144,911 research outputs found
A Study of the Quasi-elastic (e,e'p) Reaction on C, Fe and Au
We report the results from a systematic study of the quasi-elastic (e,e'p)
reaction on C, Fe and Au performed at Jefferson Lab. We
have measured nuclear transparency and extracted spectral functions (corrected
for radiation) over a Q range of 0.64 - 3.25 (GeV/c) for all three
nuclei. In addition we have extracted separated longitudinal and transverse
spectral functions at Q of 0.64 and 1.8 (GeV/c) for these three nuclei
(except for Au at the higher Q). The spectral functions are
compared to a number of theoretical calculations. The measured spectral
functions differ in detail but not in overall shape from most of the
theoretical models. In all three targets the measured spectral functions show
considerable excess transverse strength at Q = 0.64 (GeV/c), which is
much reduced at 1.8 (GeV/c).Comment: For JLab E91013 Collaboration, 19 pages, 20 figures, 3 table
Monojet versus rest of the world I: t-channel Models
Monojet searches using Effective Field Theory (EFT) operators are usually
interpreted as a robust and model independent constraint on direct detection
(DD) scattering cross-sections. At the same time, a mediator particle must be
present to produce the dark matter (DM) at the LHC. This mediator particle may
be produced on shell, so that direct searches for the mediating particle can
constrain the effective operator being applied to monojet constraints. In this
first paper, we do a case study on t-channel models in monojet searches, where
the (Standard Model singlet) DM is pair produced via a t-channel mediating
particle, whose supersymmetric analogue is the squark. We compare monojet
constraints to direct constraints on single or pair production of the mediator
from multi-jets plus missing energy searches and we identify the regions where
the latter dominate over the former. We show that computing bounds using
supersymmetric simplified models and in the narrow width approximation, as done
in previous work in the literature, misses important quantitative effects. We
perform a full event simulation and statistical analysis, and we compute the
effects of both on- and off-shell production of the mediating particle, showing
that for both the monojet and multi-jets plus missing energy searches,
previously derived bounds provided more conservative bounds than what can be
extracted by including all relevant processes in the simulation. Monojets and
searches for supersymmetry (SUSY) provide comparable bounds on a wide range of
the parameter space, with SUSY searches usually providing stronger bounds,
except in the regions where the DM particle and the mediator are very mass
degenerate. The EFT approximation rarely is able to reproduce the actual
limits. In a second paper to follow, we consider the case of s-channel
mediators.Comment: 22 pages + appendices, 10 figure
Deductive semiparametric estimation in Double-Sampling Designs with application to PEPFAR
Non-ignorable dropout is common in studies with long follow-up time, and it
can bias study results unless handled carefully. A double-sampling design
allocates additional resources to pursue a subsample of the dropouts and find
out their outcomes, which can address potential biases due to non-ignorable
dropout. It is desirable to construct semiparametric estimators for the
double-sampling design because of their robustness properties. However,
obtaining such semiparametric estimators remains a challenge due to the
requirement of the analytic form of the efficient influence function (EIF), the
derivation of which can be ad hoc and difficult for the double-sampling design.
Recent work has shown how the derivation of EIF can be made deductive and
computerizable using the functional derivative representation of the EIF in
nonparametric models. This approach, however, requires deriving the mixture of
a continuous distribution and a point mass, which can itself be challenging for
complicated problems such as the double-sampling design. We propose
semiparametric estimators for the survival probability in double-sampling
designs by generalizing the deductive and computerizable estimation approach.
In particular, we propose to build the semiparametric estimators based on a
discretized support structure, which approximates the possibly continuous
observed data distribution and circumvents the derivation of the mixture
distribution. Our approach is deductive in the sense that it is expected to
produce semiparametric locally efficient estimators within finite steps without
knowledge of the EIF. We apply the proposed estimators to estimating the
mortality rate in a double-sampling design component of the President's
Emergency Plan for AIDS Relief (PEPFAR) program. We evaluate the impact of
double-sampling selection criteria on the mortality rate estimates
Simplified Models for Dark Matter and Missing Energy Searches at the LHC
The study of collision events with missing energy as searches for the dark
matter (DM) component of the Universe are an essential part of the extensive
program looking for new physics at the LHC. Given the unknown nature of DM, the
interpretation of such searches should be made broad and inclusive. This report
reviews the usage of simplified models in the interpretation of missing energy
searches. We begin with a brief discussion of the utility and limitation of the
effective field theory approach to this problem. The bulk of the report is then
devoted to several different simplified models and their signatures, including
s-channel and t-channel processes. A common feature of simplified models for DM
is the presence of additional particles that mediate the interactions between
the Standard Model and the particle that makes up DM. We consider these in
detail and emphasize the importance of their inclusion as final states in any
coherent interpretation. We also review some of the experimental progress in
the field, new signatures, and other aspects of the searches themselves. We
conclude with comments and recommendations regarding the use of simplified
models in Run-II of the LHC.Comment: v2. references added, version submitted to journal. v1. 47 pages, 13
plot
Probabilistic RGB-D Odometry based on Points, Lines and Planes Under Depth Uncertainty
This work proposes a robust visual odometry method for structured
environments that combines point features with line and plane segments,
extracted through an RGB-D camera. Noisy depth maps are processed by a
probabilistic depth fusion framework based on Mixtures of Gaussians to denoise
and derive the depth uncertainty, which is then propagated throughout the
visual odometry pipeline. Probabilistic 3D plane and line fitting solutions are
used to model the uncertainties of the feature parameters and pose is estimated
by combining the three types of primitives based on their uncertainties.
Performance evaluation on RGB-D sequences collected in this work and two public
RGB-D datasets: TUM and ICL-NUIM show the benefit of using the proposed depth
fusion framework and combining the three feature-types, particularly in scenes
with low-textured surfaces, dynamic objects and missing depth measurements.Comment: Major update: more results, depth filter released as opensource, 34
page
Discriminating Minimal SUGRA and Minimal Gauge Mediation Models at the Early LHC
Among various supersymmetric (SUSY) standard models, the gravity mediation
model with a neutralino LSP and the gauge mediation model with a very light
gravitino are attractive from the cosmological view point. These models have
different scales of SUSY breaking and their underlying physics in high energy
is quite different. However, if the sparticles' decay into the gravitino is
prompt in the latter case, their collider signatures can be similar: multiple
jets and missing transverse momentum. In this paper, we study the
discrimination between these models in minimal cases at the LHC based on the
method using the significance variables in several different modes and show the
discrimination is possible at a very early stage after the discovery.Comment: 29 pages, 3 figures, captions improved, typos corrected, appendix
added, version published in JHE
- …