1. Elementary Process and d+Au Collision at RHIC Energy @ 大阪大学 RCNP, 28 Oct., 2003 北大理 一瀬 昌嗣 (M.Isse) ☆共同研究 原研東海研 大塚 直彦 (N.Otuka) インド物理学研 Ｐ．Ｋ．サフ (P.K.Sahu) 北大理 大西 明 (A. Ohnishi) Introduction Additional Jets study (Au+Au) Elliptic flow with two analysis method Elementary Process study (p+p, d+Au) pt-spectrum and Azimuthal Correlation Summary

2. Introduction p+p and d+Au collision has been done at RHIC (√s =200 AGeV). d+Au collision dose not show signature of QGP formation seen in Au+Au (√s = 130, 200 AGeV), like Jet Quenching. d+Au collision is not expected to form QGP. Then, Hadronic Cascade should reproduce d+Au collisions. We would like to estimate how the Jet events occur in each event at RHIC.

3. Today ’ s Two Topic Additional Jets study -> Au+Au High p T hadrons, underestimated in hadronic cascade, seems to come from jets in both Au+Au, d+Au collisions. Elliptic flow v 2 of Au+Au (130,200 AGeV) collision at RHIC is available, which may be a sensitive probe to see jet effect. We introduce jets additionally in Hadronic Cascade model JAM 1.010 and study elliptic flow v 2. Elementary Process study -> d+Au

4. Additional Jets study Au+Au

5. Final State Interaction and Jet production Final State Interaction Hadron multiple scattering Resonance and String production and decay Soft process is dominant. Jet production Hard process. QCD based scenario has to be considered. Jet-quenching or Cronin effect or shadowing are not considered in this result, but we include independent jets.

6. Additional Jets Au+Au p T - spectrum produced by JAM 1.010 is not enough at high-p T. Add some (N central =7 (Au+Au), 1.5(d+Au)) jets of p+p collision by PYTHIA 6.2 to reproduce high-p T hadrons in central events. Additional jet number is determined by N jet (b)= N central * / max, proportional to the number of binary collision assuming Glauber geometry. Glauber geometry Additional Jets N central (h + +h - ) 2

7. Analysis Methods of Elliptic Flow Reaction Plane Method The R.P. is initially known in the simulation. v n (p T,  )= Correlation Method Calculate the angle of each particles  v n (p T,  )= (p T,  ) / √ (  ) squared

8. Elliptic flow v 2 (N ch /N max ) Jets do not affect so much on v 2 Two Analysis Methods (Reac. and Corr.) do not have significant differences. Reac. Corr. Au+Au √s = 130 AGeV h ±

9. Elliptic flow v 2 (p T ) Additional Jets reduce v 2 at high-p T. Including additional Jets make v 2 reduce!! Both in Reaction Plane Method and Correlation Method. Au+Au √s = 130 AGeV h ±

10. Summary of Additional Jets study We have investigated Au+Au collision at RHIC by using hadron-string cascade model JAM 1.010 with additional jets by using PYTHIA 6.2. They are determined to fit experimental p T -spectra. We calculate elliptic flow v 2 by JAM with additional jets. In N ch /N max distribution, v 2 change little. While, in p T distribution, v 2 at high-p T is largely suppressed, both in Reaction Plane and Correlation method.

11. Elementary process study p+p, d+Au

12. Elementary Process Inelastic cross sections of p+p collision. Total cross sections of p+p collision.

13. Lower limit of allowed p T We choose a parameter in JAM (i.e. PYTHIA 6.1), which give the lower limit of allowed p T value for hard 2  2 processes. Here we denote it “c”. (“ckin(3)” in PYTHIA) The default value of “c” in JAM is 2, it is same in HIJING.

14. p+p √s= 200 AGeV p t -spectrum (h + +h - ) 2 c=2.7 seems good

15. Nuclear coherent thickness (1+a) In nucleus-nucleus collisions, we increase thickness for hard processes. Put a factor “a” on  jet Calculate p T – spectrum and Azimuthal Correlation of d+Au collision.

16. d+Au √s=200 AGeV p t -spectrum (h + +h - ) 2 Dose not increased thickness “ a ” Increased thickness “ a ”

17. d+Au M.B. Azimuthal correlation Jet Much far-side @high-p T Little near-side @low&high-p T We need more consideration.

18. Summary We have investigated p+p, d+Au collision at RHIC by using hadron-string cascade model JAM 1.010. When we put a factor “a” on  jet as nucleon coherent thickness, p T -spectrum of d+Au collision is reproduced. Independent h+h collision is not suitable for A+A collisions at RHIC energies.  correlation should be considered more carefully. High-p T (<4GeV/c) component may not come from back-to-back jets.