563 research outputs found
Searching for an anomalous coupling via single top quark production at a collider
We investigate the potential of a high-energy collider to
detect an anomalous coupling from observation of the reaction
, , where or . We find that with
-tagging and suitable kinematic cuts this process should be observable if
the anomalous coupling is no less than about 0.05/TeV, where
is the scale of new physics associated with the anomalous
interaction. This improves upon the bound possible from observation of top
decays at the Tevatron.Comment: 13 pages, RevTeX, 1 PS figur
Probing neutrino oscillations jointly in long and very long baseline experiments
We examine the prospects of making a joint analysis of neutrino oscillation
at two baselines with neutrino superbeams. Assuming narrow band superbeams and
a 100 kt water Cerenkov calorimeter, we calculate the event rates and
sensitivities to the matter effect, the signs of the neutrino mass differences,
the CP phase and the mixing angle \theta_{13}. Taking into account all possible
experimental errors under general consideration, we explored the optimum cases
of narrow band beam to measure the matter effect and the CP violation effect at
all baselines up to 3000 km. We then focus on two specific baselines, a long
baseline of 300 km and a very long baseline of 2100 km, and analyze their joint
capabilities. We found that the joint analysis can offer extra leverage to
resolve some of the ambiguities that are associated with the measurement at a
single baseline.Comment: 23 pages, 11 figure
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
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
On the Optimum Long Baseline for the Next Generation Neutrino Oscillation Experiments
For high energy long baseline neutrino oscillation experiments, we propose a
Figure of Merit criterion to compare the statistical quality of experiments at
various oscillation distances under the condition of identical detectors and a
given neutrino beam. We take into account all possible experimental errors
under general consideration. In this way the Figure of Merit is closely related
to the usual statistical criterion of number of sigmas. We use a realistic
neutrino beam for an entry level neutrino factory and a possible superbeam from
a meson source and a 100 kt detector for the calculation. We considered in
detail four oscillation distances, 300 km, 700 km, 2100 km and 3000 km, in the
neutrino energy range of 0.5-20 GeV for a 20 GeV entry level neutrino factory
and a 50 GeV superbeam. We found that the very long baselines of 2100 km and
3000 km are preferred for the neutrino factory according to the figure of merit
criterion. Our results also show that, for a neutrino factory, lower primary
muon energies such as 20 GeV are preferred rather than higher ones such as 30
or 50 GeV. For the superbeam, the combination of a long baseline such as 300 km
and a very long baseline like 2100 km will form a complete measurement of the
oscillation parameters besides the CP phase. To measure the CP phase in a
superbeam, a larger detector (a factor 3 beyond what is considered in this
article) and/or a higher intensity beam will be needed to put some significant
constraints on the size of the CP angle.Comment: 21 LaTeX pages, 13 PS figures, typos corrected, references adde
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
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
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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