Recent results from NA48/2 and NA62 experiments at CERN

Abstract

The NA48/2 and $\text{NA62}\text{-}{\text{R}}_{\text{K}}$ experiments at the CERN SPS collected a large sample of charged kaon decays in flight. $\text{NA62}\text{-}{\text{R}}_{\text{K}}$ was running in 2007-08 with a highly efficient minimum bias trigger for decays into electrons. A preliminary measurement of the electromagnetic transition form factor slope of the ${\pi }^0$ from $1.05\times 10^6$ fully reconstructed ${\pi }^0$ Dalitz decays is presented. The obtained value $a=(3.70\pm 0.53_{\text{stat}}\pm 0.36_{\text{syst}})\times 10^{-2}$ represents a $5.8\sigma$ observation of a non-zero slope in the time-like region of momentum transfer. An upper limit on the rate of a lepton number violating decay $K^{\pm }\to {\pi }^{\mp }{\mu }^{\pm }{\mu }^{\pm }$ is reported from $\sim 1.6\times 10^{11}{K}^{\pm }$ decays at NA48/2 in 2003-04: $\mathcal{B}<8.6\times 10^{-11}$ at $90\%$ CL. Searches for heavy sterile neutrino $N_4$ and inflaton $\chi$ resonances in $K^{\pm }\to \pi \mu \mu$ decays are reported. No signal is observed and upper limits on the products $\mathcal{B}(K^{\pm }\to {\mu }^{\pm }{N}_4)\mathcal{B}(N_4\to {\pi }^{\mp }{\mu }^{\pm })$ and $\mathcal{B}(K^{\pm }\to {\pi }^{\pm }\chi )\mathcal{B}(\chi \to {\mu }^{+}{\mu }^{-})$ are set in the range $10^{-10}-10^{-9}$ for resonance lifetimes up to $100\text{ps}$. The result of a search for dark photon with the same sample of decays is also reported. In the absence of observed signal, the limits on the mixing parameter ${\epsilon }^2$ in the range $9-70{\text{MeV/c}}^2$ are improved.

10 pages, 6 figures, talk given at HQL 2016, Blacksburg, 22-27 May 2016

Cited by in corpus (1)

• Dark Photons from Nuclear Transitions