Heavy Flavour Physics in ALICE Massimo Masera University and INFN, Torino - Italy for the ALICE Collaboration

9 Feb 2008M. Masera Heavy Flavour in ALICE2 Contents Heavy Flavours at the LHC ALICE Open Flavours  Physics motivations  Hadronic charm Examples: D 0  K -  +, D +  K -  +  +, D s +  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 2008M. Masera Heavy Flavour in ALICE3 Yields at LHC energies system,  s pp, 14 TeV Pb-Pb (0-5%), 5.5 TeV 11.2 / / / / 4.6 NLO pQCD calculations [Mangano, Nason, Ridolfi, NPB373 (1992) 295.]  theoretical uncertainty: factor 2-3 From p+p to Pb-Pb: binary scaling + shadowing (EKS98) Predicted yields for charm and beauty HF are abundantly produced at the LHC: Probe unexplored small-x region with HQs at low p T and/or forward y down to x~10 -4 with charm, already at y=0 ALICE acceptance for charm and beauty muon arm Central barrel

9 Feb 2008M. Masera Heavy Flavour in ALICE4 ALICE Inner Tracking System (ITS) Time Projection Chamber (TPC) Time Of Flight (TOF) Muon Arm - see B. Espagnon’s talk Transition Radiation Detector (TRD) ALICE channels:  electronic (|  |<0.9)  muonic (-4<  <-2.5)  hadronic (|  |<0.9) ALICE coverage:  Extends to low-p T region  central and forward rapidity regions Precise vertexing to identify D (c  ~  m) and B (c  ~ 500  m) decays

9 Feb 2008M. Masera Heavy Flavour in ALICE5 primary vertex decay vertex decay length = L  track impact parameter Track impact parameter in Pb-Pb PIXEL CELL z: 425  m r  : 50  m Two layers: r = 4 cm r = 7 cm < 60  m (r  ) for p t > 1 GeV/c central Pb–Pb Resolution on track impact parameter thanks to the 2 layers of Silicon Pixel Detectors Interaction point (primary vertex)  x and y coordinates with high precision averaging over fill. Good position stability expected for LHC beam,  beam =15  m  z coordinate measured from cluster correlation on the two layers of SPD

Open Flavours

9 Feb 2008M. Masera Heavy Flavour in ALICE7 Physics motivations p-p  Measurement of HF production  test of pQCD 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 2008M. Masera Heavy Flavour in ALICE8 From p-p to A-A Zero order approximation: binary scaling with N coll Initial state effects (also in p-A)  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)  Energy loss in medium  In medium hadronization Recombination vs. fragmentation shadowing antishadowing SPS RHIC LHC EMC

9 Feb 2008M. Masera Heavy Flavour in ALICE9 Suppression observed at RHIC STAR : PRL98, (2007) PHENIX : PRL98, (2007) Measurement done via non photonic electrons R AA  good agreement between Phenix and Star Suppression compatible with pure charm … But b expected to dominate for p T >4 GeV to disentangle c/b  full reconstruction of D mesons  good track impact parameter resolution is needed Radiative E loss  C R C R =4/3 for q C R =3 for gluons Non photonic electrons suppressed as light hadrons at high p T  large quark contribution for light flavours? At the LHC gluon contribution should be dominant

9 Feb 2008M. Masera Heavy Flavour in ALICE10 statistical. D0  K-+D0  K-+D0  K-+D0  K-+ Golden channel for open charm S/B ≈ 10% Significance for 1 month Pb-Pb run: S/√(S+B) ≈ 40 Sensitivity w.r.t. pQCD 1 year at standard luminosity (10 9 pp events) Sensitivity w.r.t. pQCD 1 year at standard luminosity (10 9 pp events) statistical. systematic.

9 Feb 2008M. Masera Heavy Flavour in ALICE11 D +  K -  +  + and D s +  K + K -  + Measure D 0 /D + instead of relying on Pythia Larger c  ≈300  m w.r.t. D 0 Larger combinatorial background Smaller of the decay products Performance comparable with D 0  K -  + D s + as probe of hadronization? D s + as probe of hadronization? Fragmentation/recombination Experimentally accessible? D s + (c  ~ 150 µm)  K - K +  + with BR ~ 4.4 % D s + (c  ~ 150 µm)  K - K +  + with BR ~ 4.4 % but mostly resonant decays:  + or K 0 * K + but mostly resonant decays:  + or K 0 * K +  favours backkground rejection  favours backkground rejection 2<p T <3 GeV/c 14 TeV D+K-++D+K-++D+K-++D+K-++ M K  (GeV/c 2) M KK (GeV/c 2 ) D+K-++D+K-++D+K-++D+K-++ Ds+K+K-+Ds+K+K-+Ds+K+K-+Ds+K+K-+ Under study

9 Feb 2008M. Masera Heavy Flavour in ALICE12 Beauty to e/  B  e + X  e ± identification from TRD and dE/dx in TPC  impact parameter from ITS  Subtraction of charm contribution S/(S+B) S per 10 7 central Pb-Pb events Expected ALICE performance (1 month Pb-Pb) 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. Espagnon’s talk

9 Feb 2008M. Masera Heavy Flavour in ALICE13 Performance for D and B quenching m b = 4.8 GeV Statistical error corresponding to 10 7 Pb-Pb and 10 9 p-p events Colour charge dependence Mass dependence

Quarkonia

9 Feb 2008M. Masera Heavy Flavour in ALICE15 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 2008M. Masera Heavy Flavour in ALICE16 Acceptances J/    Dielectron trigger: p T cut=3 GeV/c on individual electrons Dimuon trigger. p T cut = 1 GeV/c (2) for J/  (  )

9 Feb 2008M. Masera Heavy Flavour in ALICE17 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/  region Zoom in the  region

9 Feb 2008M. Masera Heavy Flavour in ALICE18 Quarkonia to dimuons 5.5 TeV One year of data taking -J/  : excellent ( ) -  ’: marginal -  : ok (7000) -  ’: low (2000) -  ’’: very low (1000) 14 TeV One year of data taking -J/  : 2.8   : 2.7  10 4 Invariant mass resolution: J/  peak: ~ 70 MeV/c 2  peak: ~ 100 MeV/c 2

9 Feb 2008M. Masera Heavy Flavour in ALICE19  = -1 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 (2003)) See poster by E. Scomparin  meas -  gen  polariz. 14 TeV vs p T J/  polariz. 5.5 TeV vs  Without backgorund subtraction (S/B=0.2) With backgorund subtraction  meas -  gen One year data taking

20 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) ALICE (prelim. simulation) p T >0

9 Feb 2008M. Masera Heavy Flavour in ALICE21 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 (dE/dx, TOF, TRD) Present simulations focused on the effects of realistic calibration and alignment (see poster P174 by S. Moretto)

BACKUP

9 Feb 2008M. Masera Heavy Flavour in ALICE23 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: LHC System  s NN (TeV) L 0 (*) (cm -2 s -1 ) Run time (s/year)  geom (b) p-p Pb-Pb (*) L 0 (ALICE)= 10 31

9 Feb 2008M. Masera Heavy Flavour in ALICE24 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 pQCD: Naive expectation. Binary scaling to A-A  They travel in the medium  experience the full collision history

9 Feb 2008M. Masera Heavy Flavour in ALICE25 Heavy Flavours in ALICE ALICE channels:  electronic (|  |<0.9)  muonic (-4<  <-2.5)  hadronic (|  |<0.9) ALICE coverage:  Extends to low-p T region  central and forward rapidity regions Precise vertexing to identify D (c  ~  m) and B (c  ~ 500  m) decays

9 Feb 2008M. Masera Heavy Flavour in ALICE26 Baseline: p+p collisions Hard processes (q-qbar annihilation, gluon fusion) occurring at short space-time scale (~1/2m q ) Cross section evaluation  factorized pQCD:  s /2 q q M M xaxa xbxb B or D mesons b or c quarks Cross section to produce hadron M Parton Distribution Functions – x a and x b are parton momentun fractions in the colliding hadrons Cross section at parton level: pQCD. Currently NLO used as a baseline for ALICE. FONLL  better description at high p T Fragmentation function (non perturbative)

9 Feb 2008M. Masera Heavy Flavour in ALICE27 p+p: charm cross section CDF, PRL91 (2003) FONLL: Cacciari, Nason FONLL: beauty production well described at Tevatron (J/ψ from b decay) charm production underpredicted at Tevatron RHIC p+p data underpredicted Discrepancy between Phenix and Star Cacciari, Frixione, Mangano, Nason and Ridolfi, JHEP0407 (2004) 033 PRL98, (2007)

9 Feb 2008M. Masera Heavy Flavour in ALICE28 D/B Mesons Total yield for Pb-Pb central interactions (5%  inel ) at 5.5 TeV D mesons: c  ~ 100 – 300  m Significant BR for B mesons: c  ~ 500  m large BR in semileptonic decay channels (20%) inclusive single electron measurement of B  e e X inclusive muon/dimuon measurement of B    X Main selection tool for D/B mesons: displaced secondary vertices Total yield for Pb-Pb central interactions (5%  inel ) at 5.5 TeV

9 Feb 2008M. Masera Heavy Flavour in ALICE29 D+K-++D+K-++D+K-++D+K-++ Measure D 0 /D + instead of relying on Pythia Larger c  ≈300  m w.r.t. D 0 Larger combinatorial background Smaller of the decay products Performance comparable with D 0  K -  + 2<p T <3 GeV/c d CUT (  m) cos  point CUT Significance S/  (S+B) for 2<p T <3 GeV/c (normalized to 10 7 PbPb events) p T D +  point 14 TeV Dist prim. Sec. (  m)

9 Feb 2008M. Masera Heavy Flavour in ALICE30 Ds+K+K-+Ds+K+K-+Ds+K+K-+Ds+K+K-+ M K  (GeV/c 2) M KK (GeV/c 2 ) D s + as probe of hadronization? D s + as probe of hadronization? from string fragmentation: cs / cd ~ 1/3 from string fragmentation: cs / cd ~ 1/3 after decays: D s + (cs) / D + (cd) ~ 0.6 after decays: D s + (cs) / D + (cd) ~ 0.6 from recombination: cs / cd ~ N(s) / N(d) from recombination: cs / cd ~ N(s) / N(d) How large at LHC? How large at LHC? experimentally accessible? experimentally accessible? D s + (c  ~ 150 µm)  K - K +  + with BR ~ 4.4 % D s + (c  ~ 150 µm)  K - K +  + with BR ~ 4.4 % but mostly resonant decays:  + or K 0 * K + but mostly resonant decays:  + or K 0 * K +  favours bkgnd rejection  favours bkgnd rejection M KK (GeV/c 2 )

9 Feb 2008M. Masera Heavy Flavour in ALICE31 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 B mesons via B  e e X (I)

9 Feb 2008M. Masera Heavy Flavour in ALICE32 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: B mesons via B  e e X (II) Selection of the beauty electron candidates in 3 steps beauty dominates left charm left bkg

9 Feb 2008M. Masera Heavy Flavour in ALICE33 expected statistics and systematic uncertainties p T -differential electron cross section reconstructed from ~ 1 to 20 GeV/c B mesons via B  e e X (III) Results for beauty in Pb-Pb 10 7 central (0-5%) Pb-Pb events

9 Feb 2008M. Masera Heavy Flavour in ALICE34 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: Bµ + + D + X µ - + X B B X + µ + BD same BB diff BD same BB diff

9 Feb 2008M. Masera Heavy Flavour in ALICE35 HF to single muon in p-p Signal:  from b/c decays Background:   from  /K decays Can be extracted from data   from the absorber Subtraction: tracks do not point to the vertex, no FMD hits Good preliminary results: high statistics needed Slices in p T. Correct for diamond shape

9 Feb 2008M. Masera Heavy Flavour in ALICE36 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 2008M. Masera Heavy Flavour in ALICE37 Quarkonia to dielectrons: Pb-Pb Dielectron invariant mass spectrum in central collisions after one “ALICE-year” of Pb-Pb data taking

9 Feb 2008M. Masera Heavy Flavour in ALICE38 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  v 2 vs. centrality (b=collision impact parameter)  v 2 vs. p T in different centrality bins HOW HOW: fast simulation to generate:  N D+ (  p T,  b)  N D+ (  p T,  b) with an angular distribution v 2 D,in dN D /d  = v 2 D,in cos [2(  -  RP )] N tracks  For each D + : an event made of N tracks is superimposed v 2 ev,in dN/d  = v 2 ev,in cos [2(  -  RP )] N D+ (  p T,  b)v 2 D,in, N tracks,v 2 ev,in  Inputs of the simulation: N D+ (  p T,  b), v 2 D,in, N tracks,v 2 ev,in v 2 D  Outputs: v 2 D measured.

9 Feb 2008M. Masera Heavy Flavour in ALICE39 v 2 vs. p T Large stat. errors on v 2 of D ± → K  in 2·10 7 MB events 6<b<9 fm MB trigger Semi-peripheral trigger Sum D 0 →K  and D ± →K   Sufficient for v 2 vs. centrality Semi-peripheral trigger  v 2 vs. p T that would be obtained from 2·10 7 semi-peripheral events (e.g. 6<b<9 fm) How to increase the statistics?

9 Feb 2008M. Masera Heavy Flavour in ALICE40 B elliptic flow v 2 evaluated from B  e+X Pb-Pb centrality: 20-60% 1 year at nominal luminosity

9 Feb 2008M. Masera Heavy Flavour in ALICE41 Kinematical distributions: prompt J/  versus secondary J/  “pseudo proper decay time” Primary J/ Secondary J/ x

9 Feb 2008M. Masera Heavy Flavour in ALICE42 In order to extract the fraction f B of J/  from b-hadron decays, one should fit simultaneously the invariant mass spectrum one distribution which can discriminate prompt from detached J/  (e.g. x or d 0 e+ ·d 0 e- ) the tails of the M(e + e - ) distribution measures the percentage of background How to measure the fraction of secondary J/  Events/10 MeV