Rare kaon decays (NA48/2 and NA62)

The rare decay $K^\pm\to\pi^\pm\gamma\gamma$ has been recently measured from data samples collected by the NA48/2 and NA62 experiments at CERN. These measurements are presented, including model-independent spectrum measurements and fits to the Chiral Perturbation Theory description.Comment: talk given at the EPS HEP conference, 18-24 July 2013, Stockholm, Swede

Neutral pion form factor measurement at NA62

The NA62 experiment at CERN collected a large sample of charged kaon decays with a highly efficient trigger for decays into electrons in 2007. The kaon beam represents a source of tagged neutral pion decays in vacuum. A measurement of the electromagnetic transition form factor slope of the neutral pion in the time-like region from $1.05\times10^6$ fully reconstructed $\pi^0$ Dalitz decay is presented. The limits on dark photon production in $\pi^0$ decays from the earlier kaon experiment at CERN, NA48/2, are also reported.Comment: Talk given at ICHEP 2016, Chicago, 3-10 August 2016. arXiv admin note: text overlap with arXiv:1609.0295

Kaon experiments at CERN: recent results and prospects

The NA48/2 and NA62-$R_K$ experiments at the CERN SPS collected large samples of charged kaon decays in flight in 2003--07. The data analysis is still on-going (with over 20 publications produced so far); the recent results from these experiments are presented. A new upper limit on the rate of a lepton number violating decay $K^\pm\to\pi^\mp\mu^\pm\mu^\pm$ is reported: $\mathcal{B} < 8.6\times 10^{-11}$ at 90\% CL. Searches for heavy sterile neutrino $N_4$ and neutral scalar resonances ($\chi$) in $K^\pm\to\pi\mu\mu$ decays are reported. 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 $10^{-10}$ to $10^{-9}$ for resonance lifetimes up to 100~ps. A preliminary measurement of the electromagnetic transition form factor slope of the $\pi^0$ from $1.05\times 10^6$ fully reconstructed $\pi^0\to\gamma e^+e^-$ decays is presented: the obtained result $a = (3.70 \pm 0.53_\text{stat} \pm 0.36_\text{syst})\times 10^{-2}$ represents the first observation of a non-zero slope in the time-like region of momentum transfer.Comment: Contribution to proceedings of MESON 2016 conference (Krakow, 2-6 June 2016

New results from the NA48/2 experiment at CERN SPS: radiative nonleptonic kaon decays

The NA48/2 experiment at the CERN SPS carried out data taking in 2003 and 2004. Analysis of the selected data samples of 7,146 $K^\pm\to\pi^\pm e^+e^-$ decay candidates with 0.6% background, 1,164 $K^\pm\to\pi^\pm\gamma\gamma$ candidates with 3.3% background, and 120 $K^\pm\to\pi^\pm\gamma e^+e^-$ candidates with 6.1% background allowed precise measurements of branching fractions and other characteristics of these rare kaon decays.Comment: Talk given at 22nd Rencontres de Physique de La Vallee d'Aoste, La Thuile, Aosta Valley, Italy, 24 Feb-1 Mar 2006. 15 pages, 4 figure

Searches for lepton flavour and lepton number violation in kaon decays

Searches for lepton flavour and lepton number violation in kaon decays by the NA48/2 and NA62 experiments at CERN are presented. A new measurement of the helicity suppressed ratio of charged kaon leptonic decay rates $RK=BR(Ke2)/BR(Kmu2) to sub-percent relative precision is discussed. An improved upper limit on the lepton number violating K+- --> pi-+mu+-mu+- decay rate is also presented.Comment: Talk given at Moriond EW 2011 conference (La Thuile, Italy, March 2011

Precision study of K^\pm\to\pi^\pm\pi^0\pi^0 and K^\pm\to\pi^\pm\pi^+\pi^- Dalitz plot distributions by NA48/2

The NA48/2 experiment at the CERN SPS has collected an unprecedented sample of $K^\pm\to3\pi$ decays. The high statistics and the good resolution of the detectors allow a unique investigation of the detailed phase space distributions of these decays. The effects of final state pion rescattering observed in the Dalitz plot distribution of the $K^\pm\to\pi^\pm\pi^0\pi^0$ decays turned out to be a powerful tool for extraction of the S-wave $\pi\pi$ scattering lengths. The large statistics also allowed a precise measurement of the Dalitz plot slope parameters for the $K^\pm\to3\pi^\pm$ decays.Comment: Talk given at Kaon'07 Conference, LNF, Frascati, Italy, 21--25 May, 2007. A version revised by PoS refere

Rare Kaon Decay Experiments at CERN

The NA62 experiment at the CERN SPS aims to measure the branching ratio of the rare decay $K^+\to\pi^+\nu\bar\nu$ with a relative precision of $\sim10$. To achieve that goal, it is designed to be exposed to $1.2\times 10^{13}$ $K^+$ decays in its fiducial volume. The unprecedented $K^+$ flux will lead to record sensitivities to rare and forbidden decays of $K^+$ and $\pi^0$, including those that violate lepton flavour or lepton number conservation. The expected NA62 performances for lepton flavour conservation and lepton universality tests are discussed. Relevant on-going or recently completed measurements from the $K^\pm$ decay data sets collected by earlier kaon experiments at CERN (NA48/2 and NA62-$R_K$) are also presented.Comment: Talk given at the 1st Charged Lepton Flavour Conference, Lecce, May 201

Search for the dark photon in π0\pi^0 decays

A sample of $1.69\times 10^7$ fully reconstructed $\pi^0\to\gamma e^+e^-$ decay candidates collected by the NA48/2 experiment at CERN in 2003--2004 is analysed to search for the dark photon ($A'$) production in the $\pi^0\to\gamma A'$ decay followed by the prompt $A'\to e^+e^-$ decay. No signal is observed, and an exclusion region in the plane of the dark photon mass $m_{A'}$ and mixing parameter $\varepsilon^2$ is established. The obtained upper limits on $\varepsilon^2$ are more stringent than the previous limits in the mass range $9~{\rm MeV}/c^2<m_{A'}<70~{\rm MeV}/c^2$. The prospects of the dark photon search in the $K^\pm\to\pi^\pm A'$ decay are also discussed.Comment: Contribution to the proceedings of the PLANCK 2015 conference, Ioannina, Greece, 25-29 May 201