Latest results on the hot dense partonic matter at RHIC

At the Relativistic Heavy-Ion Collider (RHIC) collisions of heavy ions at nucleon-nucleon energies of 200GeV appear to have created a new form of matter thought to be a deconfined state of the partons that ordinarily are bound in nucleons. We discuss the evidence that a thermalized partonic medium, usually called a Quark Gluon Plasma (QGP), has been produced. Then, we discuss the effect of this high-density medium on the production of jets and their pair correlations. Next, we look at direct photons as a clean electro-magnetic probe to constrain the initial hard scatterings. Finally, we review the developing picture for the effect of this medium on the production of open heavy quarks and on the screening by the QGP of heavy-quark bound states.     

Recent results on nucleon spin structure study at RHIC

Both the PHENIX and STAR experiments at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory are running polarized proton–proton collisions at s= 200 and 500 GeV. The main goal of the RHIC spin physics program is to gain deeper insight into the spin structure of the nucleon. We will give an overview of recent spin results from RHIC, particularly the study of gluon polarization via jet/hadron production and sea quark polarization via W boson production in longitudinally polarized proton–proton collisions.     

Heavy quarks at RHIC and LHC within a partonic transport model

Production and space-time evolution of heavy quarks in central and non-central heavy-ion collisions at RHIC and LHC are studied with the partonic transport model Boltzmann Approach of MultiParton Scatterings (BAMPS). In addition to the initially created heavy quarks in hard parton scatterings during nucleon-nucleon collisions, secondary heavy quark production in the quark-gluon plasma is investigated and the sensitivity on various parameters is estimated. In BAMPS heavy quarks scatter with particles of the medium via elastic collisions, whose cross section is calculated with the running coupling and a more precise implementation of Debye screening. In this framework, we compute the elliptic flow and nuclear modification factor of heavy quarks and compare it to the experimental data.     

Exploring superdense matter at RHIC

I report first results on Au + Au collisions at GeV per nucleon pair from all four experiments at the Relativistic Heavy Ion Collider.Received: 30 September 2002, Published online: 22 October 2003PACS: 25.75.Dw Particle and resonance production     

Polarized proton collisions at 205 GeV at RHIC

The Brookhaven Relativistic Heavy Ion Collider (RHIC) has been providing collisions of polarized protons at a beam energy of 100 GeV since 2001. Equipped with two full Siberian snakes in each ring, polarization is preserved during acceleration from injection to 100 GeV. However, the intrinsic spin resonances beyond 100 GeV are about a factor of 2 stronger than those below 100 GeV making it important to examine the impact of these strong intrinsic spin resonances on polarization survival and the tolerance for vertical orbit distortions. Polarized protons were first accelerated to the record energy of 205 GeV in RHIC with a significant polarization measured at top energy in 2005. This Letter presents the results and discusses the sensitivity of the polarization survival to orbit distortions.     

Models of the proton spin structure

A phenomenological model of spin sharing by the constituents of a proton is constructed, based on the recent EMC measurement of the spin dependent structure function and knowledge of the unpolarized parton densities.     

65 MeV polarized proton elastic scattering and the effective two-body interaction range

Elastic scattering of polarized protons from sd and fp shell nuclei has been studied with high-purity germanium detectors. The mean square radius of the central real part of the fitted optical potential was found to be of the form $\text{a}\text{+}\text{bA}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$. Comparison with the radius from electron scattering gives the range of the effective two-body interaction and its A dependence as $\text{〈}\text{r}{}^2\text{〉}{}_{\mathrm{d}}\text{=(4.5±0.4)+(0.16±0.03)}\text{A}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{fm}{}^2$.     

Measurement of proton proton elastic scattering in pure initial spin states at 11.75 GeV/c

The elastic cross section for proton proton scattering at 11.75 GeV/c was measured at the Argonne ZGS using a 50% polarized target. In the range p_⊥²=0.6 → 2.2 (GeV/c)² we obtained precise measurements of $\text{d}\text{σ}\text{d}\text{t(ij)}$ for the ? ?, and ? initial spin states perpendicular to the scattering plane. We confirmed that the asymmetry parameter, A, decreases with energy in the diffraction peak, but is approximately energy-independent at large p_⊥². We found that the spin correlation parameter c_nn acquires rather dramatic structure, and at large p_⊥² seems to grow with energy.     

Some theoretical aspects of the presence of spin in proton proton elastic scattering

Some theoretical aspects on the problem of spin in proton proton elastic scattering in the range of energy starting from few GeV/c up to ISR energies are discussed.Presented at the Symposium on Hadron-Hadron Scattering at High Energies, Liblice, Czechoslovakia, June 16–21, 1975.I thank A.Martin and J.Soffer for their help in preparing this talk.     

Gravitational two-body problem with acceleration-dependent spin terms

We generalize our previous work, on the gravitational two-body post-Newtonian Lagrangian with spin and parametrized post-Newtonian parameters and , by addingaccelerationdependent spin terms corresponding to anarbitrary spin supplementary condition. For the purpose of constructing the corresponding Hamiltonian we make use of our recently developedmethod of the double zero. Using this method, we remove the acceleration-dependent spin terms from the Lagrangian and, in the process, create new non-accelerationdependent terms. Use of this new Lagrangian enables us to construct the Hamiltonian corresponding to the arbitrary spin supplementary condition. Energy constants of the motion are also discussed.     

Azimuthal anisotropy and correlations in the hard scattering regime at RHIC

Azimuthal anisotropy (v(2)) and two-particle angular correlations of high p(T) charged hadrons have been measured in Au+Au collisions at sqrt[s(NN)]=130 GeV for transverse momenta up to 6 GeV/c, where hard processes are expected to contribute significantly. The two-particle angular correlations exhibit elliptic flow and a structure suggestive of fragmentation of high p(T) partons. The monotonic rise of v(2)(p(T)) for p(T)<2 GeV/c is consistent with collective hydrodynamical flow calculations. At p(T)>3 GeV/c, a saturation of v(2) is observed which persists up to p(T)=6 GeV/c.     

Hadronization and chirality in strongly interacting partonic matter — The future of the RHIC Program

New physics and detector concepts for a future pp and heavy ion program at the RHIC-II accelerator facility will be discussed. I will focus on hadronic observables which enable us to gain a better understanding on the hadronization from a sQGP and the chiral symmetry restoration in a sQGP. The ultimate question of how matter acquires mass can be addressed by this program in a complementary way to the Higgs search in high energy physics. The contributions of the RHIC program to the study of QCD will be discussed in detail.     

Measurement of the proton spin polarizabilities at MAMI

The spin polarizabilities of the nucleon are fundamental structure constants which describe the response of the nucleon spin to an incident polarized photon. The most model-independent way to measure the nucleon spin polarizabilities is the Compton scattering with polarization degrees of freedom. Three Compton scattering asymmetries on the proton were measured in the Δ(1232) region using a polarized incident photon beam and a polarized (or unpolarized) proton target at the Mainz Microtron (MAMI). These asymmetries are sensitive to values of the spin polarizabilities. Fits to asymmetry data were performed using a dispersion model calculation, and a separation of all four proton spin-polarizabilities in the multipole basis was achieved. The values of the proton spin polarizabilities are presented.     

Hadronic colliders as probes of the proton spin structure

We perform a systematic analysis of different processes with high energy polarized proton beams: jets, direct photon, lepton pairs (Drell-Yan) andWZ production. Different sets of polarized partonic densities are used that fit EMC and SLAC polarized deep inelastic scattering data with variable amount of quark and gluon components of the proton spin. The case of the future Relativistic Heavy Ion Collider (RHIC) used as a polarized collider at a maximum energy of \(\sqrt s = 500\) GeV is analyzed in detail.     

Probing proton spin structure through hadronic reactions

Inclusive and semi-inclusive photon producing polarized proton reactions have been employed to probe the spin structure of the proton. Combinations of cross-sections are suggested which may measure valence quarks polarization and gluon polarization in the proton separately. The general formalism is used to predict numerical results using a model of spin structure based on Altarelli-Parisi equations.     

Strange particle production mechanisms in proton—Proton collisions at RHIC

We present data on strange particle production in elementary proton-proton collisions at RHIC energies. Comparison to leading order and next-to-leading order (NLO) calculations shows that the fragmentation process is flavor dependent and that higher order corrections are needed to describe all spectra, in particular at these collision energies, which are modest compared to those at the Tevatron. A model (EPOS) which takes into account multiple scattering between projectile constituents seems to describe the data best.     

Leading chiral contributions to the spin structure of the proton

The leading chiral contributions to the quark and gluon components of the proton spin are calculated using heavy-baryon chiral perturbation theory. Similar calculations are done for the moments of the generalized parton distributions relevant to the quark and gluon angular momentum densities. These results provide useful insight into the role of pions in the spin structure of the nucleon and can serve as a guide for extrapolating lattice QCD calculations at large quark masses to the chiral limit.