High pt Suppression in CuCu Collsions at sNN = 200 GeV at RHIC

Collisions between hadronic systems at relativistic energies provide a window on the small-x gluon distributions of fast moving nuclei. It has been predicted that gluon saturation effects will manifest themselves as a suppression in the transverse momentum (p t) distribution at a scale which is connected with the rapidity of the measured particles. Saturation effects are most evident at large (pseudo)-rapidity, i.e., at small angles relative to the beam direction. The dependence of the nuclear modification factor on the number of participants provides a constraint on the mechanism underlying the high-p t suppression. Here we present results for the nuclear modification factor R cp at forward rapidity as a function of system mass comparing results from CuCu, AuAu and dAu collsions at √ s NN = 200 GeV. The main goal of the heavy ion program at the relativistic heavy ion collider(RHIC) is the creation and detection of the quark gluon plasma (QGP), a deconfined state of matter consisting of quarks and gluons(partons). High-p t partons going through a QGP are expected to suffer significant energy loss resulting in fewer high-p t particles in the exit channel than would be present without the QGP [1]. An experimental observation of such a supression in high energy heavy ion collisions would provide evidence that a QGP has been created. In contrast, the ratio of dAu to pp-collisions is expected to show an enhancement over a range in momentum, a phenomennon known as the Cronin effect [4]. The argument is that energy loss in the "cold matter" of dAu collisions is quite small and the Cronin effect is a result of p t broadening due to multiple scattering. On the other hand, if a suppression is observed in dAu colisions at forward rapidities instead of the Cronin effect, it may be an indication that initial state effects are important. A marked high-p t suppression with increasing pseudorapidity may thus be related to the initial conditions of the colliding deutron and gold nuclei, in particular to the possible existence of the color glass condensate(CGC)[2, 3]. The suppression of high-p t hadron yields has commonly been investigated using the nuclear modification factor R AA which is the ratio of the measured hadron spectra to a scaled reference spectra from pp collisions. The value of R AA should be unity if particle production scales with the average number of binary nucleon-nucleon collisions N coll. In the …