Measurement of the beauty production cross section in

Measurement of the beauty production cross section in Pb-Pb collisions via single electrons F. Antinori, A. Dainese, M. Lunardon and R. Turrisi Padova – University and INFN 1 05 Andrea Dainese - Physics Forum – 0103

Contents Detection strategy for the semi-electronic channel and simulation details (quick review) Estimate of the uncertainties on the p. T-differential cross section of B-decay electrons Extraction of the B-level cross section Conclusions and perspectives 2 05 Andrea Dainese - Physics Forum – 0103

Open Beauty detection in AA at LHC: the semi-leptonic decay channel The semi-electronic and semi-muonic decay channels have a good B. R. : B±/B 0 l + + X 10. 7 ± 0. 3% (l = e or ) Good detection and identification capabilities for muons (MUON ARM) and electrons (TRD, TPC and ITS) with ALICE down to low p. T 3 05 Andrea Dainese - Physics Forum – 0103

Open Beauty detection in Pb-Pb at LHC with ALICE: perspectives for the semi-electronic decay channel Assumption on beauty production at LHC: X-section from NLO calculations : flavor in Pb-Pb @ 5. 5 Te. V (5% tot) charm beauty in pp @ 14 Te. V 4. 6 N qq 115 0. 16 0. 007 high uncertainty: 1. 8 - 7. 3 Semi-electronic channel ~ 10 % , ALICE accept. for these electrons ~ 24 % in Pb-Pb ~ 0. 22 beauty electrons / event Statistics for 107 central events (~ 1 month Pb-Pb run): ~ 2 M beauty electrons 4 05 Andrea Dainese - Physics Forum – 0103

Semi-electronic beauty detection: simulation details Magnetic field: 0. 4 T Separated generation of beauty, charm and background: beauty: Pythia 6 with MSEL=5, CTEQ 4 L, forced semi-electronic decay charm: similar to beauty background: HIJING central (b < 2 fm) events (d. NCH/dy|y=0 = 6000) Normalizations according to the NLO cross section calculations Most relevant background sources included: 1) hadrons misidentified as electrons 2) e from conversions 3) e from charm 4) e from Dalitz and strange particles 5 05 Andrea Dainese - Physics Forum – 0103

Semi-electronic Beauty: detection strategy d 0 and p. T distributions for “electrons” from different sources: Distributions normalized to the same integral in order to compare their shapes 6 05 Andrea Dainese - Physics Forum – 0103

Semi-electronic Beauty: detection strategy 7 • electron identification in TRD+TPC • reject 99. 99% of pions and “all” heavier hadrons; lose ~40% of electrons • impact parameter cut • reject “photonic” electrons (conv. s, Dalitz …) • p. T cut • reduce electrons from charm 05 Andrea Dainese - Physics Forum – 0103

Semi-electronic Beauty detection simulation results Signal-to-total ratio and expected statistics in 107 Pb-Pb events Expected statistics (107 Pb-Pb events) p. T > 2 Ge. V/c , 200 < |d 0| < 600 m 8 05 Andrea Dainese - Physics Forum – 0103 90% purity 40, 000 e from B

Estimation of uncertainties on the p. T-differential cross section of beauty electrons statistical error • • Statistical uncertainty corresponding to the number of electrons expected for a sample of 107 Pb-Pb central events (5% tot) The impact parameter cut is 200 |d 0| 600 m • 11 p. T bins of different width. For the i-th bin: Entries in 107 events where 9 05 Andrea Dainese - Physics Forum – 0103

Estimation of uncertainties on the p. T-differential cross section of beauty electrons systematic error Main systematic uncertainties: • Monte Carlo corrections (detector acceptance, tracking efficiency, selection efficiency) ~ 10% (at the moment assumed to be p. T-indep. ) • Normalization to one NN collision (error on <Ncoll>: definition of the centrality range, WS Pb density profile, inelastic cross section from TOTEM) ~ 11% • Charm contribution to be subtracted from the total electron spectrum (see following slides) Note: we assume to be able to subtract the residual misid. and photonic e with negligible systematic error 10 05 Andrea Dainese - Physics Forum – 0103

Estimation of uncertainties on the p. T - differential cross section of beauty electrons evaluation of charm background 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. - Charmed hadrons (Hc=D 0, D+s, +c) cross section assumed to be proportional to the D 0 one. The Hc/D 0 ratio is assumed to be 1. 70 0. 07 (*) Errors propagated from Hc 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 (*) deduced by comparing the PYTHIA value with the ALEPH measured value [D. Abbaneo et al. , Eur. Phys. J. C 16 (2000) 597] 11 05 Andrea Dainese - Physics Forum – 0103

Estimation of uncertainties on the p. T - differential cross section of beauty electrons evaluation of charm background Effect of the D 0 statistical error on the electron p. T distribution (1) Monte Carlo method 1) the initial D 0 p. T distribution (the measured one) is fitted to the expression: 12 05 Andrea Dainese - Physics Forum – 0103

Estimation of uncertainties on the p. T - differential cross section of beauty electrons evaluation of charm background Effect of the D 0 statistical error on the electron p. T distribution (2) 2) the points are smeared according to the estimated statistical standard deviation and the fit is recalculated 3) the ratio of the new fit to the reference one is used as a weight for the charm generated electron the electron generated from a D with p. T = 2 Ge. V/c is counted as 0. 94 electrons 13 05 Andrea Dainese - Physics Forum – 0103

Estimation of uncertainties on the p. T - differential cross section of beauty electrons evaluation of charm background Effect of the D 0 statistical error on the electron p. T distribution (3) 4) the refit procedure is repeated many times and the standard deviation of the content in each electron p. T-bin is evaluated 14 05 Andrea Dainese - Physics Forum – 0103 Relative error as a function of p. T

Estimation of uncertainties on the p. T - differential cross section of beauty electrons evaluation of charm background Effect of the D 0 statistical error on the electron p. T distribution (4) Analytic method 1) for each D 0 p. T bin, the corresponding electron p. T distribution is extracted and the relative errors of all the electron p. T bins are set equal to that of the D 0 15 05 Andrea Dainese - Physics Forum – 0103

Estimation of uncertainties on the p. T - differential cross section of beauty electrons evaluation of charm background Effect of the D 0 statistical error on the electron p. T distribution (5) 2) the different electron spectra are summed with a quadratic error propagation 16 The analytic result compared to the numerical one 05 Andrea Dainese - Physics Forum – 0103

Estimation of uncertainties on the p. T - differential cross section of beauty electrons evaluation of charm background Total relative error on the charm electron p. T distribution to be subtracted 17 05 Andrea Dainese - Physics Forum – 0103

Estimation of uncertainties on the p. T - differential cross section of beauty electrons Final B-decay electron p. T distribution (11% norm. err. not shown) E loss calculations: N. Amesto, A. Dainese, C. A. Salgado, U. A. Wiedemann, hep-ph/0501225 18 05 Andrea Dainese - Physics Forum – 0103 stat pt-dep. syst 11% norm. err. (not shown)

Extraction of a minimum-p. T-differential cross section for B mesons Using UA 1 MC method (*), also adopted by ALICE (thanks to R. Guernane for useful discussions) The B meson cross section per unit of rapidity at midrapidity with p. TB > p. Tmin is obtained from a scaling of the electron-level cross section measured within a given electron phase space e The semi-electronic B. R. is included here where p. T are the previously used bins, The phase space used is = [-0. 9, 0. 9] and d 0 = [200, 600] m (*) C. Albajar et al. , UA 1 Coll. , Phys Lett B 213 (1988) 405 C. Albajar et al. , UA 1 Coll. , Phys Lett B 256 (1991) 121 19 05 Andrea Dainese - Physics Forum – 0103

Extraction of a minimum-p. T-differential cross section for B mesons Using UA 1 MC method, also adopted by ALICE Systematic error for - semi-electronic decay B. R. : ~ 3 % - dependence on the shape of the B meson p. T distribution used as input in the MC: can be minimized using a proper choice of p. Tmin for a given phase space e see following slides - Monte Carlo correction for the efficiency of the selection cuts: this is, in principle, depending on the B meson p. T distribution, and should be then evaluated at this stage of the analysis. For the present feasibility study we account for it with a 10% systematic. 20 05 Andrea Dainese - Physics Forum – 0103

Extraction of a minimum-p. T-differential cross section for B mesons Using UA 1 MC method, also adopted by ALICE Evaluation of and determination of the optimal p. Tmin 1) we used the B e + X decays from PYTHIA. is the ratio of the red area to the blue one. here p. Te = [3, 4] Ge. V/c 21 05 Andrea Dainese - Physics Forum – 0103

Extraction of a minimum-p. T-differential cross section for B mesons Evaluation of and determination of the optimal p. Tmin 2) in the HVQNMR program we changed theory parameters: a) quark mass and scales b) nuclear modification of the PDFs c) b B fragmentation (Peterson) d) add the quenching (q = 100 Ge. V 2/fm (*)) (*) N. Amesto, A. Dainese, C. A. Salgado, U. A. Wiedemann, hep-ph/0501225 22 05 Andrea Dainese - Physics Forum – 0103

Extraction of a minimum-p. T-differential cross section for B mesons Evaluation of and determination of the optimal p. Tmin F ~ 1 % Can find an optimal p. Tmin for p. Te > 2 Ge. V/c 23 05 Andrea Dainese - Physics Forum – 0103

Extraction of a minimum-p. T-differential cross section for B mesons Using electrons in 2 < p. T < 16 Ge. V/c stat pt-dep. syst 11% norm. err. (not shown) obtain B-meson 2 < p. Tmin < 23 Ge. V/c E loss calculations: N. Amesto, A. Dainese, C. A. Salgado, U. A. Wiedemann, hep-ph/0501225 24 05 Andrea Dainese - Physics Forum – 0103

Summary • The semi-electronic channel offer a good tool for the study of the beauty production at LHC • In the present study we evaluated: – purity of the electron sample (~90% for p. T>2 Ge. V/c) – uncertainties on the p. T-differential beauty electron spectrum, including: statistical error, systematic from MC corrections, AA NN normalization, charm background (using the D 0 K- + measurement results) – extraction of a min-p. T-differential cross section for the B mesons • 25 Coming up – more detailed study of B D e effect on the estimated result – study of the sensitivity of the p. Tmin-differential B distribution to different energy loss scenarios 05 Andrea Dainese - Physics Forum – 0103

THE END 26 05 Andrea Dainese - Physics Forum – 0103

BACKUP SLIDES 27 05 Andrea Dainese - Physics Forum – 0103

Semi-electronic beauty detection background analysis: direct charm - 13% semi-electronic decay and much more charm than beauty expected significant background - softer p. T spectrum and narrower d 0 distribution (c (D 0) ~ 100 m, c (D+) ~ 300 m) Distributions normalized to the same integral in order to compare their shapes 28 05 Andrea Dainese - Physics Forum – 0103

Estimation of uncertainties on the p. T - differential cross section of beauty electrons B D e effect on the electron spectrum Fraction of the b c e with respect to the direct b e Estimated effects: increase the statistics of beauty originated electrons + introduce a small uncertainty in the deconvolution = improvement on the measurement sensitivity 29 05 Andrea Dainese - Physics Forum – 0103

Estimation of uncertainties on the p. T - differential cross section of beauty electrons B D e effect on the electron spectrum d 0 distributions 30 p. T distributions 05 Andrea Dainese - Physics Forum – 0103

Semi-electronic Beauty detection p. T quark distribution Analysis of the electron p. T distribution useful for beauty production cross section measurement. But, what about the quark p. T distribution? 31 05 Andrea Dainese - Physics Forum – 0103

Semi-electronic beauty detection background analysis: misidentified pions Electron identification with Transition Radiation Detector (TRD) pion contamination ~ 1% From test beam results: 90% electron efficiency 1% misidentified pions (constant in 1 -6 Ge. V/c p. T range) 32 05 Andrea Dainese - Physics Forum – 0103

Semi-electronic beauty detection background analysis: misidentified pions Effect of the PID on the pion backgound PID used in this simulation: Number pionsfrom much greater - can assume complete rejection of K, p and heavierof particles TRD and TOF than number of electrons good rejection using - 80% electron reduction factor for identification efficiencies of TRD combined PID technique (0. 9) and TPC (0. 9) - pion contamination less than 0. 01% at low momentum p. T > 1 Ge. V/c relative magnitudes correct 33 05 Andrea Dainese - Physics Forum – 0103