The 7 th International Conference on Hyperons Charm

The 7 th 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 1 Marcello Lunardon - BEACH 2006, Lancaster, UK

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 2 Marcello Lunardon - BEACH 2006, Lancaster, UK

Why heavy ions at the LHC At the LHC we expect “deep deconfinement” In a Pb-Pb collision at √s. NN = 5. 5 Te. V we expect to reach a huge energy density > 100 Ge. V/fm 3 in a large volume entering deeply into the deconfined phase (QGP) LHC QGP signatures already observed at SPS (CERN) • multistrange baryon enhancement • J/ suppression and RHIC (BNL) • jet quenching At the LHC: higher energy density, higher temperature and longer fireball lifetime • closer to “ideal” QGP • easier comparison with theory 3 Marcello Lunardon - BEACH 2006, Lancaster, UK

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) The nuclear modification factor gluon radiation light flavored hadrons @ RHIC RAA measured at RHIC with light. Jet correlations Au-Au Central collisions flavoured hadrons: inclear suppression ) compared to pp min. bias (low ) : clear at(high p T interpreted as due to parton suppression of the away-side jet interpreted as energy loss in medium due to energy loss in the medium 4 Marcello Lunardon - BEACH 2006, Lancaster, UK What about heavy quarks?

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) system, s pp, 14 Te. V Pb-Pb (0 -5%), 5. 5 Te. V 11. 2 / 0. 5 4. 3 / 0. 2 0. 16 / 0. 007 115 / 4. 6 theoretical uncertainties of a factor 2 3 FONLO calculations with MNR code: Mangano, Nason, Ridolfi, NPB 373 (1992) 295. 5 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” Dt ~ 1/Q << t. QGP ~ 5 10 fm/c ) sample the whole collision history Which b Energy b Loss? Pb Pb b b • Heavy quark p. T distribution sensitive to many competing nuclear effects • low-p. T (<6 Ge. V/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? ) 6 Marcello Lunardon - BEACH 2006, Lancaster, UK

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 Me. V to above 100 Ge. V TOF PID TRD Electron ID TPC Tracking, d. Edx ITS MUON ARM Vertexing, Low pt tracking | | < 0. 9 7 Marcello Lunardon - BEACH 2006, Lancaster, UK 4 < < 2. 5

Open heavy flavour at the LHC with ALICE is a powerful tool to measure heavy flavour observables • • • 8 Multi purpose detector specifically designed for HI collisions • can resolve tracks in a very high density environment (up to d. Nch/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 Me. V/c Particle identification • good PID for e, , K, p Marcello Lunardon - BEACH 2006, Lancaster, UK 60 < < 62

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 of D 0 K- + • exclusive 3 -body reconstruction of D+ and Ds+ B mesons: c ~ 500 m and large semi leptonic BR (~20%) • 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) 9 Marcello Lunardon - BEACH 2006, Lancaster, UK Full performance study Under evaluation

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 rf 0 : 5 m z: 9. 8 Mch 42 PI 5 XE m L C EL L SPD Two layers: r = 4 – 7 cm 10 Marcello Lunardon - BEACH 2006, Lancaster, UK

Charm reconstruction in the D 0 K-p+ “golden” decay channel Direct measurement of the p. T distribution of the D 0 mesons - large combinatorial background in AA (for this study d. Nch/dy ~ 6000 was used): S/B ~ 10 -6 in MD 0 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 D 0 momentum should point to the primary vertex ( point ~ 0) - (K, ) invariant mass analysis to extract the D 0 yield 11 Marcello Lunardon - BEACH 2006, Lancaster, UK

Charm reconstruction in the D 0 K-p+ “golden” decay channel D 0 candidate selection in Pb Pb d 0 Kxd 0 < -40000 m && cosθpoint 0. 98 increase S/B by a factor 103! Invariant mass analysis to count D 0’s Pb-Pb p. T integrated Statistical significance: N. Carrer, A. Dainese and R. Turrisi, J. Phys. G 29 (2003) 575. - A. D. Ph. D thesis (2003), nucl-ex/0311004. 12 Marcello Lunardon - BEACH 2006, Lancaster, UK

Charm reconstruction in the D 0 K-p+ “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 d. Nch/dy = 6000 in Pb-Pb With d. Nch/dy ~ 3000 S/B x 4 Signif. x 2 13 Marcello Lunardon - BEACH 2006, Lancaster, UK

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 (d. E/dx) + TRD • key selection point: again good measurement of the track impact parameter d 0 distributions for “electrons” from different sources: rec. track Primary Vertex B d 0 14 e Marcello Lunardon - BEACH 2006, Lancaster, Distributions normalized to the same integral. UK in order to compare their shapes X

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

Beauty detection via displaced electrons Results for beauty in Pb-Pb p. T-differential electron cross section reconstructed from ~ 1 to 20 Ge. V/c (same analysis done for pp @ 14 Te. V) expected statistics and systematic uncertainties 107 central (0 -5%) Pb-Pb events 16 Marcello Lunardon - BEACH 2006, Lancaster, UK

Sensitivity to Energy Loss Observables Higt p. T suppression and energy loss for Charm BDMPS model Theory predictions* : • large suppression with ~ 25 100 Ge. V 2/fm • charm less suppressed than light hadrons (colour-charge effect) but more than beauty (mass effect) medium transport coefficient: depends on the medium properties no energy loss (107 1 year at nominal luminosity central Pb-Pb events, 109 pp events) * Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027 17 Marcello Lunardon - BEACH 2006, Lancaster, UK Baier, Dokshitzer, Mueller, Peigne‘, Schiff, NPB 483 (1997) 291. Salgado, Wiedemann, PRD 68(2003) 014008

Sensitivity to Energy Loss Observables Mass dependence of E loss with Beauty-to-Charm ratio Compare c and b: same colour charge Mass effect Enhancement of factor ~2 independent of (for ) Marcellofrom Lunardon BEACH Salgado, 2006, Lancaster, UKPRD 71 (2005) 054027 18 Adapted Armesto, - Dainese, Wiedemann,

Conclusions 19 • 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! Marcello Lunardon - BEACH 2006, Lancaster, UK