High transverse momentum identified particle spectra in 200 GeV collisions from STAR

Significant baryon over meson enhancement was measured at RHIC in the intermediate transverse momentum range of p _T =2?4 GeV/c (“baryon-meson puzzle”). With STAR detector we were able to extend particle identification towards higher transverse momentum offering further insights into the particle production mechanisms at intermediate to high p _T . In this paper we present results on charged pion, proton and anti-proton spectra and ratios at intermediate to high p _T exploiting the relativistic rise of the specific ionization energy loss measured in the STAR Time Projection Chamber. These measurements provide valuable information about the production mechanisms of particles at intermediate p _T in relativistic heavy ion collisions, e.g. coalescence/recombination versus jet fragmentation.     

Elastic scattering and transverse momentum correlations in multiperipheral models

We compute the overlap function and transverse momentum correlations in various versions of the multiperipheral model. We examine in particular how close to saturation is the bound for the pomeron slope recently derived by Krzywicki.Correlations between neighbouring transverse momentum transfers in the S-matrix element are shown to be able to bring the multiperipheral model in agreement with experiment. We also study the case of cluster production and suggest a possible improvement of Krzywicki's bound.     

Azimuthal dependence of two-particle transverse momentum current correlations

The European Physical Journal C - We present a study on inclusive emissions of a double $$\Lambda _c$$ or of a $$\Lambda _c$$ plus a light-flavored jet system as probe channels in the semi-hard...     

Measuring shear viscosity using transverse momentum correlations in relativistic nuclear collisions

Elliptic flow measurements at the Brookhaven National Laboratory Relativistic Heavy Ion Collider suggest that quark-gluon fluid flows with very little viscosity compared to weak-coupling expectations, challenging theorists to explain why this fluid is so nearly "perfect." It is therefore vital to find quantitative experimental information on the viscosity of the fluid. We propose that measurements of transverse momentum fluctuations can be used to determine the shear viscosity. We use current data to estimate the viscosity-to-entropy ratio in the range from 0.08 to 0.3 and discuss how future measurements can reduce this uncertainty.     

High transverse momentum Ξ baryon correlations in p+p collisions at √s=200 GeV

Angular correlations between produced high-p _TΞ^? baryons and unidentified charged and neutral particles are observed in high-tower triggered (on a large electromagnetic energy deposit) √s=200 GeV p+p collisions. This trigger favors events with higher average multiplicity than those in minimum bias. These events are likely to contain jets. The average multiplicity of a high-tower triggered event is similar to that of a minimum bias event containing a Ξ baryon, which implies that Ξ baryons are likely to be produced in jets. Ξ^? <p _T> is higher in the triggered data then in the minimum bias sample.     

Event-by-event fluctuations of mean transverse momentum in AuAu collisions in STAR experiment at relativistic heavy-ion collider

We report results on event-by-event fluctuations in mean transverse momentum in AuAu collisions at GeV measured by the STAR experiment at RHIC. The dynamical fluctuations, is found to be about 1.2 ±02% of the mean transverse momentum for particles in pseudo-rapidity range of −0.5 < η < 0.5 and for the top 6% central collisions.     

Non-identical particle correlations in STAR

The correlation function of non-identical particles is sensitive to the relative space-time asymmetries in particle emission. Analysing pion-kaon, pion-proton and kaon-proton correlation functions, measured in the Au+Au collisions by the STAR experiment at RHIC, we show that pions, kaons and protons are not emitted at the same average space-time coordinates. The shifts between pion, kaon and proton sources are consistent with the picture of a transverse collective flow. Results of the first measurement of proton-lambda correlations at STAR are in agreement with recent CERN and AGS data.     

Fluctuations and correlations in STAR

The study of correlations and fluctuations can provide evidence for the production of the quark-gluon plasma (QGP) in relativistic heavy-ion collisions. Various theories predict that the production of a QGP phase in relativistic heavy-ion collisions could produce significant event-by-event correlations and fluctuations in transverse momentum, multiplicity, etc. Some of the recent results using STAR at RHIC will be presented along with results from other experiments at RHIC. The focus is on forward-backward multiplicity correlations, balance function, charge and transverse-momentum fluctuations, and correlations.     

High transverse momentum physics at the large hadron collider

This note summarizes many detailed physics studies done by the ATLAS and CMS Collaborations for the LHC, concentrating on processes involving the production of high mass states. These studies show that the LHC should be able to elucidate the mechanism of electroweak symmetry breaking and to study a variety of other topics related to physics at the TeV scale. In particular, a Higgs boson with couplings given by the Standard Model is observable in several channels over the full range of allowed masses. Its mass and some of its couplings will be determined. If supersymmetry is relevant to electroweak interactions, it will be discovered and the properties of many supersymmetric particles elucidated. Other new physics, such as the existence of massive gauge bosons and extra dimensions can be searched for extending existing limits by an order of magnitude or more.     

On multiplicity correlations in the STAR data

The STAR data on the multiplicity correlations between narrow pseudorapidity bins in the pp and AuAu collisions are discussed. The PYTHIA 8.145 generator is used for the pp data, and a na?ve superposition model is presented for the AuAu data. It is shown that the PYTHIA generator with default parameter values describes the pp data reasonably well, whereas the superposition model fails to reproduce the centrality dependence seen in the data. Some possible reasons for this failure and a comparison with other models are presented.     

Angular correlations in proton-proton collisions producing a high transverse momentum π0

In an experiment at the CERN ISR, a streamer chamber detector surrounding one of the intersection regions was triggered on large transverse momentum π⁰'s by means of an array of lead-glass counters. The directions of charged particles and γ rays converted in lead-oxide plates inside the streamer chamber were measured. Data were taken at c.m. energy of √s = 53 GeV at two production angles of the high p_Tπ⁰ (90° and 53°). They indicate an enhancement of particles mostly in the hemisphere opposite to the π⁰. In the 53° data, a shift of this enhancement towards rapidities opposite to the rapidity of the π⁰ and confined to a ±30° azimuthal region around the collision plane is observed. In addition, a short-range angular correlation is evidenced between the high p_Tπ⁰ and the other collisions products (photons or charged particles). Two-particle correlations between charged particles produced in association with the high p_Tπ⁰ are found similar to those     

Two-particle azimuthal correlations at high transverse momentum in Pb−Au at 158 AGeV/c

The study of two-particle azimuthal correlations at high transverse momentum has become an important tool to investigate the interaction of hard partons with the medium formed in high-energy nucleus-nucleus collisions. At SPS energies, pioneering studies by the CERES Collaboration [1] indicated a significant modification of the away-side structure in central collisions. Here we present new results emerging from the analysis of the year 2000 data set recorded with the CERES Time-Projection Chamber, which provides excellent tracking efficiency and significantly improved momentum determination.     

Charged particle production and correlations at high transverse momentum at the CERN intersecting storage rings

We study the production of identified charged particles in pp collisions at a c.m. energy of 63 GeV in events with an identified high-p_T trigger particle. The measurements were performed at the CERN Intersecting Storage Rings using the Axial Field Spectrometer.Production ratios are presented as a function of p_T in the range 2.5 to 8 GeV/c.     

The transverse momentum of partons

It is shown that when the parton model is formulated in proper, covariant fashion the average transverse momentum of the partons in a hadron varies with their fractional longitudinal momentum x. It is small near x = 0, but could rise to a large as x → 1.     

A study of transverse and longitudinal momentum correlations in proton diffraction dissociation at 14 GeV/c

We present data on momentum correlations both in and out of the production plane for the reactions π⁺p→π_f⁺(π⁺n) and π^?p→π_f^?(π^?Δ⁺⁺). The dissociation products show strikingly similar transverse momentum distributions which in terms of exchange models suggest an equal amount of pion and baryon exchange. For both reactions, we find an approximate factorization in the projectile frame between the transverse momentum of π_f and the longitudinal momenta of the dissociation products. Exchange models predict this result equally in both reactions, but it appears much more clearly in the Δ reaction. Finally, we relate the observed longitudinal and transverse momentum distributions in a way suggested by an isotropic decay model.     

Multiparticle correlations from momentum conservation

Using a generating-function formalism, we compute the contribution of momentum conservation to multiparticle correlations between the emitted particles in high-energy collisions. In particular, we derive a compact expression of the genuine M-particle correlation, for arbitrary M.Received: 17 February 2003, Published online: 5 September 2003