Angular analysis of the decay B0 → K⁎0μ+μ− from pp collisions at √s=8 TeV

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Physics

Letters

B

www.elsevier.com/locate/physletb

Angular

analysis

of

the

decay

B

→

K

∗

μ

+

μ

−

from

pp

collisions

at

√

s

=

8 TeV

Receivedinrevisedform30November2015 Accepted7December2015

Availableonline11December2015 Editor:M.Doser

Keywords: CMS Physics B0decays

The angular distributions and the differential branching fraction of the decay B0_→K∗₍₈₉₂₎0_μ+_μ−

are studied using data corresponding to an integrated luminosity of 20.5 fb−1 _{collected with the CMS} detector at the LHC in pp collisions at √s=8 TeV. From 1430 signal decays, the forward–backward asymmetry of the muons, the K∗₍₈₉₂₎0_{longitudinal polarization fraction, and the differential branching} fraction are determined as a function of the dimuon invariant mass squared. The measurements are among the most precise to date and are in good agreement with standard model predictions.

©2015 CERN for the benefit of the CMS Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3_.

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∗0_μ+_μ−_(K∗0_{indicatestheK}∗₍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∗0_μ+_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 GeV}2_{.The q}2 _bins 8.68<q2_{<10.09 GeV}2 _and12

.90<q2_{<14.18 GeV}2_, 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_{→ ψ}_K∗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−m_B0)− (q−mJ/ψ)|>160(60)MeV. Forq<mψ (q>mψ),werequire|(m−mB0)− (q−m_ψ)|>60(30)MeV.The

requirements are set such that less than 10% of the background eventsoriginatefromthecontrolchannels.

The four-trackvertexcandidateis identifiedasa B0 _{or B}0 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 areconstructedB0_{compatiblewiththegeneratedB}0 _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-rametersY_SC andYB aretheyieldsofcorrectlytaggedsignalevents and background events, respectively, and are free parameters in thefit.Theparameter fM isthefractionofsignaleventsthat are mistaggedandisdeterminedfromMCsimulation.Thesignalmass probability functions SC_{(m) and S}M_{(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∗0_using:

dBB0→K∗0μ+μ− dq2 = YC_S C + YC_SfM (1−fM₎M  Y_NC C N + YCNfNM (1−f_NM)M N ₋1 ×B  B0→J/ψK∗0 q2 , (3)

whereYC_S andY_NC aretheyieldsofthecorrectlytaggedsignaland normalizationchannels,respectively; C

S and NC aretheefficiencies forthecorrectlytaggedsignalandnormalizationchannels, respec-tively; fM and f_NM 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 sevendisjointq2_{binsfrom1to19 GeV}2_{.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<q}2_{<6 GeV}2_{) and the highest q}2 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-q2_{region,aquantum} chromo-dynamic factorization approach [43] is used, which is applicable forq2<4m2_c,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∗0_μ+_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− invariantmassdistributionsforthesevensignalq2_{binsandthecombined1<q}2_{<6 GeV}2 _{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 GeV}2

(left)and16<q2_{<19 GeV}2

(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∗0_μ+_μ− _inbinsofq2_{.Thefirstuncertaintyisstatisticalandthesecond(when}

present)issystematic.Thebinrangesareselectedtoallowcomparisonstopreviousmeasurements. q2

(GeV2₎ Signal_yield FL AFB dB/dq

2 (10−8_GeV−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∗0_μ+_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∗0_μ+_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. References

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V. Mossolov,N. Shumeiko,J. Suarez Gonzalez

NationalCentreforParticleandHighEnergyPhysics,Minsk,Belarus

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VrijeUniversiteitBrussel,Brussel,Belgium

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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,

W. Van Driessche, E. Yazgan,N. Zaganidis

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 UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

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

a_{UniversidadeEstadualPaulista,SãoPaulo,Brazil} b_{UniversidadeFederaldoABC,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

a_{INFNSezionediBari,Bari,Italy} b_{UniversitàdiBari,Bari,Italy} c_{PolitecnicodiBari,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

a_{INFNSezionediBologna,Bologna,Italy} b_{UniversitàdiBologna,Bologna,Italy}

G. Cappelloa,M. Chiorbolia,b_{,S. Costa}a,b_{,F. Giordano}a,b_{, R. Potenza}a,b_{,A. Tricomi}a,b_{,C. Tuve}a,b

a_{INFNSezionediCatania,Catania,Italy} b_{UniversitàdiCatania,Catania,Italy} c_{CSFNSM,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

a_{INFNSezionediFirenze,Firenze,Italy} b_{UniversitàdiFirenze,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

a_{INFNSezionediGenova,Genova,Italy} b_{UniversitàdiGenova,Genova,Italy}