Implication of pA/dA Results on Future pA/eA Programs

1. Implication of pA/dA Results on Future pA/eA Programs Jen-Chieh Peng University of Illinois • Highlights of RHIC dA results • RHIC dA versus fixed-target pA results • Implications on future pA and eA programs pA/eA Workshop, May 6-7, 2005

2. Major Objectives of the RHIC dA Prgram • Provide baseline measurements for understanding A-A collisions • Disentangle initial-state effects from final-state effects • Explore nuclear effects at a s1/2 ~ 5 times higher than any existing fixed-target experiments • Parton distributions in nuclei at small x (shadowing of sea quarks and gluons, gluon saturation, etc.) • Other systematic effects of particle production in nuclei (Cronin effect, xF-scaling, pT-broadening, quark energy loss, etc.)

3. Comparison of d+Au with Au+Au Absence of jet-quenching in d+Au Cronin effect observed in d+Au at mid-rapidity (rapidity dependence, particle species dependence?)

4. Dependence of the Cronin Effect on Particle Species π+ π- Fixed-target data at 200, 300, 400 GeV p-A Particle Species dependence is observed Stronger Cronin effect for baryons and also for K- (valence quark effects?) K+ K- P P-bar Antreasyan et al., PRD 19 (1979) 764

5. Cronin pt-broadening effect is also observed in heavy quarkonium production J/Ψ (and Ψ’) production for p-A at 800 GeV (E866) and 200 GeV (NA3) J/Ψ production for d+Au at PHENIX Universal pT-broadening effects (similar slopes)? Will α continue to rise at large pT? Overall magnitude depends on xF (rapidity)?

6. pT-broadening effect is also observed in Drell-Yan Larger pT broadening effect for quarkonium than for Drell-Yan Drell-Yan at 800 GeV p+A (Upsilon) (J/Ψ) (Drell-Yan)

7. RCP and RdAu show strong rapidity dependence Brahms data Strong suppression at large rapidity (small-x) ! Gluon shadowing? Gluon saturation? Color Glass Condensate? Other effects?

8. Gluon shadowing in nuclei? Gluon shadowing in nuclei is expected Shadowing at small-x for F2 Frankfurt et al. JHEP 02 (2002) 27

9. photon - jet direct photon dijet/dihadron open charm high-pTl+l- At RHIC, many hard-processes in p-A (d-A) collisions are sensitive to gluon distributions in nuclei (identical to the tools used to determine ΔG(x) in RHIC-Spin) Gluon distributions in nuclei could be probed down to x ~ 10-2 It would be very interesting to reach x ~ 10-3 to search for gluon saturation effect at low x

10. Kinematics of single hadron production A given rapidity covers a broad range of Xtarget Guzey, Strikman, Vogelsang (hep-ph/0407201) Sub-process involves 2 final partons, but only a single hadron is detected Need to detect two particles to better determine the kinematics (Di-jet, J/Ψ, D-Y, gamma-jet, etc.)

11. J/Ψ production in d-Au from PHENIX (x ~ 10-3 is reached)

12. Nuclear effects of high-mass dihadron at 800 GeV p-A Fermilab E789 Suppression at high mass (corresponding to high pT) Nuclear effect of Pout is clearly observed (pT-broadening)

13. An universal xF-dependence in p-A hadron production? Data cover energy range from 70 to 400 GeV XF-scaling for a broad energy range  nuclear shadowing alone can not explain the data How about heavy quarkonium and Drell-Yan? Kopeliovich et al., hep-ph/0501260

14. XF-scaling is also observed for J/Ψ production J/Ψ suppression in p-A can not be due to shadowing alone

15. Suppression at large XF is also observed in Drell-Yan

16. Explanation of the universal suppression at large xF A common nuclear suppression mechanism due to Sudakov suppression, or an effective energy loss Kopeliovich et al., hep-ph/0501260

17. How about negative rapidity region? Very little data. Difficult to measure at fixed-target PHENIX Data Enhancement at negative xF (rapidity) !

18. dN/dη at negative rapidity for d-Au BRAHMS Data PHOBOS Data

19. PRL 83 (1999) 2304 The Drell-Yan p-A measurement can be extended to lower x at RHIC

20. Disappearance of shadowing at small x? Predicted nuclear dependence of Drell-Yan at small x for dilepton mass of 4.5 GeV Kopeliovich et al. (hep-ph/0501260)

21. Expected kinematic coverage and sensitivites for a two-month run at designed luminosity at PHENIX EKS98 Shadowing at low x?

22. Hard diffractive J/Ψ and di-jet production in Tevatron J/Ψ production with a rapidity gap PRL 87 (2001) 241802 Comparison of the J/Ψ and dijet data shows the gluon fraction of proton’s diffractive structure function is 0.59 ± 0.15

23. Tag the forward p (d) using Roman Pots

24. Extraction of G(x) at HERA Can not extract G(x) and test the validity of DGLAP at the same time! Need an independent determination of G(x)! Therefore, it is crucial to have both p-A and e-A for measuring G(x) AND testing DGLAP!

25. Wish list for p(d)-A program at RHIC • Desparately need additional p-A runs at RHIC • 250GeV p on 100 GeV/A Au to reach the lowest possible x2 • Need sufficient luminosity to measure Drell-Yan • Better statistics to measure J/Ψ pT and rapidity nuclear dependences • Identification of gamma-jet, gamma-gamma, hadron-hadron and other gluon-sensitive kinematic- constraining processes • Backward p-A run at BRAHMS

26. Wish list for p(d)-A program at RHIC (continued) • Detector upgrades which will enhance the p(d)-A program at RHIC • Forward calorimeter at STAR • Silicon upgrade at PHENIX for open-charm detection • Nosecone calorimeter at PHENIX • Roman Pot (from pp2pp) to STAR/PHENIX? • Inputs from theorists, RHIC-spin, and p-p • Unique experimental signatures for gluon saturation • ΔG(x) extraction method from RHIC-spin → GA(x) • G(x) extraction from p-p →GA(x) in p-A

27. Wish list for e-A • F2A(x,Q2) over a broad range of x and Q2 to measure quark and gluon distributions in nuclei • Need to measure several A, and should not depend on the centrality trigger • eA diffractive processes to study the connection between them and the gluon in nuclei, and comparison with ep diffractive processes • Experimental input from pA diffractive is crucial • Heavy quark capability for independent GA(x) measurements • Much simulation and design studies remain for eA