1. 1 Charmonium production with the ALICE experiment @ LHC Fiorella Fionda University & INFN - Bari for the ALICE Collaboration WISH – Catania (8 – 10 September 2010)

2. 2  Motivations for charmonium studies: p-p collisions p-nucleus and nucleus-nucleus collisions  Status of ALICE analyses in p-p and expectations for Pb-Pb central barrel ( J/   e + e - ) muon spectrometer ( J/   μ + μ - )  Conclusions Outline

3. 3  Several models available: CSM, NRQCD (COM), CEM  no model describes cross section and polarization simultaneously Charmonium in p-p collisions: open issues COM with CDF data: cross section well reproduced failing to predict polarization CSM (+s-channel cut) with PHENIX data: cross section better reproduced at forward rapidity problems to predict polarization at forward rapidity

4. 4  Historical prediction: J/  suppression, i.e. charmonium is melt in deconfined medium by the Color Debye Screening [T.Matsui & H. Satz PLB178 416 (1986)] Charmonium in Heavy Ion collisions  p-nucleus are very important to correct for Cold Nuclear Matter (CNM) effects (nuclear shadowing/anti-shadowing, gluon saturation, Cronin effect…)

5. 5  Hard production mechanism: charmonia are produced at the early stage of the collision in hard partonic scattering  Soft production mechanism: J/  suppression observed at RHIC and SPS suggests a regeneration for charmonia  similar suppression at RHIC and SPS  larger suppression at larger rapidities at RHIC Charmonium in Heavy Ion collisions Regeneration models: coalescence [Phys. Rev. C63 (2001) 054905]: deconfined q and q-bar pairs are recombined in QGP statistical hadronization [Phys. Lett. B490 (2000) 196]: quarkonium production takes place at the phase boundary with statistical weights (no connection with deconfinement) H. Satz, Palaiseau 31/07/2010

6. 6  melting of  (1S) only at LHC  regeneration for  states is not expected   (2S) behaves as J/  T D  (2S) ~ T D J/  ) and is not affected by regeneration   (2S) measurement fundamental for undestanding J/  suppression vs recombination  the competition between the two mechanisms determines the final J/  abundance Quarkonia in Heavy Ion collisions  Regeneration vs suppression @ LHC ?  Bottomonia measurement possible @ LHC H. Satz, J. Phys. G 32, R25 (2006)

7. 7 ALICE detector view  Central barrel (|η|<0.9): Electronic channel J/   e + e -  ’   e + e -  C  γ e + e -  Muon spectrometer (-4 < η < -2.5) Muonic channel J/   μ + μ -  ’  μ + μ - ALICE:  down to p T = 0  central and forward rapidity regions

8. 8 Strategies of charmonium analyses  CENTRAL BARREL:  good tracks quality: tracking with ITS+TPC (+TRD)  electron identification: energy loss in TPC time-of-flight from TOF to reject proton and kaon at low momentum (p<1.3GeV) transition radiation signal from TRD (coming)  Secondery vertex for displaced J/  coming from B- hadron decays  MUON SPECTROMETER:  Absorbers (to filter out the muons): Front absorber (carbon ~2m, concrete~1.5m, steel~0.5m ): limits scattering and energy loss in muon path Muon Filter(Fe): suppresses the hadron rate on trigger chambers Beam shield (Pb and W, along pipe): protects detectors  Tracking: 5 stations of Cathode Pad Chambers used; measured spazial resolution in beam test ~50 μm (< 100μm required)  Trigger chambers: RPCs planes used; reduce the background from remaining hadrons and secondary muons produced in the absorber

9. 9 Trigger and collected data  “Minimum bias” ( CINT1B, interaction trigger ) SPD or V0A or V0C: at least one charged particle in 8 η units  “Single muon trigger” (CMUS1B) forward muon in coincidence with minimum bias read out: MUON, SPD,V0, FMD, ZDC  Activated in coincidence with the BPTX beam pickups 694M minimum bias p-p collision @ 7 TeV (CINT1B) 47M of single muon trigger (CMUS1B) (until September the 1th, 2010)

10. 10 J/   e + e - mass peak  110M m.b events @ 7TeV ( ~ 1/6 of present statistic)  Single track selection: #cluster TPC > 120 inner (SPD) pixel layer p T (e ± ) > 1GeV/c  PID (only TPC used) 2 σ band electron inclusion 2 σ band pion, proton exclusion TRD coming soon p T (J/  ) > 0, |y|<0.8 Fit: Cristal Ball (signal) + exponential (background)

11. 11 Displaced J/  from Beauty  Analysis is based on a simultaneous 2D fit of 1.the invariant mass spectrum 2.an “impact parameter” to separate prompt from detached J/e.g. pseudo- proper decay time (à la CDF) D.Acosta et al Phys. Rev. D 71 (2005) 032001 10 9 MC events pp @ 14 TeV CDF p T >5 Gev x [m] -2000-10000100020003000 10 2 10 1 Entries/100m

12. 12 Expectations in Pb-Pb for J/   e + e -  2∙10 7 central (10%) Pb-Pb collisions @ √s NN =5.5TeV (and nominal L 0 ) at mid rapidity electron identification with TPC and TRD Expectations for Pb-Pb 2010: √s NN = 2.75TeV L ~ 10 25 cm -2 s -1 10 7 m.b. collisions possible 10 6 central (0-10%) collisions assuming same performances as in p-p and scaling with N bin  ~ 800 J/psi for central collisions  centrality dependence of yield possible

13. 13 J/   μ + μ - mass peak  Alignment of tracking chambers is a crucial point for J/  measurement (exact same data used for both plots) no alignment  σ J/  ~ 230MeV first alignment (with straight tracks at B=0)  σ J/y ~91MeV nominal resolution expected  σ J/y ~70MeV  fit: sum of a Crystal-Ball for the J/  + 2 exponential (background)

14. 14 Transverse momentum dependence  resolution on the J/  invariant mass vs p T compared with MC (residual misalignament is included in the simulations)  fit: gaussian (signal) + exponential (background)

15. 15 Data vs Monte Carlo comparison  distributions of p T (J/  ) and y(J/  ) corrected for acceptance and efficiency p T (J/  ) extrapolated from CDF measurements y evaluated by CEM no polarization included (λ=0) MC

16. 16 and vs energy  Fit of p T (J/  ) distribution (to extract and ), by the function proposed by Yoh et al., PRL 41 (1978) 684, and used in other experiments error bars include systematics from the fit function

17. 17  ’ observed in the dimuon channel  Collected statistics increasing fast…  …and  ’ peak showing up fit: sum of a Crystal-Ball for the J/ , a Gaussian for the  ' and 2 exponential functions for the background (maximum-likelihood used for the fit)

18. 18 central peripheral  Expected performances with nominal LHC running conditions (L=5∙10 26 cm -2 s -1, time=10 6 s): Expectations in Pb-Pb for J/   μ + μ - Expectations for Pb-Pb 2010: √s NN = 2.75TeV Assuming: L ~ 10 25 cm -2 s -1 10 6 sec data taking J/  (2S)  (1S) N.ev1.5 10 4 4 10 2 1.5 10 2

19. 19 Conclusions  ALICE is measuring quarkonium production in p-p collision @ 7TeV at central and forward rapidity down to p T =0  The experiment is currently taking data with satisfactory detector performance  Quarkonium measurements in ALICE are feasible for the first Pb-Pb run @ LHC scheduled in November 2010

20. 20 Back-up

21. 21 LHC running conditions * L max (ALICE) = 10 31 ** L int (ALICE) = 0.5 nb -1 /year  + other ions (Sn, kr, O) & energies (e.g. p-p @ 5.5TeV)

22. 22 Detector configuration 2009/2010  ITS, TPC, TOF, HMPID, MUON, V0, T0, FMD, PMD, ZDC (100%)  TRD (7/18)  EMCAL (4/12)  PHOS (3/5)

23. 23  ’ observed in the dimuon channel  CMUS1B events accepted  No physiscs selection applied  At least one of the two tracks matches a muon trigger tracks  fit is a sum of a Crystal-Ball for the J/psi, a Gaussian for the psi' and 2 exponential functions for the background (maximum- likelihood used for the fit) Adding cut p T (J/Psi) > 3GeV psi’ peak became more evident

24. 24 Muon trigger - principle  Muon p T cut helps reducing the background from light meson decays p T estimated from deviation in magnetic field, measured by the trigger stations several trigger signals: Single , UnLike and Like- Sign dimuon high and low p T Fast decision (<1μs) for p T cut: High p T (~2 GeV) for  's Low p T (~1GeV) for J/  For the moment (low luminosity), use for data taking the lowest possible trigger threshold  p T = 0.5 GeV/c

25. 25 Charmonium in p-nucleus collisions  CNM effects ≡ modification of heavy quarkonia production in collisions involving heavy nuclei with respect to p+p collisions in absence of a quark-gluon plasma  In the program for ALICE (not as first priority): for p-Pb @ √s = 8.8TeV Eskola, Paukkunen, Salgado, JHEP 0904:065 (2009) EKS98 CGC, k T kick power CGC, k T kick gauss. C. Hadjidakis, nPDF workshop, Annecy 2010 Inclusion of CGC-related effects: systematically lower ratios at all y and a steeper variation of R p-Pb as a function of p T (again with large uncertainties) Nuclear shadowing: large uncertanties depending on the chosen set of PDF

26. 26 Expectations in Pb-Pb for J/   e + e - √s NN = 2.75TeV L ~ 10 25 cm -2 s -1 10 7 m.b. collisions possible 10 6 central (0-10%) collisions assuming same performances as in p-p (1 J/  for 2M events) scaling with N bin (~1600)