Open heavy flavor analysis with the ALICE experiment at LHC Serhiy Senyukov Università del Piemonte Orientale, INFN Torino On behalf of ALICE Collaboration

Outline of the talk Physics motivation for HF analyses Probing the QGP medium Testing pQCD in pp-collisions ALICE detector and its performance Tracking and vertexing Particle identification (PID) Expected physics performance Present results D mesons via hadronic decays Single electrons Single muons 5th workshop on High pt Physics at LHC 30.09.2010

Physics motivation: HF and QGP Heavy flavor particles can be used as a penetrating probe of the medium created in a Heavy Ion collision HF quarks are produced early in the collisions (large Q2) They travel through the created medium interacting with its constituents Radiative energy loss should play dominant role and is described by the following formula: K- K+ π+ π- QGP A c Ds- D0 c̄ s Primary production Interaction with QGP Formation and decay of D mesons Detection of products The energy loss depends on: color charge (quark vs. gluon), parton mass (dead cone effect) and energy density of the medium. 5th workshop on High pt Physics at LHC 30.09.2010

Physics motivation: energy loss Experimental variable used to measure parton energy loss is the nuclear modification factor (RAA): Energy loss should appear as a suppression of the RAA . This effect has been seen at RHIC via non-photonic electrons coming from c and b quarks. However the present models fail to reproduce the experimental results. PRL, 98, 192301 (2007) Physics motivation: HF and pp Heavy flavor should be measured in pp collisions: Gives necessary normalization for heavy-ion data. (See above) Allows to test pQCD predictions in a new energy scale 5th workshop on High pt Physics at LHC 30.09.2010

Charm production at LHC SPS RHIC LHC s (GeV) 17.2 200 5500 Ncc ≈ 0.2 ≈10 ≈100 x (at y=0) ≈ 10-1 ≈ 10-2 ≈ 10-4 Large cross-section Much more abundant production with respect to SPS and RHIC central y Forward y Small x unexplored small-x region can be probed with charm at low pT and/or forward rapidity down to x~10-4 at y=0 and x~10-6 in the muon arm 5th workshop on High pt Physics at LHC 30.09.2010

ALICE detector ITS, TPC, TRD, ToF (||<0.9) (di-)electrons: J/, ’, , ’,’’, open charm, open bottom, W±, Z0 muon spectrometer (-4<<-2.5) (di-)muons: J/, ’, , ’,’’, open charm, open bottom, W±, Z0 electron-muon coincidences: open charm & bottom ITS, TPC, ToF (||<0.9) hadrons: D0, D±,… 5th workshop on High pt Physics at LHC 30.09.2010

Detector performance: Tracking/Vertexing Actual performance is very close to that expected from MC simulations 5th workshop on High pt Physics at LHC 30.09.2010

Detector performance: PID 5th workshop on High pt Physics at LHC 30.09.2010

Expected physics performance: pT spectra pp, s = 14 TeV charm (D0  Kp) beauty (B  e+X) 1 year at nominal luminosity (31030 cm-2s-1) (109 pp events) 5th workshop on High pt Physics at LHC 30.09.2010

Expected performance: RAA etc. probes mass dep. of QCD energy loss E loss calc.: Armesto, Dainese, Salgado, Wiedemann 1 year at nominal luminosity (107 central Pb-Pb events, 109 pp events) 5th workshop on High pt Physics at LHC 30.09.2010

Statistics collected by ALICE Two trigger classes: Minimum bias interaction trigger (INT1B): ≥ 1 charged particle in 8 η units Single-muon trigger (MUS1B): forward muon in coincidence with MB trigger By the 1st September ALICE collected: ~ 694 M of INT1B events ~ 50M of MUS1B events Data reconstruction and analysis is on the way. Thus results presented here are obtained using the fraction of data: 140 M INT1B events for hadronic branch and 160M for single electrons analysis 4.7 M MUS1B events for single muon analysis 5th workshop on High pt Physics at LHC 30.09.2010

Three ways to see open heavy flavor: Charged hadrons (K and π) – D mesons at central rapidity Single electrons – D and B mesons at central rapidity Single muons – D and B mesons at forward rapidity 5th workshop on High pt Physics at LHC 30.09.2010

Reconstruction via charged hadrons: analysis strategy General idea: invariant mass analysis of track combinations (pairs, triplets, quadruplets) with correct signs Single track selection Particle identification using TPC and TOF Topological cuts: impact parameter, distance between secondary and primary vertex, pointing angle Estimation of the feed-down from beauty Efficiency and acceptance correction 5th workshop on High pt Physics at LHC 30.09.2010

Results: D0K-π+ Signal pT -integrated >2 GeV/c Position: 1867±1 MeV/c2 Width: 14±1 MeV/c2 Hint of the signal down to 1 GeV/c 5th workshop on High pt Physics at LHC 30.09.2010

Results: D+K-π+π+ Signal pT -integrated >2 GeV/c Position: 1870±1 MeV/c2 Width: 13±1 MeV/c2 Hint of the signal down to 1 GeV/c 5th workshop on High pt Physics at LHC 30.09.2010

Results: D*±D0πs± Signal pT -integrated >2 GeV/c seen as ΔM(Kππ-Kπ) Position: 145.43±0.03 MeV/c2 Width: 0.62±0.03 MeV/c2 Hint of the signal down to 1 GeV/c 5th workshop on High pt Physics at LHC 30.09.2010

More results coming: D0K+π+π-π+ Signal pT -integrated for 3<pT<5 GeV/c Position: 1864±2 MeV/c2 Width: 15±2MeV/c2 5th workshop on High pt Physics at LHC 30.09.2010

More results coming: Ds+K+K-π+ Signal pT -integrated for 3<pT<5 GeV/c Position: 1971.4±1.1 MeV/c2 Width: 4.4±1.4 MeV/c2 5th workshop on High pt Physics at LHC 30.09.2010

Reconstruction via single electrons: analysis strategy Single track selection Identification as electron by TPC, TRD and TOF Subtraction of the photonic component using the cocktail 5th workshop on High pt Physics at LHC 30.09.2010

Results: B,D  e + X Only TPC and TOF are used for electrons identification. TRD calibration is ongoing Possibility to use EmCAL is considered 5th workshop on High pt Physics at LHC 30.09.2010

Reconstruction via single muons: analysis strategy remove hadrons & low pt  secondary /K: tracking-trigger matching remove  secondary /K: DCA cut (only if pt < 1.5 GeV/c studied) remove   primary /K: vertex displacement method, high pt data, models correct  dN/dpt for efficiency/acceptance convert to  differential cross section unravel charm & beauty  dN/dpt components via a combined fit from  cross sections to B (D)-hadron cross sections 5th workshop on High pt Physics at LHC 30.09.2010

B,D  μ + X: Subtraction of   primary /K using high pT data: Subtraction hadrons & low pt  secondary /K: This particles are absorbed by the iron absorber placed between tracker and trigger chambers. Effect is seen on DCA distribution  DCA – Distance of Closest Approach (distance between extrapolated track & interaction vertex in the plane perpendicular to the beam direction and containing the vertex) Subtraction of   primary /K using high pT data: Fit high pT range (i.e. charm & beauty) & extrapolate at low pT Subtraction from the total pT distribution gives an estimate of the muon yield from primary /K and allows to extract the muon yield from HF decays 5th workshop on High pt Physics at LHC 30.09.2010

Results: B,D  μ + X 5th workshop on High pt Physics at LHC 30.09.2010

Conclusions Open heavy flavor is an important tool for studying Quark Gluon Plasma and QCD: Measure of medium properties via energy loss Test of pQCD in a new energy domain ALICE is well equipped for heavy flavor: Two rapidity regions coverage Good tracking and vertexing Good PID capabilities First promising results: D+, D0, D* and Ds signal seen in a range 1<pT<12 GeV/c Uncorrected pT-spectra for single electrons and muons are obtained. Pb-Pb collisions to come 5th workshop on High pt Physics at LHC 30.09.2010