Charm and beauty with ALICE at LHC Rosario Turrisi University and INFN, Padova, Italy for the ALICE Collaboration

2 Contents Heavy flavors and heavy ions Key performances of ALICE Charm cross section and p t sensitivity Beauty cross section Conclusions and Perspectives

3 Heavy flavors and heavy-ions Why measure heavy flavors at LHC ? –Interest in its own right: discovery potential! More specific to our issue (hot and dense matter): –quarkonium suppression: deconfinement signature –probes of the medium: early formation (initial parton-parton), most energetic phase thermal (late) production ? energy loss (medium dependent?) –B J/ important background for direct J/  –open heavy flavors as natural normalization for QQ studies pp reactions, pQCD, nuclear effects (geometry, shadowing) medium properties INPUT OUTPUT =5.5 TeV not covered here KK  ee c  D  K  b  B  eX open flavors channels

4 Quark energy loss: basics Common explanation: parton energy loss due to gluon radiation –Average energy loss (BDMPS model): C R Casimir factor = 3 for gluons 4/3 for quarks q = medium transport coefficient  gluon density and momenta path length L c g R.Baier, Yu.L.Dokshitzer, A.H.Mueller, S.Peigne' and D.Schiff, Nucl. Phys. B483 (1997) 291. C.A.Salgado and U.A.Wiedemann, Phys. Rev. D68 (2003) [arXiv:hep-ph/ ]. Study to get the medium effect R AA measured at RHIC with pions: clear high-pt suppression R AA =1 if AA is superposition of independent pp collisions Quark Matter Conference ’04 A.Dainese, C.Loizides and G.Paic, hep-ph/

5 Energy loss with heavy flavors ? Effect present in light mesons, what about other particles? –D,B meson originate from c,b quarks C r = 4/3, whereas light flavors originate mainly from gluons (C=3) –Dead cone effect * : due to destructive interference, gluons radiation is suppressed at angles  < m Q /E Q q = 100 GeV 2 /fm at LHC 1 * Yu.L.Dokshitzer and D.E.Kharzeev, Phys. Lett. B519 (2001) 199 [arXiv:hep-ph/ ]. 1. K.J.Eskola, K.Kajantie, P.V.Ruuskanen and K.Tuominen, Nucl. Phys. B570 (2000) 379 [hep-ph/ ]. charm beauty Comparison among -D-B in order! extrapolation from q=15 GeV 2 /fm at RHIC… a worst case (q=100 GeV 2 /fm)! 

6 Cross sections NLO pQCD (Mangano-Nason-Ridolfi), average of MRST e CTEQ5M PDF’s, EKS98 in Pb-Pb for shadowing (shadowing = modification of PDF’s, reduction of cross section) Taking into account  F,  R a factor 4 arises between min. and max. cross section… In acceptance! D 0 / D 0 B (s) +  b pp PbPb1409 ~0.5 D 0  K ~0.2 B  eX Mesons multiplicities central collisions

7 Tracking performance impact parameter resolution:  p t =1.3 GeV < 50 μm   < 150 μm z EFFICIENCY pions kaons p t resolution: σ= 1(10) GeV 100 GeV

8 test beam:  id. as e  = 1 % PID: e,, K, p PbPb events, dN/dy=6000 TRD electrons TPC hadrons TOF Combined π/e ~ 10 p t ~1-2 GeV p (GeV/c)

9 Selection cuts D 0  K –decay topology –impact parameter of tracks (in bending plane, d 0 ~100 μm) –momenta –identification D 0 with |y|<1 ~ 0.5 D 0 with |y|<1 but also charged  /K in PbPb collisions cos(pointing angle) vs. impact parameters product

10 Performance: D 0 K K, M INV integrated over p t 10 7 PbPb events (one-month run) dN/dy(y=0) = 6000 (charged) S/B initial (M3) S/evt final (M1) S/B final (M1) Significance S/S+B (M1) 5   % 37 (for 10 7 evts) measurement of p t distribution

11 Charm energy loss in ALICE Current estimation of q = 100 GeV 2 /fm  m c =0 m c =1.2 GeV/c 2 N.Armesto, A.Dainese, C.A.Salgado and U.A.Wiedemann, in preparation

12 Task: tag ~ 0.8 e  /event from b decays among ~ 10 3 electrons from other sources Main backgrounds: –pions misidentified as electrons –Dalitz decays –charm semi-electronic decays –photon conversions in the detector materials –strange decays Strategy: –high impact parameter: c ~ 500 μm for beauty –high momenta: beauty harder than lighter flavors –electron/pion separation critical b e+X: strategy

13 p t and d 0 spectra beauty electrons charm electrons charged pions

14 b e+X: purity and statistics background cure charm electrons p t thr. light mesons electrons d 0 thr. charged pions identification p T > 1 GeV p T > 2 GeV p T > 3 GeV p T >2 GeV, 180  d 0  600  m 90% purity 50,000 B's (including TRD efficiency)

15 Conclusions & perspectives ALICE has a good potential to measure heavy flavors in different channels Charm: –production cross section –p t distribution –study of energy loss Beauty: –Production cross section Coming up –reconstruction of b decay topologies b’s p t distribution, energy loss study –additional D, D * channels –semi-electronic charm (beauty background!) –… 11% S/B, significance=37 p T > 1 GeV p T > 2 GeV p T > 3 GeV

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17 ALICE detectors Solenoid magnet B<0.5 T TPC 88 m 3, 510 cm length, 250 cm radius Ar (90%) + CO 2 (10%) 88 μs drift time main tracking device, dE/dx 2  * 1.8 units of pseudo-rapidity ITS- 6 Layers, 3 technologies Material budget < 1% of X 0 per layer! Silicon Pixels  vertices resolution in xy (0.2 m 2, 9.8 Mchannels) Silicon Drift  resolution in z (1.3 m 2, 133 kchannels) Double-sided Strip  connection w/TPC (4.9 m 2, 2.6 Mchannels) PIXEL CELL z: 425  m r  : 50  m Two layers: r = 4 – 7 cm 9.8 Mch TRD - 6 layers for: electron/pion separation at p t >1 GeV factor 100 rejection at 2 GeV tracking complement, mass resolution 100 MeV/c  high p t trigger (onia studies) TOF - Multigap Resistive Plate Chambers   < 100 ps pions, kaons, protons separation (see later) electrons/pions at low p t

18 60  <  < 62  Total charged multiplicity TPC + ITS projection of the full  range (front view) dN CH /dy (y=0) Current baseline: 6000 Tested up to: 8000

19 Quarkonia detection see Andres Sandoval’s talk (I hope…)

20 Signal & background pt

21 Centrality

22 LHC run parameters System pp PbPb √s NN (TeV) L 0 (cm -2 s -1 ) dN/dy (y=0) T RUN (s/year)  geom (b) *  * * 7.7 Fall *L max (ALICE) = ** L int (ALICE) ~ 0.7 nb -1 /year Pile-up in TPC + and ion-density limit   tuning or beam offset and, later, more systems: pA, light ions (Sn, Kr, Ar,O) & other energies 5.5 TeV).

23 x regime

24 pQCD extrapolations NLO pQCD (Mangano-Nason-Ridolfi), average of MRST e CTEQ5M PDFs (EKS98 in Pb-Pb for shadowing) Taking into account  F,  R a factor 4 arises between min and max x-section… inclusive cross section already a valuable information!

25 Hadron multiplicities pp PbPb ~8 B or b  ~0.85 B  eX ~140 D 0 /D 0  ~5 D 0  K

26 Acceptance SPD multiplicity -2<  <2

27 b->e+X: contamination p t bin [GeV/c] d 0 threshold [m] % S ( bc/b ) % B charm % B other elec. Ns [x10 4 ] 1.0 – – – 60 (30%) 30 – 20 9 – – – – 90 (15%) 20 – 10–6 – – – 300> 90 (10%) < 10–4 – – – 300> 95 (10%) < 5–4 – 1

28 Particle identification Various techniques… … in a wide momentum range 2   |  |<0.9

29 Charm detection performance S/B initial (M3) S/evt final (M1) S/B final (M1) Significance S/S+B (M1) Pb-Pb 5   % 37 (for 10 7 evts, ~1 month) pp 2   % 44 (for 10 9 evts, ~1 year)

30 Expected multiplicity/running conditions ALICE optimized for dN/dy(y=0) = , tested extensively up to 8000 Extrapolating from RHIC… hep-ph √s (GeV) N ch /(0.5N part ) dN ch /d  |  < dN ch /d  ~ 1300 dN ch /d  ~ 2500

31 D 0  K -  + : d 2 (D 0 )/dp t dy and d(D 0 )/dy d  (D 0 )/dy for |y| 1 GeV/c (65% of  (p t > 0)) statistical error = 7 % systematic error = 19 % from b = 9 % MC correction = 10% B.R. = 2.4 % from AA to NN = 13 % d  (D 0 )/dy for |y| 0 statistical error = 3 % systematic error = 14 % from b = 8 % MC correction = 10% B.R. = 2.4 %  inel = 5 % inner bars: statistical outer bars: systematic

32 Signal history, errors for PbPb Selection effectiveness… Signal Total D 0 / event 141 decaying in K  5.4 with K and  in acc. 0.5 after track rec after ( ,  ) rejection 0.13 after selection cuts Background reduced by a factor ~

33 Energy loss vs. dead cone D/h ratio: R D/h = R AA D / R AA h q = 4 GeV 2 /fm at LHC requiring same hadron suppression as at RHIC Quantitative difference heavy/light mesons measurement? R D/h ~ 2 in hot QGP sensitive to medium density E gluons/quarks energy loss ~ 2 E gluons/quarks fragmentation ~ 1/2 dead cone makes the difference!

34 General motivation A Large Ion Collider Experiment is the LHC experiment dedicated to the study of the Quark Gluon Plasma… QGP  a (locally) thermally equilibrated state of matter in which color degrees of freedom become manifest over nuclear, rather than merely nucleonic, volumes. “Partons are deconfined” strong interaction LHC = 5.5 TeV hadronic matter QGP high energy & large volume

35 Performance studies Detector description with the state-of-the-(ALICE)-art code AliRoot Charm/beauty signal tuned to NLO pQCD p t spectrum (custom tuning of PYTHIA) Background from HIJING, 6000 charged particles per unit rapidity at midrapidity Priorities: the exclusive decay of the D 0  K (golden channel): –test bench for secondary vertex detection, pid –very high background inclusive b  eX decay –secondary vertices –electron identification –“easy” measurement of cross section

36 QGP evidences and probes At LHC 5.5 ATeV): more strictly μ B =0 higher energy density SPS experiments got some evidence that matter may behave in odd ways (not just as “typical” hadrons) RHIC exps show confirmation of the new behaviour,mostly with light mesons and hadrons Possible improvements: –experimental smoking gun of QGP? (see f.e. T. Hallman talk at ICHEP 2004, Beijing, China) –study of QGP properties? DEEP DECONFINEMENT? larger volume longer lifetime Hard cross section dominant Could heavy flavors represent a good tool at LHC?