Measurements of the Drell-Yan process and of charmonium and bottomonium production at CERN and Fermilab show a depletion at high Feynman x in large relative to small nuclear targets. We can attribute this depletion to energy loss of initial and final states, provided that the loss is (dE/ ^z)DreU-Yan= 9^ (c/£'/^z)charm~1.5 GcV/fm at the highest XF measured. This small loss is magnified in the differential cross section due to the strong behavior -(1 -x)" of the projectile's structure functions at large x, PACS numbers: 25.40.Ve, 13.85.Ni, l3.85.Qk Fermilab experiment E772 has measured the A dependence of the Drell-Yan process [1] and J/y/ production [2] in proton-nucleus collisions at the center-of-mass energy Jl=40GeV. Data for the ratio A ~KdGpAldxf)/ (doppldxp) in Fig. 1 exhibit a strong depletion for J/xj/ and Drell-Yan pairs carrying a significant fraction x^ of the projectile momentum. While NA3 at CERN had reported [3] a similar behavior for J/ yf at vT = 20 GeV, E772's is the first demonstration of such a nuclear xp dependence in the Drell-Yan process. We propose that energy loss due to multiple parton scattering can consistently explain the high-xp depletion in the Drell-Yan process and JI xj/ production. Depletion arises because of a sensitive dependence of the projectile's structure functions at large x to small energy losses of the initial-and final-state partons.The fractional loss for the projectile quark needed to explain the Drell-Yan depletion at the highest JC/r^O.64The depletion from tungsten. The dotted and dashed curves are the expected depletion in J/\if production arising solely from initial-state scattering using two different sets of structure functions. Also included are the results for the Drell-Yan data (squares). The solid curve compares our calculation for charmonium including final-state energy loss to J/yf data (circles).1834 is quite small, (Ax^)^ -0.0125 in tungsten. For the E772 beam energy ^bcam^^SOO GeV, this loss corresponds to an energy degradation per unit distance dE/dz ~AjCF£'beam//?'--1.5 GcV/fm (R ^ 6.5 fm for tungsten). We will extrapolate this Drell-Yan energy loss to describe the y/v^ depletion at high XF-Our analysis implies an estimate, perhaps an upper bound, on dE/dz because other nuclear effects can also contribute to the depletion, such as sea-quark structure function modification in the target [1,4,5] in the Drell-Yan process and intrinsic charm in the projectile [6] in J/y/ production. However, evidence for multiple scattering [7l is seen in the p± data of the Drell-Yan process and Y production data [8l. The possibility that partons lose energy while traversing a nucleus is discussed elsewhere in the literature [9], most recently in the context of jet quenching [10]. Gyulassy, Pliimer, and co-workers [10,11] extract a similar dE/dz-^X-l GeV/fm for quarks from an analysis of deep inelastic lepton-nucleus scattering data from SLAC and Fermilab E665 [12].A larger fractional loss (AXF)^-f (Ax^)^ is expected for J/yf production, where the incident partons are g...

We introduce a new model of mesons as quark-antiquark bound states. The model is covariant, confining, and chirally symmetric. Our equations give an analytic solution for a zero-mass pseudoscalar bound state in the case of exact chiral symmetry, and also reduce to the familiar, highly successful nonrelativistic linear potential models in the limit of heavy-quark mass and lightly bound systems. In this fashion we are constructing a unified description of all the mesons from the .rr through the Y. Numerical solutions for other cases are also presented.

A covariant wave equation for qtj interactions with an interaction kernel composed of the sum of constant vector and linear scalar confining interactions is solved for states with two quarks with identical mass. The model includes a Nambu-Jona-Lasinio-like mechanism which links the dynamical breaking of chiral symmetry to the spontaneous generation of quark mass and the appearance of a low mass Goldstone pion. A novel feature of this approach is that it automatically explains the small mass of the pion even though the linear potential is a scalar interaction in Dirac space, and hence breaks chiral symmetry. Solutions for mesons composed of light quarks ( K , p, and low lying excited states) and heavy quarks (r),, JIP, and low lying excited states) are presented and discussed.