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Heavy flavour production and spectroscopy at LHCb⋆ DiegoMilane´sa,onbehalfoftheLHCbCollaboration INFN,SezionediBari Abstract. WesummarizethemainmeasurementsperformedwiththeLHCbdetectoronproductionandspec- troscopyintheheavyflavoursector,usingdatasamplesrecordedduring2010and2011datatakinginproton- protoncollisionsat √s=7TeV. 1 Introduction 2 The LHCb detector The LHCb detector is a single-arm forward spectrome- Measurementsoftheheavyquarkproductioncross-sections ter coveringa uniquerapidity range (2 < η < 5), where inproton-protoncollisionstestthepredictionsofquantum bb¯ crosssectionispeaked.Duetothis,althoughitcovers chromodynamics(QCD),andprobesthespectrumanddy- 4% of the solid angle, it detects 40% of heavy quark namics of the colliding partons. The formation of heavy ∼ ∼ production cross-section.The LHCb detector [8] is spe- quarkoniastates(boundedqq¯)canbefactorizedintotwo cialized in beauty and charm physics studies, exhibiting stepsaccordingtoquantumchromodynamics(QCD).First, outstandingtracking,vertexingandparticleidentification the creation of a qq¯ pair via small-distance interactions capabilities.In2010and2011,thedetectorrecordedabout (perturbative), followed by the evolution into a quarko- 1.1fb 1 of integrated luminosity in proton-proton colli- − nium state via the exchange of soft gluons (non pertur- sionsat √s =7TeV,morethanthe90%oftheluminosity bative).Thenon-relativisticQCD(NRQCD),predictsthe deliveredbytheLargeHadronCollider(LHC). probabilityofaheavyqq¯pairtoevolveintoheavyquarko- nium, as a function of color-singlet (CS) [1] and color- octet(CO) [2]matrix elements. The CS model,provides 3 Heavy flavourproduction a leading-order (LO) description of quarkonium formation,butitunderestimatesthemeasuredcross-sectionfor Inageneralform,theproductioncross-sectionatproton- J/ψproductionatTevatron[3],particularlyathightrans- protoncollisionsofagivenstateAcanbewrittenas versemomentump .Thisdiscrepancycanbereducedin- T cludingprocessessuchasquarkandgluonfragmentation, N(A f) but still it fails to reproduce the measured cross-section. σ(pp A)= → , (1) → ǫ (A f) TheintroductionofCO model,with the matrix elements L· ·B → tuned to data, improves the description of the measured whereN(A f)isthenumberofobservedsignalevents shapeandmagnitudeoftheJ/ψcross-section.Recentthe- ofAdecayin→gintothefinalstate f, istheintegratedlu- oreticalstudies[4]incorporatehigherordercorrectionsto minosityofthesample,ǫ istheefficLiencywhichaccounts the CS models, reducing significantly the observed dis- fortriggerandreconstructioneffects,and (A f)isthe crepancyinquarkoniumproductionwithoutincludingCO branchingfractionofthedecay. B → matrixelements.However,the agreementisstill notper- Usingthe2010datasampleof40pb 1,theLHCbcol- − fect,leavingopenthequestionofa completedescription laborationhasmeasuredseveralproductioncross-sections ofquarkoniaformation[5]. suchusopencharm[9],J/ψ[10],doubleJ/ψ[11],ψ(2S) Thespectrumofheavyhadronshasbeenpredictedus- [12], χ /χ ratio [13], B [14] and Υ(1S) [15]. Due to c2 c1 ± ingQCD potentialsandchiralmodels[6].Discrepancies limited space we do not discuss all the analyses in this betweenpredictionsandobservations,mainlyforhighmass document. states[7],makesspectroscopyanactiveandoftencontro- versialfield. 3.1 Double J/ψproduction ⋆ Presented at Hadron Collider Physics Symposium 2011, November14-18,Paris,France Theoretical calculations based on LO production of CS- a e-mail:[email protected] states predict a total cross-section of 24nb for J/ψJ/ψ EPJWebofConferences production in the current LHC running conditions [16]. This calculation accounts for additional feed-down from J/ψψ(2S)andψ(2S)ψ(2S)production,butnotfordouble parton scattering. The extrapolated prediction to the an- gularLHCb coveragegivesa cross-sectionofabout4nb witha30%ofuncertainty. For this analysis, we use an integrated luminosity of 37.5pb 1, collected by the LHCb detector between July − andNovemberof2010. J/ψmesoncandidatesarerecon- structed from a pair of oppositely-charged tracks identi- fiedasmuons.Therefore,weselecteventswith4ofthese tracks,originatedfromacommonvertex,withgoodtrack qualityandwith p < 650MeV/c.Muonidentificationis T achieved by comparinga globallikelihood functionpro- videdbytheparticleidentification,trackingandcalorime- tersubdetectors,withthecorrespondinglikelihoodforlight Fig.1. Raw signal yield of J/ψ (µ+µ ) in binsof (µ+µ ) hadrons.Selectedµ+µ−candidates,withaninvariantmass invariantmass,asobservedindata→. − 1 − 2 of3.0-3.2GeV/c2,arepairedtoform(µ+µ ) (µ+µ ) com- − 1 − 2 binations. Backgroundcoming from J/ψ mesons associated to different productionvertex and from B decays is Thelargestsystematiccontributionisduetotheknowl- removed by applying quality requirements to the vertex edgeofthetrack-findingefficiency.A4%uncertaintyper fit,constrainingthe4muonstocomefromthesamever- track is assigned, based on studies comparingthe recon- texandrequiringthevertextobecompatiblewithoneof struction efficiency in data and simulation, using a tag- theprimaryverticesproducedaftertheproton-protoncol- and-probe approach. Additional systematic uncertainties lision. inthemethodtoextracttheefficiencyhavebeenaccounted The number of events with two J/ψ mesons is ex- for, as well as data-simulation discrepancies. The lumi- tracted from the single J/ψ mass spectrum. The invari- nositywasdeterminedinspecificperiodsduringdatatak- antmassdistributionsofthe first muonpairare obtained ing,usingbothVanderMeerscansandbeamgasimaging in bins of the invariant mass of the second pair, where method [17]. The systematic uncertainty associated with the first µ+µ− pair is chosen to be the one with smaller these methods is of 10%. The total systematic contribu- pT. The signalis describedusinga Crystal-Ballfunction tion to the cross-section uncertainty was found to be of plus an exponential to describe the background compo- 21%. nent. The position of the J/ψ peak is extracted from an Usingthevalueof (J/ψ µ+µ ) = (5.93 0.06)% − inclusive J/ψsample.Thefitresultprojectedonthedata [18],thecross-sectionBresulti→sσ(J/ψJ/ψ) = 5.1± 1.0 sample is shown in Fig. 1, where the extracted yield is 1.1nb,wherethefirstuncertaintyisstatisticalandt±hesec±- N(J/ψJ/ψ) = 141 19 events. The yield of events with ond systematic. The differentialproductioncross-section ± both J/ψ mesons in the detector fiducial range and ex- of J/ψ pairs as a function of the invariant mass of the plicitlytriggeredbyone J/ψthroughthededicatedmuon J/ψJ/ψ system is shown in Fig. 2, where we observe a trigger lines is found to be 116 16. This is the sample reasonable agreement, within uncertainties, between the ± usedtoextractthecross-section. measurementperformedandtheprediction. Theefficiencyevaluationaccountsforreconstruction, muonmisidentificationandtriggereffects.Theefficiency isfactorizedastheproductoftheefficiencyforeach J/ψ 4 Heavy flavourspectroscopy meson.Thereconstructionefficiencyǫ =ǫ ǫ ,isthe R R1 R2 × productoftheefficiencyofthetwo J/ψmesons,anditis afunctionofthegeometricalacceptancevariablesp and SpectroscopyisoneofthemanyfrontsinwhichtheLHCb T η and cosθ , where θ is the angle betweenthe µ+ mo- collaborationisactivelyworking.Toimproveourknowl- ∗ ∗ mentum| inth|e J/ψrestframeandthe J/ψmomentumin edge and understanding on how quarks interact among the laboratoryframe.Theangulardependenceduetothe them andrecombinethem with othersto form intriguing unknown polarization of the J/ψ candidate is computed states, itis necessaryto studythespectra ofthe different from a sample of J/ψ µ+µ simulated events. Muon familiesofmesonsandbaryons,lookingforunknownob- − identification efficiency→is extracted from the analysis of jectsanddeterminingtheirproperties. the inclusive J/ψ sample. The trigger efficiency is deter- We will discuss studies on production of D(s)J and mined with a sample of independently triggered events. B(s)J [19] states, as well as searches of these states de- The effect of the global event cuts applied in the trigger caying into Ah final states, with h = π±, K± or KS0, and has been studied in detail for inclusive J/ψ events, and A=D0,D+,D +,B0orB+,aimedtoconfirmthepresence ∗ appliedhereassumingfactorization. ofhighmassstructuresobservedinotherexperiments[20, HadronColliderPhysicsSymposium2011,November14-18,Paris,France Fig.3.Q(B0π+)distribution.LHCbdata(points)andthetotalfit (blue)aresuperimposed.ThecomponentsofthePDFare,com- binatorial background and associated production (red), combi- natorialbackground(dashedgreen), B+ B0π+ (solidblack), Fig. 2. Differential production cross-section for J/ψ pairs as a B+ B0π+ (dot-dashed black) an1d→B+ ∗ B0π+ (dotted functionoftheinvariantmassoftheJ/ψJ/ψsystem.Thepoints ∗2 → ∗ ∗2 → black). correspondtothedata.Onlystatisticaluncertaintiesareincluded intheerrorbars.Theshadedareacorrespondstopredictionby themodeldescribedin[16]. 1GeV/c and p > 10GeV/c. For convenience, we study theinvariantmassrelativetothethreshold,whichhasthe 21],andexplorethehighermasspartofthespectra.Inad- formQ(B0π+)= M(B0π+) M(B0) M(π+),whereM(B0) dition, mass measurementsof the exotic X(3872)meson and M(π+)arethenomina−lmasses−ofthemesonsquoted [22]and heavy baryonssuch as Ω and Ξ [23],will be −b b− byRef.[18]. performed. Combinatorialbackgroundshapeisextractedfromdata, usingasampleofreconstructedB+π+combinations,since thewrong-signdecayB0π hasstructurescreatedbycon- − 4.1 OrbitallyexcitedB mesons tributionsfrom B0 B¯0 mixing.Asignificantexcess,not ∗∗ attributedtoanyres−onantstate,isobservedintheQ(B0π+) ThepropertiesoftheexcitedBmesonscontainingalight with respect to the Q(B+π+) distribution, interpreted as quark (B+, B0, B0 ) are predicted by Heavy Quark Ef- anassociatedproductionduetob-jethadronization.This s fective Theory (HQET) in the limit of infinite b-quark component is described using a kernel-like distribution. mass[6,24].Undertheheavyquarkapproximationthe B SignalresonancesintheQ-distributionaremodeledusing mesonsarecharacterizedbythreequantumnumbers:the relativistic Breit-Wignerlineshapes. The detector resolu- orbitalangularmomentumL (S, P, D forL= 0,1,2 re- tion is about 3MeV/c2 and can safely be neglected. The spectively),theangularmomentumofthelightquark j = fitresultsareshowninFig.3.Hereweobservethefeed- q L 1/2 ,andthetotalangularmomentumJ = j 1/2. down from the B+/B + B 0π+ and the B + B0π+ | ± | | q± | 1 ∗2 → ∗ ∗2 → For L = 1therearefourdifferentpossible(J; j ) combi- states. To improvefit convergence,the relativewidthbe- q nations,allparity-even.Theseare knownasthe orbitally tween the B+ and the B + is fixed to 0.9 and the relative 1 ∗2 ethxeciBte1d(5s7t2at1e)s0oanrdBB∗∗∗2(s5ta7t4e7s.),AombsoenrvgetdhienseBs∗+taπt−esanwdeBh+aπv−e 0y.i9el3d,fbreotmwetehneothreetiBca∗2+lp→redBic∗0tiπo+nasn[d6,B24∗2+].→ B0π+ fixedto decays[21].AtLHCb,wereconstructthesedecaymodes, but also the B0π+ and B 0π+ where we must observethe ThelargestsystematicuncertaintyinthemeanQval- ∗ ues for the observed states, arise from variations in the isospinpartnersofthementionedstates. selectionrequirements(0.95%),andfromtheuncertainty In this analysis, we use an integrated luminosity of 336.5pb 1,collectedbytheLHCbdetectorbetweenMay on the B0 mass. The mean values are corrected for pos- − and July of 2011. The soft photons from the B 0 decay sible biases, calculated from simulated toy samples gen- ∗ erated from the experimental PDF. The final results are are not reconstructed,therefore objects decaying to both B∗0π+ and B0π+ are expected to show two peaks in the M(B+1)=(5726.3±1.9±3.0±0.5)MeV/c2andM(B∗2+)= B0π+ invariantmass distribution,separatedbya quantity (5739.0 3.3 1.6 0.3)MeV/c2,wherethefirstuncer- ± ± ± corresponding to the M(B 0) M(B0) mass difference. tainty is statistical, the second systematical and the third ∗ The B0 meson is reconstructe−d into the following final one from the uncertainty on the B0 meson mass. These states: J/ψ(µ+µ )K (892)0(K+π ), D π+ and D π+π+π , masses are compatiblewith the masses ofcorresponding − ∗ − − − − with D− K+π−π−. We combinethe B0 candidatewith isospinpartnersB01andB∗20.Inaddition,weobserveasig- tracks,wh→icharerequiredtooriginatefromthesameproton- nal significance of 9.9σ and 4.0σ for B+1 → B∗0π+ and protoninteraction.Thecompaniontrackisrequiredtobe B + B0π+, respectively,correspondingto the first ob- ∗2 → identified as a pion, to have good quality track fit, p > servationofthesetwodecays. T EPJWebofConferences 5 Conclusions Wesummarizedafewselectedresultsonheavyflavorpro- ductionandspectroscopyattheLHCbdetector.Weexpect many new results with the analysis of the 2011 dataset. TheLHCbexperimenthasshownoutstandingcapabilities andisinagoodpositiontoexploretheproductionmecha- nismsandspectraofstates,aswellastoproducecompet- itiveresultsintheheavyflavorssector. Fig.4.TheinvariantmassdistributionsfortheselectedΞ (left) b− andΩ (right)candidates.Thefitprojectionisoverlaid. −b References 1. E.L. Berger and D.L. Jones, Phys. Rev. D23 (1981) 4.2 MeasurementoftheΩ andΞ masses −b b− 1521. R. Baier and R. 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