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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
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
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 (b2R), 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,
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