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Measurements of Nuclear Modification Factor and Elliptic Flow of F Mesons at RHIC

Measurements of Nuclear Modification Factor and Elliptic Flow of F Mesons at RHIC. Xiangzhou Cai For the STAR Collaboration Shanghai INstitute of Applied Physics University of California, Los Angeles. Outline Motivations F Spectra, fit function and comparison

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Measurements of Nuclear Modification Factor and Elliptic Flow of F Mesons at RHIC

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  1. Measurements of Nuclear Modification Factor and Elliptic Flow of F Mesons at RHIC Xiangzhou Cai For the STAR Collaboration Shanghai INstitute of Applied Physics University of California, Los Angeles Outline • Motivations • F Spectra, fit function and comparison • RCP: particle type or particle mass dependence • Elliptic Flow of F Mesons in AuAu 200GeV collision • Summary

  2. Particle types dependence of RCP &v2 PHENIX: PRL91, 182301(03) STAR: PRL92, 052302(04) nucl-ex/0306007 Models: Greco et al, PRC68, 034904(03) RCPsuppression of AuAu collisionsat intermediatePT. Particle type dependence of RCP from Au+Au collisions has been observed. The particle type dependence of the RCP at intermediate pT in AuAu collisions can be explained by Recombination/Coalescence model. R.C.Hwa et al. University of Oregon C.M.Ko et al. Texas A@M R. J. Fries et al. Duke/Minnesota QB Xie et al., Univ. of ShanDong …… 200GeV Au+Au Baryon Meson

  3. Saturation at intermediate pT Baryon and meson difference -- Constituent Quark Number Scaling Hydrodynamic model can describe data well at low pT while the intermediate pT range may be described by ReC/Coalescence model

  4. How about f Meson? • Phi production can be a good probe • OZI rule suppression • small cross section for scattering with nonstrange hadrons • Information from earlier time? • Sensitive to early flow? • Production mechanism: • ggg ->  • s sbar ->  • K+K- ->  • May determine whether the particle dependence of the nuclear modification factor is dividing by the particle mass or particle type mf~1019 MeV/c2 ; mL~1116 MeV/c2; mKs~498 MeV/c2 • m ~ 1019 MeV/c2 ,  ~ 4.45 MeV/c2,ct ~ 41 fm • Vector meson • quark content : s, sbar • Studied decay channel:   K+ K- (49.2%)

  5. Data set of f analysis 62.4 GeV Au+Au collision Divide into 4 Multiplicity Bins 130 GeV Au+Au collision Divide into 3 Multiplicity Bins 200 GeVAu+Au collision Divide into 5 Multiplicity Bins Run 2 &Run 4 200 GeV d+Au collision Divide into 4 Multiplicity Bins 200 GeV p+p collision Divide into 1 Multiplicity Bins Compare the f production between different collision energy & collision system 1)dE/dx identify stable charged particles in a certain momentum range. 2) Fmeson is identified by event mixing method.

  6. f double exp. fit Spectra of f and fits STAR Preliminary Exponential fit AuAu 62GeV AuAu 130GeV Exponential fit pp Double Exp. fit 1)Statistical errors only. 2)Spectra of Au+Au collisions in measured pT range can be described by an exponential function while spectra of d+Au and p+p collisions deviate from the exponential distribution and have a power-law tail at intermediate pT 3)measurements of 200GeV Au+Au collisions at STAR for Run II and Run IV are consistent d+Au200GeV

  7. Most central f spectra in different collision system STAR Preliminary Spectra ofAu+Au collisions at limited pT range can be described by exponential function Spectra ofpp and d+Au collisions have a power-law tail at intermediate PT region Double exponential function can fit the data well. Measure at (mt-mf)>2.5GeV/c2 for AuAu collision may be necessary to see a power-law tail!

  8. ’s production mechanics STAR Preliminary 1)/K- as function of system size and energy are constant • kaon coalescence ruled out for production 2)<pT> of  in AuAu collisions doesn’t change significantly as a function of collision centrality, unlike pions, kaons and proton.  does not show a significant radial flow from late hadronic stage. It is consistent with a f early freeze-out scenario.

  9. RCP of f AuAu 200 GeV Run II dAu 200 GeV • Mesons(Ks, K, f) have the similar RCP for dAu & AuAu collisions at intermediate pT • Baryons (L, X) have the similar RCP too, but higher than mesons. Particle production at intermediate pT region is divided by the particle’s types, not the masses STAR:  behaves like mesons, despite of its large mass FAVOR: Recombination/Coalescence model Run IV:AuAu 200 GeV

  10. RCP of f for different collision system STAR Preliminary • Yield suppression at intermediate PT in central Au+Au collisions • Data at 62.4 GeV Au+Au collisions is statistics limited. • RCP in d+Au collisions is enhanced Some Cronin effect for f mesons in d+Au collisions as well.

  11. F V2(use reaction plane method) • Run IV AuAu200 (FullField+ReversedFullField) • ~14M minibias events • main cuts in the analysis: |η|<1.0 NHits>15, NHits/NHitsPoss>0.52 |NSigmaKaon|<2. DipAngle>0.04 |ReactionPlanecut|<Π/20 (event mixing) |vertextZ|<30 ReactionPlane tracks:|NsigmaKaon|>2.0 1 2 1 Event-mixing techniques

  12. Analysis details 1.reaction-plane (Ψ) 2.Azimuth angle distribution a*(1+2*v2*cos(2(Φ-Ψ))) 1.0<pT<1.5GeV/c res: 0.6178 +- 0.00021 3. reaction-plane resolution v2 = v2obs/res

  13. Compared results on the different analysis methods

  14. Preliminary results v2 STAR Preliminary 1. the elliptic flow of Φ-meson is close to Ks 2. error bars in high pt range (2.5GeV,5.0GeV) are still large

  15. Summary • We have measured the productions of f for various collisions energy and collisions system. • Within our pT coverage, thef spectra of dAu and pp collisions can be described better by a double exponential function, which is different in AuAu collisions. • The RCP values of f are similar to other mesons at intermediate pT.The particle yield at intermediate pT depends on particle types, instead of on particle masses. • The elliptic flow v2 have been measured in run IV Au+Au 200GeV collisions. Since phi cannot be made via K+K- fusion, this implies partonic collective at RHIC!

  16. The End

  17. Azimuth angle distribution 0.5<pT<1.0GeV/c 1.5<pT<2.0GeV/c 2.0<pT<2.5GeV/c 2.5<pT<3.0GeV/c

  18. Back-up slide---Information via RXX  R ~1 -- no nuclear effects:A+B = C * (p+p)  deviation from 1 indicate presence of nuclear effects: R>1 enhancement  R<1 suppression (energy loss in dense medium)

  19. RAA and RdAu of f ______________ STAR Preliminary RdAu of  is closer to that of pion and kaon than that of proton Particle production at intermediate pT region is sorted by the particle’s types, not the masses

  20. Back-up slide---RAA/RCP: h± (200GeV) RAA & RdA RCP dAu dAu AuAu AuAu Charged Hadrons: • Au + Au : RCP and RAA ~ suppression • d + Au : RCP and RdA ~ enhancement

  21. STAR Discrepancy between STAR and PHENIX ?? PHENIX Johann Rafelski etc. nucl-th/0412072

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