137 research outputs found
H-->WW as the discovery mode for a light Higgs boson
The production cross section for a m_H=115 GeV, SM Higgs boson in weak boson
fusion at the LHC is sizable. However, the branching fraction for H-->WW is
expected to be relatively small. The signal, with its two forward jets, is
sufficiently different from the main backgrounds that a signal to background
ratio of better than 1:1 can nevertheless be obtained, with large enough rate
to allow for a 5 sigma signal with 35 fb^{-1} of data. The H-->WW signal in
weak boson fusion may thus prove to be the discovery mode for the Higgs boson
at the LHC.Comment: 10 pages, 4 figures, uses revte
High-Energy-Physics Event Generation with PYTHIA 6.1
PYTHIA version 6 represents a merger of the PYTHIA 5, JETSET 7 and SPYTHIA
programs, with many improvements. It can be used to generate
high-energy-physics `events', i.e. sets of outgoing particles produced in the
interactions between two incoming particles. The objective is to provide as
accurate as possible a representation of event properties in a wide range of
reactions. The underlying physics is not understood well enough to give an
exact description; the programs therefore contain a combination of analytical
results and various models. The emphasis in this article is on new aspects, but
a few words of general introduction are included. Further documentation is
available on the web.Comment: 1 + 27 pages, submitted to Computer Physics Communication
KRAS-mutation status dependent effect of zoledronic acid in human non-small cell cancer preclinical models
BACKGROUND: In non-small cell lung cancer (NSCLC) KRAS-mutant status is a negative prognostic and predictive factor. Nitrogen-containing bisphosphonates inhibit prenylation of small G-proteins (e.g. Ras, Rac, Rho) and thus may affect proliferation and migration. In our preclinical work, we investigated the effect of an aminobisphosphonate compound (zoledronic acid) on mutant and wild type KRAS-expressing human NSCLC cell lines. RESULTS: We confirmed that zoledronic acid was unable to inhibit the prenylation of mutant K-Ras unlike in the case of wild type K-Ras. In case of in vitro proliferation, the KRAS-mutant human NSCLC cell lines showed resistance to zoledronic acid wild-type KRAS-cells proved to be sensitive. Combinatory application of zoledronic acid enhanced the cytostatic effect of cisplatin. Zoledronic acid did not induce significant apoptosis. In xenograft model, zoledronic acid significantly reduced the weight of wild type KRAS-EGFR-expressing xenograft tumor by decreasing the proliferative capacity. Futhermore, zoledronic acid induced VEGF expression and improved in vivo tumor vascularization. MATERIALS AND METHODS: Membrane association of K-Ras was examined by Western-blot. In vitro cell viability, apoptotic cell death and migration were measured in NSCLC lines with different molecular background. The in vivo effect of zoledronic acid was investigated in a SCID mouse subcutaneous xenograft model. CONCLUSIONS: The in vitro and in vivo inhibitory effect of zoledronic acid was based on the blockade of cell cycle in wild type KRAS-expressing human NSCLC cells. The zoledronic acid induced vascularization supported in vivo cytostatic effect. Our preclinical investigation suggests that patients with wild type KRAS-expressing NSCLC could potentially benefit from aminobisphosphonate therapy
Z -> b b-bar b b-bar in the light gluino and light sbottom scenario
The light gluino (12 - 16 GeV) and light sbottom (2 - 6 GeV) scenario has
been used to explain the apparent overproduction of b-quarks at the Tevatron.
This scenario also predicts the decay Z -> b b-bar ~g ~g where the gluinos
subsequently decay into b-quarks and sbottoms. We show that this can contribute
to the width Gamma_4b = Gamma(Z -> b b-bar b b-bar) since most of the sbottoms
and b-quarks arising from gluino decay have a small angular separation. We find
that while no excess in Gamma_4b is observable due to large uncertainties in
experimental measurements, the ratio Gamma(Z -> b b-bar ~g ~g)/Gamma(Z -> b
b-bar b b-bar) can be large due to sensitivity to b-quark mass, the sbottom
mixing angle and the gluino mass. We calculate it to be in the range 0.05 -
0.41 inclusive of the entire parameter space.Comment: minor tex error, citation corrected in version2, to appear in Phys.
Rev.
Where the Sidewalk Ends: Jets and Missing Energy Search Strategies for the 7 TeV LHC
This work explores the potential reach of the 7 TeV LHC to new colored states
in the context of simplified models and addresses the issue of which search
regions are necessary to cover an extensive set of event topologies and
kinematic regimes. This article demonstrates that if searches are designed to
focus on specific regions of phase space, then new physics may be missed if it
lies in unexpected corners. Simple multiregion search strategies can be
designed to cover all of kinematic possibilities. A set of benchmark models are
created that cover the qualitatively different signatures and a benchmark
multiregion search strategy is presented that covers these models.Comment: 30 pages, 8 Figures, 3 Tables. Version accepted at JHEP. Minor
changes. Added figur
Physics searches at the LHC
With the LHC up and running, the focus of experimental and theoretical high
energy physics will soon turn to an interpretation of LHC data in terms of the
physics of electroweak symmetry breaking and the TeV scale. We present here a
broad review of models for new TeV-scale physics and their LHC signatures. In
addition, we discuss possible new physics signatures and describe how they can
be linked to specific models of physics beyond the Standard Model. Finally, we
illustrate how the LHC era could culminate in a detailed understanding of the
underlying principles of TeV-scale physics.Comment: 184 pages, 55 figures, 14 tables, hundreds of references; scientific
feedback is welcome and encouraged. v2: text, references and Overview Table
added; feedback still welcom
Measurement of the p\bar{p}\sqrt{s}$ = 1.8 TeV
We update the measurement of the top production cross section using the CDF
detector at the Fermilab Tevatron. This measurement uses decays to
the final states +jets and +jets. We search for quarks from
decays via secondary-vertex identification or the identification of
semileptonic decays of the and cascade quarks. The background to the
production is determined primarily through a Monte Carlo simulation.
However, we calibrate the simulation and evaluate its uncertainty using several
independent data samples. For a top mass of 175 , we measure
pb and pb using
the secondary vertex and the lepton tagging algorithms, respectively. Finally,
we combine these results with those from other decay channels and
obtain pb.Comment: The manuscript consists of 130 pages, 35 figures and 42 tables in
RevTex. The manuscript is submitted to Physical Review D. Fixed typo in
author lis
Striatal sensitivity to personal responsibility in a regret-based decision-making task
Regret and relief are complex emotional states associated with the counterfactual processing of nonobtained outcomes in a decision-making situation. In the "actor effect," a sense of agency and personal responsibility is thought to heighten these emotions. Using fMRI, we scanned volunteers (n = 22) as they played a task involving choices between two wheel-of-fortune gambles. We examined how neural responses to counterfactual outcomes were modulated by giving subjects the opportunity to change their minds, as a manipulation of personal responsibility. Satisfaction ratings to the outcomes were highly sensitive to the difference between the obtained and nonobtained outcome, and ratings following losses were lower on trials with the opportunity to change one's mind. Outcome-related activity in the striatum and orbitofrontal cortex was positively related to the satisfaction ratings. The striatal response was modulated by the agency manipulation: Following losses, the striatal signal was significantly lower when the subject had the opportunity to change his/her mind. These results support the involvement of frontostriatal mechanisms in counterfactual thinking and highlight the sensitivity of the striatum to the effects of personal responsibility.</p
HERA Collider Physics
HERA, the first electron-proton collider, has been delivering luminosity
since 1992. It is the natural extension of an impressive series of fixed-target
lepton-nucleon scattering experiments. The increase of a factor ten in
center-of-mass energy over that available for fixed-target experiments has
allowed the discovery of several important results, such as the large number of
slow partons in the proton, and the sizeable diffractive cross section at large
. Recent data point to a possible deviation from Standard Model
expectations at very high , highlighting the physics potential of HERA for
new effects. The HERA program is currently in a transition period. The first
six years of data taking have primarily elucidated the structure of the proton,
allowed detailed QCD studies and had a strong impact on the understanding of
QCD dynamics. The coming years will bring the era of electroweak studies and
high measurements. This is therefore an appropriate juncture at which to
review HERA results.Comment: 351 pages, 154 figures, submitted to Reviews of Modern Physic
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