Heavy Flavour Physics in ALICE Massimo Masera University

Heavy Flavour Physics in ALICE Massimo Masera University and INFN, Torino - Italy for the ALICE Collaboration 9 Feb 2008 M. Masera Heavy Flavour in ALICE

Contents • Heavy Flavours at the LHC • ALICE • Open Flavours § Physics motivations § Hadronic charm • Examples: D 0 K- +, D+ K- + +, Ds+ K+K- + § B e+X and B +X • Quarkonia § Quarkonia to dielectrons at midrapidity § Quarkonia to dimuons at forward rapidities • J/ and polarization • J/ from beauty • Conclusions 9 Feb 2008 M. Masera Heavy Flavour in ALICE 2

Yields at LHC energies Predicted yields for charm and 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 üNLO p. QCD calculations [Mangano, Nason, Ridolfi, NPB 373 (1992) 295. ] theoretical uncertainty: factor 2 -3 üFrom p+p to Pb-Pb: binary scaling + shadowing (EKS 98) ü HF are abundantly produced at the LHC: üProbe unexplored small-x region with HQs at low p. T and/or forward y down to x~10 -4 with charm, 9 Feb already at 2008 y=0 muon arm Central barrel M. Masera Heavy Flavour in ALICE acceptance for charm and beauty 3

ALICE • ALICE channels: Time Of Flight (TOF) § electronic (|h|<0. 9) § muonic (-4<h<-2. 5) § hadronic (|h|<0. 9) • ALICE coverage: § Extends to low-p. T region § central and forward rapidity regions Transition Radiation Detector (TRD) Muon Arm - see B. Espagnon’s talk • Precise vertexing to identify D (c ~ 100 -300 m) and B (c ~ 500 m) decays Time Projection Chamber (TPC) Inner Tracking System (ITS) 9 Feb 2008 M. Masera Heavy Flavour in ALICE 4

Track impact parameter in Pb-Pb • Resolution on track impact parameter • thanks to the 2 layers of Silicon Pixel Detectors Interaction point (primary vertex) primary vertex § x and y coordinates with high precision averaging over fill. Good position stability expected for LHC beam, sbeam=15 m § z coordinate measured from cluster correlation on the two layers of SPD track impact parameter central Pb–Pb =L decay length q decay vertex rf : 0 5 m PI z: 4 XE 25 L CE m LL < 60 mm (rf) for pt > 1 Ge. V/c 9 Feb 2008 Two layers: r = 4 incm M. Masera Heavy Flavour ALICE r = 7 cm 5

Open Flavours 9 Feb 2008 M. Masera Heavy Flavour in ALICE

Physics motivations • p-p § Measurement of HF production test of p. QCD calculations § Baseline for AA • A-A § Study of the hot and high density medium produced in central A-A collisions • Initial (also in p-A) and final state effects • Effects of the medium on fragmentation § Important for quarkonium physics • Normalization • B J/ + X • p-A § To disentangle initial and final state effects induced by the medium 9 Feb 2008 M. Masera Heavy Flavour in ALICE 7

From p-p to A-A • Zero order approximation: binary scaling with Ncoll • Initial state effects (also in p-A) antishadowing § PDFs in nucleus different from PDFs in nucleon • Anti-shadowing and shadowing § k. T broadening (Cronin effect) § Parton saturation (Color Glass Condensate) • Final state effects (only in A-A) shadowing RHIC LHC SPS EMC § Energy loss in medium § In medium hadronization • Recombination vs. fragmentation 9 Feb 2008 M. Masera Heavy Flavour in ALICE 8

Suppression observed at RHIC • Measurement done via non photonic electrons • RAA good agreement between Phenix and Star STAR : PRL 98, 192301 (2007) PHENIX : PRL 98, 172301 (2007) • Suppression compatible with pure charm … But b expected to dominate for p. T>4 Ge. V • to disentangle c/b full reconstruction of D mesons good track impact parameter resolution is needed • Radiative Eloss CR • CR=4/3 for q • CR=3 for gluons Non photonic electrons suppressed as light hadrons at high p. T large quark contribution for light flavours? 9 Feb 2008 At the LHC gluon M. contribution Masera Heavyshould Flavour be in ALICE dominant 9

D 0 K - + • Golden channel for open charm • S/B ≈ 10% • Significance for 1 month Pb-Pb run: S/√(S+B) ≈ 40 Sensitivity w. r. t. p. QCD statistical. 1 year at standard luminosity (109 pp events) Sensitivity w. r. t. p. QCD 1 year at standard luminosity (109 pp events) statistical. systematic. 9 Feb 2008 M. Masera Heavy Flavour in ALICE 10

D+ K- + + and Ds+ K+K- + D+ K - + + • Measure D 0/D+ instead of relying on l l l p-p @ 14 Te. V + + K- + + Ds+ K+DK- Fragmentation/recombination Experimentally accessible? Ds+ (c ~ 150 µm) K-K+ + with BR ~ 4. 4 % l but mostly resonant decays: + or K 0* K + favours backkground rejection l 9 Feb 2008 MKK (Ge. V/c 2) Under study • • 2<p. T<3 Ge. V/c Pythia Larger c ≈300 m w. r. t. D 0 Larger combinatorial background Smaller <p. T> of the decay products Performance comparable with D 0 K- + Ds+ as probe of hadronization? M. Masera Heavy Flavour in ALICE 11 MK (Ge. V/c 2)

Beauty to e/ • B e+X § e± identification from TRD and d. E/dx in TPC § impact parameter from ITS § Subtraction of charm contribution • B +X § Muon spectrometer § b contribution dominant at high p. T § measurement of c contribution at low p. T difficult due to high background § Crosscheck: muon pairs from B decays § See B. 9 Espagnon’s Feb 2008 talk Expected ALICE performance (1 month Pb-Pb) S/(S+B) M. Masera Heavy Flavour in ALICE S per 107 central Pb-Pb events 12

Performance for D and B quenching Colour charge dependence Mass dependence mb = 4. 8 Ge. V Statistical error corresponding to 107 Pb-Pb and 109 p-p events 9 Feb 2008 M. Masera Heavy Flavour in ALICE 13

Quarkonia 9 Feb 2008 M. Masera Heavy Flavour in ALICE

Quarkonia detection in ALICE • Quarkonia detected via § e+e- channel: electrons tracked in the central barrel, identified with the Transition Radiation Detector and the Time Projection Chamber § + - channel: forward rapidities with the Muon Spectrometer 9 Feb 2008 M. Masera Heavy Flavour in ALICE 15

Acceptances J/ Dielectron trigger: p. T cut=3 Ge. V/c on individual electrons J/ Dimuon trigger. p. T cut = 1 Ge. V/c (2) for J/ ( ) 9 Feb 2008 M. Masera Heavy Flavour in ALICE 16

Quarkonia to dielectrons: Pb-Pb Dielectron invariant mass spectrum in top 10% central collisions after one “ALICE-year” of Pb-Pb data taking Zoom in the J/Y region Zoom in the region 9 Feb 2008 M. Masera Heavy Flavour in ALICE 17

Quarkonia to dimuons p-p @ 14 Te. V One year of data taking -J/Y: 2. 8 106 - : 2. 7 104 Invariant mass resolution: • J/Y peak: ~ 70 Me. V/c 2 • peak: ~ 100 Me. V/c 2 9 Feb 2008 M. Masera Heavy Flavour in ALICE Pb-Pb @ 5. 5 Te. V One year of data taking -J/Y: excellent (670. 000) - Y’: marginal - : ok (7000) - ’: low (2000) - ’’: very low (1000) 18

J/ and polarization • p-p collisions: § Polarization measurements are a test for different quarkonia production mechanisms, since different models predict different polarizations • A-A collisions: § A significant J/ polarization in heavy-ion collisions is expected in case of QGP formation (Phys. Rev. C 68 061902 (2003)) polariz. pp@ 14 Te. V vs p. T = -1 Without backgorund subtraction (S/B=0. 2) One year data taking 9 Feb 2008 With backgorund subtraction meas- gen • See poster by E. Scomparin J/ polariz. AA@ 5. 5 Te. V vs M. Masera Heavy Flavour in ALICE 19

B J/ + X • More “exclusive” than B e/µ + X § better handle on B momentum distribution • Preliminary pp study: pseudoproper decay time (à la CDF) CDF (data) p. T>0 ALICE (prelim. simulation) 20

Conclusions • HF are a powerful tool to study the strongly interacting • • medium produced in Heavy Ion Collisions at the LHC High rates of Heavy Flavours are expected at LHC ALICE is well suited for HF physics: § Excellent vertexing and tracking capabilities § Exploits both electron and muon channels in different rapidity regions § PID with several complementary techniques (d. E/dx, TOF, TRD) • Present simulations focused on the effects of realistic calibration and alignment (see poster P 174 by S. Moretto) 9 Feb 2008 M. Masera Heavy Flavour in ALICE 21

BACKUP 9 Feb 2008 M. Masera Heavy Flavour in ALICE

LHC System s. NN L 0 (*) Run sgeom (b) (Te. V) (cm-2 s-1) time (s/year) p-p 14 1034 107 0. 07 Pb-Pb 5. 5 1027 106 7. 7 (*) L 0 (ALICE)= 1031 • Other collision systems foreseen: p-A, lighter ions and energies • Running time: 4 weeks/year integrated luminosity in one year: 0. 7 nb-1 for Pb-Pb • One Heavy Ion dedicated experiment: ALICE. Both CMS and ATLAS have also a Heavy Ion programme • Initial condition different w. r. t. RHIC • greater energy density, temperature, size and lifetime of the fireball • Significant contribution of hard processes to the total AA cross section: 9 Feb 2008 M. Masera Heavy Flavour in ALICE 23

HF: general Physics motivations • Goal: study the properties of the medium § Charm and beauty are abundantly produced at LHC § § Heavy flavours are produced (early) in the initial collisions mainly via gluon fusion they are hard probes § Production yield in p-p from p. QCD: • Naive expectation. Binary scaling to A-A § They travel in the medium experience the full collision history 9 Feb 2008 M. Masera Heavy Flavour in ALICE 24

Heavy Flavours in ALICE • ALICE channels: § electronic (|h|<0. 9) § muonic (-4<h<-2. 5) § hadronic (|h|<0. 9) • ALICE coverage: § Extends to low-p. T region § central and forward rapidity regions • Precise vertexing to identify D (c ~ 100 -300 m) and B (c ~ 500 m) decays 9 Feb 2008 M. Masera Heavy Flavour in ALICE 25

Baseline: p+p collisions Hard processes (q-qbar annihilation, gluon fusion) occurring at short space-time scale (~1/2 mq) s /2 b or c quarks xa M q B or D mesons s /2 xb q M Cross section evaluation factorized p. QCD: Cross section to produce hadron M 9 Feb 2008 Parton Distribution Functions – xa and xb are parton momentun fractions in the colliding hadrons Cross section at parton level: p. QCD. Currently NLO used as a baseline for ALICE. FONLL better description at high p. T M. Masera Heavy Flavour in ALICE Fragmentation function (non perturbative) 26

p+p: charm cross section üFONLL: ü beauty production well described at Tevatron (J/ψ from b decay) ücharm production underpredicted at Tevatron üRHIC p+p data underpredicted üDiscrepancy between Phenix and Star Cacciari, Frixione, Mangano, Nason and Ridolfi, JHEP 0407 (2004) 033 CDF, PRL 91 (2003) 241804 FONLL: Cacciari, Nason PRL 98, 192301 (2007) 9 Feb 2008 M. Masera Heavy Flavour in ALICE 27

D/B Mesons Main selection tool for D/B mesons: displaced secondary vertices Total yield for Pb-Pb central interactions (5% sinel) at 5. 5 Te. V D mesons: ü c ~ 100 – 300 m ü Significant BR for ü ü ü B mesons: ü c ~ 500 m ülarge BR in semileptonic decay channels (20%) • inclusive single electron measurement of B e e X • inclusive muon/dimuon measurement of B X Total yield for Pb-Pb central interactions (5% sinel) at 5. 5 Te. V 9 Feb 2008 M. Masera Heavy Flavour in ALICE 28

D + K - + + • Measure D 0/D+ instead of relying on Pythia Larger c ≈300 m w. r. t. D 0 Larger combinatorial background Smaller <p. T> of the decay products Performance comparable with D 0 K- + p-p @ 14 Te. V Significance S/ (S+B) for 2<p. T<3 Ge. V/c cosqpoint. CUT • • 2<p. T<3 Ge. V/c (normalized to 107 Pb. Pb events) 9 Feb 2008 M. Masera Heavy Flavour in ALICE d CUT(mm) Dist prim. Sec. ( m) qpoint p T D+ 29

Ds+ K+K- + l Ds + as probe of hadronization? string fragmentation: cs / cd ~ 1/3 lafter decays: Ds+ (cs) / D+ (cd) ~ 0. 6 lfrom recombination: cs / cd ~ N(s) / N(d) l. How large at LHC? lexperimentally accessible? (c ~ 150 µm) K-K+ + with BR ~ 4. 4 % lbut mostly resonant decays: + or K 0*K+ favours bkgnd rejection MKK (Ge. V/c 2) l. Ds+ MKK (Ge. V/c 2) lfrom 9 Feb 2008 M. Masera Heavy Flavour in ALICE MK (Ge. V/c 2) 30

B mesons via B e e X (I) Inclusive measurement of electrons coming from semielectronic decay of beauty hadrons Ø 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 e B d 0 9 Feb 2008 normalized to the M. Masera Flavour in ALICE Distributions same integral. Heavy in order to compare their shapes X 31

B mesons via B e e X (II) 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 e beauty dominates left charm left bkg 9 Feb 2008 Primary Vertex d 0 M. Masera Heavy Flavour in ALICE B X 32

B mesons via B e e X (III) Results for beauty in Pb-Pb p. T-differential electron cross section reconstructed from ~ 1 to 20 Ge. V/c expected statistics and systematic uncertainties 107 central (0 -5%) Pb-Pb events 9 Feb 2008 M. Masera Heavy Flavour in ALICE 33

HF to muons • Single muons from beauty • • are dominant at high p. T fit on distribution tail Muons from charms are dominant at low p. T difficult measurement due to large background Muon pairs from B: BDsame B µ+ + D + X µ- + X BDsame BBdiff + X 9 + µ BB Feb 2008 µ-M. +Masera X Heavy Flavour in ALICE 34

HF to single muon in p-p • Signal: from b/c decays • Background: § from /K decays • Can be extracted from data Slices in p. T. Correct for diamond shape § from the absorber • Subtraction: tracks do not point to the vertex, no FMD hits • Good preliminary results: 9 Feb 2008 M. Masera high Heavy Flavour in ALICE statistics needed 35

Quarkonia to dimuons Centrality dependence of J/ and normalized to unlike sign dimuon rates from beauty Shadowing + 2 different suppression scenarii: 1. High dissociation temeperature 2. Low dissociation temperature Error bars 1 month data taking Assumptions 1. Perfect subtraction of combinatorial background 2. Zero nuclear absorption cross section 9 Feb 2008 M. Masera Heavy Flavour in ALICE 36

Quarkonia to dielectrons: Pb-Pb Dielectron invariant mass spectrum in central collisions after one “ALICE-year” of Pb-Pb data taking 9 Feb 2008 M. Masera Heavy Flavour in ALICE 37

Perspectives for D± elliptic flow • GOAL: GOAL Evaluate the statistical error bars for measurements of v 2 for D± mesons reconstructed from their K decay in Pb-Pb collisions Ø v 2 vs. centrality (b=collision impact parameter) Ø v 2 vs. p. T in different centrality bins • HOW: HOW fast simulation to generate: § ND+ (Dp. T, Db) with an angular distribution d. ND/dj = v 2 D, in cos [2(j-YRP)] § For each D+: an event made of Ntracks is superimposed d. N/dj = v 2 ev, in cos [2(j-YRP)] § Inputs of the simulation: ND+ (Dp. T, Db) , v 2 D, in, Ntracks , v 2 ev, in § Outputs: v 2 D measured. 9 Feb 2008 M. Masera Heavy Flavour in ALICE 38

v 2 vs. p. T How to increase the statistics? Large stat. errors on v 2 of D± → K in 2· 107 MB events • Sum D 0→K and D±→K § Sufficient for v 2 vs. centrality • Semi-peripheral trigger 6<b<9 fm § v 2 vs. p. T that would be obtained from 2· 107 semi-peripheral events (e. g. 6<b<9 fm) MB trigger 9 Feb 2008 Semi-peripheral trigger M. Masera Heavy Flavour in ALICE 39

B elliptic flow üv 2 evaluated from B e+X ü Pb-Pb centrality: 20 -60% 1 year at nominal luminosity 9 Feb 2008 M. Masera Heavy Flavour in ALICE 40

Kinematical distributions: prompt J/ versus secondary J/ • “pseudo proper • decay time” x Primary J/ Secondary J/ 9 Feb 2008 M. Masera Heavy Flavour in ALICE 41

How to measure the fraction of secondary J/ from b-hadron decays, one should fit simultaneously ü the invariant mass spectrum ü one distribution which can discriminate prompt from detached J/ (e. g. x or d 0 e+·d 0 e-) Events/10 Me. V • In order to extract the fraction f. B of J/ • the tails of the M(e+e-) distribution measures the percentage of background 9 Feb 2008 M. Masera Heavy Flavour in ALICE 42