Tests of the Standard Model Using Muon Polarization Asymmetries in Kaon Decays

TL;DR

This paper explores the potential of muon polarization asymmetries in kaon decays to test the Standard Model, aiming to measure CP violation and search for new physics with feasible experimental techniques.

Contribution

It assesses the feasibility of measuring muon polarization in kaon decays to probe CP violation and new physics, highlighting potential experimental sensitivities and theoretical implications.

Findings

Muon polarization measurements can provide clean CKM parameter estimates.

Experimental techniques could achieve sensitivities near 0.0001 in T-violating polarization.

Kaon decay studies could reveal effects of non-standard CP violation.

Abstract

We have examined the physics and the experimental feasibility of studying various kaon decay processes in which the polarization of a muon in the final state is measured. Valuable information on CP violation, the quark mixing (CKM) matrix, and new physics can be obtained from such measurements. We have considered muon polarization in K_L to mu+ mu- and K to pi mu+ mu- decays. Although the effects are small, or difficult to measure because of the small branching ratios involved, these studies could provide clean measurements of the CKM parameters. The experimental difficulty appears comparable to the observation of K to pi nu barnu. New sources of physics, involving non-standard CP violation, could produce effects observable in these measurements. Limits from new results on the neutron and electron electric dipole moment, and epsilon-prime over epsilon in neutral kaon decays, do not eliminate certain models that could contribute to the signal. A detailed examination of muon polarization out of the decay plane in KMU3 and radiative KMU2 decays also appears to be of interest. With current kaon beams and detector techniques, it is possible to measure the T-violating polarization for KMU3 with uncertainties approaching 0.0001. This level of sensitivity would provide an interesting probe of new physics.