Experimental Study of the Radiative DecaysK+→μ+νe+e−andK+

Abstract

Chiral Perturbation Theory (ChPT) [1] has been a successful approach to describing the decays of pseudoscalar mesons. In the ChPT program radiative kaon decays can serve both as an important test and a source of input parameters for the theory. While the decay modes K + → e + νγ (K e2γ ) and µ + νγ (K µ2γ ) have allowed some study of the form factors involved [2,3,4], the decays) allow a more detailed investigation into the structure of these decays. We report here on such an investigation from Experiment 865 at the Brookhaven National Laboratory AGS with a 100-fold increase in the number of events in the former mode and 150-fold increase in the latter [5].The K e2ee and K µ2ee decays are assumed to proceed via exchange of a W + -boson (l + ν) and photon (e + e − ). The decay amplitude [6,7] includes inner bremsstrahlung (IB) corresponding to the tree diagrams in Fig. 1a,b, and structure dependent (SD) radiation (Fig. 1c) parameterized by vector F V , axial F A and R form factors. K e2γ and K µ2γ experiments were actually sensitive only to |F V + F A |. R, which contributes only to decays with an e + e − -pair, has not yet been measured. Inner bremsstrahlung is unambiguously predicted by the K → lν amplitude and is proportional to the kaon decay constant F K = 160 MeV. We included the kaon electromagnetic form factor in Fig. 1b (amplitude A 4 of

Constraints to new physics models for the proton charge radius puzzle from the decayK+→μ++ν+eCarlson1, Rislow2 2014Phys. Rev. D240280View full textAdd to dashboardCite

“…There is a calculated [14] and partly measured (in the higher m ee mass region) QED background [17]. New light massive particles that couple well to muons, and to electrons at least enough to decay before leaving the detector apparatus, should stand out as bumps in the e + e − spectrum at the mass of the new particles.…”

“…In the energy regions examined in this work, the Inner Brehmsstrahlung (IB) term, L ρ , dominates while H ρν contributes less than 1% to the plots. Actual values for V 1 , A 1 , A 2 , and f K can be found in Poblaguev et al [17].…”

Vector and Axial-vector form factors in radiative kaon decay and flavor SU(3) symmetry breaking

“…G αρ (k), G M (p) stand for the propagators of the photon and the meson, respectively. The matrix element (15) can be obtained by differentiating the gauged EχA in Eq. (4) with respect to the external EM field, the vector (axial-vector) field, and the kaon field…”

“…The E787 Collaboration [14] performed the first measurement of an SD component in the radiative kaon decay K µ2γ and extracted |F V + F A | = 0.165 ± 0.007 (stat) ± 0.011 (syst) and the limit −0.04 < F V − F A < 0.24 at 90 % confidence level. The E865 experiment at the Brookhaven National Laboratory (BNL) [15] studied experimentally the kaon radiative decays K + → µ + νe + e − and K + → e + νe + e − , where the photon is in a virtual state. When γ is virtual, yet an additional form factor R is involved.…”

“…Though the analysis of Ref. [15] inevitably contains the model dependence, the results were obtained to be F V = 0.112 ± 0.015 ± 0.010 ± 0.003 (model), F A = 0.035±0.014±0.013±0.003, and R = 0.227±0.013±0.010±0.009, when both the data of radiative decays K + → µ + νe + e − and K + → e + νe + e − were combined. The KLOE Collaboration [16] measured the ratio Γ(K e2(γ) /Γ(K µ2(γ) ) and obtained also the sum of the vector and axial-vector form factors as F V + F A = 0.125 ± 0.007 ± 0.001.…”