The pseudorapidity asymmetry and centrality dependence of charged hadron spectra in d+Au collisions at (square root)s{sub NN} = 200 GeV are presented. The charged particle density at mid-rapidity, its pseudorapidity asymmetry and centrality dependence are reasonably reproduced by a Multi-Phase Transport model, by HIJING, and by the latest calculations in a saturation model. Ratios of transverse momentum spectra between backward and forward pseudorapidity are above unity for p{sub T} below 5 GeV/c. The ratio of central to peripheral spectra in d+Au collisions shows enhancement at 2

(Cont.) Further, hadron production in p+Au interactions is compared to that of n+Au interactions. The single charge difference between a p+Au and a n+Au collision allows for a unique study of the ability of the interaction to transport the proton from the initial deuteron to mid-rapidity. However, no asymmetry between the positively and negatively charged hadron spectra of p+Au and n+Au interactions is observed at (qr) = 0.8. Collision centrality was determined using several different observables, including those based on the multiplicity in different regions of pseudorapidity and those based on the amount of nuclear spectator material. It is shown that measurements made on small collision systems in the mid-rapidity region are biased by centrality variables based on the mid-rapidity multiplicity. Despite this bias, a smooth evolution with centrality is observed in the Cronin enhancement of hadrons produced in d+Au collisions. It is shown that this smooth progression is independent of the choice of centrality variable when centrality is parametrized by the multiplicity measured near mid-rapidity.

(Cont.) When ... is calculated for different rapidities, a suppression is seen as the rapidity in the deuteron fragmentation region increases. This has been predicted to be seen if a CGC does form in the colliding nuclei.

The centrality dependence of the mean charged-particle multiplicity as a function of pseudorapidity is measured in approximately 1 ?b-1 of proton–lead collisions at a nucleon–nucleon centre-of-mass energy of $sqrt{s_{_ ext {NN}}} = 5.02$ TeV using the ATLAS detector at the Large Hadron Collider. Charged particles with absolute pseudorapidity less than 2.7 are reconstructed using the ATLAS pixel detector. The ? + ?b collision centrality is characterised by the total transverse energy measured in the Pb-going direction of the forward calorimeter. The charged-particle pseudorapidity distributions are found to vary strongly with centrality, with an increasing asymmetry between the proton-going and Pb-going directions as the collisions become more central. Three different estimations of the number of nucleons participating in the ? + ?b collision have been carried out using the Glauber model as well as two Glauber–Gribov inspired extensions to the Glauber model. In conclusion, charged-particle multiplicities per participant pair are found to vary differently for these three models, highlighting the importance of including colour fluctuations in nucleon–nucleon collisions in the modelling of the initial state of ? + ?b collisions.

We determine rapidity asymmetry in the production of charged pions, protons and anti-protons for large transverse momentum (p{sub T}) for d+Au collisions at √s{sub NN} = 200 GeV. The rapidity asymmetry is defined as the ratio of particle yields at backward rapidity (Au beam direction or -ve rapidity) to those at forward rapidity (d beam direction or +ve rapidity). The identified hadrons are measured in the rapidity regions.

PHENIX has measured the transverse momentum (pT) spectra and two particle angular correlations for high pT particles in d+Au collisions at psNN=200 GeV using the RHIC Year-2008 run data. The azimuthal angle correlations for two particles with a large rapidity gap exhibit a ridge-like structure. Using the pi-0s reconstructed in the EMCal, we have successfully extended the pT reach of the correlation up to 8 GeV/c. We find that the azimuthal anisotropy of hadrons found at low pT persists up to 6 GeV/c with a significant centrality and pT dependence, similar to what was observed in A+A collisions.

The properties of quantum chromodynamics (QCD), the modern theory of the strong interaction, can be investigated through the study of relativistic nucleus-nucleus collisions. Recently, the Relativistic Heavy-Ion Collider (RHIC) was completed and started taking data at ten times higher center-of-mass energies than the previous most energetic heavy-ion collisions. This thesis presents some of the first measurements at RHIC from any experiment. The PHOBOS detector is used to measure the charged particle pseudo-rapidity density at mid-rapidity (i.e., in [eta]

The centrality dependence of the charged-particle pseudorapidity density measured with ALICE in Pb-Pb collisions at √sNN = 2.76 TeV over a broad pseudorapidity range is presented. This Letter extends the previous results reported by ALICE to more peripheral collisions. No strong change of the overall shape of charged-particle pseudorapidity density distributions with centrality is observed, and when normalised to the number of participating nucleons in the collisions, the evolution over pseudorapidity with centrality is likewise small. Broadening the pseudorapidity range (-3.5