Open heavy flavour reconstruction in the ALICE central barrel Francesco Prino INFN – Sezione di Torino for the ALICE COLLABORATION ICHEP 2008, Philadelphia, July 31st 2008

2 Large cross-section  Much more abundant c and b production with respect to RHIC  ALICE baseline for heavy flavours = pQCD at NLO (MNR code) in pp + binary scaling + shadowing Charm and Beauty at the LHC (I) pppPb (min bias)PbPb (5% central)  s (TeV) N cc N bb

3 Small X  unexplored small-x region probed with charm at low p T and/or forward rapidity down to x~10 -4 with the charm already at y=0  Window on the rich phenomenology of high-density PDFs: Shadowing Gluon saturation Color Glass Condensate  Large spread in predictions! need for pA collision Charm and Beauty at the LHC (II) increasing  s x~10 -4

4 ALICE at the LHC

5 ALICE performance: Track impact parameter Resolution on track impact parameter (= Distance of Closest Approach between track and primary vertex)  Mainly provided by the 2 innermost ITS layers equipped with silicon pixel detectors  Two components: detector spatial resolution + p T (  ) dependent multiple scattering 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

6 ALICE performance: Vertexing 3D reconstruction from tracks of primary (interaction) and secondary (decay) vertices position with full error- matrix treatment  Resolution on vertex position important for Impact parameter resolution (in p-p low multiplicity events) Separation of secondary vertices from the primary Determination of the pointing angle Primary vertex in pp Decay vertex D +  K -    

7 Hadronic charm TPC (tracking) TOF (K/  id) ITS (vertexing) K  D 0  K  D +  K  D s  KK  D*  D 0  D 0  K   c   Kp under study

8 D mesons in the central barrel SELECTION STRATEGY: invariant-mass analysis of fully-reconstructed topologies originating from displaced vertices  build pairs/triplets/quadruplets of tracks with correct combination of charge signs and large impact parameters  particle identification to tag the decay products  calculate the vertex (DCA point) of the tracks  good pointing of reconstructed D momentum to the primary vertex Primary Vertex D+ flight line Secondary vertex   K ZOOM D +  K 

9 D 0  K -  + : selection Pair of opposite sign charged tracks  large and opposite sign impact parameter  Good pointing of reconstructed D momentum to primary vertex

10 D +  K -  +  + : selection SIG BKG d PRIM-SEC (  m) cos  point Triplet of charged tracks  Large distance between primary and secondary vertex (c  = 310  m)  Good pointing of the reconstructed D momentum to the primary vertex

11 2<p T <3 GeV/c 14 TeV D+K-++D+  K-++D+K-++D+  K-++ D0K-+D0K-+D0K-+D0K-+ D+D+ D0D0 D + and D 0 : expected results 5.5TeV 10 9 ev ev.

12 Beauty from single electrons ITS (vertexing) TPC (tracking + e/  id) TRD (e/  id) e

13 Beauty from displaced electrons Selection strategy: exploit the different shapes of p T and track impact parameter distributions for the various e - sources  Electron identification in TRD+TPC  Impact parameter cut to select displaced tracks  Subtraction of charm and bkg contributions (mainly at low p T ) Primary Vertex B e X d0d0 rec. track 10 9 ev ev.

14 Beauty from displaced J/  TPC (tracking + e/  id) TRD (e/  id) ITS (vertexing) e + e 

15 Primary J/  J/  from B Beauty from displaced J/  Important measurement of:  Beauty cross section (complementary to B  e/µ + X)  Fraction of J/  ’s from B decays (expected ≈ 20% at LHC) Important to investigate medium effects on primary J/  Preliminary study for pp collisions  based on pseudoproper decay time (à la CDF, D. Acosta et al Phys. Rev. D 71 (2005) ) p T >0 tot tot J/  J/  from B bkg

16 Observables: R AA D 0  K  B  eX m b = 4.8 GeV Nuclear modification factor (R AA )  R AA ≠1  binary scaling violation  Low p T : main effect on R AA is nuclear shadowing  High p T : main effect on R AA is energy loss Statistical error corresponding to 1 year at nominal luminosity  10 7 central Pb-Pb and 10 9 p-p events Energy loss from Armesto et al. Phys. Rev.D71 (2005)

17 Heavy-to-light ratios (R Dh and R BD )  R Dh probes colour-charge dependence of Eloss (  E q <  E g )  R BD probes mass dependence of Eloss (dead cone effect) Statistical error corresponding to 1 year at nominal luminosity  10 7 central Pb-Pb and 10 9 p-p events Energy loss from Armesto et al. Phys. Rev.D71 (2005) Observables: R Dh and R BD

18 Observables: v 2 Elliptic anisotropy (v 2 ) for non-central events:  Low p T : Probes charm thermalization and recombination models  High p T : probes path-length dependence of Eloss Statistical error corresponding to 1 year PbPb at nominal luminosity for events in centrality class 6 < b(fm) < 9 v 2 theoretical prediction from Ko et al., Braz J. Phys 37 (2007)  10 7 min.bias evts 2  10 7 evts with 6<b<9 fm Centrality bin: 6<b<9 fm

19 Conclusions LHC: heavy flavour machine! ALICE has promising performance for all key measurements  Precise vertexing in the central region to identify D (c  ~  m) and B (c  ~ 500  m) decays  Low-p T region  Central and forward rapidity regions  Disentangle c and b Detector commissioned Presently taking data with cosmic rays for ITS and TPC alignment

20 Cosmics in ALICE central barrel ITS+TPC cosmic track First cosmic track seen in ITS (Jun 13th 2008)

21 Coming-up: p-p Performance example: D 0  K -   in pp  Expected statistical error  Expected sensitivity in comparison to pQCD with 10 9 pp events

Backup

23 Collisions at the LHC p-p collisions  Test of pQCD (and saturation models) in a new  s and x regime  Baseline for Pb-Pb p-Pb collisions  Probe nuclear PDFs at LHC energy  Disentangle initial and final state effects Pb-Pb collisions  Probe the medium formed in the collision WARNING: pp, pPb and PbPb will have different  s values  Need to extrapolate from 14 TeV to 5.5 TeV to compute R AA Small (≈ 10%) theoretical uncertainty on the ratio of results at 14 and 5.5 TeV

24 Small X  unexplored small-x region probed with charm at low p T and/or forward rapidity down to x~10 -4 with the charm already at y=0  Window on the rich phenomenology of high-density PDFs: Gluon saturation, Color Glass Condensate Bjorken x in ALICE muon arm Central barrel increasing  s

25 Heavy-flavours in ALICE ALICE channels:  electronic (|  |<0.9)  muonic (-4<  <-2.5)  hadronic (|  |<0.9) ALICE specific features:  low-p T region  central and forward rapidity regions  Both c and b  Precise vertexing in the central region to identify D (c  ~  m) and B (c  ~ 500  m) decays

26 Rescaling pp data from 14 to 5.5 TeV Different systems (pp, p-Pb, Pb-Pb) will have different  s values Results in pp at 14 TeV will have to extrapolated to 5.5 TeV (Pb-Pb energy) to compute, e.g., nuclear modification factors R AA pQCD: “there ratio of results at 14 TeV/5.5 TeV has ‘small’ uncertainty” charm beauty  12%  8% MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295.

27 Measurement essentially from non- photonic electrons  Disagreement between STAR and PHYSICS on total charm Cross Section  R AA in agreement non photonic electrons as suppressed as light hadrons need to disentangle c and b RHIC results

28 Inner Tracking System 6 cylindrical layers of silicon detectors: L= 97.6 cm Silicon Pixel Detectors (2D) Silicon Drift Detectors (2D) Silicon Strip Detectors (1D) R= 43.6 cm Layer Technolog y Radius (cm) ±z (cm) Spatial resolution (  m) rr z 1Pixel Pixel Drift Drift Strip Strip provide also dE/dx for particle idetification

29 Main tracking detector Characteristics:  R in 90 cm  R ext 250 cm  Length (active volume)500 cm  Pseudorapidity coverage: -0.9 <  < 0.9  Azimuthal coverage: 2   # readout channels≈560k  Maximum drift time:88  s  Gas mixture: 90% Ne 10% CO 2 Provides:  Many 3D points per track  Tracking efficiency > 90%  Particle identification by dE/dx in the low-momentum region in the relativistic rise Time Projection Chamber

30 TRD for e - identification For 90% electron identification efficiency  Contamination from pions ≈  Contamination from kaons and protons negligible

31 Time Of Flight TOF Pb-Pb, dN ch /dy=6000 Multigap Resistive Plate Chambers  for pion, kaon and proton PID Characteristics:  R in 370 cm  R ext 399 cm  Length (active volume)745 cm  # readout channels≈160k  Pseudorapidity coverage: -0.9 <  < 0.9  Azimuthal coverage: 2  Provides:  pion, Kaon identification (with contamination <10%) in the momentum range GeV/c  proton identification (with contamination <10%) in the momentum range GeV/c

32 Primary vertex resolution Resolution improves if the beam profile (average position and sigma) in the transverse plane is known with diamond without diamond

33 Effect of primary vertex resolution on impact paramter Contribution to track impact parameter resolution from primary vertex uncertainty not negligible for pp low multiplicity events pp low multiplicitypp high multiplicity

34 D 0  K -  + reconstruction and selection

35 D 0  K -  + : Signal and Background Signal and Background normalized to 1 central Pb-Pb event Significance for 10 7 Pb-Pb events

36 D 0  K -  + : Feed down from beauty Expected fraction of D 0 mesons from B decays ≈5% After selection cut: D 0 (from b) / D 0 (from c) ≈ 12%  Cuts on product of impact parameters and pointing angle enhance the fraction of secondary D 0

37 B  e - + X : Purity and Statistics Alice performance in 1 month of PbPb data taking:  Cuts: p T > 2 GeV/c, 200 < |d 0 (  m)| < 600  Purity: 80%  Selected signal = e - from B

38 Beauty from displaced electrons p T distribution of selected electrons  Background mainly at low p T electron 10 7 central PbPb

39 B  J/  + X : p T bins Pseudoproper decay time:

40 B  J/  + X : comparison with CDF Pseudoproper decay time: ALICE (prelim. simulation) p T >0 CDF (data) tot tot J/  J/  from B bkg