55 research outputs found
A measurement of parity-violating gamma-ray asymmetries in polarized cold neutron capture on 35Cl, 113Cd, and 139La
An apparatus for measuring parity-violating asymmetries in gamma-ray emission
following polarized cold neutron capture was constructed as a 1/10th scale test
of the design for the forthcoming n+p->d+gamma experiment at LANSCE. The
elements of the polarized neutron beam, including a polarized 3He neutron spin
filter and a radio frequency neutron spin rotator, are described. Using CsI(Tl)
detectors and photodiode current mode readout, measurements were made of
asymmetries in gamma-ray emission following neutron capture on 35Cl, 113Cd, and
139La targets. Upper limits on the parity-allowed asymmetry were set at the level of 7 x 10^-6 for all three
targets. Parity-violating asymmetries were observed in
35Cl, A_gamma = (-29.1 +- 6.7) x 10^-6, and 139La, A_gamma = (-15.5 +- 7.1) x
10^-6, values consistent with previous measurements.Comment: 19 pages, 4 figures, submitted to Nucl. Instr. and Meth.
Radiative β decay of the free neutron
The theory of quantum electrodynamics predicts that the β decay of the neutron into a proton, electron, and antineutrino is accompanied by a continuous spectrum of emitted photons described as inner bremsstrahlung. While this phenomenon has been observed in nuclear β decay and electron-capture decay for many years, it has only been recently observed in free-neutron decay. We present a detailed discussion of an experiment in which the radiative decay mode of the free neutron was observed. In this experiment, the branching ratio for this rare decay was determined by recording photons that were correlated with both the electron and proton emitted in neutron decay. We determined the branching ratio for photons with energy between 15 and 340 keV to be (3.09±0.32)×10-3 (68% level of confidence), where the uncertainty is dominated by systematic effects. This value for the branching ratio is consistent with theoretical predictions. The characteristic energy spectrum of the radiated photons, which differs from the uncorrelated background spectrum, is also consistent with the theoretical spectrum
A gamma- and X-ray detector for cryogenic, high magnetic field applications
As part of an experiment to measure the spectrum of photons emitted in
beta-decay of the free neutron, we developed and operated a detector consisting
of 12 bismuth germanate (BGO) crystals coupled to avalanche photodiodes (APDs).
The detector was operated near liquid nitrogen temperature in the bore of a
superconducting magnet and registered photons with energies from 5 keV to 1000
keV. To enlarge the detection range, we also directly detected soft X-rays with
energies between 0.2 keV and 20 keV with three large area APDs. The
construction and operation of the detector is presented, as well as information
on operation of APDs at cryogenic temperatures
Precision Measurement of PArity Violation in Polarized Cold Neutron Capture on the Proton: the NPDGamma Experiment
The NPDGamma experiment at the Los Alamos Neutron Science Center (LANSCE) is
dedicated to measure with high precision the parity violating asymmetry in the
emission after capture of spin polarized cold neutrons in
para-hydrogen. The measurement will determine unambiguously the weak
pion-nucleon-nucleon () coupling constant {\it f}Comment: Proceedings of the PANIC'05 Conference, Santa Fe, NM, USA, October
24-28, 2005, 3 pages, 2 figure
CPT, T, and Lorentz Violation in Neutral-Meson Oscillations
Tests of CPT and Lorentz symmetry using neutral-meson oscillations are
studied within a formalism that allows for indirect CPT and T violation of
arbitrary size and is independent of phase conventions. The analysis is
particularly appropriate for studies of CPT and T violation in oscillations of
the heavy neutral mesons D, B_d, and B_s. The general Lorentz- and CPT-breaking
standard-model extension is used to derive an expression for the parameter for
CPT violation. It varies in a prescribed way with the magnitude and orientation
of the meson momentum and consequently also with sidereal time. Decay
probabilities are presented for both uncorrelated and correlated mesons, and
some implications for experiments are discussed.Comment: 11 pages, references added, accepted in Physical Review
Probing Lorentz and CPT violation with space-based experiments
Space-based experiments offer sensitivity to numerous unmeasured effects
involving Lorentz and CPT violation. We provide a classification of clock
sensitivities and present explicit expressions for time variations arising in
such experiments from nonzero coefficients in the Lorentz- and CPT-violating
Standard-Model Extension.Comment: 15 page
Measurement of the Proton and Deuteron Spin Structure Functions g2 and Asymmetry A2
We have measured the spin structure functions g2p and g2d and the virtual
photon asymmetries A2p and A2d over the kinematic range 0.02 < x < 0.8 and 1.0
< Q^2 < 30(GeV/c)^2 by scattering 38.8 GeV longitudinally polarized electrons
from transversely polarized NH3 and 6LiD targets.The absolute value of A2 is
significantly smaller than the sqrt{R} positivity limit over the measured
range, while g2 is consistent with the twist-2 Wandzura-Wilczek calculation. We
obtain results for the twist-3 reduced matrix elements d2p, d2d and d2n. The
Burkhardt-Cottingham sum rule integral - int(g2(x)dx) is reported for the range
0.02 < x < 0.8.Comment: 12 pages, 4 figures, 1 tabl
Recent Advances in Understanding Particle Acceleration Processes in Solar Flares
We review basic theoretical concepts in particle acceleration, with
particular emphasis on processes likely to occur in regions of magnetic
reconnection. Several new developments are discussed, including detailed
studies of reconnection in three-dimensional magnetic field configurations
(e.g., current sheets, collapsing traps, separatrix regions) and stochastic
acceleration in a turbulent environment. Fluid, test-particle, and
particle-in-cell approaches are used and results compared. While these studies
show considerable promise in accounting for the various observational
manifestations of solar flares, they are limited by a number of factors, mostly
relating to available computational power. Not the least of these issues is the
need to explicitly incorporate the electrodynamic feedback of the accelerated
particles themselves on the environment in which they are accelerated. A brief
prognosis for future advancement is offered.Comment: This is a chapter in a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011
Corrections to flat-space particle dynamics arising from space granularity
The construction of effective Hamiltonians describing corrections to flat
space particle dynamics arising from the granularity of space at very short
distances is discussed in the framework of an heuristic approach to the
semiclassical limit of loop quantum gravity. After some general motivation of
the subject, a brief non-specialist introduction to the basic tools employed in
the loop approach is presented. The heuristical semiclassical limit is
subsequently defined and the application to the case of photons and spin 1/2
fermions is described. The resulting modified Maxwell and Dirac Hamiltonians,
leading in particular to Planck scale corrections in the energy-momentum
relations, are presented. Alternative interpretations of the results and their
limitations, together with other approaches are briefly discussed along the
text. Three topics related to the above methods are reviewed: (1) The
determination of bounds to the Lorentz violating parameters in the fermionic
sector, obtained from clock comparison experiments.(2) The calculation of
radiative corrections in preferred frames associated to space granularity in
the framework of a Yukawa model for the interactions and (3) The calculation of
synchrotron radiation in the framework of the Myers-Pospelov effective theories
describing Lorentz invariance violations, as well as a generalized approach to
radiation in Planck scale modified electrodynamics. The above exploratory
results show that quantum gravity phenomenology provides observational guidance
in the construction of quantum gravity theories and opens up the possibility of
probing Planck scale physics.Comment: 49 pages, 6 figures and 4 tables. Extended version of the talk given
at the 339-th WE-Heraeus-Seminar: Special Relativity, will it survive the
next 100 years?, Potsdam, february 200
Precision measurement of the deuteron spin structure function
We report on a high-statistics measurement of the deuteron spin structure function g[sup d][sub 1] at a beam energy of 29 GeV in the kinematic range 0.029 < x < 0.8 and 1 < Q2 < 10 (GeV/c)2. The integral Gamma [sup d][sub 1] = (integral)[sup 1][sub 0]g[sup d][sub 1]dx evaluated at fixed Q2 = 3 (GeV/c)2 gives 0.042 ± 0.003(stat) ± 0.004(syst). Combining this result with our earlier measurement of g[sup p][sub 1], we find Gamma [sup p][sub 1]- Gamma [sup n][sub 1] = 0.163 ± 0.010(stat) ± 0.016(syst), which agrees with the prediction of the Bjorken sum rule with O( alpha [sup 3][sub s]) corrections, Gamma [sup p][sub 1]- Gamma [sup n][sub 1] = 0.171 ± 0.008. We find the quark contribution to the proton helicity to be Delta q = 0.30 ± 0.06
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