761 research outputs found
Radiative Corrections to Fixed Target Moller Scattering Including Hard Bremsstrahlung Effects
We present a calculation of the complete electroweak radiative
corrections to the Moller scattering process e^-e^- -> e^-e^-, including hard
bremsstrahlung contributions. We study the effects of these corrections on both
the total cross section and polarization asymmetry measured in low energy fixed
target experiments. Numerical results are presented for the experimental cuts
relevant for E-158, a fixed target e^-e^- experiment being performed at SLAC;
the effect of hard bremsstrahlung is to shift the measured polarization
asymmetry by approximately +4%. We briefly discuss the remaining theoretical
uncertainty in the prediction for the low energy Moller scattering polarization
asymmetry.Comment: 22 pgs; minor clarifications added and typos fixe
Measurement of the 6s - 7p transition probabilities in atomic cesium and a revised value for the weak charge Q_W
We have measured the 6s - 7p_{1/2,3/2} transition probabilities in atomic
cesium using a direct absorption technique. We use our result plus other
previously measured transition rates to derive an accurate value of the vector
transition polarizability \beta and, consequently, re-evaluate the weak charge
Q_W. Our derived value Q_W=-72.65(49) agrees with the prediction of the
standard model to within one standard deviation.Comment: 4 pages, 2 figure
Precise calculation of parity nonconservation in cesium and test of the standard model
We have calculated the 6s-7s parity nonconserving (PNC) E1 transition
amplitude, E_{PNC}, in cesium. We have used an improved all-order technique in
the calculation of the correlations and have included all significant
contributions to E_{PNC}. Our final value E_{PNC} = 0.904 (1 +/- 0.5 %) \times
10^{-11}iea_{B}(-Q_{W}/N) has half the uncertainty claimed in old calculations
used for the interpretation of Cs PNC experiments. The resulting nuclear weak
charge Q_{W} for Cs deviates by about 2 standard deviations from the value
predicted by the standard model.Comment: 24 pages, 8 figure
A Model for the Stray Light Contamination of the UVCS Instrument on SOHO
We present a detailed model of stray-light suppression in the spectrometer
channels of the Ultraviolet Coronagraph Spectrometer (UVCS) on the SOHO
spacecraft. The control of diffracted and scattered stray light from the bright
solar disk is one of the most important tasks of a coronagraph. We compute the
fractions of light that diffract past the UVCS external occulter and
non-specularly pass into the spectrometer slit. The diffracted component of the
stray light depends on the finite aperture of the primary mirror and on its
figure. The amount of non-specular scattering depends mainly on the
micro-roughness of the mirror. For reasonable choices of these quantities, the
modeled stray-light fraction agrees well with measurements of stray light made
both in the laboratory and during the UVCS mission. The models were constructed
for the bright H I Lyman alpha emission line, but they are applicable to other
spectral lines as well.Comment: 19 pages, 5 figures, Solar Physics, in pres
Parity nonconservation in heavy atoms: The radiative correction enhanced by the strong electric field of the nucleus
Parity nonconservation due to the nuclear weak charge is considered. We
demonstrate that the radiative corrections to this effect due to the vacuum
fluctuations of the characteristic size larger than the nuclear radius
and smaller than the electron Compton wave-length are enhanced
because of the strong electric field of the nucleus. The parameter that allows
one to classify the corrections is the large logarithm .
The vacuum polarization contribution is enhanced by the second power of the
logarithm. Although the self-energy and the vertex corrections do not vanish,
they contain only the first power of the logarithm. The value of the radiative
correction is 0.4% for Cs and 0.9% for Tl, Pb, and Bi. We discuss also how the
correction affects the interpretation of the experimental data on parity
nonconservation in atoms.Comment: 4 pages, 3 figures, RevTe
Accurate spline solutions of the Dirac equation with parity-nonconserving potential
The complete system of the B-spline solutions for the Dirac equation with the
parity-nonconserving (PNC) weak interaction effective potential is obtained.
This system can be used for the accurate evaluation of the radiative
corrections to the PNC amplitudes in the multicharged ions and neutral atoms.
The use of the scaling procedure allows for the evaluation of the PNC matrix
elements with relative accuracy .Comment: 7 page
Single photon emitters based on Ni/Si related defects in single crystalline diamond
We present investigations on single Ni/Si related color centers produced via
ion implantation into single crystalline type IIa CVD diamond. Testing
different ion dose combinations we show that there is an upper limit for both
the Ni and the Si dose 10^12/cm^2 and 10^10/cm^2 resp.) due to creation of
excess fluorescent background. We demonstrate creation of Ni/Si related centers
showing emission in the spectral range between 767nm and 775nm and narrow
line-widths of 2nm FWHM at room temperature. Measurements of the intensity
auto-correlation functions prove single-photon emission. The investigated color
centers can be coarsely divided into two groups: Drawing from photon statistics
and the degree of polarization in excitation and emission we find that some
color centers behave as two-level, single-dipole systems whereas other centers
exhibit three levels and contributions from two orthogonal dipoles. In
addition, some color centers feature stable and bright emission with saturation
count rates up to 78kcounts/s whereas others show fluctuating count rates and
three-level blinking.Comment: 7 pages, submitted to Applied Physics B, revised versio
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
Lepton Flavor Violation in Z and Lepton Decays in Supersymmetric Models
The observation of charged lepton flavor non-conservation would be a clear
signature of physics beyond the Standard Model. In particular, supersymmetric
(SUSY) models introduce mixings in the sneutrino and the charged slepton
sectors which could imply flavor-changing processes at rates accessible to
upcoming experiments. In this paper we analyze the possibility to observe Z -->
lep_I lep_J in the GigaZ option of TESLA at DESY. We show that although models
with SUSY masses above the current limits could predict a branching ratio BR(Z
--> mu e) accessible to the experiment, they would imply an unobserved rate of
mu --> e gamma and thus are excluded. In models with a small mixing angle
between the first and the third (or the second and the third) slepton families
GigaZ could observe Z --> tau mu (or Z --> tau e) consistently with present
bounds on lep_J --> lep_I gamma. In contrast, if the mixing angles between the
three slepton families are large the bounds from mu --> e gamma push these
processes below the reach of GigaZ. We show that in this case the masses of the
three slepton families must be strongly degenerated (with mass differences of
order 10^{-3}). We update the limits on the slepton mass insertions
delta_{LL,RR,LR} and discuss the correlation between flavor changing and g_mu-2
in SUSY models.Comment: 23 pages, 6 figures. Version to appear in Phys. Rev.
Reevaluation of the role of nuclear uncertainties in experiments on atomic parity violation with isotopic chains
In light of new data on neutron distributions from experiments with
antiprotonic atoms [ Trzcinska {\it et al.}, Phys. Rev. Lett. 87, 082501
(2001)], we reexamine the role of nuclear-structure uncertainties in the
interpretation of measurements of parity violation in atoms using chains of
isotopes of the same element. With these new nuclear data, we find an
improvement in the sensitivity of isotopic chain measurements to ``new
physics'' beyond the standard model. We compare possible constraints on ``new
physics'' with the most accurate to date single-isotope probe of parity
violation in the Cs atom. We conclude that presently isotopic chain experiments
employing atoms with nuclear charges Z < 50 may result in more accurate tests
of the weak interaction.Comment: 6 pages, 1 fig., submitted to Phys. Rev.
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