487 research outputs found
Ab initio calculation of the KRb dipole moments
The relativistic configuration interaction valence bond method has been used
to calculate permanent and transition electric dipole moments of the KRb
heteronuclear molecule as a function of internuclear separation. The permanent
dipole moment of the ground state potential is found to be
0.30(2) at the equilibrium internuclear separation with excess negative
charge on the potassium atom. For the potential the dipole moment
is an order of magnitude smaller (1 Cm) In addition, we
calculate transition dipole moments between the two ground-state and
excited-state potentials that dissociate to the K(4s)+Rb(5p) limits. Using this
data we propose a way to produce singlet KRb molecules by a
two-photon Raman process starting from an ultracold mixture of doubly
spin-polarized ground state K and Rb atoms. This Raman process is only allowed
due to relativistic spin-orbit couplings and the absence of gerade/ungerade
selection rules in heteronuclear dimers.Comment: 16 pages, 7 figure
Probing anomalous top quark interactions at the Fermilab Tevatron Collider
We study the effects of dimension-six operators contributing to the vertex in top quark pair production at the Tevatron collider. We derive both
the limits from Run 1 data and the potential bounds from future runs (Run 2 and
3). Although the current constraints are not very strong, the future runs are
quite effective in probing these operators. We investigate the possibility of
disentangling different operators with the invariant mass
distribution and the top quark polarization asymmetry. We also study the
effects of a different set of operators contributing to single top production
via the coupling. We derive the current and potential future bounds
on these anomalous operators and find that the upgraded Tevatron can improve
the existing constraints from for one of the operators.Comment: 20 pages, 2 figures, REVTEX, some clarifying remarks adde
Limits on Non-Standard Top Quark Couplings from Electroweak Measurements
We calculate the typical size of loop corrections to electroweak observables
arising from non-standard and vertices. We use an
effective Lagrangian formalism based on the electroweak gauge group
. Limits on the non-standard model
top quark couplings from electroweak observables are presented and compared
with previously obtained limits.Comment: 9 pages, uses epsf.st
Measurements of polarized photo-pion production on longitudinally polarized HD and Implications for Convergence of the GDH Integral
We report new measurements of inclusive pion production from frozen-spin HD
for polarized photon beams covering the Delta(1232) resonance. These provide
data simultaneously on both H and D with nearly complete angular distributions
of the spin-difference cross sections entering the Gerasimov-Drell-Hearn (GDH)
sum rule. Recent results from Mainz and Bonn exceed the GDH prediction for the
proton by 22 microbarns, suggesting as yet unmeasured high-energy components.
Our pi0 data reveal a different angular dependence than assumed in Mainz
analyses and integrate to a value that is 18 microbarns lower, suggesting a
more rapid convergence. Our results for deuterium are somewhat lower than
published data, considerably more precise and generally lower than available
calculations.Comment: 4 pages, 4 figures. Submitted for publication in Physical Review
Letter
Dimension-six CP-conserving operators of the third-family quarks and their effects on collider observables
We list all possible dimension-six CP-conserving invariant operators involving the third-family quarks which
could be generated by new physics at a higher scale. Expressions for these
operators after electroweak gauge symmetry breaking and the induced effective
couplings , and are
presented. Analytic expressions for the tree level contributions of all these
operators to the observables and at LEP I,
and at LEP II,
and at the NLC, as well as
at the Tevatron upgrade, are provided.
The effects of these operators on different electroweak observables are
discussed and numerical examples presented. Numerical analyses show that in the
coupling region allowed by and at LEP I, some of the new
physics operators can still have significant contributions at LEP II, the
Tevatron and the NLC.Comment: 25 page
Single top quark production as a probe of R-parity-violating SUSY at pp and p\bar p colliders
We investigate the ability of single top quark production via qq'->
squark->tb and q \bar q'->slepton->t\bar b at the LHC and Tevatron to probe the
strength of R-parity violating couplings in the minimal supersymmetric model.
We found that given the existing bounds on R-parity violating couplings, single
top quark production may be greatly enhanced over that predicted by the
standard model, and that both colliders can either discover R-parity violating
SUSY or set strong constraints on the relevant R-parity violating couplings. We
further found that the LHC is much more powerful than the Tevatron in probing
the squark couplings, but the two colliders have comparable sensitivity for the
slepton couplings.Comment: 15 pages, 4 figure
Single top production at the LHC as a probe of R parity violation
We investigate the potential of the LHC to probe the R parity violating
couplings involving the third generation by considering single top production.
This study is based on particle level event generation for both signal and
background, interfaced to a simplified simulation of the ATLAS detector.Comment: 11 pages, 5 figures, 5 tables (LaTeX, style revtex), few references
adde
Single Top Quark Production via FCNC Couplings at Hadron Colliders
We calculate single top-quark production at hadron colliders via the
chromo-magnetic flavor-changing neutral current couplings and . We find that the strength for the anomalous ()
coupling may be probed to () at the Tevatron with of data and
() at the LHC with of data. The two couplings may be
distinguished by a comparision of the single top signal with the direct top and
top decay signals for these couplings.Comment: 18 pages, 6 figures, 3 table
Unitarity Constraints on Anomalous Top Quark Couplings to Weak Gauge Bosons
If there is new physics associated with the top quark, it could show up as
anomalous couplings of the top quark to weak gauge bosons, such as Z\ttbar
and W\tbbar vector and axial-vector couplings. We use the processes
\ttbar\to Z^0Z^0, \ttbar\to W^+W^-, and \ttbar\to Z^0H to obtain the
unitarity constraints on these anomalous couplings, and combine these
constraints with those from precision electroweak data. The unitarity
constraints can impose additional limits on the anomalous couplings when the
scale of new physics is as low as 2 TeV. A nonzero measurement of such an
anomalous coupling leads to an upper limit on the new physics scale from the
unitarity condition.Comment: 12 pages, Latex, 4 postscipt figures included. Resubmitted with major
revisions, including the newest data on $R_b
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