Perspectives for charm and beauty quenching studies in ALICE F. Antinori, C. Bombonati, A. Dainese, M. Lunardon and R. Turrisi Padova – University and INFN
Contents • Heavy quarks detection at mid-rapidity with ALICE • Main results of performance studies for charm and beauty detection • Expected sensitivity with respect to the mass dependence on quenching • Conclusions and perspectives
Heavy quarks detection at mid-rapidity with ALICE Different approaches for charm and beauty due to different expected production cross sections (charm is more than 20 times larger than beauty) and decay branching ratios. Taking advantage of the expected good track impact parameter determination, the most promising channels are: Charm: exclusive reconstruction of D0 K-+ Beauty: inclusive measurement of electrons from semi-electronic decays • We explored both possibilities with a detailed performance studies including: • likely event generation (PYTHIA 6, HIJING) and cross section estimation (HVQMNR); • tracking with complete detector simulation (geant 3.21) for ITS ( good impact parameter reconstruction) and parameterized response of TPC; • realistic PID parameterization in TPC, TOF and TRD; • full analysis for Pb-Pb collisions @ 5.5 TeV and p-p @ 14 TeV.
rf: 50 mm 9.8 Mch z: 425 mm PIXEL CELL Two layers: r = 4 – 7 cm Heavy quarks detection at mid-rapidity with ALICE key factor: good measurement of track impact parameter provided by the ITS (SPD) Pb-Pb estimate better than 60 mm (rf) for pt > 1 GeV/c
Charm: exclusive reconstruction of D0 K-+ Exclusive channel that allow direct measurement of pt distribution Ideal tool to study RAA Weak decay with mean proper length c = 124 m • Large combinatorial background (dNch/dy = 6000 in central Pb-Pb!) • STRATEGY: invariant-mass analysis of fully-reconstructed topologies originating from (displaced) secondary vertices • Measurement of Impact Parameters (ITS+TPC) • Measurement of Momenta (ITS+TPC) pointing angle • Particle identification (TOF) to tag the two decay products
Charm: exclusive reconstruction of D0 K-+ inner bars: stat. errors outer bars: stat. pt-dep. syst. not shown: 9% (Pb-Pb), 5% (pp, p-Pb) normalization errors • Main systematic contributions: • corr. for PID and selection eff. (~10%) • subtraction of feed-down from B decays (~8% initially) Down to pt ~ 0 in pp and p-Pb (1 GeV/c in Pb-Pb)
Beauty: inclusive measurement of electrons from semi-electronic decays • The semi-electronic decay channels has a good intrinsic B.R.: h(b) e + + X ~ 10.2 % and almost 100% of beauty hadrons decay through a charmed hadron, which can again decay via single electron: h(b) h(c) +X e + + Y ~ 10.9 % giving a total B.R. for single electron of about 21 % • Good detection and identification capabilities for electrons at mid rapidity (TRD, TPC and Vertex detector) with ALICE down to low pt (~1 GeV/c) misidentification probability ~ 10-4 heavier particles ~ 0 loss of detected electrons ~ 40%
Beauty: inclusive measurement of electrons from semi-electronic decays • Detection strategy: • - electron ID in TPC+TRD • - impact parameter cut (B c ~ 500 m) • moreover:large b mass hard electron spectrum better selection at high pt for |d0| > ~ 100 mm beauty gets dominant
no vertex reconstruction chosen method Beauty: inclusive measurement of electrons from semi-electronic decays Additional topics for p-p study: - study of the primary vertex reconstruction tuned on electron track impact parameter distributions; - optimized impact parameter cut for each pt bin.
Beauty: inclusive measurement of electrons from semi-electronic decays • Main systematic contributions: • corr. for PID and selection eff. (~10%) • subtraction of electrons from charm decays (<5% using direct D0 meas.) inner bars: stat. errors outer bars: stat. pt-dep. syst. errors not shown: normalization error 9 (5) % for Pb-Pb (pp)
Beauty: inclusive measurement of electrons from semi-electronic decays Extraction of a ptmin-differential cross section for B mesons Using electrons in 2 < pt < 20 GeV/c obtain B meson 2 < ptmin < 30 GeV/c MC-based procedure à la UA1
Pb-Pb pp Heavy quarks detection at mid-rapidity with ALICE Sensitivity to mass dependence on quenching ‘High’ pt (10–20 GeV/c) here energy loss can be studied (it’s the only expected effect) Low pt (< 8–10 GeV/c) Nuclear shadowing, recombination? 1 year at nominal luminosity (107 central Pb-Pb events, 109 pp events) Dainese, EPJC33 (2004) 495 E loss calc: Armesto, Dainese, Salgado Wiedemann, PRD71 (2005) 054027
Pb-Pb pp Possible sensitivity to mass effects Heavy quarks detection at mid-rapidity with ALICE Sensitivity to mass dependence on quenching Low pt (< 8–10 GeV/c) Nuclear shadowing, recombination? ‘High’ pt (10–30 GeV/c) here energy loss can be studied PRELIMINARY 1 year at nominal luminosity (107 central Pb-Pb events, 109 pp events) E loss calc: Armesto, Dainese, Salgado Wiedemann, PRD71 (2005) 054027
Conclusion and perspectives • We explored the capabilites of ALICE in detecting charm and beauty at mid-rapidity via the exclusive D0 K-+ reconstruction and inclusive single-electron detection; • the results for charm show the possibility of having a precise measurement of pt–differential cross section of charmed mesons from 1 up to 20 GeV/c; • in the case of beauty, it is possible to extract a ptmin-differential cross section for B mesons from 2 up to 30 GeV/c; • the analysis of the RAA for heavy mesons seems to offer a good tool for jet quenching studies at LHC; • in particular, the preliminary analysis of the RAA for B mesons seems to be very promising and need further and better investigation.
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 pp @ 14 TeVcharm 0.16 beauty 0.007 Semi-electronic channel ~ 20 % , ALICE accept. for these electrons ~ 24 % in Pb-Pb ~ 0.4 beauty electrons / event Statistics for 107 central events (~ 1 month Pb-Pb run):~ 4 M beauty electrons
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
Extraction of a minimum-pT-differential cross section for B mesons Using UA1 MC method, also adopted by ALICE m Evaluation of and determination of the optimal pTmin 1) we used the B e + X decays from PYTHIA. is the ratio of the red area to the blue one. here pTe = [3,4] GeV/c
Error on MC corrections for tracking, selection, ID efficiencies Error on subtraction of charm electrons (curr.tly from D0 measure) Error on normalization to cross section per NN collision Systematic errors (Pb-Pb) Error on e from charm (propagated from D0 meas.)