Speaker
Description
The NA62 experiment aims to measure the $BR(K+\rightarrow \pi^+ \nu \bar{\nu})$ with a 10% precision. One of the main backgrounds comes from the decay $K^+ \rightarrow \mu^+ \nu$, therefore a highly powerful pion/muon separation is needed. The NA62 RICH, together with the calorimeter system, provides an accurate particle identification. The first results of the NA62 $K^+ \rightarrow \pi^+ \nu \bar{\nu}$ analysis, based on 2016 data, have been recently presented, showing one candidate event selected as a $K^+ \rightarrow \pi^+ \nu \bar{\nu}$ decay.
Despite that the analyzed data are only a small part of the collected data, the results demonstrate that the new “in-flight decay” approach works as expected. This outcome has been possible also thanks to the very good RICH performance. Two different algorithms have been exploited: (i) the "standalone" ring reconstruction, which makes use exclusively of information from the RICH hits and (ii) the "Likelihood" algorithm, which employs the NA62 Spectrometer measurement of the tracks. In the $K^+ \rightarrow \pi^+ \nu \bar{\nu}$ analysis these two approaches have been used in combination, getting a pion reconstruction and identification efficiency of 75%, with a muon suppression factor of about 500, in the momentum range 15-35 GeV/c.
In this work we present the way the RICH detector has been employed to get this first important NA62 result and the performances of the RICH detector obtained for $K^+ \rightarrow \pi^+ \nu \bar{\nu}$ dedicated selection.
