selection of theanalysis. Particle-level jets, builtfrom stable final-state parti-cles(defined as those with a proper lifetime τ corresponding to cτ ≥10 mm [45]) excluding muons and neutrinos, must satisfy pT>100 GeV and |η|<2.1.Events are requiredtohave atleast

oneparticle-leveljetwith pT>500 GeV andaparticle-levelmuon

with a dressed2 _p

T>25 GeV and |η|<2.4. No requirementson

promptnessareappliedtothemuonsorthedressingphotons.Any additionalmuonsthatpasstheserequirementscausetheeventto berejected.Eventswherethedistancebetweenthemuonandthe closestjetR<0.2 arealsorejected.Unliketheanalysisselection, therearenorequirementsonb-jetsorelectronsfortheﬁducial se-lection.

Theunfoldingtotheﬁducialregionalsocorrectsforeventsthat donotpasstheparticle-levelselection,butpassthedetector-level selection.EventsintheﬁducialsignalregionthatarisefromW→

τ νarealsoremovedsothatthecross-sectionisquotedexclusively forthemuondecaychannel.

2 _Photons_that_are_contained_in_a_cone_of_size_R₌₀_._{1 around} _the_muon_are summedandincludedaspartofthemuonenergy.

6. Systematic uncertainties

The dominant systematic uncertainties in the cross-section measurement arisefromthe uncertaintiesin thejet energyscale and the b-taggingeﬃciency.For eachsystematic uncertainty, the selection criteriaarere-applied,thecontrol regionnormalisations are reassessed,and the unfoldingprocedure isrepeated with the quantityunderconsiderationvariedby±1 standarddeviation.The average of the up and down variations of the ﬁnal cross-section measurementaresummedinquadrature,asthevariationsare in-dependent and not correlated.This sum isthen used as the full systematic uncertainty. The systematic uncertainties in the mea-surement, grouped by source,are summarised inTable 1 forthe inclusive cross-section, thecollinear region(0.2< R<2.4) and theback-to-backregion(R>2.4).

Sincethedijet,tt and¯ Z+jets simulatedsamplesarescaledto data intheir respectivecontrol regions,there isa systematic un-certainty inthescalingthat arisesfromthestatisticaluncertainty in the data and the MC simulations in thesecontrol regions. As the control region for dijets does not have the same kinematic selection as the signal region, there could be some bias due to mismodelling ofthedijetkinematics inthesimulatedsample. An uncertaintyaccountingforthisisderivedbyvaryingthekinematic selectionofthecontrolregion.

Theuncertaintyinthejet energyscalecomprises17 indepen-dentcomponents[46].Sixofthesearederivedfromvariousinsitu analyses and twoare relatedtothe η intercalibrationofthe jets. Therearealsofourcomponentsthataccountforthemismodelling ofthepTresponsewithrespecttopile-upandthreetopology

com-ponents that account forthedependenceofthe pT-response

un-certainty ontherelativefractionsofjetsinitiated bylightquarks, gluonsandb-quarks.

To correct the b-tagging efficiency in simulation to that ob-served in data, scale factors derived from in situ analyses are applied to the simulated samples [47,48]. These have associated uncertainties. Theuncertainties forb-,c- and τ-jets are assessed independently from those for light jets and the uncertainties in the efficiencyscale factorsare fullyanti-correlated with those in theinefficiencyscalefactors.

Ineachcontrolregion,anydisagreementbetween theR dis-tributions for data and MC simulations is taken as a systematic uncertainty forthe R predictionfrom that speciﬁc background inthesignalregion.Thisintroducesanadditionaldata-driven

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sys-Table 2

Thenumberofeventsinthesignalregionobservedindata,alongwiththe compo-sitionoftheseeventsaspredictedbyMCsimulation,splitbythedistancebetween the muonand theclosestjet.The dijet,t¯t and Z+jets backgroundshave been scaledaccordingtotheirrespectivecontrolregions.TheW+jets signalhasbeen scaledby0.71. Process 0.2< R<2.4 R>2.4 Inclusive Dijets 5% 2% 4% t¯t 7% 2% 5% Z+jets 6% 4% 5% Dibosons 2% 4% 3% W+jets 80% 88% 82% Data 1907 833 2740

tematicuncertaintytothe dijet,t¯t and Z+jets estimatesforthe R distribution. Since the diboson background prediction is not constrained by datafrom a control region,an alternative predic-tionisobtainedfromadifferentsimulatedsamplegeneratedusing SHERPA.Thedifferencebetweenthesetwopredictionsistakenas anuncertaintyinthedibosonbackgroundestimate.

The systematic uncertainty dueto thedependence ofthe un-folding on the prior signal distribution, as obtained from MC simulations, is evaluated through a data-driven closure test. The simulated signal sample is reweighted at particle-levelsuch that the distribution of the fully simulated detector-level R more closely matches the observed data. This reweighted simulated detector-leveldistributionisthenunfoldedandcomparedwiththe reweighted particle-leveldistribution.Differencesobservedinthis comparisonaretakenasasystematicuncertaintyintheunfolding. Theuncertaintyduetothedependenceonthenumberof unfold-ingiterationstepswasnegligible.

Other smalleruncertainty contributions arise from the uncer-tainty intheintegratedluminosity, theuncertaintiesinthemuon momentum scale and resolution, muon reconstruction eﬃciency andtriggereﬃciencyandtheuncertaintiesinthejetenergy reso-lution[49].Uncertaintiesintheelectron energyscale and resolu-tionwereevaluatedbutfoundtobenegligible.

7. Results

The numberofeventsinthesignalregion observedindatais listed in Table 2, along with the composition of these eventsas predicted by MC simulation.Numbers are givenfor thecollinear region (0.2< R<2.4),the back-to-backregion(R>2.4), and the inclusive sample. The uncorrected distributions of the recon-structed distancebetweenthe muonand theclosestjet observed in dataand predicted by MC simulationsare shownin Fig. 2 for thesignalregion.Ingeneralthedistributionsagreewithinthe un-certainties, exceptaround R=2.8 where there isa deﬁcit and around the most collinear region of R<0.5 where there is a slightexcessinthepredictionfromMCsimulations.

7.1. Differentialcross-sectionmeasurement

The differential cross-section of W →μν as a function of R(μ,closest jet),obtainedfromthe unfoldeddata ofthe signal region, is shown in Fig. 3.The measured total cross-sections for theinclusivecase,inthecollinearregionandtheback-to-back re-gionarealsolistedinTables 3–5.

Themeasurementsarecomparedtoseveraltheorypredictions. TheALPGEN+PYTHIA6 W+jets calculationandthenormalisation K -factorusedforthispredictionaredescribedinSection3andthe quoted uncertainties are the statistical uncertainties. The W+ j and j j+weak showercalculationprovidedbyPYTHIA v8.210, de-scribed inSection3,isshownas well.Inthiscase, the W boson

Fig. 2. PredicteddistributionfromMCsimulationoftheangularseparationbetween themuonandtheclosestjetandtheobserveddistributionfromdataforthe sig-nalregion.Thelowerpanelshowstheratioofdatatothepredicteddistribution. Theerrorbarscorrespondtothestatisticaluncertaintyandtheshadederrorband correspondstothesystematicuncertainties.Thedijet,t¯t andZ+jets backgrounds havebeenscaledaccordingtotheirrespectivecontrolregions.TheW+jets signal hasbeenscaledby0.71.

Fig. 3. Unfoldeddistributionfrombackground-subtracteddataoftheangular sepa-rationbetweenthemuonandtheclosestjetinthesignalregionalongwithseveral predictionsfromtheorycalculations.Thelowerpanelsshowtheratioofthe the-orypredictions totheunfoldeddata. Theerrorbarsintheupperpanelandthe greyshadederrorbandsinthelowerratiopanels arethe sumofthestatistical andsystematicuncertaintiesinthe measurement.Theshadederrorbandonthe ALPGEN+PYTHIA6calculationisstatisticaluncertainty,thebandonthePYTHIA8 calculationisstatisticalandPDFuncertaintiesandthoseontheSHERPA+OpenLoops andtheW +≥1 jet NjettiNNLOcalculationsarescaleuncertainties.

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Table 3

Cross-sectionforW(→μν)+≥1 jet asmeasuredindataandaspredictedbyvariouscalculations. Process σ(W(→μν)+ ≥1 jet)[fb]

Data (√s=8 TeV, 20.3 fb−1₎ _169.2_±_{3.7 (stat.)}_±_{12.3 (syst.)}_±_{3.3 (lumi.)} ALPGEN+PYTHIA6 W+jets 236.6±1.1 (stat.)

PYTHIA8 W+j & j j+weak shower 134.8±0.9 (stat.)±7.3 (pdf) SHERPA+OpenLoops W+j & W+j j 183±25 (scale)

W+ ≥1 jet NjettiNNLO 181±14 (scale)

Table 4

Cross-sectionforW(→μν)+≥1 jet inthecollinear(0.2< R<2.4)regionasmeasuredindataand aspredictedbyvariouscalculations.

Process σ(W(→μν)+ ≥1 jet, 0.2< R<2.4)[fb] Data (√s=8 TeV, 20.3 fb−1) 116.2±3.2 (stat.)±8.8 (syst.)±2.3 (lumi.) ALPGEN+PYTHIA6 W+jets 167.1±0.9 (stat.)

PYTHIA8 W+j & j j+weak shower 83.4±0.7 (stat.)±4.4 (pdf) SHERPA+OpenLoops W+j & W+j j 128±20 (scale)

Table 5

Cross-sectionforW(→μν)+≥1 jet intheback-to-back(R>2.4)regionasmeasuredindataand aspredictedbyvariouscalculations.

Process σ(W(→μν)+ ≥1 jet, R>2.4)[fb] Data (√s=8 TeV, 20.3 fb−1₎ _53.0_±_{1.9 (stat.)}_±_{3.9 (syst.)}_±_{1.0 (lumi.)} ALPGEN+PYTHIA6 W+jets 69.5±0.6 (stat.)

PYTHIA8 W+j & j j+weak shower 51.4±0.6 (stat.)±2.9 (pdf) SHERPA+OpenLoops W+j & W+j j 55±5 (scale)

caneitherbe produced bythe matrixelements ofthe W+1-jet ﬁnalstateorbeemittedaselectroweakﬁnal-stateradiationinthe partonshower of a dijet event. The quoted uncertainties are the sumsofthestatisticaluncertaintiesandtheuncertaintiesfromthe CT10NLOPDF set.Thedataarecomparedtothenominal predic-tionsfromALPGEN+PYTHIA6andPYTHIA8.

The SHERPA+OpenLoops W + j and W + j j calculation in-corporates NLO QCD and NLO EW corrections to both of these processes [50–55]. In the high-pT regime of the analysis, the

NLO EW corrections can have signiﬁcant effects – up to 20% – across the R distribution. A second-jet veto is applied to the W + j NLO predictions and this is then combined with the W+ j j NLO predictions. The SHERPA+OpenLoops calculation also includes contributions from off-shell boson production and the sub-leading Born-level contributions (O(α3₎ _for _W ₊ _{j and}

O(αSα3) for W+ j j). The NNPDF2.3QED NLO PDF [56] is used.

Boththe renormalisationand factorisationscales are setto μ0=

1/2

m2

μv+ (pμTv)2+ ipTJi+ ipγTi

, where mμv and pμTv are

themassand transversemomentumofthetotalfour-momentum ofthedressedmuon and neutrino, pJi

T isthetransverse

momen-tum of each jet, and pγi

T is the transverse momentum of each

photon not used for dressing. The quoted uncertainties are the scaleuncertainties, where the renormalisation scaleand the fac-torisationscalehavebeenvariedindependentlybyafactoroftwo.

AnNNLOQCDcalculation,whichincludesupto O(α3

S),forthe

angularseparation between the leptonfrom the W boson decay andthenearestjetin W+jets eventshasrecentlybecome avail-able [57,58]. This calculation, obtained from Ref. [5], is denoted ‘W+≥1 jet Njetti NNLO’ here. It uses a new technique based

on N-jettiness [59] to split the phase space for the real emis-sioncorrections.Itreliesonthetheoreticalformalismprovidedin soft-collineareffectivetheory.ThecalculationusestheCT14NNLO

Table 6

FiducialW+jets cross-sectionsfortheselectioncriteriaof(1)atLO,NLOandNNLO inQCDfromRef.[5].Theuncertaintiesshownarethescaleuncertainties.

σLO[fb] σNLO[fb] σNNLO[fb] 8 TeV 57+₋1310 160+ 35 −27 187+ 5 −12 PDF [60] and μ0= m2

v+ i(pTJi)2, wherem v is the invariant massoftheleptonandneutrinoand pJi

T isthetransverse

momen-tumofeach jet,isusedforboth therenormalisationand factori-sation scale. Thequoted uncertainties are thescale uncertainties, where the renormalisation scale and the factorisation scale have been varied independentlyby a factor oftwo. The resulting par-tonic ﬁnal state is clustered usingthe anti-kt jet algorithmwith R=0.4. No non-perturbative corrections are applied. The selec-tionsusedinthecalculation,

pjet_T >100 GeV, |ηjet_{| <}₂_.₁_, _pleading jet

T >500 GeV,

p _T >25 GeV, |η _{| <}₂_.₅_, ₍₁₎

are the same as the ones used for the measurement except for the muon pseudorapidity(|η|<2.5 instead of|η|<2.4). The ef-fect of thisdifference inmuon pseudorapidity isevaluated using the ALPGEN+PYTHIA6 W +jets sample and a correction factor accounting for this, which is less than 4% across the entire dis-tribution,isapplied.The calculatedcross-sections obtainedatLO, NLO and NNLO without the muon pseudorapidity correction are showninTable 6.Thescaleuncertaintydecreasesfrom∼±20%at NLOto+3%/−7% atNNLO.

ThecomparisonofthedatatoALPGEN+PYTHIA6inFig. 3shows good shape agreement to within uncertainties, except at very low R, butALPGEN+PYTHIA6predicts a signiﬁcantly higher in-tegrated cross-section. The comparison to PYTHIA8 at high R, where it is dominated by back-to-back W+jets production in

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Fig. 4. Unfoldeddistributionfrombackground-subtracteddataoftheangular separa-tionbetweenthemuonandtheclosestjetforeventswith500 GeV<pleading jet_T <

600 GeV (bluecircles)andpleading jet_T >650 GeV (redsquares)fromthesignal re-gion.Distributionsarenormalisedtounity.Theshadederrorbandontheunfolded measurementcorrespondstothesumofthestatisticalandsystematic uncertain-ties.(Forinterpretationofthereferencestocolourinthisﬁgurelegend,thereader isreferredtothewebversionofthisarticle.)

which the W boson is balanced by the hadronic recoil system, showsmuchbetteragreement.AtsmallerR,wherethecollinear processdominates,neithertheshapenortheoverallcross-section agree. Thecomparisons toSHERPA+OpenLoopsand W +≥1 jet Njetti NNLOshowmuchbetter agreementacrosstheentire

distri-bution.

7.2. EnhancementofthecollinearfractionwithjetpT

The events in the signal region are further divided into two categoriesbasedonthe transversemomentumoftheleading jet: 500 GeV<pleading jet_T <600 GeV and pleading jet_T >650 GeV. For eachofthesetwocategories,thedatadistributionisunfolded.The 50 GeVgapbetween thetwocategoriesreducesthemigrationof events fromone category to the other during unfolding. The re-sultingnormaliseddifferential W+jets cross-sectionisshownin

Fig. 4. As the leading-jet pT increases, the fraction of events in

the lower R (collinear) regionincreasesand the fractioninthe higherR (back-to-backW+jets)regiondecreases.Thismaybe interpretedasan increaseinthecollinearW emissionprobability as thejets become moreenergetic. Withhigher pT thecollinear

peak isshifted to smaller R. Thisis also understood since the massoftheW bosonbecomesproportionallysmallercomparedto the energyofthejet.The fullmeasurement resultsareshownin

Fig. 5.Thecomparisontotheorypredictionsshowsresultssimilar totheonesobtainedforpleading jet_T >500 GeV inSection7.1.

8. Conclusions

Thecross-sectionforW→μν inassociationwithatleastone very high transversemomentumjet ismeasured asa functionof theangulardistancebetween themuon fromtheW bosondecay and the closest jet. This measurement utilises data recorded by the ATLAS detectorfrom pp collisions at√s=8 TeV attheLHC, correspondingto20.3 fb−1 ofintegratedluminosity. Theseresults arerelevanttounderstandingthecontributionofrealW emissions fromhigh-pTlightpartonstoW+jets processes.

ComparisonstoavarietyofMCgeneratorsand theoretical cal-culations show varying levels of agreement. ALPGEN+PYTHIA6 overestimates thetotal cross-section, whereas PYTHIA8, which is modiﬁed to explicitly includethe process of W boson emission, disagrees with the measurement in the collinear region (R<

2.4). Ontheother hand,agreementwith theSHERPA+OpenLoops NLO QCD+EW calculation and the W+≥1 jet Njetti NNLO

cal-culation in Ref. [5] is well within the systematic and statistical uncertaintiesofthepredictionsandthemeasurement.

Thismeasurement hasimplications for MonteCarlo programs that incorporatereal W boson emission,a process whichis only justnowbeingprobeddirectlyattheenergyoftheLHC.Therate ofthisprocessincreaseswithjet pT andthusalsowith

centre-of-massenergy,andwillthereforeplayasigniﬁcantroleinW+jets measurements athigh pT,vector-boson scattering measurements,

andevenQCDmultijetmeasurementsatverylargedijetinvariant masseswherethecorrections duetorealbosonemissionare sig-niﬁcant.

Lastly,the potential ishigh for thisprocess tomimic the sig-natures of a highly Lorentz-boosted top quark. The importance of such signaturesin the search fornew physics atthe LHC ne-cessitatesathoroughunderstanding ofprocessessuchas theone measuredindetailinthispaper.Asthephysicsprogrammesofthe LHCexperimentsextendintonewterritoriesintermsofboththe centre-of-mass energyand integratedluminosity, theseonce rare processeswillbecomeaubiquitousconsideration.

Acknowledgements

We thankCERN for thevery successful operationof the LHC, as well as the support stafffromour institutions withoutwhom ATLAScouldnotbeoperatedeﬃciently.

WeacknowledgethesupportofANPCyT,Argentina;YerPhI, Ar-menia;ARC,Australia;BMWFWand FWF,Austria;ANAS, Azerbai-jan;SSTC,Belarus;CNPqand FAPESP,Brazil; NSERC,NRCand CFI, Canada;CERN;CONICYT,Chile;CAS,MOST andNSFC,China; COL-CIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Re-public; DNRF and DNSRC, Denmark; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, HGF, and MPG, Germany; GSRT, Greece;RGC,UGC,HongKongSAR,China;ISF,I-COREandBenoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Mo-rocco; FOM and NWO, Netherlands; RCN, Norway; MNiSW and NCN,Poland;FCT,Portugal;MNE/IFA,Romania;MESofRussiaand NRCKI, RussianFederation;JINR;MESTD, Serbia;MSSR,Slovakia; ARRSand MIZŠ, Slovenia;DST/NRF, SouthAfrica; MINECO,Spain; SRC and Knut and Alice Wallenberg Foundation, Sweden; SERI, SNSFandCantonsofBernandGeneva,Switzerland;MOST,Taiwan; TAEK,Turkey;STFC,UnitedKingdom;DOEand NSF,UnitedStates. Inaddition,individualgroupsandmembershavereceivedsupport fromBCKDF,theCanadaCouncil,CANARIE,CRC,ComputeCanada, FQRNT, and theOntario Innovation Trust,Canada; EPLANET, ERC, FP7,Horizon 2020and MarieSkłodowska-CurieActions,European Union; Investissementsd’AvenirLabexand Idex, ANR,Région Au-vergne and Fondation Partager le Savoir, France; DFG and AvH Foundation,Germany;Herakleitos,ThalesandAristeiaprogrammes co-ﬁnancedbyEU-ESFandtheGreekNSRF;BSF,GIFandMinerva, Israel; BRF, Norway; Generalitat de Catalunya, Generalitat Valen-ciana,Spain;theRoyalSocietyandLeverhulmeTrust,United King-dom.

The crucialcomputing support fromall WLCG partners is 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.[61].

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Fig. 5. Unfoldeddistributionfrombackground-subtracteddataofthe angularseparationbetweenthemuonandtheclosestjetinthesignalregionalongwith several predictionsfromtheorycalculationsforeventswith(a)500 GeV<pleading jet_T <600 GeV and(b)pleading jet_T >650 GeV.Thelowerpanelsshowtheratioofthetheory predictionstotheunfoldeddata.Theerrorbarsintheupperpanelandthegreyshadederrorbandsinthelowerratiopanelsarethesumofthestatisticalandsystematic uncertaintiesinthemeasurement.TheshadederrorbandontheALPGEN+PYTHIA6calculationisstatisticaluncertainty,thebandonthePYTHIA8calculationisstatistical andPDFuncertaintiesandthebandontheSHERPA+OpenLoopsisscaleuncertainty.

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The ATLAS Collaboration

M. Aaboud136d,G. Aad87,B. Abbott114,J. Abdallah8,O. Abdinov12,B. Abeloos118,R. Aben108,

O.S. AbouZeid138,N.L. Abraham152, H. Abramowicz156, H. Abreu155, R. Abreu117, Y. Abulaiti149a,149b,

B.S. Acharya168a,168b,a,S. Adachi158,L. Adamczyk40a,D.L. Adams27,J. Adelman109,S. Adomeit101,

T. Adye132, A.A. Affolder76,T. Agatonovic-Jovin14, J.A. Aguilar-Saavedra127a,127f,S.P. Ahlen24,

F. Ahmadov67,b,G. Aielli134a,134b,H. Akerstedt149a,149b,T.P.A. Åkesson83,A.V. Akimov97,

G.L. Alberghi22a,22b,J. Albert173, S. Albrand57,M.J. Alconada Verzini73,M. Aleksa32,I.N. Aleksandrov67,

C. Alexa28b,G. Alexander156, T. Alexopoulos10,M. Alhroob114,B. Ali129,M. Aliev75a,75b, G. Alimonti93a,

J. Alison33,S.P. Alkire37,B.M.M. Allbrooke152, B.W. Allen117, P.P. Allport19,A. Aloisio105a,105b,

A. Alonso38,F. Alonso73,C. Alpigiani139, A.A. Alshehri55,M. Alstaty87,B. Alvarez Gonzalez32,

D. Álvarez Piqueras171,M.G. Alviggi105a,105b,B.T. Amadio16,K. Amako68, Y. Amaral Coutinho26a,

C. Amelung25,D. Amidei91,S.P. Amor Dos Santos127a,127c,A. Amorim127a,127b,S. Amoroso32,

G. Amundsen25,C. Anastopoulos142, L.S. Ancu51,N. Andari19,T. Andeen11,C.F. Anders60b,G. Anders32,

J.K. Anders76, K.J. Anderson33,A. Andreazza93a,93b,V. Andrei60a, S. Angelidakis9,I. Angelozzi108,

A. Angerami37,F. Anghinolﬁ32, A.V. Anisenkov110,c,N. Anjos13,A. Annovi125a,125b, C. Antel60a,

M. Antonelli49,A. Antonov99,∗,F. Anulli133a, M. Aoki68, L. Aperio Bella19, G. Arabidze92, Y. Arai68,

J.P. Araque127a, A.T.H. Arce47, F.A. Arduh73, J-F. Arguin96, S. Argyropoulos65, M. Arik20a,

A.J. Armbruster146,L.J. Armitage78,O. Arnaez32,H. Arnold50, M. Arratia30,O. Arslan23,

A. Artamonov98,G. Artoni121,S. Artz85,S. Asai158,N. Asbah44, A. Ashkenazi156,B. Åsman149a,149b,

L. Asquith152, K. Assamagan27,R. Astalos147a, M. Atkinson170, N.B. Atlay144,K. Augsten129, G. Avolio32,

B. Axen16,M.K. Ayoub118, G. Azuelos96,d,M.A. Baak32, A.E. Baas60a,M.J. Baca19,H. Bachacou137,

K. Bachas75a,75b_, _{M. Backes}121_, _{M. Backhaus}32_,_{P. Bagiacchi}133a,133b_, _{P. Bagnaia}133a,133b_,_{Y. Bai}35a_,

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E. Banas41, Sw. Banerjee177,e, A.A.E. Bannoura179,L. Barak32,E.L. Barberio90,D. Barberis52a,52b,

M. Barbero87, T. Barillari102,M-S Barisits32,T. Barklow146,N. Barlow30,S.L. Barnes86, B.M. Barnett132,

R.M. Barnett16,Z. Barnovska-Blenessy59,A. Baroncelli135a,G. Barone25, A.J. Barr121,

L. Barranco Navarro171, F. Barreiro84,J. Barreiro Guimarães da Costa35a,R. Bartoldus146,A.E. Barton74,

P. Bartos147a, A. Basalaev124, A. Bassalat118,f,R.L. Bates55, S.J. Batista162, J.R. Batley30, M. Battaglia138,

M. Bauce133a,133b,F. Bauer137, H.S. Bawa146,g,J.B. Beacham112, M.D. Beattie74,T. Beau82,

P.H. Beauchemin166, P. Bechtle23,H.P. Beck18,h,K. Becker121,M. Becker85,M. Beckingham174,

C. Becot111, A.J. Beddall20e,A. Beddall20b, V.A. Bednyakov67,M. Bedognetti108, C.P. Bee151,

L.J. Beemster108, T.A. Beermann32,M. Begel27, J.K. Behr44,C. Belanger-Champagne89,A.S. Bell80,

G. Bella156, L. Bellagamba22a,A. Bellerive31, M. Bellomo88,K. Belotskiy99,O. Beltramello32,

N.L. Belyaev99,O. Benary156,∗,D. Benchekroun136a, M. Bender101, K. Bendtz149a,149b,N. Benekos10,

Y. Benhammou156, E. Benhar Noccioli180,J. Benitez65, D.P. Benjamin47,J.R. Bensinger25,

S. Bentvelsen108,L. Beresford121, M. Beretta49,D. Berge108, E. Bergeaas Kuutmann169, N. Berger5,

J. Beringer16, S. Berlendis57, N.R. Bernard88,C. Bernius111,F.U. Bernlochner23,T. Berry79,P. Berta130,

C. Bertella85, G. Bertoli149a,149b,F. Bertolucci125a,125b,I.A. Bertram74, C. Bertsche44,D. Bertsche114,

G.J. Besjes38,O. Bessidskaia Bylund149a,149b,M. Bessner44, N. Besson137,C. Betancourt50,A. Bethani57,

S. Bethke102,A.J. Bevan78,R.M. Bianchi126, L. Bianchini25,M. Bianco32, O. Biebel101, D. Biedermann17,

R. Bielski86, N.V. Biesuz125a,125b, M. Biglietti135a,J. Bilbao De Mendizabal51, T.R.V. Billoud96,

H. Bilokon49,M. Bindi56,S. Binet118,A. Bingul20b, C. Bini133a,133b, S. Biondi22a,22b,T. Bisanz56,

D.M. Bjergaard47,C.W. Black153,J.E. Black146, K.M. Black24, D. Blackburn139, R.E. Blair6,

J.-B. Blanchard137, T. Blazek147a, I. Bloch44,C. Blocker25,A. Blue55, W. Blum85,∗,U. Blumenschein56,

S. Blunier34a, G.J. Bobbink108, V.S. Bobrovnikov110,c, S.S. Bocchetta83, A. Bocci47,C. Bock101,

M. Boehler50, D. Boerner179,J.A. Bogaerts32, D. Bogavac14,A.G. Bogdanchikov110,C. Bohm149a,

V. Boisvert79,P. Bokan14,T. Bold40a,A.S. Boldyrev168a,168c,M. Bomben82, M. Bona78,

M. Boonekamp137,A. Borisov131,G. Borissov74,J. Bortfeldt32,D. Bortoletto121, V. Bortolotto62a,62b,62c,

K. Bos108, D. Boscherini22a,M. Bosman13, J.D. Bossio Sola29,J. Boudreau126,J. Bouffard2,

E.V. Bouhova-Thacker74, D. Boumediene36,C. Bourdarios118,S.K. Boutle55, A. Boveia32,J. Boyd32,

I.R. Boyko67,J. Bracinik19, A. Brandt8,G. Brandt56,O. Brandt60a,U. Bratzler159, B. Brau88,J.E. Brau117,

W.D. Breaden Madden55, K. Brendlinger123, A.J. Brennan90, L. Brenner108, R. Brenner169,S. Bressler176,

T.M. Bristow48,D. Britton55, D. Britzger44,F.M. Brochu30,I. Brock23, R. Brock92,G. Brooijmans37,

T. Brooks79, W.K. Brooks34b,J. Brosamer16,E. Brost109,J.H Broughton19,P.A. Bruckman de Renstrom41,

D. Bruncko147b,R. Bruneliere50,A. Bruni22a, G. Bruni22a,L.S. Bruni108, BH Brunt30, M. Bruschi22a,

N. Bruscino23,P. Bryant33,L. Bryngemark83, T. Buanes15,Q. Buat145, P. Buchholz144,A.G. Buckley55,

I.A. Budagov67, F. Buehrer50,M.K. Bugge120, O. Bulekov99,D. Bullock8, H. Burckhart32, S. Burdin76,

C.D. Burgard50,B. Burghgrave109,K. Burka41,S. Burke132,I. Burmeister45,J.T.P. Burr121,E. Busato36,

D. Büscher50,V. Büscher85,P. Bussey55,J.M. Butler24, C.M. Buttar55, J.M. Butterworth80,P. Butti108,

W. Buttinger27, A. Buzatu55, A.R. Buzykaev110,c, S. Cabrera Urbán171,D. Caforio129,V.M. Cairo39a,39b,

O. Cakir4a,N. Calace51,P. Calaﬁura16,A. Calandri87,G. Calderini82, P. Calfayan63,G. Callea39a,39b,

L.P. Caloba26a,S. Calvente Lopez84, D. Calvet36,S. Calvet36, T.P. Calvet87, R. Camacho Toro33,

S. Camarda32, P. Camarri134a,134b,D. Cameron120, R. Caminal Armadans170,C. Camincher57,

S. Campana32,M. Campanelli80,A. Camplani93a,93b,A. Campoverde144,V. Canale105a,105b,

A. Canepa164a,M. Cano Bret141,J. Cantero115,T. Cao42,M.D.M. Capeans Garrido32,I. Caprini28b,

M. Caprini28b, M. Capua39a,39b,R.M. Carbone37,R. Cardarelli134a, F. Cardillo50, I. Carli130, T. Carli32,

G. Carlino105a,L. Carminati93a,93b,R.M.D. Carney149a,149b,S. Caron107,E. Carquin34b,

G.D. Carrillo-Montoya32, J.R. Carter30,J. Carvalho127a,127c, D. Casadei19,M.P. Casado13,i, M. Casolino13,

D.W. Casper167, E. Castaneda-Miranda148a,R. Castelijn108,A. Castelli108,V. Castillo Gimenez171,

N.F. Castro127a,j,A. Catinaccio32,J.R. Catmore120,A. Cattai32, J. Caudron23,V. Cavaliere170, E. Cavallaro13, D. Cavalli93a,M. Cavalli-Sforza13,V. Cavasinni125a,125b,F. Ceradini135a,135b,

L. Cerda Alberich171,A.S. Cerqueira26b, A. Cerri152,L. Cerrito134a,134b_,_{F. Cerutti}16_,_{M. Cerv}32_,

A. Cervelli18,S.A. Cetin20d,A. Chafaq136a, D. Chakraborty109,S.K. Chan58, Y.L. Chan62a,P. Chang170,

J.D. Chapman30,D.G. Charlton19,A. Chatterjee51, C.C. Chau162, C.A. Chavez Barajas152, S. Che112,

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M.A. Chelstowska91, C. Chen66, H. Chen27,K. Chen151, S. Chen35b,S. Chen158,X. Chen35c,Y. Chen69,

H.C. Cheng91,H.J Cheng35a,Y. Cheng33,A. Cheplakov67, E. Cheremushkina131,

R. Cherkaoui El Moursli136e,V. Chernyatin27,∗,E. Cheu7,L. Chevalier137, V. Chiarella49,

G. Chiarelli125a,125b,G. Chiodini75a,A.S. Chisholm32,A. Chitan28b, M.V. Chizhov67, K. Choi63,

A.R. Chomont36,S. Chouridou9, B.K.B. Chow101,V. Christodoulou80,D. Chromek-Burckhart32,

J. Chudoba128,A.J. Chuinard89, J.J. Chwastowski41,L. Chytka116, G. Ciapetti133a,133b,A.K. Ciftci4a,

D. Cinca45, V. Cindro77,I.A. Cioara23, C. Ciocca22a,22b, A. Ciocio16, F. Cirotto105a,105b,Z.H. Citron176,

M. Citterio93a,M. Ciubancan28b,A. Clark51,B.L. Clark58,M.R. Clark37,P.J. Clark48,R.N. Clarke16,

C. Clement149a,149b, Y. Coadou87,M. Cobal168a,168c,A. Coccaro51, J. Cochran66, L. Colasurdo107,

B. Cole37, A.P. Colijn108,J. Collot57, T. Colombo167,G. Compostella102, P. Conde Muiño127a,127b,

E. Coniavitis50,S.H. Connell148b, I.A. Connelly79, V. Consorti50, S. Constantinescu28b, G. Conti32,

F. Conventi105a,l,M. Cooke16,B.D. Cooper80, A.M. Cooper-Sarkar121, K.J.R. Cormier162, T. Cornelissen179,

M. Corradi133a,133b, F. Corriveau89,m,A. Cortes-Gonzalez32, G. Cortiana102, G. Costa93a, M.J. Costa171,

D. Costanzo142, G. Cottin30, G. Cowan79, B.E. Cox86,K. Cranmer111, S.J. Crawley55,G. Cree31,

S. Crépé-Renaudin57,F. Crescioli82, W.A. Cribbs149a,149b, M. Crispin Ortuzar121,M. Cristinziani23,

V. Croft107,G. Crosetti39a,39b, A. Cueto84,T. Cuhadar Donszelmann142, J. Cummings180,M. Curatolo49,

J. Cúth85,H. Czirr144, P. Czodrowski3,G. D’amen22a,22b,S. D’Auria55,M. D’Onofrio76,

M.J. Da Cunha Sargedas De Sousa127a,127b,C. Da Via86,W. Dabrowski40a, T. Dado147a,T. Dai91,

O. Dale15, F. Dallaire96, C. Dallapiccola88,M. Dam38,J.R. Dandoy33,N.P. Dang50,A.C. Daniells19,

N.S. Dann86,M. Danninger172,M. Dano Hoffmann137, V. Dao50,G. Darbo52a,S. Darmora8,

J. Dassoulas3, A. Dattagupta117, W. Davey23,C. David173, T. Davidek130,M. Davies156,P. Davison80,

E. Dawe90,I. Dawson142, K. De8,R. de Asmundis105a,A. De Benedetti114,S. De Castro22a,22b,

S. De Cecco82,N. De Groot107, P. de Jong108,H. De la Torre92,F. De Lorenzi66,A. De Maria56,

D. De Pedis133a,A. De Salvo133a,U. De Sanctis152,A. De Santo152,J.B. De Vivie De Regie118,

W.J. Dearnaley74, R. Debbe27,C. Debenedetti138, D.V. Dedovich67, N. Dehghanian3, I. Deigaard108,

M. Del Gaudio39a,39b, J. Del Peso84, T. Del Prete125a,125b, D. Delgove118, F. Deliot137, C.M. Delitzsch51,

A. Dell’Acqua32, L. Dell’Asta24,M. Dell’Orso125a,125b,M. Della Pietra105a,l, D. della Volpe51,

M. Delmastro5, P.A. Delsart57,D.A. DeMarco162, S. Demers180, M. Demichev67, A. Demilly82,

S.P. Denisov131,D. Denysiuk137,D. Derendarz41,J.E. Derkaoui136d,F. Derue82, P. Dervan76,K. Desch23,

C. Deterre44,K. Dette45,P.O. Deviveiros32,A. Dewhurst132, S. Dhaliwal25,A. Di Ciaccio134a,134b,

L. Di Ciaccio5, W.K. Di Clemente123, C. Di Donato105a,105b, A. Di Girolamo32,B. Di Girolamo32,

B. Di Micco135a,135b,R. Di Nardo32,A. Di Simone50,R. Di Sipio162,D. Di Valentino31,C. Diaconu87,

M. Diamond162,F.A. Dias48, M.A. Diaz34a, E.B. Diehl91,J. Dietrich17, S. Díez Cornell44,

A. Dimitrievska14, J. Dingfelder23, P. Dita28b, S. Dita28b, F. Dittus32, F. Djama87,T. Djobava53b,

J.I. Djuvsland60a,M.A.B. do Vale26c,D. Dobos32,M. Dobre28b, C. Doglioni83,J. Dolejsi130, Z. Dolezal130,

M. Donadelli26d, S. Donati125a,125b_, _{P. Dondero}122a,122b_, _{J. Donini}36_,_{J. Dopke}132_,_{A. Doria}105a_,

M.T. Dova73, A.T. Doyle55, E. Drechsler56, M. Dris10, Y. Du140,J. Duarte-Campderros156,E. Duchovni176,

G. Duckeck101,O.A. Ducu96,n, D. Duda108, A. Dudarev32,A. Chr. Dudder85,E.M. Duﬃeld16,L. Duﬂot118,

M. Dührssen32, M. Dumancic176, M. Dunford60a, H. Duran Yildiz4a,M. Düren54,A. Durglishvili53b,

D. Duschinger46,B. Dutta44,M. Dyndal44,C. Eckardt44,K.M. Ecker102,R.C. Edgar91, N.C. Edwards48,

T. Eifert32,G. Eigen15, K. Einsweiler16, T. Ekelof169, M. El Kacimi136c,V. Ellajosyula87,M. Ellert169,

S. Elles5, F. Ellinghaus179, A.A. Elliot173,N. Ellis32,J. Elmsheuser27,M. Elsing32,D. Emeliyanov132,

Y. Enari158,O.C. Endner85, J.S. Ennis174, J. Erdmann45, A. Ereditato18, G. Ernis179, J. Ernst2,M. Ernst27,

S. Errede170,E. Ertel85, M. Escalier118, H. Esch45,C. Escobar126,B. Esposito49,A.I. Etienvre137,

E. Etzion156, H. Evans63, A. Ezhilov124,M. Ezzi136e,F. Fabbri22a,22b,L. Fabbri22a,22b,G. Facini33, R.M. Fakhrutdinov131, S. Falciano133a,R.J. Falla80, J. Faltova32,Y. Fang35a,M. Fanti93a,93b, A. Farbin8, A. Farilla135a,C. Farina126, E.M. Farina122a,122b, T. Farooque13, S. Farrell16, S.M. Farrington174,

P. Farthouat32,F. Fassi136e, P. Fassnacht32,D. Fassouliotis9,M. Faucci Giannelli79, A. Favareto52a,52b,

W.J. Fawcett121, L. Fayard118, O.L. Fedin124,o_,_{W. Fedorko}172_,_{S. Feigl}120_,_{L. Feligioni}87_,_{C. Feng}140_,

E.J. Feng32, H. Feng91,A.B. Fenyuk131, L. Feremenga8,P. Fernandez Martinez171,S. Fernandez Perez13,

J. Ferrando44, A. Ferrari169,P. Ferrari108, R. Ferrari122a,D.E. Ferreira de Lima60b,A. Ferrer171,