Classifiers for centrality determination in proton-nucleus and nucleus-nucleus collisions

Centrality, as a geometrical property of the collision, is crucial for the physical interpretation of nucleus-nucleus and proton-nucleus experimental data. However, it cannot be directly accessed in event-by-event data analysis. Common methods for centrality estimation in A-A and p-A collisions usually rely on a single detector (either on the signal in zero-degree calorimeters or on the multiplicity in some semi-central rapidity range). In the present work, we made an attempt to develop an approach for centrality determination that is based on machine-learning techniques and utilizes information from several detector subsystems simultaneously. Different event classifiers are suggested and evaluated for their selectivity power in terms of the number of nucleons-participants and the impact parameter of the collision. Finer centrality resolution may allow to reduce impact from so-called volume fluctuations on physical observables being studied in heavy-ion experiments like ALICE at the LHC and fixed target experiment NA61/SHINE on SPS.Comment: To be published in proceedings of the "XIIth Quark Confinement and the Hadron Spectrum" conference (Thessaloniki, 2016

Nucleus-Nucleus Bremsstrahlung from Ultrarelativistic Collisions

The bremsstrahlung produced when heavy nuclei collide is estimated for central collisions at the Relativistic Heavy Ion Collider. Soft photons can be used to infer the rapidity distribution of the outgoing charge. An experimental design is outlined.Comment: 12 pages, 7 figures, uses revte

Strangeness in ultrarelativistic nucleus-nucleus collisions

I discuss strangeness production in nucleus-nucleus reactions at ultrarelativistic energies (up to 200 AGeV). In these reactions matter may be created with densities and temperatures in the transition region between quark-gluon plasma (QGP) and hadron gas. Strange anti-baryon enhancement at 200 AGeV and probably even more so at 10 AGeV signals importance of interactions beyond hadron gas dynamics. The systematics of strangeness production indicates that energy and baryon density are key variables while the size of the production volume plays no visible role. Analysis of strangeness appears useful to explore thermalization, flow and the post-equilibrium stage in ultrarelativistic nucleus-nucleus collisions.Comment: 13 pages LaTeX including 6 postscript figures; needs style files espcrc1,floatfig,epsfig. Invited talk presented at 6th International Conference on Nucleus-Nucleus Collisions at Gatlinburg, June 2-6, 1997. To be published in Proceedings in Nuclear Physics

Coherent Interactions in Nucleus-Nucleus Collisions

At the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory and at the Large Hadron Collider (LHC) at CERN, particles will be produced in coherent and diffractive nuclear interactions. In extremely peripheral nuclear collisions (b$>$2R), coherent interactions occur at very high rates and are dominated by photon-Pomeron or photon-meson processes. In these reactions, the photon and the Pomeron/meson from the electromagnetic and nuclear fields couple coherently to all nucleons. The rates for photonuclear interactions are roughly two orders of magnitude larger than for two-photon interactions at comparable center-of-mass energies.Comment: 10 pages, 4 figures, Presented at the IXth Blois Workshop on Elastic and Diffractive Scattering, Pruhonice near Prague, Czech Republic, June 9-15, 200

Nucleus-nucleus collisions at highest energies

The microscopic phasespace approach URQMD is used to investigate the stopping power and particle production in heavy systems at SPS and RHIC energies. We find no gap in the baryon rapidity distribution even at RHIC. For CERN energies URQMD shows a pile up of baryons and a supression of multi-nucleon clusters at midrapidity