169 research outputs found
Nuclear recoil measurements in Superheated Superconducting Granule detectors
The response of Superheated Superconducting Granule (SSG) devices to nuclear
recoils has been explored by irradiating SSG detectors with a 70MeV neutron
beam. In the past we have tested Al SSG and more recently, measurements have
been performed with Sn and Zn detectors. The aim of the experiments was to test
the sensitivity of SSG detectors to recoil energies down to a few keV. In
this paper, the preliminary results of the neutron irradiation of a SSG
detector made of Sn granules 15-20m in diameter will be discussed. For the
first time, recoil energy thresholds of 1keV have been measured.Comment: 7pages in Latex format, Preprint Bu-He 93/6 (University of Berne,
Switzerland), four figures available upon request via
[email protected] or [email protected]
High Purity Pion Beam at TRIUMF
An extension of the TRIUMF M13 low-energy pion channel designed to suppress
positrons based on an energy-loss technique is described. A source of beam
channel momentum calibration from the decay pi+ --> e+ nu is also described.Comment: 5 page
T-Odd Correlations in pi->e nu_e gamma and pi->mu nu_mu gamma Decays
The transverse lepton polarization asymmetry in pi_l2gamma decays may probe
T-violating interactions beyond the Standard Model. Dalitz plot distributions
of the expected effects are presented and compared to the contribution from the
Standard Model final state interactions. We give an example of a
phenomenologically viable model, where a considerable contribution to the
transverse lepton polarization asymmetry arises.Comment: 19 pages, 5 figures. To be published in Phys.Rev.D. Fixed sign in FSI
contribution figure, fixed formulas in K-bar{K} mixing analysis, added some
minor comment
Supersymmetric Effects in Deep Inelastic Neutrino-Nucleus Scattering
We compute the supersymmetric (SUSY) contributions to neutrino
(antineutrino)-nucleus deep inelastic scattering in the Minimal Supersymmetric
Standard Model (MSSM). We consider the ratio of neutral current to charged
current cross sections, and , and compare with the
deviations of these quantities from the Standard Model predictions implied by
the recent NuTeV measurement. After performing a model-independent analysis, we
find that SUSY loop corrections generally have the opposite sign from the NuTeV
anomaly. We discuss one scenario in which a right-sign effect arises, and show
that it is ruled out by other precision data. We also study for R
parity-violating (RPV) contributions. Although RPV effects could, in principle,
reproduce the NuTeV anomaly, such a possibility is also ruled out by other
precision electroweak measurements.Comment: 30 pages, 13 figure
Simultaneous Extraction of the Fermi constant and PMNS matrix elements in the presence of a fourth generation
Several recent studies performed on constraints of a fourth generation of
quarks and leptons suffer from the ad-hoc assumption that 3 x 3 unitarity holds
for the first three generations in the neutrino sector. Only under this
assumption one is able to determine the Fermi constant G_F from the muon
lifetime measurement with the claimed precision of G_F = 1.16637 (1) x 10^-5
GeV^-2. We study how well G_F can be extracted within the framework of four
generations from leptonic and radiative mu and tau decays, as well as from K_l3
decays and leptonic decays of charged pions, and we discuss the role of lepton
universality tests in this context. We emphasize that constraints on a fourth
generation from quark and lepton flavour observables and from electroweak
precision observables can only be obtained in a consistent way if these three
sectors are considered simultaneously. In the combined fit to leptonic and
radiative mu and tau decays, K_l3 decays and leptonic decays of charged pions
we find a p-value of 2.6% for the fourth generation matrix element |U_{e 4}|=0
of the neutrino mixing matrix.Comment: 19 pages, 3 figures with 16 subfigures, references and text added
refering to earlier related work, figures and text in discussion section
added, results and conclusions unchange
Constraints on a Massive Dirac Neutrino Model
We examine constraints on a simple neutrino model in which there are three
massless and three massive Dirac neutrinos and in which the left handed
neutrinos are linear combinations of doublet and singlet neutrinos. We examine
constraints from direct decays into heavy neutrinos, indirect effects on
electroweak parameters, and flavor changing processes. We combine these
constraints to examine the allowed mass range for the heavy neutrinos of each
of the three generations.Comment: latex, 29 pages, 7 figures (not included), MIT-CTP-221
Tau Physics: Theoretical Perspective
The leptonic decays of the tau lepton provide relevant tests on the structure
of the weak currents and the universality of their couplings to the gauge
bosons. The hadronic tau decay modes constitute an ideal tool for studying
low--energy effects of the strong interaction in very clean conditions.
Accurate determinations of the QCD coupling and the strange quark mass have
been obtained with tau decay data. New physics phenomena, such as a non-zero
tau neutrino mass or violations of conservation laws can also be searched for
with tau decays.Comment: 12 pages, 10 figures. Invited talk at the Sixth International
Workshop on Tau Lepton Physics (Victoria, Canada, 18-21 September 2000
Testing new physics with the electron g-2
We argue that the anomalous magnetic moment of the electron (a_e) can be used
to probe new physics. We show that the present bound on new-physics
contributions to a_e is 8*10^-13, but the sensitivity can be improved by about
an order of magnitude with new measurements of a_e and more refined
determinations of alpha in atomic-physics experiments. Tests on new-physics
effects in a_e can play a crucial role in the interpretation of the observed
discrepancy in the anomalous magnetic moment of the muon (a_mu). In a large
class of models, new contributions to magnetic moments scale with the square of
lepton masses and thus the anomaly in a_mu suggests a new-physics effect in a_e
of (0.7 +- 0.2)*10^-13. We also present examples of new-physics theories in
which this scaling is violated and larger effects in a_e are expected. In such
models the value of a_e is correlated with specific predictions for processes
with violation of lepton number or lepton universality, and with the electric
dipole moment of the electron.Comment: 34 pages, 7 figures. Minor changes and references adde
Tau Lepton Physics: Theory Overview
The pure leptonic or semileptonic character of tau decays makes them a good
laboratory to test the structure of the weak currents and the universality of
their couplings to the gauge bosons. The hadronic tau decay modes constitute an
ideal tool for studying low-energy effects of the strong interactions in very
clean conditions; a well-known example is the precise determination of the QCD
coupling from tau-decay data. New physics phenomena, such as a non-zero
tau-neutrino mass or violations of (flavour / CP) conservation laws can also be
searched for with tau decays.Comment: 20 pages, latex, 5 Postscript figures, uses espcrc2.sty, Invited Talk
at the Fourth International Workshop on Tau Lepton Physics (TAU96), Colorado,
September 199
Leptonic and Semileptonic Decays of Charm and Bottom Hadrons
We review the experimental measurements and theoretical descriptions of
leptonic and semileptonic decays of particles containing a single heavy quark,
either charm or bottom. Measurements of bottom semileptonic decays are used to
determine the magnitudes of two fundamental parameters of the standard model,
the Cabibbo-Kobayashi-Maskawa matrix elements and . These
parameters are connected with the physics of quark flavor and mass, and they
have important implications for the breakdown of CP symmetry. To extract
precise values of and from measurements, however,
requires a good understanding of the decay dynamics. Measurements of both charm
and bottom decay distributions provide information on the interactions
governing these processes. The underlying weak transition in each case is
relatively simple, but the strong interactions that bind the quarks into
hadrons introduce complications. We also discuss new theoretical approaches,
especially heavy-quark effective theory and lattice QCD, which are providing
insights and predictions now being tested by experiment. An international
effort at many laboratories will rapidly advance knowledge of this physics
during the next decade.Comment: This review article will be published in Reviews of Modern Physics in
the fall, 1995. This file contains only the abstract and the table of
contents. The full 168-page document including 47 figures is available at
http://charm.physics.ucsb.edu/papers/slrevtex.p
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