62 research outputs found
Time-reversal violation in threshold (n)over-right-arrow(p)over-right-arrow scattering
AbstractWe investigate parity and time-reversal violation in neutron–proton scattering in the optical regime. We calculate the neutron spin rotation and analyzing power in scattering on polarized protons. This allows us to quantify the sensitivity that such experiments should aim for in order to be competitive to present-day measurements of the neutron electric dipole moment in constraining the P- and T-odd two-nucleon interaction. While state-of-the-art techniques fall short by some three orders of magnitude for the neutron–proton case, specific neutron–nucleus experiments look promising, provided certain experimental and theoretical challenges are met
Pion and photon couplings of N* resonances from scattering on the proton
Results of a relativistic model for pion- and photon-induced reactions on the
proton are presented. The model is crossing symmetric and gauge invariant. The
nucleon resonances P_11 (1440), P_11 (1710), D_13 (1520), S_11 (1535), S_11
(1650), P_33 (1232), P_33 (1600), S_31 (1620), and D_33 (1700) have been
included explicitly in the calculation. Unitarity within the channel space \pi
N + \gamma N below the two-pion production threshold has been achieved by using
the K-matrix approach. Strong and electromagnetic coupling parameters of the N*
resonances have been determined from a fit to the pion-nucleon phase shifts,
pion-photoproduction multipoles and Compton-scattering cross sections. The
model is shown to describe simultaneously most of the available data. Results
for the electric and magnetic polarizabilities of the nucleon are presented.Comment: 12 pages, 3 figures, Revte
Hyperon-nucleon scattering and hyperon masses in the nuclear medium
We analyze low-energy hyperon-nucleon scattering using an effective field
theory in next-to-leading order. By fitting experimental cross sections for
laboratory hyperon momenta below 200 MeV/c and using information from the
hypertriton we determine twelve contact-interaction coefficients. Based on
these we discuss the low-density expansion of hyperon mass shifts in the
nuclear medium.Comment: 10 pages, 2 figure
Determination of the chiral coupling constants c3 and c4 in new pp and np partial-wave analyses
As a first result of two new partial-wave analyses, one of the pp and another
one of the np scattering data below 500 MeV, we report a study of the
long-range chiral two-pion exchange interaction which contains the chiral
coupling constants c1, c3, and c4. By using as input a theoretical value for c1
we are able to determine in pp as well as in np scattering accurate values for
c3 and c4. The values determined from the pp data and independently from the np
data are in very good agreement, indicating the correctness of the chiral
two-pion exchange interaction. The weighted averages are c3 = -4.78(10) / GeV
and c4 = 3.96(22) / GeV, where the errors are statistical. The value of c3 is
best determined from the pp data and that of c4 from the np data.Comment: 9 pages, 1 figure. Accepted for publication in Phys. Rev.
On the pion-nucleon coupling constant
In view of persisting misunderstanding about the determination of the
pion-nucleon coupling constants in the Nijmegen multienergy partial-wave
analyses of pp, np, and pbar-p scattering data, we present additional
information which may clarify several points of discussion. We comment on
several recent papers addressing the issue of the pion-nucleon coupling
constant and criticizing the Nijmegen analyses.Comment: 19 pages, Nijmegen preprint THEF-NYM-92-0
Pion Content of the Nucleon as seen in the NA51 Drell-Yan experiment
In a recent CERN Drell-Yan experiment the NA51 group found a strong asymmetry
of and densities in the proton at . We interpret
this result as a decisive confirmation of the pion-induced sea in the nucleon.Comment: 10 pages + 3 figures, Preprint KFA-IKP(TH)-1994-14 .tex file. After
\enddocument a uu-encodeded Postscript file comprising the figures is
appende
g_{\pi \Lambda \Sigma} and g_{K \Sigma \Xi} from QCD sum rules
The coupling constants g_{\pi \Lambda \Sigma} and g_{K \Sigma \Xi} are
calculated in the QCD sum rule approach using the three-point function method
and taking into account the SU(3) symmetry breaking effects. The pattern of
SU(3) breaking appears to be different from that based on SU(3) relations.Comment: revtex, 9 page
The Nucleon Electric Dipole Form Factor From Dimension-Six Time-Reversal Violation
We calculate the electric dipole form factor of the nucleon that arises as a
low-energy manifestation of time-reversal violation in quark-gluon interactions
of effective dimension 6: the quark electric and chromoelectric dipole moments,
and the gluon chromoelectric dipole moment. We use the framework of two-flavor
chiral perturbation theory to one loop
Dynamical effects in proton-proton bremsstrahlung for non-coplanar geometries
The proton-proton bremsstrahlung process, including both coplanar and non-coplanar kinematics, has been measured with polarized protons of 190 MeV. High-precision cross sections and analyzing powers have been obtained. Cross sections as a function of non-coplanarity angle are presented and show large variations of dynamical origin. Non-coplanar analyzing powers have been measured for the first time and are compared to theoretical predictions. (C) 2000 Elsevier Science B.V. All rights reserved
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