J. Sromicki

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.

New facility for fundamental research in nuclear physics with polarized cold neutrons at PSI

Abstract A polarized neutron beam of 40×150 mm 2 cross-section and record intensity was formed by a unique optical system of 7 m length for fundamental physics research at the Swiss Spallation Neutron Source (SINQ) at the Paul Scherrer Institute in collaboration with Petersburg Nuclear Physics Institute and Institute for Particle Physics. The measured cold neutron flux density at the exit of the guide system was found to be 2×10 8 n ( cm 2 s mA ) −1 . The routinely used proton current of SINQ is 1.2 mA . The mean polarization averaged over the spectrum was found to be 〈P〉=0.97. An optimization of geometrical parameters of the neutron guide system using numerical methods was made. Calculated flux neutron density and mean beam polarization, correspondingly, 1.6– 1.8×10 8 n ( cm 2 s mA ) −1 and 0.975–0.98, are close to the measured values. High efficiency polarizing supermirrors with FeCo/TiZr coating are used in the multichannel polarizer. Ni/Ti supermirrors used in a beam condenser allow compressing the beam from 80×150 mm 2 to 40×150 mm 2 increasing the flux density by two times. Non-magnetic NiMo/Ti supermirrors were developed and used in the beam condenser for the first time. Neutron transparent quartz spacers provide perfect junctions between thin glass mirrors in the polarizer. A high efficiency (f=0.99) adiabatic radio-frequency compact spin-flipper was installed.

New facility for particle physics with polarized cold neutrons

Abstract Over the half century since the first observation that the free neutron is an unstable particle, the neutron decay process has always posed questions at the forefront of particle physics. Nowadays the neutron attracts great attention as a tool for investigating subtle effects in the interaction between quarks and leptons [l]. This concerns hadronic corrections to the dominating “vector—axial vector” (V–A) component, as well as searches for the other weak interaction terms, “vector + axial vector,” scalar, tensor and pseudoscalar (V+A, S, T and P), which conform to relativistic quantum field theory. The main questions considered at present are: why does nature not make use of all interaction terms which are allowed by the Lorentz invariance? what is the role of parity and time reversal symmetries and/or their violation? and what are the characteristics (masses and coupling constants) of the subnuclear or subquarkllepton virtual particles responsible for a hypothetical, very weak and short range new interaction?

Energy dependence of fusion and reaction cross sections in the 9Be + 12C system

Abstract Angular distributions of protons, deuterons. tritons and α-particles were measured for the system 9 Be + 12 C at lab energies between 12 and 27 MeV. The compound nucleus model with level densities calculated according to the Gilbert-Cameron formula describes satisfactorily the measured proton, deuteron and triton data. In the α-particle spectra contributions from other processes seem to be present. In the analysis the fusion cut-off angular momentum was adjusted at each energy in order to reproduce correctly the proton, deuteron and triton channels. From this analysis the fusion cross section was determined as a function of the energy. The results were compared with fusion and total reaction cross section values calculated from a potential model with the real part of the interaction potential obtained from the double folding procedure of Satchler.

Light charged-particle production in the 9Be + 12C reaction at 11.4 MeV c.m. energy

Abstract Angular distributions of protons, deuterons, tritons and α-particles have been measured for the 9 Be + 12 C system at a c.m. energy of 11.4 MeV. The dominant process is compound nucleus formation. The fusion cut-off angular momentum and the fusion cross section were estimated from an analysis of the proton, deuteron and triton data. Contributions from other reaction mechanisms, e.g. cluster transfer, are responsible for α-particle emission. Spin selectivity in the excitation of a few states of the residua] nuclei was observed mainly in the proton channel.

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.

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.