529 research outputs found
\b{eta}-delayed three-proton decay of 31Ar
The beta decay of 31Ar, produced by fragmentation of a 36Ar beam at 880
MeV/nucleon, was investigated. Identified ions of 31Ar were stopped in a
gaseous time projection chamber with optical readout allowing to record decay
events with emission of protons. In addition to \b{eta}-delayed emission of one
and two protons we have clearly observed the beta-delayed three-proton branch.
The branching ratio for this channel in 31Ar is found to be 0.07(2)%.Comment: 5 pages, 3 figures, submitted to Physical Rev.
Higher Partial Waves in p+p->p+p+eta near Threshold
Exclusive measurements of the production of eta mesons in the p+p->p+p+eta
reaction have been carried out at excess energies of 16 and 37 MeV above
threshold. The deviations from phase space are dominated by the proton-proton
final state interaction and this influences particularly the energy
distribution of the eta meson. However, evidence is also presented at the
higher energy for the existence of an anisotropy in the angular distributions
of the eta meson and also of the final proton-proton pair, probably to be
associated with D-waves in this system interfering with the dominant S-wave
term. The sign of the eta angular anisotropy suggests that rho-exchange is
important for this reaction.Comment: 16 pages, LaTeX2e, 3 EPS Figures, Updated version, Accepted for
publication in Phys. Lett.
Challenges of beta-deformation
A brief review of problems, arising in the study of the beta-deformation,
also known as "refinement", which appears as a central difficult element in a
number of related modern subjects: beta \neq 1 is responsible for deviation
from free fermions in 2d conformal theories, from symmetric omega-backgrounds
with epsilon_2 = - epsilon_1 in instanton sums in 4d SYM theories, from
eigenvalue matrix models to beta-ensembles, from HOMFLY to super-polynomials in
Chern-Simons theory, from quantum groups to elliptic and hyperbolic algebras
etc. The main attention is paid to the context of AGT relation and its possible
generalizations.Comment: 20 page
Pion interferometry in Au+Au collisions at sqrt[sNN]=200GeV
We present a systematic analysis of two-pion interferometry in Au+Au collisions at sqrt[sNN]=200GeV using the STAR detector at Relativistic Heavy Ion Collider. We extract the Hanbury-Brown and Twiss radii and study their multiplicity, transverse momentum, and azimuthal angle dependence. The Gaussianness of the correlation function is studied. Estimates of the geometrical and dynamical structure of the freeze-out source are extracted by fits with blast-wave parametrizations. The expansion of the source and its relation with the initial energy density distribution is studied
Azimuthally sensitive Hanbury Brown-Twiss interferometry in Au+Au collisions at sqrt(s_{NN}) = 200 GeV
We present the results of a systematic study of the shape of the pion
distribution in coordinate space at freeze-out in Au+Au collisions at RHIC
using two-pion Hanbury Brown-Twiss (HBT) interferometry. Oscillations of the
extracted HBT radii vs. emission angle indicate sources elongated perpendicular
to the reaction plane. The results indicate that the pressure and expansion
time of the collision system are not sufficient to completely quench its
initial shape.Comment: 6 pages, 4 figures, published versio
Pion interferometry in Au+Au collisions at = 200 GeV
We present a systematic analysis of two-pion interferometry in Au+Au
collisions at = 200 GeV using the STAR detector at RHIC. We
extract the HBT radii and study their multiplicity, transverse momentum, and
azimuthal angle dependence. The Gaussianess of the correlation function is
studied. Estimates of the geometrical and dynamical structure of the freeze-out
source are extracted by fits with blast wave parameterizations. The expansion
of the source and its relation with the initial energy density distribution is
studied.Comment: 21 pages, 30 figures. As published in Physics Review
Rapidity and centrality dependence of proton and antiproton production from 197Au + 197Au collisions at √SNN = 130 GeV
We report on the rapidity and centrality dependence of proton and antiproton transverse mass distributions from 197Au + 197Au collisions at sqrt[sNN ]=130 GeV as measured by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). Our results are from the rapidity and transverse momentum range of |y| <0.5 and 0.35< pt <1.00 GeV/c . For both protons and antiprotons, transverse mass distributions become more convex from peripheral to central collisions demonstrating characteristics of collective expansion. The measured rapidity distributions and the mean transverse momenta versus rapidity are flat within |y| <0.5 . Comparisons of our data with results from model calculations indicate that in order to obtain a consistent picture of the proton (antiproton) yields and transverse mass distributions the possibility of prehadronic collective expansion may have to be taken into account
Evidence from d+Au measurements for final-state suppression of high hadrons in Au+Au collisions at RHIC
We report measurements of single-particle inclusive spectra and two-particle
azimuthal distributions of charged hadrons at high transverse momentum (high
) in minimum bias and central d+Au collisions at =200 GeV.
The inclusive yield is enhanced in d+Au collisions relative to binary-scaled
p+p collisions, while the two-particle azimuthal distributions are very similar
to those observed in p+p collisions. These results demonstrate that the strong
suppression of the inclusive yield and back-to-back correlations at high
previously observed in central Au+Au collisions are due to final-state
interactions with the dense medium generated in such collisions.Comment: Final journal version. Data tables for figures may be downloaded from
the STAR home page: http://www.star.bnl.gov --> Publications --> Access to
STAR published dat
Transverse-momentum dependent modification of dynamic texture in central Au+Au collisions at sqrt(S_NN)=200 GeV
Correlations in the hadron distributions produced in relativistic Au+Au
collisions are studied in the discrete wavelet expansion method. The analysis
is performed in the space of pseudorapidity (|eta| < 1) and azimuth (full 2 pi)
in bins of transverse momentum (p_t) from 0.14 < p_t < 2.1 GeV/c. In peripheral
Au+Au collisions a correlation structure ascribed to mini-jet fragmentation is
observed. It evolves with collision centrality and p_t in a way not seen before
which suggests strong dissipation of minijet fragmentation in the
longitudinally-expanding medium.Comment: 6 pages, 3 figure, accepted as Phys.Rev.C Rapid Communication. This
version fixes journal style issue
Transverse momentum and collision energy dependence of high hadron suppression in Au+Au collisions at ultrarelativistic energies
We report high statistics measurements of inclusive charged hadron production
in Au+Au and p+p collisions at \sqrtsNN=200 GeV. A large, approximately
constant hadron suppression is observed in central Au+Au collisions for
5\lt\pT\lt12 GeV/c. The collision energy dependence of the yields and the
centrality and \pT dependence of the suppression provide stringent constraints
on theoretical models of suppression. Models incorporating initial-state gluon
saturation or partonic energy loss in dense matter are largely consistent with
observations. We observe no evidence of \pT-dependent suppression, which may be
expected from models incorporating jet attentuation in cold nuclear matter or
scattering of fragmentation hadrons.Comment: Final journal version. Data tables for figures may be downloaded from
the STAR home page: http://www.star.bnl.gov --> Publications --> Access to
STAR published dat
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