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Open-charm and J/ ψ production at the ALICE experiment

Open-charm and J/ ψ production at the ALICE experiment. Pietro Cortese Universit à del Piemonte Orientale and INFN Alessandria, Italy on behalf of the ALICE Collaboration. Outline. Open-charm in p-p collisions D meson reconstruction in ALICE central barrel

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Open-charm and J/ ψ production at the ALICE experiment

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  1. Open-charm and J/ψproduction at the ALICE experiment PietroCortese Università del Piemonte Orientale and INFN Alessandria, Italy on behalf of the ALICE Collaboration Purdue University, Jan. 6, 2011 Pietro Cortese

  2. Outline Open-charm in p-p collisions • D meson reconstruction in ALICE central barrel • D0 and D+ production measurement • Single muons and single electrons J/ψ in p-p • First results: J/+- and J/e+e- in p-p collisions at 7 TeV Perspectives for Pb-Pb Purdue University, Jan. 6, 2011 Pietro Cortese

  3. The ALICE experiment • ALICEis the dedicated heavy-ion experiment at the LHC Pb-Pb collisions: main focus of the experiment • QGP studies p-p collisions: important aspect of the physics program • reference for heavy-ion collision studies • p-p physics Muon spectrometer (-4<<-2.5) Central barrel (||<0.9) Tracking: 10 CPC planes Trigger: 4 RPC planes Tracking: ITS,TPC,TRD PID: ITS,TPC,TRD, TOF,EMCAL,PHOS Trigger: ITS, TOF, TRD… Event characterization: V0, T0, FMD, ZDC

  4. Charm in pp at LHC • Important test of pQCD in a new energy domain (3.5  sTEVATRON) • c production on the upper edge of prediction, at Tevatron and RHIC • Ultimately, ALICE aims at measuring charm production below pT~1 GeV/c • Probe gluon PDF down to xBjorken ~ 10-4 • Does the factorization approach still hold? Gluon saturation? • Reference for heavy quark quenching studies in Pb-Pb PHENIX, STAR, 0.2 TeV, c,b e+X CDF, 1.96 TeV, D* CDF, PRL91 (2003) 241804 FONLL: Cacciari, Nason GM-VFNS: Knihel et al. Purdue University, Jan. 6, 2011 Pietro Cortese

  5. D meson reconstruction in ALICE • Main selection: displaced-vertex topology • Example: D0K-p+ • good pointing of reconstructed D momentum to the primary vertex • pair of opposite-charge tracks with large impact parameters • K ID in TPC+TOF helps in rejecting background at low pt TPC TOF Purdue University, Jan. 6, 2011 Pietro Cortese

  6. Signals: D0K-p+ 108events 1-12 GeV in 7 bins Purdue University, Jan. 6, 2011 Pietro Cortese

  7. Signals: D+K-p+p+ 108 events; 2-12 GeV in 6 bins Purdue University, Jan. 6, 2011 Pietro Cortese

  8. Corrections for D cross sections • Corrections: 1) efficiency • 1%  10% from low to high pt • factor 2 larger for B feed-down D mesons D0 D+ • Corrections: 2) feed-down BD: ~20-25% • for now, subtract using FONLL BD predictions • FONLL describes well B production at Tev and LHC • with full 2010 statistics will be corrected based on data (D displacement to vertex, à la CDF) Purdue University, Jan. 6, 2011 Pietro Cortese

  9. D0 and D+ ds/dpt, |y|<0.5, pp 7 TeV • 2 < pt < 10 GeV/c, with 1.4 nb-1 (~20% of 2010 statistics) • Total systematic error 20-40% pt-dep. + 10% on normalization • pQCD predictions (FONLL and GM-VFNS) compatible with our data Purdue University, Jan. 6, 2011 Pietro Cortese

  10. Soft pion reconstruction down to 100 MeV/c using ITS as standalone tracker Evaluation of systematics ongoing Coming soon: D*+ D*+D0p+ 2-12 GeV/c Purdue University, Jan. 6, 2011 Pietro Cortese

  11. D*+ dN/dpt and D ratios • Only statistical errors • Shape compares well with pQCD (FONLL) ee, H1, ZEUS: JHEP07 (2007) 074 CDF: PRL 91 (2003) 241804 Purdue University, Jan. 6, 2011 Pietro Cortese

  12. Other ongoing analyses: D0K-p+below 1 GeV/c D0K-p+p-p+ Lc+pK-p+ (ct = 60 mm) p/K/p ID crucial here! Ds+K-K+p+ Purdue University, Jan. 6, 2011 Pietro Cortese

  13. Heavy flavour in the muon spectrometer In p-p collisions charm and beauty decays are the main source of single muons with pT>2 GeV/c in -4<η<-2.5 Monte-Carlo • Analysis chain: • Remove beam-gas (global event selection) • Remove punch-through hadrons and low-pT secondary µ • → muon trigger • Remove background decay µ • → models and MC (present), exploit correlation with vertex displacement • Correct for acceptance/efficiency • Estimate the cross-section PurdueUniversity, Jan. 6, 2011 Pietro Cortese

  14. Single muons from HF decays Conservative systematics • pQCD calculations are in agreement with data within the systematic errors • the shape of the distribution is well reproduced • Analysis on the full statistics will improve the pT reach • data-driven methods will improve the background subtraction (expecially important at low-pT) Purdue University, Jan. 6, 2011 Pietro Cortese

  15. Coming soon: electrons from HF decays After TOF cut Electron ID with TOF time and TPC dE/dx cut (TRD and EMCAL will join soon) Contamination from <1% to 15% at 4 GeV/c Inclusive electron spectrum compared with cocktail of sources (conversion electrons from π0 decays are derived from data) HF signal above the electron cocktail Purdue University, Jan. 6, 2011 Pietro Cortese

  16. Quarkonium measurement in ALICE • Quarkonium in ALICE can be measured in two ways: • in the central barrel in the e+e- channel (|y|<0.9) • in the forward spectrometer in the +- channel (2.5<y<4) • 3 sources of J/ 1) Direct production 2) Feed down from heavier cc states 3) J/ from b-hadron decay Prompt J/ radiative decay cJ/ in the central barrel can be identified in the central barrel, good impact parameter resolution (r < 60 m for pT>1 GeV/c) • forward detection more difficult •  3-muon events • B cross section from single- • Semileptonic decays of B pairs Preliminary ALICE results refer to inclusive J/ production

  17. J/  +- : p+p @ √s=7 TeV sample • Data sample: • Integrated luminosity = 13.6 nb-1, corresponding to data • collected between May and July 2010 (~ 10-15% of the 2010 • total statistics) • Trigger: muon in the forward spectrometer, in coincidence • with minimum bias interaction trigger • Run Selection: • Runs selected according to quality checks on the stability of the • muon spectrometer tracking and trigger performances • Event Selection: • at least one vertex reconstructed in the silicon pixel detector • at least one muon reconstructed in the tracking and trigger chambers satisfying the trigger algorithm • cut on the track position at the end of the front absorber (20<abs<90) rapidity window: 2.5<y<4 transverse momentum window0<pT<8 GeV/c (statistics)

  18. J/  +- : signal extraction • The number of J/ is extracted from a fit to the invariant mass spectrum, using Crystal Ball shape for thesignal(J/ and ’) Sum of twoexponentials for thebackground The available J/ statistics, used for the cross section determination is NJ/ = 1909 ± 78 S/B (2.9<M<3.3) ~ 2.4 With a suitable pT cut (smaller background), also the (2S) signal is visible, but with a much lower statistical significance

  19. J/  +- : acceptance  efficiency • Inputs: • realistic y and pT J/ distributions • detector status and efficiency pT CDF extrapolation y  CEM calculation • Study of differential distributions: 1D acceptance correction • Main source of uncertainty: unknown J/ψ polarization Good coverage down to pT =0! Polarization in Helicity reference frame

  20. NJ/ = 123  15 J/  e+e- : p+p @ √s=7 TeV sampleand signal extraction • Analysis is based, for the • moment, on a smaller data • sample wrt to J/+- •  L=4.0 nb-1 (~15% of 2010 stat.) Track selection: |e+,e-|<0.88 and |yJ/|<0.88 pT e+,e- > 1 GeV/c TPC-based PID

  21. Integrated cross section(s) • The ALICE results, integrated pT, are: • J/ψ(-0.88<y<0.88)=12.952.15(stat)2.32(syst)+1.26-2.55(syst. pol) μb • J/ψ(2.5<y<4)=7.250.29(stat)0.98(syst)+0.87-1.50(syst. pol) μb (polarization-related errors calculated in the helicity frame) Very good agreement with the corresponding LHCb result obtained at forward rapidity (ICHEP2010) • Main sources of systematic errors are: • Unknown polarization • Luminosity determination • In the dielectron channel: • track quality cuts and PID • In the dimuon channel: • signal extraction and trigger efficiency

  22. (ICHEP 2010) (stat errors only) Differential cross section: dJ//dpT (2.5<y<4) • Very good agreement with the LHCb result in the same rapidity range • Other sources of point to point systematic errors • (signal extraction, acceptance input) vary between 3 and 10% • (not yet fully evaluated)

  23. Differential cross section: dJ//dy (pT>0) • ALICE can measure the distribution of the inclusive J/ productionin a wide rapidity range • coverage reaches zero pTat both central and forward rapidities

  24. Preliminary comparison(s) • Model calculations: • R.Vogt, Phys. Rev. C 81 (2010) 044903 • J.P. Lansberg, arXiv:1006.2750 • CMS: pT-integrated cross section 1.6<y<2.4 from (arXiv:1011.4193) • ATLAS: d/dy 1.5<y<2.25, ATLAS-CONF-2010-062 • LHCb: d/dy 2.5<y<4 from LHCb-CONF-2010-010

  25. √s-dependence of inclusive J/ • NLO calculation for cc by Mangano et al., normalized to the CDF point • Same √s-dependence for the inclusive J/ cross section

  26. November 2010:moving from p-p to Pb-Pb • Higher occupancy with respect to Pb-Pb • Re-tuning of reconstruction parameters

  27. First J/ signal from Pb-Pb collisions • Expected final statistics for Pb run  O(103) • Extract RAAin (some) centrality bins

  28. Prospects for Pb-Pb Detector perfoms well! • ~ 45 M Pb-Pb inelastic events on tape (~6 mb-1) • ~ 4.5 M in 0-10% most central Purdue University, Jan. 6, 2011 Pietro Cortese

  29. Summary on Open-Charm • D0 and D+ meson cross section at mid-y • measured in 2-10 GeV/c • pQCD predictions agree with data • Ongoing: • increase statistics • extend to lower and higher pt • B-feed-down from data • will allow to reduce systematics • Coming soon: D*+ • D*+ , other D0 channel, Ds, Lc • Single electrons • Will serve as a reference for Pb-Pb studies Purdue University, Jan. 6, 2011 Pietro Cortese

  30. On Quarkonia ALICE has measured inclusive J/ production Over a wide rapidity range (-0.88<y<0.88, 2.5<y<4) With good coverage down to pT=0 Next steps, in the dimuon channel, with higher statistics: Extend the analysis to (2S) and to bottomoniumstates Integrated and differential J/ polarization study Pb-Pb run completed J/ signal observed Next step: nuclear modification factor vs centrality

  31. D backup slides Purdue University, Jan. 6, 2011 Pietro Cortese

  32. Trigger & Data sample, pp 7 TeV • “Minimum bias”, based on interaction trigger: • SPDorV0-A or V0-C • at least one charged particle in 8 h units • ~95% of sinel • read out all ALICE • single-muon trigger: • forward muon in coincidence with Min Bias • read out MUON, SPD, V0, FMD, ZDC • Both activated in coincidence with the BPTX beam pickups • Since March 31st 2010, collected • ~8.5×108 minimum bias triggers • ~1.3×108 muon triggers • Results presented today based on ~108 minimum bias triggers Purdue University, Jan. 6, 2011 Pietro Cortese 32

  33. D0 Kp D+ Kpp D*  D0p Ds KKp D0 Kppp LcpKp TOF (PID) K p TPC (tracking, PID dE/dx) ITS (tracking & vertexing) Charm reconstruction in the ALICE barrel, |h|<0.9 Purdue University, Jan. 6, 2011 Pietro Cortese

  34. D meson reconstruction in ALICE • Main selection: displaced-vertex topology • Tracking and vertexing precision is crucial here • Inner Tracking System (ITS) was aligned using cosmics and collisions • current resolution for pixels: 14 mm (nominal: ≈11 mm) • rf impact parameter resolution of 75 mm at 1 GeV/c • particle-mass dependence well understood 7.8 cm The inner pixel layer proton kaon pion Purdue University, Jan. 6, 2011 Pietro Cortese

  35. From signals to cross sections • Corrections: 1) efficiency 2) feed-down BD • then, normalization to cross section, using sMB from VdM scan • Detector response well described in MC D0: mass resolution cut variables D+: Purdue University, Jan. 6, 2011 Pietro Cortese

  36. FONLL vs. data, beauty production 2-7 TeV CDF, B CMS, arXiv:1011.4193 FONLL, MC@NLO: Cacciari, Frixione, Mangano, Nason and Ridolfi, JHEP0407 (2004) 033 Purdue University, Jan. 6, 2011 Pietro Cortese

  37. D0 and D+ dN/dpt • Only statistical errors • Shape compares well with pQCD (FONLL) Purdue University, Jan. 6, 2011 Pietro Cortese

  38. D mesons: from signals to cross sections • Corrections: feed-down BD: ~15-20% • main method (“Nb-subtraction”): FONLL input is only the DfromB cross section • where: • second method (“prompt fraction fc”): FONLL input is the ratio of prompt to total D meson cross sections • use the total envelope of the • error bands (from FONLL) of two • methods as a systematic error Purdue University, Jan. 6, 2011 Pietro Cortese

  39. J/ψ backup slides Purdue University, Jan. 6, 2011 Pietro Cortese

  40. Acceptance  efficiency J/  e+e- : acceptance  efficiency • Also in the electron channel, very good coverage down to pT= 0

  41. Systematic errors Muons Electrons

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