Early data of ATLAS will allow several B-physics measurements. Already with few pb-1 the ratio of the cross section of prompt J/ψ to indirect J/ψ cross-section will be measured with statistical precision of &lt;5%. With 10 pb−1, the cross section of heavy quarkonia like J/Ψ and Y will be measured in a pT range from 10-50 GeV/c. The J/y and Y polarization is expected to be measured with a precision of 0.02 to 0.06 and 0.2 for Y, respectively. Another measurement with first data will be the estimation of the cross section of the exclusive decay B+ →J/yK+, which will be used as a reference channel for e.g. rare B-decay searches as well as for detector performance studies. The measurement of the invariant masses of the B-mesons and lifetimes using these decays will allow detector performance checks

Sampsonidis, D

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ATL-PHYS-SLIDE-2009-26114September2009Beauty 2009, Heidelberg, Sept 7-11Early ATLAS B physics withthe first 10 – 100 pb-1Dimos SampsonidisAristotle University of ThessalonikiOn behalf of ATLAS CollaborationBeauty 2009, Heidelberg, Sept 7-11 2D.SampsonidisOutline? The ATLAS detector and the Trigger system? B-physics program with early data ? B-physics trigger ? Total and differential cross sections of Exclusive channels? Heavy quarkonia physics.? Polarization measurements ? B masses and lifetime measurements? SummaryBeauty 2009, Heidelberg, Sept 7-11 3D.SampsonidisThe ATLAS Detector•Inner Detector(High granularity, tracking coverage:|η|<2.5)•Si pixel detector•SCT (strip detector)•TRT (transition radiation)•Point resolution of Pixel Detector ~(10x100)µm (φ-z)•3 silicon layers, innermost @ 5cmSee talk of Sofia Chouridou•Muon Spectrometer•Fast trigger chambersRPC, TGC (<10 ns time resol)•High resolution tracking detectors: MDT, CSC (40 µm spatial resolution)Beauty 2009, Heidelberg, Sept 7-11 4D.SampsonidisThe ATLAS triggerThree stage systemLevel1: Hardware, High Level Trigger: (LVL2+EF) Software? LVL1? hardware-based, identifies Regions of Interest (RoI) for further processing, Total rate 75 kHz? LVL2? Confirmation of LVL1 data using precition detectors? Muon tracks extrapolation to inner detector? Track reconstruction in ROIs? Total rate 2 kHz? EF? refines LVL2 selection using offline-like algorithms? Vertexing, transverse decay length cut, angular distribution cut, full event, alignment and calibration data available hardwaresoftwareTotal rate 200 Hz ? to tape(5-10% dedicated to B-Physics)Beauty 2009, Heidelberg, Sept 7-11 5D.SampsonidisB-physics program for early dataLint = 10 – 100 pb-1? Detector & trigger understanding : calibration with J/ψ, Υ and exclusive B-channels as a tester, alignment, material, field, reconstruction.? Physics? cross section measurements at new energy in order to test QCD predictions.? Prompt J/ψ →µµ and Υ →µµ differential production cross-sections? Polarisation of J/ψ and Υ as a function of quarkonium transverse momentum? χc(nP) → J/ψ(µµ)γ cross-section(s)? Mass and lifetime measurements.? Large b cross section allows extraction of exclusive decays like B+ → J/Ψ K+, Bd → J/ψ K*0 , Bs → J/ψ φ, which serves as reference channels for themuonic rare decays.? Use measurement of well known B-physics quantities to test and monitor the detector performance, later with increasing integrated luminosity improve precisions of these.Beauty 2009, Heidelberg, Sept 7-11 6D.SampsonidisThe B physics Di-muon triggersTrigDiMuonOne L1 muon(confirm muon at HLT) → HLT BphysicsPerform tracking in extended RoI, search for second muon, (mass & vertex cuts)Trigger EfficiencyEstimate Level1, Level2 and EFefficiencies using Tag & Probe method with reconstructed J/ψ’s, using  single muon trigger (µ+track)L1_MUL1_MUL1_MU? B-physics has an efficient, fast and clean trigger based on muonsMany B-physics channels involve a di-muon signature, (B→J/ψ(µµ)X, b→sµµ, B→µµ etc)? The most effective trigger for such events uses the di-muon signature from the lowest trigger level.Topological triggerTwo L1 muonsPerform tracking in small RoIConfirm muons at L2Two HLT muons → HLT Bphysics(mass & vertex cuts)(µ4µ4, µ6µ4)Beauty 2009, Heidelberg, Sept 7-11 7D.SampsonidisB+ → J/ψ(µ+µ-) K+•Selection and reconstruction of eventsDi-µ J/ψ trigger (µ6µ4)•First reconstruction of J/ψ by combining 2µ•pT1(2)> 6(3) GeV, common vertex, ±120 MeVαround mJ/ψ, Proper decay length λ > 0.1 mm, Fit a common vertex of K+ and J/ψ candidate ?B+ candidatefor ℒ=10 pb-1 efficiency: 29.8±0.8 %uncert. :M(B+)~0.02%, σ(B+)~3.5%Signalbb→ J /Ψ(µ+µ-) X  background•Width σ and efficiency A for various pT bins and for pT>10 GeV for the total cross-section:Statistical and systematic uncertainties (for ℒ=10 pb-1)•Statistical uncertainty <5% for total and ~10% for differential cross-section measurement•Systematic uncertainty includes the uncertainties from the luminosity (~10%) and the BR (~10%)ATLASBeauty 2009, Heidelberg, Sept 7-11 8D.SampsonidisHeavy Prompt Quarkonia motivationCDF data[arXiv:hep-ph/0106120]COMCSM? Production was described via the Color Singlet Model (CSM).? Inconsistency with the Tevatron Xsection=>Color Octet Model suggested (COM).? COM failed to predict quarkoniapolarization dependence on its PT.? Alternative suggestions kT factorization.D0 dataCDF data[D0 Note 5089-conf] CDF data require Color OctetModel contributions to describe J/ψcross sectionATLAS is capable of detail checks of the predictions of various models and the degree of polarisation of J/ψ and YCOM prediction disagrees withpolarization data in Y→µµBeauty 2009, Heidelberg, Sept 7-11 9D.Sampsonidis? J/ψ from B-decays form significant background to prompt J/ψ,  in addition to muons from b-quark decays ? Measurement of prompt J/ψ to indirect cross-section relies on separation (and understanding of separation) of these two processes ? Prompt J/ψ typically have zero proper time while Indirect J/ψ have positive proper time? Cut on pseudo-proper time to separate indirect/prompt? ‘Pseudo-proper time’ cut of <0.2 ps gives prompt J/ψefficiency of 95% with 5% contaminationHeavy Prompt Quarkonia, background separationPrimary VertexIndirect J/ψpT(B)Secondary VertexLxyBeauty 2009, Heidelberg, Sept 7-11 10D.SampsonidisHeavy Prompt Quarkonia, Invariant massDedicated J/ψ and Υ  trigger signatures?Seeded by Level1 Di-µ trigger (µ6µ4)•µ tracks from primary vertex, •pseudo-proper time < 0.2 ps(background suppression)σ=54MeVσ=161 MeV?150 000 J/ψ and 25 000 Υ for 10 pb–1using di-µ trigger (µ6µ4)?S/B (at peak) = 60 (J/ψ), 10 (Υ)Beauty 2009, Heidelberg, Sept 7-11 11D.SampsonidisSpin-alignment measurement?Single-µ trigger => larger background Still: S/B = 1.2 (J/ψ) and 0.05 (Υ)µ10µ6µ4J/ψATLAS? Dimuon triggers:little or no information for high cosθ*Using di-muon trigger, both muons from J/Ψ must have relatively large pT.=> affects the polarization angle distribution.Angle defined between positive muon direction in quarkonium rest frame and quarkoniumdirection in lab frame.? Single µ10 trigger:? Second track can be reconstructed offline (>0.5 GeV pT)? |cos θ*| ~ 1 corresponds to a configuration where one muon is fast, the other slow? Provides similar pT range of onia to µ6µ4configuration and similar rates!Measurements using µ6µ4 and µ10 trigger have to be combinedto achieve full coverage in cosθ*Beauty 2009, Heidelberg, Sept 7-11 12D.SampsonidisSpin-alignment measurementCombined and corrected distributions in J/ψpolarisation angle cosθ*, for various pT slices (unpolarised data)Combined and corrected distributions in J/ψpolarisation angle cosθ*, for various pT slices, for Longitudinal (αgen=-1, dotted line) and Transversely (αgen=1, dashed line) polarisedBeauty 2009, Heidelberg, Sept 7-11 13D.SampsonidisSpin-alignment measurementJ/ψ and Y polarisation and cross sections measured in various pT slices, for 10 pb-1J/ψ polarisationJ/ψ cross-sectionResults at extrema of polarisation statesϒ polarisationϒ cross-sectionWe can expect cross-section measurement precision in bins of pT of the order of 1% (dependent on the polarisation)The precision of the J/ψ polarisation measurement can reach 0.02-0.06,  while the expected error on Y polarisation is unlike to be better than 0.2. Beauty 2009, Heidelberg, Sept 7-11 14D.Sampsonidisχ decays χc→J/ψ+γ events• For J/ψs, ~30% of total cross-section comes from χc→J/ψ+γInterested in χc decays to J/ψ or ϒ and a soft photon.Low χ reconstruction efficiency due to the difficulty in retrieving this photon. Preliminary studies suggest we can recover few % of those χc events from reconstructed J/ψ’s1. Have a J/ψ candidate2. Look in narrow cone (cos θ>0.98) aroundquarkonium momentum direction for photon(reduces combinatorics)3. µµγ-µµ invariant mass difference shows peaks whereχc0, χc1 or χc2 was reconstructed4. Α simultaneous fit of three Gaussians and quadraticbackground, can find the three peaks with a typicalresolution of 40 MeV10 pb-1 of dataχc→J/Ψ+γbb→ J /Ψ(µ+µ-) X  ?Only ~4% of χc decays into J/ψ γ have the right kinematics for photons to be reliablyreconstructed and identified in ECAL ?Studies on-going to include photon conversions using ID tracks, which should have betterresolution, at the price of much reduced efficiency.Beauty 2009, Heidelberg, Sept 7-11 15D.SampsonidisBd→J/ψK0*Ιt will be possible to measure the masses and proper lifetimes for these decayswith sufcient precision to allow them to be used for detector performance checks.? Bd→J/ψ K0* vertex reconstructed from two muons, one kaon and one pion track: this channel allows sensitive performance tests from 10pb-1? In early data, loose cuts will be used (No vertex displacement cut)? Simultaneous fit to mass and decay time used to extract signal mass and lifetime from data? Mass can be measured with a precision of ~10-3? B-Lifetime can be measured with a precision of ~10% with 10 pb-1. ? Measurement of resolution possible with 10 pb-1allowing for ID tests stability.ATLASSee talk of Weina JiBeauty 2009, Heidelberg, Sept 7-11 16D.SampsonidisSummary? The ATLAS B-physics program will run from the earliest days and will concentrate on:? total and differential cross sections of B-hadrons and onia? Polarization measurements? Mass and lifetime measurements? An efficient, fast and clean di-muon trigger will allow to collect large samples of B-hadrons and Quarkonium throughout the lifetime of the experiment.? Already with the first pb-1,? mass and lifetime measurements of exclusive channels will serve to validate and monitor ID performance and alignment? J/ψ and Upsilon resonances will provide calibration pointsWaiting for the data …its going to be interesting!Beauty 2009, Heidelberg, Sept 7-11 17D.Sampsonidis? Thank you!

Early ATLAS B-physics with the first 10 – 100 pb-1

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