M. Allet

Positron polarization in the decay of polarized N-12: a precision test of the Standard Model

The longitudinal polarization of positrons emitted along and opposite to the nuclear spin direction has been measured in the decay of polarized N-12. The results are consistent with the Standard Model prediction. In manifest left-right symmetric models this measurement provides a lower bound of 310 GeV/c(2) at 90% CL on the mass of a possible right-handed gauge boson contributing to the electroweak interaction. In generalized versions of this model our measurement provides constraints complementary to those set by high-energy experiments

Search for right-handed weak currents in the beta-asymmetry-polarization correlation from N-12 decay

Abstract The polarization of positrons emitted along and opposite to the nuclear spin direction has been measured in the decay of polarized 12 N. The results are consistent with the Standard Model prediction. In manifest left-right symmetric models this measurement provides a lower limit of 220 GeV/c 2 at 90% CL on the mass of an eventual right-handed gauge boson contributing to the electroweak interaction.

Helicity structure in low- and intermediate-energy weak interaction

Abstract We report on the status of the measurements of the longitudinal polarization of positrons emitted by polarized 107In and 12N nuclei. Present results yield a lower limit of 306 GeV/c2 (90 % CL) for the mass of a possible W gauge boson with predominantly right-handed couplings, if interpreted in the framework of the manifest left-right symmetric model. In addition, the helicity structure of the weak interaction is discussed on the basis of experimental results at low and intermediate energies in the leptonic, semileptonic and hadronic sectors. Whereas in the minimal manifest left-right symmetric extension of the Standard Model the results from collider experiments are superior to results from other experiments, experiments in the three sectors of the weak interaction yield complementary information on the helicity structure of the interaction if interpreted in general left-right symmetric models.

Effects of the Tucson-Melbourne three-nucleon force in the proton-deuteron breakup process at Ep = 65 MeV

Abstract We present the calculated cross sections and vector analyzing powers using the Bonn B nucleon-nucleon potential and the Tucson-Melbourne three-nucleon force ( 3NF ) for six collinearity and quasi-free scattering breakup configurations. These calculations are compared to the results of the recent kinematically complete pd experiments at E p = 65 MeV. The Tucson-Melbourne 3NF , adjusted together with the Bonn B potential to reproduce the triton binding energy, leads to small effects both in cross sections and analyzing powers in all six studied configurations.

Cross Sections and Vector Analyzing Powers in the Proton Induced Deuteron Breakup Reaction at 65 MeV: Star Configurations

New experimental cross-section and vector-analyzing-power data for three star configurations of the kinematically complete breakup reaction 2H(p, pp)n are compared to the rigorous Faddeev calculations involving four realistic NN potentials — Argonne AV14, Bonn B, Nijmegen and Paris. A satisfactory agreement between theory and experiment has been found. The effects of the Tucson-Melbourne three-body force included in the calculations are also discussed.

Cross Section and Analyzing Power Ay in the Proton Induced Deuteron Breakup Reaction at 65 MeV

One of the basic questions in nuclear physics deals with the nature of the two-nucleon (2N) interaction. While QCD can not yet be solved in the nonperturbative regime required for an answer, meson theory has achieved some maturity and provides realistic 2N-forces, which are able to describe very well the great amount of 2N data. It is now of interest to see whether those forces can also be used in systems, where more than two nucleons interact. The simplest one, the three-nucleon system (3N) has always been considered as an ideal testing ground for our understanding of the 2N-interactions. Assuming 2N forces only, the Hamiltonian for the 3N system is fixed. Does it describe the experimental 3N observables? Is it necessary to introduce additionally genuine 3N forces in the dynamics of the 3N system? Now, with the advent of supercomputers, the 3N Faddeev equations can be solved in a numerically rigorous way for any local or nonlocal 2N interaction [1,2]. Therefore, the meson-exchange dynamics in nucleon-nucleon forces can be tested reliably in the 3N system by comparing the calculations with precise experimental data. The aim of the reported experiment is to provide accurate continuum 3N observables in those kinematical regions where, according to model calculations, the 3N force effects are enhanced and, simultaneously, the sensitivity to details of the 2N potential is small [3].

Cross section and analyzing power Ay in the 2H(p↘,pp)n breakup reaction at 65 MeV; three‐body force effects

New experimental cross‐sections and analyzing‐power data for the kinematically complete breakup reaction 2H(p↘,pp)n will be compared to the rigorous Faddeev calculations involving realistic NN potentials. The implications due to the Tucson‐Melbourne three‐body force included in the calculation will be discussed.

Cross section and analyzing power [ital A][sub [ital y]] in the breakup reaction [sup 2]H([ital [rvec p]],[ital pp])[ital n] at 65 MeV: Collinearity configurations

Kinematically complete breakup cross section and proton analyzing power data for four different collinearity configurations (neutron at rest in the c.m. system) have been measured in the reaction [sup 2]H([ital [rvec p]],[ital pp])[ital n] at [ital E][sub [ital p]][sup lab]=65 MeV. The experimental data are compared with rigorous solutions of the Faddeev equations using the Argonne AV14, Bonn B, Nijmegen, and Paris potentials. While the overall agreement is quite good there exist distinct discrepancies between theoretical and experimental cross section and analyzing power data in some regions of phase space.

Cross section and analyzing powerAyin the breakup reactionH2(p→,pp)nat 65 MeV: Collinearity configurations

Kinematically complete breakup cross section and proton analyzing power data for four different collinearity configurations (neutron at rest in the c.m. system) have been measured in the reaction [sup 2]H([ital [rvec p]],[ital pp])[ital n] at [ital E][sub [ital p]][sup lab]=65 MeV. The experimental data are compared with rigorous solutions of the Faddeev equations using the Argonne AV14, Bonn B, Nijmegen, and Paris potentials. While the overall agreement is quite good there exist distinct discrepancies between theoretical and experimental cross section and analyzing power data in some regions of phase space.

Bounds on right-handed currents from a relative beta-polarization measurement with polarized in-107

Abstract The first measurements of the longitudinal polarization of positrons emitted by polarized 107 In are reported. The positron polarization is deduced from the time-resolved decay spectrum of positronium hyperfine states. Our result is in agreement with the standard electro-weak model and provides a new lower limit for the mass of an eventual, predominantly right-handed charged W-gauge boson of 220 GeV/c 2 .