1 Andrea Dainese - Physics Forum – 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 Andrea Dainese - Physics Forum – 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

3 Andrea Dainese - Physics Forum – The semi-electronic and semi-muonic decay channels have a good B.R.: Open Beauty detection in AA at LHC: the semi-leptonic decay channel B ± /B 0  l + + X10.7 ± 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

4 Andrea Dainese - Physics Forum – X-section from NLO calculations : flavorN qq in 5.5 TeV (5%  tot ) charm115 beauty4.6 in 14 TeV charm0.16 beauty0.007 high uncertainty: Assumption on beauty production at LHC: Open Beauty detection in Pb-Pb at LHC with ALICE: perspectives for the semi-electronic decay channel Semi-electronic channel ~ 10 %, ALICE accept. for these electrons ~ 24 %  in Pb-Pb ~ 0.22 beauty electrons / event Statistics for 10 7 central events (~ 1 month Pb-Pb run): ~ 2 M beauty electrons

5 Andrea Dainese - Physics Forum – Semi-electronic beauty detection: simulation details 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 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 (dN CH /dy| y=0 = 6000) Normalizations according to the NLO cross section calculations Magnetic field: 0.4 T

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

7 Andrea Dainese - Physics Forum – 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 Semi-electronic Beauty: detection strategy

8 Andrea Dainese - Physics Forum – Semi-electronic Beauty detection simulation results Expected statistics (10 7 Pb-Pb events) Signal-to-total ratio and expected statistics in 10 7 Pb-Pb events p T > 2 GeV/c, 200  < |d 0 | < 600  m 90% purity 40,000 e from B

9 Andrea Dainese - Physics Forum – Entries in 10 7 events Statistical uncertainty corresponding to the number of electrons expected for a sample of 10 7 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: Estimation of uncertainties on the p T -differential cross section of beauty electrons statistical error where

10 Andrea Dainese - Physics Forum – 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 : 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 Estimation of uncertainties on the p T -differential cross section of beauty electrons systematic error

11 Andrea Dainese - Physics Forum – 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]

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

13 Andrea Dainese - Physics Forum – Effect of the D 0 statistical error on the electron p T distribution (2) Estimation of uncertainties on the p T - differential cross section of beauty electrons evaluation of charm background 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 GeV/c is counted as 0.94 electrons

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

15 Andrea Dainese - Physics Forum – Effect of the D 0 statistical error on the electron p T distribution (4) Estimation of uncertainties on the p T - differential cross section of beauty electrons evaluation of charm background 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

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

17 Andrea Dainese - Physics Forum – 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

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

19 Andrea Dainese - Physics Forum – 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 with p T B > p T min 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 iswhere  p T are the previously used bins,  = [-0.9, 0.9] and  d 0 = [200,600]  m (thanks to R.Guernane for useful discussions)

20 Andrea Dainese - Physics Forum – 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 T min 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. Extraction of a minimum-p T -differential cross section for B mesons Using UA1 MC method, also adopted by ALICE 

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

22 Andrea Dainese - Physics Forum – Evaluation of and determination of the optimal p T min 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 GeV 2 /fm (*) ) (*) N. Amesto, A. Dainese, C. A. Salgado, U. A. Wiedemann, hep-ph/  Extraction of a minimum-p T -differential cross section for B mesons

23 Andrea Dainese - Physics Forum – Can find an optimal p T min for p T e > 2 GeV/c Evaluation of and determination of the optimal p T min  F ~ 1 % Extraction of a minimum-p T -differential cross section for B mesons

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

25 Andrea Dainese - Physics Forum – 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 GeV/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 Coming up – more detailed study of B  D  e effect on the estimated result – study of the sensitivity of the p T min -differential B distribution to different energy loss scenarios

26 Andrea Dainese - Physics Forum – THE END

27 Andrea Dainese - Physics Forum – BACKUP SLIDES

28 Andrea Dainese - Physics Forum – % 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) Semi-electronic beauty detection background analysis: direct charm Distributions normalized to the same integral in order to compare their shapes

29 Andrea Dainese - Physics Forum – 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

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

31 Andrea Dainese - Physics Forum – 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?

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

33 Andrea Dainese - Physics Forum – 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 Semi-electronic beauty detection background analysis: misidentified pions relative magnitudes correct Effect of the PID on the pion backgound Number of pions much greater than number of electrons  good rejection using combined PID technique p T > 1 GeV/c