Measurement of muon tagged open heavy flavor production in Pb+Pb collisions at 2.76 TeV with ATLAS

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1 Measurement of muon tagged open heavy flavor production in Pb+Pb collisions at 2.76 TeV with Dennis V. Perepelitsa Columbia University for the Collaboration Quark Matter 2012 Parallel 7A Washington, D.C., USA (1/ 15) 17 August 2012

2 Heavy flavor suppression at RHIC and the LHC (2/ 15) -CONF PRC 84, (2011) PRL 101, (2008) Heavy quark measurements complement light quark/gluon dominated measurements (jets, leading hadrons): larger mass, different formation time, etc. essential for full picture of jet quenching RHIC experiments indicate that heavy quarks are suppressed at the same level as light q/g... what about the LHC? -CONF

3 detector (3/ 15) µ ± reconstruction: silicon pixel detectors/silicon microstrip detectors/straw tube tracker (ID), muon spectrometer (MS) centrality determination: forward calorimeters (FCal) -CONF

4 Data & event selection Data: 2010 Pb+Pb 2.76 TeV, L = 7 µb 1 all data taken Minimum Bias, events analyzed Event selection: timing, ZDC coincidence + primary vertex requirements sample 98 ± 2% of Pb+Pb cross-section µ ± selection: η < 1.05 (inner detector + muon spectrometer) p T > 4 GeV (good reconstruction efficiency) p T < 14 GeV (statistics, < 1% W ± contribution) (4/ 15) Monte Carlo: PYTHIA dijets with ˆp T = GeV + overlay with HIJING Pb+Pb events -CONF

5 determination in (5/ 15) ΣE FCal T used to categorize centrality 3.2 < η < 4.9, far removed from mid-rapidity physics good agreement between data and Glauber + p+p simulation This analysis: 0-10%, 10-20%, 20-40%, 40-60%, 60-80% 60-80% used as common reference (expect small hot nuclear matter effects) -CONF

6 Reconstructing µ ± s (6/ 15) number of reconstructed µ ± Reconstruction efficiency for µ ± from semi-leptonic b- or c-decays: centrality-independent above p T > 5 GeV (ɛ plateau = 80 ± 2%) weak centrality dependence for p T 4-5 GeV (More information on µ ± /e ± reco in p+p: PLB 707 (2012), ) -CONF

7 Heavy flavor extraction: template definition Discriminant #1 (expected momentum loss while moving through calorimeters): p loss = p ID p MS p MC param Discriminant #2 (angular deflection in inner detector): s i = q φ i φ msc i ) S = 1 n (Σ j 1 s i Σ k j+1 s i Composite: C = p loss p ID S (7/ 15) Composite discriminant from µ ± momentum loss (#1) and scattering angle (#2): heavy quark signal well-separated from π ± /K ± background no centrality dependence increasing separation with muon p T -CONF

8 Heavy flavor extraction: template fitting Composite fit: dp dc = f s dp dc S +(1 f s ) dp dc B Limited data adaptation allows template to: shift stretch smear Extract heavy flavor component from inclusive µ ± yield (8/ 15) Toy MC re-sampling to determine systematic uncertainty -CONF

9 Heavy flavor extraction: signal fraction (9/ 15) Fraction of heavy flavor µ ± is higher in central events!... hint that open heavy flavor is less suppressed than inclusive hadrons... -CONF

10 uncertainty overview (10/ 15) dp/dc : Fit : possible centrality dependence in signal/background templates use C < C cut as alternate signal extraction method restrict shift/stretch/smear template distortion π/k : ɛ : separately double π/k contribution in background template µ ± reconstruction efficiency uncertainty -CONF

11 : yields from heavy flavor decays (11/ 15) Invariant yields of muons from heavy flavor: R cent CP = (1/N cent evt )(dn cent /dp T) R cent coll (1/N60 80% evt )(dn 60 80% /dp T) R coll : ratio of # binary collisions between central and peripheral 56.7 ± 6.2 (0-10%), 34.9 ± 3.5 (10-20%),16.7 ± 1.5 (20-40%), 4.9 ± 0.2 (40-60%) (1) -CONF

12 : (p T ) from heavy flavor decays (12/ 15) Corr. syst. (shaded boxes) and uncorr. syst. + stat. (bars) suppression with centrality ( 0.45 for 0-10%/60-80%) No p T dependence, even as bottom overtakes charm! different suppression than in single hadron (-CONF , P. Balek, Parallel 5C, 5/16) -CONF

13 : R PC (p T ) from heavy flavor decays (13/ 15) R PC uses 0-10% central bin as reference: does not suffer from statistical fluctuations and large systematic uncertainties in peripheral reference Better gauge of p T dependence. -CONF

14 : (N part ) from heavy flavor decays (14/ 15) Replot vs N part: suppression evolves smoothly with centrality. similar N part dependence at all p T. -CONF

15 has measured muon yields from heavy quark decays in Pb+Pb collisions. 4 GeV < p T < 14 GeV and η < 1.05 template fitting method to extract heavy quark signal from π/k background indicates factor of 2 suppression flat with p T (as charm/bottom ratio evolves) (15/ 15) smooth with centrality Distinct suppression pattern from charged hadron! indication that heavy flavor behaves differently at the LHC than at RHIC -CONF