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Open heavy flavor in STAR

STAR. Open heavy flavor in STAR. David Tlusty NPI ASCR, CTU Prague for STAR collaboration. QCD phase diagram and RHIC. RHIC is an intersecting storage ring and particle accelerator Two independent rings each 3.834 km circumference Can collide any nuclear species on any other.

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Open heavy flavor in STAR

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  1. STAR Open heavy flavor in STAR David Tlusty NPI ASCR, CTU Prague for STAR collaboration

  2. QCD phase diagram and RHIC RHIC is an intersecting storage ring and particle accelerator Two independent rings each 3.834 km circumference Can collide any nuclear species on any other. Max Energy: • How was the Universe created • What are properties of strong interaction • Search for and characterize the new state of matter – Quark Gluon Plasma WWND Puerto Rico

  3. Why to study heavy quarks X. Zhu, et al, PLB 647, 366(2007) • Produced in initial hard partonic collisions – following number-of-binary-collisions scaling • Mass is believed to be external to QCD but doesn’t fully correspond to FONLL • Sensitive to initial gluon density and gluon distribution – pQCD test at RHIC • Interact with the medium differently from light quarks. Reveal critical features of the medium • Charm collectivity => Light flavor thermalization. WWND Puerto Rico

  4. How to measure charm quarks • Direct reconstruction • direct access to heavy quark kinematics • hard to trigger (high energy trigger only for correlation measurements) • smaller Branching Ratio (B.R.) • large combinatorial background (need handle on decay vertex) • Indirect measurements through decay Leptons • can be triggered easily (high pT) • Higher B.R. • Indirect access to the heavy quark kinematics WWND Puerto Rico

  5. The STAR detector • VPD EW coincidence: minimum bias trigger, TOF start time • TPC : PID, tracking • TOF : PID (b, time resolution = 110 ps) • BEMC : remove pile-up tracks, ET triggers, E/p • BSMD : electrons • TPC dE/dx vs p : pions PID • TOF 1/b vs p : kaons PID Year 2009 72% of full TOF Year 2010/2011 100% of full TOF WWND Puerto Rico

  6. Particle Identification Kaons: TOF only Pions: TOF if available, otherwise TPC dE/dx with matching to BEMC required to remove pile-up tracks e± Electrons: TPC dE/dx with help of BEMC E/p and SMD cluster shape WWND Puerto Rico

  7. D0 and D* signal in p+p 200 GeV K*0 K2*(1430) STAR Preliminary p+p minimum bias 105 M Different methods reproduce combinatorial background. Consistent results from two background methods. WWND Puerto Rico

  8. D0 and D* pT spectra in p+p 200 GeV D0 scaled by ND0/Ncc= 0.56[1] D* scaled by ND*/Ncc= 0.22[1] Consistent with FONLL[2] upper limit. Xsec = dN/dy|ccy=0 * F * spp F = 4.7 ± 0.7 scale to full rapidity. spp(NSD) = 30 mb STAR preliminary The charm cross section at mid-rapidity is: The charm total cross section is extracted as: [1] C. Amsler et al. (Particle Data Group), PLB 667 (2008) 1. [2] Fixed-Order Next-to-Leading Logarithm: M. Cacciari, PRL 95 (2005) 122001. WWND Puerto Rico

  9. Background of NPE measurement Background Dominated by Photonic Electrons from : Same for All Experiments BR: 1.2%. Depend on Experiment BR: 0.7%. • Mostly from • Conversion probability: 7/9* X0 When X0 islarge, gamma conversion dominate all the background. PHENIX: Less Material Thickness & Smaller Acceptance STAR: Larger Material Thickness & Larger Acceptance WWND Puerto Rico

  10. NPE analysis method • Reconstruction method: pT(partner)>0.3GeV/c • Photonic Electronic Reconstruction Efficiency • Estimated from embedding • Small variation in ε can leads to large difference in NPE

  11. Separate Measurement of B and D meson Spectra at RHIC STAR Phys. Rev. D 83, 052006 (2011) PHENIX Phys. Rev. Lett. 103, 082002 (2009)

  12. D0 signal in Au+Au 200 GeV Minimum bias 0-80% 280M Au+Au 200 GeV events. S/√(S+B) = 8 Mass = 1863 ± 2 MeV (PDG value is 1864.5 ± 0.4 MeV) Width = 12 ± 2 MeV WWND Puerto Rico

  13. Charm cross section vs Nbin All of the measurements are consistent. Year 2003 d+Au : D0 + e Year 2009 p+p : D0 + D* Year 2010 Au+Au: D0 Charm cross section in Au+Au 200 GeV: Mid-rapidity: 186 ± 22 (stat.) ± 30 (sys.) ± 18 (norm.) mb Total cross section: 876 ± 103 (stat.) ± 211 (sys.) mb [1] FONLL: M. Cacciari, PRL 95 (2005) 122001. [2] NLO:  R. Vogt, Eur.Phys.J.ST 155 (2008) 213    [3] PHENIX e: A. Adare, et al., PRL 97 (2006) 252002. Charm cross section follows number of binary collisions scaling => Charm quark produced at early stage of collisions. WWND Puerto Rico

  14. D0 RAA vs pT BW(πKp): B. I. Abelev et al., PRC79 (2009) 34909. Below 3 GeV/c, RAA consistent with unity => Consistent with D0 yield Nbin scaling behavior. Blast-wave describes data with <bT> = 0.21 ± 0.20 (small, not sensitive). T = 287 ± 106 MeV T > Th~ 100 MeV, larger than light hadrons WWND Puerto Rico

  15. p+p 500 GeV Like-sign background subtracted. s = 3.2 from 52 M events Rotated background subtracted. s = 3.3

  16. D* in pp 500 GeV Minimum bias events Selected events WWND Puerto Rico

  17. Summary • D0 and D* are measured in p+p 200 GeV up to 6 GeV/c – the first measurement at STAR • D0 are measured in Au+Au 200 GeV up to 5 GeV/c. • 1) Charm cross sections at mid-rapidity follow number of binary collisions scaling • 2) RAA is consistent with unity. • Indicate charm is produced at early stage of the collisions. • and consistent with FONLL upper limit whereas follows FONLL => questions about c-quark mass and QCD influence • Blast-wave fit favors larger temperature and smaller velocity compared to light hadrons, which could indicate that D0 decoupled earlier from the medium than light hadrons. • Reasonable signal from pp 500 GeV collisions promises first open charm cross section calculation in such energy with pT coverage being 0.4 – 7.0 GeV/c WWND Puerto Rico

  18. Outlook TPC SSD IST PXL • STAR Heavy Flavor Tracker Project. • Reconstruct secondary vertex. • Dramatically improve the precision of measurements. • Address physics related to heavy flavor. • v2 : thermalization • RCP: charm quark energy loss mechanism. FGT WWND Puerto Rico

  19. Systematic error study • Raw Counts – Difference between methods • nFitPoints - difference between • MC(nFitPts>25)/MC(nFitPts>15) and • Data(nFitPts>25)/Data(nFitPts>15) • 3) DCA - difference between MC(dca<1)/MC(dca<2) and Data(dca<1)/Data(dca<2) WWND Puerto Rico

  20. Pile-up removal • pp collisions peak luminosity Lpeak = 5*1031 cm-2s-1 in year 2009. • EventRate = Lpeak*sNSD(30 mb) = 1.5 MHz • TPC readout ~ 80 ms => TPC sees tracks from 120‎ collisions. Pile-ups are removed by‎ • ‎ |VpdVz - TpcVz| < 6cm cut • ‎ TPC PPV reconstruction algorithm • ‎‎ WWND Puerto Rico

  21. Charm cross section vs Most precise measurement so far, provide constraint for theories. WWND Puerto Rico

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