Highmass Dilepton Physics at RHICII JenChieh Peng University

High-mass Dilepton Physics at RHIC-II Jen-Chieh Peng University of Illinois RHIC-II Workshop, April 29, 2005 • Quark and Gluon Distributions in Nuclei • Flavor Structure of Nucleon Quark Distributions • Forward Tagging and Measurement of Meson Cloud 1

What are the quark and gluon contents of nuclei? (How do they differ from a free nucleon? ) Spin and flavor decomposition of parton distributions in nuclei? 2

PRL 83 (1999) 2304 The Drell-Yan p-A measurement can be extended to lower x at RHIC 3

Expected kinematic coverage and sensitivites for a two-month run at designed luminosity at PHENIX EKS 98 Shadowing at low x? 4

Disappearance of shadowing at small x? Predicted nuclear dependence of Drell-Yan at small x for dilepton mass of 4. 5 Ge. V Kopeliovich et al. (hep-ph/0501260) 5

Prediction of nuclear modification in the Color Glass Condensate formalism Dilepton production in p. A and d. A at RHIC energy Jalilian-Marian (nuclth/0402014) Rd(p)A shows strong mass dependence at y=2. 2 6

Gluon distributions in nuclei deduced from Q 2 – dependences of F 2 Sn/F 2 C NMC data 7

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) • photon - jet • direct photon • dijet/dihadron • open charm • high-p. T l+l- 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 8

J/Ψ production is dominated by gluon-gluon fusion (x ~ 10 -3 could be reached) 9

Flavor asymmetry of the nucleon sea Comparison of p+d with p+p Drell-Yan 10

Flavor asymmetry of the nucleon sea can be measured at small x at RHIC 11

Meson-cloud around the nucleon: Sullivan Process 12

Can one probe the meson cloud directly? Electron DIS scattering off pomeron or meson was studied at HERA by tagging forward-going proton/neutron Pion structure functions at 10 -4 < x < 10 -2 were measured Can one study analogous processes at RHIC? 13

Tagged Drell-Yan production at RHIC? One can tag on forward-going proton, neutron, Δ, Λ in coincidence with lepton-pair 14

Can one detect Drell-Yan events tagged by forward-going nucleons at RHIC? 15

Angular distribution of tagged neutrons Zero-Degree Calorimeter for neutron detection 16

Tag the forward p (d) using Roman Pots 17

Other possible tagged Drell-Yan measurements 18

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 19

Hard diffractive production of W and Z bosons at the Tevatron Sensitive to quark contents of the diffractive structure functions hep-ex/0308032 The unique features of RHIC for hard diffractive physics are the availability of polarized protons and p-A 20

Summary • The quark and gluon structures of protons, nuclei and mesons could be studied at RHIC-II. • Dilepton production can probe many interesting features of the partonic structure of hadrons. • Capability of forward-tagging with a Roman Pot in conjuction with di-lepton detection could significantly enhance the physics reach of p-p and p-A programs at RHIC. 21