Studies of the Effects of Oxygen and CO_2 Contamination of the Neon Gas Radiator on the Performance of the NA62 RICH Detector

TL;DR

This study evaluates how oxygen and CO2 contamination in neon radiators affect the performance of the NA62 RICH detector, focusing on pion-muon separation and the impact of gas purity on detection accuracy.

Contribution

It provides experimental insights into the effects of gas contamination on RICH detector performance, highlighting the importance of controlling CO2 levels for accurate particle identification.

Findings

Muon misidentification probability around 0.7%

Time resolution better than 100 ps across momentum range

Contamination affects ring radius via refractive index changes

Abstract

The NA62 RICH detector is used for the separation of pions and muons in the momentum range 15 -- 35 GeV/c and is expected to provide a muon suppression factor better than $10^{-2}$. A prototype of the final detector equipped with about 400 PMs (RICH-400 prototype) was built and tested in a dedicated run in 2009. The $\pi-\mu$ separation was tested, as well as the effect of the pollution of the neon radiator with different amounts of oxygen and CO_2. The $\mu$ misidentification probability is about 0.7% and the time resolution better than 100 ps in the whole momentum range. We did not observe any absorption of the light due to the pollution of the radiator, however an effect on the ring radius is clearly observed due to the change of the change of the refractive index of the medium. The conclusion of the studies is that the amount of CO_2 in the final detector should be well known or the quality of the pion identification could be seriously compromised.