ALICE Physics Week Heavy Flavors Session Beauty detection
ALICE Physics Week Heavy Flavors Session Beauty detection in Pb. Pb in the central detector Rosario Turrisi Università & INFN – Padova
2 Rosario Turrisi ALICE Physics Week Tuesday, December 6, 2005 Contents In this talk: n n Baseline beauty and background crosssections Strategy: n n n key performances combined TRD+TPC electron identification Beauty purity and statistics B mesons ptmin spectrum Conclusions & perspectives TRD TPC ITS
3 Background and signal multiplicities n Rosario Turrisi ALICE Physics Week Tuesday, December 6, 2005 ALICE baseline: n NLO p. QCD (MNR), average of MRST e CTEQ 5 pdf’s (pp yields) n extrapolation to Pb. Pb, shadowing according to EKS 98 system shadowing pp 14 Te. V charm / beauty B(s)+ b 11. 2 / 0. 5 1 / 1 0. 16 / 0. 007 0. 0143 6. 6 / 0. 2 0. 65 / 0. 85 115 / 4. 6 9 Pb-Pb 5. 5 Te. V (5% cent) varying F, R inside a reasonable range the cross sections span a factor ~ 4 B D e The assumed background multiplicity (mainly pions) is the ALICE baseline: ~0. 85 B e X 0. 2 + 0. 2 electrons/event in barrel acceptance ALICE baseline: N. Carrer and A. Dainese, ALICE-INT-2003 -019, hep-ph/0311225.
4 Simulation n Background: HIJING, ~104 tracks in barrel acceptance n n Rosario Turrisi ALICE Physics Week Tuesday, December 6, 2005 2 104 events Signal: PYTHIA n beauty: MNR-tuned events, ~5 106 electrons n charm: MNR-tuned events, ~2 106 electrons (background for beauty) n parameterised TPC tracks for acceptable computing time n full tracking in ITS with KF-based code impact parameter resolution n normalization of signal cross sections to p. QCD MNR n results are relative to 107 Pb. Pb central events (5% of total x-section) i. e. one month run
5 Rosario Turrisi ALICE Physics Week Tuesday, December 6, 2005 Tracking performance impact parameter resolution: σ < 50 μm < 150 μm z @ pt=1. 3 Ge. V pt resolution: σ= 1(2)% @ 1(10) Ge. V 9% @ 100 Ge. V EFFICIENCY pions kaons
6 Beauty detection strategy Main sources of background: n n n identified as e’s Dalitz decays charm electrons photon conversions strangeness decays n n 0. 4 e - beauty ~103 e - other sources ~104 Key elements: n n minimum distance of track from primary vertex, in bending plane separation e/ d 0 = impact parameter n n B’s c ~ 500 m ! beauty has harder pt spectrum a. u. after tracking a. u. n Rosario Turrisi ALICE Physics Week Tuesday, December 6, 2005
7 Rosario Turrisi ALICE Physics Week Tuesday, December 6, 2005 (Mis)identification of TRD+TPC TRD PIDPID NO PID p. T>1 Ge. V pt>1
8 Purity and statistics Rosario Turrisi ALICE Physics Week Tuesday, December 6, 2005 Signal-to-total ratio and expected statistics in 10 7 Pb-Pb events • dominated by charm • dominated by other sources p. T > 2 Ge. V/c , 200 < |d 0| < 600 m purity>80% ~80, 000 e from B
9 Statistical error on beauty e’s n n Statistical error on 107 central events (5% x-section) 200 < |d 0| < 600 m electrons Rosario Turrisi ALICE Physics Week Tuesday, December 6, 2005
10 Systematic error on beauty e’s: charm source Rosario Turrisi ALICE Physics Week Tuesday, December 6, 2005 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. 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 (*) - Charmed 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 (*) error estimated by comparing the PYTHIA value with the ALEPH measured value [D. Abbaneo et al. , Eur. Phys. J. C 16 (2000) 597]
11 Systematic error on charm e’s Rosario Turrisi ALICE Physics Week Tuesday, December 6, 2005 Total relative error on the charm electron p. T distribution to be subtracted
12 Electrons (from b) pt spectrum stat syst error stat error 11% from overall normalization not included Rosario Turrisi ALICE Physics Week Tuesday, December 6, 2005 Error composition
13 Extraction of a minimum-p. T-differential cross section for B mesons (UA 1 method*, used also by R. Guernane for -arm data) Using PYTHIA events: • choose e’s pt range (e. g. 3 -4 Ge. V/c) • get the corresponding B differential x-section • scale this x-section to that with a chosen ptmin • wise choice of ptmin can minimize the method uncertainty, ~1% attainable! is the ratio of the red area to the blue one electrons in p. Te [3, 4] Ge. V/c (*)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 Rosario Turrisi ALICE Physics Week Tuesday, December 6, 2005
14 Extraction of a minimum-p. T-differential Rosario Turrisi ALICE Physics Week cross section for B mesons Tuesday, December 6, 2005 Using electrons in 2 < p. T < 16 Ge. V/c obtain B-meson 2 < p. Tmin < 23 Ge. V/c stat pt-dep. syst e’s pt syst + } B’s BR 3% ~1% MC e B extrap 10% 11% norm. err. (not shown) ptmin threshold E-loss calculations: N. Amesto, A. Dainese, C. A. Salgado, U. A. Wiedemann, hep-ph/0501225
15 Software status n n n n Events generation Reconstruction Tracking } Rosario Turrisi ALICE Physics Week Tuesday, December 6, 2005 standard tools Dedicated simulation for TPC electron identification (500 events with e+ ), parameterization of the effect (Ali)Root macros for electrons identification and a few other parameterized effects (e. g. TRD efficiency) Total of ~1000 lines of C/C++ code Analysis class on the way
16 Summary and perspectives Rosario Turrisi ALICE Physics Week Tuesday, December 6, 2005 n Study of beauty detection in semielectronic channel performed, attained 80% purity and 8 104 electrons in 107 events (one-ALICE-month run) n The excellent tracking, vertexing and PID capabilities of the ALICE central barrel allow to reconstruct B mesons in a wide pt range (~0– 15 Ge. V/c) and, thus, to address this rich physics item n Study extended to pp (see next talk) n Software integration in Ali. Root planned
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