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

2 Outline Open-charm in p-p collisions D meson reconstruction in ALICE central barrel D 0 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 ALICE is the dedicated heavy-ion experiment at the LHC p-p collisions: important aspect of the physics program Pb-Pb collisions: main focus of the experiment reference for heavy-ion collision studies p-p physics Central barrel (| |<0.9) Muon spectrometer (-4< <-2.5) Tracking: ITS,TPC,TRD PID: ITS,TPC,TRD, TOF,EMCAL,PHOS Trigger: ITS, TOF, TRD… Tracking: 10 CPC planes Trigger: 4 RPC planes QGP studies Event characterization: V0, T0, FMD, ZDC

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

5 D meson reconstruction in ALICE Main selection: displaced-vertex topology Example: D 0 K - + 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 p t Purdue University, Jan. 6, 2011 Pietro Cortese TPC TOF

6 Signals: D 0 K - Purdue University, Jan. 6, 2011 Pietro Cortese 10 8 events 1-12 GeV in 7 bins

7 Signals: D + K - Purdue University, Jan. 6, 2011 Pietro Cortese 10 8 events; 2-12 GeV in 6 bins

8 Corrections for D cross sections Purdue University, Jan. 6, 2011 Pietro Cortese Corrections: 1) efficiency 1% 10% from low to high p t factor 2 larger for B feed- down D mesons D0D0 D+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)

9 Purdue University, Jan. 6, 2011 Pietro Cortese 2 < p t < 10 GeV/c, with 1.4 nb -1 (~20% of 2010 statistics) Total systematic error 20-40% p t -dep. + 10% on normalization pQCD predictions (FONLL and GM-VFNS) compatible with our data D 0 and D + d /dp t, |y|<0.5, pp 7 TeV

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

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

12 Other ongoing analyses: Purdue University, Jan. 6, 2011 Pietro Cortese D 0 K D s + K - K + + D 0 K - + below 1 GeV/c c + pK - + (c = 60 m) /K/p ID crucial here!

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

14 Single muons from HF decays 14 Purdue University, Jan. 6, 2011 Pietro Cortese 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-p T ) Conservative systematics

15 Coming soon: electrons from HF decays 15 Purdue University, Jan. 6, 2011 Pietro Cortese 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 π 0 decays are derived from data) After TOF cut HF signal above the electron cocktail

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/ can be identified in the central barrel, good impact parameter resolution ( r 1 GeV/c) Preliminary ALICE results refer to inclusive J/ production forward detection more difficult 3-muon events B cross section from single- Semileptonic decays of B pairs radiative decay c J/ in the central barrel

17 J/ + - : 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 (2 0 < abs <9 0 ) rapidity window: 2.5<y<4 transverse momentum window 0<p T <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 the signal (J/ and ) Sum of two exponentials for the background The available J/ statistics, used for the cross section determination is N J/ = 1909 ± 78 S/B (2.9<M<3.3) ~ 2.4 With a suitable p T cut (smaller background), also the (2S) signal is visible, but with a much lower statistical significance

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

20 J/ e + e - : s=7 TeV sample and signal extraction Track selection: | e+,e- |<0.88 and |y J/ |<0.88 p T e+,e- > 1 GeV/c TPC-based PID N J/ = Analysis is based, for the moment, on a smaller data sample wrt to J/ + - L=4.0 nb -1 (~15% of 2010 stat.)

21 Integrated cross section(s) The ALICE results, integrated p T, are: J/ψ (-0.88<y<0.88)= (stat) 2.32(syst) (syst. pol) μb J/ψ (2.5<y<4)= (stat) 0.98(syst) (syst. pol) μb Very good agreement with the corresponding LHCb result obtained at forward rapidity (ICHEP2010) (polarization-related errors calculated in the helicity frame) 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 Differential cross section: d J/ /dp T (2.5<y<4) Very good agreement with the LHCb result in the same rapidity range (ICHEP 2010) (stat errors only) 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 (p T >0) ALICE can measure the distribution of the inclusive J/ production in a wide rapidity range coverage reaches zero p T at both central and forward rapidities

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

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(10 3 ) Extract R AA in (some) centrality bins

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

29 Summary on Open-Charm Purdue University, Jan. 6, 2011 Pietro Cortese D 0 and D + meson cross section at mid-y measured in 2-10 GeV/c pQCD predictions agree with data Ongoing: increase statistics o extend to lower and higher p t B-feed-down from data will allow to reduce systematics Coming soon: D* + D* +, other D 0 channel, D s, c Single electrons Will serve as a reference for Pb-Pb studies

30 On Quarkonia Next steps, in the dimuon channel, with higher statistics: Extend the analysis to (2S) and to bottomonium states Integrated and differential J/ polarization study Pb-Pb run completed J/ signal observed 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 p T =0 Next step: nuclear modification factor vs centrality

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

32 Minimum bias, based on interaction trigger: SPD or V0-A or V0-C o at least one charged particle in 8 units o ~95% of inel 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 31 st 2010, collected ~8.5×10 8 minimum bias triggers ~1.3×10 8 muon triggers Results presented today based on ~10 8 minimum bias triggers Trigger & Data sample, pp 7 TeV 32 Purdue University, Jan. 6, 2011 Pietro Cortese 32

33 TPC (tracking, PID dE/dx) TOF (PID) ITS (tracking & vertexing) K D 0 K D + K D* D 0 D s KK D 0 K c Kp Charm reconstruction in the ALICE barrel, | |<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 m (nominal: 11 m) r impact parameter resolution of 75 m at 1 GeV/c particle-mass dependence well understood Purdue University, Jan. 6, 2011 Pietro Cortese The inner pixel layer 7.8 cm proton kaon pion

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

36 Systematic Uncertainties Purdue University, Jan. 6, 2011 Pietro Cortese Total systematic 20-40% p t -dep. + 10% on normalization (VdM scan) Main systematic error: B feed-down from FONLL+MC conservative estimate of error o FONLL uncertainty (small for B) o two methods considered (subtr. of D from B, fraction of prompt D) to be reduced using data-driven method with full 2010 statistics D0D0 D+D+

37 Purdue University, Jan. 6, 2011 Pietro Cortese FONLL vs. data, beauty production 2-7 TeV CDF, B 37 FONLL, Cacciari, Frixione, Mangano, Nason and Ridolfi, JHEP0407 (2004) 033 CMS, arXiv:

38 Purdue University, Jan. 6, 2011 Pietro Cortese 38 Only statistical errors Shape compares well with pQCD (FONLL) D 0 and D + dN/dp t

39 D mesons: from signals to cross sections Purdue University, Jan. 6, 2011 Pietro Cortese 39 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

40 Purdue University, Jan. 6, 2011 Pietro Cortese Prospects for Pb-Pb NLO predictions (charm & beauty) ~ factor 2 uncertainty from NLO and shadowing (Pb-Pb) system : s NN : Pb-Pb (0-5%) 5.5 TeV Pb-Pb (0-5%) 2.76 TeV 90 / / 2 MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295. EKS98, EPS08: Eskola et al., EPJC9 (1999) 61; JHEP07 (2008) 102 Energy loss based predictions: factor 5 suppression for D mesons (R AA ~0.2) Wicks, Gyulassy, Last Call for LHC Predictions workshop ALICE charged particles R AA arXiv: v1

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

42 J/ e + e - : acceptance efficiency Also in the electron channel, very good coverage down to p T = 0 Acceptance efficiency

43 Systematic errors Source of systematic error Uncertainty on signal extraction7.5 % p T and y shapes in the MC2% Trigger efficiency4% Tracking efficiency2% Normalization10 % Total systematic error13.5 % Source of systematic error Kinematics<1% Track quality,#clusters TPC10% PID cuts10% Signal extraction range4% Normalization10 % Total systematic error18 % Muons Electrons polarization =-1=1 Helicity-20%+10% Collins-Soper-25%+12% polarization =-1=1 Helicity-21%+12% Collins-Soper-31%+15%