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Prospects for quarkonium studies at LHCb

Patrick Robbe, LAL Orsay, 19 Feb 2010. Prospects for quarkonium studies at LHCb. « Quarkonium Production at the LHC » workshop. LHCb Detector. Forward Spectrometer Geometry, with angular acceptance 15< q <300 mrad Performance numbers relevant to quarkonium analyses:

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Prospects for quarkonium studies at LHCb

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  1. Patrick Robbe, LAL Orsay, 19 Feb 2010 Prospects for quarkonium studies at LHCb « Quarkonium Production at the LHC » workshop

  2. LHCb Detector • Forward Spectrometer Geometry, with angular acceptance 15<q<300 mrad • Performance numbers relevant to quarkonium analyses: • Charged tracksDp/p = 0.35 % - 0.55%, s(m)=12-25 MeV/c2 • ECALs(E)/E= 10% E-1/2 1 % (E in GeV) • muon ID: e(mm) = 94 %, mis-ID rate (pm) = 3 % • Vertexing: s(L)=250 mm (Primary Vertex Resolution: 10mm in x/y, 60 mm in z)

  3. Introduction • Unique acceptance between LHC experiments: • Quarkonium Physics Program: • Measurement of J/y production cross-section in LHCb acceptance (3<h<5, pT<7 GeV/c), • Measurement of J/y polarization • Similar measurements with y(2S), Y(1S), Y(2S), Y(3S). • Production of cc, hc • Extensive studies of Bc, X(3872)

  4. Monte Carlo Tools • PYTHIA 6.3 for the studies shown here: • Production of J/y through Color Single Model. • PYTHIA 6.4 for the current Monte Carlo productions: • With Color Octet Model added, tuned to reproduce CDF measurements see note CERN-LHCb-2007-042. • EvtGen for decays: • Generator package which allows to have a detailed description of b J/y X decays. • Also allows correct angular correlations in decays of polarized particles. • PHOTOS for radiative corrections.

  5. Monte Carlo J/y Samples LHCb MC (14 TeV, Pythia 6.3) 3<h<5 • In LHCb acceptance (3<h<5, pT<7 GeV/c): • s(pp  prompt J/y X) x Br(J/y m+ m-) = 2.7 mb • s(pp  (b  J/y X) X') x Br(J/y m+ m-) = 0.15 mb NB: the analysis presented here does not depend on the exact spectrum of the J/y.

  6. J/y  m+ m- Reconstruction • Selection based on positive muon identification of the two m, cut on the m transverse momentum pT>0.7 GeV/c and on the quality of the m+m- vertex. • Invariant mass plot on fully simulated minimum bias events (with all background included): • Mass resolution: 11.0 ± 0.4 MeV/c2, • S/B=17.6 ± 2.3 in ±3s mass window, • 1.3x109 reconstructed after L0 trigger J/y for 1 fb-1 ( =14 TeV) • Or 0.65x106 for 1 pb-1at = 7 TeV LHCb Minimum Bias Monte Carlo (14 TeV)

  7. Separating prompt J/y from J/y from b • Use pseudo-propertime: • Prompt component characterized by peak at 0, • Exponential decay for J/y from b component, • Long tail due to association of the J/y to a not-related primary vertex. LHCb Inclusive J/y Monte Carlo (14 TeV) • Combined mass/pseudo-propertime fit will allow to measure both prompt and J/y from b production cross sections in h and pT bins: • 4 pseudo-rapidity h bins, 3 < h < 5. • 7 transverse momentum bins pT, pT<7 GeV/c.

  8. Example: fit on MC at = 14 TeV • Sample corresponding to 0.8 pb-1, = 14 TeV • Signal: Inclusive J/y sample • Background: toy Monte-Carlo reproducing behaviour (mass and pseudo-lifetime) seen on the Minimum Bias sample. LHCb Inclusive J/y Monte Carlo + Toy MC (14 TeV) • Results (J/y with 3<h<5 and pT<7 GeV/c): • s(prompt J/y) x Br(J/y → m+m-) = 2597  12 (stat)  24 (eff) nb [Input: 2667 nb] • s(J/y from b) x Br(J/y → m+m-) = 161  4 (stat)  2 (eff) nb [Input: 153 nb] Statistical error at maximum 10% in each of the analysis bin, for 5pb-1 of data at = 7 TeV.

  9. Systematics from J/y polarization • Acceptance as a function of cosq, q = helicity angle • Large LHCb detector acceptance dependance on assumed initial polarization of J/y.

  10. Systematics from J/y polarization • Study the effect of ignoring the polarization dependance of the efficiency (J/y are not polarized in the LHCb Monte Carlo) a«data» Measured cross-section, assuming a=0 Input s«data» 0 2758 nb ± 27 nb 2820 nb +1 2738 nb ± 27 nb 3190 nb -1 2787 nb ± 28 nb 2286 nb • Systematic error up to 25 % when ignoring polarization. • Polarization will be measured (in a second step): • in bins of h and pT, • separating prompt and J/y from b, • With full angular analysis, in different reference frames.

  11. y(2S) m+m- • Similar performances than J/y: • Mass resolution: 13 MeV/c2 • S/B = 2 • Number of reconstructed y(2S) = 2-4 % of the number of reconstructed J/y. • Measurement of the ratio s(y(2S))/s(J/y), as a function of pT, separating prompt and from b. • Polarization effects complicate also the measurement: systematic error up to 22% on the cross section ratio.

  12. Y(1S) → m+m- • Loose muon ID selection, and transverse momentum requirement (pT(m)>1.5 GeV/c). • L0 trigger efficiency: 96 % • Mass resolution: 37 MeV/c2 • Similar reconstruction and resolutions will be obtained for the Y(2S) and Y(3S) states: this will allow to separate the 2 Upsilon states. • Goal is to measure cross-sections and polarization for all di-muon states, as a function of pT. LHCb Inclusive Y Monte Carlo (14 TeV)

  13. cc reconstruction • J/y selection, adding a photon detected in the ECAL with pT(g)>500 MeV/c. • Dm=m(J/y g)-m(J/y) distribution obtained on fully simulated events containing on J/y. Since the J/y background is very low, the plot contains a large fraction of the total background. • Dm resolution = 27 MeV/c2. LHCb Inclusive J/y Monte Carlo (14 TeV) cc2 cc1

  14. cb2 reconstruction • Reconstruction of cb2(1P) → Y(1S) g • Photon detected in ECAL, with pT(g) > 500 MeV/c • Mass resolution: 47 MeV/c2 LHCb Inclusive Y Monte Carlo (14 TeV)

  15. hc reconstruction • Besides di-muon states, LHCb detector performances will allow to study other states though hadronic decay modes. • Reconstruction of hc → hcg is difficult (E(g)~500 MeV in the hc rest frame). • Hadronic decay channels look promising: hc → pp, hc → f K+ K-, hc → fp+p-. • In particular, hc → pp probably visible with first year data, which will give access to s(hc)xBr(hc → pp) relative to s(J/y)xB(J/y → pp). LHCb Signal Monte Carlo + Toy MC (10 TeV) • Expected pp mass distribution: • Assuming Br(hc → pp) = 0.12 %, • Toy Monte Carlo for background, reproducing background seen on fully simulated minimum bias events, • 100 pb-1 at = 10 TeV J/y cc0 hc cc1 cc2 m(pp) (GeV/c2)

  16. X(3872) and Z(4430) • Reconstruction of X(3872) → J/yp+p- (and the control channel y(2S) → J/yp+p-), prompt or from b: systematic study of this state. • Expect 1800 reconstructed B → X(3872) K, with 2 fb-1 at = 14 TeV, allowing to disentangle unknown quantum number JPC: 1++/2-+. • Reconstruction of X(3872) → J/yp+p- (and the control channel y(2S) → J/yp+p-), prompt or from b: systematic study of this state. • Expect 1800 reconstructed B → X(3872) K, with 2 fb-1 at = 14 TeV, allowing to disentangle unknown quantum number JPC: 1++/2-+. LHCb Generator Only signal 1++/2-+ • Similar studies for B0 →Z(4430)+( →y(2S)p+)K- • About 6200signal events can be selected from 2 fb-1of data at =14 TeV, assuming B(B0 →Z(4430)+K-)xB(Z(4430)+→y(2S)p+) = 4.1x10-5 • Possible to confirm the Belle discovery with about 100 pb-1of data at = 7 TeV.

  17. Bc • Measurement of mass, lifetime and production cross section using the decay modes: • Bc+ → J/yp+ assuming s(Bc+)=0.4 mb, and Br(Bc+ → J/yp+) =0.13 %, expect 310 signal events for 1 fb-1 of data at = 14 TeV. • Production cross section relative to B+(→ J/y K+) • Bc+ → J/ym+ X: signal yield one order of magnitude larger, production cross section measurement possible with 2010 data. 1 fb-1, 14 TeV

  18. Conclusions • LHCb will measure production cross sections and polarization of di-muon states, in the LHCb acceptance: 3 < h < 5, pT<7 GeV/c. • Other quarkonium states will also be looked at: hc, cc, cb, Bc. • LHCb performances will allow to also study associate productions: J/y+J/y, J/y+cc, either reconstructing D or tagging it with a displaced e or m. • Study of « exotic » states: X(3872) and Z(4430). • Similar states can also be searched in (Quarkonium p+p-) mass spectra: Yb → Y(1S) p+p-, Bc** → Bc+p+ p-.

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