Despite the challenges, neutron resonance spin echo still holds the promise to improve upon neutron spin echo for the measurement of slow dynamics in materials. We present a bootstrap, radio frequency neutron spin flipper using high temperature superconducting technology capable of flipping neutron spin with either nonadiabatic or adiabatic modes. A frequency of 2 MHz has been achieved, which would achieve an effective field integral of 0.35 T m for a meter of separation in a neutron resonance spin echo spectrometer at the current device specifications. In bootstrap mode, the self-cancellation of Larmor phase aberrations can be achieved with the appropriate selection of the polarity of the gradient coils.
Modulation of Intensity Emerging from Zero Effort (MIEZE) is a neutron resonant spin echo technique that allows one to measure time correlation scattering functions in materials by implementing radio-frequency (RF) intensity modulation at the sample and the detector. The technique avoids neutron spin manipulation between the sample and the detector and, thus, could find applications in cases where the sample depolarizes the neutron beam. However, the finite sample size creates a variance in the path length between the locations where scattering and detection happen, which limits the contrast in intensity modulation that one can detect, in particular, toward long correlation times or large scattering angles. We propose a modification to the MIEZE setup that will enable one to extend those detection limits to longer times and larger angles. We use Monte Carlo simulations of a neutron scattering beamline to show that by tilting the RF flippers in the primary spectrometer with respect to the beam direction, one can shape the wave front of the intensity modulation at the sample to compensate for the path variance from the sample and the detector. The simulation results indicate that this change enables one to operate a MIEZE instrument at much increased RF frequencies, thus improving the effective energy resolution of the technique. For the MIEZE instrument simulated, it shows that for an incident beam with the maximum divergence of 0.33°, the maximum Fourier time can be increased by a factor of 3.
The first direct observation of time-reversal (T) violation in the BB system has been reported by the BaBar collaboration, employing the method of Bañuls and Bernabéu. Given this, we generalize their analysis of the time-dependent T-violating asymmetry (A T ) to consider different choices of CP tags for which the dominant amplitudes have the same weak phase. As one application, we find that it is possible to measure departures from the universality of sin(2β) directly. If sin(2β) is universal, as in the Standard Model, the method permits the direct determination of penguin effects in these channels. Our method, although no longer a strict test of T, can yield tests of the sin(2β) universality, or, alternatively, of penguin effects, of much improved precision even with existing data sets. (Xinshuai Yan) 1where V i j is an element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. In this paper we use "penguin contributions" to connote all wrong phase contributions to the decay amplitude.
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