10 research outputs found
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Combination of CDF and D0 Measurements of the Single Top Production Cross Section
We report a combination of the CDF and D0 measurements of the inclusive single top quark production cross section in the s- and t-channels, {sigma}{sub s+t}, in p{bar p} collisions at a center of mass energy of 1.96 TeV. The total integrated luminosity included in CDF's analysis is 3.2 fb{sup -1} and D0's analysis has 2.3 fb{sup -1}. A Bayesian analysis is used to extract the cross section from the distributions of multivariate discriminants provided by the collaborations. For a top quark mass m{sub t} = 170 GeV/c{sup 2}, we measure a cross section of 2.76{sub -0.47}{sup +0.58} pb. We extract the CKM matrix element |V{sub tb}| = 0.88 {+-} 0.07 with a 95% C.L. lower limit of |V{sub tb}| > 0.77
Non-universal gauge boson and the spin correlation of top quark pair production at colliders
In the off-diagonal basis, we discuss the contributions of the non-universal
gauge boson predicted by the topcolor-assisted technicolor () model
to the spin configurations and the spin correlation observable of the top quark
pair production via the process . Our numerical results
show that the production cross sections for the like-spin states, which vanish
in the standard model, can be significantly large as .
With reasonable values of the mass and the coupling parameter
,
exchange can generate large corrections to the spin correlation
observable.Comment: 16 pages, 5 figure
On the detectability of the CMSSM light Higgs boson at the Tevatron
We examine the prospects of detecting the light Higgs h^0 of the Constrained
MSSM at the Tevatron. To this end we explore the CMSSM parameter space with
\mu>0, using a Markov Chain Monte Carlo technique, and apply all relevant
collider and cosmological constraints including their uncertainties, as well as
those of the Standard Model parameters. Taking 50 GeV < m_{1/2}, m_0 < 4 TeV,
|A_0| < 7 TeV and 2 < tan(beta) < 62 as flat priors and using the formalism of
Bayesian statistics we find that the 68% posterior probability region for the
h^0 mass lies between 115.4 GeV and 120.4 GeV. Otherwise, h^0 is very similar
to the Standard Model Higgs boson. Nevertheless, we point out some enhancements
in its couplings to bottom and tau pairs, ranging from a few per cent in most
of the CMSSM parameter space, up to several per cent in the favored region of
tan(beta)\sim 50 and the pseudoscalar Higgs mass of m_A\lsim 1 TeV. We also
find that the other Higgs bosons are typically heavier, although not
necessarily much heavier. For values of the h^0 mass within the 95% probability
range as determined by our analysis, a 95% CL exclusion limit can be set with
about 2/fb of integrated luminosity per experiment, or else with 4/fb (12/fb) a
3 sigma evidence (5 sigma discovery) will be guaranteed. We also emphasize that
the alternative statistical measure of the mean quality-of-fit favors a
somewhat lower Higgs mass range; this implies even more optimistic prospects
for the CMSSM light Higgs search than the more conservative Bayesian approach.
In conclusion, for the above CMSSM parameter ranges, especially m_0, either
some evidence will be found at the Tevatron for the light Higgs boson or, at a
high confidence level, the CMSSM will be ruled out.Comment: JHEP versio
SUSY QCD impact on top-pair production associated with a -boson at a photon-photon collider
The top-pair production in association with a -boson at a photon-photon
collider is an important process in probing the coupling between top-quarks and
vector boson and discovering the signature of possible new physics. We describe
the impact of the complete supersymmetric QCD(SQCD) next-to-leading order(NLO)
radiative corrections on this process at a polarized or unpolarized photon
collider, and make a comparison between the effects of the SQCD and the
standard model(SM) QCD. We investigate the dependence of the lowest-order(LO)
and QCD NLO corrected cross sections in both the SM and minimal supersymmetric
standard model(MSSM) on colliding energy in different polarized
photon collision modes. The LO, SM NLO and SQCD NLO corrected distributions of
the invariant mass of -pair and the transverse momenta of final
-boson are presented. Our numerical results show that the pure SQCD
effects in \ggttz process can be more significant in the polarized photon
collision mode than in other collision modes, and the relative SQCD radiative
correction in unpolarized photon collision mode varies from 32.09% to
when goes up from to .Comment: 22 pages and 13 figure
Cosmological implications of the Higgs mass measurement
We assume the validity of the Standard Model up to an arbitrary high-energy
scale and discuss what information on the early stages of the Universe can be
extracted from a measurement of the Higgs mass. For Mh < 130 GeV, the Higgs
potential can develop an instability at large field values. From the absence of
excessive thermal Higgs field fluctuations we derive a bound on the reheat
temperature after inflation as a function of the Higgs and top masses. Then we
discuss the interplay between the quantum Higgs fluctuations generated during
the primordial stage of inflation and the cosmological perturbations, in the
context of landscape scenarios in which the inflationary parameters scan. We
show that, within the large-field models of inflation, it is highly improbable
to obtain the observed cosmological perturbations in a Universe with a light
Higgs. Moreover, independently of the inflationary model, the detection of
primordial tensor perturbations through the B-mode of CMB polarization and the
discovery of a light Higgs can simultaneously occur only with exponentially
small probability, unless there is new physics beyond the Standard Model.Comment: 28 LaTeX pages, 6 figure
Phenomenology of GUT-less Supersymmetry Breaking
We study models in which supersymmetry breaking appears at an intermediate
scale, M_{in}, below the GUT scale. We assume that the soft
supersymmetry-breaking parameters of the MSSM are universal at M_{in}, and
analyze the morphology of the constraints from cosmology and collider
experiments on the allowed regions of parameter space as M_{in} is reduced from
the GUT scale. We present separate analyses of the (m_{1/2},m_0) planes for
tan(beta)=10 and tan(beta)=50, as well as a discussion of non-zero trilinear
couplings, A_0. Specific scenarios where the gaugino and scalar masses appear
to be universal below the GUT scale have been found in mirage-mediation models,
which we also address here. We demand that the lightest neutralino be the LSP,
and that the relic neutralino density not conflict with measurements by WMAP
and other observations. At moderate values of M_{in}, we find that the allowed
regions of the (m_{1/2},m_0) plane are squeezed by the requirements of
electroweak symmetry breaking and that the lightest neutralino be the LSP,
whereas the constraint on the relic density is less severe. At very low M_{in},
the electroweak vacuum conditions become the dominant constraint, and a
secondary source of astrophysical cold dark matter would be necessary to
explain the measured relic density for nearly all values of the soft
SUSY-breaking parameters and tan(beta). We calculate the neutralino-nucleon
cross sections for viable scenarios and compare them with the present and
projected limits from direct dark matter searches.Comment: 35 pages, 9 figures; typos corrected, references adde
Supersymmetry Without Prejudice
We begin an exploration of the physics associated with the general
CP-conserving MSSM with Minimal Flavor Violation, the pMSSM. The 19 soft SUSY
breaking parameters in this scenario are chosen so as to satisfy all existing
experimental and theoretical constraints assuming that the WIMP is a
conventional thermal relic, ie, the lightest neutralino. We scan this parameter
space twice using both flat and log priors for the soft SUSY breaking mass
parameters and compare the results which yield similar conclusions. Detailed
constraints from both LEP and the Tevatron searches play a particularly
important role in obtaining our final model samples. We find that the pMSSM
leads to a much broader set of predictions for the properties of the SUSY
partners as well as for a number of experimental observables than those found
in any of the conventional SUSY breaking scenarios such as mSUGRA. This set of
models can easily lead to atypical expectations for SUSY signals at the LHC.Comment: 61 pages, 24 figs. Refs., figs, and text added, typos fixed; This
version has reduced/bitmapped figs. For a version with better figs please go
to http://www.slac.stanford.edu/~rizz
Prospects for dark matter detection with IceCube in the context of the CMSSM
We study in detail the ability of the nominal configuration of the IceCube
neutrino telescope (with 80 strings) to probe the parameter space of the
Constrained MSSM (CMSSM) favoured by current collider and cosmological data.
Adopting conservative assumptions about the galactic halo model and the
expected experiment performance, we find that IceCube has a probability between
2% and 12% of achieving a 5sigma detection of dark matter annihilation in the
Sun, depending on the choice of priors for the scalar and gaugino masses and on
the astrophysical assumptions. We identify the most important annihilation
channels in the CMSSM parameter space favoured by current constraints, and we
demonstrate that assuming that the signal is dominated by a single annihilation
channel canlead to large systematic errors in the inferred WIMP annihilation
cross section. We demonstrate that ~ 66% of the CMSSM parameter space violates
the equilibrium condition between capture and annihilation in the center of the
Sun. By cross-correlating our predictions with direct detection methods, we
conclude that if IceCube does detect a neutrino flux from the Sun at high
significance while direct detection experiments do not find a signal above a
spin-independent cross section sigma_SI^p larger than 5x10^{-9} pb, the CMSSM
will be strongly disfavoured, given standard astrophysical assumptions for the
WIMP distribution. This result is robust with respect to a change of priors. We
argue that the proposed low-energy DeepCore extension of IceCube will be an
ideal instrument to focus on relevant CMSSM areas of parameter space.Comment: 32 pages, 12 figures. Updated discussion of comparison with direct
detection. References added. Main results unchanged. Matches version accepted
by JCA