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Khachatryan, V. et al. “Angular analysis of the decay B⁰ → K*⁰
μ# μ# from pp collisions at √s = 8 TeV.” Physics Letters B 753
(February 2016): 424–448 © 2015 CERN for the benefit of the CMS
Collaboration
As Published
http://dx.doi.org/10.1016/J.PHYSLETB.2015.12.020
Publisher
Elsevier
Version
Final published version
Citable link
http://hdl.handle.net/1721.1/117183
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Creative Commons Attribution 4.0 International License
Contents lists available atScienceDirect
Physics
Letters
B
www.elsevier.com/locate/physletb
Angular
analysis
of
the
decay
B
0→
K
∗
0μ
+
μ
−
from
pp
collisions
at
√
s
=
8 TeV
.CMSCollaboration CERN,Switzerland a r t i c l e i n f o a b s t ra c t Articlehistory: Received29July2015Receivedinrevisedform30November2015 Accepted7December2015
Availableonline11December2015 Editor:M.Doser
Keywords:
CMS Physics B0decays
The angular distributions and the differential branching fraction of the decay B0→K∗(892)0μ+μ−
are studiedusingdatacorresponding toanintegratedluminosity of20.5 fb−1 collectedwiththeCMS detector at the LHCin pp collisions at√s=8 TeV. From1430 signal decays,the forward–backward asymmetryofthemuons,theK∗(892)0longitudinalpolarizationfraction,andthedifferentialbranching fraction are determined as afunction ofthe dimuoninvariant mass squared.The measurements are amongthemostprecisetodateandareingoodagreementwithstandardmodelpredictions.
©2015CERNforthebenefitoftheCMSCollaboration.PublishedbyElsevierB.V.Thisisanopenaccess articleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3.
1. Introduction
Phenomenabeyondthestandardmodel(SM)ofparticlephysics can manifestthemselves directly, via the productionof new par-ticles,or indirectly, by affectingthe production anddecayof SM particles. Analyses of flavor-changing neutral current (FCNC) de-cays are particularly sensitive to the effectof newphysics, since such decays are highly suppressed in the SM. The FCNC decay, B0→K∗0μ+μ−(K∗0indicatestheK∗(892)0,andcharge-conjugate
states are implied for all particles unless statedotherwise), pro-videsmanyopportunitiesto search fornewphenomena. In addi-tion to the branching fraction, other properties of the decaycan be measured, including theforward–backward asymmetry ofthe muons, AFB,andthelongitudinalpolarization fractionoftheK∗0,
FL.Tobetterunderstandthisdecay,thesequantitiescanbe
mea-sured as a function of the dimuon invariant mass squared (q2).
Newphysicsmaymodifyanyofthesequantities[1–17]relativeto theirSMvalues[1,18–24].WhilepreviousmeasurementsbyBaBar, Belle, CDF, LHCb, and CMS are consistent with the SM [25–29], theyarestill statisticallylimited, andmoreprecisemeasurements offerthepossibilitytouncoverphysicsbeyondthe SM.
InthisLetter,wepresentmeasurementsofAFB,FL,andthe
dif-ferential branchingfractiondB/dq2 fromB0→K∗0μ+μ− decays,
using data collected from pp collisions at the CERN LHC by the CMSexperimentatacenter-of-massenergyof8 TeV.Thedata cor-respondto an integratedluminosity of 20.5 ±0.5 fb−1 [30].The
E-mailaddress:cms-publication-committee-chair@cern.ch.
K∗0 is reconstructed through its decay to K+π−, and the B0 is reconstructed by fitting the two identified muon tracks and the two hadron tracks to a common vertex. The values of AFB and
FL are measured by fitting the distribution of events asa
func-tion of two angular variables: the angle between the positively chargedmuonandtheB0inthedimuonrestframe,andtheangle between the K+ and the B0 in the K∗0 rest frame. All measure-ments are performed inq2 bins from1 to 19 GeV2.The q2 bins
8.68<q2<10.09 GeV2 and12
.90<q2<14.18 GeV2,
correspond-ing tothe B0→J/ψK∗0 andB0→ ψK∗0 decays(ψ refers tothe ψ(2S)), respectively,areused tovalidate theanalysis.The former isalsousedtonormalizethedifferentialbranchingfraction.
2. CMSdetector
AdetaileddescriptionoftheCMSdetector,togetherwitha def-inition ofthecoordinatesystemusedandthestandardkinematic variables,canbefoundinRef.[31].Themaindetectorcomponents used inthisanalysisare thesilicon trackerandthemuon detec-tion systems. The silicon tracker, located in the 3.8 T field of a superconducting solenoid, consists of three pixel layers and ten strip layers (four ofwhich have a stereoview) in the barrel re-gion accompanied by similarendcap pixelandstrip detectors on each side that extendcoverage out to |η| <2.5. For tracks with transverse momenta 1<pT<10 GeV and |η|<1.4, the
resolu-tionsaretypically1.5%inpTand25–90(45–150) μminthe
trans-verse(longitudinal)impactparameter[32].Muonsaremeasuredin therange |η| <2.4,withdetectionplanesmadeusingthree tech-nologies: drift tubes, cathode strip chambers, and resistiveplate
http://dx.doi.org/10.1016/j.physletb.2015.12.020
0370-2693/©2015CERNforthebenefitoftheCMSCollaboration.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3.
estingevents.Ahigh-leveltriggerprocessorfarmfurtherdecreases theeventratefromaround90 kHztoaround400 Hz,beforedata storage.
3. Reconstruction,eventselection,andefficiency
Thecriteriausedtoselectthecandidateeventsduringdata tak-ing(trigger)andafterfull eventreconstructiontake advantageof thefact that B0 mesons have relativelylong lifetimes and there-foredecay on average about 1 mm from their production point. Thetriggeronlyusesmuonstoselectevents,whiletheoffline se-lectionincludesthefullreconstructionofalldecayproducts.
Allevents used inthis analysiswere recorded withthe same trigger,requiringtwoidentifiedmuonsofopposite chargetoform avertexthatisdisplacedfromtheppcollisionregion(beamspot). The beamspot position (most probable collision point) and size (theextent ofthe luminousregion covering68% ofthe collisions in each dimension) were continuously measured through Gaus-sianfitstoreconstructedverticesaspartoftheonlinedataquality monitoring.ThetriggerrequiredeachmuontohavepT>3.5 GeV,
|η| <2.2,andtopasswithin2 cm ofthebeamaxis.Thedimuon systemwas requiredtohave pT>6.9 GeV,avertexfit χ2
proba-bilitylargerthan10%,andaseparationofthevertexrelativetothe beamspotinthetransverseplaneofatleast3σ,where σ includes thecalculateduncertaintyinthevertexpositionandthemeasured sizeof thebeamspot. Inaddition, thecosine oftheangle, inthe transverseplane,betweenthedimuonmomentumvector andthe vector fromthe beamspot tothe dimuon vertexwas requiredto begreaterthan0.9.
The offline reconstruction requires two muons of opposite charge and two oppositely charged hadrons. The muons are re-quiredto matchthosethat triggered the eventreadout,andalso topassgeneralmuonidentificationrequirements.Theseincludea trackmatchedtoatleastonemuonsegment(collectionofhitsin amuon chamber consistent withthepassage ofa charged parti-cle),atrackfit χ2 per degreeoffreedom lessthan1.8, hitsinat
leastsixtrackerlayers withat leasttwo fromthe pixeldetector, anda transverse(longitudinal) impactparameter withrespect to thebeamspotlessthan 3 cm(30 cm).The reconstructeddimuon systemmustalsosatisfythesamerequirementsthatwereapplied inthetrigger.
Thehadron tracks arerequired tofail the muonidentification criteria,have pT>0.8 GeV, andhavean extrapolateddistanceof
closestapproach tothe beamspot inthetransverse plane greater thantwicethesuminquadratureofthedistanceuncertaintyand thebeamspot transversesize.The two hadronsmusthavean in-variant mass within 90 MeV of the accepted K∗0 mass [34] for
eitherthe K+π− or K−π+ hypothesis. To remove contamination fromφ (1020) →K+K− decays,the invariant mass ofthe hadron pairmustbegreaterthan1.035 GeV whenthechargedkaonmass isassignedtobothhadrons.TheB0 candidatesareobtainedby fit-tingthefourchargedtracks toa commonvertex, andapplyinga vertexconstraint toimprove the resolution ofthe track parame-ters.The B0 candidates must have pT>8 GeV, |η| <2.2, vertex
fit χ2 probability larger than 10%, vertex transverse separation
fromthebeamspotgreaterthan12timesthesuminquadratureof theseparationuncertaintyandthebeamspot transversesize,and cosαxy>0.9994,where αxy is theangle,inthe transverseplane,
betweenthe B0 momentum vectorandtheline-of-flightbetween
atleastonecandidateisfoundcontainonaverage1.05candidates. AsinglecandidateischosenfromeacheventbasedonthebestB0 vertexfit χ2.
From the selected events, the dimuon invariant mass q and its calculated uncertainty σq are used to distinguish the signal
fromthe control samples.The control samples B0→J/ψK∗0 and
B0→ ψK∗0 are definedby |q −m
J/ψ| <3σq and|q −mψ| <3σq,
respectively, where mJ/ψ and mψ are the accepted masses[34].
The average value for σq is about26 MeV. The signal sample is
composed oftheevents that arenot assignedto theJ/ψ and ψ samples.
The signal sample still contains contributions from the con-trol samples,mainly dueto unreconstructed soft photons inthe charmoniumdecay.Theseeventswillhavealow q valueandfall outsidetheselection describedabove.Theseeventswillalsohave
a lowm value andthereforetheycan be selectivelyremoved
us-ing a combined selection on q andm. For q<mJ/ψ (q>mJ/ψ),
werequire |(m−mB0)− (q −mJ/ψ)| >160(60)MeV. Forq<mψ
(q>mψ),werequire |(m −mB0) − (q −mψ)| >60(30)MeV.The
requirements are set such that less than 10% of the background eventsoriginatefromthecontrolchannels.
The four-trackvertexcandidateis identifiedasa B0 or B0
de-pendingonwhethertheK+π− orK−π+invariantmassisclosest to the acceptedK∗0 mass.The fraction ofcandidates assignedto
the incorrect state is estimated from simulations to be 12–14%, dependingonq2.
The global efficiency, , is the product ofthe acceptance and thecombinedtrigger,reconstruction,andselectionefficiency,both ofwhichareobtainedfromMonteCarlo(MC)simulations.Thepp collisions are simulatedusing pythia [35] version 6.424, the un-stableparticlesaredecayedby evtgen[36] version9.1(using the defaultmatrixelementforthesignal),andtheparticlesare prop-agatedthroughadetailedmodelofthedetectorwith Geant4[37]. The reconstructionandselection ofthegeneratedeventsproceed asfordata.ThreesimulatedsampleswerecreatedinwhichtheB0 wasforcedtodecaytoK∗0(K+π−)μ+μ−,J/ψ(μ+μ−)K∗0(K+π−),
orψ(μ+μ−)K∗0(K+π−).Thesampleswereconstructedtoensure
thatthenumberandspatialdistributionofppcollisionverticesin each eventmatchthedistributions foundindata.The acceptance isobtainedfromgeneratedevents,beforetheparticlepropagation with Geant4, and is calculated as the fraction ofevents passing thesingle-muonrequirementofpT(μ)>3.3 GeV and |η(μ)| <2.3
relative to all events with pT(B0)>8 GeV and |η(B0)| <2.2. As
theacceptance requirementsare placedon thegenerated quanti-ties,they arelessrestrictivethanthefinalselectionrequirements, whichare basedonthereconstructed quantities,toallow forthe effectoffiniteresolution.Onlyeventspassingtheacceptance cri-teriaareprocessedthroughthe geant simulation,thetrigger sim-ulation,andthereconstructionsoftware.Thecombinedtrigger, re-construction,andselectionefficiencyistheratioofthenumberof eventsthat pass thetrigger andselectionrequirements andhave areconstructedB0compatiblewiththegeneratedB0 intheevent,
relative to the number ofevents that pass the acceptance crite-ria. The compatibility ofgenerated and reconstructed particles is enforced by requiringthe reconstructed K+, π−, μ+, and μ− to have(η)2+ (ϕ)2 lessthan 0.3(0.004)forhadrons(muons),
where η andϕ are the differencesin η and ϕ between the reconstructed andgeneratedparticles. Requiringall fourparticles in the B0 decay to be matched results in an efficiency of99.6%
Fig. 1. Sketch showing the definition of the angular observablesθl(left),θK(middle), andφ(right) for the decay B0→K∗0(K+π−)μ+μ−.
(0.4% of theevents have a correctlyreconstructed B0 that is not
matched to a generated B0) and a purity of 99.5% (0.5% of the matchedcandidatesarenotacorrectlyreconstructedB0). Efficien-ciesare determined forboth correctlytagged(the K and π have the correctcharge) and mistagged(the K and π chargesare re-versed)candidates.
4. Analysismethod
Thisanalysismeasures AFB,FL,anddB/dq2ofthedecayB0→
K∗0μ+μ− as a function of q2. Fig. 1 shows the angular observ-ablesneededtodefinethedecay:θKistheanglebetweenthekaon
momentum andthedirectionopposite to the B0 B0 in theK∗0
K∗0 rest frame, θ
l is the angle between the positive (negative)
muonmomentumandthedirectionoppositetotheB0 B0inthe dimuonrestframe,andφistheanglebetweentheplane contain-ing thetwo muons andtheplane containing thekaon andpion. Astheextractedangularparameters AFBandFLdonotdependon
φandtheproductoftheacceptanceandefficiencyisnearly con-stant asa function of φ, the angleφ isintegrated out. Although the K+π− invariant mass mustbe consistent withthat ofa K∗0,
therecanbe acontributionfromspinless(S-wave)K+π− combi-nations[24,38–40].Thisisparametrizedwithtwoterms:FS,which
is related to the S-wave fraction, and AS, which is the
interfer-enceamplitudebetweentheS-waveandP-wavedecays.Including thiscomponent,theangulardistributionofB0→K∗0μ+μ−canbe writtenas[24]: 1 d3 d cosθKd cosθldq2 = 9 16 2 3 FS+AScosθK 1−cos2θl + (1−FS) 2FLcos2θK 1−cos2θl +1 2(1−FL) 1−cos2θK 1+cos2θl +4 3AFB 1−cos2θK cosθl . (1)
Foreachq2 bin,theobservablesofinterest areextractedfrom an unbinnedextendedmaximum-likelihoodfitto threevariables: theK+π−μ+μ− invariant massm andthe twoangularvariables θK and θl. Foreach q2 bin, theunnormalized probability density
function(PDF)hasthefollowingexpression:
PDF(m, θK, θl)=YCS SC(m)Sa(θK, θl)C(θK, θl) + fM 1−fM S M(m)Sa(−θ K,−θl)M(θK, θl) +YBBm(m)BθK(θK)Bθl(θl), (2)
where the contributions correspond to correctly tagged signal events, mistagged signal events,and background events.The pa-rametersYSC andYB aretheyieldsofcorrectlytaggedsignalevents
and background events, respectively, and are free parameters in thefit.Theparameter fM isthefractionofsignaleventsthat are mistaggedandisdeterminedfromMCsimulation.Thesignalmass probability functions SC(m) and SM(m)are each thesumof two
Gaussianfunctionsanddescribethemassdistributionforcorrectly tagged andmistaggedsignal events, respectively.In thefit, there isone freeparameterforthemassvalueinbothsignalfunctions, whiletheother parameters(fourGaussian σ parametersandtwo fractions relatingthecontributionof eachGaussian)are obtained from MC simulation, which has been found to accurately repro-duce the data.The function Sa(θK,θl) describes thesignal in the
two-dimensional (2D) space of the angular observables and cor-responds to Eq.(1).The combination Bm(m)BθK(θK)Bθl(θ
l) is
ob-tainedfromB0 sidebanddataanddescribesthebackgroundinthe space of (m,θK,θl), where the mass distribution is an
exponen-tialfunctionandtheangulardistributionsarepolynomialsranging from second to fourthdegree, depending on the q2 binand the angularvariable.Thefunctions C(θ
K,θl)and M(θK,θl)arethe
ef-ficiencies in the 2D space of−1 ≤cosθK≤1,−1 ≤cosθl≤1 for
correctlytaggedandmistaggedsignalevents,respectively.The ef-ficiencyfunctionforcorrectlytaggedeventsisobtainedfromafit tothe2D-binnedefficiencyfromsimulationandisconstrainedto bepositive.Thereare30bins(5incosθKand6incosθl),andthe
efficiencyfitfunctionisapolynomialofthirddegreeincosθKand
fifthdegreeincosθl (andallcrossterms),foratotalof24free
pa-rameters.This proceduredoesnotwork forthemistaggedevents becauseofthemuchsmallernumberofevents(resultinginempty bins)andamorecomplicatedefficiency.Formistaggedevents,the 2D efficiency is calculated in 5×5 bins of cosθK andcosθl, and
an interpolation is performed.This interpolation functionis used to generatea newbinned efficiency(in 120 ×120 bins), withall bincontentsconstrainedtobenonnegative.Theefficiencyfunction usesthisfinelybinnedefficiency,withlinearinterpolationbetween bins. The efficiencies for both correctly tagged and mistagged events peak at cosθl near 0for q2<10 GeV2, becoming flat for
largervaluesofq2.Theefficiencyforcorrectlytaggedeventstends to decreasewith increasing cosθK,andforq2>14 GeV2 a small
decrease isseen forcosθK near −1.The efficiencyformistagged
eventsismaximalnearcosθK=0,withan increaseascosθK
ap-proaches+1 thatbecomesmorepronouncedasq2 increases. The fitis performedintwo steps.The initial fitusesthe data from the sidebands of the B0 mass to obtain the BθK(θK) and
Bθl(θ
l)distributions(thesignalcomponentisabsentfromthisfit).
The sidebandregions are 3σm<|m −mB0| <5.5σm, where σm is
theaveragemassresolution(≈45 MeV),obtainedfromfittingthe MC simulationsignal to asumoftwo Gaussianswithacommon mean.Thedistributionsobtainedinthissteparethenfixedforthe secondstep,whichisafittothedataoverthefullmassrange.The free parameters in thisfit are AFB, FL, FS, AS,the parameters in
theprecisephysicalregion isa morecomplicatedexpression,the approximateranges ofvalidityare: 0<FL<1, |AFB| <34(1−FL),
0<FS<min 3(1−FL) 1+3FL ,1 , and |AS| <FS+3FL(1−FS). In
addi-tion, the interference term AS must vanish if either of the two
interfering components vanish. From Ref. [24], this constraint is implementedas|AS| <
√
12FS(1−FS)FLR,where R is aratio
re-latedtothe S-waveandP-wavelineshapes,estimatedtobe0.89 neartheK∗0 mass.Duringthe minuit[41] minimization, penalty terms are introduced to ensure that parameters remain in the physicalregion. When assessing the statisticaluncertainties with Minos[41], the penalty terms are removed. However, a negative valueforEq.(2)resultsintheminimizing algorithmgeneratinga large positive jump inthe negative log-likelihood,tending to re-movetheunphysicalregion.Theresultsofthefitineachsignalq2
binare AFB,FL, AS,FS,andthecorrectlytaggedsignalyieldYSC.
Thedifferentialbranchingfraction,dB/dq2,ismeasuredrelative
tothenormalizationchannelB0→J/ψK∗0using:
dBB0→K∗0μ+μ− dq2 = YCS C + YCSfM (1−fM)M YNC C N + YCNfNM (1−fNM)M N −1 ×B B0→J/ψK∗0 q2 , (3)
whereYCS andYNC aretheyieldsofthecorrectlytaggedsignaland normalizationchannels,respectively; C
S and NC aretheefficiencies
forthecorrectlytaggedsignalandnormalizationchannels, respec-tively; fM and fNM arethemistagratesforthesignaland normal-izationchannels, respectively; M
S and NM are the efficiencies for
themistaggedsignalandnormalizationchannels,respectively;and BB0→J/ψ(μ+μ−)K∗0=0.132%×5.96% istheaccepted branch-ing fractionforthe normalization channel [34], corresponding to theq2 bin q2=8.68–10.09 GeV2. The efficiencies are obtained byintegrating theefficiencyfunctions overthe angularvariables, weighted by the decayratein Eq.(1), usingthe values obtained fromthefitofEq.(2)tothedata.
The fit formalism and results are validated through fits to pseudo-experimentalsamples,MCsimulationsamples,andcontrol channels. Additional details,including thesizes of thesystematic uncertaintiesassignedfromthesefits,aredescribedinSection5.
5. Systematicuncertainties
Sincetheefficiencyiscomputedwithsimulatedevents,itis es-sentialthat the MC simulation program correctly reproduces the data,andextensivecheckshavebeenperformedtoverifythe ac-curacy ofthe simulation. The systematic uncertainties associated withtheefficiencies, andother sources ofsystematicuncertainty aredescribedbelowandsummarizedinTable 1.
Thecorrectnessofthefitfunctionandtheprocedurefor mea-suring the variables of interest are verified in three ways. First, ahigh-statisticsMC sample (approximately400timesthat ofthe data)isused toverifythat thefittingprocedure producesresults consistentwiththeinputvaluestothesimulation.ThisMCsample includesthe full simulationof signal and control channel events
Simulation mismodeling 1–17 0–37 1.0–5.5 Fit bias 0–34 2–42 – MC statistical uncertainty 3–10 5–18 0.5–2.0 Efficiency 34 5 – Kπmistagging 1–4 0–7 0.1–4.1 Background distribution 20–36 12–31 0.0–1.2 Mass distribution 3 1 3.2 Feed-through background 0–27 0–5 0.0–4.0 Angular resolution 6–24 0–5 0.2–2.1 Normalization to B0→J/ψK∗0 – – 4.6
Total systematic uncertainty 41–65 18–74 6.4–8.6
plusbackgroundeventsobtainedfromthePDFinEq.(2).The dis-crepancy between the input and output values in this check is assigned as a simulation mismodeling systematic uncertainty. It wasalsoverifiedthatfittingasamplewithonlymistaggedevents gives thecorrect results.Second, 1000pseudo-experiments, each with the same number of events as the data sample, are gen-erated in each q2 bin using thePDF in Eq.(2), withparameters
obtainedfromthefit tothedata.Theseare usedto estimate the fitbias.Much oftheobserved biasisaconsequence ofthefitted parameterslyingclosetotheboundariesofthephysicalregion.In addition,thedistributionsofresultsareusedtocheckthereturned statistical uncertainty from the fit and are found to be consis-tent. Third, the high-statistics MC signal sample is divided into 400 subsamples andcombinedwithbackground eventstomimic 400independentdatasetsofsimilarsizetothedata.Fitstothese 400samplesdonotrevealanyadditionalsystematicuncertainty.
Because the efficiency functions are estimated from a finite number of simulated events, there is a corresponding statistical uncertaintyintheefficiency.Theefficiencyfunctionsareobtained from fits to simulated data.Alternatives to the default efficiency functionare generatedbyrandomlyvaryingthefittedparameters withintheiruncertainties(includingallcorrelations).Theeffectof these different efficiencyfunctions on the final resultis used to estimatethesystematicuncertainty.
Themaincheckofthecorrectnessoftheefficiencyisobtained bycomparingtheefficiency-correctedresultsforthecontrol chan-nels with the corresponding world-average values. The efficiency asafunctionoftheangularvariablesischeckedbycomparingthe FL and AFB measurements from the B0→J/ψK∗0 sample,
com-posed of165 000 signal events.The value of FL obtainedin this
analysisis0.537 ±0.002(stat),comparedwiththeworld-average value of 0.571 ±0.007(stat+syst) [34],indicating a discrepancy of0.034,whichistakenasthesystematicuncertaintyforthe sig-nal measurementsof FL.For AFB,the measuredvalue is 0.008 ±
0.003(stat),compared to a SM expectationof ≈0. Adding an S-wave contribution in the fit changes the measured value of AFB
bylessthan0.001.Fromthis,weconcludethattheS-waveeffects areminimal,andassignasystematicuncertaintyof0.005 for AFB.
Tovalidatethatthesimulationaccuratelyreproducestheefficiency asafunctionofq2,we measurethebranchingratiobetweentwo
differentq2 bins,namelythetwocontrolchannels.Thebranching ratioresult, BB0→ ψK∗0/BB0→J/ψK∗0=0.479 ±0.005, is in excellent agreement with themost precise reported measure-ment:0.476 ±0.014(stat)±0.010(syst)[42].
The PDF used in the analysis accommodates cases in which thekaon andpionchargesarecorrectlyandincorrectly assigned. Both ofthesecontributionsaretreatedassignal. Themistag
frac-tion is fixed to the value obtained from MC simulation. In the high-statisticscontrolchannel B0→J/ψK∗0,themistagfractionis allowed to float in the fit anda value of fM= (14.5±0.5)% is found,tobecomparedtothesimulatedvalueof(13.7±0.1)%.The effect ofthis 5.8% difference in the mistag fraction on the mea-suredvaluesistakenasasystematicuncertainty.
Thesystematicuncertainty associatedwiththefunctionsused to model the angular distribution of the background is obtained fromthesuminquadratureoftwo uncertainties.Thefirst uncer-tainty isevaluated byfittingthe backgroundwithpolynomialsof onedegreegreaterthanusedinthedefaultanalysisandtakingthe differenceintheobservablesofinterestbetweenthesetwofitsas thesystematicuncertainty.Theseconduncertaintyisowingtothe statisticaluncertaintyinthebackgroundshape,astheseshapesare fixed in the final fit. This uncertainty is obtained by taking the difference in quadrature between the returned statistical uncer-taintiesontheparametersofinterestwhenthebackgroundshapes arefixedandallowedtovary.Inq2 binswheretheunconstrained fitdoesnot converge,theassociateduncertaintyisobtainedfrom extrapolationofnearbybins.
Themass distributions forthecorrectlytagged andmistagged eventsare eachdescribed by thesumof twoGaussian functions, witha common mean forall four Gaussian functions. The mean valueisobtainedfromthefittothedata,whiletheother parame-ters(four σandtworatios)areobtainedfromfitstoMC-simulated events,withtheuncertaintyfromthosefitsusedasGaussian con-straintsinthefitstothedata.Forthehigh-statisticscontrol chan-nels, it is possible to fit the data, while allowing some of the parameters to vary. The maximumchanges in themeasured val-uesinthe two control channelq2 binswhen theparameters are
variedaretakenasthesystematicuncertaintyforallq2 bins. Theq2 binsjustbelowandabovetheJ/ψ regionmaybe con-taminated with B0→J/ψK∗0 feed-through events that are not
removed by the selection criteria. Aspecial fitin thesetwo bins ismade, inwhichanadditionalbackgroundtermisaddedtothe PDF. Thisbackgrounddistributionisobtainedfromthe MC simu-lationandthebackgroundyieldisafreeparameter.Theresulting changesinthefitparametersareusedasestimatesofthe system-aticuncertaintyassociatedwiththiscontribution.
Theeffectsfromangularresolutioninthereconstructedvalues for the angular variables θK and θl are estimated by performing
two fitson the sameMC-simulated events.One fituses thetrue valuesoftheangularvariablesandtheotherfittheirreconstructed values.Thedifferenceinthefittedparametersbetweenthetwofits istakenasanestimateofthesystematicuncertainty.
Thedifferentialbranchingfractionhasanadditionalsystematic uncertaintyof4.6%comingfromtheuncertaintyinthebranching fractionofthenormalizationmodeB0→J/ψK∗0.
Thesystematicuncertaintiesaremeasuredandappliedineach q2 bin, withthe total systematicuncertainty obtainedby adding theindividualcontributionsinquadrature.
6. Results
Thesignaldata,corresponding to1430signal events,are fitin sevendisjointq2binsfrom1to19 GeV2.Resultsarealsoobtained
for a wide, low-q2 bin (1<q2<6 GeV2), where the theoretical uncertaintiesarebestunderstood.TheK+π−μ+μ−invariantmass distributionsforalloftheq2 signalbins,aswellasthefit
projec-tions, are shownin Fig. 2. Fig. 3 plots the projectionsof the fit andthedata onthe cosθK (top) andcosθl (bottom) axesforthe
combined low-q2 bin (left, 1<q2<6 GeV2) and the highest q2
bin (right, 16<q2<19 GeV2). The fitted values of signal yield, FL, AFB,anddB/dq2,alongwiththeirassociateduncertainties,are
givenforeachof thedisjointq2 regions inTable 2.These results
arealsoshowninFig. 4,alongwithtwoSMpredictions.Thefitted values for FS are all lessthan0.03, whilethe valuesfor AS vary
from −0.3 to +0.3.
The SM predictions, derived from Refs. [18,20], combine two calculationaltechniques.Inthelow-q2region,aquantum
chromo-dynamic factorization approach [43] is used, which is applicable forq2<4m2c,wheremc isthecharm quark mass.Inthe high-q2
region,anoperatorproductexpansionintheinverseb quarkmass and 1/q2 [44,45] iscombined withheavy-quarkform-factor
re-lations [46]. This isvalid above the open-charm threshold (q2 13.9 GeV2).The twoSM predictionsshowninFig. 4 differinthe calculation of the form factors. The light-cone sum rules (LCSR) calculation is made at low q2 [47] and is extrapolated to high
q2 [48].The latticegauge (Lattice)calculationofthe formfactors is fromRef. [49]. Controlledtheoretical predictions are not avail-able nearthe J/ψ andψ resonances. The SM predictions are in goodagreementwiththeCMSexperimentalresults,indicatingno strongcontributionfromphysicsbeyondthestandardmodel.
The results described are combined with previous CMS mea-surements,obtainedfromanindependentdatasamplecollectedat
√
s=7 TeV[29].Thesystematicuncertaintiesassociatedwiththe efficiency, Kπ mistagging, mass distribution, angular resolution, andthe B0→J/ψK∗0 branching fractionare assumedto be fully
correlated between the two samples, with the remaining uncer-tainties assumedtobeuncorrelated. Tocombinetheresultsfrom the 7 TeVand8 TeVdata,the uncorrelatedsystematic uncertain-tiesare combinedinquadraturewiththe statisticaluncertainties. To account for the asymmetric uncertainties, the linear variance methodfromRef.[50]isusedtoaveragethe7 TeVand8 TeV mea-surements,aswell astoaveragethetwoq2 binscovering4.30 to 8.68 GeV2,whichwasasinglebininthe7 TeVanalysis.Afterthe
combination, thecorrelated systematicuncertainties are addedin quadrature.ThecombinedCMSmeasurementsof AFB, FL,andthe
differentialbranchingfractionversusq2 arecomparedtoprevious measurements[26–29,51,52]inFig. 5.TheCMSmeasurementsare consistentwiththeotherresults,withcomparableorhigher preci-sion.Table 3providesacomparisonofthemeasuredquantitiesin thelowdimuoninvariantmassregion:1<q2<6 GeV2,aswellas thecorrespondingtheoreticalcalculations.
7. Summary
Using pp collisiondata recordedat√s=8 TeV withtheCMS detectorattheLHC,corresponding toan integratedluminosity of 20.5 fb−1,an angularanalysis hasbeencarriedout on thedecay
B0→K∗0μ+μ−.The datausedforthisanalysisinclude1430
sig-nal decays. For each bin of the dimuon invariant mass squared (q2), unbinned maximum-likelihood fits were performed to the distributionsoftheK+π−μ+μ−invariantmassandtwodecay an-gles, toobtain valuesoftheforward–backwardasymmetry ofthe muons, AFB, the fraction of longitudinal polarization of the K∗0,
FL,andthedifferentialbranchingfraction,dB/dq2.Theresultsare
amongthemostprecisetodateandareconsistent withstandard modelpredictionsandpreviousmeasurements.
Acknowledgements
WecongratulateourcolleaguesintheCERNaccelerator depart-ments for the excellent performance of the LHC and thank the technical andadministrativestaffs atCERNand atother CMS in-stitutes for their contributions to the success of the CMS effort. Inaddition,wegratefullyacknowledgethecomputingcentersand personneloftheWorldwideLHCComputingGridfordeliveringso effectively thecomputinginfrastructure essentialto our analyses.
Fig. 2. TheK+π−μ+μ− invariantmassdistributionsforthesevensignalq2binsandthecombined1<q2<6 GeV2 bin.Overlaidoneachistheprojectionoftheresults
forthetotalfit,aswellasthethreecomponents:correctlytaggedsignal,mistaggedsignal,andbackground.Theverticalbarsgivethestatisticaluncertainties,thehorizontal barsthebinwidths.
Finally, we acknowledge the enduring support for the construc-tion and operation of the LHC and the CMS detector provided by the following funding agencies: BMWFW and FWF (Austria); Fonds De La Recherche Scientifique - FNRS and FWO (Belgium); CNPq,CAPES,FAPERJ,andFAPESP(Brazil); MES (Bulgaria); CERN;
CAS,MoST,andNSFC(China); COLCIENCIAS(Colombia);MSESand CSF (Croatia); RPF (Cyprus); MoER, ERC IUT and ERDF (Estonia); AcademyofFinland,MEC,andHIP(Finland);CEAandCNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA andNIH(Hungary);DAEandDST(India);IPM(Iran);SFI(Ireland);
Fig. 3. Dataandfitresultsfor1<q2<6 GeV2
(left)and16<q2<19 GeV2
(right),projectedontothecosθKaxis(top),andcosθlaxis(bottom).Thefitresultsshowthe
totalfit,aswellasthethreecomponents:correctlytaggedsignal,mistaggedsignal,andbackground.Theverticalbarsgivethestatisticaluncertainties,thehorizontalbars thebinwidths.
Table 2
Themeasuredvaluesofsignalyield(includingboth correctlytaggedand mistaggedevents), FL, AFB,and differential
branchingfractionforthedecayB0→K∗0μ+μ− inbinsofq2.Thefirstuncertaintyisstatisticalandthesecond(when
present)issystematic.Thebinrangesareselectedtoallowcomparisonstopreviousmeasurements.
q2
(GeV2) Signalyield FL AFB dB/dq 2 (10−8GeV−2 ) 1.00–2.00 84±11 0.64+0.10 −0.09±0.07 −0.27+ 0.17 −0.40±0.07 4.6±0.7±0.3 2.00–4.30 145±16 0.80±0.08±0.06 −0.12+0.15 −0.17±0.05 3.3±0.5±0.2 4.30–6.00 117±15 0.62+−00..1009±0.07 0.01±0.15±0.03 3.4±0.5±0.3 6.00–8.68 254±21 0.50±0.06±0.06 0.03±0.10±0.02 4.7±0.4±0.3 10.09–12.86 362±25 0.39±0.05±0.04 0.16±0.06±0.01 6.2±0.4±0.5 14.18–16.00 225±18 0.48−+00..0506±0.04 0.39+ 0.04 −0.06±0.01 6.7±0.6±0.5 16.00–19.00 239±18 0.38+0.05 −0.06±0.04 0.35±0.07±0.01 4.2±0.3±0.3 Table 3
MeasurementsfromCMS(the7 TeVresults[29],thisworkfor8 TeV,andthecombination),LHCb[28],BaBar[52],CDF[27, 51],andBelle[26]ofFL, AFB,anddB/dq2 intheregion1<q2<6 GeV2forthedecayB0→K∗0μ+μ−.TheCMSand
LHCbresultsarefromB0→K∗0μ+μ−decays.TheremainingexperimentsaddthecorrespondingB+decay,andtheBaBar
andBelleexperimentsalsoincludethedielectronmode.Thefirstuncertaintyisstatisticalandthesecondissystematic. ForthecombinedCMSresults,onlythetotaluncertaintyisreported.ThetwoSMpredictionsarealsogiven.
Experiment FL AFB dB/dq2(10−8GeV−2)
CMS (7 TeV) 0.68±0.10±0.02 −0.07±0.12±0.01 4.4±0.6±0.4 CMS (8 TeV, this analysis) 0.73±0.05±0.04 −0.16+−00..1009±0.05 3.6±0.3±0.2
CMS (7 TeV+8 TeV) 0.72±0.06 −0.12±0.08 3.8±0.4 LHCb 0.65−+00..0807±0.03 −0.17±0.06±0.01 3.4±0.3+ 0.4 −0.5 BaBar – – 4.1+1.1 −1.0±0.1 CDF 0.69+0.19 −0.21±0.08 0.29+ 0.20 −0.23±0.07 3.2±1.1±0.3 Belle 0.67±0.23±0.05 0.26+0.27 −0.32±0.07 3.0+ 0.9 −0.8±0.2 SM (LCSR) 0.79+0.09 −0.12 −0.02+ 0.03 −0.02 4.6+ 2.3 −1.7 SM (Lattice) 0.73+0.08 −0.10 −0.03+ 0.04 −0.03 3.8+ 1.2 −1.0
Fig. 4. MeasuredvaluesofFL,AFB,anddB/dq2versusq2forB0→K∗0μ+μ−.The
statisticaluncertaintyisshownbytheinnerverticalbars,whiletheoutervertical barsgivethetotaluncertainty.Thehorizontalbarsshowthebinwidths.Thevertical shadedregionscorrespondtotheJ/ψandψresonances.Theothershadedregions showthetwoSMpredictionsafterrateaveragingacrosstheq2 binstoprovidea
directcomparisontothedata.Controlledtheoreticalpredictionsarenotavailable neartheJ/ψandψresonances.
INFN (Italy); MSIP andNRF (Republic ofKorea); LAS (Lithuania); MOE andUM (Malaysia); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); MBIE (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland);FCT (Portugal); JINR (Dubna); MON, RosAtom, RAS andRFBR(Russia);MESTD(Serbia);SEIDIandCPAN(Spain);Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter, IPST, STAR and NSTDA (Thailand); TUBITAK and TAEK (Turkey); NASU andSFFR(Ukraine);STFC(UnitedKingdom);DOEandNSF(USA).
Individuals have received support from the Marie-Curie pro-gramandtheEuropeanResearchCouncilandEPLANET(European Union); the Leventis Foundation; the A.P. Sloan Foundation; the AlexandervonHumboldt Foundation;theBelgianFederal Science Policy Office; the Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium); theMinistryofEducation, YouthandSports (MEYS)ofthe Czech Republic;theCouncilofScienceandIndustrialResearch,India;the
Fig. 5. MeasuredvaluesofFL,AFB,anddB/dq2versusq2forB0→K∗0μ+μ−from
CMS(combinationofthe7 TeV[29]resultsandthisanalysis),Belle[26],CDF[27, 51],BaBar[52],andLHCb[28].TheCMSandLHCbresultsarefromB0→K∗0μ+μ−
decays.TheremainingexperimentsaddthecorrespondingB+decay,andtheBaBar andBelleexperimentsalsoincludethedielectronmode.Theverticalbarsgivethe totaluncertainty.Thehorizontalbarsshowthebinwidths.Thehorizontalpositions ofthedatapointsarestaggeredtoimprovelegibility.Theverticalshadedregions correspondtotheJ/ψandψresonances.
HOMING PLUSprogram of theFoundation for Polish Science, co-financed fromEuropean Union, Regional Development Fund;the CompagniadiSanPaolo(Torino); theConsorzioperlaFisica (Tri-este); MIUR project 20108T4XTM (Italy); the Thalis and Aristeia programscofinancedbyEU-ESFandtheGreek NSRF;theNational Priorities ResearchProgrambyQatar NationalResearchFund;the Rachadapisek Sompot Fund for Postdoctoral Fellowship, Chula-longkornUniversity(Thailand);andtheWelchFoundation.
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InstitutfürHochenergiephysikderOeAW,Wien,Austria
V. Mossolov,N. Shumeiko,J. Suarez Gonzalez
NationalCentreforParticleandHighEnergyPhysics,Minsk,Belarus
S. Alderweireldt, 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
S. Abu Zeid,F. Blekman, J. D’Hondt, N. Daci,I. De Bruyn, K. Deroover, N. Heracleous,J. Keaveney, S. Lowette,L. Moreels,A. Olbrechts, Q. Python, D. Strom, S. Tavernier,W. Van Doninck, P. Van Mulders, G.P. Van Onsem,I. Van Parijs
VrijeUniversiteitBrussel,Brussel,Belgium
P. Barria, C. Caillol, B. Clerbaux, G. De Lentdecker, H. Delannoy, G. Fasanella, L. Favart, A.P.R. Gay,
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UniversitéLibredeBruxelles,Bruxelles,Belgium
K. Beernaert,L. Benucci, A. Cimmino, S. Crucy, D. Dobur, A. Fagot,G. Garcia,M. Gul, J. Mccartin, A.A. Ocampo Rios,D. Poyraz, D. Ryckbosch, S. Salva, M. Sigamani,N. Strobbe, M. Tytgat,
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GhentUniversity,Ghent,Belgium
S. Basegmez, C. Beluffi4, O. Bondu,S. Brochet,G. Bruno, R. Castello,A. Caudron, L. Ceard,
G.G. Da Silveira,C. Delaere, D. Favart,L. Forthomme,A. Giammanco5, J. Hollar,A. Jafari,P. Jez, M. Komm, V. Lemaitre,A. Mertens, C. Nuttens,L. Perrini, A. Pin, K. Piotrzkowski,A. Popov6, L. Quertenmont,
M. Selvaggi,M. Vidal Marono
UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium
N. Beliy,G.H. Hammad
UniversitédeMons,Mons,Belgium
W.L. Aldá Júnior, G.A. Alves,L. Brito,M. Correa Martins Junior, M. Hamer,C. Hensel,C. Mora Herrera, A. Moraes,M.E. Pol, P. Rebello Teles
CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil
E. Belchior Batista Das Chagas, W. Carvalho,J. Chinellato7, A. Custódio, E.M. Da Costa,
D. De Jesus Damiao,C. De Oliveira Martins, S. Fonseca De Souza, L.M. Huertas Guativa, H. Malbouisson, D. Matos Figueiredo,L. Mundim, H. Nogima,W.L. Prado Da Silva, A. Santoro,A. Sznajder,
E.J. Tonelli Manganote7,A. Vilela Pereira
S. Ahujaa, C.A. Bernardesb, A. De Souza Santosb,S. Dograa, T.R. Fernandez Perez Tomeia,
E.M. Gregoresb, P.G. Mercadanteb,C.S. Moona,8,S.F. Novaesa,Sandra S. Padulaa,D. Romero Abad, J.C. Ruiz Vargas
aUniversidadeEstadualPaulista,SãoPaulo,Brazil bUniversidadeFederaldoABC,SãoPaulo,Brazil
A. Aleksandrov, R. Hadjiiska, P. Iaydjiev,M. Rodozov, S. Stoykova, G. Sultanov, M. Vutova
InstituteforNuclearResearchandNuclearEnergy,Sofia,Bulgaria
A. Dimitrov, I. Glushkov,L. Litov, B. Pavlov,P. Petkov
UniversityofSofia,Sofia,Bulgaria
M. Ahmad, J.G. Bian, G.M. Chen, H.S. Chen,M. Chen, T. Cheng, R. Du,C.H. Jiang, R. Plestina9,F. Romeo, S.M. Shaheen, J. Tao, C. Wang,Z. Wang, H. Zhang
InstituteofHighEnergyPhysics,Beijing,China
C. Asawatangtrakuldee, Y. Ban, Q. Li, S. Liu,Y. Mao, S.J. Qian, D. Wang,Z. Xu, 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, I. Puljak,P.M. Ribeiro Cipriano
UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia
Z. Antunovic, M. Kovac
UniversityofSplit,FacultyofScience,Split,Croatia
V. Brigljevic,K. Kadija, J. Luetic, S. Micanovic,L. Sudic
InstituteRudjerBoskovic,Zagreb,Croatia
A. Attikis, G. Mavromanolakis, J. Mousa,C. Nicolaou, F. Ptochos, P.A. Razis,H. Rykaczewski
UniversityofCyprus,Nicosia,Cyprus
M. Bodlak,M. Finger10,M. Finger Jr.10
CharlesUniversity,Prague,CzechRepublic
M. El Sawy11,12,E. El-khateeb13,T. Elkafrawy13, A. Mohamed14,A. Radi11,13,E. Salama13,11
AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt
B. Calpas, M. Kadastik, M. Murumaa, M. Raidal, A. Tiko, C. Veelken
NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia
P. Eerola, J. Pekkanen,M. Voutilainen
DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland
J. Härkönen,V. Karimäki, R. Kinnunen, 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
I. Antropov,S. Baffioni, F. Beaudette, P. Busson, L. Cadamuro, E. Chapon,C. Charlot,T. Dahms, O. Davignon,N. Filipovic, A. Florent, R. Granier de Cassagnac,S. Lisniak, L. Mastrolorenzo, P. Miné, I.N. Naranjo,M. Nguyen, C. Ochando, G. Ortona, P. Paganini,S. Regnard, R. Salerno, J.B. Sauvan, Y. Sirois, T. Strebler, Y. Yilmaz,A. Zabi
LaboratoireLeprince-Ringuet,EcolePolytechnique,IN2P3-CNRS,Palaiseau,France
J.-L. Agram15,J. Andrea, A. Aubin,D. Bloch, J.-M. Brom,M. Buttignol, E.C. Chabert,N. Chanon, C. Collard, E. Conte15,X. Coubez, J.-C. Fontaine15, D. Gelé, U. Goerlach,C. Goetzmann, A.-C. Le Bihan, J.A. Merlin2, K. Skovpen,P. Van Hove
InstitutPluridisciplinaireHubertCurien,UniversitédeStrasbourg,UniversitédeHauteAlsaceMulhouse,CNRS/IN2P3,Strasbourg,France
S. Gadrat
CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France
S. Beauceron,C. Bernet, G. Boudoul,E. Bouvier, C.A. Carrillo Montoya, J. Chasserat, R. Chierici, D. Contardo, B. Courbon, P. Depasse, H. El Mamouni,J. Fan, J. Fay, S. Gascon, M. Gouzevitch,B. Ille, F. Lagarde,I.B. Laktineh, M. Lethuillier,L. Mirabito, A.L. Pequegnot, 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
T. Toriashvili16
GeorgianTechnicalUniversity,Tbilisi,Georgia
Z. Tsamalaidze10
TbilisiStateUniversity,Tbilisi,Georgia
C. Autermann,S. Beranek, M. Edelhoff,L. Feld, A. Heister, M.K. Kiesel, K. Klein, M. Lipinski, A. Ostapchuk, M. Preuten,F. Raupach, S. Schael, J.F. Schulte,T. Verlage, H. Weber, B. Wittmer, V. Zhukov6
RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany
M. Ata, M. Brodski,E. Dietz-Laursonn, D. Duchardt, M. Endres,M. Erdmann, S. Erdweg, T. Esch, 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,T. Pook, M. Radziej, H. Reithler,M. Rieger, F. Scheuch,L. Sonnenschein, D. Teyssier, S. Thüer
RWTHAachenUniversity,III.PhysikalischesInstitutA,Aachen,Germany
V. Cherepanov, Y. Erdogan,G. Flügge, H. Geenen, M. Geisler, F. Hoehle, B. Kargoll, T. Kress, Y. Kuessel, A. Künsken,J. Lingemann2,A. Nehrkorn, A. Nowack, I.M. Nugent,C. Pistone, O. Pooth,A. Stahl
RWTHAachenUniversity,III.PhysikalischesInstitutB,Aachen,Germany
M. Aldaya Martin,I. Asin, N. Bartosik, O. Behnke,U. Behrens, A.J. Bell,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,E. Gallo17, J. Garay Garcia, A. Geiser,A. Gizhko,
P. Gunnellini, J. Hauk, M. Hempel18,H. Jung, A. Kalogeropoulos, O. Karacheban18, M. Kasemann, P. Katsas, J. Kieseler, C. Kleinwort,I. Korol, W. Lange, J. Leonard,K. Lipka, A. Lobanov, W. Lohmann18, R. Mankel, I. Marfin18,I.-A. Melzer-Pellmann, A.B. Meyer, G. Mittag, J. Mnich, A. Mussgiller,
M.Ö. Sahin,P. Saxena, T. Schoerner-Sadenius,M. Schröder, C. Seitz,S. Spannagel, K.D. Trippkewitz, R. Walsh, C. Wissing
DeutschesElektronen-Synchrotron,Hamburg,Germany
V. Blobel, M. Centis Vignali, A.R. Draeger,J. Erfle, E. Garutti, K. Goebel, D. Gonzalez, M. Görner, J. Haller, M. Hoffmann,R.S. Höing, A. Junkes, R. Klanner, R. Kogler,T. Lapsien, T. Lenz, I. Marchesini, D. Marconi, M. Meyer, D. Nowatschin, J. Ott, F. Pantaleo2,T. Peiffer, A. Perieanu, N. Pietsch,J. Poehlsen, D. Rathjens, C. Sander, H. Schettler,P. Schleper, E. Schlieckau,A. Schmidt, J. Schwandt, M. Seidel,V. Sola, H. Stadie, G. Steinbrück, H. Tholen, D. Troendle,E. Usai, L. Vanelderen, A. Vanhoefer, B. Vormwald
UniversityofHamburg,Hamburg,Germany
M. Akbiyik, C. Barth, C. Baus,J. Berger, C. Böser,E. Butz, T. Chwalek, F. Colombo, W. De Boer, A. Descroix, A. Dierlamm, S. Fink,F. Frensch, M. Giffels,A. Gilbert, F. Hartmann2,S.M. Heindl, U. Husemann,
I. Katkov6, A. Kornmayer2, P. Lobelle Pardo, B. Maier, H. Mildner, M.U. Mozer, T. Müller,Th. Müller, M. Plagge, G. Quast, K. Rabbertz,S. Röcker, F. Roscher, H.J. Simonis,F.M. Stober,R. Ulrich,
J. Wagner-Kuhr, S. Wayand,M. Weber, T. Weiler, C. Wöhrmann, R. Wolf
InstitutfürExperimentelleKernphysik,Karlsruhe,Germany
G. Anagnostou, G. Daskalakis,T. Geralis,V.A. Giakoumopoulou, A. Kyriakis, D. Loukas, A. Psallidas, I. Topsis-Giotis
InstituteofNuclearandParticlePhysics(INPP),NCSRDemokritos,AghiaParaskevi,Greece
A. Agapitos, S. Kesisoglou, A. Panagiotou, N. Saoulidou, E. Tziaferi
UniversityofAthens,Athens,Greece
I. Evangelou, G. Flouris,C. Foudas, P. Kokkas, N. Loukas, N. Manthos, I. Papadopoulos,E. Paradas, J. Strologas
UniversityofIoánnina,Ioánnina,Greece
G. Bencze,C. Hajdu, A. Hazi,P. Hidas, D. Horvath19,F. Sikler, V. Veszpremi, G. Vesztergombi20, A.J. Zsigmond
WignerResearchCentreforPhysics,Budapest,Hungary
N. Beni, S. Czellar, J. Karancsi21,J. Molnar, Z. Szillasi
InstituteofNuclearResearchATOMKI,Debrecen,Hungary
M. Bartók22,A. Makovec, P. Raics, Z.L. Trocsanyi,B. Ujvari
UniversityofDebrecen,Debrecen,Hungary
P. Mal, K. Mandal, N. Sahoo, S.K. Swain
NationalInstituteofScienceEducationandResearch,Bhubaneswar,India
S. Bansal, S.B. Beri,V. Bhatnagar, R. Chawla, R. Gupta,U. Bhawandeep, A.K. Kalsi,A. Kaur, M. Kaur, R. Kumar,A. Mehta, M. Mittal, J.B. Singh, G. Walia
PanjabUniversity,Chandigarh,India
Ashok Kumar, A. Bhardwaj,B.C. Choudhary, R.B. Garg,A. Kumar, S. Malhotra, M. Naimuddin,N. Nishu, K. Ranjan,R. Sharma, V. Sharma
UniversityofDelhi,Delhi,India
S. Banerjee, S. Bhattacharya, K. Chatterjee,S. Dey, S. Dutta, Sa. Jain, N. Majumdar, A. Modak, K. Mondal, S. Mukherjee,S. Mukhopadhyay, A. Roy, D. Roy, S. Roy Chowdhury, S. Sarkar, M. Sharan
S. Mitra, G.B. Mohanty, B. Parida,T. Sarkar ,K. Sudhakar, N. Sur, B. Sutar, N. Wickramage
TataInstituteofFundamentalResearch,Mumbai,India
S. Chauhan,S. Dube, S. Sharma
IndianInstituteofScienceEducationandResearch(IISER),Pune,India
H. Bakhshiansohi,H. Behnamian,S.M. Etesami26, A. Fahim27, R. Goldouzian, M. Khakzad,
M. Mohammadi Najafabadi,M. Naseri, S. Paktinat Mehdiabadi, F. Rezaei Hosseinabadi, B. Safarzadeh28, M. Zeinali
InstituteforResearchinFundamentalSciences(IPM),Tehran,Iran
M. Felcini,M. Grunewald
UniversityCollegeDublin,Dublin,Ireland
M. Abbresciaa,b, C. Calabriaa,b, C. Caputoa,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,G. Minielloa,b,S. Mya,c,S. Nuzzoa,b, A. Pompilia,b, G. Pugliesea,c,R. Radognaa,b,A. Ranieria, G. Selvaggia,b, L. Silvestrisa,2,R. Vendittia,b, P. Verwilligena
aINFNSezionediBari,Bari,Italy bUniversitàdiBari,Bari,Italy cPolitecnicodiBari,Bari,Italy
G. Abbiendia,C. Battilana2,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,S.S. Chhibraa,b,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
G. Cappelloa,M. Chiorbolia,b,S. Costaa,b,F. Giordanoa,b, 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,S. Gonzia,b,V. Goria,b, P. Lenzia,b, M. Meschinia, S. Paolettia,G. Sguazzonia,A. Tropianoa,b,L. Viliania,b
aINFNSezionediFirenze,Firenze,Italy bUniversitàdiFirenze,Firenze,Italy
L. Benussi,S. Bianco, F. Fabbri, D. Piccolo,F. Primavera
INFNLaboratoriNazionalidiFrascati,Frascati,Italy
V. Calvellia,b, F. Ferroa, M. Lo Veterea,b, M.R. Mongea,b,E. Robuttia, S. Tosia,b aINFNSezionediGenova,Genova,Italy