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Heavy-flavor correlation measurements via electron azimuthal correlations with open charm mesons André Mischke for the STAR Collaboration Amsterdam Outline • Motivation • Correlation technique • Data analysis • Results • Data-model comparison • Summary and conclusions Strangeness in Quark Matter 24–29 June 2007, Levoča (Slovakia) Heavy quark energy loss • Due to their large mass heavy quarks are primarily produced by gluon fusion parton production rates can be calculated in pQCD sensitivity to initial state gluon distribution M. Gyulassy and Z. Lin, PRC 51, 2177 (1995) • Heavy quarks lose less energy due to suppression of small angle gluon radiation (dead-cone effect) hot and dense medium M. Djordjevic, PRL 94 (2004) light Dokshitzer and Kharzeev, PLB 519, 199 (2001) • Amount of collisional and radiative energy losses seems to be similar M.G. Mustafa, PRC72, 014905; A.K. Dutt-Mazumder et al., PRD71, 094016 (2005) Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 2 Heavy flavour measurement • Hadronic decay channels D0 Kp B.R.: 3.83% D Kpp B.R.: 9.51% D* D0p B.R.: ~65% Difficulty: large combinatoric background, especially in high multiplicity environments Event-mixing and/or vertex tracker needed to obtain a signal QM 2005, Nucl. Phys. A774 (2006) 701, publication in preparation • Semi-leptonic channels (inclusive modes) c e+ + X B.R.: 9.6% D0 e+ + X B.R.: 6.87% D e + X B.R.: 17.2% b e- + X B.R.: 10.9% B e + X B.R.: 10.2% Single (non-photonic) electrons sensitive to charm and beauty Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 3 Non-photonic electron spectra in Au+Au • Non-photonic electrons exhibit a similar yield suppression at high-pT in central Au+Au as light hadrons Phys. Rev. Lett. 98, 192301 (2007) • Models implying D and B energy loss are inconclusive yet Disentangle D and B contribution to non-photonic electron spectrum experimentally At which pT does B contribution start to dominate ? • Approach: Non-photonic electron D0 meson azimuthal correlations Andre Mischke (UU) Large suppression not expected due to dead-cone effect SQM 2007, Levoča, 7/17/2015 4 Correlation technique Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 5 Electron tagged correlations • Experimental approach trigger side - non-photonic electrons from semileptonic D/B decays are used to trigger on c-cbar or b-bbar pairs - associate D0 mesons are reconstructed via their hadronic decay channel (probe) • Underlying production mechanism can be identified using second c/b particle 0 c charm production c g c g c p flavor creation Andre Mischke (UU) g g g g probe side gluon splitting/fragmentation SQM 2007, Levoča, 7/17/2015 6 Electron tagged correlations: p B production + eKe D0 D*0 B- unlike-sign pairs away-side correlation b like-sign pairs near-side correlation b B+ D0 p- Near and away correlation peak expected for b production K+ Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 7 PYTHIA simulations: 3<pTtrg<7 GeV/c like-sign (e,K) unlike-sign (e,K) • Different decay channels for D and B • Charge-sign requirement on (e,K) pairs gives an additional constraint on production process - Like-sign (e,K) means charge(electron) = charge(Kaon) • Separation of D and B contribution to non-photonic electrons Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 8 PYTHIA simulations: Electron triggers with 8<pTtrg<20 GeV/c like-sign (e,K) unlike-sign (e,K) • Near-side: - B decays (dominant) • Away-side: • Away-side: - charm meson pair production (dominant) - small B contribution Andre Mischke (UU) - B decays (dominant) - small charm contribution SQM 2007, Levoča, 7/17/2015 9 Data analysis Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 10 STAR experiment Solenoidal Tracker at RHIC Energy measurement - Barrel EMC • || < 1 • Pb/scintillator (21 X0) • dE/E ~ 16%/E • Shower maximum detector Large acceptance magnetic spectrometer advantage e- PID and tracking - TPC • || < 1.5 • p/p = 2-4% • dE/dx/dEdx = 8% Kp+ - Magnet • 0.5 Tesla Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 11 • 2006 p+p at sNN = 200 GeV Dataset and triggering - Ldt = 9 pb-1 - 1.2M events after trigger and vertex cut • BEMC fully installed ~97% operational • Level-0 trigger used to enhance particle yield at high-pT BEMC tower energy threshold 5.4 GeV Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 Run 06 04 BEMC acceptance 12 Electron selection: Procedure • TPC tracks are extrapolated onto BEMC surface • Select tracks with well developed shower in SMD - p measurement in TPC - E measurement in BEMC Shower Maximum Detector (SMD) • Quality cuts: - p/Etower ratio – wire proportional counter with strip read-out - specific energy loss dE/dx – located after 5 X0 – = 0.007 x 0.007 Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 13 Electron selection: Quality cuts p/Etower • Ratio of momentum and tower-energy should be one for electrons cut: 0 < p/Etower < 2 • 3.5 < dE/dx < 5.0 keV/cm after p/E and SMD cuts d p K electron candidates dE/dx cut e p Andre Mischke (UU) hadrons (essentially pions) SQM 2007, Levoča, 7/17/2015 14 Electron purity and hadron suppression • Purity: ~100% for pT < 7 GeV/c • Hadron suppression factor: 102 - 105 Clean electron sample Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 15 Photonic background • Measured electron candidates have a photonic and non-photonic contribution e+ e- • Photonic contribution from gamma conversions and (p0, ) Dalitz decays dca • Procedure - electron candidates are combined with TPC tracks which passed loose dE/dx cuts around the electron band (global track) (assigned as primary track) e- (primary track) - invariant mass is calculated at dca of these pairs • Electrons having a low invariant mass (minv < 150 MeV/c2) are excluded • Correction for background rejection efficiency not implemented yet Non-photonic electron excess at high-pT Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 16 Topological reconstruction of open charm mesons • Non-photonic electron trigger (sub-leading particle) present in event • No measurement of decay vertex • dE/dx cut (±3) around Kaon band • Charge sign requirement: sign(e) = sign(K) • (Kp) invariant mass: m m m 2 1 Andre Mischke (UU) 2 2 2 E1 E2 p1 p2 SQM 2007, Levoča, 7/17/2015 17 Results Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 18 (Kp) invariant mass distribution dn/dm w/o electron trigger w/ non-photonic electron trigger p+p 200 GeV STAR preliminary combinatorial background is evaluated using like-sign pairs Clear D0 signal w/o background subtraction Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 19 p+p 200 GeV STAR preliminary D0+D0 PDG mass dn/dm D0 mesons in p+p collisions • S/B = 1/7 factor ~100 better than in d+Au w/o trigger • Signal significance = 3.7 • Peak content ~200 Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 20 D0 yield versus (e,hadron pair) • Calculate between nonphotonic electron trigger (pTtrg > 3 GeV/c) and hadron-pair pT • Extract D0 yield from invariant mass distribution for different bins py px cut Andre Mischke (UU) pTelectron pThadron-pair SQM 2007, Levoča, 7/17/2015 21 Non-photonic electron – D0 meson azimuthal correlation p+p at sNN = 200 GeV like-sign (e,K) pairs: (e- - D0) + (e+ -D0) statistical errors only • Near- and away-side correlation peak observed, yields are about the same • First heavy flavour correlation measurement at RHIC Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 22 Data – PYTHIA comparison Procedure: unlike-sign (e,K) (1) Away-side yield for unlike-sign (e,K) pairs is essentially from B decays 3<pTtrg<7 GeV/c Scale PYTHIA distribution to fit measured away-side yield (2) Compare near-side yield from scaled PYTHIA distribution for like-sign (e,K) pairs to data Difference is expected to come from gluon splitting like-sign (e,K) (3) Compare away-side yield from scaled PYTHIA distribution for like-sign (e,K) pairs to data Disentangle charm and beauty contribution Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 23 Comparison: Unlike-sign (e,K) pairs Away-side yield: • yielddata ~ 0.012 0.0061 • yieldPYTHIA = 0.0042 scaling factor = 2.86 Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 24 MC@NLO for charm production • Near-side yield for like-sign (e,K) pairs - yielddata ~ 0.011 0.0046 - yieldPYTHIA (scaled) = 0.0096 • Difference is attributed to gluon splitting MC@NLO* MinBias PYTHIA like-sign (e,K) pairs from charm production • NLO QCD computations plus Herwig • Remarkable agreement of the away-side peak shape between PYTHIA and MC@NLO • Indications for small gluon-splitting contribution (~310-4) • More statistics needed for final conclusions * private version from S. Frixione (CERN) Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 25 Comparison: Like-sign (e,K) pairs p+p at sNN = 200 GeV scaled by 2.86 essentially from B decays only Andre Mischke (UU) ~70% from charm ~30% from beauty SQM 2007, Levoča, 7/17/2015 26 Summary and conclusions • Non-photonic electron trigger helps to suppress the combinatorial background significantly - S/B ratio = 1/7 and signal significance = 3.7 • First heavy flavour correlation measurement in p+p at RHIC • Non photonic electron - D0 meson azimuthal correlations allow to disentangle charm and beauty contributions to the non-photonic electron spectrum - near-side: essentially from B decays - away-side: high charm contribution • Data shows hints for prompt charm meson pair production • Comparison between PYTHIA and MC@NLO - good agreement for LO processes (flavor creation) - small gluon-splitting contribution for 3 < pT < 7 GeV/c Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 27 Backup Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 28 D0D*- cross section measurement at the Tevatron D0 or D+ D*B. Reisert et al., Beauty 2006, to be published in Nucl. Phys. B (Proc. Suppl.) • Within errors near- and away-side yields are the same gluon splitting as important as flavour creation • Near-side yield: PYTHIA underestimates gluon splitting Note: Results are obtained at 10 times higher collision energy than at RHIC Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 29 MC@NLO simulations Near-side contribution seems to be from gluon-splitting Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 30 Open charm in d+Au PRL 94, 062301 (2005) “Conventional” reconstruction technique: Combination of all positive and negative tracks after quality and dE/dx cuts Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 31 Invariant mass spectra D0 3.1k non-photonic electron trigger, 105 D0 D0 3.3k non-photonic positron trigger, 120D0 Andre Mischke (UU) SQM 2007, Levoča, 7/17/2015 32 minv(Kp) for photonic e- trigger • Di-jet events produce many pions, which can make a, e.g., Dalitz decay • What is the correlation contribution from these photonic electrons? p+p at sNN = 200 GeV p+p 200 GeV STAR preliminary pTtrg > 6 GeV/c p0 e+ec c D0 Andre Mischke (UU) No D0 signal observed SQM 2007, Levoča, 7/17/2015 33