488 research outputs found
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 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
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 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
Fusion of light proton-rich exotic nuclei at near-barrier energies
We study theoretically fusion of the light proton-rich exotic nuclei F
and B at near-barrier energies in order to investigate the possible role of
breakup processes on their fusion cross sections. To this end, coupled channel
calculations are performed considering the couplings to the breakup channels of
these projectiles. In case of F, the coupling arising out of the
inelastic excitation from the ground state to the bound excited state and its
couplings to the continuum have also been taken into consideration. It is found
that the inelastic excitation/breakup of F affect the fusion cross
sections very nominally even for a heavy target like Pb. On the other hand,
calculations for fusion of the one-proton halo nucleus B on a Pb target
show a significant suppression of the complete fusion cross section above the
Coulomb barrier. This is due to the larger breakup probability of B as
compared to that of F. However, even for B, there is little change
in the complete fusion cross sections as compared to the no-coupling case at
sub-barrier energies.Comment: 11 pages, 3 figures, Revtex.st
Density and expansion effects on pion spectra in relativistic heavy-ion collisions
We compute the pion inclusive momentum distribution in heavy-ion collisions
at AGS energies, assuming thermal equilibrium and accounting for density and
expansion effects at the time of decoupling. We compare to data on mid rapidity
charged pions produced in central Au + Au collisions and find a very good
agreement. The shape of the distribution at low is explained in part as
an effect arising from the high mean pion density achieved in these reactions.
The difference between the positive and negative pion distributions in the same
region is attributed in part to the different average yields of each kind of
charged pions.Comment: Minor changes, typo in Fig. 2b corrected, version to appear in Phys.
Rev.
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
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The trigger supervisor: Managing triggering conditions in a high energy physics experiment
A trigger supervisor, implemented in VME-bus hardware, is described, which enables the host computer to dynamically control and monitor the trigger configuration for acquiring data from multiple detector partitions in a complex experiment
Semi-classical Characters and Optical Model Description of Heavy Ion Scattering, Direct Reactions, and Fusion at Near-barrier Energies
An approach is proposed to calculate the direct reaction (DR) and fusion
probabilities for heavy ion collisions at near-Coulomb-barrier energies as
functions of the distance of closest approach D within the framework of the
optical model that introduces two types of imaginary potentials, DR and fusion.
The probabilities are calculated by using partial DR and fusion cross sections,
together with the classical relations associated with the Coulomb trajectory.
Such an approach makes it possible to analyze the data for angular
distributions of the inclusive DR cross section, facilitating the determination
of the radius parameters of the imaginary DR potential in a less ambiguous
manner. Simultaneous -analyses are performed of relevant data for the
O+Pb system near the Coulomb-barrier energy
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