Event anisotropy in 4.2A GeV/c C+C collisions

The directed and elliptic flow of protons and negative pions in 4.2A GeV/c C+C collisions is studied using the Fourier analysis of azimuthal distributions. It is found that the protons exhibit pronounced directed flow, while the flow of pions is either non existent or too weak to be detected experimentally. Also, it is found that in the entire rapidity interval the elliptic flow is very small if not zero. These results are confirmed by the Quark-Gluon-String Model (QGSM) and the relativistic transport model (ART 1.0), except that these models predict very weak antiflow of pions. The more detailed comparison with the QGSM suggests that the decay of resonances and rescattering of secondaries dominantly determine the proton and negative pion flow at this energy.Comment: 7 pages, 3 figures, TeX file changed from double to single-spacin

Correlator Analysis of Multiparticle Events

A procedure for the evaluation of correlators of any order in a reasonable computer time is presented. Connection between correlators and fluctuations of the event mean values of observables is discussed. Extension of the procedure to event-by-event approach is suggested. The usefulness of the method is demonstrated using the events simulated within various models of multipaticle production.Comment: LaTeX, 15 pages including 4 table

Light-Front Analysis of pi^{-} Mesons Produced in Mg - Mg Collisions at 4.3 a Gev/c

Light-front analysis of pi^{-} mesons in Mg-Mg collisions is carried out. The phase space of secondary pions is naturally divided into two parts in one of which the thermal equilibration assumption seems to be in a good agreement with data. Corresponding temperatures are extracted and compared to the results of other experiments. The experimental results have been compared with the predictions of the Quark Gluon String Model (QGSM) and satisfactory agreement between the experimental data and the model has been found.Comment: 14 pages with 7 postscript figures. accepted for publication in Nucl. Phys.

Synchonisation of Resonances with Thresholds

The mechanism by which a resonance may be attracted to a sharp threshold is described with several examples. It involves a threshold cusp interfering constructively with either or both (i) a resonance produced via confinement, (ii) attractive t- and u-channel exchanges. More generally, it is suggested that resonances are eigenstates generated by mixing between confined states and long-range meson and baryon exchanges.Comment: 8 pages, 4 figures. For Meson08 Proceedings. One important typo correcte

Microscopic study of freeze-out in relativistic heavy ion collisions at SPS energies

The freeze-out conditions in the light (S+S) and heavy (Pb+Pb) colliding systems of heavy nuclei at 160 AGeV/$c$ are analyzed within the microscopic Quark Gluon String Model (QGSM). We found that even for the most heavy systems particle emission takes place from the whole space-time domain available for the system evolution, but not from the thin ''freeze-out hypersurface", adopted in fluid dynamical models. Pions are continuously emitted from the whole volume of the reaction and reflect the main trends of the system evolution. Nucleons in Pb+Pb collisions initially come from the surface region. For both systems there is a separation of the elastic and inelastic freeze-out. The mesons with large transverse momenta, $p_t$, are predominantly produced at the early stages of the reaction. The low $p_t$-component is populated by mesons coming mainly from the decay of resonances. This explains naturally the decreasing source sizes with increasing $p_t$, observed in HBT interferometry. Comparison with S+S and Au+Au systems at 11.6 AGeV/$c$ is also presented.Comment: REVTEX, 26 pages incl. 9 figures and 2 tables, to be published in the Physical Review

The initial state of ultra-relativistic heavy ion collision

A model for energy, pressure and flow velocity distributions at the beginning of ultra-relativistic heavy ion collisions is presented, which can be used as an initial condition for hydrodynamic calculations. Our model takes into account baryon recoil for both target and projectile, arising from the acceleration of partons in an effective field, produced in the collision. The typical field strength (string tension) for RHIC energies is about 5-12 GeV/fm, what allows us to talk about "string ropes". The results show that a QGP forms a tilted disk, such that the direction of the largest pressure gradient stays in the reaction plane, but deviates from both the beam and the usual transverse flow directions. Such initial conditions may lead to the creation of "antiflow" or "third flow component".Comment: 28 pages, 9 figures. The presentation has been changed considerably. Some parts of the model have been reformulated, what led to modifications in several equations: (20-38), Apps. A, B. All the figures have been changed from 100 GeV/nucl initial energy to the achieved RHIC energy of 65 GeV/nucl. The last subplots in the Figs. 3, 4, 5, 6 present E=T^{00} in the laboratory frame now, instead of the energy density in the local rest frame, e, shown in the initial version. We also added the App. C to clarify the transformation from space-time to lightcone coordinates and bac

Cross-sections for nuclide production in 56Fe target irradiated by 300, 500,750, 1000, 1500, and 2600 MeV protons compared with data on hydrogen target irradiation by 300, 500, 750, 1000, and 1500 MeV/nucleon 56Fe ions

Cross-sections for radioactive nuclide production in 56Fe(p,x) reactions at 300, 500, 750, 1000, 1500, and 2600 MeV were measured using the ITEP U-10 proton accelerator. In total, 221 independent and cumulative yields of products of half-lives from 6.6 min to 312 days have been obtained via the direct-spectrometry method. The measured data have been compared with the experimental data obtained elsewhere by the direct and inverse kinematics methods and with calculations by 15 codes, namely: MCNPX (INCL, CEM2k, BERTINI, ISABEL), LAHET (BERTINI, ISABEL), CEM03 (.01, .G1, .S1), LAQGSM03 (.01, .G1, >.S1), CASCADE-2004, LAHETO, and BRIEFF. Most of our data are in a good agreement with the inverse kinematics results and disprove the results of some earlier activation measurements that were quite different from the inverse kinematics measurements. The most significant calculation-to-experiment differences are observed in the yields of the A<30 light nuclei, indicating that further improvements in nuclear reaction models are needed, and pointing out as well to a necessity of more complete measurements of such reactions.Comment: 53 pages, 9 figures, 6 tables, only pdf file, submitted to Phys. Rev.

Universal Mass Dependence for Particle Production Rates in e+e−e^+e^-, pppp and AAAA Collisions from the Quark-Gluon Plasma Perspective

It is demonstrated that universal mass dependence for meson and baryon inclusive cross-sections advocated recently in $e^+e^-$ annihilation and in hadronic reactions is consistent also with heavy ion collisions data and can therefore be used as a reference for quark-gluon plasma studies.Comment: LaTex file, 8 pages, hard copies of 3 (multiple) figures available on request to [email protected] or [email protected]. PROCSLA.STY file appended at the end of the LaTeX file for convenienc

The origin of short-lived radionuclides and the astrophysical environment of solar system formation

Based on early solar system abundances of short-lived radionuclides (SRs), such as $^{26}$Al (T$_{1/2} = 0.74$ Myr) and $^{60}$Fe (T$_{1/2} = 1.5$ Myr), it is often asserted that the Sun was born in a large stellar cluster, where a massive star contaminated the protoplanetary disk with freshly nucleosynthesized isotopes from its supernova (SN) explosion. To account for the inferred initial solar system abundances of short-lived radionuclides, this supernova had to be close ($\sim$ 0.3 pc) to the young ($\leqslant$ 1 Myr) protoplanetary disk. Here we show that massive star evolution timescales are too long, compared to typical timescales of star formation in embedded clusters, for them to explode as supernovae within the lifetimes of nearby disks. This is especially true in an Orion Nebular Cluster (ONC)-type of setting, where the most massive star will explode as a supernova $\sim$ 5 Myr after the onset of star formation, when nearby disks will have already suffered substantial photoevaporation and/or formed large planetesimals. We quantify the probability for {\it any} protoplanetary disk to receive SRs from a nearby supernova at the level observed in the early solar system. Key constraints on our estimate are: (1) SRs have to be injected into a newly formed ($\leqslant$ 1 Myr) disk, (2) the disk has to survive UV photoevaporation, and (3) the protoplanetary disk must be situated in an enrichment zone permitting SR injection at the solar system level without disk disruption. The probability of protoplanetary disk contamination by a supernova ejecta is, in the most favorable case, 3 $\times$ 10$^{-3}$