72 research outputs found
Dark Matter as a Guide Toward a Light Gluino at the LHC
Motivated by specific connections to dark matter signatures, we study the
prospects of observing the presence of a relatively light gluino whose mass is
in the range ~(500-900) GeV with a wino-like lightest supersymmetric particle
with mass in the range of ~(170-210) GeV. The light gaugino spectra studied
here is generally different from other models, and in particular those with a
wino dominated LSP, in that here the gluinos can be significantly lighter. The
positron excess reported by the PAMELA satellite data is accounted for by
annihilations of the wino LSP and their relic abundance can generally be
brought near the WMAP constraints due to the late decay of a modulus field
re-populating the density of relic dark matter. We also mention the recent
FERMI photon constraints on annihilating dark matter in this class of models
and implications for direct detection experiments including CDMS and XENON. We
study these signatures in models of supersymmetry with non-minimal soft
breaking terms derived from both string compactifications and related
supergravity models which generally lead to non-universal gaugino masses. At
the LHC, large event rates from the three-body decays of the gluino in certain
parts of the parameter space are found to give rise to early discovery
prospects for the gaugino sector. Excess events at the 5 sigma level can arise
with luminosity as low as order 100 pb^{-1} at a center of mass energy of 10
TeV and less than ~ 1 fb^{-1} at a center of mass energy of 7 TeV.Comment: 2 columns, 9 pages, 5 figure caption
A Study of the Residual 39Ar Content in Argon from Underground Sources
The discovery of argon from underground sources with significantly less 39Ar
than atmospheric argon was an important step in the development of
direct-detection dark matter experiments using argon as the active target. We
report on the design and operation of a low background detector with a single
phase liquid argon target that was built to study the 39Ar content of the
underground argon. Underground argon from the Kinder Morgan CO2 plant in
Cortez, Colorado was determined to have less than 0.65% of the 39Ar activity in
atmospheric argon.Comment: 21 pages, 10 figure
Discovery of underground argon with low level of radioactive 39Ar and possible applications to WIMP dark matter detectors
We report on the first measurement of 39Ar in argon from underground natural
gas reservoirs. The gas stored in the US National Helium Reserve was found to
contain a low level of 39Ar. The ratio of 39Ar to stable argon was found to be
<=4x10-17 (84% C.L.), less than 5% the value in atmospheric argon
(39Ar/Ar=8x10-16). The total quantity of argon currently stored in the National
Helium Reserve is estimated at 1000 tons. 39Ar represents one of the most
important backgrounds in argon detectors for WIMP dark matter searches. The
findings reported demonstrate the possibility of constructing large multi-ton
argon detectors with low radioactivity suitable for WIMP dark matter searches.Comment: 6 pages, 2 figures, 2 table
Probing R-parity violating models of neutrino mass at the Tevatron via top Squark decays
We have estimated the limiting branching ratio of the R-parity violating
(RPV) decay of the lighter top squark, \tilde t_1 \ar l^+ d ( or
and d is a down type quark of any flavor), as a function of top squark
mass(\MST) for an observable signal in the di-lepton plus di-jet channel at
the Tevatron RUN-II experiment with 2 fb luminosity. Our simulations
indicate that the lepton number violating nature of the underlying decay
dynamics can be confirmed via the reconstruction of \MST. The above decay is
interesting in the context of RPV models of neutrino mass where the RPV
couplings () driving the above decay are constrained to be
small (\lsim 10^{-3} - 10^{-4} ). If is the next lightest super
particle - a theoretically well motivated scenario - then the RPV decay can
naturally compete with the R-parity conserving (RPC) modes which also have
suppressed widths. The model independent limiting BR can delineate the
parameter space in specific supersymmetric models, where the dominating RPV
decay is observable and predict the minimum magnitude of the RPV coupling that
will be sensitive to Run-II data. We have found it to be in the same ballpark
value required by models of neutrino mass, for a wide range of \MST. A
comprehensive future strategy for linking top squark decays with models of
neutrino mass is sketched.Comment: 28 pages, 14 Figure
The fully differential single-top-quark cross section in next-to-leading order QCD
We present a new next-to-leading order calculation for fully differential
single-top-quark final states. The calculation is performed using phase space
slicing and dipole subtraction methods. The results of the methods are found to
be in agreement. The dipole subtraction method calculation retains the full
spin dependence of the final state particles. We show a few numerical results
to illustrate the utility and consistency of the resulting computer
implementations.Comment: 37 pages, latex, 2 ps figure
Measurements of the Production, Decay and Properties of the Top Quark: A Review
With the full Tevatron Run II and early LHC data samples, the opportunity for
furthering our understanding of the properties of the top quark has never been
more promising. Although the current knowledge of the top quark comes largely
from Tevatron measurements, the experiments at the LHC are poised to probe
top-quark production and decay in unprecedented regimes. Although no current
top quark measurements conclusively contradict predictions from the standard
model, the precision of most measurements remains statistically limited.
Additionally, some measurements, most notably the forward-backward asymmetry in
top quark pair production, show tantalizing hints of beyond-the-Standard-Model
dynamics. The top quark sample is growing rapidly at the LHC, with initial
results now public. This review examines the current status of top quark
measurements in the particular light of searching for evidence of new physics,
either through direct searches for beyond the standard model phenomena or
indirectly via precise measurements of standard model top quark properties
Measurement of the scintillation time spectra and pulse-shape discrimination of low-energy beta and nuclear recoils in liquid argon with DEAP-1
The DEAP-1 low-background liquid argon detector was used to measure
scintillation pulse shapes of electron and nuclear recoil events and to
demonstrate the feasibility of pulse-shape discrimination (PSD) down to an
electron-equivalent energy of 20 keV.
In the surface dataset using a triple-coincidence tag we found the fraction
of beta events that are misidentified as nuclear recoils to be (90% C.L.) for energies between 43-86 keVee and for a nuclear recoil
acceptance of at least 90%, with 4% systematic uncertainty on the absolute
energy scale. The discrimination measurement on surface was limited by nuclear
recoils induced by cosmic-ray generated neutrons. This was improved by moving
the detector to the SNOLAB underground laboratory, where the reduced background
rate allowed the same measurement with only a double-coincidence tag.
The combined data set contains events. One of those, in the
underground data set, is in the nuclear-recoil region of interest. Taking into
account the expected background of 0.48 events coming from random pileup, the
resulting upper limit on the electronic recoil contamination is
(90% C.L.) between 44-89 keVee and for a nuclear recoil
acceptance of at least 90%, with 6% systematic uncertainty on the absolute
energy scale.
We developed a general mathematical framework to describe PSD parameter
distributions and used it to build an analytical model of the distributions
observed in DEAP-1. Using this model, we project a misidentification fraction
of approx. for an electron-equivalent energy threshold of 15 keV for
a detector with 8 PE/keVee light yield. This reduction enables a search for
spin-independent scattering of WIMPs from 1000 kg of liquid argon with a
WIMP-nucleon cross-section sensitivity of cm, assuming
negligible contribution from nuclear recoil backgrounds.Comment: Accepted for publication in Astroparticle Physic
Search for new physics in events with opposite-sign leptons, jets, and missing transverse energy in pp collisions at sqrt(s) = 7 TeV
A search is presented for physics beyond the standard model (BSM) in final
states with a pair of opposite-sign isolated leptons accompanied by jets and
missing transverse energy. The search uses LHC data recorded at a
center-of-mass energy sqrt(s) = 7 TeV with the CMS detector, corresponding to
an integrated luminosity of approximately 5 inverse femtobarns. Two
complementary search strategies are employed. The first probes models with a
specific dilepton production mechanism that leads to a characteristic kinematic
edge in the dilepton mass distribution. The second strategy probes models of
dilepton production with heavy, colored objects that decay to final states
including invisible particles, leading to very large hadronic activity and
missing transverse energy. No evidence for an event yield in excess of the
standard model expectations is found. Upper limits on the BSM contributions to
the signal regions are deduced from the results, which are used to exclude a
region of the parameter space of the constrained minimal supersymmetric
extension of the standard model. Additional information related to detector
efficiencies and response is provided to allow testing specific models of BSM
physics not considered in this paper.Comment: Replaced with published version. Added journal reference and DO
TRY plant trait database - enhanced coverage and open access
Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives
Radial velocity confirmation of a hot super-Neptune discovered by TESS with a warm Saturn-mass companion
We report the discovery and confirmation of the planetary system TOI-1288.
This late G dwarf harbours two planets: TOI-1288 b and TOI-1288 c. We combine
TESS space-borne and ground-based transit photometry with HARPS-N and HIRES
high-precision Doppler measurements, which we use to constrain the masses of
both planets in the system and the radius of planet b. TOI-1288~b has a period
of d, a radius of
R, and a mass of M, making this planet a hot
transiting super-Neptune situated right in the Neptunian desert. This desert
refers to a paucity of Neptune-sized planets on short period orbits. Our
2.4-year-long Doppler monitoring of TOI-1288 revealed the presence of a
Saturn-mass planet on a moderately eccentric orbit ()
with a minimum mass of M and a period of
d. The 5 sectors worth of TESS data do not cover our expected mid-transit time
for TOI-1288 c, and we do not detect a transit for this planet in these
sectors.Comment: 16 pages, 17 figures, under review MNRA
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