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The 7th International Conference on Hyperons, Charm And Beauty Hadrons - BEACH 2006

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. Open Heavy Flavour Detection in ALICE. Contents Why heavy ion collisions at the LHC

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The 7th International Conference on Hyperons, Charm And Beauty Hadrons - BEACH 2006

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  1. 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. Open Heavy Flavour Detection in ALICE • 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

  3. Why heavy ions at the LHC At the LHC we expect “deep deconfinement” In a Pb-Pb collision at √sNN = 5.5 TeV we expect to reach a huge energy density  > 100 GeV/fm3 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 LHC • At the LHC: higher energy density, higher temperatureandlonger fireball lifetime • closer to “ideal” QGP • easier comparison with theory

  4. Heavy ion collisions: some result from RHIC gluon radiation light-flavored hadrons @ RHIC Compare pT distributions of leading particles in pp and nucleus-nucleus collisions (+ p-nucleus as a control) The nuclear modification factor RAA measured at RHIC with light-flavoured hadrons: clear suppression at high pT interpreted as due to parton energy loss in medium 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 What about heavy quarks?

  5. Heavy flavour at the LHC in AA Heavy flavours are useful probes: • Novelty of the LHC: large cross section SPS→ RHIC→ LHC Hard processes contribute significantly to the total AA cross-section (σhard/σtot=98%): • Bulk properties dominated by hard processes • Very hard probes are abundantly produced • NLO predictions (ALICE baseline for charm & beauty) theoretical uncertainties of a factor 23 FONLO calculations with MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295.

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

  7. TPC Tracking, dEdx Measuring Open Heavy Flavour at the LHC: the ALICE Detector 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 TOF PID TRD Electron ID ITS Vertexing, Low pt tracking MUON ARM  tracking -4 <  < ­2.5 || < 0.9

  8. 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 dNch/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 pT distributions down to a few 100 MeV/c 60 <  < 62 • Particle identification • good PID for e,,K,p

  9. Open heavy flavour at the LHC with ALICE Studies of the expected ALICE performances in open heavy flavour detection D mesons: c ~ 100  300 m and significant BR for kaon-pion(s) decay modes • exclusive reconstruction ofD0 K-p+ • exclusive 3-body reconstruction ofD+ and Ds+ B mesons: c ~ 500 m and large semi-leptonic BR (~20%) • inclusive single electron measurement ofB e e X at || < 0.9 • inclusive muon/dimuon measurement ofB  X at -4 <  < -2.5 (not presented here) Full performance study Under evaluation

  10. 9.8 Mch rf: 50 mm z: 425 mm PIXEL CELL Two layers: r = 4 – 7 cm Open heavy flavour at the LHC with ALICE Measurement of displaced tracks (track impact parameter resolution) the track position resolution is mainly provided by the 2 layers of silicon pixels ITS SPD

  11. Charm reconstruction in the D0 K-p+ “golden” decay channel Direct measurement of the pT distribution of the D0 mesons - large combinatorial background in AA (for this study dNch/dy ~ 6000 was used): S/B ~ 10-6 in MD03 before selection  need to reduce bkg by 6-7 orders of magnitude! Detection strategy - main selection on displaced vertices asking for opposite-sign track pairs with large impact parameter - the reconstructed D0 momentum should point to the primary vertex (point~ 0) - (K,) invariant mass analysis to extract the D0 yield

  12. Charm reconstruction in the D0 K-p+ “golden” decay channel D0 candidate selection in Pb-Pb d0Kxd0 < -40000 m && cosθpoint 0.98  increase S/B by a factor 103! Invariant mass analysis to count D0’s Pb-Pb pT integrated Statistical significance: N.Carrer, A.Dainese and R.Turrisi, J. Phys. G29 (2003) 575. - A.D. PhD thesis (2003), nucl-ex/0311004.

  13. Charm reconstruction in the D0 K-p+ “golden” decay channel Charm reconstruction final performance results pT-differential cross section can be reconstructed down to pT~0! Estimated significance for 1 year at nominal luminosity and dNch/dy = 6000 in Pb-Pb WithdNch/dy ~ 3000  S/B x4  Signif. x2

  14. rec. track e Primary Vertex B d0 X Beauty detection via displaced electrons 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 d0 distributions for “electrons” from different sources: Distributions normalized to the same integral in order to compare their shapes

  15. 1) Electron PID: reject most of the hadrons rec. track e Primary Vertex B beauty dominates d0 X left charm left bkg Beauty detection via displaced electrons Selection of the beauty electron candidates in 3 steps 2) Impact parameter cut: reduce charm and bkg electrons 3) Subtract (small) residual background |d0| distributions for “electrons” from different sources:

  16. Beauty detection via displaced electrons Results for beauty in Pb-Pb (same analysis done for pp @ 14 TeV) pT-differential electron cross section reconstructed from ~ 1 to 20 GeV/c expected statistics and systematic uncertainties 107 central (0-5%) Pb-Pb events

  17. Sensitivity to Energy Loss Observables Higt pT suppression and energy loss for Charm • Theory predictions* : • large suppression with ~ 25100 GeV2/fm • charm less suppressed than light hadrons (colour-charge effect) but more than beauty (mass effect) BDMPS model medium transport coefficient: depends on the medium properties no energy loss 1 year at nominal luminosity (107 central Pb-Pb events, 109 pp events) * Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027 Baier, Dokshitzer, Mueller, Peigne‘, Schiff, NPB 483 (1997) 291. Salgado, Wiedemann, PRD 68(2003) 014008

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

  19. 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 pT differential distributions both in pp and AA (vertexing and particle identification down to low pT) • ALICE has a large heavy flavour program for both open heavy flavours and quarkonia: a lot of work for the next years!

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