Constraints on a Parity-even/Time-Reversal-odd Interaction

Time-Reversal-Invariance non-conservation has for the first time been unequivocally demonstrated in a direct measurement, one of the results of the CPLEAR experiment. What is the situation then with regard to time-reversal-invariance non-conservation in systems other than the neutral kaon system? Two classes of tests of time-reversal-invariance need to be distinguished: the first one deals with parity violating (P-odd)/time-reversal-invariance non-conserving (T-odd) interactions, while the second one deals with P-even/T-odd interactions (assuming CPT conservation this implies C-conjugation non-conservation). Limits on a P-odd/T-odd interaction follow from measurements of the electric dipole moment of the neutron. This in turn provides a limit on a P-odd/T-odd pion-nucleon coupling constant which is 10^-4 times the weak interaction strength. Limits on a P-even/T-odd interaction are much less stringent. The better constraint stems also from the measurement of the electric dipole moment of the neutron. Of all the other tests, measurements of charge-symmetry breaking in neutron-proton elastic scattering provide the next better constraint. The latter experiments were performed at TRIUMF (at 477 and 347 MeV) and at IUCF (at 183 MeV). Weak decay experiments (the transverse polarization of the muon in K+ -> pi0 mu+ nu and the transverse polarization of the positrons in polarized muon decay) have the potential to provide comparable or possibly better constraints.Comment: 7 Pages LaTeX, 2 PostScript figures, uses aipproc.sty. Written version of Invited Paper presented at the 3rd International Symposium on Symmetries in Subatomic Physics, Adelaide, SA, Australia, March 13-17, 200

Symmetries and Symmetry Breaking

Several new proton-proton parity violation experiments are presently either being performed or are being prepared for execution in the near future. Similarly, a new measurement of the parity-violating gamma-ray asymmetry in polarized neutron capture on the proton is being developed with a ten-fold improvement over previous measurements. These experiments are intended to provide stringent constraints on the set of seven effective weak meson-nucleon coupling constants. Time-reversal-invariance non-conservation has now been unequivocally demonstrated in a direct measurement at CPLEAR. Tests may also be made of time-reversal-invariance non-conservation in systems other than the kaon system. There exist two classes of time-reversal invariance breaking interactions: P-odd/T-odd and P-even/T-odd interactions. Constraints on the first ones stem from measurements of the electric dipole moment of the neutron, while constraints on the second ones stem from the same and measurements of charge symmetry breaking in neutron-proton elastic scattering and from $K$ semi-leptonic decays. A series of precision experiments, either ongoing or being prepared, will determine the neutral weak current of the proton by measuring the parity-violating normalized asymmetry in electron-proton elastic scattering. A direct comparison between the electromagnetic and neutral weak ground state currents of the nucleon will allow a delineation of the contributions to these currents of the various quark flavours, including quarks which belong exclusively to the nucleon sea. An extension of these precision experiments to very low momentum transfer would permit stringent limits to be placed on physics beyond the standard model.Comment: 11 Pages LaTeX, including 5 PostScript figures. Uses esprc1.sty. Invited Paper presented at 16th International Conference on Few-Body Problems in Physics, Taipei, March 6-10, 200

Charge Independence and Charge Symmetry

Charge independence and charge symmetry are approximate symmetries of nature, violated by the perturbing effects of the mass difference between up and down quarks and by electromagnetic interactions. The observations of the symmetry breaking effects in nuclear and particle physics and the implications of those effects are reviewed.Comment: 41 pages, report # DOE/ER/40427-17-N94, Chapter for a book titled "Symmetries and Fundamental Interactions in Nuclei" eds. E.M. Henley and W. Haxton, to be published by World Scientifi

The Three-Nucleon System at Next-To-Next-To-Leading Order

We calculate higher order corrections for the three-nucleon system up to next-to-next-to-leading within an effective field theory with contact interactions alone. We employ a subtraction formalism previously developed and for which it has been shown that no new three-body force counterterm is needed for complete renormalization up to this order. We give results for the neutron-deuteron phaseshifts and the triton binding energy. Our results are in very good agreement with experimental results and calculations using realistic nucleon-nucleon potentials.Comment: 4 pages, 2 eps figures, revised version to appear in PR

From Hadronic Parity Violation to Parity-Violating Electron Scattering and Tests of the Standard Model

After almost five decades of study of parity violation in hadronic systems, the determination of the seven weak meson-nucleon couplings is still incomplete. Whereas parity violation in nuclear systems is complicated by the intricacies of QCD, measurements of parity violation in the much simpler proton-proton system are more straightforward to interpret. We now have three such precision pp experiments at 13.6, at 45, and 221 MeV. Today there are also better possibilities for theoretical interpretation using effective field theory. In electron-proton scattering, parity violating ep experiments such as SAMPLE, G0, HAPPEX, and PVA4 have already shown that the strange quark contributions to the charge and magnetization distributions of the nucleon are tiny. When analyzed together, the results have also greatly improved knowledge of the proton's "weak charge" (Q^p_weak = 1-4sin^2\theta_W at tree level). The Q^p_weak experiment at JLab will further improve this, determining the proton's weak charge to a precision of about 4%. Such a precision will either establish conformity with the Standard Model of quarks and leptons or point to New Physics. Following the upgrade of CEBAF at JLab to 12 GeV, a parity violating electron-electron (Moller) scattering experiment similar to SLAC E158, will measure the weak charge of the electron and hence sin^2\theta_W at low energy with a precision comparable to the most precise individual measurements at the Z0 pole (to about +/- 0.00025). This experiment will be complementary to Q^p_weak in terms of sensitivity to New Physics.Comment: 12 pages, 8 figures, LaTeX. Invited talk at the International Symposium on Cosmology and Particle Astrophysics (CosPA07), Taipei, Taiwan, Nov 13-15, 200

Dispersion γZ\gamma Z-box correction to the weak charge of the proton

We consider elastic scattering of electrons off a proton target. The parity violating (PV) asymmetry arises at leading order in $\alpha$ due to interference of $\gamma$ and $Z$ exchange. The radiative corrections to this leading mechanism were calculated in the literature and included in experimental analyses, except for $\gamma Z$ box and cross-box contributions. We present here a dispersion calculation of these corrections in forward kinematics. We demonstrate that at the GeV energies of current PV experiments, such corrections are not suppressed by the small vector weak charge of the electron, as occurs in the atomic PV. Our results suggest that the current theoretical uncertainty in the analysis of the QWEAK experiment might be substantially underestimated, and more accurate account of the dispersion corrections are needed in order to interprete the PV data.Comment: 4 pages, 3 figures, revtex

Listening to young children's voices: the evaluation of a coding system

Listening to young children’s voices is an issue with increasing relevance for many researchers in the field of early childhood research. At the same time, teachers and researchers are faced with challenges to provide children with possibilities to express their notions, and to find ways of comprehending children’s voices. In our research we aim to provide a method for listening to, and analyzing young children’s voices on educational issues. In this article we describe a new step in our research in which we are dealing with the issues of validity and reliability for the evaluation of our coding system: is our coding system for analyzing young children’s voices valid and reliable? Escuchar las voces de niños pequeños es un tema de creciente relevancia para muchos investigadores en el campo de estudios sobre la infancia. Al mismo tiempo, profesorado y personal investigador se encuentran con retos para dar a los niños posibilidades de expresar sus nociones y encontrar formas de comprender sus voces. En nuestra investigación nos proponemos proveer un método para escuchar y analizar las voces de los niños acerca de temas educativos. En este artículo describimos un nuevo paso en nuestra investigación en la que estamos trabajando cuestiones de validez y fiabilidad para la evaluación de un sistema de codificación: Es nuestro sistema de codificación para analizar las voces de los niños válido y fiable