O. Naviliat-Cuncic

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.

Cross section and analyzing power A y in the breakup reaction H 2 ( p →, pp ) 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.

Production of polarized 12N with the 12C(p, 12N)n0 reaction

Abstract The polarization transferred to 12N in the 12 C ( p , 12 N ) n 0 reaction has been measured at Ep = 50 and 72 MeV. In agreement with previous work, the 12N polarization was a strong function of the material in which the ions stop, implying a complex depolarization mechanism. The largest nuclear polarization observed, P0 = 0.260 ± 0.002, was for 12N implanted in Al. This result gives the lower bound Kyy1 ⩾ 0.377 ± 0.003 for the transverse polarization-transfer coefficient. Distorted-wave calculations predict Kyy1 should be approximately 2 3 . The angular distribution of Kyy1 at Ep = 72 MeV is nearly isotropic, in agreement with the distorted-wave prediction. The electronic polarization relaxation time T1 for 12N implanted in C, Al, Ni and Au was found to be approximately constant and much longer than the 12N half-life; viz, T1 = 0.150 ± 0.014 s.

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.

Measurement of the asymmetry parameter for 35Ar β-decay as a test of the CVC hypothesis

Abstract The asymmetry parameter for the superallowed, mixed Fermi-Gamow-Teller s-decay of polarized 35 Ar to the mirror nucleus 35 Cl ground state has been measured. The result, A gs = 0.427 ± 0.023, is in good agreement with the Standard Model expectation A F t = 0.4303 ± 0.0084 and more than five standard deviations from earlier results which suggested a violation of CVC in heavy nuclei.

PROTON INDUCED DEUTERON BREAKUP REACTION AT 65 MEV : UNSPECIFIC CONFIGURATIONS

Cross sections and vector-analyzing powers for four unspecific configurations of the 2H(p,pp)n breakup reaction at E lab p = 65MeV were measured in a kinematically complete experiment. Measured observables are compared with rigorous Faddeev calculations using four realistic charge-dependent interaction models, the CD Bonn, Argonne v18, Nijmegen I, and Nijmegen II potentials with or without inclusion of the Tucson-Melbourne three-nucleon force. Coulomb effects are completely omitted. A satisfactory agreement between theory and experiment has been found. There exist, however, some discrepancies between measured and calculated analyzing-power distributions in certain kinematical regions. The effects of the Tucson-Melbourne three-body force are either negligible or slightly increasing the disagreement.

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.