1. PPR meeting 13.12.2002 Marcello Lunardon 1 Semi-electronic beauty detection: status and perspectives THE COLLABORATION Rosario Turrisi and Marcello Lunardon University & INFN - Padova for

2. PPR meeting 13.12.2002 Marcello Lunardon 2 Table of contents Motivations for Beauty measurement in ALICE First level simulation: event features Detection strategy in the B  e+X channel Results and perspectives

3. PPR meeting 13.12.2002 Marcello Lunardon 3 Why beauty in ALICE ? Measurement of total b cross section in Pb-Pb @  s NN = 5.5 TeV  Low p T threshold essential for total beauty cross section measurement in open beauty channels Quark energy loss in medium by comparison with p-p in the high p T region Necessary baseline for quarkonia measurement B  J/  +X important background to direct charmonia

4. PPR meeting 13.12.2002 Marcello Lunardon 4 The semi-electronic channel Branching ratio for the B  e + X channel ~ 10 % Questions: which performance can expect in detection of semi- electronic channel in Pb-Pb @ 5.5 TeV ? how low in p T ?

5. PPR meeting 13.12.2002 Marcello Lunardon 5 First level simulation Beauty: Pythia6, CTEQ4L, forced decay Charm:same as above Background: HIJING cent2 (dN CH /dy| y=0 = 6000) Separated generation of: Normalization: X-section from NLO calculations (5%  tot ) :  qq [b]N qq cc45115 bb1.8 4.6 e ± /event produced in 4  : Beauty 0.85 Charm 20 Background ~ 1200 (p T >0.2 GeV, vertex inside SPD) high uncertainty: 1.8-7.3

6. PPR meeting 13.12.2002 Marcello Lunardon 6 Analysis AliRoot version 3.07.04 TPC parameterization Kalman Filter in ITS (request for SPD layers) Tracking: PID: Most relevant background sources: e  identification in TRD && TPC direct charm other decays (Dalitz, strange particles) conversions hadrons misidentified as electrons

7. PPR meeting 13.12.2002 Marcello Lunardon 7 Strategy: starting point How to select electrons from beauty: p T : electrons from b-hadrons have hard p T spectrum d 0 (impact parameter in bending plane): c  [mm] B mesons ~ 0.5 D mesons ~ 0.1 charged  ~ 0 strange mesons large d 0 but low p T For a given p T threshold we can use d 0 cut to increase the purity of the sample

8. PPR meeting 13.12.2002 Marcello Lunardon 8 Electron ID techniques TRD: transition radiation technique: rejection of  and heavier particles TPC: dE/dx technique dN CH /dy| y=0 = 6000   eff =0.01 and e eff =0.9 assuming: - constant with p T - K,p totally rejected

9. PPR meeting 13.12.2002 Marcello Lunardon 9 Electron identification TRD PID TRD+TPC PID p T > 1 GeV/c Combined identification in TRD and TPC

10. PPR meeting 13.12.2002 Marcello Lunardon 10 Contributions to the electron spectrum Definition of 3 classes with the main contributions I) electrons from beauty : B  e+X B  D  e+X II) electrons from charm : D  e+X III) other processes: h  e+X   e + e -  as e  in TRD both contributions have the same origin (  beauty cross section). No need for external relative normalization. info from first measurements info from charm study

11. PPR meeting 13.12.2002 Marcello Lunardon 11 S/(S+B) at a glance Signal: class I (b  e, b  c  e) Background: class II+III (c  e, h  e,   e, mis.  ± ) d 0 threshold [  m] % S ( ) % B charm % B other elec. Ns [x10 4 ] 150 – 25090 – 95 (10%) 10 – 5- Relative composition of the electron sample for different d 0 threshold (upper limit of d 0 cut is 600  m) and expected signal statistics in 10 7 Pb+Pb events p T > 2 GeV/c

12. PPR meeting 13.12.2002 Marcello Lunardon 12 S/(S+B): p T analysis p T bin [GeV/c] d 0 threshold [  m] % S ( ) % B charm % B other elec. Ns [x10 4 ] 1.0 – 1.6200 – 30040 – 60 (30%) 30 – 20 9 – 5 1.6 – 2.2150 – 30080 – 90 (15%) 20 – 10–6 – 2 2.2 – 3.0150 – 300> 90 (10%) < 10–4 – 2 3.0 – 5.0100 – 300> 95 (10%) < 5–4 – 1 Relative composition of the electron sample for different d 0 threshold (upper limit of d 0 cut is 600  m) and expected signal statistics in 10 7 Pb+Pb events

13. PPR meeting 13.12.2002 Marcello Lunardon 13 Status and perspective Most relevant background sources included: charm, conversions,  ± misidentified as electrons, other decays Strategy for detection based on: p T /d 0 - windows, PID in TRD and TPC Can reach 90 % purity b-sample for p T > 2 GeV/c, 150 <d 0 <600  m with expected statistics of 10 4 -10 5 First simulation Next steps Determination of minimum p T accessible Study of the high p T region Improvement of signal and background description: signal: NLO-tuned beauty and charm events ready to be analysed background: dedicated high p T production, detailed TRD simulation Unfolding of b/c contribution to electrons spectrum Estimate of the error on total cross section

14. PPR meeting 13.12.2002 Marcello Lunardon 14 THE END

15. PPR meeting 13.12.2002 Marcello Lunardon 15 Why class I Direct contribution: B  e+X Most of other B decays: B  D + X e+X softer p T spectrum but broader d 0 distribution Both contributions have the same origin (  beauty X-section). No need for external normalization

16. PPR meeting 13.12.2002 Marcello Lunardon 16 Backup - From p T el to p T b b vs. B p T B vs. e p T

17. PPR meeting 13.12.2002 Marcello Lunardon 17 Background analysis Due to pair production topology and our d 0 definition,  conversions in the material have mostly d 0 <0 p T > 1 GeV/c

18. PPR meeting 13.12.2002 Marcello Lunardon 18 Backup B/(B+C) ratio p T > 1 GeV p T > 2 GeV p T > 3 GeV p T > 1 GeV p T > 2 GeV p T > 3 GeV

19. PPR meeting 13.12.2002 Marcello Lunardon 19 Impact parameter resolution