Introduction

This paper reports on the development of the Ring Imaging Cherenkov (RICH) detector for LHC-B. The LHC-B experiment is a proposed single arm spectrometer for the LHC optimised for B physics. Particle identification is crucial for the study of B-physics and CP violation at the LHC. The many B-meson decay modes to be studied makes it necessary to have $\pi$/K separation over a momentum range of 1 < p < 150 GeV/c. This reduces the background of the selected final state and, in addition, provides an efficient flavour tag of the signal B-meson. The overall concept and performance of LHC-B is discussed in more detail elsewhere in these proceedings [1].

  

Figure 1: The LHC-B spectrometer

RICH detectors meet the experimental criteria for particle identification in the required momentum range. It is proposed to use two RICH detectors in the LHC-B experiment, see fig 1. The upstream detector (RICH1), fig. 2, has a combined gas and aerogel radiator and is situated in front of the dipole magnet. The aerogel radiator is placed against the entrance window of the second gaseous ( C₄F₁₀) radiator. A spherical mirror with a radius of curvature of 190 cm is tilted by $\approx$ 250 mrad to reflect the Cherenkov light onto an array of photodetectors situated outside the experimental acceptance. The downstream RICH (RICH2), fig. 2, uses CF₄ as its radiator with a spherical mirror with a radius of curvature of 820 cm tilted by 370 mrad. An additional flat mirror is tilted by 240 mrad to bring the Cherenkov photons out of the acceptance of the experiment.

  

Figure 2: Layout of the LHC-B RICH detectors(note different scales).

Each RICH detector has two photodetector planes giving a total area of 2.9 m². The chosen detector technology must have a high quantum efficiency, a spatial resolution of at least 2.5 x 2.5I>mm² and to have a fast readout consistent with 25 ns bunch crossing of the LHC. Two candidate technologies exists [3]: hybrid photodiodes (HPDs) and multianode photomultipliers. These detectors are commercially available but not in designs that meet the experimental needs of LHC-B. A program of R&D is currently underway on the development of a HPD with a large active area.