7,369 research outputs found
Reduced Fine-Tuning in Supersymmetry with R-parity violation
Both electroweak precision measurements and simple supersymmetric extensions
of the standard model prefer a mass of the Higgs boson less than the
experimental lower limit of 114 GeV. We show that supersymmetric models with R
parity violation and baryon number violation have a significant range of
parameter space in which the Higgs dominantly decays to six jets. These decays
are much more weakly constrained by current LEP analyses and would allow for a
Higgs mass near that of the . In general, lighter scalar quark and other
superpartner masses are allowed and the fine-tuning typically required to
generate the measured scale of electroweak symmetry breaking is ameliorated.
The Higgs would potentially be discovered at hadron colliders via the
appearance of new displaced vertices. The lightest neutralino could be
discovered by a scan of vertex-less events LEP I data.Comment: 5 pages, 2 figures. Significant detail added to the arguments
regarding LEP limits - made more quantitative. Better figures used, plotting
more physical quantities. Typos corrected and references updated. Conclusions
unchange
Searches for Long-lived Particles at the Tevatron Collider
Several searches for long-lived particles have been performed using data from
p-pbar collisions from Run II at the Tevatron. In most cases, new analysis
techniques have been developed to carry out each search and/or estimate the
backgrounds. These searches expand the discovery potential of the CDF and D0
experiments to new physics that may have been missed by traditional search
techniques. This review discusses searches for (1) neutral, long-lived
particles decaying to muons, (2) massive, neutral, long-lived particles
decaying to a photon and missing energy, (3) stopped gluinos, and (4) charged
massive stable particles. It summarizes some of the theoretical and
experimental motivations for such searches.Comment: submitted to Mod. Phys. Lett.
Single and Pair Production of Doubly Charged Higgs Bosons at Hadron Colliders
Current searches for doubly charged Higgs bosons (H^{\pm\pm}) at the Fermilab
Tevatron are sensitive to single production of H^{\pm\pm}, although the pair
production mechanism q\bar q\to H^{++}H^{--} is assumed to be dominant. In the
context of a Higgs Triplet Model we study the mechanism q'\bar q\to
H^{\pm\pm}H^{\mp} at the Tevatron and CERN Large Hadron Collider, and show that
its inclusion can significantly improve the search potential for H^{\pm\pm}.
Moreover, assuming that the neutrino mass is generated solely by the triplet
field Yukawa coupling to leptons, we compare the branching ratios of
H^{\pm\pm}\to l^\pm l^\pm and H^{\pm\pm}\to H^\pm W^* for the cases of a normal
hierarchical, inverted hierarchical and degenerate neutrino mass spectrum.Comment: 17 pages, 15 figures, references added, version to appear in PR
Inclusive B-Meson Production at the LHC in the GM-VFN Scheme
We calculate the next-to-leading-order cross section for the inclusive
production of B mesons in pp collisions in the general-mass
variable-flavor-number scheme, an approach which takes into account the finite
mass of the b quarks. We use realistic evolved non-perturbative fragmentation
functions obtained from fits to e+e- data and compare results for the
transverse-momentum and rapidity distributions at a center-of-mass energy of 7
TeV with recent data from the CMS Collaboration. We find good agreement, in
particular at large values of pT.Comment: Minor changes to the text, accepted for publication in Phys. Rev.
Discrimination of SUSY breaking models using single-photon processes at future e+e- linear colliders
We examine the single-photon processes in the frame work of supersymmetric
models at future e+e- linear colliders. According to the recent experimental
achievement, the optimistic polarization degrees for both electron and positron
beams are taken into account to enhance the signal-to-noise ratio revealing the
observable difference between supersymmetry breaking models. The minimal
supergravity model and the minimal SU(5) grand unified model in gaugino
mediation have been examined as examples. We see that after several years of
accummulating data, the difference of the number of single-photon events
between the two models received from the collider would be in excess of three
times the statistical error, providing us the possibility to probe which model
would be realized in nature. The result is well suitable for the future running
of the International Linear Collider.Comment: 14 pages, 4 figures, version to be published in Mod. Phys. Lett.
An effective mass theorem for the bidimensional electron gas in a strong magnetic field
We study the limiting behavior of a singularly perturbed
Schr\"odinger-Poisson system describing a 3-dimensional electron gas strongly
confined in the vicinity of a plane and subject to a strong uniform
magnetic field in the plane of the gas. The coupled effects of the confinement
and of the magnetic field induce fast oscillations in time that need to be
averaged out. We obtain at the limit a system of 2-dimensional Schr\"odinger
equations in the plane , coupled through an effective selfconsistent
electrical potential. In the direction perpendicular to the magnetic field, the
electron mass is modified by the field, as the result of an averaging of the
cyclotron motion. The main tools of the analysis are the adaptation of the
second order long-time averaging theory of ODEs to our PDEs context, and the
use of a Sobolev scale adapted to the confinement operator
Analysis of events with b-jets and a pair of leptons of the same charge in pp collisions at √s = 8 TeV with the ATLAS detector
An analysis is presented of events containing jets including at least one b-tagged jet, sizeable missing transverse momentum, and at least two leptons including a pair of the same electric charge, with the scalar sum of the jet and lepton transverse momenta being large. A data sample with an integrated luminosity of 20.3 fb−1 of pp collisions at √s=8 TeV recorded by the ATLAS detector at the Large Hadron Collider is used. Standard Model processes rarely produce these final states, but there are several models of physics beyond the Standard Model that predict an enhanced rate of production of such events; the ones considered here are production of vector-like quarks, enhanced four-top-quark production, pair production of chiral b′-quarks, and production of two positively charged top quarks. Eleven signal regions are defined; subsets of these regions are combined when searching for each class of models. In the three signal regions primarily sensitive to positively charged top quark pair production, the data yield is consistent with the background expectation. There are more data events than expected from background in the set of eight signal regions defined for searching for vector-like quarks and chiral b′-quarks, but the significance of the discrepancy is less than two standard deviations. The discrepancy reaches 2.5 standard deviations in the set of five signal regions defined for searching for four-top-quark production. The results are used to set 95% CL limits on various models
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