985 research outputs found
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
A search for two body muon decay signals
Lepton family number violation is tested by searching for
decays among the 5.8 positive muon decay events analyzed by the
TWIST collaboration. Limits are set on the production of both massless and
massive bosons. The large angular acceptance of this experiment allows
limits to be placed on anisotropic decays, which can arise
from interactions violating both lepton flavor and parity conservation.
Branching ratio limits of order are obtained for bosons with masses
of 13 - 80 MeV/c and with different decay asymmetries. For bosons with
masses less than 13 MeV/c the asymmetry dependence is much stronger and
the 90% limit on the branching ratio varies up to . This is
the first study that explicitly evaluates the limits for anisotropic two body
muon decays.Comment: 7 pages, 5 figures, 2 tables, accepted by PR
Parton energy loss limits and shadowing in Drell-Yan dimuon production
A precise measurement of the ratios of the Drell-Yan cross section per
nucleon for an 800 GeV/c proton beam incident on Be, Fe and W targets is
reported. The behavior of the Drell-Yan ratios at small target parton momentum
fraction is well described by an existing fit to the shadowing observed in
deep-inelastic scattering. The cross section ratios as a function of the
incident parton momentum fraction set tight limits on the energy loss of quarks
passing through a cold nucleus
Neutrino induced transitions between the ground states of the A=12 triad
Neutrino induced reactions on C, an ingredient of liquid
scintillators, have been studied in several experiments. We show that for
currently available neutrino energies, 300 MeV, calculated
exclusive cross sections CN for both muon
and electron neutrinos are essentially model independent, provided the
calculations simultaneously describe the rates of several other reactions
involving the same states or their isobar analogs. The calculations agree well
with the measured cross sections, which can be therefore used to check the
normalization of the incident neutrino spectrum and the efficiency of the
detector.Comment: 9 pages REVTEX, 2 postscript figures, text and figures available at
http://www.krl.caltech.edu/preprints/MAP.htm
Measurement of Angular Distributions of Drell-Yan Dimuons in Interactions at 800 GeV/c
We report a measurement of the angular distributions of Drell-Yan dimuons
produced using an 800 GeV/c proton beam on a hydrogen target. The polar and
azimuthal angular distribution parameters have been extracted over the
kinematic range GeV/c (excluding the
resonance region), GeV/c, and . The angular
distributions are similar to those of , and both data sets are compared
with models which attribute the distribution either to the
presence of the transverse-momentum-dependent Boer-Mulders structure function
or to QCD effects. The data indicate the presence of both
mechanisms. The validity of the Lam-Tung relation in Drell-Yan is also
tested.Comment: 4 pages, 3 figure
Measurement of Angular Distributions of Drell-Yan Dimuons in p + d Interaction at 800 GeV/c
We report a measurement of the angular distributions of Drell-Yan dimuons
produced using an 800 GeV/c proton beam on a deuterium target. The muon angular
distributions in polar angle and azimuthal angle have been
measured over the kinematic range GeV/c, GeV/c, and . No significant cos dependence is found
in these proton-induced Drell-Yan data, in contrast to the situation for
pion-induced Drell-Yan. The data are compared with expectations from models
which attribute the cos distribution to a QCD vacuum effect or to the
presence of the transverse-momentum-dependent Boer-Mulders structure function
. Constraints on the magnitude of the sea-quark
structure functions are obtained.Comment: 4 pages, 3 figure
Measurement of the Light Antiquark Flavor Asymmetry in the Nucleon Sea
A precise measurement of the ratio of Drell-Yan yields from an 800 GeV/c
proton beam incident on hydrogen and deuterium targets is reported. Over
140,000 Drell-Yan muon pairs with dimuon mass M_{mu+ mu-} >= 4.5 GeV/c^2 were
recorded. From these data, the ratio of anti-down (dbar) to anti-up (ubar)
quark distributions in the proton sea is determined over a wide range in
Bjorken-x. A strong x dependence is observed in the ratio dbar/ubar, showing
substantial enhancement of dbar with respect to ubar for x<0.2. This result is
in fair agreement with recent parton distribution parameterizations of the sea.
For x>0.2, the observed dbar/ubar ratio is much nearer unity than given by the
parameterizations.Comment: REVTeX, to be published in Phys. Rev. Let
- …