P. Walters

System Size, Energy, Pseudorapidity, and Centrality Dependence of Elliptic Flow

This Letter presents measurements of the elliptic flow of charged particles as a function of pseudorapidity and centrality from Cu-Cu collisions at 62.4 and 200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider. The elliptic flow in Cu-Cu collisions is found to be significant even for the most central events. For comparison with the Au-Au results, it is found that the detailed way in which the collision geometry (eccentricity) is estimated is of critical importance when scaling out system-size effects. A new form of eccentricity, called the participant eccentricity, is introduced which yields a scaled elliptic flow in the Cu-Cu system that has the same relative magnitude and qualitative features as that in the Au-Au system.

System size dependence of cluster properties from two-particle angular correlations in Cu+Cu and Au+Au collisions at sq root(s{sub NN})=200 GeV

B.Alver, B.B.Back, M.D.Baker, M.Ballintijn, D.S.Barton, R.R.Betts, R.Bindel, W.Busza, Z.Chai, V.Chetluru, E.Garćıa, T.Gburek, K.Gulbrandsen, J.Hamblen, I.Harnarine, C.Henderson, D.J.Hofman, R.S.Hollis, R.Ho lyński, B.Holzman, A.Iordanova, J.L.Kane, P.Kulinich, C.M.Kuo, W.Li, W.T.Lin, C.Loizides, S.Manly, A.C.Mignerey, R.Nouicer, A.Olszewski, R.Pak, C.Reed, E.Richardson, C.Roland, G.Roland, J.Sagerer, I.Sedykh, C.E.Smith, M.A.Stankiewicz, P.Steinberg, G.S.F.Stephans, A.Sukhanov, A.Szostak, M.B.Tonjes, A.Trzupek, G.J.van Nieuwenhuizen, S.S.Vaurynovich, R.Verdier, G.I.Veres, P.Walters, E.Wenger, D.Willhelm, F.L.H.Wolfs, B.Wosiek, K.Woźniak, S.Wyngaardt, B.Wys louch

System size and centrality dependence of charged hadron transverse momentum spectra in Au + Au and Cu + Cu collisions at s(NN)**(1/2) = 62.4-GeV and 200-GeV

We present transverse momentum distributions of charged hadrons produced in Cu+Cu collisions at sqrt(s) = 62.4 and 200 GeV. The spectra are measured for transverse momenta of 0.25<p_T<5.0 GeV/c at sqrt(s) = 62.4 GeV and 0.25<p_T<7.0 GeV/c at sqrt(s) = 200 GeV, in a pseudo-rapidity range of 0.2<eta<1.4. The nuclear modification factor R_AA is calculated relative to p+p data at both collision energies as a function of collision centrality. At a given collision energy and fractional cross-section, R_AA is observed to be systematically larger in Cu+Cu collisions compared to Au+Au. However, for the same number of participating nucleons, R_AA is essentially the same in both systems over the measured range of p_T, in spite of the significantly different geometries of the Cu+Cu and Au+Au systems.

Cluster properties from two-particle angular correlations in p + p collisions at s**(1/2) = 200-GeV and 410-GeV

B.Alver, B.B.Back, M.D.Baker, M.Ballintijn, D.S.Barton, R.R.Betts, R.Bindel, W.Busza, Z.Chai, V.Chetluru, E.Garćıa, T.Gburek, K.Gulbrandsen, J.Hamblen, I.Harnarine, C.Henderson, D.J.Hofman, R.S.Hollis, R.Ho lyński, B.Holzman, A.Iordanova, J.L.Kane, P.Kulinich, C.M.Kuo, W.Li, W.T.Lin, C.Loizides, S.Manly, A.C.Mignerey, R.Nouicer, A.Olszewski, R.Pak, C.Reed, E.Richardson, C.Roland, G.Roland, J.Sagerer, I.Sedykh, C.E.Smith, M.A.Stankiewicz, P.Steinberg, G.S.F.Stephans, A.Sukhanov, A.Szostak, M.B.Tonjes, A.Trzupek, G.J.van Nieuwenhuizen, S.S.Vaurynovich, R.Verdier, G.I.Veres, P.Walters, E.Wenger, D.Willhelm, F.L.H.Wolfs, B.Wosiek, K.Woźniak, S.Wyngaardt, B.Wys louch

System Size and Centrality Dependence of Charged Hadron Transverse Momentum Spectra inAu+AuandCu+CuCollisions atsNN=62.4and 200 GeV

We present transverse momentum distributions of charged hadrons produced in Cu+Cu collisions at sqrt(s) = 62.4 and 200 GeV. The spectra are measured for transverse momenta of 0.25<p_T<5.0 GeV/c at sqrt(s) = 62.4 GeV and 0.25<p_T<7.0 GeV/c at sqrt(s) = 200 GeV, in a pseudo-rapidity range of 0.2<eta<1.4. The nuclear modification factor R_AA is calculated relative to p+p data at both collision energies as a function of collision centrality. At a given collision energy and fractional cross-section, R_AA is observed to be systematically larger in Cu+Cu collisions compared to Au+Au. However, for the same number of participating nucleons, R_AA is essentially the same in both systems over the measured range of p_T, in spite of the significantly different geometries of the Cu+Cu and Au+Au systems.

MULTIPLICITY FLUCTUATIONS IN Au+Au COLLISIONS AT RHIC

In the PHOBOS experiment, charged particles are measured in almost the full solid angle. This enables the study of fluctuations and correlations in the particle production over a very wide kinematic range. In this paper, we show results of a direct search for fluctuations identified by an unusual shape of the pseudorapidity distribution. In addition, we use analysis of correlations of the multiplicity in similar pseudorapidity bins, placed symmetrically in the forward and backward hemispheres, to test the hypothesis of production of particles in clusters.

Scaling properties in bulk and p(T)-dependent particle production near midrapidity in relativistic heavy ion collisions

The centrality dependence of the midrapidity charged-particle multiplicity density (|η| < 1) is presented for Au + Au and Cu + Cu collisions at RHIC over a broad range of collision energies. The multiplicity measured in the Cu + Cu system is found to be similar to that measured in the Au + Au system, for an equivalent Npart, with the observed factorization in energy and centrality still persistent in the smaller Cu + Cu system. The extent of the similarities observed for bulk particle production is tested by a comparative analysis of the inclusive transverse momentum distributions for Au + Au and Cu + Cu collisions near midrapidity. It is found that, within the uncertainties of the data, the ratio of yields between the various energies for both Au + Au and Cu + Cu systems are similar and constant with centrality, both in the bulk yields and as a function of pT ,u p to at least 4 GeV/c. The effects of multiple nucleon collisions that strongly increase with centrality and energy appear to only play a minor role in bulk and intermediate transverse momentum particle production.

Participant and spectator scaling of spectator fragments in Au + Au and Cu + Cu collisions at √sNN = 19.6 and 22.4 GeV

Spectator fragments resulting from relativistic heavy ion collisions, consisting of single protons and neutrons along with groups of stable nuclear fragments up to nitrogen

Properties of the matter created in heavy ion collisions – results from the PHOBOS experiment

(Z=7)

Properties of the matter created in heavy ion collisions: Results from the PHOBOS experiment

, are measured in PHOBOS. These fragments are observed in Au+Au