977 research outputs found
Expected Performance of CryoArray
WIMP-nucleon cross sections below 10^(-9) pb may be probed by ton-scale
experiments with low thresholds and background rates ~20 events per year. An
array of cryogenic detectors ("CryoArray") could perform well enough to reach
this goal. Sufficient discrimination and background suppression of photons has
already been demonstrated. Reduction of neutron backgrounds may be achieved by
siting the experiment deep enough. Removal of the surface-electron backgrounds
alone has not yet been demonstrated, but the reductions required even for this
troublesome background are quite modest and appear achieveable.Comment: 4 pages, 2 figures. Talk at DM2002 Conference, Marina del Rey, CA,
Feb 20-22, 200
Aspects of Heavy Quark Production in Polarized Proton-Proton Collisions
We examine the spin-dependence of b-quark production at large transverse
momentum in polarized proton-proton collisions. The leading-order (LO) 2 -> 2
subprocesses, g + g -> Q + Q-bar and q+ q-bar -> Q + Q-bar have a large
`analyzing power', as measured by the average spin-spin asymmetry ,
at large p_T, approaching -100%. The contributions from next-to-leading order
(NLO) 2 -> 3 processes are also discussed and found to be dominated at large
transverse momentum by subprocesses with a large and positive partonic level
spin asymmetry leading to strong cancellations with the LO predictions. The
results suggest that b-quark production might constitute an interesting test of
the spin-dependence of NLO QCD but they also point up the importance of a full
calculation of the complete O(\alpha_S^3) spin-dependent corrections for a
successful extraction of the polarized gluon distribution. Similarities to
gluino pair production are also briefly discussed.Comment: 23 pages (LaTeX) + 8 postscript figures encoded through uufiles;
PSU/TH/135, TAUP 2099-9
Momentum Distributions in
We apply the Green function formalism for production and decay
near threshold in a study of the effects due to the momentum dependent width
for such a system. We point out that these effects are likely to be much
smaller than expected from the reduction of the available phase space. The
Lippmann--Schwinger equation for the QCD chromostatic potential is solved
numerically for partial wave. We compare the results on the total cross
section, top quark intrinsic momentum distributions and on the energy spectra
of bosons from top quark decays with those obtained for the constant width.Comment: 12 pages (without figures) (11 (sub)figures available on request),
Karlsruhe preprint TTP93-11, hep-ph/yymmnn
Brane cosmology with an anisotropic bulk
In the context of brane cosmology, a scenario where our universe is a
3+1-dimensional surface (the ``brane'') embedded in a five-dimensional
spacetime (the ``bulk''), we study geometries for which the brane is
anisotropic - more specifically Bianchi I - though still homogeneous. We first
obtain explicit vacuum bulk solutions with anisotropic three-dimensional
spatial slices. The bulk is assumed to be empty but endowed with a negative
cosmological constant. We then embed Z_2-symmetric branes in the anisotropic
spacetimes and discuss the constraints on the brane energy-momentum tensor due
to the five-dimensional anisotropic geometry. We show that if the bulk is
static, an anisotropic brane cannot support a perfect fluid. However, we find
that for some of our bulk solutions it is possible to embed a brane with a
perfect fluid though its energy density and pressure are completely determined
by the bulk geometry.Comment: 20 pages, 1 figur
Prospects of Open Charm Production at GSI-FAIR and J-PARC
We present a detailed phenomenological study of the prospects of open charm
physics at the future and facilities GSI-FAIR and J-PARC,
respectively. In particular, we concentrate on differential cross sections and
the charge and longitudinal double-spin asymmetries at next-to-leading order
accuracy. Theoretical uncertainties for the proposed observables are estimated
by varying the charm quark mass and the renormalization and factorization
scales.Comment: 11 pages, 13 figure
A High Luminosity e+e- Collider to study the Higgs Boson
A strong candidate for the Standard Model Scalar boson, H(126), has been
discovered by the Large Hadron Collider (LHC) experiments. In order to study
this fundamental particle with unprecedented precision, and to perform
precision tests of the closure of the Standard Model, we investigate the
possibilities offered by An e+e- storage ring collider. We use a design
inspired by the B-factories, taking into account the performance achieved at
LEP2, and imposing a synchrotron radiation power limit of 100 MW. At the most
relevant centre-of-mass energy of 240 GeV, near-constant luminosities of 10^34
cm^{-2}s^{-1} are possible in up to four collision points for a ring of 27km
circumference. The achievable luminosity increases with the bending radius, and
for 80km circumference, a luminosity of 5 10^34 cm^{-2}s^{-1} in four collision
points appears feasible. Beamstrahlung becomes relevant at these high
luminosities, leading to a design requirement of large momentum acceptance both
in the accelerating system and in the optics. The larger machine could reach
the top quark threshold, would yield luminosities per interaction point of
10^36 cm^{-2}s^{-1} at the Z pole (91 GeV) and 2 10^35 cm^{-2}s^{-1} at the W
pair production threshold (80 GeV per beam). The energy spread is reduced in
the larger ring with respect to what is was at LEP, giving confidence that beam
polarization for energy calibration purposes should be available up to the W
pair threshold. The capabilities in term of physics performance are outlined.Comment: Submitted to the European Strategy Preparatory Group 01-04-2013 new
version as re-submitted to PRSTA
The Landau–Lifshitz equation in atomistic models
The Landau–Lifshitz (LL) equation, originally proposed at the macrospin level, is increasingly used in Atomistic
Spin Dynamic (ASD) models. These models are based on a spin Hamiltonian featuring atomic spins of
fixed length, with the exchange introduced using the Heisenberg formalism. ASD models are proving a powerful
approach to the fundamental understanding of ultrafast magnetization dynamics, including the prediction of the
thermally induced magnetization switching phenomenon in which the magnetization is reversed using an ultrafast
laser pulse in the absence of an externally applied field. This paper outlines the ASD model approach and
considers the role and limitations of the LL equation in this context
A two-mass expanding exact space-time solution
In order to understand how locally static configurations around
gravitationally bound bodies can be embedded in an expanding universe, we
investigate the solutions of general relativity describing a space-time whose
spatial sections have the topology of a 3-sphere with two identical masses at
the poles. We show that Israel junction conditions imply that two spherically
symmetric static regions around the masses cannot be glued together. If one is
interested in an exterior solution, this prevents the geometry around the
masses to be of the Schwarzschild type and leads to the introduction of a
cosmological constant. The study of the extension of the Kottler space-time
shows that there exists a non-static solution consisting of two static regions
surrounding the masses that match a Kantowski-Sachs expanding region on the
cosmological horizon. The comparison with a Swiss-Cheese construction is also
discussed.Comment: 15 pages, 5 figures. Replaced to match the published versio
CDMS, Supersymmetry and Extra Dimensions
The CDMS experiment aims to directly detect massive, cold dark matter
particles originating from the Milky Way halo. Charge and lattice excitations
are detected after a particle scatters in a Ge or Si crystal kept at ~30 mK,
allowing to separate nuclear recoils from the dominating electromagnetic
background. The operation of 12 detectors in the Soudan mine for 75 live days
in 2004 delivered no evidence for a signal, yielding stringent limits on dark
matter candidates from supersymmetry and universal extra dimensions. Thirty Ge
and Si detectors are presently installed in the Soudan cryostat, and operating
at base temperature. The run scheduled to start in 2006 is expected to yield a
one order of magnitude increase in dark matter sensitivity.Comment: To be published in the proceedings of the 7th UCLA symposium on
sources and detection of dark matter and dark energy in the universe, Marina
del Rey, Feb 22-24, 200
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