11 research outputs found
Intrinsic quadrupole moment of the nucleon
We address the question of the intrinsic quadrupole moment Q_0 of the nucleon
in various models. All models give a positive intrinsic quadrupole moment for
the proton. This corresponds to a prolate deformation. We also calculate the
intrinsic quadrupole moment of the Delta(1232). All our models lead to a
negative intrinsic quadrupole moment of the Delta corresponding to an oblate
deformation.Comment: 17 pages, 5 figure
(gamma,np) reactions in <sup>12</sup>C , <sup>6</sup>Li and <sup>3,4</sup>He
The emission of neutron-proton pairs is the most probable outcome of photon absorbtion in the energy region above the giant resonance at least up to the pion threshold, but little detailed information on the process has been obtained due to experimental difficulties. Two nucleon emission following photon absorbtion by a correlated pair is favoured
compared to direct knockout of a single nucleon, which is suppressed by the large momentum mismatch between the ingoing photon and a single outgoing fast nucleon. Studies of the (gamma,np) process seek firstly to obtain a quantitative
understanding of the photon interaction mechanism, and through this to open the door to investigations of nucleon
correlations in nuclei [1], information about which is long sought but not readily obtainable
Measurement of the recoil polarization in the p (\vec e, e' \vec p) pi^0 reaction at the \Delta(1232) resonance
The recoil proton polarization has been measured in the p (\vec e,e'\vec p)
pi^0 reaction in parallel kinematics around W = 1232 MeV, Q^2 = 0.121 (GeV/c)^2
and epsilon = 0.718 using the polarized c.w. electron beam of the Mainz
Microtron. Due to the spin precession in a magnetic spectrometer, all three
proton polarization components P_x/P_e = (-11.4 \pm 1.3 \pm 1.4) %, P_y =
(-43.1 \pm 1.3 \pm 2.2) %, and P_z/P_e = (56.2 \pm 1.5 \pm 2.6) % could be
measured simultaneously. The Coulomb quadrupole to magnetic dipole ratio CMR =
(-6.4\pm 0.7_{stat}\pm 0.8_{syst}) % was determined from P_x in the framework
of the Mainz Unitary Isobar Model. The consistency among the reduced
polarizations and the extraction of the ratio of longitudinal to transverse
response is discussed.Comment: 5 pages LaTeX, 1 table, 2 eps figure
Delta-to-N-gamma Coulomb Quadrupole Amplitude in PQCD
We present a leading-order pQCD calculation of the helicity-flip matrix element (Coulomb quadrupole amplitude ), taking
into account the transverse momenta of the quarks and the contribution from the
gluons. In the large limit, its scaling behavior acquires a
double-logarithmic correction compared with the
standard scaling analysis, due to the contribution from the orbital motion of
the small- partons. Based on this and on the latest JLab experimental
results of the ratio at = 3 4 GeV, we make a
phenomenological prediction for the latter at higher values of .Comment: 9 pages, two figure
Measurement of the R response function for electroproduction at = 0.070 (GeV/c) in the transition}
Quadrupole amplitudes in the transition are associated
with the issue of nucleon deformation. A search for these small amplitudes has
been the focus of a series of measurements undertaken at Bates/MIT by the OOPS
collaboration. We report on results from H data obtained
at (GeV/c) and invariant mass of W=1155 MeV using the
out-of-plane detection technique with the OOPS spectrometers. The
and response functions were isolated.
These results, along with those of previous measurements at =1172 MeV and
(GeV/c), aim in elucidating the interplay between resonant and
non resonant amplitudes