STAR Patricia Fachini QM20081 ρ 0 Production at High p T in Central Au+Au and p+p collisions at  s NN = 200 GeV in STAR STAR Patricia Fachini Brookhaven National Laboratory for the STAR Collaboration Motivation Data Analysis Results Conclusions

STAR Patricia Fachini QM20082 Motivation - I ρ 0 mass measured in STAR shifted at low p T  ~30 to ~70 MeV/c 2  what about high p T ? PDG value e + e -  ρ 0 mass in the vacuum ρ0ρ0

STAR Patricia Fachini QM20083 Motivation - II Hadron production at high p T : p+p  information on pQCD, parton distribution functions (PDF) in the proton, fragmentation functions (FF) of partons ρ 0 FF  same as pions? Au+Au  probe properties of the strongly interacting QCD matter J. Adams et al., Phys. Lett. B 637 (2006) 161 pTpT 1.7 GeV/c2.5 GeV/c ρ0/π-ρ0/π ± ± 0.15 ISR p+p  s = 52.2 GeV E. E. Kluge, Phys. Scrip. 19 (1979) 109 ρ0ρ0 π-π- ISR  = 1

STAR Patricia Fachini QM20084 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) Kretzer  S. Kretzer, Phys. Rev. D 62 (2000)

STAR Patricia Fachini QM20085 Ratios  Data and NLO  π + and π - pQCD calculations reproduce well the pion spectra up to p T = 15 GeV/c

STAR Patricia Fachini QM20086 Ratios  Data and NLO  p and p pQCD NLO calculations need improvement for describing proton and anti-proton spectra

STAR Patricia Fachini QM20087 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)

STAR Patricia Fachini QM20088 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

STAR Patricia Fachini QM20089 HIJING events with a realistic simulation of detector response Use ω shape from HIJING to fit the data At high p T  η and K 0 S productions negligible NO K *0  clean particle identification ρ 0 (770)  π + π - STAR Preliminary ρ0ρ0  s NN = 200 GeV K0S  π+ π-K0S  π+ π- K0SK0S ω(782)  (π + π - ) π 0 and π + π - ω η  (π + π - ) π 0 and (π + π - )  η’  (π + π - ) η and (π + π - ) ρ 0 η + η’ K*(892) 0  K π with K misidentified as π K *0 + K *0 misidentified π + π - Invariant Mass Distribution from Monte Carlo

STAR Patricia Fachini QM ρ 0 at High p T  p+p Jet Triggered Data Background parameterized to a polynomial function Invariant mass distribution is fit before background subtraction ρ 0, f 0 and f 2 masses and widths  fixed according PDG ρ 0 /ω = 2.1 and fixed in the fit  constraining the fit f 0 (600)? like-sign background

STAR Patricia Fachini QM ρ 0 at High p T  p+p Jet Triggered Data ρ 0 mass as a free parameter  approaching ρ 0 mass in the vacuum PDG value e + e -  ρ 0 mass in the vacuum

STAR Patricia Fachini QM ρ 0 at High p T  Au+Au Au+Au Minimum BiasAu+Au Central 0-12% Invariant mass distribution is fit after background subtraction ρ 0, f 0 and f 2 masses and widths  fixed according PDG ρ 0 and ω  free parameter in the fit

STAR Patricia Fachini QM ρ 0 Spectra ρ 0 spectrum in p+p  ρ 0 /π - from jet triggered data multiplied by π yield measured in p+p minimum bias  trigger effects cancel out in the ratio at first order ρ 0 spectrum in p+p  fit to a powerlaw function ρ 0 spectrum in p+p  pion NLO calculations

STAR Patricia Fachini QM Ratios  Data and NLO  ρ 0 and π pQCD calculations for π similar to ρ 0 spectra

STAR Patricia Fachini QM Particle Ratios  ρ 0 /π ± 5 < p T < 10GeV/cp+pAu+Au minbiasAu+Au central ρ0/π±ρ0/π± 1.78 ± 0.12 ± ± 0.08 ± ± 0.05 ±0.22 π ± = π + + π - 2 RHIC  s = 200 GeV T ISR p+p  s = 52.2 GeV pTpT 1.7 GeV/c2.5 GeV/c ρ0/π-ρ0/π ± ± 0.15 E. E. Kluge, Phys. Scrip. 19 (1979) 109

STAR Patricia Fachini QM Nuclear Modification Factor π more suppressed than protons  opposite to color charge effect ρ 0 nuclear modification factor comparable to pions R AA

STAR Patricia Fachini QM Conclusions p+p spectra for pions and protons extended to p T = 15 GeV/c  π data reasonably reproduced by NLO pQCD calculations R AA  central collisions  pion more suppressed than protons up to 12 GeV/c First measurement of ρ 0 at 5 < p T < 10 GeV/c ρ 0 mass in p+p  approaching ρ 0 mass in the vacuum ρ 0 p+p spectrum  similar to NLO pQCD calculations for π and ρ 0 R AA  similar to π R AA

STAR Patricia Fachini QM Back-up Slides

STAR Patricia Fachini QM STAR Detector Using jet triggered data for p+p  TPC + EMC  minimum amount of energy requested in the EMC

STAR Patricia Fachini QM 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/ ; H.W. Barz et al., Phys. Lett. B 265, 219 (1991); R. Rapp, hep-ph/ ρ0ρ0 π-π- π+π+ π-π- π+π+ M = Invariant Mass; p T = 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 emitted T = 120 MeV E.V. Shuryak and G.E. Brown, Nucl. Phys. A 717 (2003) 322 e -  M 2 + p T 2 T M  M 2 + p T 2 Phase Space = Γ(M) = Γ ρ M 2 – 4m π 2 M ρ 2 – 4m π MρMρ M BW(M) = Γ(M) (M 2 – M ρ 2 ) 2 + M ρ 2 Γ(M) 2 Phase Space

STAR Patricia Fachini QM Transport Model - UrQMD UrQMD  Only imaginary part  No medium modification Central Au+Au  ρ 0 mass shifted ~30 MeV at low p T ρ 0 shape reproduced by p-wave Breit-Wigner × Phase Space –M ρ = MeV for 0.2 ≤ p T < 0.4 GeV/c –M ρ = MeV for 1.2 ≤ p T < 1.4 GeV/c –M ρ = 769 MeV/c 2 input Г = 150 MeV 00 b ≤ 3 fm √s NN = 200 GeV 1.2 ≤ p T < 1.4 GeV/c |y| ≤ 0.5 Au+Au BW × PS M ρ = 769 MeV/c 2 b ≤ 3 fm Au+Au ρ0ρ0 0.2 ≤ p T < 0.4 GeV/c |y| ≤ 0.5

STAR Patricia Fachini QM 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

STAR Patricia Fachini QM π Spectra π spectra in p+p obtained from jet triggered data  using Pythia to correct the spectra Pythia reproduces well both triggered and minimum bias data

STAR Patricia Fachini QM Particle Ratios ρ±ρ± ω e + e -  OPAL  ρ ± /ω > 1 Au+Au minimum bias and central  STAR  ρ 0 /ω ~ 1.67 p+p  STAR  ρ 0 /ω ~ 2.1 K. Ackerstaff et al. Eur. Phys. J. C 5, (1998) 411 ρ0ρ0 ω

STAR Patricia Fachini QM Pythia