PT Journal
AU NA62 Collaboration (Cortina Gil, Eea
   Husek, T
TI An investigation of the very rare K+ -> pi+ nu nubar decay
SO Journal of High Energy Physics
JI J. High Energy Phys.
PY 2020
BP 042
EP 57pp
VL 11
IS 11
DI 10.1007/JHEP11(2020)042
LA English
DE Fixed target experiments; Flavor physics; Flavour Changing Neutral Currents; Rare decay
AB The NA62 experiment reports an investigation of the K+-> pi+nu nu <overbar></mml:mover> mode from a sample of K+ decays collected in 2017 at the CERN SPS. The experiment has achieved a single event sensitivity of (0.389 +/- 0.024) x 10(-10), corresponding to 2.2 events assuming the Standard Model branching ratio of (8.4 +/- 1.0) x 10(-11). Two signal candidates are observed with an expected background of 1.5 events. Combined with the result of a similar analysis conducted by NA62 on a smaller data set recorded in 2016, the collaboration now reports an upper limit of 1.78 x 10(-10) for the K+-> pi+nu nu <overbar></mml:mover> branching ratio at 90% CL. This, together with the corresponding 68% CL measurement of (0.48<mml:mo>-0.48<mml:mo>+0.72) x 10(-10), are currently the most precise results worldwide, and are able to constrain some New Physics models that predict large enhancements still allowed by previous measurements.
ER