arXiv subjects

Willem T. H. van Oers

Publications and source records attributed to Willem T. H. van Oers.

8 recordsLinked to original sources

arXiv2022

The Precision nEDM Measurement with UltraCold Neutrons at TRIUMF

The TRIUMF Ultra-Cold Advanced Neutron (TUCAN) collaboration aims at a precision neutron electric dipole moment (nEDM) measurement with an uncertainty of $10^{-27}\,e\cdot\mathrm{cm}$, which is an order-of-magnitude better than the current nEDM upper limit and enables us to test Supersymmetry. To achieve this precision, we are developing a new high-intensity ultracold neutron (UCN) source using super-thermal UCN production in superfluid helium (He-II) and a nEDM spectrometer. The current development status of them is reported in this article.

physics.ins-det↗

arXiv2008

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^2θ_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^2θ_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.

nucl-ex↗

arXiv2007

The Qweak Experiment -- A search for new physics at the TeV Scale

A new precision measurement of the parity violating analyzing power in longitudinally polarized electron scattering from the proton at very low Q^2 at an incident energy of 1.16 GeV is in the final stages of preparation for execution at Jefferson Laboratory (JLab). A 2200 hour measurement of the parity violating asymmetry in elastic electron-proton scattering at Q^2 = 0.03 (GeV/c)^2 employing 180 microamp of 85% polarized beam on a 0.35 m long liquid hydrogen target will determine the weak charge of the proton, Q_w = 1 - 4sin^2(theta_W), with 4% combined statistical and systematic errors. The Standard Model makes a firm prediction of Q_w, based on the `running' of the weak mixing angle sin^2(theta_W) from the Z-pole down to lower energies. Any significant deviation of sin^2(theta_W) from its Standard Model prediction at low Q^2 would constitute a signal of new physics. In the absence of new physics, the envisaged experiment will provide a 0.3% determination of sin^2(theta_W), making this a very competitive measurement of the weak mixing angle. Complementary to the present experiment is a measurement of the weak charge of the electron in parity violating Moller scattering at 11 GeV, currently under consideration, with the upgraded CEBAF at JLab. The objective of that experiment would be a measurement of sin2(theta_W) with a precision comparable to or better than any individual measurement at the Z-pole.

nucl-ex↗

arXiv2003

Symmetries and Symmetry Breaking

In understanding the world of matter, the introduction of symmetry principles following experimentation or using the predictive power of symmetry principles to guide experimentation is most profound. The conservation of energy, linear momentum, angular momentum, charge, and CPT involve fundamental symmetries. All other conservation laws are valid within a restricted subspace of the four interactions: the strong, the electromagnetic, the weak, and the gravitational interaction. In this paper comments are made regarding parity violation in hadronic systems, charge symmetry breaking in two nucleon and few nucleon systems, and time-reversal-invariance in hadronic systems.

hep-ph↗

arXiv2000

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.

hep-ph↗

arXiv2000

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.

hep-ph↗

arXiv1999

Constraints on a Parity-Conserving/Time-Reversal-Non-Conserving Interaction

Time-Reversal-Invariance non-conservation has now been unequivocally demonstrated in a direct measurement at CPLEAR. What about tests of time-reversal-invariance in systems other than the kaon system? Tests of time-reversal-invariance belong to two classes: searches for parity violating (P-odd)/time-reversal-invariance-odd (T-odd) interactions, and for 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 (with a present upper limit of 6 x 10^-26 e.cm [95% C.L.]). It provides a limit on a P-odd/T-odd pion-nucleon coupling constant which is less than 10^-4 times the weak interaction strength. Experimental limits on a P-even/T-odd interaction are much less stringent. Following the standard approach of describing the nucleon-nucleon interaction in terms of meson exchanges, it can be shown that only charged rho-meson exchange and A_1 meson exchange can lead to a P-even/T-odd interaction. The better constraints stem from measurements of the electric dipole moment of the neutron and from measurements of charge-symmetry breaking in neutron-proton elastic scattering. The latter experiments were executed at TRIUMF (497 and 347 MeV) and at IUCF (183 MeV). Weak decay experiments may provide limits which will possibly be comparable. All other experiments, like gamma decay experiments, detailed balance experiments, polarization - analyzing power difference determinations, and five-fold correlation experiments with polarized incident nucleons and aligned nuclear targets, have been shown to be at least an order of magnitude less sensitive.

hep-ph↗

arXiv1994

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.

nucl-th↗