The NA62 RICH detector

Abstract

The NA62 experiment is designed to measure the very rare kaon dacay K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> →π <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> νν̅ at the CERN SPS with a 10% accuracy. The Standard Model prediction for the branching ratio is (8.5 ± 07) × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-11</sup> . One of the challenging aspect of the experiment is the suppression of the K+ -J-L+v!, background at the 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> level. To satisfy this requirement a Ring Imaging Cherenkov Detector (RICH), able to separate π from μ in the momentum range between 15 and 35 GeV/c, with a μ rejection factor better than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , is needed. The RICH must also have a time resolution of about 100 ps to disentangle accidental time associations of beam particles with pions. The RICH will have a very long focal length (17 m) and will be filled with Ne gas at atmospheric pressure. Two test beams were held at CERN in 2007 and 2009 with a RICH prototype. The results of the two test beams will be presented: the μ misidentification probability is found to be about 0.7% and the time resolution better than 100 ps in the whole momentum range.