Multistrange baryon production in relativistic heavy ion collisions

Using a multiphase transport model, we study the production of multistrange baryons from the hadronic matter formed in relativistic heavy ion collisions. The mechanism we introduce is the strangeness-exchange reactions between antikaons and hyperons. We find that these reactions contribute significantly to the production of multistrange baryons in heavy ion collisions at SPS energies, which has been found to be appreciably enhanced. We have also made predictions for multistrange baryon production in heavy ion collisions at RHIC and found a similar enhancement.Comment: 6 pages, RevTex, 8 figs include

Transverse flow and hadro-chemistry in Au+Au collisions at \sqrt{s_{NN}}=200 GeV

We present a hydrodynamic assessment of preliminary particle spectra observed in Au+Au collisions at \sqrt{s_{NN}}=200 GeV. The hadronic part of the underlying equation of state is based on explicit conservation of (measured) particle ratios throughout the resonance gas stage after chemical freezeout by employing chemical potentials for stable mesons, nucleons and anti-nucleons. We find that under these conditions the data (in particular the proton spectra) favor a low freeze-out temperature of around 100 MeV. Furthermore we show that through inclusion of a moderate pre-hydrodynamic transverse flow field the shape of the spectra improves with respect to the data. The effect of the initial transverse boost on elliptic flow and the freeze-out geometry of the system is also elucidated.Comment: as published: more data included in Fig. 1, discussions throughout the text improved, 6 pages, 4 figure

Effect of tensor couplings in a relativistic Hartree approach for finite nuclei

The relativistic Hartree approach describing the bound states of both nucleons and anti-nucleons in finite nuclei has been extended to include tensor couplings for the $\omega$- and $\rho$-meson. After readjusting the parameters of the model to the properties of spherical nuclei, the effect of tensor-coupling terms rises the spin-orbit force by a factor of 2, while a large effective nucleon mass $m^{*}/M_{N} \approx 0.8$ sustains. The overall nucleon spectra of shell-model states are improved evidently. The predicted anti-nucleon spectra in the vacuum are deepened about 20 -- 30 MeV.Comment: 31 pages, 4 postscript figures include

Open charm and charmonium production at relativistic energies

We calculate open charm and charmonium production in $Au+Au$ reactions at $\sqrt{s}$ = 200 GeV within the hadron-string dynamics (HSD) transport approach employing open charm cross sections from $pN$ and $\pi N$ reactions that are fitted to results from PYTHIA and scaled in magnitude to the available experimental data. Charmonium dissociation with nucleons and formed mesons to open charm ($D+\bar{D}$ pairs) is included dynamically. The 'comover' dissociation cross sections are described by a simple phase-space model including a single free parameter, i.e. an interaction strength $M_0^2$, that is fitted to the $J/\Psi$ suppression data for $Pb+Pb$ collisions at SPS energies. As a novel feature we implement the backward channels for charmonium reproduction by $D \bar{D}$ channels employing detailed balance. From our dynamical calculations we find that the charmonium recreation is comparable to the dissociation by 'comoving' mesons. This leads to the final result that the total $J/\Psi$ suppression at $\sqrt{s}$ = 200 GeV as a function of centrality is slightly less than the suppression seen at SPS energies by the NA50 Collaboration, where the 'comover' dissociation is substantial and the backward channels play no role. Furthermore, even in case that all directly produced $J/\Psi$ mesons dissociate immediately (or are not formed as a mesonic state), a sizeable amount of charmonia is found asymptotically due to the $D+\bar{D} \to J/\Psi$ + meson channels in central collisions of $Au+Au$ at $\sqrt{s}$ = 200 GeV which, however, is lower than the $J/\Psi$ yield expected from binary scaling of $pp$ collisions.Comment: 42 pages, including 14 eps figures, discussions extended and references added, to be published in Phys. Rev.

Comparison of space-time evolutions of hot/dense matter in sNN\sqrt{s_{NN}}=17 and 130 GeV relativistic heavy ion collisions based on a hydrodynamical model

Based on a hydrodynamical model, we compare 130 GeV/$A$ Au+Au collisions at RHIC and 17 GeV/$A$ Pb+Pb collisions at SPS. The model well reproduces the single-particle distributions of both RHIC and SPS. The numerical solution indicates that huge amount of collision energy in RHIC is mainly used to produce a large extent of hot fluid rather than to make a high temperature matter; longitudinal extent of the hot fluid in RHIC is much larger than that of SPS and initial energy density of the fluid is only 5% higher than the one in SPS. The solution well describes the HBT radii at SPS energy but shows some deviations from the ones at RHIC.Comment: 28 pages, 21 figures, REVTeX4, one figure is added and some figures are replace

Collective flow and two-pion correlations from a relativistic hydrodynamic model with early chemical freeze out

We investigate the effect of early chemical freeze-out on radial flow, elliptic flow and HBT radii by using a fully three dimensional hydrodynamic model. When we take account of the early chemical freeze-out, the space-time evolution of temperature in the hadron phase is considerably different from the conventional model in which chemical equilibrium is always assumed. As a result, we find that radial and elliptic flows are suppressed and that the lifetime and the spatial size of the fluid are reduced. We analyze the p_t spectrum, the differential elliptic flow, and the HBT radii at the RHIC energy by using hydrodynamics with chemically non-equilibrium equation of state.Comment: One subsection and two figures adde

Global Observations from PHOBOS

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 $dN/d\eta'$ ($\eta' \equiv \eta-y_{beam}$), 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).Comment: QM2002 plenary talk, 10 pages, 11 figure

Genuine Correlations of Like-Sign Particles in Hadronic Z0 Decays

Correlations among hadrons with the same electric charge produced in Z0 decays are studied using the high statistics data collected from 1991 through 1995 with the OPAL detector at LEP. Normalized factorial cumulants up to fourth order are used to measure genuine particle correlations as a function of the size of phase space domains in rapidity, azimuthal angle and transverse momentum. Both all-charge and like-sign particle combinations show strong positive genuine correlations. One-dimensional cumulants initially increase rapidly with decreasing size of the phase space cells but saturate quickly. In contrast, cumulants in two- and three-dimensional domains continue to increase. The strong rise of the cumulants for all-charge multiplets is increasingly driven by that of like-sign multiplets. This points to the likely influence of Bose-Einstein correlations. Some of the recently proposed algorithms to simulate Bose-Einstein effects, implemented in the Monte Carlo model PYTHIA, are found to reproduce reasonably well the measured second- and higher-order correlations between particles with the same charge as well as those in all-charge particle multiplets.Comment: 26 pages, 6 figures, Submitted to Phys. Lett.

Counterpoint. Early intervention for psychosis risk syndromes: Minimizing risk and maximizing benefit

Background: Malhi et al. in this issue critique the clinical high risk (CHR) syndrome for psychosis. Method: Response to points of critique. Results: We agree that inconsistency in CHR nomenclature should be minimized. We respectfully disagree on other points. In our view: a) individuals with CHR and their families need help, using existing interventions, even though we do not yet fully understand disease mechanisms; b) substantial progress has been made in identification of biomarkers; c) symptoms used to identify CHR are specific to psychotic illnesses; d) CHR diagnosis is not “extremely difficult”; e) the pattern of progression, although heterogenous, is discernible; f) “psychosis-like symptoms” are common but are not used to identify CHR; and g) on the point described as ‘the real risk,’ CHR diagnosis does not frequently cause harmful stigma. Discussion: Malhi et al.'s arguments do not fairly characterize progress in the CHR field nor efforts to minimize stigma. That said, much work remains in areas of consistent nomenclature, mechanisms of disease, dissecting heterogeneity, and biomarkers. With regard to what the authors term the “real risk” of stigma associated with a CHR “label,” however, our view is that avoiding words like “risk” and “psychosis” reinforces the stigma that both they and we mean to oppose. Moreover, patients and their families benefit from being given a term that describes what is happening to them

Long-range Angular Correlations On The Near And Away Side In P-pb Collisions At √snn=5.02 Tev

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