1. IOPB Dipak Mishra (IOPB), ICPAQGP5, Kolkata Feb 8 – 12 1 Measurement of  ++ Resonance Production in d+Au Collisions @ sqrt(s NN ) = 200 GeV Dipak Mishra Institute of Physics, Bhubaneswar. (for the STAR Collaboration) Outline  Motivation  Data Analysis  Results  Summary B. R. ~ 99.5 % c  ~ 1.6 fm p   Mass : 1232 +- 2 MeV Width: 120 +- 5 MeV

2. Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 2 Motivation...  Measurement of the yields, masses, widths and the transverse momentum distributions of the resonances can provide information about the hadronization and the time span between the chemical and kinetic freeze-out.  In-medium modification of mass and/or width ----> Collision broadening or phase space ● Hadronic and Leptonic decay channels probes the early as well as the late stage of the collision dynamics  Resonances have short lifetimes (~ few fm) comparable with the lifetime of the fire ball source ( which created in the high energy collisions ).

3. Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 3 Motivation...  Inside the medium, resonances have re-scattering, re- generation which affects --> Yields of the resonance production  ++  p  p  p   p p  ++ measured  ++ lost  Large fraction of decays occur inside the reaction zone.  In-medium effects related to the high density and/or high temperature of the medium, which can modify the resonance properties ● Broadening of width ● Mass shift ● Change in p T spectra

4. Motivation... ( Why Delta is interesting?) Theoritical predictions:  The chemical freeze-out temperature can be extracted from Delta  / N ratio. ( Ref: G. E. Brown, J. Stachel, et al, Phys. Lett. B 253 (1991)19 ) Where  Lifespan between Chemical and Thermal freeze-out: J. Rafelski: “ It will be interesting to see if the Delta state can be observed at all, as this would be suggesting that chemical and thermal freeze-out indeed nearly coincident” (Ref: Phys. Lett. B 509 (2001)239)  Medium modification of Delta mass and width Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 4

5. Experimental setup and Data Analysis: Event cut: 0 <= Ref Multi < 80, Trigger cut : 2001 and 2003 MinBias |VertexZ| < 50 cm, Total ~ 11M events used Centrality Selection (using FTPC): Centrality bin Ref. Mult in East FTPC %of Events 1 >= 17 (0-20) 2 = 10 (20-40) 3 < 10 (40-100) Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 5

6. Other cuts used (Track and Pair Cuts): Nsigma : -2 to +2, -0.8 < eta < +0.8, 0.0 < gDCA < 3.0 Proton: Pion : 0.3 < Pt < 1.1 GeV/c 0.1 < Pt < 0.6 GeV/c 0.3 < P < 1.1 GeV/c 0.1 < P < 0.6 GeV/c 22 < Nhits < 46 15 <Nhits < 46 Pair : rapidity cut : -0.5 to +0.5 Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 6 STAR Preliminary Data Analysis

7. Invariant Mass Reconstruction: D(M)=S(M) - Ns/Nm [1-R/Ns] B(M) D(M) ---correlated pairs S(M) --- pairs from the same events B(M)--- background pairs from mixed events Ns --- entries of S(M) ; Nm---entries of B(M) ; R---- entries of D(M) R is found by minimizing chi2 of fitting to D(M) using a chosen function : Phase factor*P-wave BW (signal)+Gaussian (residual background) Phase factor =exp(-(M-M0)/T) T=160 MeV Back Ground substraction and fitting procedure Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 7 Raw Signal STAR Preliminary

8. (0-20)% (20-40)% (40-100)% Invariant Mass for different centralities  ++  -- Get the: Yield, Mass, Width for different p T bins and for different centralities Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 8 Minbias STAR Preliminary

9. Raw Yield vs. p T Eff. vs p T Reconstruction efficiency for diff. p T bins obtained from the embedding data Corrected Yield = Raw Yield / Eff. Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 9 STAR Preliminary

10. Corrected p T spectra for different Centralities Fitted with Exponential function Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 10 STAR Preliminary

11. Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 11 K* study in dAu Inv. Mass spectra fitted with B-W function + Linear BG STAR Preliminary Event cut: 0 <= refMult < 80, 2001 & 2003 MinBias trigger |Zveterx| < 75cm Track cuts for K*: Nhits >= 15, |eta| < 0.8, gDCA < 1.5 cm Kaon: Pion: | NsigmaK | < 2 |NsigmaPi| < 3 0.2 < p < 0.7 GeV/c 0.2 < p < 10 GeV/c 0.2 < p T < 0.7 GeV/c 0.2 < p T < 10 GeV/c Pair Cut : |y| < 1

12. Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 12 Fitted with Levy function STAR Preliminary Corrected p T spectra for K* for different Centralities

13. ●  ++ +  -- )/(p + pbar) ratios independent of centrality ● dN/dy of  increases with centrality ● K*/K ratio decreasing with centrality (K* daughter particles' rescattering effect may destroy part of K* signal) ●   /  ++ independent of p T similar as pbar/p ratio Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 13 Results: STAR Preliminary

14. Nuclear Modification factor: The high p T supression by comparing the p T spectra relative to reference data from NN collisions. Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 14 Also can be checked by comparing the p T spectra in central and peripheral collisions Results: STAR Preliminary

15. Summary: Delta, AntiDelta & K* are measured in dAu collsions. Yield, mass obtained for different p T bins for different centralities. (  ++ +  -- )/ppbar ratio is independent of centrality K*/K ratio decreases with centrality AntiDelta/Delta ratio is independent of p T Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 15

16. Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 16 Thank you STAR Collaborators

17. Dipak Mishra ICPAQGP5, Kolkata Feb 8 – 12 17 All pT range Works at low pT Fits well in high pT Power law exponential Levy Extra slide....

18. Invariant Mass Reconstruction:  signal Large background in the signal Mixed Event Signal D(M)=S(M) - Ns/Nm [1-R/Ns] B(M) D(M) ---correlated pairs S(M) --- pairs from the same events B(M)--- background pairs from mixed events Ns --- entries of S(M) ; Nm---entries of B(M) ; R---- entries of D(M) R is found by minimizing chi2 of fitting to D(M) using a chosen function : Phase factor*P-wave BW (signal)+Gaussian (residual background) Phase factor =exp(-(M-M0)/T) T=160 MeV Back Ground substraction and fitting procedure Dipak Mishra (IOPB) ICPAQGP5, Kolkata Feb 8 – 12 18 STAR Preliminary