Contents lists available atScienceDirect
Physics
Letters
B
www.elsevier.com/locate/physletb
Study
of
W
boson
production
in
pPb
collisions
at
√
s
NN=
5
.
02 TeV
.CMSCollaboration
CERN,Switzerland
a r t i c l e i n f o a b s t ra c t
Articlehistory: Received19March2015
Receivedinrevisedform6September2015 Accepted23September2015
Availableonline28September2015 Editor:M.Doser
Keywords: CMS Wboson pPbcollisions
ThefirststudyofWbosonproductioninpPbcollisionsispresented,forbosonsdecayingtoamuonor
electron,andaneutrino.Themeasurementsarebasedonadatasamplecorrespondingtoanintegrated
luminosity of34.6 nb−1atanucleon–nucleon centre-of-massenergyof√s
NN=5.02 TeV,collectedby
the CMSexperiment.TheWbosondifferential crosssections,leptonchargeasymmetry, andforward–
backwardasymmetriesaremeasuredforleptonsoftransversemomentumexceeding25 GeV/c,andasa
functionoftheleptonpseudorapidityinthe|ηlab|<2.4 range.Deviationsfromtheexpectationsbasedon
currentlyavailablepartondistributionfunctionsareobserved,showingtheneedforincludingWboson
datainnuclearpartondistributionglobalfits.
©2015CERNforthebenefitoftheCMSCollaboration.PublishedbyElsevierB.V.Thisisanopenaccess
articleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3.
1. Introduction
Electroweakbosonproductioninproton–nucleusandnucleus– nucleuscollisionsattheCERNLHCoffersauniqueopportunityto probenuclearpartondistributionfunctions(nPDFs)[1–4].Leptonic decaysofelectroweakbosons are ofparticular interestsince lep-tonsdonot interactstronglywiththemediumproduced inthese collisions [5,6].As compared to thosein aproton, thenPDFs are expected to be depleted (shadowing) for partons carrying small momentumfractions x10−2,andenhanced (anti-shadowing)in the5×10−2x10−1 range[7].However,becauseofthelackof availabledata,partondensitiesarelesspreciselyknownfornuclei thanfornucleons.Asa consequence,precise calculations describ-inghardprocessesinhigh-energyheavyioncollisionsare limited byuncertaintiesinthenPDFs.ForWboson production,the dom-inant processes at LHC energies are ud→W+ and du→W−, principallyreflectinginteractions thattake placebetweenvalence quarksandseaantiquarks.AccordingtoRef.[4],PDFnuclear mod-ifications could affect theyield of W bosons inpPb collisions at theLHC by asmuch as15% in certain kinematic regions. There-fore,precise measurements ofW boson productionin heavy ion collisionsmightlead toan improveddeterminationofthenPDFs. Moreover, asymmetries in the individual yields of W+ and W− shouldpermit theflavour decompositionofuanddquark distri-butionsinnuclei.
The ATLAS [8,9] and CMS[10,11] Collaborations reported the observations of Z bosons in heavy ion interactions, at a
centre- E-mailaddress:cms-publication-committee-chair@cern.ch.
of-massenergy of2.76 TeV per nucleonpair. Thesedata showed thattheZbosonyieldspernucleon–nucleon(NN)collisionare es-sentially unmodified by the medium produced in the collisions. Although W bosons decaying to a lepton and a neutrino are more difficultto detect, their rateis abouttentimes larger than that ofZbosons decayingto leptonicfinal states.The production of W bosons in PbPb collisions was reported by CMS [12] and ATLAS [13], usingdatacorresponding toan integratedluminosity of7.3 μb−1and150 μb−1,collectedin2010and2011,respectively. TheW bosonyield perNNcollisionwas showntobe compatible withtheonemeasuredinppcollisions,whentakingintoaccount isospineffectsarisingfromthemixtureofprotonsandneutronsin thecollidingnuclei.However,thepresenceof10–20%nPDFeffects on ZandW boson production could not be excluded dueto the relativelylargeexperimentalandtheoreticaluncertaintiesofthese results.
The 2013 pPb LHC run provides the best currently available data sample to look for initial-stateeffects (such asPDF modifi-cations) usingelectroweak bosons. The NN-equivalent luminosity isofthesameorderofmagnitudeasforthe2011PbPb run,and the production cross sections are approximately a factor of two greater owingtotheincreasedenergy,5.02 TeV pernucleon pair. Furthermore,theasymmetryofthepPbcollisionsystemallowsfor themeasurement ofotherobservablessuch asforward–backward pseudorapidityasymmetries.ThisLetter reportsa studyofW bo-son productioninasample ofpPbcollisions corresponding toan integrated luminosity of (34.6±1.2)nb−1 [14], collected by the CMSexperiment.
http://dx.doi.org/10.1016/j.physletb.2015.09.057
0370-2693/©2015CERNforthebenefitoftheCMSCollaboration.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3.
2. Experimentalmethods
Thedirectionoftheprotonbeamwas initiallyopposite tothe positive directionof the CMSlongitudinal axis [15], andwas re-versedafter60%ofthedataweretaken. Thebeamenergieswere 4 TeV for protons and 1.58 TeV per nucleon for lead nuclei, re-sulting in a centre-of-mass energy per nucleon pair of √sNN= 5.02 TeV. As a result of the energy difference of the colliding beams, the NN centre-of-mass frame in pPb collisions was not at rest with respect to the laboratory frame. Massless particles emitted atpseudorapidity ηin the NNcentre-of-mass frame are detected at ηlab=η−0.465 (firstproton beam orientation) and
ηlab=η+0.465 (second proton beam orientation) in the CMS coordinate system, as defined inRef. [15]. The results presented hereafter are expressed in the usual convention of the proton-going side defining the positive pseudorapidity. It coincides with theCMSconvention inthesecondperiodofdata taking,thefirst onebeingreversedbeforesummingyieldsfromthetwobeam con-figurations.
Adetaileddescriptionof theCMSdetectorcan befound else-where [15]. Its central feature is a superconducting solenoid of 6 minternaldiameter,providingamagneticfieldof3.8 T.Within the field volume are the silicon pixel-and-strip tracker, a lead tungstate crystalelectromagnetic calorimeter(ECAL), and a brass and scintillator hadron calorimeter (HCAL), each composed of a barrel and two endcap sections. The silicon tracker consists of 66 Mpixeland10 Mstripsensorelements,andmeasures charged-particletrajectories inthepseudorapidity range |ηlab| <2.5. Out-sideofthesolenoid, muonsaredetected inthe|ηlab| <2.4 range, withgas-ionization detectorplanes based on three technologies: drift tubes,cathodestrip chambers, andresistive-plate chambers. Electrons are identified in the ECAL, which is made of 75 848 lead tungstatecrystals andcovers |ηlab| <1.48 in thebarrel and 1.48 <|ηlab| <3.00 inthetwoendcapregions.TheCMSapparatus alsohasextensiveforwardcalorimetry,includingtwo steel/quartz-fiberCherenkovhadronforward(HF)calorimeters,whichcoverthe 2.9 <|ηlab| <5.2 range. For online event selection, CMS uses a two-leveltriggersystem.
SelectioncriteriasimilartotheonesdevelopedinRef.[16]are appliedtothepPbsampletoremoveeventswithelectromagnetic, beam-gas,ormultiple collisions (pileup).The W bosonyields are correctedfortheinduced (4.0±0.5)% signalloss.
Theprimary signature of aW boson isa hightransverse mo-mentum(pT)lepton.Thecurrentanalysisisrestrictedtoleptonsof pT greater than25 GeV/c.The muonanalysisisbasedona sam-pletriggeredbyrequiringasingle muonwith pTabove12 GeV/c, whiletheelectron analysisuses anECAL-triggered samplewitha transverseenergy thresholdof15 GeV.Leptons arereconstructed withthe same algorithms asin proton–proton collisions [17,18], and standard selection criteria are applied, as in Refs. [12,19]. A specialelectroncharge determination,asdescribed inRef.[20], isusedinordertoreducetheelectronchargemisidentificationtoa sub-percentlevel.Eventsarereconstructedusingparticle-flow(PF) techniques[21,22],whichreconstructandclassifyindividual parti-cleswithanoptimised combinationofallsubdetectorinformation. Two criteriaare used to remove specific background sources. First,eventswithtwooppositelychargedleptons,withthesecond lepton pT greater than 15 (10) GeV/c for muons (electrons) are removed, since they correspond to well-identified processes like Drell–Yan,Zbosonorhigh-pT quarkoniumproduction.Second,the leptons are required to be isolated, in order to reduce the con-taminationcomingfromjet fragmentation. The energiesof allPF candidatesaresummed withina conecentredaroundthelepton, with the exception of the lepton itself. The lepton is considered isolated if the total transverse energyin the cone is small
com-pared to its transverse momentum. Formuons, a cone of radius
R=(η)2+ (φ)2=0.3 is used,where η andφ are the pseudorapidity andazimuthal distances tothe lepton.The candi-date is rejected if the in-cone transverse energy is greater than 10% ofthe muon pT.For electrons, a cone of R=0.4 is used, andonly particles with pT greater than 1 GeV/c aresummed, to reduce the underlying-event enhanced contribution. The electron candidate is rejectedifthe resulting transverseenergy is greater than 11.5% (9.5%) ofthe electron 4pT, forthe ECAL barrel (end-caps).
AnimportantcharacteristicofeventscontainingaW→ ν de-cay isthemissingtransverseenergy(/ET) associatedwiththe un-detectedneutrino.Itiscomputedasthemagnitudeofthevectorial sumoftransversemomentaofallthePFcandidatesintheevent. The analysis is performed using ten lepton pseudorapidity bins, each 0.5wideexceptforthemostforwardandbackwardregions (2 <|ηlab| <2.4).Afterhavingappliedtheleptonselectioncriteria, examples ofthe resulting/ET distributionsare showninFig. 1for
μ+ ande+, inthe mostcentral (−0.5 <ηlab<0.0) andfurthest forward(2.0 <ηlab<2.4) ranges.The distributionsforother bins andforthenegativeleptonsaresimilar.
Toextract thenumberofevents witha leptoncoming froma W boson,binned fitsofthesedistributionsareperformed, includ-ingthesignalandmainbackgroundcontributions,ineach ηlabbin. The/ET shapesassumedfortheelectroweakprocesses,namelythe W±→ ±ν signal as well as background from W±→τ±ν and Z→ +−,aredeterminedbythesimulationsdescribedhereafter, taking into account the acceptance and efficiency. Their relative normalizationisgivenbytheunmodifiedtheoreticalcrosssections (as computedin Ref. [23]). A maximal 20% variation of theW/Z normalizationratioistakenintoaccount,duetopotentially differ-entnuclearmodificationsoftheZandWbosons,andresultingina 1–3%systematicuncertaintyintheextractedWyields.The notice-abledifferencebetweenthe/ETdistributionsfortheZ→e+e−and Z→μ+μ−processesintheforwardregion(bottomplotsofFig. 1) results fromthegreater ECALcoverageallowing missed electrons with 2.4 <|ηlab| <3.0 to be accountedforinthe /ET calculation. The shape of the QCD multijet background is modelled by the functionalform f(/ET) = (/ET+/ET0)α exp(β
/
ET+/ET0).Itisshown to reproducethe/ET shape ofdataeventscontainingnon-isolated leptons, withthe /ET0, α, andβ parameters, which are observed to depend mildly andlinearly on the cone/lepton transverse en-ergy ratio. These fitted parameters are then extrapolated to the isolatedleptonsignalregimeandtheresultingfunctionisusedas the QCDbackgroundshape.The multijetbackgroundcontribution is largerintheelectron channel becausethemisidentified lepton rate ishigher, particularly dueto a contribution fromphoton-jet events.Contributionsfromothersources,suchastt productionand high-pTquarkonia,werefoundtobenegligible.
A small charge misidentification correction (less than 0.2%) is applied to the electron yields; this correction is negligible for muons. All fits are of good quality, as illustrated by the bottom panels of Fig. 1 that show the ratio of the data to the fit out-come. The observed numbers of leptons coming from W boson decaysovertheentirepseudorapidityrangeare:11660±111μ+, 9459±99μ−,9892±116 e+,and7872±101 e−,wherethe un-certaintyisstatistical,determinedbythefitprocedure.
Inordertocorrectforinefficienciesintheleptontrigger, recon-struction, and selection,the electroweak processesW→ ν have beensimulatedusingthe pythia 6.424generator[24] witha mix-tureofppandpninteractionscorrespondingtopPbcollisions.The detector response to each pythia signal event is simulated with Geant4 [25] and then embedded in a minimum bias pPb back-ground event. These background events are produced with the hijing eventgenerator [26] andpassed through Geant4 as well.
Fig. 1. MissingtransverseenergydistributionforW+→μ+ν (left)andW+→e+ν (right)eventswithinthe−0.5<ηlab<0.0 (top)and2.0<ηlab<2.4 (bottom)ranges.
Binnedfitstothedata(redpoints)areperformedwithfourcontributions,stackedfrombottomtotop:multijet(QCD,blue),W+→τ+ν (brown),Z→ (white)and W+→ +ν(yellow).Theηlabregionsaredefinedsuchthattheprotonismovingtowardspositiveηlabvalues.Errorbarsrepresentstatisticaluncertainties.Thelowerpanels
displaythedatadividedbytheresultofthefit,withthebandrepresentingthestatisticaluncertaintiesonthesumofthefitcomponents,foreach/ETbin.(Forinterpretation
ofthereferencestocolorinthisfigurelegend,thereaderisreferredtothewebversionofthisarticle.) Eachsimulationis done twice, onceforeach proton beam
direc-tion,andincludesaboosttoreproducethe0.465rapidityshift.The embeddingisdoneatthelevelofdetectorhits,andthesignaland backgroundeventssharethesamegenerated vertexlocation. The embeddedeventis thenprocessedthrough thetrigger emulation andthefulleventreconstructionchain.Theresultingreconstructed events are then reweighted to match the distributions observed indata of the event vertexand activity (as measured in the HF calorimeters).Theobtainedefficienciesvarywith ηlab(withhigher efficienciesatmid-rapidity),from59%to89%formuons,andfrom 51%to84%forelectrons.
Thevariouscomponentsofthesingle-leptonefficiencyarealso directlycomputedfrompPbdata,usingZ→ samples,and tech-niquesdescribedinRef.[23].Theseefficienciesarethencompared to the corresponding efficiencies computed from simulations. In thecaseoftriggerandreconstruction efficiencies, theyare found to be consistent. The isolation criterion rejects more leptons in data,becausethelocal activityoftheunderlying eventis greater thaninthesimulation.Toaccountforsuchdiscrepancies,the effi-ciencyfromW→ νsimulationismultipliedbycorrectionfactors,
whicharedeterminedastheratioofthesingle-leptonefficiencies measured in Z→ datato those estimated insimulations. The so-called“tag-and-probe” methodused forthis estimationis de-scribedinRef.[27].Thesecorrectionfactorsarecomputedinbins of ηlabandforpositivelyandnegativelychargedmuonsseparately. Inthe electroncase, thelow statisticalprecisionmotivatesa cor-rectionfactorestimatedforelectronsandpositronscombined.
The total systematic uncertainty in the lepton yields is esti-mated by adding the different contributions in quadrature. The
ηlab-dependent sources of systematic uncertainty arise from the methodused forthe estimationof multijetbackground(0.1–2.0% formuons, 0.5–3.8%forelectrons),thenormalizationofthe elec-troweakbackground(1–3%formuonsandelectrons),theefficiency correctionfactors(2.2–7.5%formuons,2.6–7.4%forelectrons),and the energy scale of electrons (0.1–2.0%). The uncertainty in the momentum scale of muons is found to be negligible. The inte-gratedluminositymeasurementuncertainty(3.5%[14])affectsonly the W bosonproduction crosssections andcancelsin the asym-metry measurements, as does the additional global uncertainty arising from the efficiency of the filter rejecting pileup events
Fig. 2. ProductioncrosssectionsforW+→ +ν (top)andW−→ −ν (bottom), asafunctionoftheleptonpseudorapidity.Errorbarsrepresentthestatistical un-certainties,whilebracketsshowstatisticalandsystematicuncertaintiessummedin quadrature.Thegloballuminosityuncertaintyof±3.5%isnotincluded.Toimprove visibility,the muon(electron)measurements, inredcircles (bluesquares),have beenshifted by−0.05 (+0.05)inpseudorapidity.(Forinterpretationofthe ref-erencestocolorinthisfigurelegend,thereaderisreferredtothewebversionof thisarticle.)
(0.5% for both channels). Though the common electron/positron correction factors cancel, a residual systematicuncertainty of 3% isassignedtothechargeasymmetry,basedonsimulationstudies and ηlab-integratedefficiencies determined fromZ→e+e− data. Noothersystematicuncertaintycancellationsareassumedforthe asymmetryresults.
3. Results
Fig. 2 shows the production cross sections for pPb→W±+ X→ ±ν+X asafunctionofthechargedleptonpseudorapidityin thelaboratory frame,withthe leptonhaving pT>25 GeV/c.The crosssectionsaredetermined by dividingtheefficiency-corrected leptonyieldsbytheintegratedluminosity.
Since the cross sections measured in the electron and muon channelsarefoundtobeingoodagreementwitheachother,they are combined using the BLUE method [28]. Fig. 3 compares the combinedcrosssectionswithnext-to-leading-order (NLO)
pertur-Fig. 3. Productioncrosssectionsfor W+→ +ν (top)and W−→ −ν (bottom), asafunctionoftheleptonpseudorapidity.Errorbarsrepresentthestatistical un-certainties,whilebracketsshowstatisticalandsystematicuncertaintiessummedin quadrature.Thegloballuminosityuncertaintyof±3.5%isnotdisplayed. Theoreti-calpredictionswith(CT10+EPS09,dashedgreenline)andwithout(CT10,solidred line)PDFnuclearmodificationsarealsoshown,with theuncertaintybands.The bottompanelsshowtheratioofthedata(blackpoints)andCT10+EPS09(dashed greenline)totheCT10baseline.AlltheoryuncertaintybandsincludescaleandPDF uncertainties,excepttheEPS09ofthebottompanelswhichonlyincludestheEPS09 PDFuncertainties.(Forinterpretationofthereferencestocolorinthisfigurelegend, thereaderisreferredtothewebversionofthisarticle.)
bative QCD predictions provided by theauthors of Ref. [4]using CT10 [29] proton parton distribution functions (PDF) without or withEPS09[30] nPDFcorrections,termedCT10andCT10+EPS09, respectively. Their uncertainties are estimated as prescribed in Refs. [29,30]. Table 1gives the measured cross sections for each channelseparatelyandcombined,asafunctionofthelepton pseu-dorapidity, for positive andnegative leptons. The theoretical pre-dictionsandtheiruncertainties(comingfromthePDFsetandfrom the renormalisation and factorisation scales) are also given. The agreement between the data and both theoretical predictions is withintheuncertainties,althoughasmallexcessofW−candidates appearsatnegative ηlab,i.e. inthePbionbeamdirection.
The comparison between the CT10 and CT10+EPS09 calcula-tions shows that the predicted modifications of the PDFs are of thesameorderasthetheoreticaluncertainties.Thisindicatesthat cross sectionsalonelackdiscriminatingpower, andmotivatesthe
Table 1
ProductioncrosssectionforpPb→W+X→ ν+X forpositively(top)andnegatively(bottom)chargedleptonsofpTlargerthan25 GeV/c,innanobarns,asafunction
oftheleptonpseudorapidity.Valuesaregivenfirstformuonsandelectronsseparately,thencombined.Quoteduncertaintiesarefirststatistical,thensystematic.Theoretical predictionswith(CT10+EPS09)andwithout(CT10)PDFnuclearmodificationsarealsogiven,withtheiruncertainties.Theglobalnormalizationuncertaintyof3.5%isnot includedinthelisteduncertainties.
dσ dη (nb) [ηbin] [−2.4,−2.0] [−2.0,−1.5] [−1.5,−1.0] [−1.0,−0.5] [−0.5,0] μ+ 43.0±2.2±3.1 62.5±2.1±2.6 86.9±2.6±3.4 98.1±2.7±2.6 98.3±2.8±3.3 e+ 46.5±2.6±3.6 64.0±3.1±4.2 84.2±3.1±4.8 99.8±3.0±4.6 102.0±2.9±4.6 + 44.5±1.7±2.3 62.9±1.8±2.2 85.9±2.0±2.7 98.6±2.1±2.3 99.7±2.1±2.7 CT10+EPS09 42.1+−22..68 66.0+ 3.8 −4.2 84.6+ 4.8 −5.4 93.4+ 5.3 −6.0 96.0+ 5.8 −6.3 CT10 43.4+−22..58 65.8+ 3.7 −4.2 82.4+ 4.6 −5.2 90.5+ 5.1 −5.7 94.4+ 5.7 −6.1 dσ dη (nb) [ηbin] [0,0.5] [0.5,1.0] [1.0,1.5] [1.5,2.0] [2.0,2.4] μ+ 113.9±3.1±4.5 101.3±2.8±2.9 102.3±2.8±3.6 107.9±3.1±5.7 107.8±3.7±8.4 e+ 99.6±2.7±3.6 102.8±2.9±4.6 95.6±3.4±5.8 95.4±3.5±6.2 108.3±4.3±8.7 + 105.3±2.1±2.8 101.8±2.1±2.5 100.2±2.2±3.1 102.3±2.3±4.2 108.1±2.8±6.0 CT10+EPS09 95.9+−66..24 95.5+ 6.6 −6.7 95.7+ 6.8 −7.5 95.3+ 7.5 −8.4 91.6+ 7.9 −8.9 CT10 97.0+5.8 −6.4 100.0+ 6.4 −6.6 103.4+ 6.3 −6.8 105.7+ 6.2 −7.2 103.6+ 6.0 −7.3 dσ dη (nb) [ηbin] [−2.4,−2.0] [−2.0,−1.5] [−1.5,−1.0] [−1.0,−0.5] [−0.5,0] μ− 74.5±3.0±5.6 84.5±2.8±4.4 89.4±2.6±3.5 81.4±2.5±2.6 80.6±2.6±2.6 e− 70.2±3.2±4.8 74.3±3.3±4.8 79.6±3.1±4.3 80.7±2.7±3.7 81.3±2.6±4.0 − 72.1±2.2±3.7 79.9±2.1±3.3 85.4±2.0±2.7 81.1±1.8±2.1 80.8±1.9±2.2 CT10+EPS09 65.2+4.0 −4.6 72.4+ 4.4 −5.0 75.9+ 4.6 −4.9 76.9+ 4.6 −5.0 76.1+ 4.9 −5.3 CT10 64.2+3.9 −4.4 70.1+ 4.2 −4.7 73.3+ 4.3 −4.8 74.8+ 4.4 −4.8 75.1+ 4.7 −5.1 dσ dη (nb) [ηbin] [0,0.5] [0.5,1.0] [1.0,1.5] [1.5,2.0] [2.0,2.4] μ− 81.7±2.5±3.0 78.8±2.5±3.3 69.8±2.3±3.0 62.9±2.1±3.3 63.1±2.8±5.1 e− 73.5±2.5±3.5 74.0±2.5±3.5 70.6±2.8±4.6 55.0±2.7±4.1 64.6±3.3±6.0 − 78.0±1.8±2.3 76.5±1.8±2.4 70.1±1.8±2.5 59.8±1.7±2.6 63.7±2.1±3.9 CT10+EPS09 73.6+5.1 −5.2 69.7+ 4.9 −5.1 64.8+ 4.5 −4.9 59.1+ 4.3 −4.8 53.4+ 4.3 −4.8 CT10 74.3+4.9 −5.2 72.4+ 4.8 −5.1 69.1+ 4.2 −4.9 64.5+ 3.8 −4.3 59.3+ 3.6 −4.0
studyofvariousasymmetriesofthe +and − crosssections.The interest in such asymmetries is twofold. First, some of the ex-perimental(e.g. integrated luminosity) and theoretical (e.g. scale dependence)uncertaintiescancelinsuchasymmetries.Second,the various asymmetries exhibit different sensitivities to the nuclear modificationsofthePDFs,asdiscussedbelow.
Theleptonchargeasymmetry,definedas (N+−N−)/(N++N−)
with N± being the efficiency-corrected lepton yields, is shown in Fig. 4, as a function of ηlab, and compared to the theoret-ical predictions. For ηlab>−1, both calculations reproduce the presentmeasurements. For ηlab<−1, however, the two calcula-tions overpredict the asymmetry values. A possible physical ori-gin of this disagreement could be a different modification of u andd quark distributions in nuclei. In proton–(anti)proton colli-sions, the W-boson charge asymmetry is known to be a sensi-tiveprobe ofthedown-to-up quark PDF ratioina proton,dp/up [20,31,32]. Similarly, this asymmetry in pPb collisions measured in the lead fragmentation region (i.e. ηlab<0.465) probes these quark densities in a nucleon inside the lead nucleus. Assuming the standard isospin symmetry (up=dn, un=dp), one can de-fine a similar ratio, dp/A/up/A=dp/up ×Rd/Ru, where Ri are
the nPDF ratios, Ru ≡up/A/up and Rd ≡dp/A/dp. The typical quark momentum fraction probed in the Pb nucleus is given by xMW/√sNN×exp(−ηlab+0.465)(assumingthattheW boson rapidity issimilar to that of thelepton), thereforex0.02–0.20 in the range −2 <ηlab<0. In most global fit analyses of the nPDFs (as in the caseof EPS09), it is assumed that the nuclear ratiosrespect the isospin symmetry, namely Ru=Rd, essentially tominimise the numberof free parameters inthe fits. However, nophysical reasonpreventsnuclear modifications tobe different forup and down quark PDFs. Forexample, it is known that the
Fig. 4. Leptonchargeasymmetry,(N+−N−)/(N++N−),asafunctionofthe lep-tonpseudorapidity.Errorbarsrepresentthestatisticaluncertainties,whilebrackets show statisticaland systematicuncertainties summedinquadrature. Theoretical predictionswith(CT10+EPS09,dashed greenline)and without(CT10,solidred line)PDFnuclearmodificationsarealsoshown,withtheiruncertaintybands.(For interpretationofthereferencestocolorinthisfigurelegend,thereaderisreferred tothewebversionofthisarticle.)
shapesoftheupanddownquarkdistributionsinprotonsare dif-ferent [33]. Furthermore,the presentdisparitybetweendata and theoryisunlikelytocomefromtheprotonPDFassumption,given theexcellent agreementoflepton chargeasymmetry measuredin
Fig. 5. Forward–backwardasymmetries,N(+ηlab)/N(−ηlab),forthepositive(top)
and negative (bottom)leptons.Error barsrepresent the statistical uncertainties, whilebracketsshowstatisticalandsystematicuncertaintiessummedinquadrature. Theoreticalpredictionswith(CT10+EPS09,dashedgreenline)andwithout(CT10, solidredline)PDFnuclearmodificationsarealsoshown, withtheir uncertainty bands.(Forinterpretationofthereferencestocolorinthisfigurelegend,thereader isreferredtothewebversionofthisarticle.)
pp collisions by CMS [32] and ATLAS [34] with NLO calculations usingCT10partondensities.
Atraditionalwaytoprobenuclearpartondensitiesis to com-pare the forward and backward W yields, that are respectively sensitivetothenPDFsatsmallandlargex.Theforward–backward asymmetriesN±(+ηlab)/N±(−ηlab)areshowninFig. 5,separately forthepositivelyandnegativelychargedleptons,andcomparedto thesamepredictionsasmentionedabove.Giventheexperimental accuracy andthe magnitude of the differencesbetween the two setsofpredictions,themeasurementshaveapotentialto discrim-inatebetweenthem.However,althoughthenegativeleptondecay channelappearstoslightlyfavourtheCT10+EPS09predictionover theCT10calculation,thepositiveleptonchanneldoesnot,thusno firmconclusioncanbedrawn.
Another asymmetry variable, (N+(+ηlab) − N+(−ηlab))/
(N−(+ηlab) −N−(−ηlab)),wasproposed inRef.[4]toreach max-imum sensitivityto nuclear modifications of PDFs.However, this asymmetryprobabilitydistributionshowsaverynon-Gaussian be-haviour, when its denominator approacheszero, andits signcan
Fig. 6. Theforward–backwardasymmetryofcharge-summedWbosons,asa func-tionoftheleptonpseudorapidity.Errorbarsrepresentthestatisticaluncertainties, whilebracketsshowstatisticalandsystematicuncertaintiessummedinquadrature. Theoreticalpredictionswith(CT10+EPS09,dashedgreenline)andwithout(CT10, solidredline)PDFnuclearmodifications arealso shown,with theiruncertainty bands.(Forinterpretationofthereferencestocolorinthisfigurelegend,thereader isreferredtothewebversionofthisarticle.)
Table 2
Valuesoftheχ2testbetweenthemeasurementsandthetheoreticalpredictions,
with(CT10+EPS09)orwithout(CT10)nuclearmodificationsofthePDFs.The prob-ability(Prob.)tomeasureavaluegreatertothatmeasuredindataisalsogivenfor tendegreesoffreedominthecaseofthefirstthreeobservablesandfivedegreesof freedomforthethreeothersobservables.
Observable CT10 CT10+EPS09 χ2 Prob. (%) χ2 Prob. (%) dσ/dη(+) 13 25 8.6 57 dσ/dη(−) 15 14 8.2 60 (N+−N−)/(N++N−) 15 12 11 35 N+(+ηlab)/N+(−ηlab) 3.1 68 3.2 68 N−(+ηlab)/N−(−ηlab) 9.7 8.4 3.5 63 N(+ηlab)/N(−ηlab) 6.2 29 2.1 83
be flippedwithin the uncertainty. Adifferent asymmetry is pro-posedhere, N(+ηlab)/N(−ηlab),aforward–backwardasymmetry of the charge-summed W bosons, which achieves a similar sen-sitivity. As in the caseofthe charge asymmetry,thisasymmetry can be related to the nuclear modifications of the PDFs within the lead nucleus. Here, forward (backward) W boson production is sensitive to the PDFs of the sea quark at x∼10−3 (valence quark at x∼10−1) in the lead nucleus. Therefore, the forward– backwardratioprobesthesmall-x modificationoftheleadnucleus PDF (shadowing)over thelarge-x modifications (anti-shadowing). Thisasymmetry isshowninFig. 6,anddeviatesfromunmodified PDFs,moreclearlyfavouringCT10+EPS09overCT10.
In orderto quantifythe agreement betweenthedata andthe expectationfromtheCT10andCT10+EPS09calculations,a χ2 test isperformedforeach oftheabove(correlated)variables.Thefew correlations in experimental uncertainties described above, only relevantforW±bosoncrosssectionsbutnotforasymmetries,are taken into account,as well asthe correlations intheoretical un-certainties. Theresulting χ2 valuesandprobabilitiesare givenin Table 2.TheCT10+EPS09calculationsprovideabetterdescription of the data, with still a relatively low probability for the lepton chargeasymmetry,becauseofthebackwardregion.
4. Summary
The first measurement of W boson production in pPb colli-sionshasbeenreported,usingtheelectronandmuondecaymodes forleptons of pT above 25 GeV/c and |ηlab| <2.4. The differen-tialcrosssectionsasafunctionoftheleptonpseudorapidityagree withtheoreticalpredictionsassumingbothunmodified(CT10)and modified (CT10+EPS09) nPDFs, exceptin the most backward re-gion(Pbionbeamdirection),whereahintofan enhancementis seen for the W− bosons. In the same region, the related lepton charge asymmetry deviates slightly from the predictions, some-thing that could potentially arise from different nuclear modifi-cationsoftheup anddownquark PDFs.Ina relatedobservation, forward–backwardasymmetriesshowadeviationfromunmodified PDFs.Takentogether,thesemeasurements show the needfor in-cludingWbosondatainnuclearpartondistributionglobalfits.
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,wegratefullyacknowledgethecomputingcentresand 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,andNSFC(China);COLCIENCIAS (Colombia);MSESandCSF(Croatia);RPF(Cyprus);MoER,ERCIUT andERDF(Estonia); AcademyofFinland,MEC, andHIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); MSIP and NRF (Republic ofKorea); LAS (Lithuania);MOE andUM (Malaysia); CINVESTAV, CONACYT,SEP,andUASLP-FAI(Mexico);MBIE(NewZealand);PAEC (Pakistan);MSHE andNSC (Poland);Faculdadede Ciênciase Tec-nologia, Universidade Nova de Lisboa (Portugal); JINR (Dubna); MON,RosAtom,RASandRFBR(Russia);MESTD(Serbia);SEIDIand CPAN(Spain);SwissFundingAgencies(Switzerland);MST(Taipei); ThEPCenter,IPST,STARandNSTDA(Thailand);TUBITAKandTAEK (Turkey);NASUandSFFR(Ukraine);STFC (UnitedKingdom);DOE andNSF(USA).
Individuals have received support from the Marie-Curie pro-gramme and the European Research Council and EPLANET (Eu-ropean Union); the Leventis Foundation; the A.P. Sloan Founda-tion; the Alexander von Humboldt Foundation; the Belgian Fed-eral Science Policy Office; the Fonds pour la Formation à la Recherchedansl’Industrieetdansl’Agriculture(FRIA-Belgium);the AgentschapvoorInnovatiedoorWetenschapenTechnologie (IWT-Belgium);the Ministryof Education,Youth andSports(MEYS) of theCzechRepublic;theCouncilofScienceandIndustrialResearch, India;theHOMINGPLUSprogrammeoftheFoundationforPolish Science, cofinanced fromEuropean Union, Regional Development Fund;theCompagnia diSanPaolo (Torino); theConsorzioper la Fisica(Trieste); MIURproject 20108T4XTM(Italy); theThalisand Aristeia programmes cofinancedby EU-ESF and the Greek NSRF; andtheNationalPrioritiesResearchProgrambyQatarNational Re-searchFund.
References
[1] V.Kartvelishvili, R.Kvatadze, R.Shanidze,OnZ andZ + jetproduction in heavyioncollisions, Phys.Lett.B356(1995)589,http://dx.doi.org/10.1016/ 0370-2693(95)00865-I,arXiv:hep-ph/9505418.
[2] R.Vogt,Shadowingeffectsonvectorbosonproduction,Phys.Rev.C64(2001) 044901,http://dx.doi.org/10.1103/PhysRevC.64.044901,arXiv:hep-ph/0011242. [3] X.-F.Zhang,G.I. Fai, Z0 production asatest ofnucleareffectsatthe LHC,
Phys.Lett.B545(2002)91,http://dx.doi.org/10.1016/S0370-2693(02)02558-3, arXiv:hep-ph/0205155.
[4] H.Paukkunen,C.A.Salgado,Constraintsfor thenuclearparton distributions from Z andWproduction at theLHC,J. HighEnergy Phys.03 (2011)071,
http://dx.doi.org/10.1007/JHEP03(2011)071,arXiv:1010.5392.
[5] Z. Conesa delValle, A. Dainese,H.-T. Ding,G. Martinez Garcia, D.C.Zhou, Effectofheavy-quarkenergylossonthemuondifferentialproduction cross-sectioninPb–Pbcollisionsat√sNN=5.5 TeV,Phys.Lett.B663(2008)202,
http://dx.doi.org/10.1016/j.physletb.2008.03.073,arXiv:0712.0051.
[6] Z. ConesadelValle, Vectorbosonsinheavy-ioncollisions at the LHC,Eur. Phys. J. C 61 (2009) 729,http://dx.doi.org/10.1140/epjc/s10052-009-0980-8, arXiv:0903.1432.
[7] N.Armesto, Nuclearshadowing,J.Phys.G32(2006)R367,http://dx.doi.org/ 10.1088/0954-3899/32/11/R01,arXiv:hep-ph/0604108.
[8] ATLASCollaboration,MeasurementofthecentralitydependenceofJ/ψ yields andobservationofzproductioninlead–leadcollisionswiththeATLASdetector at theLHC,Phys.Lett.B697(2011)294,http://dx.doi.org/10.1016/j.physletb. 2011.02.006,arXiv:1012.5419.
[9] ATLAS√ Collaboration,MeasurementofZ bosonproductioninPbPbcollisionsat sNN=2.76 TeV withtheATLASdetector,Phys.Rev.Lett.110(2013)022301,
http://dx.doi.org/10.1103/PhysRevLett.110.022301,arXiv:1210.6486.
[10] CMSCollaboration,StudyofZbosonproductioninPbPbcollisionsatnucleon– nucleoncentreofmassenergy=2.76 TeV,Phys.Rev.Lett.106(2011)212301,
http://dx.doi.org/10.1103/PhysRevLett.106.212301,arXiv:1102.5435.
[11] CMSCollaboration,StudyofZproductioninPbPbandppcollisionsat√sNN=
2.76 TeV inthedimuonanddielectrondecaychannels,J.HighEnergyPhys.03 (2015)022,http://dx.doi.org/10.1007/JHEP03(2015)022,arXiv:1410.4825. [12] CMSCollaboration,StudyofW bosonproduction inPbPbandpp collisions
at √sNN=2.76 TeV,Phys. Lett. B715(2012) 66, http://dx.doi.org/10.1016/
j.physletb.2012.07.025,arXiv:1205.6334.
[13] ATLASCollaboration,Measurementoftheproductionandleptoncharge asym-metry of W bosons inPbPb collisions at √sNN=2.76 TeV with the
AT-LAS detector, Eur. Phys. J. C 75 (2015) 23, http://dx.doi.org/10.1140/epjc/ s10052-014-3231-6,arXiv:1408.4674.
[14] CMS Collaboration, Luminosity calibration for the 2013 proton–lead and proton–proton data taking, CMS Physics Analysis Summary CMS-PAS-LUM-13-002,2013,http://cds.cern.ch/record/1643269.
[15] CMSCollaboration,TheCMSexperimentattheCERNLHC,J.Instrum.3(2008) S08004,http://dx.doi.org/10.1088/1748-0221/3/08/S08004.
[16] CMSCollaboration,Multiplicityandtransversemomentumdependenceof two-and four-particle correlations inpPband PbPbcollisions, Phys.Lett. B724 (2013)213,http://dx.doi.org/10.1016/j.physletb.2013.06.028,arXiv:1305.0609. [17] CMSCollaboration,PerformanceofCMSmuonreconstructioninppcollision
eventsat √s=7TeV,J.Instrum.7(2012)P10002,http://dx.doi.org/10.1088/ 1748-0221/7/10/P10002.
[18] CMSCollaboration,EnergycalibrationandresolutionoftheCMS electromag-neticcalorimeterinppcollisionsat√s=7 TeV,J.Instrum.8(2013)P09009,
http://dx.doi.org/10.1088/1748-0221/8/09/P09009,arXiv:1306.2016.
[19] CMS Collaboration, Performance of electron reconstruction and se-lection with the CMS detector in proton–proton collisions at √
s = 8 TeV, arXiv:1502.02701, J. Instrum. 10 (2015) P06005,
http://dx.doi.org/10.1088/1748-0221/10/06/P06005.
[20] CMSCollaboration,Measurementoftheelectronchargeasymmetryin inclu-siveW productioninppcollisionsat√s=7 TeV,Phys.Rev.Lett.109(2012) 111806,http://dx.doi.org/10.1103/PhysRevLett.109.111806,arXiv:1206.2598. [21] CMSCollaboration,Particle-floweventreconstructioninCMSandperformance
forjets,taus,and EmissT ,CMSPhysicsAnalysisSummaryCMS-PAS-PFT-09-001,
2009,http://cdsweb.cern.ch/record/1194487.
[22] CMSCollaboration, Commissioningofthe particle-flowevent reconstruction with the first LHC collisions recorded in the CMS detector, CMS Physics Analysis Summary CMS-PAS-PFT-10-001, 2010, http://cdsweb.cern.ch/record/ 1247373.
[23] CMSCollaboration,MeasurementoftheinclusiveW and Z productioncross sectionsinppcollisionsat√s=7 TeV,J.HighEnergyPhys.10(2011)132,
http://dx.doi.org/10.1007/JHEP10(2011)132,arXiv:1107.4789.
[24] T. Sjöstrand, S.Mrenna, P.Skands,PYTHIA 6.4 physicsand manual,J. High EnergyPhys.05(2006)026,http://dx.doi.org/10.1088/1126-6708/2006/05/026, arXiv:hep-ph/0603175.
[25] S. Agostinelli,et al., GEANTCollaboration, GEANT4 —a simulation toolkit, Nucl. Instrum. Methods A 506(2003) 250, http://dx.doi.org/10.1016/S0168-9002(03)01368-8.
[26] M. Gyulassy, X.-N. Wang, HIJING 1.0: a Monte Carlo program for par-ton and particle production in high-energy hadronic and nuclear colli-sions,Comput.Phys.Commun.83(1994)307, http://dx.doi.org/10.1016/0010-4655(94)90057-4,arXiv:nucl-th/9502021.
[27] CMSCollaboration,MeasurementsofinclusiveW andZ crosssectionsinpp collisionsat√s=7 TeV,J.HighEnergyPhys.01(2011)080,http://dx.doi.org/ 10.1007/JHEP01(2011)080,arXiv:1012.2466.
[28] L. Lyons, D. Gibaut, P. Clifford, Howto combine correlatedestimates of a single physicalquantity, Nucl.Instrum. MethodsA 270 (1988)110, http:// dx.doi.org/10.1016/0168-9002(88)90018-6.
[29] H.-L.Lai, M. Guzzi, J. Huston, Z. Li,P.M. Nadolsky, J. Pumplin, C.-P.Yuan, Newpartondistributionsforcolliderphysics,Phys.Rev.D82(2010)074024,
http://dx.doi.org/10.1103/PhysRevD.82.074024,arXiv:1007.2241.
[30] K.J.Eskola,H.Paukkunen,C.A.Salgado,EPS09:anewgenerationofNLOand LOnuclearparton distributionfunctions,J.HighEnergyPhys.04(2009)065,
http://dx.doi.org/10.1088/1126-6708/2009/04/065,arXiv:0902.4154.
[31] T.Aaltonen,etal.,CDFCollaboration,DirectmeasurementoftheW production chargeasymmetryinpp collisionsat√s=1.96 TeV,Phys.Rev.Lett.102(2009) 181801,http://dx.doi.org/10.1103/PhysRevLett.102.181801,arXiv:0901.2169. [32] CMS Collaboration, Measurementof the muoncharge asymmetryin
inclu-sivepp→W+X productionat √s=7 TeV and animproved determina-tionoflight parton distributionfunctions, Phys. Rev.D90 (2014) 032004,
http://dx.doi.org/10.1103/PhysRevD.90.032004,arXiv:1312.6283.
[33] A.D. Martin, W.J.Stirling,R.S. Thorne, G. Watt,Partondistributions for the LHC,Eur.Phys.J.C63(2009)189, http://dx.doi.org/10.1140/epjc/s10052-009-1072-5,arXiv:0901.0002.
[34] ATLASCollaboration, Measurementofthe muonchargeasymmetryfromW bosonsproduced inpp collisions at √s=7 TeV withthe ATLAS detector, Phys. Lett. B701 (2011) 31, http://dx.doi.org/10.1016/j.physletb.2011.05.024, arXiv:1103.2929.
CMSCollaboration
V. Khachatryan,A.M. Sirunyan, A. Tumasyan
YerevanPhysicsInstitute,Yerevan,Armenia
W. Adam, T. Bergauer, M. Dragicevic,J. Erö, M. Friedl,R. Frühwirth1,V.M. Ghete, C. Hartl, N. Hörmann, J. Hrubec, M. Jeitler1, W. Kiesenhofer,V. Knünz, M. Krammer1, I. Krätschmer,D. Liko, I. Mikulec, D. Rabady2,B. Rahbaran, H. Rohringer, R. Schöfbeck, J. Strauss, W. Treberer-Treberspurg,
W. Waltenberger, C.-E. Wulz1
InstitutfürHochenergiephysikderOeAW,Wien,Austria
V. Mossolov,N. Shumeiko, J. Suarez Gonzalez
NationalCentreforParticleandHighEnergyPhysics,Minsk,Belarus
S. Alderweireldt, S. Bansal,T. Cornelis, E.A. De Wolf,X. Janssen, A. Knutsson,J. Lauwers, S. Luyckx, S. Ochesanu,R. Rougny, M. Van De Klundert, H. Van Haevermaet,P. Van Mechelen, N. Van Remortel, A. Van Spilbeeck
UniversiteitAntwerpen,Antwerpen,Belgium
F. Blekman,S. Blyweert, J. D’Hondt,N. Daci, N. Heracleous, J. Keaveney,S. Lowette, M. Maes, A. Olbrechts, Q. Python, D. Strom, S. Tavernier,W. Van Doninck, P. Van Mulders, G.P. Van Onsem, I. Villella
VrijeUniversiteitBrussel,Brussel,Belgium
C. Caillol, B. Clerbaux, G. De Lentdecker, D. Dobur, L. Favart, A.P.R. Gay, A. Grebenyuk,A. Léonard, A. Mohammadi, L. Perniè2, A. Randleconde, T. Reis,T. Seva, L. Thomas, C. Vander Velde, P. Vanlaer, J. Wang, F. Zenoni
UniversitéLibredeBruxelles,Bruxelles,Belgium
V. Adler,K. Beernaert, L. Benucci, A. Cimmino,S. Costantini, S. Crucy, S. Dildick,A. Fagot, G. Garcia, J. Mccartin, A.A. Ocampo Rios,D. Poyraz, D. Ryckbosch, S. Salva Diblen, M. Sigamani,N. Strobbe, F. Thyssen,M. Tytgat, E. Yazgan, N. Zaganidis
GhentUniversity,Ghent,Belgium
S. Basegmez, C. Beluffi3,G. Bruno,R. Castello, A. Caudron, L. Ceard, G.G. Da Silveira, C. Delaere, T. du Pree,D. Favart, L. Forthomme,A. Giammanco4,J. Hollar, A. Jafari, P. Jez,M. Komm, V. Lemaitre, C. Nuttens, L. Perrini, A. Pin, K. Piotrzkowski,A. Popov5,L. Quertenmont, M. Selvaggi, M. Vidal Marono, J.M. Vizan Garcia
UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium
N. Beliy, T. Caebergs,E. Daubie, G.H. Hammad
W.L. Aldá Júnior, G.A. Alves,L. Brito,M. Correa Martins Junior, T. Dos Reis Martins, J. Molina, C. Mora Herrera,M.E. Pol, P. Rebello Teles
CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil
W. Carvalho,J. Chinellato6, A. Custódio, E.M. Da Costa, D. De Jesus Damiao,C. De Oliveira Martins, S. Fonseca De Souza, H. Malbouisson,D. Matos Figueiredo, L. Mundim, H. Nogima,W.L. Prado Da Silva, J. Santaolalla,A. Santoro, A. Sznajder,E.J. Tonelli Manganote6, A. Vilela Pereira
UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil
C.A. Bernardesb, S. Dograa,T.R. Fernandez Perez Tomeia, E.M. Gregoresb, P.G. Mercadanteb, S.F. Novaesa, Sandra S. Padulaa
aUniversidadeEstadualPaulista,SãoPaulo,Brazil bUniversidadeFederaldoABC,SãoPaulo,Brazil
A. Aleksandrov, V. Genchev2, R. Hadjiiska,P. Iaydjiev, A. Marinov, S. Piperov,M. Rodozov, S. Stoykova, G. Sultanov,M. Vutova
InstituteforNuclearResearchandNuclearEnergy,Sofia,Bulgaria
A. Dimitrov,I. Glushkov, L. Litov, B. Pavlov,P. Petkov
UniversityofSofia,Sofia,Bulgaria
J.G. Bian,G.M. Chen, H.S. Chen, M. Chen, T. Cheng,R. Du, C.H. Jiang, R. Plestina7, F. Romeo,J. Tao, Z. Wang
InstituteofHighEnergyPhysics,Beijing,China
C. Asawatangtrakuldee, Y. Ban,S. Liu, Y. Mao,S.J. Qian, D. Wang, Z. Xu,L. Zhang, W. Zou
StateKeyLaboratoryofNuclearPhysicsandTechnology,PekingUniversity,Beijing,China
C. Avila,A. Cabrera, L.F. Chaparro Sierra, C. Florez,J.P. Gomez, B. Gomez Moreno, J.C. Sanabria
UniversidaddeLosAndes,Bogota,Colombia
N. Godinovic, D. Lelas,D. Polic, I. Puljak
UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia
Z. Antunovic,M. Kovac
UniversityofSplit,FacultyofScience,Split,Croatia
V. Brigljevic,K. Kadija, J. Luetic,D. Mekterovic, L. Sudic
InstituteRudjerBoskovic,Zagreb,Croatia
A. Attikis, G. Mavromanolakis,J. Mousa, C. Nicolaou, F. Ptochos,P.A. Razis
UniversityofCyprus,Nicosia,Cyprus
M. Bodlak,M. Finger,M. Finger Jr.8
CharlesUniversity,Prague,CzechRepublic
Y. Assran9,A. Ellithi Kamel10,M.A. Mahmoud11,A. Radi12,13
AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt
M. Kadastik, M. Murumaa, M. Raidal, A. Tiko
P. Eerola, M. Voutilainen
DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland
J. Härkönen,V. Karimäki, R. Kinnunen, M.J. Kortelainen, T. Lampén, K. Lassila-Perini,S. Lehti, T. Lindén, P. Luukka, T. Mäenpää,T. Peltola, E. Tuominen, 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, A. Givernaud, P. Gras, G. Hamel de Monchenault, P. Jarry,E. Locci, J. Malcles,J. Rander, A. Rosowsky, M. Titov
DSM/IRFU,CEA/Saclay,Gif-sur-Yvette,France
F. Arleo,S. Baffioni, F. Beaudette, P. Busson, E. Chapon, C. Charlot,T. Dahms, M. Dalchenko,L. Dobrzynski, N. Filipovic, A. Florent,R. Granier de Cassagnac, L. Mastrolorenzo, P. Miné, I.N. Naranjo, M. Nguyen, C. Ochando, G. Ortona,P. Paganini, S. Regnard, R. Salerno, J.B. Sauvan, Y. Sirois, C. Veelken,Y. Yilmaz, A. Zabi
LaboratoireLeprince-Ringuet,EcolePolytechnique,IN2P3–CNRS,Palaiseau,France
J.-L. Agram14, J. Andrea, A. Aubin, D. Bloch,J.-M. Brom, E.C. Chabert,C. Collard, E. Conte14, J.-C. Fontaine14,D. Gelé, U. Goerlach, C. Goetzmann,A.-C. Le Bihan, K. Skovpen, P. Van Hove
InstitutPluridisciplinaireHubertCurien,UniversitédeStrasbourg,UniversitédeHauteAlsaceMulhouse,CNRS/IN2P3,Strasbourg,France
S. Gadrat
CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France
S. Beauceron,N. Beaupere, C. Bernet7,G. Boudoul2, E. Bouvier, S. Brochet, C.A. Carrillo Montoya,
J. Chasserat, R. Chierici,D. Contardo2,P. Depasse,H. El Mamouni, J. Fan, J. Fay, S. Gascon, M. Gouzevitch, B. Ille, T. Kurca, M. Lethuillier, L. Mirabito,S. Perries, J.D. Ruiz Alvarez,D. Sabes, L. Sgandurra,V. Sordini, M. Vander Donckt, P. Verdier, S. Viret,H. Xiao
UniversitédeLyon,UniversitéClaudeBernardLyon1,CNRS-IN2P3,InstitutdePhysiqueNucléairedeLyon,Villeurbanne,France
Z. Tsamalaidze8
InstituteofHighEnergyPhysicsandInformatization,TbilisiStateUniversity,Tbilisi,Georgia
C. Autermann, S. Beranek,M. Bontenackels, M. Edelhoff,L. Feld, A. Heister, K. Klein,M. Lipinski, A. Ostapchuk, M. Preuten,F. Raupach, J. Sammet, S. Schael, J.F. Schulte, H. Weber, B. Wittmer, V. Zhukov5
RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany
M. Ata, M. Brodski,E. Dietz-Laursonn, D. Duchardt, M. Erdmann, R. Fischer,A. Güth, T. Hebbeker, C. Heidemann,K. Hoepfner, D. Klingebiel,S. Knutzen,P. Kreuzer, M. Merschmeyer,A. Meyer, P. Millet, M. Olschewski, K. Padeken,P. Papacz, H. Reithler,S.A. Schmitz, L. Sonnenschein, D. Teyssier,S. Thüer, M. Weber
RWTHAachenUniversity,III.PhysikalischesInstitutA,Aachen,Germany
V. Cherepanov, Y. Erdogan,G. Flügge, H. Geenen, M. Geisler, W. Haj Ahmad, F. Hoehle, B. Kargoll, T. Kress, Y. Kuessel,A. Künsken, J. Lingemann2, A. Nowack,I.M. Nugent,O. Pooth, A. Stahl
M. Aldaya Martin,I. Asin, N. Bartosik, J. Behr, U. Behrens,A.J. Bell, A. Bethani,K. Borras, A. Burgmeier, A. Cakir,L. Calligaris, A. Campbell,S. Choudhury, F. Costanza, C. Diez Pardos,G. Dolinska,S. Dooling, T. Dorland,G. Eckerlin, D. Eckstein, T. Eichhorn, G. Flucke, J. Garay Garcia, A. Geiser, A. Gizhko, P. Gunnellini, J. Hauk, M. Hempel15,H. Jung, A. Kalogeropoulos, M. Kasemann,P. Katsas, J. Kieseler, C. Kleinwort,I. Korol, D. Krücker,W. Lange, J. Leonard, K. Lipka,A. Lobanov, W. Lohmann15, B. Lutz, R. Mankel, I. Marfin15,I.-A. Melzer-Pellmann, A.B. Meyer, G. Mittag, J. Mnich, A. Mussgiller,
S. Naumann-Emme,A. Nayak,E. Ntomari, H. Perrey,D. Pitzl, R. Placakyte, A. Raspereza,
P.M. Ribeiro Cipriano,B. Roland, E. Ron, M.Ö. Sahin,J. Salfeld-Nebgen, P. Saxena,T. Schoerner-Sadenius, M. Schröder,C. Seitz, S. Spannagel, A.D.R. Vargas Trevino, R. Walsh, C. Wissing
DeutschesElektronen-Synchrotron,Hamburg,Germany
V. Blobel, M. Centis Vignali, A.R. Draeger,J. Erfle, E. Garutti,K. Goebel, M. Görner, J. Haller,
M. Hoffmann,R.S. Höing,A. Junkes, H. Kirschenmann, R. Klanner, R. Kogler,J. Lange, T. Lapsien, T. Lenz, I. Marchesini,J. Ott, T. Peiffer, A. Perieanu, N. Pietsch,J. Poehlsen, T. Poehlsen, D. Rathjens, C. Sander, H. Schettler,P. Schleper, E. Schlieckau, A. Schmidt, M. Seidel, V. Sola,H. Stadie, G. Steinbrück,
D. Troendle,E. Usai, L. Vanelderen, A. Vanhoefer
UniversityofHamburg,Hamburg,Germany
C. Barth,C. Baus, J. Berger,C. Böser, E. Butz, T. Chwalek, W. De Boer,A. Descroix, A. Dierlamm, M. Feindt,F. Frensch, M. Giffels, A. Gilbert,F. Hartmann2,T. Hauth, U. Husemann, I. Katkov5,
A. Kornmayer2, P. Lobelle Pardo, M.U. Mozer,T. Müller, Th. Müller, A. Nürnberg, G. Quast, K. Rabbertz, S. Röcker,H.J. Simonis, F.M. Stober,R. Ulrich, J. Wagner-Kuhr, S. Wayand, T. Weiler, R. Wolf
InstitutfürExperimentelleKernphysik,Karlsruhe,Germany
G. Anagnostou,G. Daskalakis, T. Geralis,V.A. Giakoumopoulou, A. Kyriakis, D. Loukas,A. Markou, C. Markou, A. Psallidas,I. Topsis-Giotis
InstituteofNuclearandParticlePhysics(INPP),NCSRDemokritos,AghiaParaskevi,Greece
A. Agapitos,S. Kesisoglou, A. Panagiotou,N. Saoulidou, E. Stiliaris
UniversityofAthens,Athens,Greece
X. Aslanoglou,I. Evangelou, G. Flouris,C. Foudas, P. Kokkas, N. Manthos, I. Papadopoulos,E. Paradas, J. Strologas
UniversityofIoánnina,Ioánnina,Greece
G. Bencze,C. Hajdu, P. Hidas,D. Horvath16, F. Sikler,V. Veszpremi, G. Vesztergombi17, A.J. Zsigmond
WignerResearchCentreforPhysics,Budapest,Hungary
N. Beni,S. Czellar, J. Karancsi18,J. Molnar, J. Palinkas, Z. Szillasi
InstituteofNuclearResearchATOMKI,Debrecen,Hungary
A. Makovec,P. Raics, Z.L. Trocsanyi, B. Ujvari
UniversityofDebrecen,Debrecen,Hungary
S.K. Swain
NationalInstituteofScienceEducationandResearch,Bhubaneswar,India
S.B. Beri,V. Bhatnagar, R. Gupta, U. Bhawandeep, A.K. Kalsi,M. Kaur, R. Kumar,M. Mittal, N. Nishu, J.B. Singh
Ashok Kumar, Arun Kumar,S. Ahuja, A. Bhardwaj, B.C. Choudhary,A. Kumar, S. Malhotra,M. Naimuddin, K. Ranjan,V. Sharma
UniversityofDelhi,Delhi,India
S. Banerjee, S. Bhattacharya, K. Chatterjee,S. Dutta, B. Gomber, Sa. Jain, Sh. Jain,R. Khurana, A. Modak, S. Mukherjee,D. Roy, S. Sarkar, M. Sharan
SahaInstituteofNuclearPhysics,Kolkata,India
A. Abdulsalam, D. Dutta, V. Kumar, A.K. Mohanty2,L.M. Pant, P. Shukla, A. Topkar
BhabhaAtomicResearchCentre,Mumbai,India
T. Aziz, S. Banerjee, S. Bhowmik19,R.M. Chatterjee, R.K. Dewanjee, S. Dugad, S. Ganguly,S. Ghosh, M. Guchait,A. Gurtu20,G. Kole, S. Kumar, M. Maity19, G. Majumder, K. Mazumdar,G.B. Mohanty, B. Parida,K. Sudhakar, N. Wickramage21
TataInstituteofFundamentalResearch,Mumbai,India
H. Bakhshiansohi,H. Behnamian, S.M. Etesami22, A. Fahim23, R. Goldouzian, M. Khakzad,
M. Mohammadi Najafabadi, M. Naseri, S. Paktinat Mehdiabadi, F. Rezaei Hosseinabadi, B. Safarzadeh24, M. Zeinali
InstituteforResearchinFundamentalSciences(IPM),Tehran,Iran
M. Felcini,M. Grunewald
UniversityCollegeDublin,Dublin,Ireland
M. Abbresciaa,b, C. Calabriaa,b,S.S. Chhibraa,b, A. Colaleoa, D. Creanzaa,c,L. Cristellaa,b,
N. De Filippisa,c, M. De Palmaa,b,L. Fiorea,G. Iasellia,c,G. Maggia,c,M. Maggia, S. Mya,c, S. Nuzzoa,b, A. Pompilia,b,G. Pugliesea,c,R. Radognaa,b,2, G. Selvaggia,b, A. Sharmaa, L. Silvestrisa,2, R. Vendittia,b, P. Verwilligena
aINFNSezionediBari,Bari,Italy bUniversitàdiBari,Bari,Italy cPolitecnicodiBari,Bari,Italy
G. Abbiendia,A.C. Benvenutia,D. Bonacorsia,b, S. Braibant-Giacomellia,b, L. Brigliadoria,b, R. Campaninia,b, P. Capiluppia,b,A. Castroa,b,F.R. Cavalloa, G. Codispotia,b, M. Cuffiania,b,
G.M. Dallavallea,F. Fabbria, A. Fanfania,b, D. Fasanellaa,b,P. Giacomellia,C. Grandia,L. Guiduccia,b, S. Marcellinia, G. Masettia, A. Montanaria, F.L. Navarriaa,b,A. Perrottaa, A.M. Rossia,b,T. Rovellia,b, G.P. Sirolia,b,N. Tosia,b, R. Travaglinia,b
aINFNSezionediBologna,Bologna,Italy bUniversitàdiBologna,Bologna,Italy
S. Albergoa,b,G. Cappelloa, M. Chiorbolia,b, S. Costaa,b, F. Giordanoa,2,R. Potenzaa,b, A. Tricomia,b, C. Tuvea,b
aINFNSezionediCatania,Catania,Italy bUniversitàdiCatania,Catania,Italy cCSFNSM,Catania,Italy
G. Barbaglia, V. Ciullia,b,C. Civininia, R. D’Alessandroa,b,E. Focardia,b,E. Galloa,S. Gonzia,b,V. Goria,b, P. Lenzia,b,M. Meschinia,S. Paolettia, G. Sguazzonia,A. Tropianoa,b
aINFNSezionediFirenze,Firenze,Italy bUniversitàdiFirenze,Firenze,Italy
L. Benussi, S. Bianco, F. Fabbri,D. Piccolo
R. Ferrettia,b,F. Ferroa,M. Lo Veterea,b,E. Robuttia, S. Tosia,b
aINFNSezionediGenova,Genova,Italy bUniversitàdiGenova,Genova,Italy
M.E. Dinardoa,b, S. Fiorendia,b, S. Gennaia,2, R. Gerosaa,b,2,A. Ghezzia,b, P. Govonia,b,M.T. Lucchinia,b,2, S. Malvezzia, R.A. Manzonia,b, A. Martellia,b, B. Marzocchia,b,2, D. Menascea,L. Moronia,
M. Paganonia,b,D. Pedrinia, S. Ragazzia,b, N. Redaellia,T. Tabarelli de Fatisa,b
aINFNSezionediMilano-Bicocca,Milano,Italy bUniversitàdiMilano-Bicocca,Milano,Italy
S. Buontempoa, N. Cavalloa,c,S. Di Guidaa,d,2, F. Fabozzia,c,A.O.M. Iorioa,b, L. Listaa,S. Meolaa,d,2, M. Merolaa, P. Paoluccia,2
aINFNSezionediNapoli,Napoli,Italy bUniversitàdiNapoli‘FedericoII’,Napoli,Italy cUniversitàdellaBasilicata,Potenza,Italy dUniversitàG.Marconi,Roma,Italy
P. Azzia, N. Bacchettaa, D. Biselloa,b, A. Brancaa,b,R. Carlina,b,P. Checchiaa, M. Dall’Ossoa,b, T. Dorigoa, U. Gasparinia,b,A. Gozzelinoa,K. Kanishcheva,c, S. Lacapraraa,M. Margonia,b,A.T. Meneguzzoa,b, J. Pazzinia,b, N. Pozzobona,b, P. Ronchesea,b,F. Simonettoa,b, E. Torassaa,M. Tosia,b, S. Vaninia,b, S. Venturaa,P. Zottoa,b,A. Zucchettaa,b,G. Zumerlea,b
aINFNSezionediPadova,Padova,Italy bUniversitàdiPadova,Padova,Italy cUniversitàdiTrento,Trento,Italy
M. Gabusia,b,S.P. Rattia,b, V. Rea,C. Riccardia,b,P. Salvinia,P. Vituloa,b aINFNSezionediPavia,Pavia,Italy
bUniversitàdiPavia,Pavia,Italy
M. Biasinia,b,G.M. Bileia,D. Ciangottinia,b,2,L. Fanòa,b, P. Laricciaa,b, G. Mantovania,b, M. Menichellia, A. Sahaa, A. Santocchiaa,b,A. Spieziaa,b,2
aINFNSezionediPerugia,Perugia,Italy bUniversitàdiPerugia,Perugia,Italy
K. Androsova,25,P. Azzurria,G. Bagliesia,J. Bernardinia,T. Boccalia,G. Broccoloa,c,R. Castaldia,
M.A. Cioccia,25,R. Dell’Orsoa, S. Donatoa,c,2,G. Fedi, F. Fioria,c,L. Foàa,c,A. Giassia, M.T. Grippoa,25, F. Ligabuea,c,T. Lomtadzea,L. Martinia,b, A. Messineoa,b, C.S. Moona,26, F. Pallaa,2, A. Rizzia,b, A. Savoy-Navarroa,27,A.T. Serbana, P. Spagnoloa, P. Squillaciotia,25,R. Tenchinia,G. Tonellia,b, A. Venturia,P.G. Verdinia,C. Vernieria,c
aINFNSezionediPisa,Pisa,Italy bUniversitàdiPisa,Pisa,Italy
cScuolaNormaleSuperiorediPisa,Pisa,Italy
L. Baronea,b, F. Cavallaria,G. D’imperioa,b,D. Del Rea,b, M. Diemoza,C. Jordaa, E. Longoa,b,
F. Margarolia,b, P. Meridiania,F. Michelia,b,2,G. Organtinia,b, R. Paramattia,S. Rahatloua,b, C. Rovellia, F. Santanastasioa,b, L. Soffia,b,P. Traczyka,b,2
aINFNSezionediRoma,Roma,Italy bUniversitàdiRoma,Roma,Italy
N. Amapanea,b,R. Arcidiaconoa,c, S. Argiroa,b, M. Arneodoa,c,R. Bellana,b,C. Biinoa,N. Cartigliaa, S. Casassoa,b,2, M. Costaa,b,R. Covarelli,A. Deganoa,b,N. Demariaa, L. Fincoa,b,2,C. Mariottia, S. Masellia,G. Mazzaa,E. Migliorea,b, V. Monacoa,b, M. Musicha, M.M. Obertinoa,c, L. Pachera,b, N. Pastronea,M. Pelliccionia,G.L. Pinna Angionia,b, A. Romeroa,b, M. Ruspaa,c,R. Sacchia,b, A. Solanoa,b,A. Staianoa, U. Tamponia
aINFNSezionediTorino,Torino,Italy bUniversitàdiTorino,Torino,Italy
S. Belfortea,V. Candelisea,b,2, M. Casarsaa,F. Cossuttia, G. Della Riccaa,b,B. Gobboa,C. La Licataa,b, M. Maronea,b,A. Schizzia,b, T. Umera,b,A. Zanettia
aINFNSezionediTrieste,Trieste,Italy bUniversitàdiTrieste,Trieste,Italy
S. Chang, A. Kropivnitskaya,S.K. Nam
KangwonNationalUniversity,Chunchon,RepublicofKorea
D.H. Kim,G.N. Kim, M.S. Kim,D.J. Kong, S. Lee, Y.D. Oh,H. Park, A. Sakharov, D.C. Son
KyungpookNationalUniversity,Daegu,RepublicofKorea
T.J. Kim, M.S. Ryu
ChonbukNationalUniversity,Jeonju,RepublicofKorea
J.Y. Kim, D.H. Moon,S. Song
ChonnamNationalUniversity,InstituteforUniverseandElementaryParticles,Kwangju,RepublicofKorea
S. Choi, D. Gyun,B. Hong, M. Jo,H. Kim, Y. Kim,B. Lee, K.S. Lee, S.K. Park,Y. Roh
KoreaUniversity,Seoul,RepublicofKorea
H.D. Yoo
SeoulNationalUniversity,Seoul,RepublicofKorea
M. Choi,J.H. Kim, I.C. Park, G. Ryu
UniversityofSeoul,Seoul,RepublicofKorea
Y. Choi,Y.K. Choi, J. Goh,D. Kim, E. Kwon, J. Lee, I. Yu
SungkyunkwanUniversity,Suwon,RepublicofKorea
A. Juodagalvis
VilniusUniversity,Vilnius,Lithuania
J.R. Komaragiri, M.A.B. Md Ali
NationalCentreforParticlePhysics,UniversitiMalaya,KualaLumpur,Malaysia
E. Casimiro Linares, H. Castilla-Valdez, E. De La Cruz-Burelo,I. Heredia-de La Cruz, A. Hernandez-Almada,R. Lopez-Fernandez, A. Sanchez-Hernandez
CentrodeInvestigacionydeEstudiosAvanzadosdelIPN,MexicoCity,Mexico
S. Carrillo Moreno, F. Vazquez Valencia
UniversidadIberoamericana,MexicoCity,Mexico
I. Pedraza, H.A. Salazar Ibarguen
BenemeritaUniversidadAutonomadePuebla,Puebla,Mexico
A. Morelos Pineda
UniversidadAutónomadeSanLuisPotosí,SanLuisPotosí,Mexico
D. Krofcheck
P.H. Butler,S. Reucroft
UniversityofCanterbury,Christchurch,NewZealand
A. Ahmad, M. Ahmad, Q. Hassan,H.R. Hoorani, W.A. Khan,T. Khurshid, M. Shoaib
NationalCentreforPhysics,Quaid-I-AzamUniversity,Islamabad,Pakistan
H. Bialkowska,M. Bluj, B. Boimska,T. Frueboes, M. Górski, M. Kazana, K. Nawrocki, K. Romanowska-Rybinska,M. Szleper, P. Zalewski
NationalCentreforNuclearResearch,Swierk,Poland
G. Brona,K. Bunkowski, M. Cwiok,W. Dominik,K. Doroba, A. Kalinowski,M. Konecki, J. Krolikowski, M. Misiura, M. Olszewski
InstituteofExperimentalPhysics,FacultyofPhysics,UniversityofWarsaw,Warsaw,Poland
P. Bargassa,C. Beirão Da Cruz E Silva, P. Faccioli, P.G. Ferreira Parracho,M. Gallinaro, L. Lloret Iglesias, F. Nguyen, J. Rodrigues Antunes,J. Seixas, J. Varela, P. Vischia
LaboratóriodeInstrumentaçãoeFísicaExperimentaldePartículas,Lisboa,Portugal
S. Afanasiev,P. Bunin,M. Gavrilenko,I. Golutvin, I. Gorbunov, A. Kamenev,V. Karjavin, V. Konoplyanikov, A. Lanev,A. Malakhov,V. Matveev28, P. Moisenz, V. Palichik,V. Perelygin, S. Shmatov, N. Skatchkov, V. Smirnov,A. Zarubin
JointInstituteforNuclearResearch,Dubna,Russia
V. Golovtsov,Y. Ivanov, V. Kim29,E. Kuznetsova, P. Levchenko, V. Murzin, V. Oreshkin, I. Smirnov, V. Sulimov,L. Uvarov, S. Vavilov, A. Vorobyev,An. Vorobyev
PetersburgNuclearPhysicsInstitute,Gatchina(St.Petersburg),Russia
Yu. Andreev,A. Dermenev,S. Gninenko, N. Golubev, M. Kirsanov, N. Krasnikov, A. Pashenkov, D. Tlisov, A. Toropin
InstituteforNuclearResearch,Moscow,Russia
V. Epshteyn,V. Gavrilov, N. Lychkovskaya,V. Popov, I. Pozdnyakov,G. Safronov, S. Semenov, A. Spiridonov,V. Stolin, E. Vlasov,A. Zhokin
InstituteforTheoreticalandExperimentalPhysics,Moscow,Russia
V. Andreev,M. Azarkin30,I. Dremin30, M. Kirakosyan, A. Leonidov30,G. Mesyats, S.V. Rusakov, A. Vinogradov
P.N.LebedevPhysicalInstitute,Moscow,Russia
A. Belyaev,E. Boos,A. Demiyanov, A. Ershov, A. Gribushin, O. Kodolova,V. Korotkikh, I. Lokhtin, S. Obraztsov,S. Petrushanko,V. Savrin, A. Snigirev, I. Vardanyan
SkobeltsynInstituteofNuclearPhysics,LomonosovMoscowStateUniversity,Moscow,Russia
I. Azhgirey,I. Bayshev,S. Bitioukov, V. Kachanov, A. Kalinin, D. Konstantinov,V. Krychkine, V. Petrov, R. Ryutin, A. Sobol,L. Tourtchanovitch, S. Troshin, N. Tyurin, A. Uzunian,A. Volkov
StateResearchCenterofRussianFederation,InstituteforHighEnergyPhysics,Protvino,Russia
P. Adzic31,M. Ekmedzic, J. Milosevic,V. Rekovic
J. Alcaraz Maestre, C. Battilana,E. Calvo, M. Cerrada,M. Chamizo Llatas, N. Colino, B. De La Cruz, A. Delgado Peris,D. Domínguez Vázquez, A. Escalante Del Valle, C. Fernandez Bedoya,
J.P. Fernández Ramos,J. Flix, M.C. Fouz,P. Garcia-Abia,O. Gonzalez Lopez, S. Goy Lopez, J.M. Hernandez, M.I. Josa,E. Navarro De Martino, A. Pérez-Calero Yzquierdo, J. Puerta Pelayo, A. Quintario Olmeda, I. Redondo,L. Romero, M.S. Soares
CentrodeInvestigacionesEnergéticasMedioambientalesyTecnológicas(CIEMAT),Madrid,Spain
C. Albajar, J.F. de Trocóniz, M. Missiroli, D. Moran
UniversidadAutónomadeMadrid,Madrid,Spain
H. Brun, J. Cuevas,J. Fernandez Menendez, S. Folgueras, I. Gonzalez Caballero
UniversidaddeOviedo,Oviedo,Spain
J.A. Brochero Cifuentes, I.J. Cabrillo, A. Calderon, J. Duarte Campderros,M. Fernandez, G. Gomez, A. Graziano, A. Lopez Virto,J. Marco, R. Marco,C. Martinez Rivero, F. Matorras, F.J. Munoz Sanchez, J. Piedra Gomez, T. Rodrigo,A.Y. Rodríguez-Marrero,A. Ruiz-Jimeno, L. Scodellaro,I. Vila,
R. Vilar Cortabitarte
InstitutodeFísicadeCantabria(IFCA),CSIC-UniversidaddeCantabria,Santander,Spain
D. Abbaneo, E. Auffray, G. Auzinger, M. Bachtis,P. Baillon, A.H. Ball, D. Barney, A. Benaglia, J. Bendavid, L. Benhabib,J.F. Benitez, P. Bloch, A. Bocci, A. Bonato, O. Bondu,C. Botta, H. Breuker, T. Camporesi, G. Cerminara, S. Colafranceschi32,M. D’Alfonso, D. d’Enterria, A. Dabrowski, A. David,F. De Guio, A. De Roeck, S. De Visscher, E. Di Marco,M. Dobson, M. Dordevic, B. Dorney, N. Dupont-Sagorin, A. Elliott-Peisert, G. Franzoni, W. Funk, D. Gigi,K. Gill, D. Giordano, M. Girone,F. Glege, R. Guida, S. Gundacker, M. Guthoff,J. Hammer, M. Hansen,P. Harris,J. Hegeman, V. Innocente, P. Janot, K. Kousouris,K. Krajczar, P. Lecoq,C. Lourenço, N. Magini, L. Malgeri,M. Mannelli, J. Marrouche,
L. Masetti, F. Meijers, S. Mersi,E. Meschi, F. Moortgat, S. Morovic, M. Mulders, L. Orsini, L. Pape,E. Perez, A. Petrilli, G. Petrucciani,A. Pfeiffer, M. Pimiä, D. Piparo, M. Plagge, A. Racz,G. Rolandi33, M. Rovere, H. Sakulin, C. Schäfer, C. Schwick,A. Sharma,P. Siegrist, P. Silva,M. Simon, P. Sphicas34,D. Spiga,
J. Steggemann,B. Stieger, M. Stoye,Y. Takahashi, D. Treille, A. Tsirou, G.I. Veres17,N. Wardle, H.K. Wöhri, H. Wollny, W.D. Zeuner
CERN,EuropeanOrganizationforNuclearResearch,Geneva,Switzerland
W. Bertl,K. Deiters, W. Erdmann, R. Horisberger, Q. Ingram, H.C. Kaestli, D. Kotlinski,U. Langenegger, D. Renker, T. Rohe
PaulScherrerInstitut,Villigen,Switzerland
F. Bachmair, L. Bäni, L. Bianchini, M.A. Buchmann,B. Casal, N. Chanon, G. Dissertori, M. Dittmar, M. Donegà, M. Dünser,P. Eller, C. Grab,D. Hits, J. Hoss,W. Lustermann, B. Mangano,A.C. Marini, M. Marionneau, P. Martinez Ruiz del Arbol, M. Masciovecchio, D. Meister,N. Mohr, P. Musella, C. Nägeli35,F. Nessi-Tedaldi, F. Pandolfi, F. Pauss,L. Perrozzi, M. Peruzzi,M. Quittnat, L. Rebane, M. Rossini,A. Starodumov36, M. Takahashi, K. Theofilatos,R. Wallny, H.A. Weber
InstituteforParticlePhysics,ETHZurich,Zurich,Switzerland
C. Amsler37, M.F. Canelli,V. Chiochia,A. De Cosa, A. Hinzmann, T. Hreus, B. Kilminster, C. Lange, J. Ngadiuba,D. Pinna, P. Robmann, F.J. Ronga,S. Taroni, M. Verzetti, Y. Yang
UniversitätZürich,Zurich,Switzerland
M. Cardaci, K.H. Chen,T.H. Doan, C. Ferro,C.M. Kuo, W. Lin,Y.J. Lu, S.Y. Tseng,R. Volpe, S.S. Yu
P. Chang, Y.H. Chang,Y. Chao, K.F. Chen, P.H. Chen, C. Dietz, U. Grundler,W.-S. Hou,Y.F. Liu, R.-S. Lu, E. Petrakou,Y.M. Tzeng,R. Wilken
NationalTaiwanUniversity(NTU),Taipei,Taiwan
B. Asavapibhop,G. Singh, N. Srimanobhas, N. Suwonjandee
ChulalongkornUniversity,FacultyofScience,DepartmentofPhysics,Bangkok,Thailand
A. Adiguzel, M.N. Bakirci38,S. Cerci39, C. Dozen,I. Dumanoglu, E. Eskut, S. Girgis, G. Gokbulut, Y. Guler, E. Gurpinar,I. Hos, E.E. Kangal, A. Kayis Topaksu,G. Onengut40, K. Ozdemir, S. Ozturk38, A. Polatoz, D. Sunar Cerci39, B. Tali39, H. Topakli38, M. Vergili, C. Zorbilmez
CukurovaUniversity,Adana,Turkey
I.V. Akin,B. Bilin, S. Bilmis, H. Gamsizkan41, B. Isildak42, G. Karapinar43,K. Ocalan44,S. Sekmen, U.E. Surat,M. Yalvac, M. Zeyrek
MiddleEastTechnicalUniversity,PhysicsDepartment,Ankara,Turkey
E.A. Albayrak45, E. Gülmez,M. Kaya46,O. Kaya47, T. Yetkin48
BogaziciUniversity,Istanbul,Turkey
K. Cankocak,F.I. Vardarlı
IstanbulTechnicalUniversity,Istanbul,Turkey
L. Levchuk,P. Sorokin
NationalScientificCenter,KharkovInstituteofPhysicsandTechnology,Kharkov,Ukraine
J.J. Brooke,E. Clement, D. Cussans,H. Flacher, J. Goldstein,M. Grimes, G.P. Heath, H.F. Heath,J. Jacob, L. Kreczko,C. Lucas, Z. Meng, D.M. Newbold49,S. Paramesvaran, A. Poll, T. Sakuma,S. Seif El Nasrstorey, S. Senkin,V.J. Smith
UniversityofBristol,Bristol,UnitedKingdom
A. Belyaev50,C. Brew, R.M. Brown, D.J.A. Cockerill, J.A. Coughlan, K. Harder, S. Harper, E. Olaiya,D. Petyt, C.H. Shepherd-Themistocleous, A. Thea,I.R. Tomalin, T. Williams, W.J. Womersley, S.D. Worm
RutherfordAppletonLaboratory,Didcot,UnitedKingdom
M. Baber,R. Bainbridge, O. Buchmuller, D. Burton,D. Colling, N. Cripps,P. Dauncey, G. Davies, M. Della Negra,P. Dunne, A. Elwood, W. Ferguson, J. Fulcher, D. Futyan,G. Hall, G. Iles, M. Jarvis, G. Karapostoli,M. Kenzie, R. Lane,R. Lucas49,L. Lyons, A.-M. Magnan, S. Malik,B. Mathias, J. Nash, A. Nikitenko36,J. Pela, M. Pesaresi, K. Petridis,D.M. Raymond, S. Rogerson, A. Rose,C. Seez, P. Sharp†, A. Tapper,M. Vazquez Acosta, T. Virdee,S.C. Zenz
ImperialCollege,London,UnitedKingdom
J.E. Cole, P.R. Hobson,A. Khan, P. Kyberd,D. Leggat, D. Leslie,I.D. Reid, P. Symonds, L. Teodorescu, M. Turner
BrunelUniversity,Uxbridge,UnitedKingdom
J. Dittmann, K. Hatakeyama,A. Kasmi, H. Liu, T. Scarborough,Z. Wu
BaylorUniversity,Waco,USA
O. Charaf,S.I. Cooper, C. Henderson, P. Rumerio