495 research outputs found
The ring imaging Cherenkov detector for the BRAHMS experiment at RHIC
A ring imaging Cherenkov counter, to be read out by four 100-channel PMTs, is
a key element of the BRAHMS experiment. We report here the most recent results
obtained tested at the BNL AGS using several radiator gases, including the
heavy fluorocarbon C4F10. Ring radii were measured for different particles
(pions, muons, and electrons) for momenta ranging from 2 to 12 GeV/c employing
pure C4F10 as radiator.Comment: 3 pages 3 figure
Proton stopping in C+C, d+C, C+Ta and d+Ta collisions at 4.2A GeV/c
The shape of proton rapidity distributions is analysed in terms of their
Gaussian components, and the average rapidity loss is determined in order to
estimate the amount of stopping in C+C, d+C, C+Ta and d+Ta collisions at 4.2A
GeV/c. Three Gaussians correspond to the nuclear transparency and describe well
all peripheral and also C+C central collisions. Two-component shape is obtained
in case of d+C and C+Ta central collisions. Finally one Gaussian, found in d+Ta
central collisions, corresponds to the full stopping. The calculated values of
the average rapidity loss support the qualitative relationship between the
number of Gaussian components and the corresponding stopping power. It is also
observed, in central collisions, that the average rapidity loss increases with
the ratio of the number of target and the number of projectile participants.Comment: 9 pages REVTeX, 1 PS figure replaced, to be published in Phys.Rev.
Single-Transverse Spin Asymmetry in Dijet Correlations at Hadron Colliders
We present a phenomenological study of the single-transverse spin asymmetry
in azimuthal correlations of two jets produced nearly "back-to-back" in pp
collisions at RHIC. We properly take into account the initial- and final-state
interactions of partons that can generate this asymmetry in QCD
hard-scattering. Using distribution functions fitted to the existing
single-spin data, we make predictions for various weighted single-spin
asymmetries in dijet correlations that are now readily testable at RHIC.Comment: 14 pages, 2 figure
The Spectator Electromagnetic Effect on Charged Pion Spectra in Peripheral Ultrarelativistic Heavy-Ion Collisions
We estimate the electromagnetic effect of the spectator charge on the
momentum spectra of and produced in peripheral Pb+Pb collisions
at SPS energies. We find that the effect is large and results in strongly
varying structures in the dependence of the ratio,
especially at low transverse momenta where a deep valley in the above ratio is
predicted at 0.15 -- 0.20.
It appears that the effect depends on initial conditions. Thus, it provides
new information on the space and time evolution of the non-perturbative pion
creation process.Comment: 20 pages and 8 figure
Single Transverse-Spin Asymmetries at Large-x
The large- behavior of the transverse-momentum dependent quark
distributions is analyzed in the factorization-inspired perturbative QCD
framework, particularly for the naive time-reversal-odd quark Sivers function
which is responsible for the single transverse-spin asymmetries in various
semi-inclusive hard processes. By examining the dominant hard gluon exchange
Feynman diagrams, and using the resulting power counting rule, we find that the
Sivers function has power behavior at , which is one power
of suppressed relative to the unpolarized quark distribution. These
power-counting results provide important guidelines for the parameterization of
quark distributions and quark-gluon correlations.Comment: 20 pages, 4 figure
Single Spin Asymmetry Scaling in the Forward Rapidity Region at RHIC
We investigate the scaling properties in inclusive hadron production and the
associated single transverse spin asymmetry in the forward rapidity region at
RHIC. We find that the spin-averaged experimental data in both and
collisions demonstrates a transverse-momentum-dependent geometric scaling. We
introduce the transverse momentum dependent Collins fragmentation function to
study the scaling of the single transverse spin asymmetries. The general
feature of the scaling analysis is consistent with the experimental
observations, in particular, for the transverse momentum dependence of the spin
asymmetries at RHIC energy. We further propose to probe the saturation scale of
nucleus by measuring the spin asymmetry normalized by that in scattering
at low transverse momentum.Comment: 13 pages, 4 figure
Single Transverse-Spin Asymmetry in Drell-Yan Production at Large and Moderate Transverse Momentum
We study the single-transverse spin asymmetry for the Drell-Yan process. We
consider production of the lepton pair at large transverse momentum,
, where is the pair's mass. The spin asymmetry is then of
higher twist and may be generated by twist-three quark-gluon correlation
functions. Expanding the result for , we make contact with the
transverse-momentum-dependent QCD factorization involving the so-called Sivers
functions. We find that the two mechanisms, quark-gluon correlations on one
hand and the Sivers effect on the other, contain the same physics in this
region. This ties the two together and imposes an important constraint on
phenomenological studies of single transverse spin asymmetries.Comment: 29 pages, 10 figure
Is Strangeness still interesting at RHIC ?
With the advent of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven
National Laboratory (BNL), Heavy Ion Physics will enter a new energy regime.
The question is whether the signatures proposed for the discovery of a phase
transition from hadronic matter to a Quark Gluon Plasma (QGP), that were
established on the basis of collisions at the BEVALAC, the AGS, and the SPS,
respectively, are still useful and detectable at these high incident energies.
In the past two decades, measurements related to strangeness formation in the
collision were advocated as potential signatures and were tested in numerous
fixed target experiments at the AGS and the SPS. In this article I will review
the capabilities of the RHIC detectors to measure various aspects of
strangeness, and I will try to answer the question whether the information
content of those measurements is comparable to the one at lower energies.Comment: 12 pages, 7 figures, Invited Talk at the IV International Conference
on Strangeness in Quark Matter, Padova (Italy), July 20-24, 199
Fusion of light exotic nuclei at near-barrier energies : effect of inelastic excitation
The effect of inelastic excitation of exotic light projectiles (proton- as
well as neutron-rich) F and Be on fusion with heavy target has
been studied at near-barrier energies. The calculations have been performed in
the coupled channels approach where, in addition to the normal coupling of the
ground state of the projectile to the continuum, inelastic excitation of the
projectile to the bound excited state and its coupling to the continuum have
also been taken into consideration. The inclusion of these additional couplings
has been found to have significant effect on the fusion excitation function of
neutron-rich Be on Pb whereas the effect has been observed to be
nominal for the case of proton-rich F on the same target. The pronounced
effect of the channel coupling on the fusion process in case of Be is
attributed to its well-developed halo structure.Comment: 9 pages, 3 figures, Revtex.st
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