Tracking, tracker layout and RICH performance

We first examine the role played by station T11 and by the $y$ layers in stations T1, T2 and T10 on the PID performance of both RICH\,1 and RICH\,2. We study the conditions under which station T11 and all $y$ layers can be removed from the tracking setup, keeping unchanged the particle identification quality, with special emphasis on performance at high momentum. The performance has been assessed both through the angular resolution on track direction, and the particle misidentification rates after RICH reconstruction. The two methods lead to similar conclusions. The role of station T1 (as a whole) on particle identification performance is also considered within a sample of events including pile--up effects and realistic material for the VELO. Issues related to track curvature generated by the fringe field in the RICH\,2 gas volume are also considered.