ALICE Physics Week, Muenster, Andrea Dainese 1 Status of B analysis via single electrons Andrea Dainese INFN – Legnaro based on work with: F.Antinori, C.Bombonati, M.Lunardon, R.Turrisi

ALICE Physics Week, Muenster, Andrea Dainese 2 Layout Beauty measurement using displaced electrons Detection strategy Experimental issues: tracking and PID Results for pp and Pb-Pb Physics Performance: Sensitivity to pQCD predictions in pp Beauty quenching Conclusions / Outlook

ALICE Physics Week, Muenster, Andrea Dainese 3 Measuring beauty via electrons Expected yields of charm (b.r.: 10%) and beauty (b.r.: 11% +10% as b  c  e) decay electrons: b quark has c  500  m decay electrons d 0 ~ few-100  m Primary Vertex B e X d0d0 rec. track system :  s NN : Pb-Pb (0-5% centr.) 5.5 TeV pp 14 TeV pp 900 GeV 115 / / / / 1 (+1)0.03 / ( ) / ( ) 6 / 0.25 (+0.25) / ( ) / ( ) transverse plane What’s the background?

ALICE Physics Week, Muenster, Andrea Dainese 4 Background 1: charm decays pp Heavy-quark decays: b → B→e b→B→D→e c→D→e beauty charm (background)

ALICE Physics Week, Muenster, Andrea Dainese 5 Background 2: other sources 1.Decays of light mesons and Dalitz decays (mostly  0 ) 2.Photon conversions (  → e + e - ) in the beam pipe and ITS innermost layer 3.Charged pions mis-identified as electrons NO PID pp

ALICE Physics Week, Muenster, Andrea Dainese 6 Detection strategy 1)Electron PID: reject most of the hadrons 2)Impact parameter cut: reduce charm and bkg electrons 3)Subtract (small) residual background Primary Vertex B e X d0d0 rec. track

ALICE Physics Week, Muenster, Andrea Dainese 7 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 1 GeV/c) outdated: latest info from TRD group on  rejection probability 99.3% – 0.3% p (GeV/c), for 90% electron eff. TPC further rejects residual pions (up to 99% at low p) About 20% of electrons rejected fraction of misidentified pions outdated: latest info from TRD group on p rejection probability 99.3% – 0.3% p (GeV/c), for 90% electron eff. thanks to A.Andronic, S.Masciocchi

ALICE Physics Week, Muenster, Andrea Dainese 8 In a given p t -bin, N “electrons” are counted, after PID and d 0 cut: N = N b + N c + N bkg 1.Subtract the contribution from charm: N b + N bkg = N - N c estimated from D 0 measurement (source of error) 2.Subtract the contribution from background: N b = (N – N c ) - N bkg estimated from measured pions dN/dp t plus MC (source of error) 3.Correct for acceptance/efficiency: dN b corr /dy = (N b /  ) efficiency calculated with MC (source of error) 4.Multiply by the inelastic pp cross section (or by Pb-Pb overlap functions): d  e from b /dy =  pp. dN b corr /dy pp cross section measured at LHC (source of error) Cross section extraction procedure

ALICE Physics Week, Muenster, Andrea Dainese 9 Error contributions Statistical: Systematic: Error from subtractions: Error from acc./effic. corrections: 10% (in principle p t -dependent) Error from cross section normalization: 5% for pp, 9% for Pb-Pb (p t -independent) ~10% dep. on d 0 cut pp

ALICE Physics Week, Muenster, Andrea Dainese 10 Optimization of d 0 cut in bins of p t pp, 10 9 events Systematic error: prefers tight cut (high signal purity) dominates at low p t Statistical error: prefers loose cut (small d 0 MIN) dominates only at high p t “old TRD PID”

ALICE Physics Week, Muenster, Andrea Dainese 11 Statistics Summary 10 9 pp events 10 7 central (0-5%) Pb-Pb events “old TRD PID” “new TRD PID” “old TRD PID”

ALICE Physics Week, Muenster, Andrea Dainese 12 Errors Summary 10 9 pp events 10 7 central (0-5%) Pb-Pb events “old TRD PID”

ALICE Physics Week, Muenster, Andrea Dainese 13 pp: Sensitivity vs. pQCD 10 9 pp events From electrons in 2 < p t < 20 GeV/c, B mesons in 2 < p t min < 30 GeV/c “old TRD PID”

ALICE Physics Week, Muenster, Andrea Dainese 14 Beauty Energy Loss : R AA 1 year at nominal luminosity (10 7 central Pb-Pb events, 10 9 pp events) Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) “old TRD PID”

ALICE Physics Week, Muenster, Andrea Dainese 15 Heavy-to-light ratios: R B/D 1 year at nominal luminosity (10 7 central Pb-Pb events, 10 9 pp events) Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) “old TRD PID”

ALICE Physics Week, Muenster, Andrea Dainese 16 First-year scenario Only few TRD supermodules for 2008 pp run What can we do with TPC(&TOF) PID only? Optimization of dE/dx cuts for electrons ID N e =N  =N  =N K =N p p=4 GeV/c 40% 0.1% TOF C.Bombonati

ALICE Physics Week, Muenster, Andrea Dainese 17 First year: Statistical error TPC+TRDTPC C.Bombonati

ALICE Physics Week, Muenster, Andrea Dainese 18 Outlook One year at nominal luminosity: pp 1-18 GeV/c ➔ comparison with pQCD calc. Pb-Pb 1-18 GeV/c ➔ R AA & v 2 of beauty First year pp: up to 14 GeV/c (with larger errors) using ITS+TPC+TOF Next steps: preparation of Analysis task for ESD/AOD analysis of PDC events preparation of procedure for background subtraction (charm, misid. pions) and for corrections (cuts, PID)

ALICE Physics Week, Muenster, Andrea Dainese 19 EXTRA SLIDES

ALICE Physics Week, Muenster, Andrea Dainese 20 LHC running conditions  Ldt = cm -2 s -1 x 10 6 s cm -2 PbPb run, 5.5 TeV N PbPb collisions = collisions  Ldt dt = cm -2 s -1 x 10 7 s cm -2 for pp run, 14 TeV N pp collisions = collisions Muon triggers: ~ 100% efficiency, ~ 1kHz Electron triggers: Bandwidth limitation N PbPb central = collisions  Muon triggers: ~ 100% efficiency, < 1kHz Pb-PB nominal run pp nominal run Electron triggers: ~ 50% efficiency of TRD L1 20 physics events per event Hadron triggers: N PbPb central = collisions Hadron triggers: N pp minb = collisions 

ALICE Physics Week, Muenster, Andrea Dainese 21 Model Comparisons (HERA-LHC Workshop) Compare predictions by several different models Good agreement between collinear-factorization-based calculations: FO NLO and FONLL k T factorization (CASCADE) higher at large p T beautycharm CERN/LHCC hep-ph/

ALICE Physics Week, Muenster, Andrea Dainese 22 Energy extrapolation via pQCD? 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.

ALICE Physics Week, Muenster, Andrea Dainese 23 Cuts Summary p t bin [GeV/c] |d 0 | cut [  m] 1.0 – – – – – – – – – – –

ALICE Physics Week, Muenster, Andrea Dainese 24 - Charmed hadrons ( H c =D 0,D +,D + s,  + c ) cross section assumed to be proportional to the D 0 one. The H c / D 0 ratio is assumed to be 1.70  0.07 (*) Errors propagated from H c to e level: - Monte Carlo corrections for the D 0 measurement ~ 10% - Statistical error on the D 0 p T distribution - NN normalization not considered at this level (same as beauty) - The 6  9% uncertainty of D 0 from b should become negligible after the beauty direct measurement The charm contribution to the total electron spectrum is evaluated using the MC by introducing the charmed hadron p T distributions deduced from the D 0  K -  + measurement. Estimation of uncertainties on the p T - differential cross section of beauty electrons evaluation of charm background (*) deduced by comparing the PYTHIA value with the ALEPH measured value [D.Abbaneo et al., Eur. Phys. J. C16 (2000) 597]

ALICE Physics Week, Muenster, Andrea Dainese 25 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)

ALICE Physics Week, Muenster, Andrea Dainese 26 Extraction of a minimum-p t -differential cross section for B mesons Using UA1 MC method (*), also adopted by ALICE  (*) C. Albajar et al., UA1 Coll., Phys Lett B213 (1988) 405 C. Albajar et al., UA1 Coll., Phys Lett B256 (1991) 121 The B meson cross section per unit of rapidity at midrapidity for p t B > p t min is obtained from a scaling of the electron-level cross section measured within a given electron parameters space  e The semi-electronic B.R. is included here We use, where  p T are the previously used bins,  = [-0.9, 0.9] and  d 0 = [d 0 MIN, +  ]  m (thanks to R.Guernane for useful discussions) Problem: depends on B cross section shape used in simulation systematic error. How large?

ALICE Physics Week, Muenster, Andrea Dainese 27 Robusteness of the procedure  F ~ 1 % Extraction of a minimum-p t -differential cross section for B mesons For p t e > 2 GeV/c, can find an “optimal” p t min, for which the additional systematic error is negligible