Kto π ν overline{ν} and ∊'/ ∊ in simplified new physics models
Abstract
The decays {K}^{+}to {π}^{+}ν overline{ν} and {K}_Lto {π}^0ν overline{ν} , being the theoretically cleanest rare decays of mesons, are very sensitive probes of New Physics (NP). In view of the excellent prospects of reaching the Standard Model (SM) sensitivity for {K}^{+}to {π}^{+}ν overline{ν} by the NA62 experiment at CERN and for {K}_Lto {π}^0ν overline{ν} by the KOTO experiment at JPARC, we study them in the simplest extensions of the SM in which stringent correlations between these two decays and other flavour observables are present. We first consider simple models with treelevel Z and Z' contributions in which either Minimal Flavour Violation (MFV) or a U(2)^{3} symmetry is imposed on the quark flavourviolating couplings. We then compare the resulting correlations with those present in generic models in which the latter couplings are arbitrary, subject to the constraints from ∆ F = 2 processes, electroweak and collider data. Of particular interest are the correlations with ∊'/ ∊ and K _{ L } → μ ^{+} μ ^{} which limit the size of NP contributions to {K}^{+}to {π}^{+}ν overline{ν} and {K}_Lto {π}^0ν overline{ν} , depending on the Dirac structure of couplings and the relevant operators. But in MFV models also the constraint from B _{ s } → μ ^{+} μ ^{} turns out to be important. We take into account the recent results from lattice QCD and large N approach that indicate ∊'/ ∊ in the SM to be significantly below the data. While in many models the enhancement of ∊'/ ∊ implies the suppression of {K}_Lto {π}^0ν overline{ν} , we present two models in which ∊'/ ∊ and {K}_Lto {π}^0ν overline{ν} can be simultaneously enhanced relative to SM predictions. A correlation between {K}^{+}to {π}^{+}ν overline{ν} and B → K( K ^{*}) μ ^{+} μ ^{}, found by us in the simple models considered here, should be of interest for NA62 and LHCb experimentalists at CERN in the coming years. The one with Bto K({K}^{ast})ν overline{ν} will be tested at Belle II.
 Publication:

Journal of High Energy Physics
 Pub Date:
 November 2015
 DOI:
 10.1007/JHEP11(2015)166
 arXiv:
 arXiv:1507.08672
 Bibcode:
 2015JHEP...11..166B
 Keywords:

 Rare Decays;
 Beyond Standard Model;
 Kaon Physics;
 BPhysics;
 High Energy Physics  Phenomenology;
 High Energy Physics  Experiment;
 High Energy Physics  Lattice
 EPrint:
 32 pages, 6 figures, 1 table. v2: updated analysis in section 4, matches version published in JHEP