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Authors
D. J. Hofman
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This manuscript contains a summary of the latest physics results from PHOBOS, as reported at Quark Matter 2006. Highlights include the first measurement from PHOBOS of dynamical elliptic flow fluctuations as well as an explanation of their possible origin, two-particle correlations, identified particle ratios, identified particle spectra and the latest results in global charged particle production.
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The NA60 experiment has measured the production of muon pairs and of charged particles in In+In collisions at a beam energy of 158 AGeV. For invariant dimuon masses below the phi the space-time averaged rho spectral function was isolated by a novel procedure. It shows a strong broadening but essentially no shift in mass. The production of J/psi was measured as a function of the collision centrality. As in previous experiments studying Pb+Pb collisions an anomalous supression is observed, setting in at approximately 90 participant nucleons. Using the charged particles the reaction plane was reconstructed. The elliptic flow of charged particles increases with pt showing a saturation for pt > 2GeV/c. For the first time azimuthal distributions for J/psi are shown.
Thank to the stable operation at intense beam power, T2K data with neutrino-mode operation almost doubled in one year. A number of critical improvements to the oscillation analysis have been introduced and resulted in an unprecedented level of sensitivity in searching for CP violation in the neutrino sector. T2K firstly reports that the CP-conserving values of parameter $delta_{CP}$ in the PMNS mixing matrix fall out of its 2$sigma$ C.L. measured range.
The Dafne Frascati phi factory has continously improved its performances reaching in 2002 an instantaneous luminosity of 8x10^31 cm-2 s-1. The DEAR experiment, concluded in 2002, has measured the de-excitation of kaonic atoms. The KLOE experiment, still running, has measured several branching ratios for neutral and charged kaons decays, rho, eta, eta, a0 and f0 mesons parameters and, via the radiative return, the e+e- -> pi+pi- cross section. Preliminary and final results are presented.
Particle production in Au+Au collisions has been measured in the PHOBOS experiment at RHIC for a range of collision energies. Three empirical observations have emerged from this dataset which require theoretical examination. First, there is clear evidence of limiting fragmentation. Namely, particle production in central Au+Au collisions, when expressed as $dN/deta$ ($eta equiv eta-y_{beam}$), becomes energy independent at high energy for a broad region of $eta$ around $eta=0$. This energy-independent region grows with energy, allowing only a limited region (if any) of longitudinal boost-invariance. Second, there is a striking similarity between particle production in e+e- and Au+Au collisions (scaled by the number of participating nucleon pairs). Both the total number of produced particles and the longitudinal distribution of produced particles are approximately the same in e+e- and in scaled Au+Au. This observation was not predicted and has not been explained. Finally, particle production has been found to scale approximately with the number of participating nucleon pairs for $N_{part}>65$. This scaling occurs both for the total multiplicity and for high $pT$ particles (3 $<pT<$ 4.5 GeV/c).
PHOBOS is one of four experiments studying Au-Au collisions at RHIC. During the first running period RHIC provided Au+Au collisions at $sqrt{s_{_{NN}}}$ = 56 GeV and 130 GeV. The data collected during this period allowed us to study the energy and centrality dependence of particle production, the anisotropy of the final state azimuthal distribution and particle ratios at mid-rapidity.
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