La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 1 Andrea Dainese INFN Legnaro Preparazione per la misura di produzione di D 0 2° Convegno Italiano sulla Fisica di ALICE Vietri sul Mare (SA), 30/5-1/6, misura del beauty nel canale semi-elettronico

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 2 Contents Charm and beauty in ALICE: motivations D 0  K  reconstruction D 0 cross section measurement in pp, pPb, Pb-Pb A.D. & R.Grosso PhD theses, PPR v2 Beauty measurement via displaced electrons in pp and Pb-Pb Antinori, A.D., Bombonati, Lunardon, Turrisi, Internal Notes to appear, PPR v2 Sensitivity in comparison to predictions, in pp (pQCD) and Pb-Pb (energy loss)

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 3 c and b production at the LHC Important test of pQCD in a new energy domain remember the “15-years saga of b production at the Tevatron” *… …and c production not yet fully reconciled LHC: NLO predictions (ALICE baseline for charm / beauty) system :  s : Pb-Pb (0-5% centr.) 5.5 TeV p-Pb (min. bias) 8.8 TeV pp 14 TeV 4.3 / / / / / / LHC: Theoretical uncertainty of a factor 2--3 beautycharm HERA-LHC Workshop Proceedings using: Mangano, Nason, Ridolfi, NPB373 (1992) 295 * M.Mangano CDF, PRL91 (2003) FONLL: Cacciari, Nason Cacciari, Frixione, Mangano, Nason and Ridolfi, JHEP0407 (2004) 033

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 4 increasing  s HQs as a probe of small-x gluons 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 Eskola, Kolhinen, Vogt, PLB582 (2004) 157 Gotsmann, Levin, Maor, Naftali, hep-ph/ Cartoon charm beauty Window on the rich phenomenology of high-density PDFs gluon saturation / recombination effects non-linear terms in PDFs evolution Possible effect: enhancement of charm production at low p t w.r.t. to standard DGLAP-based predictions  c (DGLAP+non-linear)  c (DGLAP)

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 5 Pb-Pb collisions: Parton Energy Loss Partons travel ~ 4 fm in the high colour-density medium Energy loss (gluon radiation + collisional? ) Casimir coupling factor: 4/3 for quarks 3 for gluons Medium transport coefficient  gluon density Baier, Dokshitzer, Mueller, Peigne‘, Schiff, (BDMPS), NPB483 (1997) 291 (BDMPS) Probe the medium  Carlos

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 6 Lower E loss for heavy quarks? In vacuum, gluon radiation suppressed at  < m Q /E Q  “dead cone” effect Dead cone implies lower energy loss (Dokshitzer-Kharzeev, 2001) Detailed calculation confirms this qualitative feature, although effect is small and uncertainties significant (Armesto- Salgado-Wiedemann, 2003) Exploit abundant massive probes at LHC & study the effect by measuring the nuclear modification factor for D and B Q Dokshitzer, Kharzeev, PLB519 (2001) 199 Armesto, Salgado, Wiedemann, PRD69 (2004) Gluonstrahlung probability

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 7 News from RHIC: heavy-flv decay electrons suppressed! Armesto, Cacciari, Dainese, Salgado, Wiedemann, hep-ph/ Djordjevic, Gyulassy, Wicks, nucl-th/ Radiative Radiative + Collisional Energy loss calculations tend to underpredict suppression Indirect measurement: non-photonic electrons (Dalitz and conversions subtracted); charm / beauty inclusive (uncertainty on pp baseline)

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 8 mass effect Color-charge and mass dep. of E loss with Heavy-to-Light ratios at LHC Heavy-to-light ratios: Compare g  h, c  D and b  B For 10 < p t < 20 GeV, charm behaves like a m=0 quark, light-flv hadrons come mainly from gluons R D/h enhancement probes color-charge dep. of E loss R B/h enhancement probes mass dep. of E loss Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005)

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 9 Beauty-to-Charm ratio: R B/D Compare c and b  same colour charge Mass effect  Enhancement of factor ~2, independent of (for ) Adapted from Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005)

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 10 D 0  K -  + in ALICE Exclusive reconstruction direct measurement of the p t distribution Weak decay with mean proper length c  = 124  m Large combinatorial background  (dN ch /dy) 2 STRATEGY: invariant-mass analysis of fully-reconstructed topologies originating from (displaced) secondary vertices Measurement of Impact Parameters (ITS+TPC) Measurement of Momenta (ITS+TPC) Particle identification (TOF) to tag the two decay products

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 11 Vertexing: track d 0 resolution < 60  m (r  ) for p t > 1 GeV/c Resolution mainly provided by the 2 layers of silicon pixels PIXEL CELL z: 425  m r  : 50  m Two layers: r = 4 cm r = 7 cm  9.8 M INFN Legnaro

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 12 Interaction vertex reconstruction in pp collisions Vertex diamond stable for few hours; if beam focused, precise vertex position from average over many events “Nominal” size of the beam:  = 15  m in Pb-Pb  = 15  m in pp ( L ~ cm -2 s -1 )   150  m in pp (if L is reduced at ALICE IP to ~ cm -2 s -1 ) In pp the E-by-E vertex position has to be reconstructed in 3D using tracks Finding/fitting algorithm developed and optimized A.D. and M.Masera, ALICE-INT as in Pb-Pb pp with charm pp min. bias

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 13 Selection of D 0 candidates increase S/B by factor ~10 3 !

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 14 Time-of-flight PID TOF Pb-Pb, dN ch /dy=6000 Optimization for hadronic charm decays was studied: minimize probability to tag K as  K id. required for D 0 p t < 2 GeV/c

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 15 S/B initial (M  3  ) S/B final (M  1  ) Significance S/  S+B (M  1  ) Pb-Pb central 5  % ~35 (for 10 7 evts, ~1 month) pPb min. bias 2  % ~30 (for 10 8 evts, ~1 month) pp 2  % ~40 (for 10 9 evts, ~7 months) Results Note: with dN ch /dy = 3000 in Pb-Pb, S/B larger by  4 and significance larger by  2 central Pb-Pb

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 16 Statistical Errors (R.Grosso)

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 17 Feed-down from Beauty At LHC energies Fraction of D 0 from chain b  B 0 /B +  D 0 not negligible “Standard” NLO pQCD + Pythia fragmentation + BR: Selections increase this ratio to ~10-15% Results have to be eventually corrected for feed-down systematic error from uncertainty on b cross section Possibility to have direct estimate by D 0 d 0 (à la CDF)

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 18 D 0 cross section measurement inner bars: stat. errors outer bars: stat.  p t -dep. syst. errors normalization error not shown: 9% Pb-Pb and p-Pb, 5% pp

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 19 B  e + X: Detection strategy 1)Electron PID: reject most of the hadrons 2)d 0 cut: reduce charm and bkg electrons (Dalitz,  conv.) 3)Subtract (small) residual background (ALICE data + MC) Primary Vertex B e X d0d0 rec. track

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 20 Electron identification Combined info from TRD (trans. rad.) and TPC (dE/dx) TRD rejects 99% of the   and ALL heavier hadrons (p t > 1 GeV/c) TPC further rejects residual pions (up to 99% at low p) About 20% of electrons rejected fraction of misidentified pions

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 21 Effect of electron identification (pp)

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 22 Errors Summary d 0 cut tuned vs p t to find best compromise between statistical and systematic errors from charm and bkg subtractions

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 23 Cross section of electrons from B inner bars: stat. errors outer bars: stat.  p t -dep. syst. errors not shown: norm. error (5% pp, 9% Pb-Pb) 1 year at nominal luminosity (10 7 central Pb-Pb events, 10 9 pp events)

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 24 pp,  s = 14 TeV Comparison to pQCD predictions & perspectives for 1 st month 1 year at nominal luminosity 1 month at ~ end 2007 Detector configuration: ITS + TPC + TOF Expectations for first pp run: Scaling of stat. errors according to  N evts No dedicated cuts study D 0  K 

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 25 pp,  s = 14 TeV Comparison to pQCD predictions & perspectives for 1 st month 1 year at nominal luminosity 1 month at ~ end 2007 Detector configuration: ITS + TPC + TRD (~1/5 at end ’07) Expectations for first pp run: Scaling of stat. errors according to  N evts No dedicated cuts study B  e + X

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 26 Charm and Beauty E Loss : R AA m b = 4.8 GeV Low p T (< 6–7 GeV) Also nuclear shadowing (here EKS98), in-medium hadr… High p T (> 6–7 GeV) Only parton energy loss D 0  K  B  e + X 1 year at nominal luminosity (10 7 central Pb-Pb events, 10 9 pp events)

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 27 Interpretation of R AA : The role of hadronisation Lowish p t D and B mesons may hadronise inside the medium via coalescence  no clean study of parton E loss Up to which p t is this relevant?  Study particle type-dependence of R CP LHC: kaons and hyperons D meson R CP sensitivity under study E loss only Statistical errors for 10 7 min. bias Pb-Pb evts

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 28 Heavy-to-light ratios: R D/h 1 year at nominal luminosity (10 7 central Pb-Pb events, 10 9 pp events)

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 29 Heavy-to-light ratios: R B/D 1 year at nominal luminosity (10 7 central Pb-Pb events, 10 9 pp events)

La Fisica di ALICE - Vietri sul Mare, Andrea Dainese 30 Summary Feasibility studies for D 0 and B measurements in pp, Pb-Pb (and pPb,only D 0 ) carried out many critical items identified and partially addressed: PID, d 0 & primary vertex measurement, feed-down from beauty to charm Results are very promising p t coverage in the range GeV/c for D 0 and electrons from B some physics “applications” identified and studied First measurements in pp already after “first month” (10 7 evts) D 0 : coverage up to p t ~ 7 GeV/c B: total cross section; not much on p t dependence Getting ready for first collisions: Long to-do list presented at May PWG3 Analyses to be performed / tuned on 2006 pp production (PDC06)