TY - JOUR AU - NA62 Collaboration (Cortina Gil, E. et al AU - Husek, T. PY - 2020 DA - 2020// TI - An investigation of the very rare K+ -> pi+ nu nubar decay T2 - J. High Energy Phys. JO - Journal of High Energy Physics SP - 042 EP - 57pp VL - 11 IS - 11 PB - Springer KW - Fixed target experiments KW - Flavor physics KW - Flavour Changing Neutral Currents KW - Rare decay AB - The NA62 experiment reports an investigation of the K+-> pi+nu nu 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 branching ratio at 90% CL. This, together with the corresponding 68% CL measurement of (0.48-0.48+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. SN - 1029-8479 UR - https://arxiv.org/abs/2007.08218 UR - https://doi.org/10.1007/JHEP11(2020)042 DO - 10.1007/JHEP11(2020)042 LA - English N1 - WOS:000593745600001 ID - NA62CollaborationCortinaGil+Husek2020 ER -