1,853 research outputs found
Electroweak Radiative Corrections To Polarized M{\o}ller Scattering Asymmetries
One loop electroweak radiative corrections to left-right parity violating
M{\o}ller scattering () asymmetries are presented. They
reduce the standard model (tree level) prediction by 40 \% where the
main shift and uncertainty stem from hadronic vacuum polarization loops. A
similar reduction also occurs for the electron-electron atomic parity violating
interaction. That effect can be attributed to an increase of
by in running from to 0. The
sensitivity of the asymmetry to ``new physics'' is also discussed.Comment: 14 pages, Revtex, postscript file including figures is available at
ftp://ttpux2.physik.uni-karlsruhe.de/ttp95-14/ttp95-14.ps or via WWW at
http://ttpux2.physik.uni-karlsruhe.de/cgi-bin/preprints/ (129.13.102.139
Semileptonic decays of light quarks beyond the Standard Model
We describe non-standard contributions to semileptonic processes in a model
independent way in terms of an SU(2)_L X U(1)_Y invariant effective lagrangian
at the weak scale, from which we derive the low-energy effective lagrangian
governing muon and beta decays. We find that the deviation from Cabibbo
universality, \Delta_CKM = |V_ud|^2 + |V_us|^2 + |V_ub|^2 - 1, receives
contributions from four effective operators. The phenomenological bound of
\Delta_CKM = -1E-4 +- 6E-4 provides strong constraints on all four operators,
corresponding to an effective scale greater than 11 TeV (90% CL). Depending on
the operator, this constraint is at the same level or better then the Z pole
observables. Conversely, precision electroweak constraints alone would allow
universality violations as large as \Delta_CKM = -0.01 (90% CL). An observed
nonzero \Delta_CKM at this level could be explained in terms of a single
four-fermion operator which is relatively poorly constrained by electroweak
precision measurements.Comment: 23 pages, 1 table and 5 eps figure
Evidence for Bosonic Electroweak Corrections in the Standard Model
We present strong indirect evidence for the contribution of bosonic
electroweak corrections in the Standard Model. Although important conceptually,
these corrections give subleading contributions in current high energy
experiments, and it was previously thought that they are difficult to detect.
We also discuss the separate contribution of the Higgs boson.Comment: 9 pages (LaTeX + 3 PS figures, needs psfig
K_L \ra \mu^\pm e^\mp \nu \overline{\nu} as background to K_L \ra \mu^\pm e^\mp
We consider the process K_L \ra \mu^\pm e^\mp \nu \overline{\nu} at next to
leading order in chiral perturbation theory. This process occurs in the
standard model at second order in the weak interaction and constitutes a
potential background in searches for new physics through the modes K_L \ra
\mu^\pm e^\mp. We find that the same cut, ~MeV, used to remove
the sequential decays K_{l3}\ra \pi_{l2} pushes the B(K_L \ra \mu^\pm e^\mp
\nu \overline{\nu}) to the level, effectively removing it as a
background.Comment: 8 pages, LaTeX, 1 figure appended as postscript file after
\end{document}. Fermilab-Pub-93/024-
Inelastic Channels in the Electroweak Symmetry-Breaking Sector
It has been argued that if light Higgs bosons do not exist then the
self--interactions of 's become strong in the TeV region and can be observed
in longitudinal scattering. We present a model with many inelastic
channels in the scattering process, corresponding to the creation of heavy
fermion pairs. The presence of these heavy fermions affects the elastic
scattering of 's by propagating in loops, greatly reducing the amplitudes in
some charge channels. Consequently, the symmetry--breaking sector cannot be
fully explored by using, for example, the mode alone; all scattering modes must be measured.}Comment: 10 pages, phyzzx, JHU-TIPAC-92001
Electroweak higher-order effects and theoretical uncertainties in deep-inelastic neutrino scattering
A previous calculation of electroweak O(alpha) corrections to deep-inelastic
neutrino scattering, as e.g. measured by NuTeV and NOMAD, is supplemented by
higher-order effects. In detail, we take into account universal two-loop
effects from \Delta\alpha and \Delta\rho as well as higher-order final-state
photon radiation off muons in the structure function approach. Moreover, we
make use of the recently released O(alpha)-improved parton distributions
MRST2004QED and identify the relevant QED factorization scheme, which is DIS
like. As a technical byproduct, we describe slicing and subtraction techniques
for an efficient calculation of a new type of real corrections that are induced
by the generated photon distribution. A numerical discussion of the
higher-order effects suggests that the remaining theoretical uncertainty from
unknown electroweak corrections is dominated by non-universal two-loop effects
and is of the order 0.0003 when translated into a shift in
sin^2\theta_W=1-MW^2/MZ^2. The O(alpha) corrections implicitly included in the
parton distributions lead to a shift of about 0.0004.Comment: 25 pages, latex, 8 postscript figure
Fermi Constants and ``New Physics''
Various precision determinations of the Fermi constant are compared. Included
are muon and (leptonic) tau decays as well as indirect prescriptions employing
\alpha, m_Z, m_W, \ssthwmzms, \Gamma(Z\to\ell^+\ell^-), and as input. Their good agreement tests the standard model at the
level and provides stringent constraints on new physics. That
utility is illustrated for: heavy neutrino mixing, 2 Higgs doublet models, S,
T, and U parameters and excited bosons (Kaluza-Klein
excitations). For the last of those examples, m_{W^\ast}\gsims 2.9 TeV is
found.Comment: 14 page
Dimuon production by laser-wakefield accelerated electrons
We analyze pair production generated by high-energy electrons
emerging from a laser-wakefield accelerator. The pairs are created
in a solid thick high- target, following the electron accelerating plasma
region. Numerical estimates are presented for electron beams obtained presently
in the LBL TW laser experiment \cite{C2} and possible future developments.
Reactions induced by the secondary bremsstrahlung photons dominate the dimuon
production. According to our estimates, a 20 pC electron bunch with energy of 1
(10) GeV may create about 200 (6000) muon pairs. The produced can be
used in studying various aspects of muon-related physics in table top
installations. This may be considered as an important step towards the
investigation of more complicated elementary processes induced by laser driven
electrons.Comment: 14 pages, 5 figure
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