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Open heavy flavours: perspectives of ALICE for the detection of quark energy loss

Heavy Ion Forum, April 13 th 2005. 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. Summary. Motivations Environment: simulation, cross sections, detector

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Open heavy flavours: perspectives of ALICE for the detection of quark energy loss

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  1. Heavy Ion Forum, April 13th 2005 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

  2. Summary • Motivations • Environment: simulation, cross sections, detector • Beauty detection in semileptonic channel • Charm detection in hadronic channel • Energy loss sensitivity • Conclusions

  3. Motivations Heavy flavours in heavy-ions @ LHC: interest in its own right: high yields & small x More specific to QGP: natural baseline B  J/ background open flavours B,D quarkonia J/, suppression Medium probes: early formation thermal production energy loss K e 

  4. Choice of channels • D0 K-p+,“golden channel” • Exclusive channel direct measurement of the pt distribution ideal tool to study RAA • 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% • pt measurement achievable • explores electron identification techniques

  5. system shadowing pp 14 TeV 11.2/0.5 1/1 0.16/0.007 Pb-Pb 5.5 TeV (5% cent) 6.6 /0.2 0.65 /0.85 115 /4.6 Cross sections baseline • ALICE baseline: • NLO pQCD (MNR), average of MRST e CTEQ5 pdf’s (pp yields) • extrapolation to PbPb, shadowing according to EKS98 charm/beauty varying F,R inside a reasonable range the cross sections spans a factor ~ 4 Mesons (produced) multiplicities in barrel acceptance: 0.5 0.2 ~13.7 D0  K ~0.85 B  eX ALICE baseline: N.Carrer and A.Dainese, ALICE-INT-2003-019, hep-ph/0311225.

  6. Background in PbPb @ 5.5 TeV • Background is given by: • D0: pairs of uncorrelated tracks w/large impact parameter • 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

  7. Simulation • Background: HIJING, ~104 tracks in barrel acceptance • 2104 events • Signal: PYTHIA • D0: MNR-tuned events, reproduces pt spectrum, ~2106 D0 • beauty: forced production (MSEL=5), 5.2 106 electrons • charm: forced production (MSEL=4), 2.3106 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 107 PbPb central events (5% of total x-section), i.e. one month run

  8. rf: 50 mm 9.8 Mch z: 425 mm PIXEL CELL Two layers: r = 4 – 7 cm 2 * 1.8 units of pseudo-rapidity 2.4 <  < 4 Solenoid magnet B<0.5 T Highlights on the ALICE detector TPC (the largest ever…): 88 m3 , 510 cm length, 250 cm radius Ar (90%) + CO2 (10%) 88 μs drift time main tracking device, dE/dx • 6 Layers, 3 technologies • Material budget < 1% of X0 per layer! • Silicon Pixels vertices resolution in xy • (0.2 m2, 9.8 Mchannels) • Silicon Drift  resolution in z • (1.3 m2, 133 kchannels) • Double-sided Strip  connection w/TPC • (4.9 m2, 2.6 Mchannels) • 6 layers for: • electron/pion separation at pt>1 GeV • factor 100 rejection at 2 GeV • tracking complement, mass resolution • 100 MeV/c2 @  • high pt trigger (onia studies) { • Central tracking system: • Inner Tracking System • Time Projection Chamber • Transition Radiation Detector • Time Of Flight MUON Spectrometer Multigap Resistive Plate Chambers 5 years R&D, and  < 100 ps pions, kaons, protons separation electrons/pions at low pt

  9. impact parameter resolution:  σ @ pt=1.3 GeV < 50 μm   < 150 μm z pt resolution: σ= 1(2)% @ 1(10) GeV 9% @ 100 GeV EFFICIENCY pions kaons Tracking performance

  10. BEAUTY

  11. after tracking a. u. a. u. Beauty detection strategy • Main sources of background: •  identified as e • Dalitz decays • charm electrons • photon conversions • strangeness decays • 0.22 e - beauty • ~103e - other sources • ~104  • Key elements: • separation e/ • d0= impact parameter • B’s c ~ 500m ! • beauty has harder pt spectrum minimum distance of track from primary vertex, in bending plane

  12. (Mis)identification of  TRD+TPC PID TRD PID NO PID pT>1 GeV pt>1

  13. Purity and statistics Signal-to-total ratio and expected statistics in 107 Pb-Pb events Expected statistics (107 Pb-Pb events) • dominated by charm • dominated by other sources 90% purity 40,000 e from B pT > 2 GeV/c , 200 < |d0| < 600 m

  14. Entries in 107 events Statistical error on beauty e’s • Statistical error on 107 central events (5% x-section) • 200 < |d0| < 600 m electrons

  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 pt distributions deduced from the D0K-+ measurement. - Charmed hadrons (Hc=D0,D+,D+s,+c) cross section assumed to be proportional to the D0 one. The Hc/D0 ratio is assumed to be 1.70  0.07 (*) Errors propagated from Hc to e level: - Monte Carlo corrections for the D0 measurement ~ 10% - Statistical error on the D0 pTdistribution - NN normalization not considered at this level (same as beauty) - The 69% uncertainty of D0 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]

  16. Systematic error on charm e’s Total relative error on the charm electron pT distribution to be subtracted

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

  18. stat pt-dep. syst 11% norm. err. (not shown) Extraction of a minimum-pT-differential cross section for B mesons Using electrons in 2 < pT < 16 GeV/c obtain B-meson 2 < pTmin < 23 GeV/c E loss calculations: N. Amesto, A. Dainese, C.A. Salgado, U.A. Wiedemann, hep-ph/0501225 ptmin threshold

  19. Beauty in the muon channel • Similar study in ALICE: • beauty in the Muon Spectrometer • No vertex, but clean muon sample • Rapidity range: 2.5<y<4 • Systematic error evaluation in • progress • Derivation of meson pt with same • technique as for e’s channel • Parallel analyses within same exp! bars: stat err ptmin threshold See talk of R. Guernane (Clermont-Ferrand group) at Moriond 2005: http://moriond.in2p3.fr/QCD/2005/Index.html

  20. CHARM

  21. Strategy • Exclusive channel D0 K-p+ direct measurement of the pt distribution ideal tool to study RAA • Weak decay with mean proper length ct = 124 mm • STRATEGY: invariant-mass analysis of fully-reconstructed topologies originating from (displaced) secondary vertices • Measurement of Impact Parameters • Measurement of Momenta • Particle identification to tag the two decay products

  22. Time-of-flight PID TOF Pb-Pb, dNch/dy=6000 Optimization for hadronic charm decays was studied: minimize probability to tag K as p

  23. D0 K-p+:Selection of D0 candidates 2-dim cut increases S/B by factor ~103!

  24. bars: stat err yellow band: syst err D0 Results (K,) Invariant Mass distribution (pt –integrated) in Pb-Pb (~ 1 month run) ds(D0)/dy for |y| < 1 and pt > 1 GeV/c (65% of s(pt > 0)) statistical error = 7 % systematic error = 19 % from b = 9 % MC correction = 10% B.R. = 2.4 % from AA to NN = 13 % Pb-Pb Statistical significance: up to 14 GeV/c ! currently studying extension to >20 GeV/c N.Carrer, A.D. and R.Turrisi, J. Phys. G29 (2003) 575. A.D. PhD thesis (2003), nucl-ex/0311004.

  25. Beauty & charm energy loss As seen in the previous talk… b & c show a different sensitivity CHARM BEAUTY

  26. Pb-Pb pp Charm E-loss sensitivity ‘High’ pt (6–15 GeV/c) here energy loss can be studied (it’s the only expected effect) Low pt (< 6–7 GeV/c) Nuclear shadowing ?

  27. Conclusion & perspectives • The LHC energy will provide new tools for the study of high-density QCD matter; in particular heavy quarks! • High pt: 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 pt 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 • Work in progress to perform a thorough comparison of energy loss among heavy and light probes (,D,B) and explore more complex/rare decays

  28. Backup Slides

  29. Estimation of uncertainties on the pT - 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. Identification of e - TRD -eff vs e-eff • Transition Radiation Detector: • separation of e from  and heavier particles (K, p) pions efficiency vs pt dNCH/dy½y=0 =6000Þep=0.01 fissato eel=0.9 appross. costante con il pt in un ampio intervallo

  31. Identification of e - TPC • Hadrons heavier than pions rejected by TRD. • Futher reduction of /e ratio by dE/dx in TPC

  32. Impact parameter of conversions Due to pair production topology and our d0 definition, g conversions in the material have mostly d0 <0 e's from h pT> 1 GeV

  33. d0 resolution parameterization 7 samples of 500 e± injected in full HIJING-cent2 events at PT = 0.25, 0.39, 0.67, 1.19, 2.36, 4.00, 6.00 GeV fully reconstructed and tracked transverse impact parameter (d0) spectra have been fitted with 2 gaussians and the trend of the 6 constants against PT parameterized

  34. Impact parameter signs

  35. d0 spectra from e's impact parameter [cm]

  36. 2nd gaussian 1st gaussian p res. in rj sigma [cm] Parameters fit: widths

  37. pt correlation b-B and B-e

  38. Sensitivity to NLO pQCD params s = 14 TeV pp

  39. D0 K-p+: Results 0.5 < pt < 1 GeV/c 2 < pt < 2.5 GeV/c 12 < pt < 14 GeV/c

  40. What if multiplicity in Pb-Pb is lower? • We used dNch/dy = 6000, which is a pessimistic estimate • Recent analyses of RHIC results seem to suggest as a more realistic value dNch/dy = 3000 (or less) • Charm production cross section: • estimate from NLO pQCD (only primary production, no collective effects) • average of theoretical uncertainties (choice of: mc, mF, mR, PDF) • BKG proportional to (dNch/dy)2 • We can scale the results to the case of dNch/dy = 3000: S/B = 44 % SGNC = 74 (this only from scaling, obviously better with retuning of cuts)

  41. D/hadrons ratio • Ratio expected to be enhanced because: • D comes from (c) quark, while p, K, p come mainly (~80%) from gluons, which lose twice energy as quarks • dead cone for heavy quarks D/h ratio: RD/h = RDAA / RhAA RD/h ~ 2-3 in hot QGP sensitive to medium density OUTDATED

  42. Centrality

  43. ds(D0)/dy for |y| < 1 and pt > 0 statistical error = 3 % systematic error = 14 % from b = 8 % MC correction = 10% B.R. = 2.4 % sinel = 5 %

  44. Estimation of uncertainties on the pT - differential cross section of beauty electrons evaluation of charm background Effect of the D0 statistical error on the electron pT distribution (1) Monte Carlo method 1) the initial D0pT distribution (the measured one) is fitted to the expression:

  45. 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 pT = 2 GeV/c is counted as 0.94 electrons Estimation of uncertainties on the pT - differential cross section of beauty electrons evaluation of charm background Effect of the D0 statistical error on the electron pT distribution (2) 2) the points are smeared according to the estimated statistical standard deviation and the fit is recalculated

  46. Estimation of uncertainties on the pT - differential cross section of beauty electrons evaluation of charm background Effect of the D0 statistical error on the electron pT distribution (3) 4) the refit procedure is repeated many times and the standard deviation of the content in each electron pT-bin is evaluated Relative error as a function of pT

  47. Estimation of uncertainties on the pT - differential cross section of beauty electrons evaluation of charm background Effect of the D0 statistical error on the electron pT distribution (4) Analytic method 1) for each D0 pT bin, the corresponding electron pT distribution is extracted and the relative errors of all the electron pT bins are set equal to that of the D0

  48. Estimation of uncertainties on the pT - differential cross section of beauty electrons evaluation of charm background Effect of the D0 statistical error on the electron pT distribution (5) 2) the different electron spectra are summed with a quadratic error propagation The analytic result compared to the numerical one

  49. Extraction of a minimum-pT-differential cross section for B mesons Using UA1 MC method (*), also adopted by ALICE m (thanks to R.Guernane for useful discussions) The B meson cross section per unit of rapidity at midrapidity with pTB > pTmin 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 is where pT are the previously used bins,  = [-0.9, 0.9] and d0 = [200,600] m (*) C. Albajar et al., UA1 Coll., Phys Lett B213 (1988) 405 C. Albajar et al., UA1 Coll., Phys Lett B256 (1991) 121

  50. Extraction of a minimum-pT-differential cross section for B mesons Using UA1 MC method, also adopted by ALICE m Systematic error for - semi-electronic decay B.R.: ~ 3 % - dependence on the shape of the B meson pT distribution used as input in the MC: can be minimized using a proper choice of pTmin 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 pT 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.

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