From pitzl@mail.desy.de Mon Oct 21 12:25:37 2002 Date: Sat, 28 Sep 2002 14:46:01 +0200 (MEST) From: Daniel Pitzl To: Armen Bunyatyan , Samvel Ghazaryan , Leonid Lytkine , Vladimir Volchinski , Alexandr Hovhannisyan , Petr A. Smirnov , Karsten Gadow , Gert Falley Cc: Hans-Christian Schultz-Coulon , Max Klein , Tim Greenshaw Subject: Summary: new BToF 1st meeting Dear colleagues, 1st meeting on the new BToF on Fri 27.9.2002 The present BToF has only 20% rejection power for upstream proton background. Possible reasons: - small geometrical acceptance outer dimension: 52 cm square inner dimension: 13 cm radius circle around GG magnet => area 0.217 m**2 the large veto wall has an inner square opening of 85x85 cm**2 = 0.72 m**2 => large uncovered area between veto wall and present BToF. - low efficiency due to low light yield. scintillator thickness is 1 cm, 2 layers uses 1 inch EM Spacal PMTs Proposal: new, larger, thicker BToF - same z position: -3.0m (+-10cm, check!) - use full area available between GG and iron: outer dimension: 48 cm radius circle inner dimension: 13 cm radius circle around GG magnet => area 0.67 m**2 The 4 corners of the veto wall opening are still not covered, but this is almost a factor 3 improvement in coverage. - use 2cm thick scintillators, 2 layers, separated by 1mm lead to avoid coincidences from synchrotron radiation. - Time resolution: at -3.0m the proton peak is 20 ns earlier than the ep peak. Start the IA window at 10ns. A resolution of 8ns FWHM gives a 2.75 sigma containment, or 0.6% mis-tag. We should not be worse than that. Check these numbers! - use 2 inch HAD Spacal PMTs, for larger light collection 1 PMT per quadrant and per layer => need 8 photocathode area is 81 cm**2 in each layer (4*pi*2.54**2), or 1.2% of the scintillator area. - PMTs must be mounted as in the present BToF: axial (along z) at R = 25 cm pointing towards the IP In this region the magnetic field lines are still reasonably axial. We've had bad experiences with the VLQ ToF and a BToF with radial PMTs. - Produce 5 separate quadrants, for easier handling, one as spare. - K.Gadow will take care of the mechanical installation in the iron. Task list: - Design drawing: Samuel - Calculate/simulate light yield: Leonid - Order scintillator material: Gert Cutting to be done in DESY central workshop - Check 2" PMT inventory: Sam, Petr - Order 2" PMTs, for 10 in total: Gert - PMT bases, housing, fixtures: Petr Can be machined in HN workshop. - Prepare cables, electronics: Vladimir Schedule: start now to make drawings and order materials. PMT supports should be made before the shutdown starts (March 03). The HN workshop will be busy afterwards. Produce and test quadrants as soon as parts arrive. Final installation in June 2003. I'll create a web page at http://www-h1.desy.de/h1/www/h1det/tracker/upg/btof/btof.html with pictures, drawings, summaries. Cheers, Daniel Daniel Pitzl DESY FH1 Geb 1/324 Tel (49)(40) 8998 4626 Fax (49)(40) 8998 3093 Mobile 9-4626 = 0175 583 7471