arXiv subjects

Daheng He

Publications and source records attributed to Daheng He.

3 recordsLinked to original sources

arXiv2013

A T-odd Momentum Correlation in Radiative β-Decay

We consider neutron radiative β-decay, n\to p e^- \barν_eγ, and compute the T-odd momentum correlation in the decay rate characterized by the kinematical variable ξ= {\bf l}_ν\cdot ({\bf l}_e\times{\bf k}) arising from electromagnetic final-state interactions in the Standard Model. Our expression for the corresponding T-odd asymmetry A_ξ^{SM} is exact in O(α) up to terms of recoil order, and we evaluate it numerically under various kinematic conditions. Noting the universality of the V-A law in the absence of recoil order terms, we retain the parametric dependence on masses and coupling constants throughout, so that our results serve as a template for the computation of A_ξ^{SM} in allowed nuclear radiative β-decays and hyperon radiative β-decays as well. We consider the pattern of A_ξ^{SM} which appears in nuclear decays and show that A_ξ^{SM} can be suppressed in particular cases, facilitating searches for new sources of CP-violation in such processes.

hep-ph↗

arXiv2013

Radiative Beta Decay for Studies of CP Violation

A triple-product correlation in the radiative β-decay rate of neutrons or of nuclei, characterized by the kinematic variable ξ\equiv (\vec{l}_ν\times\vec{l}_e)\cdot\vec{k}, where, e.g., n(p) \to p(p') + e^-(l_e) + \barν_e(l_ν) + γ(k), can be generated by the pseudo-Chern-Simons term found by Harvey, Hill, and Hill as a consequence of the baryon vector current anomaly and SU(2)_{L} x U(1)_Y gauge invariance at low energies. The correlation probes the imaginary part of its coupling constant, so that its observation at anticipated levels of sensitivity would reflect the presence of sources of CP violation beyond the standard model. We compute the size of the asymmetry in n\to p e^- \barν_e γdecay in chiral effective theory, compare it with the computed background from standard-model final-state interactions, and consider the new physics scenarios which would be limited by its experimental study.

hep-ph↗

arXiv2011

Tracing Remnants of the Baryon Vector Current Anomaly in Neutron Radiative Beta Decay

Harvey, Hill, and Hill have found that unexpected interactions involving the nucleon, photon, and weak gauge bosons at low energies emerge from gauging the axial anomaly of QCD under the full electroweak symmetry of the Standard Model (SM). In this contribution we consider how such interactions can be isolated through a triple-product momentum correlation in neutron radiative beta-decay. The correlation is both parity- and naively time-reversal-odd, so that it vanishes in the Standard Model save for effects induced by final-state interactions (FSI). Nevertheless, the correlation can be generated by sources of CP violation beyond the Standard Model, and such couplings, being spin-independent, are not constrained by the nonobservation of the neutron electric dipole moment (EDM). We consider the sorts of limits on its strength which can be determined at existing and anticipated facilities, as well as the size of induced correlations from known FSI. We also briefly consider the possibility of nuclear beta-decay studies as well as the prospects for muon-induced reaction studies.

hep-ph↗