118 research outputs found
Accelerator experiments on the contribution of secondary particles to the production of cosmogenic nuclides in meteorites
Through the interaction of galactic cosmic particle radiation (GCR) a wide variety of cosmogenic nuclides is produced in meteorites. They provide historical information about the cosmic radiation and the bombarded meteorites. An important way to understand the production mechanisms of cosmogenic nuclides in meteorites is to gather information about the depth and size dependence of the build-up of Galactic Rays Cosmic-secondary particles within meteorites of different sizes and chemical compositions. Simulation experiments with meteorite models offer an alternative to direct observation providing a data basis to describe the development and action of the secondary cascade induced by the GCR in meteorites
Q^2 Dependence of the S_{11}(1535) Photocoupling and Evidence for a P-wave resonance in eta electroproduction
New cross sections for the reaction are reported for total
center of mass energy =1.5--2.3 GeV and invariant squared momentum transfer
=0.13--3.3 GeV. This large kinematic range allows extraction of new
information about response functions, photocouplings, and coupling
strengths of baryon resonances. A sharp structure is seen at 1.7 GeV.
The shape of the differential cross section is indicative of the presence of a
-wave resonance that persists to high . Improved values are derived for
the photon coupling amplitude for the (1535) resonance. The new data
greatly expands the range covered and an interpretation of all data with
a consistent parameterization is provided.Comment: 31 pages, 9 figure
Photoproduction of phi(1020) mesons on the proton at large momentum transfer
The cross section for meson photoproduction on the proton has been
measured for the first time up to a four-momentum transfer -t = 4 GeV^2, using
the CLAS detector at the Thomas Jefferson National Accelerator Facility. At low
four-momentum transfer, the differential cross section is well described by
Pomeron exchange. At large four-momentum transfer, above -t = 1.8 GeV^2, the
data support a model where the Pomeron is resolved into its simplest component,
two gluons, which may couple to any quark in the proton and in the .Comment: 5 pages; 7 figure
Measurement of the Polarized Structure Function for in the Resonance Region
The polarized longitudinal-transverse structure function
has been measured using the reaction in the
resonance region at and 0.65 GeV. No previous
data exist for this reaction channel. The kinematically
complete experiment was performed at Jefferson Lab with the CEBAF Large
Acceptance Spectrometer (CLAS) using longitudinally polarized electrons at an
energy of 1.515 GeV. A partial wave analysis of the data shows generally better
agreement with recent phenomenological models of pion electroproduction
compared to the previously measured channel. A fit to both
and channels using a unitary isobar model suggests the unitarized
Born terms provide a consistent description of the non-resonant background. The
-channel pion pole term is important in the channel through a
rescattering correction, which could be model-dependent.Comment: 6 pages, LaTex, 5 eps figures: Submitted to PRC/Brief Reports v2:
Updated referenc
Deeply virtual and exclusive electroproduction of omega mesons
The exclusive omega electroproduction off the proton was studied in a large
kinematical domain above the nucleon resonance region and for the highest
possible photon virtuality (Q2) with the 5.75 GeV beam at CEBAF and the CLAS
spectrometer. Cross sections were measured up to large values of the
four-momentum transfer (-t < 2.7 GeV2) to the proton. The contributions of the
interference terms sigma_TT and sigma_TL to the cross sections, as well as an
analysis of the omega spin density matrix, indicate that helicity is not
conserved in this process. The t-channel pi0 exchange, or more generally the
exchange of the associated Regge trajectory, seems to dominate the reaction
gamma* p -> omega p, even for Q2 as large as 5 GeV2. Contributions of handbag
diagrams, related to Generalized Parton Distributions in the nucleon, are
therefore difficult to extract for this process. Remarkably, the high-t
behaviour of the cross sections is nearly Q2-independent, which may be
interpreted as a coupling of the photon to a point-like object in this
kinematical limit.Comment: 15 pages,19 figure
A Precise Measurement of the Neutron Magnetic Form Factor GMn in the Few-GeV2 Region
The neutron elastic magnetic form factor GMn has been extracted from
quasielastic electron scattering data on deuterium with the CEBAF Large
Acceptance Spectrometer (CLAS) at Jefferson Lab. The kinematic coverage of the
measurement is continuous from Q2=1 GeV2 to 4.8 GeV2. High precision was
achieved by employing a ratio technique in which many uncertainties cancel, and
by a simultaneous in-situ calibration of the neutron detection efficiency, the
largest correction to the data. Neutrons were detected using the CLAS
electromagnetic calorimeters and the time-of-flight scintillators. Data were
taken at two different electron beam energies, allowing up to four
semi-independent measurements of GMn to be made at each value of Q2. The dipole
parameterization is found to provide a good description of the data over the
measured Q2 range.Comment: 14 pages, 5 figures, revtex4, submitted to Physical Review Letters,
Revised version has changes recommended by journal referee
Measurement of Inclusive Spin Structure Functions of the Deuteron
We report the results of a new measurement of spin structure functions of the
deuteron in the region of moderate momentum transfer ( = 0.27 -- 1.3
(GeV/c)) and final hadronic state mass in the nucleon resonance region (
= 1.08 -- 2.0 GeV). We scattered a 2.5 GeV polarized continuous electron beam
at Jefferson Lab off a dynamically polarized cryogenic solid state target
(ND) and detected the scattered electrons with the CEBAF Large
Acceptance Spectrometer (CLAS). From our data, we extract the longitudinal
double spin asymmetry and the spin structure function . Our
data are generally in reasonable agreement with existing data from SLAC where
they overlap, and they represent a substantial improvement in statistical
precision. We compare our results with expectations for resonance asymmetries
and extrapolated deep inelastic scaling results. Finally, we evaluate the first
moment of the structure function and study its approach to both the
deep inelastic limit at large and to the Gerasimov-Drell-Hearn sum rule
at the real photon limit (). We find that the first moment varies
rapidly in the range of our experiment and crosses zero at between
0.5 and 0.8 (GeV/c), indicating the importance of the resonance at
these momentum transfers.Comment: 13 pages, 8 figures, ReVTeX 4, final version as accepted by Phys.
Rev.
Dependence of Quadrupole Strength in the Transition
Models of baryon structure predict a small quadrupole deformation of the
nucleon due to residual tensor forces between quarks or distortions from the
pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through
the dependence of the magnetic (), electric (), and
scalar () multipoles in the
transition. We report new experimental values for the ratios
and over the range = 0.4-1.8 GeV, extracted from
precision data using a truncated multipole expansion.
Results are best described by recent unitary models in which the pion cloud
plays a dominant role.Comment: 5 pages, 5 figures, 1 table. To be published in Phys. Rev. Lett.
(References, figures and table updated, minor changes.
Measurement of Beam-Spin Asymmetries for Deep Inelastic Electroproduction
We report the first evidence for a non-zero beam-spin azimuthal asymmetry in
the electroproduction of positive pions in the deep-inelastic region. Data have
been obtained using a polarized electron beam of 4.3 GeV with the CLAS detector
at the Thomas Jefferson National Accelerator Facility (JLab). The amplitude of
the modulation increases with the momentum of the pion relative to
the virtual photon, , with an average amplitude of for range.Comment: 5 pages, RevTEX4, 3 figures, 2 table
The e p -> e' p eta reaction at and above the S11(1535) baryon resonance
New cross sections for the reaction e p -> ep eta are reported for total
center of mass energy W = 1.5--1.86 GeV and invariant momentum transfer Q^2 =
0.25--1.5 GeV^2. This large kinematic range allows extraction of important new
information about response functions, photocouplings, and eta N coupling
strengths of baryon resonances. Expanded W coverage shows sharp structure at W
\~ 1.7 GeV; this is shown to come from interference between S and P waves and
can be interpreted in terms of known resonances. Improved values are derived
for the photon coupling amplitude for the S11(1535) resonance.Comment: 11 pages, RevTeX, 5 figures, submitted to Phys. Rev. Let
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