Search results for "PARITY"
showing 10 items of 513 documents
ELECTROWEAK THEORY AND THE NEUTRINO-MASS AND NEUTRINO-OSCILLATION QUESTIONS
2007
It is shown that both conjectures of neutrino mass and neutrino oscillation can be made really well-grounded within the Standard Model provided that one adopts a recent new version of the electroweak scheme spontaneously giving also a fundamental explanation for the so-called "maximal parity-violation" effect. A crucial role is played by the prediction of two distinct, scalar and pseudoscalar, replicas of (electron, muon, and tau) lepton numbers that could fully account for an actual non-coincidence between neutrino mass-eigenstates and gauge-eigenstates.
Reconciling neutrino anomalies in a simple four-neutrino scheme with R-parity violation
2000
We propose a simple extension of the MSSM based on extra compact dimensions which includes an $SU(2) \otimes U(1)$ singlet superfield. The fermion present in this superfield is the sterile neutrino, which combines with one linear combination of $\nu_e-\nu_{\mu}-\nu_{\tau}$ to form a Dirac pair whose mass accounts for the LSND anomaly. Its small mass can be ascribed to a volume suppression factor associated with extra compact dimensions. On the other hand the sterile neutrino scalar partner can trigger the spontaneous violation of R-parity, thereby inducing the necessary mass splittings to fit also the solar and atmospheric neutrino data. Thus the model can explain all neutrino oscillation d…
Parity Violating Electron Scattering at the MAMI Facility in Mainz
2005
We report here on a new measurement of the parity violating (PV) asymmetry in the scattering of polarized electrons on unpolarized protons performed with the setup of the A4-collaboration at the MAMI accelerator facility in Mainz. This experiment is the first to use counting techniques in a parity violation experiment. The kinematics of the experiment is complementary to the earlier measurements of the SAMPLE collaboration at the MIT Bates accelerator and the HAPPEX collaboration at Jefferson Lab. After discussing the experimental context of the experiments, the setup at MAMI and preliminary results are presented.
Top-quark phenomenology in models with bilinearly and spontaneously broken R-parity
1999
We study unconventional decays of the top-quark in the framework of SUSY models with spontaneously broken R-parity. In particular we discuss an effective theory which consists of the MSSM plus bilinearly broken R-parity. We demonstrate that the decay modes t -> stau + b and t -> tau + sbottom can have large branching ratios even in scenarios where the tau-neutrino mass is very small. We show that existing Tevatron data already probe the theoretical parameters, with promising prospects for further improvement at the Run 2 of the Tevatron.
Parity non-conservation at the peak of p-resonances in low-energy neutron-nucleus scattering
1993
Abstract Parity-non-conserving effects at the top of ρ-wave resonances in low-energy neutron-nucleus scattering are revisited in view of recent measurements in 238 U and 232 Th. This is done in the framework of the valence model. A quite simple expression in terms of the strength of the neutron-nucleus parity-non-conserving force is derived for the P ( E p ) asymmetry. The result, which is independent on the nucleus, can usefully be considered as a benchmark for those effects. Comparison of experiment to theory confirms earlier conclusions, namely the expected strength of the neutron-nucleus parity-non-conserving force is much too low to account for observations in this approach, even if th…
Maximally aligned states in $^{99}$Ag
2003
Excited states of Ag-99 were populated via the Cr-50 + Ni-58 (261 MeV) reaction using the NORDBALL detector array equipped with charged-particle and neutron. detector systems for reaction channel separation. On the basis of the measured gammagamma-coincidence relations and angular distribution ratios a significantly extended level scheme has been constructed up to E-x similar to 7.8 MeV and I = 35/2. The experimental results were described within the framework of the shell model. Candidates for states fully aligned in the pig(9/2)(-3)nu(d(5/2),g(7/2))(2) valence configuration space were found at 4109 and 6265 keV.
Properties of the 12C 10 MeV state determined through β-decay
2005
16 pages, 1 table, 10 figures.-- PACS nrs.: 23.40.-s; 26.20.+f; 27.20.+n.-- Printed version published Oct 3, 2005.
Beta decay of $^{61}$Ga
1999
The β decay of 61Ga to its mirror nucleus 61Zn has been measured for the first time by using on-line mass separation and β-delayed gamma-ray spectroscopy. The observed decay strength to the ground state implies superallowed character in accordance with the systematics of the mirror decays in the sd and fp shell. The β feedings observed to four excited states in 61Zn are consistent with earlier spin-parity assignments based on in-beam experiments. The ground-state spin and parity for 61Ga were determined to be 3/2−.
Is the standard, parity-non-conserving, nucleon-nucleus interaction a surface one?
1995
Abstract Claims that the standard single-particle, parity-non-conserving, nucleon-nucleus interaction, V pnc = ct · 1 2 { σ · p , ϱ(r)} , is a surface one are considered. It is shown that examination of integrands entering some quantity involving Vpnc leads to quite puzzling results. These are further supported by a similar examination for a term [ σ · p , ϱ(r) ] which is odd under time-reversal, but has a priori a well-defined surface character. Alternative approaches to determine whether Vpnc is a surface or volume interaction are developed, based on using wave functions as test functions. From these approaches, the volume character of Vpnc is unambiguous.
Beam parameter stabilization for the P2 experiment at MESA
2020
Abstract The P2 Experiment at MESA (Mainz Energy-recovering Superconducting Accelerator) will measure the weak mixing angle via electron proton scattering at 155 MeV. The expected measured parity violation asymmetry will be about 40 ppb. This requires a high precision beam diagnostic and control system in order to minimize asymmetries that derive from helicity correlated fluctuations of the beam parameters. A control system for position and angle has been installed and tested at MAMI (Mainz Microtron) and the P2 precision requirements for determining the asymmetry and controlling the transverse beam parameters have been met.