Parity Violating Measurements of Neutron Densities

Parity violating electron nucleus scattering is a clean and powerful tool for measuring the spatial distributions of neutrons in nuclei with unprecedented accuracy. Parity violation arises from the interference of electromagnetic and weak neutral amplitudes, and the $Z^0$ of the Standard Model couples primarily to neutrons at low $Q^2$. The data can be interpreted with as much confidence as electromagnetic scattering. After briefly reviewing the present theoretical and experimental knowledge of neutron densities, we discuss possible parity violation measurements, their theoretical interpretation, and applications. The experiments are feasible at existing facilities. We show that theoretical corrections are either small or well understood, which makes the interpretation clean. The quantitative relationship to atomic parity nonconservation observables is examined, and we show that the electron scattering asymmetries can be directly applied to atomic PNC because the observables have approximately the same dependence on nuclear shape.Comment: 38 pages, 7 ps figures, very minor changes, submitted to Phys. Rev.

A quark model analysis of the charge symmetry breaking in nuclear force

In order to investigate the charge symmetry breaking (CSB) in the short range part of the nuclear force, we calculate the difference of the masses of the neutron and the proton, $\Delta {\rm M}$, the difference of the scattering lengths of the p-p and n-n scatterings, $\Delta a$, and the difference of the analyzing power of the proton and the neutron in the n-p scattering, $\Delta A(\theta)$, by a quark model. In the present model the sources of CSB are the mass difference of the up and down quarks and the electromagnetic interaction. We investigate how much each of them contributes to $\Delta {\rm M}$, $\Delta a$ and $\Delta A(\theta)$. It is found that the contribution of CSB of the short range part in the nuclear force is large enough to explain the observed $\Delta A(\theta)$, while $\Delta a$ is rather underestimated.Comment: 26 pages,6 figure

An accurate nucleon-nucleon potential with charge-independence breaking

We present a new high-quality nucleon-nucleon potential with explicit charge dependence and charge asymmetry, which we designate Argonne $v_{18}$. The model has a charge-independent part with fourteen operator components that is an updated version of the Argonne $v_{14}$ potential. Three additional charge-dependent and one charge-asymmetric operators are added, along with a complete electromagnetic interaction. The potential has been fit directly to the Nijmegen $pp$ and $np$ scattering data base, low-energy $nn$ scattering parameters, and deuteron binding energy. With 40 adjustable parameters it gives a $\chi^{2}$ per datum of 1.09 for 4301 $pp$ and $np$ data in the range 0--350 MeV.Comment: 36 pages, PHY-7742-TH-9

(12^{12}C,12^{12}B) and (12^{12}C,12^{12}N) reactions at E/A=70 MeV as spin probes: calibration and application to 1+^+ states in 56^{56}Mn

International audienc

Mass of 57Cu

The ground state Q value of the reaction 58Ni(7Li, 8He)57Cu has been measured [Q = -29.564(50) MeV]. The cross section for this reaction was found to be 130(30) nb/sr at 5.0 deg in the laboratory. This is the first report of the use of the (7Li,8He) reaction and the first measurement of the 57Cu mass excess. The deduced 57Cu atomic mass excess is -47.35(5) MeV. The implications of this result with respect to Coulomb displacement energy anomalies and nucleosynthesis of elements with A > 56 by the rp process are discussed.

DECAY STUDIES OF EXOTIC NUCLEI USING A REACTION PRODUCT MASS SEPARATOR AT MSU

A reaction products mass separator (RPMS) has been used to separate, by the ratio of mass to charge, the reaction products from the collisions of light, intermediate energy (appr. E/A = 30 MeV) nuclei with various targets. The decay modes of the separated nuclei were then studied in a low background environment. Measured in the first experiments with this device were the previously unknown lifetimes of 14Be(4.2(7)ms) and 17C (202(17)ms), and the β-branching ratios for the decay of 9C . The results are compared to shell-model calculations in order to understand the structure of the nuclei involved