1. 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

2. 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

3. 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

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

5. 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

6. 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

7. 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

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

9. 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

10. 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

11. 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

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