1. 1 Marcello Lunardon - BEACH 2006, Lancaster, UK The 7th International Conference on Hyperons, Charm And Beauty Hadrons - BEACH 2006 Lancaster, July 2-8 / 2006 Open Heavy Flavour Detection in ALICE Marcello Lunardon for the ALICE collaboration

2. 2 Marcello Lunardon - BEACH 2006, Lancaster, UK Contents Why heavy ion collisions at the LHC Heavy flavour at the LHC with ALICE The ALICE detector Exclusive charm reconstruction in the hadronic decays Inclusive beauty detection in the semi-leptonic channels Conclusions Open Heavy Flavour Detection in ALICE

3. 3 Marcello Lunardon - BEACH 2006, Lancaster, UK Why heavy ions at the LHC At the LHC we expect “deep deconfinement” At the LHC: higher energy density, higher temperature and longer fireball lifetime closer to “ideal” QGP easier comparison with theory LHC In a Pb-Pb collision at √s NN = 5.5 TeV we expect to reach a huge energy density  > 100 GeV/fm 3 in a large volume  entering deeply into the deconfined phase (QGP) QGP signatures already observed at SPS (CERN) multistrange baryon enhancement J/  suppression and RHIC (BNL) jet quenching

4. 4 Marcello Lunardon - BEACH 2006, Lancaster, UK gluon radiation Heavy ion collisions: some result from RHIC Compare p T distributions of leading particles in pp and nucleus-nucleus collisions (+ p-nucleus as a control) What about heavy quarks? light-flavored hadrons @ RHIC R AA measured at RHIC with light- flavoured hadrons: clear suppression at high p T interpreted as due to parton energy loss in medium The nuclear modification factor Jet correlations in Au-Au Central collisions (high  ) compared to pp min. bias (low  ) : clear suppression of the away-side jet interpreted as due to energy loss in the medium

5. 5 Marcello Lunardon - BEACH 2006, Lancaster, UK Heavy flavour at the LHC in AA Novelty of the LHC: large cross section FONLO calculations with MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295. Heavy flavours are useful probes: SPS → RHIC → LHC Hard processes contribute significantly to the total AA cross-section (σ hard /σ tot =98%): –Bulk properties dominated by hard processes –Very hard probes are abundantly produced NLO predictions (ALICE baseline for charm & beauty) system,  s pp, 14 TeVPb-Pb (0-5%), 5.5 TeV 11.2 / 0.54.3 / 0.2 0.16 / 0.007115 / 4.6 theoretical uncertainties of a factor 2  3

6. 6 Marcello Lunardon - BEACH 2006, Lancaster, UK Heavy flavour at the LHC in AA Heavy flavours are useful probes: Large virtuality Q  happen at initial time (small “formation time”  t ~ 1/Q << t QGP ~ 5  10 fm/c )  sample the whole collision history Pb b b b b Heavy quark p T distribution sensitive to many competing nuclear effects low-p T (<6 GeV/c at LHC) region sensitive to non-perturbative effects (flow, quark coalescence, gluon shadowing, CGC state…) high-p T region sensitive to jet quenching (mass and/or colour-charge dependence?) Which Energy Loss?

7. 7 Marcello Lunardon - BEACH 2006, Lancaster, UK Measuring Open Heavy Flavour at the LHC: the ALICE Detector -4 <  < ­2.5 TOF PID TOF PID TRD Electron ID TRD Electron ID ITS Vertexing, Low p t tracking ITS Vertexing, Low p t tracking TPC Tracking, dEdx TPC Tracking, dEdx MUON ARM  tracking MUON ARM  tracking |  | < 0.9 The dedicated HI experiment at the LHC with a large number of detectors with high tracking efficiency and particle identification across a wide range of momenta from below 100 MeV to above 100 GeV

8. 8 Marcello Lunardon - BEACH 2006, Lancaster, UK Open heavy flavour at the LHC with ALICE ALICE is a powerful tool to measure heavy flavour observables Multi-purpose detector specifically designed for HI collisions can resolve tracks in a very high density environment (up to dN ch /dy ~ 8000 ) can provide several different HF measurements within the same experiment Precise tracking and vertexing can resolve D’s and B’s decay vertices can measure p T distributions down to a few 100 MeV/c Particle identification good PID for e, ,K,p 60  <  < 62 

9. 9 Marcello Lunardon - BEACH 2006, Lancaster, UK D mesons: c  ~ 100  300  m and significant BR for kaon-pion(s) decay modes exclusive reconstruction of D 0  K -  + exclusive 3-body reconstruction of D + and D s + B mesons: c  ~ 500  m and large semi-leptonic BR (~20%) Studies of the expected ALICE performances in open heavy flavour detection Full performance study Under evaluation inclusive single electron measurement of B  e e X at |  | < 0.9 inclusive muon/dimuon measurement of B    X at -4 <  < -2.5 (not presented here) Open heavy flavour at the LHC with ALICE

10. 10 Marcello Lunardon - BEACH 2006, Lancaster, UK Measurement of displaced tracks (track impact parameter resolution) the track position resolution is mainly provided by the 2 layers of silicon pixels ITS PIXEL CELL z: 425  m r  : 50  m Two layers: r = 4 – 7 cm 9.8 Mch SPD Open heavy flavour at the LHC with ALICE

11. 11 Marcello Lunardon - BEACH 2006, Lancaster, UK Charm reconstruction in the D 0  K -  + “golden” decay channel - large combinatorial background in AA (for this study dN ch /dy ~ 6000 was used): S/B ~ 10 -6 in M D 0  3  before selection  need to reduce bkg by 6-7 orders of magnitude! - main selection on displaced vertices asking for opposite-sign track pairs with large impact parameter - the reconstructed D 0 momentum should point to the primary vertex (  point ~ 0) - (K,  ) invariant mass analysis to extract the D 0 yield Direct measurement of the p T distribution of the D 0 mesons Detection strategy

12. 12 Marcello Lunardon - BEACH 2006, Lancaster, UK Charm reconstruction in the D 0  K -  + “golden” decay channel D 0 candidate selection in Pb-Pb d 0 K xd 0  < -40000  m && cosθ point  0.98  increase S/B by a factor 10 3 ! Invariant mass analysis to count D 0 ’s N.Carrer, A.Dainese and R.Turrisi, J. Phys. G29 (2003) 575. - A.D. PhD thesis (2003), nucl-ex/0311004. Statistical significance: Pb-Pb p T integrated

13. 13 Marcello Lunardon - BEACH 2006, Lancaster, UK Charm reconstruction in the D 0  K -  + “golden” decay channel Charm reconstruction final performance results p T -differential cross section can be reconstructed down to p T ~0! Estimated significance for 1 year at nominal luminosity and dN ch /dy = 6000 in Pb-Pb With dN ch /dy ~ 3000  S/B x4  Signif. x2

14. 14 Marcello Lunardon - BEACH 2006, Lancaster, UK Beauty detection via displaced electrons Primary Vertex B e X d0d0 rec. track Distributions normalized to the same integral in order to compare their shapes d 0 distributions for “electrons” from different sources: Inclusive measurement of electrons coming from semi-electronic decay of beauty hadrons need good electron identification: combined PID in TPC (dE/dx) + TRD key selection point: again good measurement of the track impact parameter

15. 15 Marcello Lunardon - BEACH 2006, Lancaster, UK 1) Electron PID: reject most of the hadrons Primary Vertex B e X d0d0 rec. track 3) Subtract (small) residual background 2) Impact parameter cut: reduce charm and bkg electrons |d 0 | distributions for “electrons” from different sources: Beauty detection via displaced electrons Selection of the beauty electron candidates in 3 steps beauty dominates left charm left bkg

16. 16 Marcello Lunardon - BEACH 2006, Lancaster, UK 10 7 central (0-5%) Pb-Pb events expected statistics and systematic uncertainties p T -differential electron cross section reconstructed from ~ 1 to 20 GeV/c Beauty detection via displaced electrons Results for beauty in Pb-Pb (same analysis done for pp @ 14 TeV)

17. 17 Marcello Lunardon - BEACH 2006, Lancaster, UK 1 year at nominal luminosity (10 7 central Pb-Pb events, 10 9 pp events) Sensitivity to Energy Loss Observables Higt p T suppression and energy loss for Charm medium transport coefficient: depends on the medium properties no energy loss Theory predictions* : large suppression with ~ 25  100 GeV 2 /fm charm less suppressed than light hadrons (colour-charge effect) but more than beauty (mass effect) Baier, Dokshitzer, Mueller, Peigne‘, Schiff, NPB 483 (1997) 291. Salgado, Wiedemann, PRD 68(2003) 014008 * Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027 BDMPS model

18. 18 Marcello Lunardon - BEACH 2006, Lancaster, UK Mass dependence of E loss with Beauty-to-Charm ratio Adapted from Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027 Compare c and b: same colour charge Mass effect  Enhancement of factor ~2 independent of (for ) Sensitivity to Energy Loss Observables

19. 19 Marcello Lunardon - BEACH 2006, Lancaster, UK Conclusions Heavy flavours are fundamental probes for testing QCD in AA collisions at the LHC (non perturbative effects, energy loss in medium,...) ALICE is well equipped for measuring open heavy flavour production cross sections and p T differential distributions both in pp and AA (vertexing and particle identification down to low p T ) ALICE has a large heavy flavour program for both open heavy flavours and quarkonia: a lot of work for the next years!