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ρ 0 Production at High p T in Central Au+Au and p+p collisions at s NN = 200 GeV in STAR

STAR. ρ 0 Production at High p T in Central Au+Au and p+p collisions at s NN = 200 GeV in STAR. Patricia Fachini Brookhaven National Laboratory for the STAR Collaboration. Motivation Data Analysis Results Conclusions. PDG value e + e -  ρ 0 mass in the vacuum. Motivation - I.

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ρ 0 Production at High p T in Central Au+Au and p+p collisions at s NN = 200 GeV in STAR

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  1. STAR ρ0 Production at High pT in Central Au+Au and p+p collisions at sNN = 200 GeV in STAR Patricia Fachini Brookhaven National Laboratory for the STAR Collaboration Motivation Data Analysis Results Conclusions Patricia Fachini QM2008

  2. PDG value e+e- ρ0 massin the vacuum Motivation - I • ρ0mass measured in STAR shifted at low pT  ~30 to ~70 MeV/c2  what about high pT? ρ0 Patricia Fachini QM2008

  3. J. Adams et al., Phys. Lett. B 637 (2006) 161 ρ0 ISR  = 1 π- Motivation - II Hadron production at high pT: • p+p information on pQCD, parton distribution functions (PDF) in the proton, fragmentation functions (FF) of partons • ρ0FF same as pions? • Au+Au probe properties of the strongly interacting QCD matter ISR p+p s = 52.2 GeV E. E. Kluge, Phys. Scrip. 19 (1979) 109 Patricia Fachini QM2008

  4. π and p Spectra • Spectra compared to NLO pQCD calculations AKK  S. Albino, B. A. Kniehl and G. Kramer, Nucl. Phys. B 725 (2005) 181 KKP  B. A. Kniehl, G. Kramer and B. PotterNucl. Phys. B 597 (2001) 337 DSS  D. de Florian, R. Sassot, and M. Stratmann, Phys.Rev.D75 (2007) 114010 Kretzer  S. Kretzer, Phys. Rev. D 62 (2000) 054001 Patricia Fachini QM2008

  5. Ratios  Data and NLO  π+and π- • pQCD calculations reproduce well the pion spectra up to pT = 15 GeV/c Patricia Fachini QM2008

  6. Ratios  Data and NLO  p and p • pQCD NLO calculations need improvement for describing proton and anti-proton spectra Patricia Fachini QM2008

  7. Particle Ratios • Ratios extended to 15 GeV/c • The effect of the jet trigger on the ratios is negligible(comparison between Pythia minimum bias and Pythia jet triggered data) Patricia Fachini QM2008

  8. Particle Ratios • Ratios extended to 15 GeV/c • The effect of the jet trigger on the ratios is negligible(comparison between Pythia minimum bias and Pythia jet triggered data) • π-/π+ effect of valence quark • p/p significant quark jet fragmentation to baryon production Patricia Fachini QM2008

  9. K0Sπ+π- ω(782) (π+π-) π0and π+ π- K0S ω η (π+π-) π0 and (π+π-) η’ (π+π-)ηand (π+π-) ρ0 η + η’ K*(892)0 Kπwith K misidentified as π K*0 + K*0misidentified π+π- Invariant Mass Distribution from Monte Carlo • HIJING events with a realistic simulation of detector response STAR Preliminary ρ0(770)  π+π- sNN= 200 GeV ρ0 • Use ωshape from HIJING to fit the data • At high pT  ηand K0Sproductions negligible • NO K*0  clean particle identification Patricia Fachini QM2008

  10. ρ0 at High pT  p+p Jet Triggered Data • Background parameterized to a polynomial function • Invariant mass distribution is fit before background subtraction • ρ0, f0 and f2 masses and widths fixed according PDG • ρ0/ω= 2.1 and fixed in the fit  constraining the fit • f0(600)? like-sign background Patricia Fachini QM2008

  11. ρ0 at High pT  p+p Jet Triggered Data PDG value e+e- ρ0 massin the vacuum • ρ0 mass as a free parameter approaching ρ0mass in the vacuum Patricia Fachini QM2008

  12. ρ0 at High pT  Au+Au Au+Au Central 0-12% Au+Au Minimum Bias • Invariant mass distribution is fit after background subtraction • ρ0, f0 and f2 masses and widths fixed according PDG • ρ0 and ω free parameter in the fit Patricia Fachini QM2008

  13. ρ0 spectrum in p+pfit to a powerlaw function • ρ0 spectrum in p+ppion NLO calculations ρ0Spectra • ρ0 spectrum in p+pρ0/π-from jet triggered data multiplied by πyield measured in p+p minimum bias  trigger effects cancel out in the ratio at first order Patricia Fachini QM2008

  14. Ratios  Data and NLO  ρ0 and π • pQCD calculations for π similar to ρ0spectra Patricia Fachini QM2008

  15. π++ π- π± = 2 T Particle Ratios  ρ0/π± ISR p+p s = 52.2 GeV E. E. Kluge, Phys. Scrip. 19 (1979) 109 RHIC s = 200 GeV Patricia Fachini QM2008

  16. ρ0nuclear modification factor comparable to pions RAA Nuclear Modification Factor • πmore suppressed than protons  opposite tocolor charge effect Patricia Fachini QM2008

  17. Conclusions • p+p spectra for pions and protons extended to pT = 15 GeV/c πdata reasonably reproduced by NLO pQCD calculations • RAA central collisions pionmore suppressed than protonsup to 12 GeV/c • First measurement of ρ0 at 5 < pT < 10 GeV/c • ρ0mass in p+papproaching ρ0mass in the vacuum • ρ0p+p spectrum  similar to NLO pQCD calculations for π and ρ0RAA similar to πRAA Patricia Fachini QM2008

  18. Back-up Slides Patricia Fachini QM2008

  19. STAR Detector • Using jettriggered data for p+p  TPC + EMC  minimum amount of energy requested in the EMC Patricia Fachini QM2008

  20. Phase Space = π+ ρ0 π+ π- π- -  M2 + pT2 M e T  M2 + pT2 Γ(M) BW(M) = (M2 – Mρ2)2+ Mρ2Γ(M)2 3 Mρ M2– 4mπ2 2 Γ(M) = Γρ M Mρ2– 4mπ2 Phase Space • M = Invariant Mass; pT= transverse momentum; T = Inverse Slope • pp particle composition reasonably reproduced by statistical model  T = 160 MeV also dAu F. Becattini, Nucl. Phys. A 702, 336 (2002); Z. Phys. C 69, 485 (1996); F. Becattini and U. Heinz, Z. Phys. C 76, 269 (1997) • Au+Au between chemical and kinetic freeze-out  resonances formed until particles too far apart  resonances emittedT = 120 MeV E.V. Shuryak and G.E. Brown, Nucl. Phys. A 717 (2003) 322 P. Braun-Munzinger et.al., CERES Int. Note, March 2000, unpublished; E.V. Shuryak and G.E. Brown, Nucl. Phys. A 717 (2003) 322; P.K. Kolb and M. Prakash, nucl-th/0301007; H.W. Barz et al., Phys. Lett. B 265, 219 (1991); R. Rapp, hep-ph/0305011. Patricia Fachini QM2008

  21. BW ×PS Transport Model - UrQMD Au+Au Au+Au b ≤ 3 fm b ≤ 3 fm 0 ρ0 √sNN = 200 GeV 1.2 ≤ pT < 1.4 GeV/c |y| ≤ 0.5 0.2 ≤ pT < 0.4 GeV/c |y| ≤ 0.5 Mρ = 769 MeV/c2 • UrQMD  Only imaginary part  No medium modification • Central Au+Au ρ0 mass shifted ~30 MeV at low pT • ρ0 shape reproduced by p-wave Breit-Wigner × Phase Space • Mρ= 765.6 MeVfor 0.2 ≤ pT< 0.4 GeV/c • Mρ = 761.2 MeVfor 1.2 ≤ pT< 1.4 GeV/c • Mρ = 769 MeV/c2 input Г= 150 MeV Patricia Fachini QM2008

  22. Particle Identification • Relativistic rise of dE/dx • π particle identification with a Nσ cut • Nσ energy loss expressed in the units of standard deviation of a Gaussian formed by the logarithm of truncated energy loss (top 30%) π+K+p Only π within ~3% purity Patricia Fachini QM2008

  23. π Spectra • π spectra in p+pobtained from jet triggered data using Pythia to correct the spectra • Pythia reproduces well both triggered and minimum bias data Patricia Fachini QM2008

  24. ρ± ω ρ0 ω Particle Ratios K. Ackerstaff et al. Eur. Phys. J. C 5, (1998) 411 • e+e-  OPAL ρ±/ω > 1 • Au+Au minimum bias and central STAR  ρ0/ω ~ 1.67 • p+p  STAR  ρ0/ω ~ 2.1 Patricia Fachini QM2008

  25. Pythia Patricia Fachini QM2008

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