180 research outputs found
Resonant slepton production at the LHC in models with an ultralight gravitino
We examine resonant slepton production at the LHC with gravitinos in the
final state. The slepton undergoes gauge decay into a neutralino and a lepton,
the neutralino decays into a photon and a gravitino. By measuring the
transverse masses of the gamma- G and the l-gamma- G subsystems it is possible
to accurately reconstruct both the slepton and neutralino masses. In some
regions of parameter space the slepton decays directly into a lepton and
gravitino, giving an identical experimental topology to W production (l missing
E_T). We present the novel matrix element squared for lepton-gravitino
production. A peak in the tail of the lepton-missing momentum transverse mass
distribution of the W provides a signature for the process and an accurate
measurement of the slepton mass. We display the search reach for the LHC and
300 fb^{-1} of integrated luminosity.Comment: 13 pages. Minor changes in v
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
Bounding the MSSM Higgs sector from above with the Tevatron's B_s --> mu^+ mu^-
The discovery potential of the Tevatron CDF for the rare B-decay B_s --> mu^+
mu^- is analysed. We find that with an integrated luminosity of 2 fb^(-1), and
using CDF as the example detector, a 5 sigma combined discovery reach of the
Tevatron is possible if the Branching ratio for B_s --> mu^+ mu^- is (1.7 +-
0.46) \times 10^(-7). Such a possible signal for the decay B_s --> mu^+ mu^-
will invite large tan(beta) values and set an upper bound on the heaviest mass
of the MSSM Higgs sector in a complete analogy to the upper bound of the
lightest observable supersymmetric particle set from the excess over the SM
prediction of the muon anomalous magnetic moment. If for example, the decay B_s
-->mu^+ mu^- is found at Tevatron with branching ratio 2 \times 10^(-7) then
the heaviest Higgs boson mass in the MSSM should be less than 790 GeV for
tan(beta) < 50 provided that the CKM matrix is the only source for (s)quark
flavour changing processes.Comment: 14 pages, 3 figures, (v2) Minor changes, version to appear in Phys
Lett
Studies of a three-stage dark matter and neutrino observatory based on multi-ton combinations of liquid xenon and liquid argon detectors
We study a three stage dark matter and neutrino observatory based on
multi-ton two-phase liquid Xe and Ar detectors with sufficiently low
backgrounds to be sensitive to WIMP dark matter interaction cross sections down
to 10E-47 cm^2, and to provide both identification and two independent
measurements of the WIMP mass through the use of the two target elements in a
5:1 mass ratio, giving an expected similarity of event numbers. The same
detection systems will also allow measurement of the pp solar neutrino
spectrum, the neutrino flux and temperature from a Galactic supernova, and
neutrinoless double beta decay of 136Xe to the lifetime level of 10E27 - 10E28
y corresponding to the Majorana mass predicted from current neutrino
oscillation data. The proposed scheme would be operated in three stages G2, G3,
G4, beginning with fiducial masses 1-ton Xe + 5-ton Ar (G2), progressing to
10-ton Xe + 50-ton Ar (G3) then, dependent on results and performance of the
latter, expandable to 100-ton Xe + 500-ton Ar (G4). This method of scale-up
offers the advantage of utilizing the Ar vessel and ancillary systems of one
stage for the Xe detector of the succeeding stage, requiring only one new
detector vessel at each stage. Simulations show the feasibility of reducing or
rejecting all external and internal background levels to a level <1 events per
year for each succeeding mass level, by utilizing an increasing outer thickness
of target material as self-shielding. The system would, with increasing mass
scale, become increasingly sensitive to annual signal modulation, the agreement
of Xe and Ar results confirming the Galactic origin of the signal. Dark matter
sensitivities for spin-dependent and inelastic interactions are also included,
and we conclude with a discussion of possible further gains from the use of
Xe/Ar mixtures
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
Revised Properties and Dynamical History for the HD 17156 System
From the thousands of known exoplanets, those that transit bright host stars
provide the greatest accessibility toward detailed system characterization. The
first known such planets were generally discovered using the radial velocity
technique, then later found to transit. HD 17156b is particularly notable among
these initial discoveries because it diverged from the typical hot Jupiter
population, occupying a 21.2 day eccentric () orbit, offering
preliminary insights into the evolution of planets in extreme orbits. Here we
present new data for this system, including ground and space-based photometry,
radial velocities, and speckle imaging, that further constrain the system
properties and stellar/planetary multiplicity. These data include photometry
from the Transiting Exoplanet Survey Satellite (TESS) that cover five transits
of the known planet. We show that the system does not harbor any additional
giant planets interior to 10 AU. The lack of stellar companions and the age of
the system indicate that the eccentricity of the known planet may have resulted
from a previous planet-planet scattering event. We provide the results from
dynamical simulations that suggest possible properties of an additional planet
that culminated in ejection from the system, leaving a legacy of the observed
high eccentricity for HD 17156b.Comment: 15 pages, 7 figures, accepted for publication in the Astronomical
Journa
Status and Prospects of Top-Quark Physics
The top quark is the heaviest elementary particle observed to date. Its large
mass of about 173 GeV/c^2 makes the top quark act differently than other
elementary fermions, as it decays before it hadronises, passing its spin
information on to its decay products. In addition, the top quark plays an
important role in higher-order loop corrections to standard model processes,
which makes the top quark mass a crucial parameter for precision tests of the
electroweak theory. The top quark is also a powerful probe for new phenomena
beyond the standard model. During the time of discovery at the Tevatron in 1995
only a few properties of the top quark could be measured. In recent years,
since the start of Tevatron Run II, the field of top-quark physics has changed
and entered a precision era. This report summarises the latest measurements and
studies of top-quark properties and gives prospects for future measurements at
the Large Hadron Collider (LHC).Comment: 76 pages, 35 figures, submitted to Progress in Particle and Nuclear
Physic
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
Upper Bounds on Rare K and B Decays from Minimal Flavour Violation
We study the branching ratios of rare K and B decays in models with minimal
flavour violation, using the presently available information from the universal
unitarity triangle analysis and from the measurements of Br(B -> X_s gamma),
Br(B -> X_s l^+l^-) and Br(K^+ -> pi^+ nu nubar). We find the following upper
bounds: Br(K^+ -> pi^+ nu nubar) pi^0 nu nubar)< 4.6
10^{-11}, Br(K_L -> mu mubar)_{SD} X_s nu nubar)< 5.2
10^{-5}, Br(B -> X_d nu nubar) mu mubar)< 7.4 10^{-9},
Br(B_d -> mu mubar)< 2.2 10^{-10} at 95 % probability. We analyze in detail
various possible scenarios with positive or negative interference of Standard
Model and New Physics contributions, and show how an improvement of
experimental data corresponding to the projected 2010 B factory integrated
luminosities will allow to disentangle and test these different possibilities.
Finally, anticipating that subsequently the leading role in constraining this
kind of new physics will be taken over by the rare decays K^+ -> pi^+ nu nubar,
K_L -> pi^0 nu nubar and B_{s,d} -> mu mubar, that are dominated by the Z^0
-penguin function C, we also present plots for several branching ratios as
functions of C . We point out an interesting triple correlation between K^+ ->
pi^+ nu nubar, B -> X_s gamma and B -> X_s l^+l^- present in MFV models.Comment: 26 pages, 12 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
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