Measurement of the beauty production cross section in Pb-Pb collisions via single electrons

1. 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

2. Contents • Detection strategy for the semi-electronic channel and simulation details (quick review) • Estimate of the uncertainties on the pT-differential cross section of B-decay electrons • Extraction of the B-level cross section • Conclusions and perspectives

3. 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±/B0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 pT

4. high uncertainty: 1.8 - 7.3 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 :flavorNqq in Pb-Pb @ 5.5 TeV (5% tot)charm 115 beauty 4.6 in pp @ 14 TeVcharm 0.16 beauty 0.007 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

5. Separated generation of beauty, charm and background: beauty: Pythia6 with MSEL=5, CTEQ4L, forced semi-electronic decay charm: similar to beauty background: HIJING central (b < 2 fm) events (dNCH/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 Semi-electronic beauty detection: simulation details Magnetic field: 0.4 T

6. Semi-electronic Beauty: detection strategy d0 and pT distributions for “electrons” from different sources: Distributions normalized to the same integral in order to compare their shapes

7. Semi-electronic Beauty: detection strategy • 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 …) • pT cut • reduce electrons from charm

8. Semi-electronic Beauty detection simulation results Signal-to-total ratio and expected statistics in 107 Pb-Pb events Expected statistics (107 Pb-Pb events) 90% purity 40,000 e from B pT > 2 GeV/c , 200 < |d0| < 600 m

9. Entries in 107 events Estimation of uncertainties on the pT-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  |d0|  600 m • 11 pT bins of different width. For the i-th bin: where

10. Estimation of uncertainties on the pT-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 pT-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. p and photonic e with negligible systematic error

11. Estimation of uncertainties on the pT - 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 pT distributions deduced from the D0K-+ measurement. - Charmed hadrons (Hc=D0,D+,D+s,+c) cross section assumed to be proportional to the D0 one. The Hc/D0 ratio is assumed to be 1.70  0.07 (*) Errors propagated from Hc to e level: - Monte Carlo corrections for the D0 measurement ~ 10% - Statistical error on the D0 pTdistribution - NN normalization not considered at this level (same as beauty) - The 69% uncertainty of D0 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. C16 (2000) 597]

12. Estimation of uncertainties on the pT - differential cross section of beauty electrons evaluation of charm background Effect of the D0 statistical error on the electron pT distribution (1) Monte Carlo method 1) the initial D0pT distribution (the measured one) is fitted to the expression:

13. 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 pT = 2 GeV/c is counted as 0.94 electrons Estimation of uncertainties on the pT - differential cross section of beauty electrons evaluation of charm background Effect of the D0 statistical error on the electron pT distribution (2) 2) the points are smeared according to the estimated statistical standard deviation and the fit is recalculated

14. Estimation of uncertainties on the pT - differential cross section of beauty electrons evaluation of charm background Effect of the D0 statistical error on the electron pT distribution (3) 4) the refit procedure is repeated many times and the standard deviation of the content in each electron pT-bin is evaluated Relative error as a function of pT

15. Estimation of uncertainties on the pT - differential cross section of beauty electrons evaluation of charm background Effect of the D0 statistical error on the electron pT distribution (4) Analytic method 1) for each D0 pT bin, the corresponding electron pT distribution is extracted and the relative errors of all the electron pT bins are set equal to that of the D0

16. Estimation of uncertainties on the pT - differential cross section of beauty electrons evaluation of charm background Effect of the D0 statistical error on the electron pT distribution (5) 2) the different electron spectra are summed with a quadratic error propagation The analytic result compared to the numerical one

17. Estimation of uncertainties on the pT - differential cross section of beauty electrons evaluation of charm background Total relative error on the charm electron pT distribution to be subtracted

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

19. Extraction of a minimum-pT-differential cross section for B mesons Using UA1 MC method (*), also adopted by ALICE m (thanks to R.Guernane for useful discussions) The B meson cross section per unit of rapidity at midrapidity with pTB > pTmin 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 The phase space used is where pT are the previously used bins,  = [-0.9, 0.9] and d0 = [200,600] m (*) C. Albajar et al., UA1 Coll., Phys Lett B213 (1988) 405 C. Albajar et al., UA1 Coll., Phys Lett B256 (1991) 121

20. Extraction of a minimum-pT-differential cross section for B mesons Using UA1 MC method, also adopted by ALICE m Systematic error for - semi-electronic decay B.R.: ~ 3 % - dependence on the shape of the B meson pT distribution used as input in the MC: can be minimized using a proper choice of pTmin 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 pT 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.

21. Extraction of a minimum-pT-differential cross section for B mesons Using UA1 MC method, also adopted by ALICE m Evaluation of and determination of the optimal pTmin 1) we used the B  e + X decays from PYTHIA. is the ratio of the red area to the blue one. here pTe = [3,4] GeV/c

22. Extraction of a minimum-pT-differential cross section for B mesons Evaluation of and determination of the optimal pTmin 2) in the HVQNMR program we changed the theory parameters: a) quark mass and scales b) nuclear modification of the PDFs c) b  B fragmentation (Peterson) d) add the quenching (q = 100 GeV2/fm (*))  (*) N. Amesto, A. Dainese, C. A. Salgado, U. A. Wiedemann, hep-ph/0501225

23. F ~ 1 % Extraction of a minimum-pT-differential cross section for B mesons Evaluation of and determination of the optimal pTmin Can find an optimal pTmin for pTe > 2 GeV/c

24. stat pt-dep. syst 11% norm. err. (not shown) Extraction of a minimum-pT-differential cross section for B mesons Using electrons in 2 < pT < 16 GeV/c obtain B-meson 2 < pTmin < 23 GeV/c E loss calculations: N. Amesto, A. Dainese, C.A. Salgado, U.A. Wiedemann, hep-ph/0501225

25. 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 pT>2 GeV/c) • uncertainties on the pT-differential beauty electron spectrum, including: statistical error, systematic from MC corrections, AANN normalization, charm background (using the D0K-+measurement results) • extraction of a min-pT-differential cross section for the B mesons • Coming up • more detailed study of B  D  e effect on the estimated result • study of the sensitivity of the pTmin-differential B distribution to different energy loss scenarios

26. THE END

27. BACKUP SLIDES

28. Semi-electronic beauty detection background analysis: direct charm - 13% semi-electronic decay and much more charm than beauty expected significant background - softer pT spectrum and narrower d0 distribution (c(D0) ~ 100 m, c(D+) ~ 300 m) Distributions normalized to the same integral in order to compare their shapes

29. Estimation of uncertainties on the pT - 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

30. Estimation of uncertainties on the pT - differential cross section of beauty electrons B  D  e effect on the electron spectrum d0 distributions pT distributions

31. Semi-electronic Beauty detection pT quark distribution Analysis of the electron pT distribution useful for beauty production cross section measurement. But,what about the quark pT distribution?

32. 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 GeV/c pT range)

33. relative magnitudes correct Semi-electronic beauty detection background analysis: misidentified pions Effect of the PID on the pion backgound PID used in this simulation: - can assume complete rejection of K,p and heavier particles from TRD and TOF - 80% electron reduction factor for identification efficiencies of TRD (0.9) and TPC (0.9) - pion contamination less than 0.01% at low momentum • Number of pions much greater than number of electrons • good rejection using combined PID technique pT > 1 GeV/c