458 research outputs found
Realistic Calculation of the hep Astrophysical Factor
The astrophysical factor for the proton weak capture on 3He is calculated
with correlated-hyperspherical-harmonics bound and continuum wave functions
corresponding to a realistic Hamiltonian consisting of the Argonne v18
two-nucleon and Urbana-IX three-nucleon interactions. The nuclear weak charge
and current operators have vector and axial-vector components, that include
one- and many-body terms. All possible multipole transitions connecting any of
the p-3He S- and P-wave channels to the 4He bound state are considered. The
S-factor at a p-3He center-of-mass energy of 10 keV, close to the Gamow-peak
energy, is predicted to be 10.1 10^{-20} keV b, a factor of five larger than
the standard-solar-model value. The P-wave transitions are found to be
important, contributing about 40 % of the calculated S-factor.Comment: 8 pages RevTex file, submitted to Phys. Rev. Let
Status of the LUX Dark Matter Search
The Large Underground Xenon (LUX) dark matter search experiment is currently
being deployed at the Homestake Laboratory in South Dakota. We will highlight
the main elements of design which make the experiment a very strong competitor
in the field of direct detection, as well as an easily scalable concept. We
will also present its potential reach for supersymmetric dark matter detection,
within various timeframes ranging from 1 year to 5 years or more.Comment: 4 pages, in proceedings of the SUSY09 conferenc
System size and centrality dependence of charged hadron transverse momentum spectra in Au+Au and Cu+Cu collisions at sqrt(s) = 62.4 and 200 GeV
We present transverse momentum distributions of charged hadrons produced in
Cu+Cu collisions at sqrt(s) = 62.4 and 200 GeV. The spectra are measured for
transverse momenta of 0.25 < p_T < 5.0 GeV/c at sqrt(s) = 62.4 GeV and 0.25 <
p_T < 7.0 GeV/c at sqrt(s) = 200 GeV, in a pseudo-rapidity range of 0.2 < eta <
1.4. The nuclear modification factor R_AA is calculated relative to p+p data at
both collision energies as a function of collision centrality. At a given
collision energy and fractional cross-section, R_AA is observed to be
systematically larger in Cu+Cu collisions compared to Au+Au. However, for the
same number of participating nucleons, R_AA is essentially the same in both
systems over the measured range of p_T, in spite of the significantly different
geometries of the Cu+Cu and Au+Au systems.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
System Size, Energy and Centrality Dependence of Pseudorapidity Distributions of Charged Particles in Relativistic Heavy Ion Collisions
We present the first measurements of the pseudorapidity distribution of
primary charged particles in Cu+Cu collisions as a function of collision
centrality and energy, \sqrtsnn = 22.4, 62.4 and 200 GeV, over a wide range of
pseudorapidity, using the PHOBOS detector. Making a global comparison of Cu+Cu
and Au+Au results, we find that the total number of produced charged particles
and the rough shape (height and width) of the pseudorapidity distributions are
determined by the number of nucleon participants. More detailed studies reveal
that a more precise matching of the shape of the Cu+Cu and Au+Au pseudorapidity
distributions over the full range of pseudorapidity occurs for the same
Npart/2A value rather than the same Npart value. In other words, it is the
collision geometry rather than just the number of nucleon participants that
drives the detailed shape of the pseudorapidity distribution and its centrality
dependence at RHIC energies.Comment: Submitted to Physical Review Letter
The ZEPLIN-III dark matter detector: instrument design, manufacture and commissioning
We present details of the technical design and manufacture of the ZEPLIN-III
dark matter experiment. ZEPLIN-III is a two-phase xenon detector which measures
both the scintillation light and the ionisation charge generated in the liquid
by interacting particles and radiation. The instrument design is driven by both
the physics requirements and by the technology requirements surrounding the use
of liquid xenon. These include considerations of key performance parameters,
such as the efficiency of scintillation light collection, restrictions placed
on the use of materials to control the inherent radioactivity levels,
attainment of high vacuum levels and chemical contamination control. The
successful solution has involved a number of novel design and manufacturing
features which will be of specific use to future generations of direct dark
matter search experiments as they struggle with similar and progressively more
demanding requirements.Comment: 25 pages, 19 figures. Submitted to Astropart. Phys. Some figures down
sampled to reduce siz
Identified charged antiparticle to particle ratios near midrapidity in Cu+Cu collisions at sqrt(s) = 62.4 and 200 GeV
Antiparticle to particle ratios for identified protons, kaons and pions at
sqrt(s) = 62.4 and 200 GeV in Cu+Cu collisions are presented as a function of
centrality for the midrapidity region of 0.2 < eta < 1.4. No strong dependence
on centrality is observed. For the / ratio at ~ 0.51 GeV/c, we
observe an average value of 0.50 +/- 0.003_(stat) +/- 0.04_(syst) and 0.77 +/-
0.008_(stat) +/- 0.05_(syst) for the 10% most central collisions of 62.4 and
200 GeV Cu+Cu, respectively. The values for all three particle species measured
at sqrt(s) = 200 GeV are in agreement within systematic uncertainties with that
seen in both heavier and lighter systems measured at the same RHIC energy. This
indicates that system size does not appear to play a strong role in determining
the midrapidity chemical freeze-out properties affecting the antiparticle to
particle ratios of the three most abundant particle species produced in these
collisions.Comment: 5 Pages, 4 figures Made changes to the figures to include the panel
numbers. Slight changes to the text. Updated data points from other
experiment
Pseudorapidity Distributions of Charged Particles in d + Au and p + p Collisions at = 200GeV
The measured pseudorapidity distributions of primary charged particles are
presented for d + Au and p + p collisions at 200 GeV
over a wide pseudorapidity range of 5.4. The results
for d + Au collisions are presented for minimum-bias events and as a function
of collision centrality. The measurements for p + p collisions are shown for
minimum-bias events. The ratio of the charged particle multiplicity in d + Au
and p + A collisions relative to that for inelastic p + p collisions is found
to depend only on , and it is remarkably independent of
collision energy and system mass. The deuteron and gold fragmentation regions
in d + Au collisions are in good agreement with proton nucleus data at lower
energies.Comment: 4 pages, 3 figures. To appear in the proceedings of Seventeenth
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions
(Quark Matter 2004), Oakland, California from January 11-17, 2004. Submitted
to Journal of Physics G: Nuclear and Particle Physic
Measurement of single electron emission in two-phase xenon
We present the first measurements of the electroluminescence response to the
emission of single electrons in a two-phase noble gas detector. Single
ionization electrons generated in liquid xenon are detected in a thin gas layer
during the 31-day background run of the ZEPLIN-II experiment, a two-phase xenon
detector for WIMP dark matter searches. Both the pressure dependence and
magnitude of the single-electron response are in agreement with previous
measurements of electroluminescence yield in xenon. We discuss different
photoionization processes as possible cause for the sample of single electrons
studied in this work. This observation may have implications for the design and
operation of future large-scale two-phase systems.Comment: 11 pages, 6 figure
Charged antiparticle to particle ratios near midrapidity in p+p collisions at sqrt(s_NN)=200 GeV
The ratios of the yields of primary charged antiparticles to particles have
been obtained for pions, kaons, and protons near midrapidity for p+p collisions
at sqrt(s_NN) = 200 GeV. Ratios of =1.000 +/- 0.012 (stat.) +/- 0.019
(syst.), =0.93 +/- 0.05 (stat.) +/- 0.03 (syst.), and =0.85 +/-
0.04 (stat.) +/- 0.03 (syst.) have been measured. The reported values represent
the ratio of the yields averaged over the rapidity range of 0.1<y_{pi}<1.3 and
0<y_{K,p}<0.8, and for transverse momenta of 0.1<p_T^{pi,K}<1.0 GeV/c and
0.3<p_T^{p}<1.0 GeV/c. Within the uncertainties, all three ratios are
consistent with the values measured in d+Au collisions at the same energy. The
data are compared to results from other collision systems and energies.Comment: 3 pages, 2 figures, 1 table, submitted to Phys. Rev.
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