5 research outputs found
Double radiative pion capture on hydrogen and deuterium and the nucleon's pion cloud
We report measurements of double radiative capture in pionic hydrogen and
pionic deuterium. The measurements were performed with the RMC spectrometer at
the TRIUMF cyclotron by recording photon pairs from pion stops in liquid
hydrogen and deuterium targets. We obtained absolute branching ratios of for hydrogen and for deuterium, and
relative branching ratios of double radiative capture to single radiative
capture of for hydrogen
and for
deuterium. For hydrogen, the measured branching ratio and photon energy-angle
distributions are in fair agreement with a reaction mechanism involving the
annihilation of the incident on the cloud of the target proton.
For deuterium, the measured branching ratio and energy-angle distributions are
qualitatively consistent with simple arguments for the expected role of the
spectator neutron. A comparison between our hydrogen and deuterium data and
earlier beryllium and carbon data reveals substantial changes in the relative
branching ratios and the energy-angle distributions and is in agreement with
the expected evolution of the reaction dynamics from an annihilation process in
S-state capture to a bremsstrahlung process in P-state capture. Lastly, we
comment on the relevance of the double radiative process to the investigation
of the charged pion polarizability and the in-medium pion field.Comment: 44 pages, 7 tables, 13 figures, submitted to Phys. Rev.
3N Scattering in a Three-Dimensional Operator Formulation
A recently developed formulation for a direct treatment of the equations for
two- and three-nucleon bound states as set of coupled equations of scalar
functions depending only on vector momenta is extended to three-nucleon
scattering. Starting from the spin-momentum dependence occurring as scalar
products in two- and three-nucleon forces together with other scalar functions,
we present the Faddeev multiple scattering series in which order by order the
spin-degrees can be treated analytically leading to 3D integrations over scalar
functions depending on momentum vectors only. Such formulation is especially
important in view of awaiting extension of 3N Faddeev calculations to
projectile energies above the pion production threshold and applications of
chiral perturbation theory 3N forces, which are to be most efficiently treated
directly in such three-dimensional formulation without having to expand these
forces into a partial wave basis.Comment: 25 pages, 0 figure
Faddeev Calculations of Proton-Deuteron Radiative Capture with Exchange Currents
pd capture processes at various energies have been analyzed based on
solutions of 3N-Faddeev equations and using modern NN forces. The application
of the Siegert theorem is compared to the explicit use of - and
-like exchange currents connected to the AV18 NN interaction. Overall
good agreement with cross sections and spin observables has been obtained but
leaving room for improvement in some cases. Feasibility studies for 3NF's
consistently included in the 3N continuum and the 3N bound state have been
performed as well.Comment: Minor changes in notation, ps files for figure
Multiplicity fluctuations in Au+Au collisions at GeV
We present the results of charged particle fluctuations measurements in Au +
Au collisions at GeV using the STAR detector. Dynamical
fluctuations measurements are presented for inclusive charged particle
multiplicities as well as for identified charged pions, kaons, and protons. The
net charge dynamical fluctuations are found to be large and negative providing
clear evidence that positive and negative charged particle production is
correlated within the pseudorapidity range investigated. Correlations are
smaller than expected based on model-dependent predictions for a resonance gas
or a quark gluon gas which undergoes fast hadronization and freeze-out.
Qualitative agreement is found with comparable scaled p+p measurements and a
HIJING model calculation based on independent particle collisions, although a
small deviation from the 1/N scaling dependence expected from this model is
observed.Comment: 9 pages, 2 figures in 3 files, submitted PR