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Open heavy flavours: perspectives of ALICE for the detection of quark energy loss Rosario Turrisi Università & INFN – Padova in collaboration with F.Antinori, A.Dainese, M.Lunardon Heavy Ion Forum, April 13 th 2005

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 2 Summary Motivations Motivations Environment: simulation, cross sections, detector Environment: simulation, cross sections, detector Beauty detection in semileptonic channel Beauty detection in semileptonic channel Charm detection in hadronic channel Charm detection in hadronic channel Energy loss sensitivity Energy loss sensitivity Conclusions Conclusions

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 3 Motivations Heavy flavours in heavy-ions @ LHC: interest in its own right: high yields & small x More specific to QGP: J/, suppression natural baseline B J/ background Medium probes: early formation thermal production energy loss quarkonia open flavours B,D KK ee

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 4 Choice of channels D 0 K - +,“golden channel” Exclusive channel direct measurement of the p t distribution ideal tool to study R AA Relatively simple approach B.R. 3.8% deployment of vertexing capabilities B e+X, semielectronic channel first-order approach to beauty inclusive channel for high-statistics measurement, BR ~10% p t measurement achievable explores electron identification techniques

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 5 Cross sections baseline ALICE baseline: ALICE baseline: NLO pQCD (MNR), average of MRST e CTEQ5 pdf’s (pp yields) NLO pQCD (MNR), average of MRST e CTEQ5 pdf’s (pp yields) extrapolation to PbPb, shadowing according to EKS98 extrapolation to PbPb, shadowing according to EKS98 varying F, R inside a reasonable range the cross sections spans a factor ~ 4 in barrel acceptance: 0.5 0.2 D 0 / D 0 B (s) + b pp0.190.0143 PbPb1409 ~0.85 B eX Mesons (produced) multiplicities 115 / 4.6 0.65 / 0.85 6.6 / 0.2 Pb-Pb 5.5 TeV (5% cent) 0.16 / 0.007 1 / 1 11.2 / 0.5 pp 14 TeV shadowingsystem ~13.7 D 0 K ALICE baseline: N.Carrer and A.Dainese, ALICE-INT-2003-019, hep-ph/0311225. charm / beauty

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 6 Background in PbPb @ 5.5 TeV Background is given by: Background is given by: D 0 : pairs of uncorrelated tracks w/large impact parameter D 0 : pairs of uncorrelated tracks w/large impact parameter B: single electrons (true and misidentified pions) B: single electrons (true and misidentified pions) In either case the multiplicity is our issue (signal~1-2 tracks per event): need for ad hoc simulation strategy ALICE baseline for these studies: hep-ph/0104010

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 7 Simulation Background: HIJING, ~10 4 tracks in barrel acceptance 210 4 events Signal: PYTHIA D 0 : MNR-tuned events, reproduces p t spectrum, ~210 6 D 0 beauty: forced production (MSEL=5), 5.2 10 6 electrons charm: forced production (MSEL=4), 2.310 6 electrons (background for beauty) parameterised TPC tracks for acceptable computing time full tracking in ITS with KF-based code impact parameter resolution normalization of signal cross sections to pQCD MNR results are relative to 10 7 PbPb central events (5% of total x-section), i.e. one month run

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 8 Highlights on the ALICE detector Solenoid magnet B<0.5 T Central tracking system: Inner Tracking System Time Projection Chamber Transition Radiation Detector Time Of Flight TPC (the largest ever…): 88 m 3, 510 cm length, 250 cm radius Ar (90%) + CO 2 (10%) 88 μs drift time main tracking device, dE/dx 2 * 1.8 units of pseudo-rapidity 6 Layers, 3 technologies Material budget < 1% of X 0 per layer! Silicon Pixels vertices resolution in xy (0.2 m 2, 9.8 Mchannels) Silicon Drift resolution in z (1.3 m 2, 133 kchannels) Double-sided Strip connection w/TPC (4.9 m 2, 2.6 Mchannels) PIXEL CELL z: 425 m r : 50 m Two layers: r = 4 – 7 cm 9.8 Mch 6 layers for: electron/pion separation at p t >1 GeV factor 100 rejection at 2 GeV tracking complement, mass resolution 100 MeV/c 2 @ high p t trigger (onia studies) Multigap Resistive Plate Chambers 5 years R&D, and < 100 ps pions, kaons, protons separation electrons/pions at low p t 2.4 < < 4 MUON Spectrometer

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 9 Tracking performance impact parameter resolution: σ @ p t =1.3 GeV < 50 μm < 150 μm z p t resolution: σ= 1(2)% @ 1(10) GeV 9% @ 100 GeV 9% @ 100 GeV EFFICIENCY pions kaons

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 10 BEAUTY

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 11 Beauty detection strategy Beauty detection strategy 0.22 e - beauty 0.22 e - beauty ~10 3 e - other sources ~10 3 e - other sources ~10 4 ~10 4 Main sources of background: Main sources of background: identified as e identified as e Dalitz decays Dalitz decays charm electrons charm electrons photon conversions photon conversions strangeness decays strangeness decays Key elements: Key elements: separation e/ separation e/ d 0 = impact parameter d 0 = impact parameter B ’ s c ~ 500m ! B ’ s c ~ 500m ! beauty has harder p t spectrum beauty has harder p t spectrum minimum distance of track from primary vertex, in bending plane after tracking a. u.

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 12 (Mis)identification of NO PID p T >1 GeV TRD PID TRD+TPC PID p t >1

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 13 Purity and statistics 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 dominated by charm dominated by other sources

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 14 Statistical error on beauty e’s Entries in 10 7 events Statistical error on 10 7 central events (5% x-section) Statistical error on 10 7 central events (5% x-section) 200 < |d0| < 600 m 200 < |d0| < 600 m electrons

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 15 Systematic error on beauty e’s: charm source 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. - 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 69% uncertainty of D 0 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]

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 16 Systematic error on charm e’s Total relative error on the charm electron p T distribution to be subtracted

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 17 Beauty p t spectrum E loss calculations: N. Amesto, A. Dainese, C.A. Salgado, U.A. Wiedemann, hep-ph/0501225 (11% norm. err. not shown) stat p t -dep. syst 11% norm. err. (not shown) This is not meant for the final analysis: ratio with pp spectrum to come soon, w.i.p.! approximation from BDMPS model

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 18 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/0501225 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) p t min threshold

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 19 Beauty in the muon channel See talk of R. Guernane (Clermont-Ferrand group) at Moriond 2005: http://moriond.in2p3.fr/QCD/2005/Index.html Similar study in ALICE: beauty in the Muon Spectrometer No vertex, but clean muon sample No vertex, but clean muon sample Rapidity range: 2.5

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 20 CHARM

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 21 Exclusive channel direct measurement of the p t distribution ideal tool to study R AA Exclusive channel D 0 K - + direct measurement of the p t distribution ideal tool to study R AA Weak decay with mean proper length c = 124 mm Weak decay with mean proper length c = 124 mm STRATEGY: invariant-mass analysis of fully-reconstructed topologies originating from (displaced) secondary vertices STRATEGY: invariant-mass analysis of fully-reconstructed topologies originating from (displaced) secondary vertices Measurement of Impact Parameters Measurement of Impact Parameters Measurement of Momenta Measurement of Momenta Particle identification to tag the two decay products Particle identification to tag the two decay products Strategy

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 22 Time-of-flight PID TOF Pb-Pb, dN ch /dy=6000 Optimization for hadronic charm decays was studied: minimize probability to tag K as

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 23 D 0 K - + : Selection of D 0 candidates 2-dim cut increases S/B by factor ~10 3 !

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 24 D 0 Results (K,) Invariant Mass distribution (p t –integrated) in Pb-Pb (~ 1 month run) N.Carrer, A.D. and R.Turrisi, J. Phys. G29 (2003) 575. A.D. PhD thesis (2003), nucl-ex/0311004. Statistical significance: bars: stat err yellow band: syst err Pb-Pb up to 14 GeV/c ! currently studying extension to > 20 GeV/c d (D 0 )/dy for |y| 1 GeV/c (65% of (p t > 0)) statistical error = 7 % systematic error = 19 % from b = 9 % MC correction = 10% B.R. = 2.4 % from AA to NN = 13 %

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 25 Beauty & charm energy loss BEAUTY CHARM As seen in the previous talk… b & c show a different sensitivity

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 26 Charm E-loss sensitivity Low p t (< 6–7 GeV/c) Nuclear shadowing ‘High’ p t (6–15 GeV/c) here energy loss can be studied (it’s the only expected effect) Pb-Pb pp ?

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 27 Conclusion & perspectives The LHC energy will provide new tools for the study of high-density QCD matter; in particular heavy quarks! The LHC energy will provide new tools for the study of high-density QCD matter; in particular heavy quarks! High p t : probe the medium via energy loss High p t : probe the medium via energy loss The excellent tracking, vertexing and PID capabilities of the ALICE central barrel allow to reconstruct D,B mesons in a wide p t range (~0–15 GeV/c) and, thus, to address this rich physics item The excellent tracking, vertexing and PID capabilities of the ALICE central barrel allow to reconstruct D,B mesons in a wide p t range (~0–15 GeV/c) and, thus, to address this rich physics item ALICE has the potential to probe the (partonic) medium with these tools ALICE has the potential to probe the (partonic) medium with these tools Work in progress to perform a thorough comparison of energy loss among heavy and light probes (,D,B) and explore more complex/rare decays Work in progress to perform a thorough comparison of energy loss among heavy and light probes (,D,B) and explore more complex/rare decays

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 28

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 29 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

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 30 Identification of e - TRD Transition Radiation Detector: Transition Radiation Detector: separation of e from and heavier particles (K, p) separation of e from and heavier particles (K, p) dN CH /dy y=0 =6000 fissato el =0.9 appross. costante con il p t in un ampio intervallo -eff vs e-eff pions efficiency vs p t

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 31 Identification of e - TPC Hadrons heavier than pions rejected by TRD. Hadrons heavier than pions rejected by TRD. Futher reduction of /e ratio by dE/dx in TPC Futher reduction of /e ratio by dE/dx in TPC

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 32 Impact parameter of conversions Due to pair production topology and our d 0 definition, conversions in the material have mostly d 0 <0 p T > 1 GeV e's from h

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 33 7 samples of 500 e injected in full HIJING-cent2 events at P T = 0.25, 0.39, 0.67, 1.19, 2.36, 4.00, 6.00 GeV fully reconstructed and tracked transverse impact parameter (d 0 ) spectra have been fitted with 2 gaussians and the trend of the 6 constants against P T parameterized d 0 resolution parameterization

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 34 Impact parameter signs

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 35 d 0 spectra from e's impact parameter [cm]

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 36 Parameters fit: widths sigma [cm] 2 nd gaussian 1 st gaussian res. in r

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 37 p t correlation b-B and B-e

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 38 Sensitivity to NLO pQCD params s = 14 TeV pp

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 39 D 0 K - + : Results S/Binitial (M3) S/evtfinal (M1) S/Bfinal Significance S/S+B (M1) 2 10 -3 1.9 10 -5 11 % 44 44 (for 10 9 evts, ~9 months at 10 30 cm -2 s -1 ) 2 < p t < 2.5 GeV/c 12 < p t < 14 GeV/c 0.5 < p t < 1 GeV/c

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 40 What if multiplicity in Pb-Pb is lower? We used dN ch /dy = 6000, which is a pessimistic estimate We used dN ch /dy = 6000, which is a pessimistic estimate Recent analyses of RHIC results seem to suggest as a more realistic value dN ch /dy = 3000 (or less) Recent analyses of RHIC results seem to suggest as a more realistic value dN ch /dy = 3000 (or less) Charm production cross section: Charm production cross section: estimate from NLO pQCD (only primary production, no collective effects) estimate from NLO pQCD (only primary production, no collective effects) average of theoretical uncertainties (choice of: m c, F, R, PDF) average of theoretical uncertainties (choice of: m c, F, R, PDF) BKG proportional to (dN ch /dy) 2 BKG proportional to (dN ch /dy) 2 We can scale the results to the case of dN ch /dy = 3000: We can scale the results to the case of dN ch /dy = 3000: S/B = 44 % SGNC = 74 (this only from scaling, obviously better with retuning of cuts) (this only from scaling, obviously better with retuning of cuts)

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 41 D/hadrons ratio Ratio expected to be enhanced because: Ratio expected to be enhanced because: D comes from (c) quark, while , K, p come mainly (~80%) from gluons, which lose twice energy as quarks D comes from (c) quark, while , K, p come mainly (~80%) from gluons, which lose twice energy as quarks dead cone for heavy quarks dead cone for heavy quarks D/h ratio: R D/h = R D AA / R h AA R D/h ~ 2-3 in hot QGP sensitive to medium density OUTDATED

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 42 Centrality

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 43 d (D 0 )/dy for |y| 0 statistical error = 3 % systematic error = 14 % from b = 8 % MC correction = 10% B.R. = 2.4 % inel = 5 %

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 44 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

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 45 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

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 46 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

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 47 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

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 48 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

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 49 The phase space used iswhere p T are the previously used bins, = [-0.9, 0.9] and d 0 = [200,600] m 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 (thanks to R.Guernane for useful discussions)

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 50 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

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 51 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

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 52 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/0501225 Extraction of a minimum-p T -differential cross section for B mesons

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 53 Can find an optimal p T min for p T e > 2 GeV/c F ~ 1 % Extraction of a minimum-p T -differential cross section for B mesons Evaluation of and determination of the optimal p T min

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 54 Eloss references Baier, Dokshitzer, Mueller, Peigne‘, Schiff, NPB 483 (1997) 291. Zakharov, JTEPL 63 (1996) 952. Salgado, Wiedemann, PRD 68(2003) 014008. back

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 55 Main systematic uncertainties: Monte Carlo corrections (detector acceptance, tracking efficiency, selection efficiency) ~ 10% (at the moment assumed to be p T -indep.) 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% 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 Charm contribution to be subtracted from the total electron spectrum (see following slides) (see following slides) Note: we assume to be able to subtract the residual misid. and photonic e with negligible systematic error Errors on p t spectrum of beauty e’s - 2

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Rosario Turrisi Heavy Ion Forum Wednesday, April 13, 2005 56 Charm R AA Errors on the quenched charm R AA Errors on the quenched charm R AA back

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