2,562 research outputs found
Hot Topics in Ultra-Peripheral Collisions
Ultra-peripheral collisions of relativistic heavy ions involve long-ranged
electromagnetic interactions at impact parameters too large for hadronic
interactions to occur. The nuclear charges are large; with the coherent
enhancement, the cross sections are also large. Many types of photonuclear and
purely electromagnetic interactions are possible. We present here an
introduction to ultra-peripheral collisions, and present four of the most
compelling physics topics. This note developed from a discussion at a workshop
on ``Electromagnetic Probes of Fundamental Physics,'' in Erice, Italy, Oct.
16-21, 2001.Comment: 7 pages, with 3 figures. This developed from a discussion at the
workshop on "Electromagnetic Probes of Fundamental Physics," Oct. 16-21,
Erice, Ital
Photoproduction at collider energies: from RHIC and HERA to the LHC
We present the mini-proceedings of the workshop on ``Photoproduction at
collider energies: from RHIC and HERA to the LHC'' held at the European Centre
for Theoretical Studies in Nuclear Physics and Related Areas (ECT*, Trento)
from January 15 to 19, 2007. The workshop gathered both theorists and
experimentalists to discuss the current status of investigations of high-energy
photon-induced processes at different colliders (HERA, RHIC, and Tevatron) as
well as preparations for extension of these studies at the LHC. The main
physics topics covered were: (i) small- QCD in photoproduction studies with
protons and in electromagnetic (aka. ultraperipheral) nucleus-nucleus
collisions, (ii) hard diffraction physics at hadron colliders, and (iii)
photon-photon collisions at very high energies: electroweak and beyond the
Standard Model processes. These mini-proceedings consist of an introduction and
short summaries of the talks presented at the meeting
Performance of prototypes for the ALICE electromagnetic calorimeter
The performance of prototypes for the ALICE electromagnetic sampling
calorimeter has been studied in test beam measurements at FNAL and CERN. A
array of final design modules showed an energy resolution of about
11% / 1.7 % with a uniformity of the response
to electrons of 1% and a good linearity in the energy range from 10 to 100 GeV.
The electromagnetic shower position resolution was found to be described by 1.5
mm 5.3 mm /. For an electron identification
efficiency of 90% a hadron rejection factor of was obtained.Comment: 10 pages, 10 figure
Event Reconstruction in the PHENIX Central Arm Spectrometers
The central arm spectrometers for the PHENIX experiment at the Relativistic
Heavy Ion Collider have been designed for the optimization of particle
identification in relativistic heavy ion collisions. The spectrometers present
a challenging environment for event reconstruction due to a very high track
multiplicity in a complicated, focusing, magnetic field. In order to meet this
challenge, nine distinct detector types are integrated for charged particle
tracking, momentum reconstruction, and particle identification. The techniques
which have been developed for the task of event reconstruction are described.Comment: Accepted for publication in Nucl. Instrum. A. 34 pages, 23 figure
Centrality and dE_{T}/d\etadN_{ch}/d\eta$ in Heavy Ion Collisions at Mid-Rapidity
The PHENIX experiment at RHIC has measured transverse energy and charged
particle multiplicity at mid-rapidity in Au + Au collisions at
= 19.6, 130, 62.4 and 200 GeV as a function of centrality. The presented
results are compared to measurements from other RHIC experiments, and
experiments at lower energies. The dependence of
and per pair of participants is consistent with logarithmic
scaling for the most central events. The centrality dependence of
and is similar at all measured incident
energies. At RHIC energies the ratio of transverse energy per charged particle
was found independent of centrality and growing slowly with . A
survey of comparisons between the data and available theoretical models is also
presented.Comment: Proccedings of the Workshop: Focus on Multiplcity at Bari, Italy,
June 17-19,2004. To be submitted to the Jornal of Physics, "Conference
series". Includes: 20 Pages, 15 figures, 3 Tables, 80 Referencie
Nuclear dependence of the transverse-single-spin asymmetry for forward neutron production in polarized collisions at GeV
During 2015 the Relativistic Heavy Ion Collider (RHIC) provided collisions of
transversely polarized protons with Au and Al nuclei for the first time,
enabling the exploration of transverse-single-spin asymmetries with heavy
nuclei. Large single-spin asymmetries in very forward neutron production have
been previously observed in transversely polarized collisions at
RHIC, and the existing theoretical framework that was successful in describing
the single-spin asymmetry in collisions predicts only a moderate
atomic-mass-number () dependence. In contrast, the asymmetries observed at
RHIC in collisions showed a surprisingly strong dependence in
inclusive forward neutron production. The observed asymmetry in Al
collisions is much smaller, while the asymmetry in Au collisions is a
factor of three larger in absolute value and of opposite sign. The interplay of
different neutron production mechanisms is discussed as a possible explanation
of the observed dependence.Comment: 315 authors, 8 pages, 4 figures, 1 table. v2 is version accepted for
publication in Phys. Rev. Lett. Plain text data tables for the points plotted
in figures for this and previous PHENIX publications are (or will be)
publicly available at http://www.phenix.bnl.gov/papers.htm
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