55 research outputs found
Compilation and analysis of charge asymmetry measurements from electron and positron scattering on nucleon and nuclei
World data on the lepton-charge asymmetry in the elastic and inelastic lepton
scattering off the proton and nuclei are compiled and discussed. After
reviewing the published results, we compare the elastic data to a model
calculation of the two-photon exchange mechanism. We show that the existing
data do not provide any evidence for the two-photon contribution. At
significance level 0.05 the data allow to exclude the two-photon exchange as an
explanation for the difference between Rosenbluth and polarization measurements
of proton electromagnetic form factors.Comment: 20 pages, 7 figures 2 table
PEN: a low energy test of lepton universality
Allowed charged meson decays are characterized by simple dynamics, few
available decay channels, mainly into leptons, and extremely well controlled
radiative and loop corrections. In that sense, pion decays represent a
veritable triumph of the standard model (SM) of elementary particles and
interactions. This relative theoretical simplicity makes charged pion decays a
sensitive means for testing the underlying symmetries and the universality of
weak fermion couplings, as well as for studying pion structure and chiral
dynamics. Even after considerable recent improvements, experimental precision
is lagging far behind that of the theoretical description for pion decays. We
review the current state of experimental study of the pion electronic decay
, or , where the
indicates inclusion and explicit treatment of radiative decay events. We
briefly review the limits on non-SM processes arising from the present level of
experimental precision in decays. Focusing on the PEN
experiment at the Paul Scherrer Institute (PSI), Switzerland, we examine the
prospects for further improvement in the near term.Comment: 11 pages, 5 figures; paper presented at the XIII International
Conference on Heavy Quarks and Leptons, 22-27 May 2016, Blacksburg, Virginia,
US
PEN experiment: a precise measurement of the pi+ -> e+ nu decay branching fraction
A new measurement of , the decay
branching ratio, is currently under way at the Paul Scherrer Institute. The
present experimental result on constitutes the most accurate test
of lepton universality available. The accuracy, however, still lags behind the
theoretical precision by over an order of magnitude. Because of the large
helicity suppression of the decay, its branching ratio is
susceptible to significant contributions from new physics, making this decay a
particularly suitable subject of study.Comment: 4 pages, 3 figures, talk given at the Tenth Conference on the
Intersections of Particle and Nuclear Physics (CIPANP 2009), La Jolla/San
Diego, CA, 26-31 May 2009; to appear in Proceedings to be published by the
American Institute of Physic
Search for the Radiative Capture d+d->^4He+\gamma Reaction from the dd\mu Muonic Molecule State
A search for the muon catalyzed fusion reaction dd --> ^4He +\gamma in the
dd\mu muonic molecule was performed using the experimental \mu CF installation
TRITON and NaI(Tl) detectors for \gamma-quanta. The high pressure target filled
with deuterium at temperatures from 85 K to 800 K was exposed to the negative
muon beam of the JINR phasotron to detect \gamma-quanta with energy 23.8 MeV.
The first experimental estimation for the yield of the radiative deuteron
capture from the dd\mu state J=1 was obtained at the level n_{\gamma}\leq
2\times 10^{-5} per one fusion.Comment: 9 pages, 3 Postscript figures, submitted to Phys. At. Nuc
Precise Measurement of pi+ -> e+ nu Branching Ratio
The PEN Collaboration is conducting a new measurement of the pi+ -> e+ nu
branching ratio at the Paul Scherrer Institute, with the goal uncertainty of
delta B/B(pie2)=5E-4 or lower. At present, the combined accuracy of all
published pie2 decay measurements lags behind the theoretical calculation by a
factor of 40. In this contribution we report on the PEN detector configuration
and its performance during two development runs done in 2007 and 2008.Comment: pdflatex, 11 pages, 5 figures, to be published in "Progress in
High-Energy Physics and Nuclear Safety", NATO Science for Peace Series: B -
Physics and Biophysic
Radiative corrections to radiative \pi e 2 decay
The lowest order radiative corrections (RC) to width and spectra of radiative
decay are calculated. We take into account virtual photon emission
contribution as well as soft and hard real photon emission one. The result
turns out to be consistent with the standard Drell-Yan picture for the width
and spectra in the leading logarithmical approximation which permits us to
generalize it to all orders of perturbation theory. Explicit expressions of
nonleading contributions are obtained. The contribution of short distance is
found to be in agreement with Standard Model predictions. It is presented as a
general normalization factor. We check the validity of the
Kinoshita-Lee-Nauenberg theorem about cancellation in the total width of the
mass singularities at zero limit of electron mass. We discuss the results of
the previous papers devoted to this problem. The Dalitz plot distribution is
illustrated numerically.Comment: 21 pages, 3 figures, 3 tables; a table with K-factor values was adde
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