Perspectives for the measurement of the beauty production cross section at LHC with ALICE

1. Perspectives for the measurement of the beauty production cross section at LHC with ALICE Marcello Lunardon for the ALICE collaboration Phase Transitions in Strongly Interacting Matter PRAHA 2004

2. Contents • Why to measure beauty in AA at LHC • Performances study for the open beauty detection in Pb-Pb in the semi-electronic channel with ALICE • Conclusions and perspectives

3. Why beauty? Measurement of b production in Pb-Pb, p-Pb and p-p • interesting in its own right: • discovery potential (new physics window) ! • probe of the medium ( e. g.: energy loss of beauty in the medium • to be compared with charm energy loss  study of dead-cone • effect ); • B J/important background • normalization forstudies

4. g c path length L b energy loss? Hard processes in AA at the LHC Useful tools: - significant part of the cross section - large virtuality Q happen at initial time (small “formation time” Dt ~ 1/Q << tQGP ~ 5–10 fm/c) -Initial yields and pt distributions in AA can be predicted usingpp measurements + pQCD + collision geometry+“known” nuclear effects  deviations from such predictions can be attributed to the medium

5. h Experimental study of energy loss Compare pt distributions of leading particles in pp and nucleus-nucleus collisions (+ p-nucleus as a control) Study of the nuclear modification factor to get information on the medium RAA measured at RHIC with pions: clear suppression at high pT interpreted as due to parton energy loss in medium What about heavy quarks?

6. charm beauty RAA for electrons from semi-electronic decay of D and B mesons (integrated pT) N.Armesto, A.Dainese, C.A.Salgado and U.A.Wiedemann, in preparation. Which energy loss for Heavy Quarks? RAA ratio at LHC expected to be less suppressed for heavy flavours because: • D,B come from c,b quarks, while , K, p come mainly (~80% in PYTHIA) from gluons, which are expected to lose  9/4 more energy w.r.t. quarks (due to the difference in the Casimir coupling factor) • dead cone for heavy quarks: gluons radiation is suppressed at Q < mQ/EQ • lower energy loss for heavier partons(Dokshitzer-Kharzeev, 2001)  due to the mass dependence of dead cone effect lower energy loss for beauty compared to charm(Armesto-Dainese-Salgado-Wiedemann, 2004) Expectation for charm: estimated RAA for D0 mesons at LHC (A. Dainese) Yu.L.Dokshitzer and D.E.Kharzeev, Phys. Lett. B519 (2001) 199 [arXiv:hep-ph/0106202].

7. 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 Vertex detector) with ALICE down to low pT • (for semi-muonic beauty detection see talk of G. Martinez)

8. 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 p-p 14 @ TeVcharm 0.16 beauty 0.007 Semi-electronic channel ~ 10 % , ALICE acceptance for beauty ~ 24 %  in Pb-Pb ~ 0.22 beauty electrons / event Statistics for 107 central events (one year Pb-Pb run):~ 2 M beauty electrons

9. L3 Magnet B < 0.5 T: 0.2 T low pt acceptance, 0.5 T pt resolution at high pt ITS < 60 mm for pt > 1 GeV/c TOF PID TRD Electron ID SPD TPC Tracking, dEdx rf: 50 mm ITS Vertexing, Low pt tracking 9.8 Mch z: 425 mm PIXEL CELL Two layers: r = 4 – 7 cm The ALICE Detector The dedicated HI experiment at LHC Designed to measure most observables

10. Semi-electronic Beauty: detection strategy • 1) electron identification in TRD+TPC 2) cuts on - transverse momentum pT B and B products have higher pT than primary particles - track impact parameter in b.p. d0 long d0 for beauty electrons due to long B life c ~ 500 m

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

12. 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)  conversions 3) direct charm 4) other decays (Dalitz, strange particles) Semi-electronic beauty detection: simulation details Magnetic field: 0.4 T

13. 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)

14. Semi-electronic beauty detection background analysis: misidentified pions Electron identification with dE/dx in TPC Combined TRD + TPC particle identification technique brings low momentum pion contamination to less than 10-4

15. 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

16. a) first reduction asking for first SPD layer Semi-electronic beauty detection background analysis:  conversions Semi-electronic charm measurement at RHIC from PHENIX: photon conversions are a large part of the background ( have to use a removable converter ) • Similar situation expected at • ALICE for electrons entering the • TPC, but: • a) request of 1st SPD layer • b) select positive d0 electrons

17. Semi-electronic beauty detection background analysis:  conversions b) More reduction with d0 positive cut

18. 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 d0 spectrum (c(D0) ~ 100 m, c(D+) ~ 300 m) - separated generation with pythia6 and normalization according with NLO calculations Distributions normalized to the same integral in order to compare their shapes

19. Semi-electronic beauty detection background analysis: other decays Simulation with HIJING generally: low pT, low d0 Strange particle decays: low pT but very long d0 upper d0 threshold at 600 m

20. 90% purity • 50,000 B's pT>2 GeV/c , 180  d0 600m Semi-electronic Beauty detection simulation results Signal-to-total ratio and expected statistics in 107 Pb-Pb events Expected statistics (107 Pb-Pb events)

21. Semi-electronic Beauty detection simulation results Analysis of the relative electron sample composition as a function of the electron pT Direct charm is the most important source of background ( cross check of the extracted c production with direct D0K measurement ) 200  d0 600m Expected statistics (107 Pb-Pb events)

22. Example: B  e + D0 (  K+p ) + X 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? Can get significantly better quark pT distribution if we are able to reconstruct a bigger fraction of the B meson mass.

23. Semi-electronic Beauty detection pT quark distribution • Under way: performance study to evaluate • exclusive reconstruction of the D0 coming from semi-electronic B decay • reconstruction of B secondary vertices using topological variables

24. Summary • ALICE has a good potential to measure beauty production cross section ( vertexing and particle identification down to low pT) this will allow us to extract information about the effect on heavy flavour production of the dense strongly interacting system created in ultra-relativistic heavy-ion collisions • Coming up • semi-electronic b/c deconvolution • b’s pt distribution • exclusive b decays

25. THE END

26. BACKUP SLIDES

27. TPC TPC+ITS 1 % at low pt < 2% up to 10 GeV/c < 60 mm for pt > 1 GeV/c

28. PID

30. LHC: we expect “Deep de-confinement”  closer to “ideal” QGP  easier comparison with theory Lattice QCD, mB=0

31. charm beauty minimum electron pT Energy loss and semi-electronic channel this region could be sensitive to different b/c dead-cone effect N.Armesto, A.Dainese, C.A.Salgado and U.A.Wiedemann, in preparation.

32. Experimentally can use double ratio: RAAD/RAAh • almost all systematic errors of both Pb-Pb and pp cancel out! D/h ratio: RD/h = RAAD / RAAh • RD/h is enhanced only by the dead-cone effect • Enhancement due to different quark/gluon loss not seen • It is compensated by the harder fragmentation of charm

33. Possible direct measurement of  conversions using invariant mass and topological variables

34. Muon Arm simulations: R. Guernane, Muon physics and offline meeting CERN, 22.4.2004

35. B measurement a la CDF Simulation by A. Dainese