Different approaches to calculate the $$K^{\pm }\rightarrow \pi ^{\pm }\pi ^0e^+e^-$$ K ± → π ± π 0 e + e - decay width

Abstract

The rare K ± → π ± π 0 e + e − decay, currently under analysis by the NA62 Collaboration, is considered. We have followed two theoretical approaches to calculate the differential decay width-in the kaon rest frame, where we use Cabibbo-Maksymowicz variables, and in the center-of-mass system of the lepton pair. The latter essentially simplifies the computations. A comparison between the two approaches has been performed. We have also found the dependencies of the differential decay rate as a function of the virtual photon and dipion system masses.

Theory of rare $K$ decays

“…± 0.13 ext. ) × 10 to be compared to our prediction dominated from Bremsstrahlung [27,28] B(IB) = (4.19) × 10 4. Bardeen Buras Gerard approach and K ± → π ± l + l − form factor…”

“…Also several short distance observables can be measured by appropriate kinematical analyses [27,28]. In Table 1 we show the ratios of Bremsstrahlung (B) to magnetic (M) and to various interferences.…”

Rare kaon decay: challenges and perspectives

“…4, obtained at q 2 = 50 MeV. Also several short distance observables (Fig.6) can be measured by appropriate kinematical analyses [32,33]. The big news is that NA62 has reported a measurement…”

“…We computed the large long distance contributions and the relatively small short distance ones in Ref. [32,33], see in Fig.5 the size of the different LD contributions. Relatively to the K ± → π ± π 0 γ the possibility to go kinematically at large q 2 opens the possibility to beat the bremsstrahlung (Fig.5): at large dilepton invariant mass the bremsstrahlung can be even 100 time smaller than the magnetic contribution, however at the price of decreasing the statistics.…”

Lepton-mass effects in the decaysH→ZZ*→ℓ+ℓ−Berge1, Groote2, Körner3 et al. 2015Phys. Rev. D150110View full textAdd to dashboardCite

“…[14] for the decay H → Zℓℓ and in Ref. [30,31] for the decay K ± → π ± π 0 e + e − . One then arrives at the desired three-fold joint angular decay distribution.…”