125 research outputs found
Calculations of parity nonconserving s-d transitions in Cs, Fr, Ba II, and Ra II
We have performed ab initio mixed-states and sum-over-states calculations of
parity nonconserving (PNC) electric dipole (E1) transition amplitudes between
s-d electron states of Cs, Fr, Ba II, and Ra II. For the lower states of these
atoms we have also calculated energies, E1 transition amplitudes, and
lifetimes. We have shown that PNC E1 transition amplitudes between s-d states
can be calculated to high accuracy. Contrary to the Cs 6s-7s transition, in
these transitions there are no strong cancelations between different terms in
the sum-over-states approach. In fact, there is one dominating term which
deviates from the sum by less than 20%. This term corresponds to an s-p_{1/2}
weak matrix element, which can be calculated to better than 1%, and a
p_{1/2}-d_{3/2} E1 transition amplitude, which can be measured. Also, the s-d
amplitudes are about four times larger than the corresponding s-s transitions.
We have shown that by using a hybrid mixed-states/sum-over-states approach the
accuracy of the calculations of PNC s-d amplitudes could compete with that of
Cs 6s-7s if p_{1/2}-d_{3/2} E1 amplitudes are measured to high accuracy.Comment: 15 pages, 8 figures, submitted to Phys. Rev.
Split Fermions in Extra Dimensions and Exponentially Small Cross-Sections at Future Colliders
We point out a dramatic new experimental signature for a class of theories
with extra dimensions, where quarks and leptons are localized at slightly
separated parallel ``walls'' whereas gauge and Higgs fields live in the bulk of
the extra dimensions. The separation forbids direct local couplings between
quarks and leptons, allowing for an elegant solution to the proton decay
problem. We show that scattering cross sections for collisions of fermions
which are separated in the extra dimensions vanish exponentially at energies
high enough to probe the separation distance. This is because the separation
puts a lower bound on the attainable impact parameter in the collision. We
present cross sections for two body high energy scattering and estimate the
power with which future colliders can probe this scenario, finding sensitivity
to inverse fermion separations of order 10-70 TeV.Comment: 18 pages, 3 figure
Inverse seesaw and dark matter in models with exotic lepton triplets
We show that models with exotic leptons transforming as E ~ (1,3,-1) under
the standard model gauge symmetry are well suited for generating neutrino mass
via a radiative inverse seesaw. This approach realizes natural neutrino masses
and allows multiple new states to appear at the TeV scale. The exotic leptons
are therefore good candidates for new physics that can be probed at the LHC.
Furthermore, remnant low-energy symmetries ensure a stable dark matter
candidate, providing a link between dark matter and the origins of neutrino
mass.Comment: 6 pages, 3 figures (revtex4.1, two-columns
Combined effect of coherent Z exchange and the hyperfine interaction in atomic PNC
The nuclear spin-dependent parity nonconserving (PNC) interaction arising
from a combination of the hyperfine interaction and the coherent,
spin-independent, PNC interaction from Z exchange is evaluated using many-body
perturbation theory. For the 6s-7s transition in 133Cs, we obtain a result that
is about 40% smaller than that found previously by Bouchiat and Piketty [Phys.
Lett. B 269, 195 (1991)]. Applying this result to 133Cs, leads to an increase
in the experimental value of nuclear anapole moment and exacerbates differences
between constraints on PNC meson coupling constants obtained from the Cs
anapole moment and those obtained from other nuclear parity violating
experiments. Nuclear spin-dependent PNC dipole matrix elements, including
contributions from the combined weak-hyperfine interaction, are also given for
the 7s-8s transition in 211Fr and for transitions between ground-state
hyperfine levels in K, Rb, Cs, Ba+, Au, Tl, Fr, and Ra+.Comment: Revtex4 preprint 19 pages 4 table
Can R-parity violation explain the LSND data as well?
The recent Super-Kamiokande data now admit only one type of mass hierarchy in
a framework with three active and one sterile neutrinos. We show that neutrino
masses and mixings generated by R-parity-violating couplings, with values
within their experimental upper limits, are capable of reproducing this
hierarchy, explaining all neutrino data particularly after including the LSND
results.Comment: 7 pages, Latex, 3 PS figures; in v2 a few clarifying remarks included
and two references added (to appear in Physical Review D
Experimental Probes of Localized Gravity: On and Off the Wall
The phenomenology of the Randall-Sundrum model of localized gravity is
analyzed in detail for the two scenarios where the Standard Model (SM) gauge
and matter fields are either confined to a TeV scale 3-brane or may propagate
in a slice of five dimensional anti-deSitter space. In the latter instance, we
derive the interactions of the graviton, gauge, and fermion Kaluza-Klein (KK)
states. The resulting phenomenological signatures are shown to be highly
dependent on the value of the 5-dimensional fermion mass and differ
substantially from the case where the SM fields lie on the TeV-brane. In both
scenarios, we examine the collider signatures for direct production of the
graviton and gauge KK towers as well as their induced contributions to
precision electroweak observables. These direct and indirect signatures are
found to play a complementary role in the exploration of the model parameter
space. In the case where the SM field content resides on the TeV-brane, we show
that the LHC can probe the full parameter space and hence will either discover
or exclude this model if the scale of electroweak physics on the 3-brane is
less than 10 TeV. We also show that spontaneous electroweak symmetry breaking
of the SM must take place on the TeV-brane.Comment: 62 pages, Latex, 22 figure
The yield of head CT in syncope: a pilot study
Although head CT is often routinely performed in emergency department (ED) patients with syncope, few studies have assessed its value
Recommended from our members
Parallel computing in information retrieval - An updated review
The progress of parallel computing in Information Retrieval (IR) is reviewed. In particular we stress the importance of the motivation in using parallel computing for Text Retrieval. We analyse parallel IR systems using a classification due to Rasmussen [1] and describe some parallel IR systems. We give a description of the retrieval models used in parallel Information Processing.. We describe areas of research which we believe are needed
Model-independent search for CP violation in D0âKâK+ÏâÏ+ and D0âÏâÏ+Ï+Ïâ decays
A search for CP violation in the phase-space structures of D0 and View the MathML source decays to the final states KâK+ÏâÏ+ and ÏâÏ+Ï+Ïâ is presented. The search is carried out with a data set corresponding to an integrated luminosity of 1.0 fbâ1 collected in 2011 by the LHCb experiment in pp collisions at a centre-of-mass energy of 7 TeV. For the KâK+ÏâÏ+ final state, the four-body phase space is divided into 32 bins, each bin with approximately 1800 decays. The p-value under the hypothesis of no CP violation is 9.1%, and in no bin is a CP asymmetry greater than 6.5% observed. The phase space of the ÏâÏ+Ï+Ïâ final state is partitioned into 128 bins, each bin with approximately 2500 decays. The p-value under the hypothesis of no CP violation is 41%, and in no bin is a CP asymmetry greater than 5.5% observed. All results are consistent with the hypothesis of no CP violation at the current sensitivity
Branching fraction and CP asymmetry of the decays B+âK0SÏ+ and B+âK0SK+
An analysis of B+ â K0
SÏ+ and B+ â K0
S K+ decays is performed with the LHCb experiment. The pp
collision data used correspond to integrated luminosities of 1 fbâ1 and 2 fbâ1 collected at centre-ofmass
energies of
â
s = 7 TeV and
â
s = 8 TeV, respectively. The ratio of branching fractions and the
direct CP asymmetries are measured to be B(B+ â K0
S K+
)/B(B+ â K0
SÏ+
) = 0.064 ± 0.009 (stat.) ±
0.004 (syst.), ACP(B+ â K0
SÏ+
) = â0.022 ± 0.025 (stat.) ± 0.010 (syst.) and ACP(B+ â K0
S K+
) =
â0.21 ± 0.14 (stat.) ± 0.01 (syst.). The data sample taken at
â
s = 7 TeV is used to search for
B+
c
â K0
S K+ decays and results in the upper limit ( fc · B(B+
c
â K0
S K+
))/( fu · B(B+ â K0
SÏ+
)) <
5.8 Ă 10â2 at 90% confidence level, where fc and fu denote the hadronisation fractions of a ÂŻb
quark
into a B+
c or a B+ meson, respectively
- âŠ