Parity Violation in Proton—Deuteron Scattering

JETP Letters - Effects of parity violation in the interaction of relativistic polarized protons and deuterons are discussed. P-odd asymmetries in the total and elastic scattering cross sections, in...     

Parity-violating electron scattering at the MAMI facility in Mainz

We report here on a new measurement of the parity-violating (PV) asymmetry in the scattering of polarized electrons on unpolarized protons performed 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.Received: 1 November 2002, Published online: 15 July 2003PACS: 12.15.-y Electroweak interactions - 25.30.Bf Elastic electron scatteringF.E. Maas: For the A4 Collaboration     

Weak neutral current effects in elastic electron deuteron scattering

We study the effect of weak neutral currents in elastic electron deuteron scattering on both unpolarized and polarized deuteron targets. Theoretical expressions have been derived for the polarized electron asymmetry, polarized target asymmetry and recoil deuteron vector polarization within the framework of impulse approximation. We show that these polarization parameters can give vital information on the space-time and isospin structure of the hadronic weak neutral current. In particular, our numerical estimates show that a measurement of polarized target asymmetry is sensitive to the isoscalar axial vector piece in the hadronic neutral current which, though zero in the Weinberg-Salam model, is not completely ruled out by the data.     

The Lead Radius Experiment PREX

The Lead Radius Experiment PREX will run in Spring of 2010. The experiment measures the parity-violating asymmetry in the elastic scattering of polarized electrons from a lead nucleus at an energy of 1.05 GeV and a scattering angle of 5°. The Z ₀ boson couples mainly to neutrons, and provides a clean measurement of R _n with a projected experimental precision of ±1%. The measurement is a fundamental test of nuclear theory and pins down the density-dependence of the symmetry energy of neutron rich nuclear matter which has impacts on neutron star structure, heavy ion collisions, and atomic parity violation experiments. Recent developments in the experiment are described.     

Parity non-conservation effects in neutron elastic scattering reactions

Energy dependence of parity non-conservation effects is derived for neutron elastic scattering on nuclei: emission asymmetry and the rotation of the polarization plane for the polarized neutron beam and longitudinal polarization for unpolarized neutrons. Both potential scattering and scattering through the compound-nucleus resonances (multi-level approximation) are taken into account. The expressions obtained are compared with experimental data on thermal neutron scattering.     

Parity violation in polarised electron deuteron scattering

Preliminary calculations show that the parity violating asymmetry in polarised electron deuteron elastic scattering can be as large as observed in the SLAC experiment even in the intermediate energy region. We propose that experiments should be done to search for these asymmetries.     

Scalar quark mass splitting effects in lepton-proton interactions

The mass splitting of scalar quarks of the same flavour leads to parity violation in deep inelastic scattering, even at one photon exchange level. This effect modifies the asymmetries measured in the polarized lepton-proton scattering. We calculate them in leading order and give numerical estimates of their shapes.     

Muon anomaly and dark parity violation

The muon anomalous magnetic moment exhibits a 3.6σ discrepancy between experiment and theory. One explanation requires the existence of a light vector boson, Z_{d} (the dark Z), with mass 10-500?MeV that couples weakly to the electromagnetic current through kinetic mixing. Support for such a solution also comes from astrophysics conjectures regarding the utility of a U(1)_{d} gauge symmetry in the dark matter sector. In that scenario, we show that mass mixing between the Z_{d} and ordinary Z boson introduces a new source of "dark" parity violation, which is potentially observable in atomic and polarized electron scattering experiments. Restrictive bounds on the mixing (m_{Z_{d}}/m_{Z})δ are found from existing atomic parity violation results, δ^{2}<2×10^{-5}. Combined with future planned and proposed polarized electron scattering experiments, a sensitivity of δ^{2}～10^{-6} is expected to be reached, thereby complementing direct searches for the Z_{d} boson.     

Parity violation in electron-deuteron scattering I. Methodology and elastic scattering

In this paper, we present methodology for investigating theoretically parity violation in both the elastic and break-up channels of electron-deuteron scattering, restricting ourselves to energies in which non-relativistic expansions are allowed for nucleons. The deficiency in the standard impulse approximation related to gauge invariance is remedied by relating it to the “elementary-particle” treatment. Results for parity violation in elastic electrondeuteron scattering are presented and discussed.     

Asymmetry in polarized e-d inelastic scattering

The parity violating asymmetry is calculated for polarized electron-deuteron inelastic scattering in the closure approximation for the outgoing nucleons. The results are applicable in the intermediate-energy region of the incident electron where asymmetries are found to be in the range accessible to the present experiments.     

Parity-violating effects in elastic electron deuteron scattering

The general expressions for parity violation observables in elastic scattering of polarized and/or unpolarized electrons from unpolarized deuterons are given and are numerically evaluated for the kinematics of SAMPLE, PVA4 and G0 experiments. The dominant contribution from the interference of and Z exchange as well as the smaller contributions from strangeness (s components of the nucleon, parity odd admixtures in the deuteron wave function, anapole moments and radiative corrections are included and discussed in the context of parity-violating electron scattering experiments of present interest.     

Parity Violating Electron Scattering in the Relativistic Eikonal Approximation

The parity violating electron scattering is investigated in the relativistic Eikonal approximation. The parity violating asymmetry parameters for many isotopes are calculated. In calculations the proton and neutron densities are obtained from the relativistic mean-field theory. We take Ni isotopes as examples to analyse the behaviour of the parity violating asymmetry parameters. The results show that the parity violating asymmetry parameter is sensitive to the difference between the proton and neutron densities. The amplitude of the parity violating asymmetry parameter increases with the distance between the minima of proton and neutron form factors. Our results are useful for future parity violating electron scattering experiments. By comparing our results with experimental data one can test the validity of the relativistic mean-field theory in calculating the neutron densities of nuclei.     

Measurement of strange-quark contributions to the nucleon's form factors at Q(2) = 0.230 (GeV/c)(2)

We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a Q2 of 0.230 (GeV/c)(2) and a scattering angle of theta (e) = 30 degrees - 40 degrees. Using a large acceptance fast PbF2 calorimeter with a solid angle of delta omega = 0.62 sr, the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is A(phys)=(-5.44+/-0.54(stat)+/-0.26(sys))x10(-6). The standard model expectation assuming no strangeness contributions to the vector form factors is A(0) = (-6.30+/-0.43) x 10(-6). The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is G(s)(E) + 0.225G(s)(M) = 0.039+/-0.034 or F(s)(1) + 0.130F(s)(2) = 0.032+/-0.028.     

Evidence for strange-quark contributions to the nucleon's form factors at Q2=0.108 (GeV/c)2

We report on a measurement of the parity violating asymmetry in the elastic scattering of polarized electrons off unpolarized protons with the A4 apparatus at MAMI in Mainz at a four momentum transfer value of Q(2)=0.108 (GeV/c)(2) and at a forward electron scattering angle of 30 degrees p)=[-1.36+/-0.29(stat)+/-0.13(syst)]x10(-6). The expectation from the standard model assuming no strangeness contribution to the vector current is A(0)=(-2.06+/-0.14)x10(-6). We have improved the statistical accuracy by a factor of 3 as compared to our previous measurements at a higher Q2. We have extracted the strangeness contribution to the electromagnetic form factors from our data to be G(s)(E)+0.106G(s)(M)=0.071+/-0.036 at Q(2)=0.108 (GeV/c)(2). We again find the value for G(s)(E)+0.106G(s)(M) to be positive, this time at an improved significance level of two sigma.     

Single spin asymmetries in the (quasi)elastic electron-proton and electron-deuteron scattering Strangeness in the nucleon and two-photon exchange amplitude

Single spin asymmetries in (quasi)elastic electron-proton and electron-deuteron scattering give insight into the structure of the nucleon. In case of a longitudinally polarized electron beam, the parity violating asymmetries can be used to determine the contribution of strange quarks to the vector form factors of the nucleon, whereas the asymmetries using a transversely polarized electron beam allow a determination of the imaginary part of the two-photon exchange amplitude which is related to the nucleon structure due to excited intermediate proton states. Both cases are presented here.     

Parity Violation in Proton–Proton Scattering at High Energies

JETP Letters - A new approach has been proposed to describe parity violation in the scattering of polarized protons by protons at high energies. It has been shown that the P-odd proton- proton...     

Testing weak interaction models after the null bismuth result

The theories advanced to explain the absence of parity violation in bismuth vapour need further experiments to discriminate between them. We show that any observed asymmetry in ep scattering with polarized electrons must have a specific y-dependence if it is to be consistent with the bismuth experiments. Different charge asymmetries in e⁺e^? → μ⁺μ^? and μ^±p → μ^±X are also predicted in the different types of theory.     

Low-lying excitations in the odd-odd nucleus154Eu

The analysis of experiments on parity mixing in compound nuclear resonances is described, with the nuclear spectroscopic aspects of the parity violation experiments emphasized. Expressions are derived for polarized neutron scattering and polarized neutron capture on unpolarized targets, and the resonance interference is treated explicitly. Examples are presented to illustrate the effects of entrance channel mixing for the case of target spin 1/2 and resonance spin 1. Results are also presented for targets with spins 0 and 3/2.     

Relativistic scattering calculations: On the study of surface magnetism by polarized and unpolarized electrons

A relativistic theory of elastic electron scattering, in which spin-orbit coupling and magnetic exchange interaction are both taken into account, has been applied to crystal atoms of the ferromagnets Ni, Fe and Gd. The spin-orbit- and exchange-induced scattering asymmetries obtained for polarized electrons are in good agreement with results from spin-orbit- only and exchange-only calculations. The residual deviations decrease with increasing energy. Interference effects give rise to sizeable values (up to about 4%) of a left-right scattering asymmetry for unpolarized electrons. This implies the possibility of studying surface ferromagnetism by unpolarized electron scattering.     

Weak interactions in polarized electron-nucleus scattering

Scattering of longitudinally polarized electrons from nuclei is analysed in view of information on weak interactions. Emphasis is given to the competition of contributions due to Z-boson and photon exchange. In some kinematical domains parity mixing of nuclear states and similar processes become predominant. The asymmetry of elastic deuteron scattering is well suited for studying the polar isoscalar current, even independently of the nuclear structure. At deuteron disintegration in principle all parts of the neutral weak currents may be observed. Both cases allow for clean tests of weak interaction theories.