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Heavy Flavor Physics in HIC with STAR Heavy Flavor Tracker

Heavy Flavor Physics in HIC with STAR Heavy Flavor Tracker. Yifei Zhang (for the STAR HFT Group). Lawrence Berkeley National Lab. Outline: Physics motivation Charmed hadron D&B  e Summary. Hirschegg 2010, Austria. Partonic energy loss at RHIC. STAR: Nucl. Phys. A757 , 102(2005).

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Heavy Flavor Physics in HIC with STAR Heavy Flavor Tracker

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  1. Heavy Flavor Physics in HIC with STAR Heavy Flavor Tracker Yifei Zhang (for the STAR HFT Group) Lawrence Berkeley National Lab • Outline: • Physics motivation • Charmed hadron • D&B  e • Summary Hirschegg 2010, Austria

  2. Partonic energy loss at RHIC STAR: Nucl. Phys. A757, 102(2005). Light quark hadrons strongly suppressed in central Au+Au collisions. Jet quenching: The away-side correlation in back-to-back ‘jets’. How about heavy quarks? Explore pQCD in hot dense medium RAA(c,b) measurements are needed! September 3, 2014 Yifei ZhangLBNL 2

  3. Heavy quark energy loss STAR PRL 98 (2007) 192301 E-loss: b < c < q The RAA of single electron from heavy flavor decay is suppressed as strong as that of light flavor hadrons at high pT (> 6 GeV/c). Directly measure D-meson RAA Separately measure RAA of De & Be Heavy quark energy loss mechanism, interactions with hot dense medium. September 3, 2014 Yifei ZhangLBNL 3

  4. Partonic collectivity at RHIC STAR: preliminary STAR: QM2009 Low pT (≤ 2 GeV/c): hydrodynamic mass ordering High pT (> 2 GeV/c): number of quarks ordering s-quark hadron: smaller interaction strength in hadronic medium light- and s-quark hadrons: similar v2 pattern Collectivity developed at partonic stage! In order to test early thermalization: v2(pT) of c- and b-hadrons data are needed! September 3, 2014 Yifei ZhangLBNL 4

  5. Charmed baryon c Lee, et. al, PRL 100 (2008) 222301 • c yield (rare 10%, small c ~ 60m, 3-body decay). • measure c/ D0 ratio enhancement, di-quark? Yifei ZhangLBNL

  6. Bottom from electron channel Important for understanding the bottom contribution in current NPE measurements. Large systematic errors for both theory (FONLL) and data (STAR e-h correlation). Need improve the measurement accuracy. Measure this ratio directly from spectra. • No B meson spectra measured. • Separately measure Be spectrum will indirectly measure B meson spectrum from its decay kinematics. • Be = NPE  De STAR HFT has the capability to measure D0 decay vertex topologically via hadronic decay channel. Measured D0 spectrum constrains De. Yifei ZhangLBNL

  7. PXL STAR Detector TOF+TPC+HFT Large acceptance Mid-rapidity || < 1 Full barrel coverage 0 <  < 2p Yifei ZhangLBNL

  8. Inner Tracking Detectors HFT SSD IST PXL Inner Field Cage FGT Magnet Return Iron Outer Field Cage TPC Volume EAST Solenoid WEST September 3, 2014 Yifei ZhangLBNL 8

  9. Inner Tracking Detectors • SSD existing single layer detector, double side trips. • IST 500 m x 1cm strips along beam direction, it guides tracks from the SSD through PIXEL detector. It is composed of 24 liquid cooled ladders equipped with 6 silicon strip-pad sensors.. • PIXEL double layers, 18.4x18.4 m pixel pitch, 2 cm x 20 cm each ladder. Deliver ultimate pointing resolution, hit density for 1st layer ~ 60 cm.-2 September 3, 2014 Yifei ZhangLBNL 9

  10. Simulation Performance pointing resolution in r- to primary vertex for single particles (of K, +, p.) including all hits in HFT. < 20 m at high pT. Tracking efficiency of single + for 3 pileup hits densities. 1xRICHII pile up effect was included in the simulation. September 3, 2014 Yifei ZhangLBNL 10

  11. Hadronic channels D0 C STAR HFT has the capability to reconstruct the displaced vertex of D0K (B.R.=3.8%) and c Kp (B.R.=5.0%, cc=59.9 m) September 3, 2014 Yifei ZhangLBNL 11

  12. D0 reconstruction After topological cut - Central Au+Au collisions: top 10% events. - The thin detector allows measurements down to pT ~ 0.5 GeV/c. September 3, 2014 Yifei ZhangLBNL 12

  13. Error estimate of D0 Rcp RCP=a*N10%/N(60-80)% • Assuming D0 Rcp distribution as charged hadron: directly measure charm quark energy loss. • 500M Au+Au m.b. events at 200 GeV. • Charm RAAenergy loss mechanism! September 3, 2014 Yifei ZhangLBNL 13

  14. Error estimate of D0 v2 Charm-quark flow  Thermalization of light-quarks! Charm-quark does not flow  Drag coefficients Assuming D0 v2 distribution from quark coalescence. 500M Au+Aum.b. events at 200 GeV. September 3, 2014 Yifei ZhangLBNL 14

  15. c reconstruction Good D0pT distribution measurement as reference. The unique charmed baryon. c / D0 ratio => enhancement? September 3, 2014 Yifei ZhangLBNL 15

  16. B capability -- electron channels B.R. = Branching Ratio F.R. = Fragmentation Ratio 1) Be = NPE  De 2) The distance of closest approach to primary vertex (dca): Due to larger c, B e has broader distribution than D  e Dca of D+ e is more close to that of B  e. need more constraint. Pixel layers dca Yifei ZhangLBNL

  17. Dca distributions and spectra Electrons: nFitPts > 15, -1 < eta < 1, 2 PXL hits required, in several pT bins. The photon converted electron outside of pixel detector (~ 70%) can be removed due to their random large DCA distributions. The main background are conversion from beam pipe and electron from 0, Dalitzdecays. Normalized by the F.R. and B.R., and total electron yield was normalized to STAR measured NPE spectrum. Yifei ZhangLBNL

  18. (Be)/NPE ratio • (Be)/NPE ratio can be directly measured from spectra with HFT, no model dependence, reduce systematic errors. • Expected errors are estimated for 50 M Au+Au central events (open circles) and 500 μb-1 sampled luminosity with a “high tower” trigger (filled circles). Open stars represent preliminary results from 200 GeV p+p collisions via e-h correlation. Yifei ZhangLBNL

  19. Electron RCP Curves:  H. van Hees et al. Eur. Phys. J. C61, 799(2009). Nuclear modification factor RCP of electrons from D meson and B meson decays. Expected errors are estimated for 500 M Au+Au minimum-bias events (open symbols) and 500 μb-1 sampled luminosity with a “high tower” trigger (filled symbols). Yifei ZhangLBNL

  20. Measure v2 from dca B e v2 and D  e v2 can be measured from different dca cuts. For example: r  v2(B) + (1-r)  v2(D) = v2(NPE) v2(B) is B e v2 v2(D) is D e v2 v2(NPE) is the total non-photonic electron v2 after dca selection. Yifei ZhangLBNL

  21. Error estimate for electron v2 Assuming D meson v2 from quark coalescence (curves). Decay form factor[1] was used to generate D e v2 distributions. r  v2(B) + (1-r)  v2(D) = v2(NPE) v2(D) is D e v2 v2(B) is B e v2 , which can be extracted from this equation. Blue: c-quark flows // Red:c-quark does not Dashed-curves: Assumed D0-mesom v2(pT) Symbols: D decay e v2(pT) Vertical bars: errors for b decaye v2(pT) from 200 GeV 500M minimum bias Au + Au events Cuts: DCA on decay electrons [1] H.D. Liu et. al, PLB 639, 441 (2006) Yifei ZhangLBNL

  22. Charm and bottom cross section NLO pQCD predictions of charm and bottom total cross sections per nuclear nuclear collisions. Statistics estimated for charm cross section in p+p, Au+Au mb, Au+Au central at 200 and 500 GeV. Statistics estimated for bottom cross section in Au+Au mb and central at 200 GeV. Systematic errors are estimated from D0 e pT shape uncertainties (open box). Yifei ZhangLBNL

  23. Physics of the Heavy Flavor Tracker at STAR1) The STAR HFT measurements (p+p and Au+Au)(1) Heavy-quark cross sections: D0,±,*, DS, C , B… (2) Both spectra (RAA, RCP) and v2 in a wide pT region. (3) Charm hadron correlation functions (4) Full spectrum of the heavy quark hadron decay electrons2) Physics(1) Measure heavy-quark hadron v2, heavy-quark collectivity, to study the medium propertiese.g.light-quark thermalization (2) Measure heavy-quark energy loss to study pQCD in hot/dense medium.e.g. energy loss mechanism (3) Measure charm/bottom cross section to test pQCD in hot/dense medium. (4) Analyze hadro-chemistry including heavy flavors

  24. Projected Run Plan1) First run with HFT: 200 GeV Au+Au v2 and RCP with 500M M.B. collisions2) Second run with HFT: 200 GeV p+p RAA3) Third run with HFT: 200 GeV Au+Au Centrality dependence of v2 and RAA Charm background and first attempt for electron pair measurements C baryon with sufficient statistics

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