524 research outputs found
Neutrino-Nucleus Reactions and Muon Capture in 12C
The neutrino-nucleus cross section and the muon capture rate are discussed
within a simple formalism which facilitates the nuclear structure calculations.
The corresponding formulae only depend on four types of nuclear matrix
elements, which are currently used in the nuclear beta decay. We have also
considered the non-locality effects arising from the velocity-dependent terms
in the hadronic current. We show that for both observables in 12C the higher
order relativistic corrections are of the order of ~5 only, and therefore do
not play a significant role. As nuclear model framework we use the projected
QRPA (PQRPA) and show that the number projection plays a crucial role in
removing the degeneracy between the proton-neutron two quasiparticle states at
the level of the mean field. Comparison is done with both the experimental data
and the previous shell model calculations. Possible consequences of the present
study on the determination of the neutrino oscillation
probability are briefly addressed.Comment: 29 pages, 6 figures, Revtex4. Several changes were made to the
previous manuscript, the results and final conclusions remain unalterable. It
has been accepted for publication as a Regular Article in Physical Review
Light response of pure CsI calorimeter crystals painted with wavelength-shifting lacquer
We have measured scintillation properties of pure CsI crystals used in the
shower calorimeter built for a precise determination of the pi+ -> pi0 e+ nu
decay rate at the Paul Scherrer Institute (PSI). All 240 individual crystals
painted with a special wavelength-shifting solution were examined in a
custom-build detection apparatus (RASTA=radioactive source tomography
apparatus) that uses a 137Cs radioactive gamma source, cosmic muons and a light
emitting diode as complementary probes of the scintillator light response. We
have extracted the total light output, axial light collection nonuniformities
and timing responses of the individual CsI crystals. These results predict
improved performance of the 3 pi sr PIBETA calorimeter due to the painted
lateral surfaces of 240 CsI crystals. The wavelength-shifting paint treatment
did not affect appreciably the total light output and timing resolution of our
crystal sample. The predicted energy resolution for positrons and photons in
the energy range of 10-100 MeV was nevertheless improved due to the more
favorable axial light collection probability variation. We have compared
simulated calorimeter ADC spectra due to 70 MeV positrons and photons with a
Monte Carlo calculation of an ideal detector light response.Comment: Elsevier LaTeX, 35 pages in e-print format, 15 Postscript Figures and
4 Tables, also available at
http://pibeta.phys.virginia.edu/~pibeta/subprojects/csipro/tomo/rasta.p
Ratios of Elastic Scattering of Pions from 3H and 3He
We have measured the elastic-scattering ratios of normalized yields for
charged pions from 3H and 3He in the backward hemisphere. At 180 MeV, we
completed the angular distribution begun with our earlier measurements, adding
six data points in the angular range of 119 deg to 169 deg in the pi-nucleus
center of mass. We also measured an excitation function with data points at
142, 180, 220, and 256 MeV incident pion energy at the largest achievable angle
for each energy between 160 deg and 170 deg in the pi-nucleus center of mass.
This excitation function corresponds to the energies of our forward-hemisphere
studies. The data, taken as a whole, show an apparent role reversal of the two
charge-symmetric ratios r1 and r2 in the backward hemisphere. Also, for data >
100 deg we observe a strong dependence on the four-momentum transfer squared
(-t) for all of the ratios regardless of pion energy or scattering angle, and
we find that the superratio R data match very well with calculations based on
the forward-hemisphere data that predicts the value of the difference between
the even-nucleon radii of 3H and 3He. Comparisons are also made with recent
calculations incorporating different wave functions and double scattering
models.Comment: RevTex 8pages, 12 figure file
Measurement of Inverse Pion Photoproduction at Energies Spanning the N(1440) Resonance
Differential cross sections for the process pi^- p -> gamma n have been
measured at Brookhaven National Laboratory's Alternating Gradient Synchrotron
with the Crystal Ball multiphoton spectrometer. Measurements were made at 18
pion momenta from 238 to 748 MeV/c, corresponding to E_gamma for the inverse
reaction from 285 to 769 MeV. The data have been used to evaluate the gamma n
multipoles in the vicinity of the N(1440) resonance. We compare our data and
multipoles to previous determinations. A new three-parameter SAID fit yields 36
+/- 7 (GeV)^-1/2 X 10^-3 for the A^n_1/2 amplitude of the P_11.Comment: 14 pages, 8 figures, submitted to PR
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
Global proteomics analysis of the response to starvation in <i>C. elegans</i>
Periodic starvation of animals induces large shifts in metabolism but may also influence many other cellular systems and can lead to adaption to prolonged starvation conditions. To date, there is limited understanding of how starvation affects gene expression, particularly at the protein level. Here, we have used mass-spectrometry-based quantitative proteomics to identify global changes in the Caenorhabditis elegans proteome due to acute starvation of young adult animals. Measuring changes in the abundance of over 5,000 proteins, we show that acute starvation rapidly alters the levels of hundreds of proteins, many involved in central metabolic pathways, highlighting key regulatory responses. Surprisingly, we also detect changes in the abundance of chromatin-associated proteins, including specific linker histones, histone variants, and histone posttranslational modifications associated with the epigenetic control of gene expression. To maximize community access to these data, they are presented in an online searchable database, the Encyclopedia of Proteome Dynamics (http://www.peptracker.com/epd/)
Influence of spin-rotation measurements on partial-wave analyses of elastic pion-nucleon scattering
Recent measurements of spin-rotation parameters in elastic
scattering are in marked disagreement with predictions of the
Carnegie-MellonBerkeley and Karlsruhe-Helsinki analyses. Using the method of
Barrelet, we show how this discrepancy can be removed. We then show how this
Barrelet transformation alters the partial-wave amplitudes. The effect of
unitarity and analyticity constraints is also considered.Comment: 9 pages, 4 figures. Postscript figures also available from
ftp://clsaid.phys.vt.edu/pub/said/pin/barrele
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