Induced pseudoscalar coupling of the proton weak interaction

Abstract

The induced pseudoscalar coupling gp is the least well known of the weak coupling constants of the proton's charged-current interaction. Its size is dictated by chiral symmetry arguments, and its measurement represents an important test of quantum chromodynamics at low energies. During the past decade a large body of new data relevant to the coupling gp has been accumulated. This data includes measurements of radiative and non radiative muon capture on targets ranging from hydrogen and few-nucleon systems to complex nuclei. Herein the authors review the theoretical underpinnings of gp, the experimental studies of gp, and the procedures and uncertainties in extracting the coupling from data. Current puzzles are highlighted and future opportunities are discussed.

Baryons as relativistic three-quark bound states

“…Its Q 2 dependence can be extracted from pion electroproduction, whereas ordinary muon capture on the proton (µ − + p → ν µ + n) determines the induced pseudoscalar coupling constant g p := m µ /(2m) G P (Q 2 = 0.88 m 2 µ ). The value reported by the MuCap Collaboration, g p = 7.3 ± 1.1 [597], is consistent with chiral perturbation theory but smaller than the previous world average [447,583].…”

“…The nucleon's axial and pseudoscalar form factors are of fundamental significance for the properties of the nucleon that are probed in weak interaction processes; see [447,448,583] for reviews. They are experimentally hard to extract and therefore considerably less well known than their electromagnetic counterparts.…”

Framework for maximum likelihood analysis of neutronβdecay observables to resolve the limits of theV−Alaw

“…Consequently we set g 3 = 0 in all that follows; we refer the reader to the reviews of Refs. [75,76] for information on this quantity. In the next section where we show results from example fits for different scenarios, we define for each scenario which of the y mod,i parameters are to be considered a free or calculated parameter.…”

Ordinary muon capture on a proton in manifestly Lorentz invariant baryon chiral perturbation theory

“…As a consequence of using the dimensional regularization procedure for regularizing the integrals, [33] the one loop graphs containing only vertices from L (1) πN contribute at O(p 3 ) and those containing one vertex from L (2) πN contribute at O(p 4 ). Two or more loop graphs contribute only at O(p 5 ) or higher.…”

“…Thus we see this calculation as a basis or starting point for planned similar consistent applications of this approach to processes such as πp → nγ where there are puzzles in the HBChPT approach arising from the appearance of unnaturally large LEC's [22]. It is also intended to be a starting point for a similar calculation of radiative muon capture, µ + p → n + ν + γ, [23,24], where there are still unresolved problems relative to the extraction of G P [1,25,26,27].…”