NA62 Highlights: Observation of the $ B(K^+ \to \pi^+ \nu \bar{\nu})$ decay and Measurement of its Branching Ratio.

par Augusto Ceccucci (CERN)

lundi 14 avr. 2025, 11:00 → 12:00 Europe/Paris

200/1-101 - Salle 101 (IJCLab)

Historically important for the development of the standard model, rare kaon decays are still a privileged tool to look beyond it. The main reason to study them is to test the quark-mixing mechanism comparing $K$ decays with other quark systems and looking for deviations from precise theoretical calculations. NA62 completes the long tradition of kaon experiments at CERN focusing on the elusive, very suppressed but precisely predicted $K^+ \to \pi^+ \nu \bar{\nu}$ decay. Employing a novel decay-in-flight technique, NA62 has observed this decay and determined its branching ratio with 25 % precision: $B(K^+ \to \pi^+ \nu \bar{\nu})= (13.0 ^{3.3}_{3.0})\times 10^{-11}$. With 51 candidates observed and a background expected of $18^3_2$, $ B(K^+ \to \pi^+ \nu \bar{\nu})$ becomes the smallest branching ratio measured with a significance greater than five standard deviations. The seminar will also present other recent NA62 results and the status and prospects of the experiment.