V. F. Peresedov

Azimuthal Anisotropy of {pi}{sup 0} Production in Au+Au Collisions at {radical}(s{sub NN})=200 GeV: Path-Length Dependence of Jet Quenching and the Role of Initial Geometry

We have measured the azimuthal anisotropy of pi(0) production for 1 < p(T) < 18 GeV/c for Au + Au collisions at root s(NN) = 200 GeV. The observed anisotropy shows a gradual decrease for 3 less than or similar to p(T) less than or similar to 7-10 GeV/c, but remains positive beyond 10 GeV/c. The magnitude of this anisotropy is underpredicted, up to at least similar to 10 GeV/c, by current perturbative QCD (PQCD) energy-loss model calculations. An estimate of the increase in anisotropy expected from initial-geometry modification due to gluon saturation effects and fluctuations is insufficient to account for this discrepancy. Calculations that implement a path-length dependence steeper than what is implied by current PQCD energy-loss models show reasonable agreement with the data.

Measurement of the tensor analyzing power for relativistic-deuteron fragmentation as a means for studying the deuteron structure within light-front dynamics

New data on the vector (Ay) and tensor (Ayy) analyzing powers for the reaction 9Be (d, p)X at a primary deuteron momentum of 5 GeV/c for a proton emission angle of 178 mrad are obtained by using the synchrophasotron of the Joint Institute for Nuclear Research (JINR, Dubna). The experimental data on Ayy are analyzed within the approach based on light-front dynamics, the relativistic wave function obtained by Karmanov and his colleagues being used for the deuteron. It is shown that, in contrast to what one has from calculations with standard nonrelativistic deuteron wave functions, all relevant data can be explained in this approximation without resort to additional degrees of freedom.