97 research outputs found
A particle-hole model approach for hypernuclei
A particle-hole model is developed to describe the excitation spectrum of
single lambda hypernuclei and the possible presence of collective effects is
explored by making a comparison with the mean-field calculations. Results for
the spectra of 12C, 16O, 40Ca, 90Zr and 208Pb single lambda hypernuclei are
shown. The comparison with the available experimental data is satisfactory. We
find that collective phenomena are much less important in hypernuclei than in
ordinary nuclei.Comment: 24 pages, 5 eps figures, accepted for publication in Nucl. Phys.
Gamma-Ray Spectroscopy of O and N Hypernuclei via the O reaction
he bound-state level structures of the O and
N hypernuclei were studied by -ray spectroscopy using
a germanium detector array (Hyperball) via the O ()
reaction. A level scheme for O was determined from the
observation of three -ray transitions from the doublet of states
(,) at MeV to the ground-state doublet (,). The
N hypernuclei were produced via proton emission from unbound
states in O . Three -rays were observed and the
lifetime of the state in N was measured by the
Doppler shift attenuation method. By comparing the experimental results with
shell-model calculations, the spin-dependence of the interaction is
discussed. In particular, the measured O ground-state doublet
spacing of 26.4 1.6 0.5 keV determines a small but nonzero strength
of the tensor interaction.Comment: 22 pages, 17 figure
Mesonic and nonmesonic weak decay widths of medium-heavy lambda hypernuclei
We have measured the energy spectra of pions and protons emitted in the weak
decay of 12_Lambda_C, 28_Lambda_Si, and Lambda_Fe hypernuclei produced via the
(pi+, K+) reaction. The decay widths of the pi- mesonic decay (Lambda -> p +
pi-) and the nonmesonic decay (Lambda + N -> N + N) were extracted. The present
results demonstrate an increase of the mesonic decay width due to a distortion
of the pion wave function in nuclear medium for the first time. The ratios of
the neutron- to proton-induced nonmesonic decay widths, Gamma_n(Lambda + n -> n
+ n)/Gamma_p(Lambda + p -> n + p), were evaluated by a direct comparison of the
measured proton energy spectra with the calculated ones. No theoretical
calculation which has been proposed so far can simultaneously account for both
the nonmesonic decay widths and the Gamma_n/Gamma_p ratios in the present data.Comment: 28 pages, 11 figures, Published in Physical Review
Strangeness nuclear physics: a critical review on selected topics
Selected topics in strangeness nuclear physics are critically reviewed. This
includes production, structure and weak decay of --Hypernuclei, the
nuclear interaction and the possible existence of bound
states in nuclei. Perspectives for future studies on these issues are also
outlined.Comment: 63 pages, 51 figures, accepted for publication on European Physical
Journal
Study of the Sigma-nucleus potential by the (pi^-,K^+) reaction on medium-to-heavy nuclear targets
In order to study the Sigma-nucleus optical potential, we measured inclusive
(pi^-,K^+) spectra on medium-to-heavy nuclear targets: CH_2, Si, Ni, In and Bi.
The CH_2 target was used to calibrate the excitation energy scale by using the
elementary process p + pi^- -> K^+ + Sigma^-, where the C spectrum was also
extracted. The calibration was done with +-0.1 MeV precision. The angular
distribution of the elementary cross section was measured, and agreed well with
the previous bubble chamber data, but with better statistics, and the
magnitudes of the cross sections of the measured inclusive (pi^-,K^+) spectra
were also well calibrated. All of the inclusive spectra were found to be
similar in shape at a region near to the Sigma^- binding energy threshold,
showing a weak mass-number dependence on the magnitude of the cross section.
The measured spectra were compared with a theoretical calculation performed
within the framework of the Distorted Wave Impulse Approximation (DWIA). It has
been demonstrated that a strongly repulsive \sig-nucleus potential with a
non-zero size of the imaginary part is required to reproduce the shape of the
measured spectra.Comment: 21 pages, 24 figures, submitted to PR
Gamma-Ray Spectroscopy in Lambda Hypernuclei
The present status of hypernuclear gamma-ray spectroscopy with Hyperball is
summarized. We observed two gamma transitions of 16-Lambda-O(1- -> 1-,0-) and
obtained the strength of the Lambda-N tensor force. In 10B(K-,pi- gamma) data,
we did not observe the spin-flip M1 transition of 10-Lambda-B(2- -> 1-), but
gamma rays from hyperfragments such as 7-Lambda-Li(7/2+ -> 5/2+) and
9-Lambda-Be(3/2+ ->1/2+) were observed. In 11B(pi+,K+ gamma) data, we observed
six gamma transitions of 11_Lambda-B. We also attempted an inclusive gamma-ray
measurement with stopped K- beam.Comment: 10 pages, 9 figures, 8th International Conference on Hypernuclear and
Strange Particle Physics (HYP2003), Newport News, Virginia, 14-18 Oct 2003,
to appear in Nuclear Physics
First Results on 12Lambda-C production at DAPHNE
Lambda-hypernuclei are produced and studied, with the FINUDA spectrometer,
for the first time at an e+e- collider: DAPHNE, the Frascati phi-factory. The
slow negative kaons from phi(1020) decay are stopped in thin (0.2 g/cm^2)
nuclear targets, and Lambda-hypernuclei formation is detected by measuring the
momentum of the outgoing pi^-. A preliminary analysis on 12Lambda-C shows an
energy resolution of 1.29 MeV FWHM on the hypernuclear levels, the best
obtained so far with magnetic spectrometers at hadron facilities. Capture rates
for the ground state and the excited ones are reported, and compared with
previous experiments.Comment: 15 pages, 5 figures. v2: one reference updated. Accepted for
publication in Phys. Lett.
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