Development of a Large Area Advanced Fast RICH Detector for Particle Identification at the Large Hadron Collider Operated with Heavy Ions

%RD26 %title\\ \\During the past two years, RD26 groups have focused their activities on the production of CsI-RICH prototypes of large area, up to a square meter, to demonstrate their application in High Energy experiments. Many large CsI-photocathodes (up to 40) were produced following the processing techniques furthermore developped in the collaboration. Taking the Quantum Efficiency (QE) measured at 180 nm as a comparative figure of merit of a CsI-PC. Figure 1 shows the increase of the performance while improvements were successively implemented in the PC processing sequence. Most efficient were the use of substrates made of nickel, the heat treatment and handling of the PCs under inert gas. Actually, three large systems based on CsI-RICH have got approval in the following HEP experiments: HADES at GSI, COMPASS/NA58 at CERN and HMPID/ALICE at LHC implying up to 14 square metres of CsI-PC. In addition, several CsI-RICH detectors have been successfully operated in the Threshold Imaging Detector at NA44 and the HIRICH at GSI.\\ \\Although a number of experimental results have been accumulated during this period, several questions are still open: \begin{enumerate} \item The highest QE achieved with large area PCs is still 30-40~\% inferior to the best results obtained on small samples. \item Ageing processes initiated by contaminents (oxygen, moisture) and by operation in gaseous wire chambers still need further evaluation and understanding. \item Correlations between the QE performance and the structure of the CsI layer should be evaluated in order to characterize the ageing mechanisms.\\ \\Answering these questions is of prime importance in order to optimize the final techniques for the production of the large number of PCs composing the above mentioned systems, achieving the highest QE performance and stability. \end{enumerate} For these purposes, two new systems are under completion in RD26: \begin{enumerate} \item The ASSET system, (A Small Sample Evaporation and Test) facility allowing for morphological studies of the CsI thin film and QE optimization. \item The Main CsI-PC Evaporation Plant. \end{enumerate} The evaporation system used up to now to process large area CsI-PCs has been improved by adding a second vessel allowing for immediate "in situ" QE evaluation. Compared to the QE evaluation made up to now at the test beam facilities, these two instruments are more flexible and versatile and will allow to carry out the necessary optimization.\\ \\