170 research outputs found
Evidence for a three-nucleon-force effect in proton-deuteron elastic scattering
Developments in spin-polarized internal targets for storage rings have
permitted measurements of 197 MeV polarized protons scattering from vector
polarized deuterons. This work presents measurements of the polarization
observables A_y, iT_11, and C_y,y in proton-deuteron elastic scattering. When
compared to calculations with and without three-nucleon forces, the
measurements indicate that three-nucleon forces make a significant contribution
to the observables. This work indicates that three-body forces derived from
static nuclear properties appear to be crucial to the description of dynamical
properties.Comment: 8 pages 2 figures Latex, submitted to Phys. Rev. Letter
Effects of the magnetic moment interaction between nucleons on observables in the 3N continuum
The influence of the magnetic moment interaction of nucleons on
nucleon-deuteron elastic scattering and breakup cross sections and on elastic
scattering polarization observables has been studied. Among the numerous
elastic scattering observables only the vector analyzing powers were found to
show a significant effect, and of opposite sign for the proton-deuteron and
neutron-deuteron systems. This finding results in an even larger discrepancy
than the one previously established between neutron-deuteron data and
theoretical calculations. For the breakup reaction the largest effect was found
for the final-state-interaction cross sections. The consequences of this
observation on previous determinations of the ^1S_0 scattering lengths from
breakup data are discussed.Comment: 24 pages, 6 ps figures, 1 png figur
Three-Nucleon Force Effects in Nucleon Induced Deuteron Breakup: Predictions of Current Models (I)
An extensive study of three-nucleon force effects in the entire phase space
of the nucleon-deuteron breakup process, for energies from above the deuteron
breakup threshold up to 200 MeV, has been performed. 3N Faddeev equations have
been solved rigorously using the modern high precision nucleon-nucleon
potentials AV18, CD Bonn, Nijm I, II and Nijm 93, and also adding 3N forces. We
compare predictions for cross sections and various polarization observables
when NN forces are used alone or when the two pion-exchange Tucson-Melbourne
3NF was combined with each of them. In addition AV18 was combined with the
Urbana IX 3NF and CD Bonn with the TM' 3NF, which is a modified version of the
TM 3NF, more consistent with chiral symmetry. Large but generally model
dependent 3NF effects have been found in certain breakup configurations,
especially at the higher energies, both for cross sections and spin
observables. These results demonstrate the usefulness of the kinematically
complete breakup reaction in testing the proper structure of 3N forces.Comment: 42 pages, 20 ps figures, 2 gif figure
A new form of three-body Faddeev equations in the continuum
We propose a novel approach to solve the three-nucleon (3N) Faddeev equation
which avoids the complicated singularity pattern going with the moving
logarithmic singularities of the standard approach. In this new approach the
treatment of the 3N Faddeev equation becomes essentially as simple as the
treatment of the two-body Lippmann-Schwinger equation. Very good agreement of
the new and old approaches in the application to nucleon-deuteron elastic
scattering and the breakup reaction is found.Comment: 20 pages, 3 eps figure
Observation of a Coherence Length Effect in Exclusive Rho^0 Electroproduction
Exclusive incoherent electroproduction of the rho^0(770) meson from 1H, 2H,
3He, and 14N targets has been studied by the HERMES experiment at squared
four-momentum transfer Q**2>0.4 GeV**2 and positron energy loss nu from 9 to 20
GeV. The ratio of the 14N to 1H cross sections per nucleon, known as the
nuclear transparency, was found to decrease with increasing coherence length of
quark-antiquark fluctuations of the virtual photon. The data provide clear
evidence of the interaction of the quark- antiquark fluctuations with the
nuclear medium.Comment: RevTeX, 5 pages, 3 figure
Flavor Decomposition of the Polarized Quark Distributions in the Nucleon from Inclusive and Semi-inclusive Deep-inelastic Scattering
Spin asymmetries of semi-inclusive cross sections for the production of
positively and negatively charged hadrons have been measured in deep-inelastic
scattering of polarized positrons on polarized hydrogen and 3He targets, in the
kinematic range 0.023<x<0.6 and 1 GeV^2<Q^2<10 GeV^2. Polarized quark
distributions are extracted as a function of x for up $(u+u_bar) and down
(d+d_bar) flavors. The up quark polarization is positive and the down quark
polarization is negative in the measured range. The polarization of the sea is
compatible with zero. The first moments of the polarized quark distributions
are presented. The isospin non-singlet combination Delta_q_3 is consistent with
the prediction based on the Bjorken sum rule. The moments of the polarized
quark distributions are compared to predictions based on SU(3)_f flavor
symmetry and to a prediction from lattice QCD.Comment: 14 pages, 6 figures (eps format), 10 tables in Latex New version
contains tables of asymmetries and correlation matri
Demonstration of the temporal matter-wave Talbot effect for trapped matter waves
We demonstrate the temporal Talbot effect for trapped matter waves using
ultracold atoms in an optical lattice. We investigate the phase evolution of an
array of essentially non-interacting matter waves and observe matter-wave
collapse and revival in the form of a Talbot interference pattern. By using
long expansion times, we image momentum space with sub-recoil resolution,
allowing us to observe fractional Talbot fringes up to 10th order.Comment: 17 pages, 7 figure
Kaon Production and Kaon to Pion Ratio in Au+Au Collisions at \snn=130 GeV
Mid-rapidity transverse mass spectra and multiplicity densities of charged
and neutral kaons are reported for Au+Au collisions at \snn=130 GeV at RHIC.
The spectra are exponential in transverse mass, with an inverse slope of about
280 MeV in central collisions. The multiplicity densities for these particles
scale with the negative hadron pseudo-rapidity density. The charged kaon to
pion ratios are and
for the most central collisions. The ratio is lower than the same
ratio observed at the SPS while the is higher than the SPS result.
Both ratios are enhanced by about 50% relative to p+p and +p
collision data at similar energies.Comment: 6 pages, 3 figures, 1 tabl
The energy dependence of angular correlations inferred from mean- fluctuation scale dependence in heavy ion collisions at the SPS and RHIC
We present the first study of the energy dependence of angular
correlations inferred from event-wise mean transverse momentum
fluctuations in heavy ion collisions. We compare our large-acceptance
measurements at CM energies $\sqrt{s_{NN}} =$ 19.6, 62.4, 130 and 200 GeV to
SPS measurements at 12.3 and 17.3 GeV. $p_t$ angular correlation structure
suggests that the principal source of $p_t$ correlations and fluctuations is
minijets (minimum-bias parton fragments). We observe a dramatic increase in
correlations and fluctuations from SPS to RHIC energies, increasing linearly
with $\ln \sqrt{s_{NN}}$ from the onset of observable jet-related
fluctuations near 10 GeV.Comment: 10 pages, 4 figure
Partonic flow and -meson production in Au+Au collisions at = 200 GeV
We present first measurements of the -meson elliptic flow
() and high statistics distributions for different
centralities from = 200 GeV Au+Au collisions at RHIC. In
minimum bias collisions the of the meson is consistent with the
trend observed for mesons. The ratio of the yields of the to those of
the as a function of transverse momentum is consistent with a model
based on the recombination of thermal quarks up to GeV/,
but disagrees at higher momenta. The nuclear modification factor () of
follows the trend observed in the mesons rather than in
baryons, supporting baryon-meson scaling. Since -mesons are
made via coalescence of seemingly thermalized quarks in central Au+Au
collisions, the observations imply hot and dense matter with partonic
collectivity has been formed at RHIC.Comment: 6 pages, 4 figures, submit to PR
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