1,257 research outputs found
The decays within the standard model
We study the reactions within the
minimal standard model. We use isospin symmetry to relate the matrix elements
to the form factors measured in . We argue that these modes are
short distance dominated and can be used for precise determinations of the CKM
parameters and . Depending on the value of the CKM angles we find
branching ratios in the following ranges: ; ; . We also discuss a possible -odd
observable.Comment: 10 pages, LaTeX, 2 Postscript figures. Title and abstract have been
revised to better reflect the content of the paper. This is the final version
as publishe
Top Quark Spin Polarization in ep Collision
We discuss the degree of spin polarization of single top quarks produced via
fusion process in collision at TESLA+HERAp and CLIC+LHC energies
and 5.3 TeV. For subprocess we show that
the top quark spin is completely polarized when the spin basis is chosen in the
direction of the incoming positron beam in the rest frame of top quark. A
description on how to combine the cross sections of and
processes is given. -beam direction is
taken to be the favorite top quark spin decomposition axis in its rest frame
and it is found to be comparable with the ones in collision. It is argued
that theoretical simplicity and experimental clearness are the advantage of
collision.Comment: Revised version of Phys. Rev. D69 (2004)03401
Long Distance Contribution to
We revisit the calculation of the long distance contribution to . We discuss this process within the framework of chiral
perturbation theory, and also using simple models for the vertex. We argue that it is unlikely that this mode can be used to
extract information on short distance parameters. The process
is also long-distance dominated and we find that .Comment: References added, one typo corrected. Version to appear in Nuclear
Physics
Rare K decays in a model of quark and lepton masses
An extension of a model of neutrino masses to the quark sector provides an
interesting link between these two sectors. A parameter which is important to
describe neutrino oscillations and masses is found to be a crucial one
appearing in various ``penguin'' operators, in particular the so-called Z
penguin. This parameter is severely constrained by the rare decay process
. This in turn has interesting implications on the
decay rates of other rare processes such as , etc..., as well
as on the masses of the neutrinos and the masses of the vector-like quarks and
leptons which appear in our model.Comment: 34 pages, 10 figures, corrected some typos in the introductio
Integrated and explicit boundary conditions of electromagnetic fields at arbitrary interfaces between two anisotropic media
This paper derives two new integrated and explicit boundary conditions, named the “explicit normal version” and “explicit tangential versions” respectively for electromagnetic fields at an arbitrary interface between two anisotropic media. The new versions combine two implicit boundary equations into a single explicit matrix formula and reveal the boundary values linked by a 3 × 3 matrix, which depends on the interface topography and model property tensors. We analytically demonstrate the new versions equivalent to the common implicit boundary conditions and their application to transformation of the boundary values in the boundary integral equations. We also give two synthetic examples that show recovery of the boundary values on a hill and a ridge, and highlight the advantage of the new versions of being a simpler and more straightforward method to compute the electromagnetic boundary values.Bing Zhou, Graham Heinson, Aixa Rivera-Rio
Subdomain Chebyshev spectral method for 2D and 3D numerical differentiations in a curved coordinate system
A new numerical approach, called the “subdomain Chebyshev spectral method” is presented for calculation of the spatial derivatives in a curved coordinate system, which may be employed for numerical solutions of partial differential equations defined in a 2D or 3D geological model. The new approach refers to a “strong version” against the “weak version” of the subspace spectral method based on the variational principle or Galerkin’s weighting scheme. We incorporate local nonlinear transformations and global spline interpolations in a curved coordinate system and make the discrete grid exactly matches geometry of the model so that it is achieved to convert the global domain into subdomains and apply Chebyshev points to locally sampling physical quantities and globally computing the spatial derivatives. This new approach not only remains exponential convergence of the standard spectral method in subdomains, but also yields a sparse assembled matrix when applied for the global domain simulations. We conducted 2D and 3D synthetic experiments and compared accuracies of the numerical differentiations with traditional finite difference approaches. The results show that as the points of differentiation vector are larger than five, the subdomain Chebyshev spectral method significantly improve the accuracies of the finite difference approaches.Bing Zhou, Graham Heinson, Aixa Rivera-Rio
Electromagnetic monitoring of fluid injection - lessons learned
GeoCat; 74874Magnetotelluric data acquired over the Paralana project has provided valuable insight into the resistivity distribution across geothermal sedimentary basins. The time-lapse MT measurements during an EGS fluid injection trace the preferential fluid connection in a NNE direction aligned with the regional stress field. The results add information to existing micro-seismic measurements by providing the preferential fluid-filled fracture connection at depth. New results using 2D forward magnetotelluric anisotropy codes are able to reproduce the direction of enhanced fluid flow by fitting measured against modelled phase tensor residuals. Future surveys will need to address limited resolution issues between EM measurements from the surface compared to standard micro-seismic monitoring techniques.S. Thiel, J.R. Peacock, J. MacFarlane and G. Heinso
Tests of the Standard Model Using Muon Polarization Asymmetries in Kaon Decays
We have examined the physics and the experimental feasibility of studying
various kaon decay processes in which the polarization of a muon in the final
state is measured. Valuable information on CP violation, the quark mixing (CKM)
matrix, and new physics can be obtained from such measurements. We have
considered muon polarization in K_L to mu+ mu- and K to pi mu+ mu- decays.
Although the effects are small, or difficult to measure because of the small
branching ratios involved, these studies could provide clean measurements of
the CKM parameters. The experimental difficulty appears comparable to the
observation of K to pi nu barnu. New sources of physics, involving non-standard
CP violation, could produce effects observable in these measurements. Limits
from new results on the neutron and electron electric dipole moment, and
epsilon-prime over epsilon in neutral kaon decays, do not eliminate certain
models that could contribute to the signal. A detailed examination of muon
polarization out of the decay plane in KMU3 and radiative KMU2 decays also
appears to be of interest. With current kaon beams and detector techniques, it
is possible to measure the T-violating polarization for KMU3 with uncertainties
approaching 0.0001. This level of sensitivity would provide an interesting
probe of new physics.Comment: 24 pages, 3 figures, To be published in the International Journal of
Modern Physics
CP Violation In Single Top Production And Decay Via p p-bar -> t b-bar +X -> W^+ b b-bar +X Within The MSSM: A Possible Application For Measuring \arg(A_t) At Hadron Colliders
CP-nonconserving effects in the reaction p p-bar -> t b-bar +X -> W^+ b b-bar
+X, driven by the supersymmetric CP-odd phase of the stop trilinear soft
breaking term, \arg(A_t), are studied. We discuss the CP-nonconserving effects
in both production and the associated decay amplitudes of the top. We find
that, within a plausible low energy scenario of the MSSM and keeping the
neutron electric dipole moment below its current limit, a CP-violating
cross-section asymmetry as large as 2-3% can arise if some of the parameters
lie in a favorable range. A partial rate asymmetry originating only in the top
decay t -> W^+ b is found to be, in general, below the 0.1% level which is
somewhat smaller than previous claims. For a low \tan\beta of order one the
decay asymmetry can reach at the most ~0.3%. This (few) percent level overall
CP-violating signal in p p-bar -> t b-bar +X -> W^+ b b-bar +X might be within
the reach of the future 2(4) TeV pp-bar Tevatron collider that may be able to
produce ~10000(~30000) such tb-bar events with an integrated luminosity of 30
fb^{-1}. In particular, it may be used to place an upper bound on \arg(A_t) if
indeed \arg(\mu) -> 0, as implied from the present experimental limit on the
neutron electric dipole moment. The partial rate asymmetry in the top decay
(~few \times 10^{-3}) may also be within the reach of the LHC with ~10^7 pairs
of tt-bar produced, provided detector systematics are sufficiently small. We
also show that if the GUT-scale universality of the soft breaking trilinear
terms is relaxed, then the phases associated with \arg A_u and \arg A_d can
take values up to ~few \times 10^{-1} even with squarks and gluino masses of
several hundred GeV's without contradicting the experimental limit on the
neutron electric dipole moment.Comment: 39 pages, plain latex, 20 figures embadded in the text using epsfi
Understanding single-top-quark production and jets at hadron colliders
I present an analysis of fully differential single-top-quark production plus
jets at next-to-leading order. I describe the effects of jet definitions,
top-quark mass, and higher orders on the shapes and normalizations of the
kinematic distributions, and quantify all theoretical uncertainties. I explain
how to interpret next-to-leading-order jet calculations, and compare them to
showering event generators. Using the program ZTOP, I show that HERWIG and
PYTHIA significantly underestimate both s-channel and t-channel
single-top-quark production, and propose a scheme to match the relevant samples
to the next-to-leading-order predictions.Comment: 40 pgs., revtex4, 35 ps figs; added Fig. 4, 1 Ref., minor
clarifications, to appear in Phys. Rev.
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