Vacuum chamber for the CMS forward region To measure with good precision the total inelastic rate it has been shown by TOTEM (G. Matthiae and V. Verzi) that the inelastic detector must be able to measure over 4 units of rapidity for eta>3 due to the necessity to properly evaluate the fraction of diffractive events. The possibility of extending the study of diffractive physics to larger eta by a joint CMS-TOTEM effort also depends on a better configuration of the vacuum chamber in the CMS very forward region. Marco BOZZO INFN Genoa CMS-TOTEM meeting on diffraction studies March 8, 2002

The TOTEM Vacuum chamber The actual design of the vacuum chamber is not optimized for either TOTEM or diffraction studies. After some general comments on the shape of the vacuum chamber, I will show a possible design. What do we have now? The region between 10 and 15 m. General remarks. Feasible proposal. The region between 15 and 18 m ???? The plots have been prepared by Marco Oriunno Marco BOZZO INFN Genoa CMS-TOTEM meeting on diffraction studies March 8, 2002

CMS-TOTEM meeting on diffraction studies 10.5 m to 15 m (HF Pipe) Present CMS version: three cylindrical sections 200, 280 and 420 mm diam. and a thin window of 506mm inner diameter (bad for smaller eta range: 5 to 6) RF compliance with a 10 degrees copper cone, perforated, 0.2 mm thick (?) to a diam of 56 mm and bellows at entrance of small diameter region (bad for large eta range: 6 to 8) Design constraints due to: transitions (RF reasons) may have a maximum slope of 15 degrees. bellows at 11m must be of same diameter as the one fitted in the conical part at z=3.1m (now in the region of 5.8<  < 6.1) (i.d. 78mm, o.d.160 mm) with complicated sliding mechanism Limitations in diameter due to HF (max diam. 200mm at z=13m) Marco BOZZO INFN Genoa CMS-TOTEM meeting on diffraction studies March 8, 2002

CMS-TOTEM meeting on diffraction studies The present design Marco BOZZO INFN Genoa CMS-TOTEM meeting on diffraction studies March 8, 2002

CMS-TOTEM meeting on diffraction studies The material in the 3 regions Marco BOZZO INFN Genoa CMS-TOTEM meeting on diffraction studies March 8, 2002

CMS-TOTEM meeting on diffraction studies Region A 1 2 3 7 8 4 5,6 9 2 8 4 1 5,6 3 7 9 Marco BOZZO INFN Genoa CMS-TOTEM meeting on diffraction studies March 8, 2002

CMS-TOTEM meeting on diffraction studies Region B 3 4 5 6 2 3 1 6 3 Marco BOZZO INFN Genoa CMS-TOTEM meeting on diffraction studies March 8, 2002

CMS-TOTEM meeting on diffraction studies Region C Marco BOZZO INFN Genoa CMS-TOTEM meeting on diffraction studies March 8, 2002

CMS-TOTEM meeting on diffraction studies 15m to 18m (Forward pipe) At present: Cylindrical Aluminum pipe with i.d. 55mm and 2mm thick Cantilevered pipe support fixed to shielding. very important for overall vacuum chamber stability Present design greatly limits access for T2. Max. radius for detectors in the shielding is 250mm ( = 4.75) OK for Total Cross section Min. radius or max eta is less than 7… NOT adequate for diffraction studies. Marco BOZZO INFN Genoa CMS-TOTEM meeting on diffraction studies March 8, 2002

CMS-TOTEM meeting on diffraction studies Towards a New Design (1) For particles in range of interest present design requires multiple vacuum chamber crossing and large amount of material in detector region. Cannot ask to make the bellow at 11 m larger in diameter: Has to be same size as the bellow in the conical section in order to balance the hydrostatic pressure, in order not to load the tracker which supports the vacuum chamber at z~3.5m Increasing the diameter of both bellows implies moving the one in the cone at larger z and will jeopardize the installation scenario of the Pixel detector Marco BOZZO INFN Genoa CMS-TOTEM meeting on diffraction studies March 8, 2002

CMS-TOTEM meeting on diffraction studies Towards a New Design (2) To avoid re-entry of tracks in the vacuum chamber need pointing conical section (possibly only one). will concentrate all material in one eta region PROPOSAL Cone from a diam. of 78 mm at z = 11 (~5.82) At z~x? start reduction of diameter to TAS opening complying with RF requirements Decreasing 15 degree cone Traditional T2 (outside the vacuum) covering an eta range between 5 and 5.8 New more sophisticated T3 (to detect particle still inside the vacuum chamber) … can go to eta ~8.5 Marco BOZZO INFN Genoa CMS-TOTEM meeting on diffraction studies March 8, 2002

Diffractive friendly design Marco BOZZO INFN Genoa CMS-TOTEM meeting on diffraction studies March 8, 2002