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Answer:tracking-1From: CommentsDear LHCb colleagues, Here are the outline of answers presented to the LHCC
referees during the meetings on Tuesday next week. Please e-mail any comments to
Werner Ruckstuhl
Main Tracking: * Have you studied a scenario with two-dimensional readout? Anwser by B.Koene: In the initial survey of possible detection techniques it has been considered, but it was quickly discarded. It is clearly not the way to go for a) robust and efficient performance with b) minimized number of readout channels and c) minimization of price/channel. Extensive studies of cathode strip readout of honeycomb chambers had already been performed by the inventors of the honeycomb chamber (H. van de Graaff en H.Tolsma at NIKHEF). The problems of strip readout in the LHCb environment were discussed with them (high track density, short charge integration time on the strips due to the high repetition rate, cross talk due to capacitive coupling, minimization of effective thickness, ..). The conclusion that it would be highly impractical was quickly reached. * Given a close similarity of LHC-b and HERA-b tracking detectors could you explain an origin of much better mass resolution in LHC-b detector (15MeV in LHC-b vs. 23 MeV in HERA-b for B-->pi+pi-). Answer by W.Ruckstuhl: The relative momentum resolution in HERA-B is dp/d = 0.5% as compared to 0.3% in LHCb. This is due to the smaller B-kick (2.2 Tm in HERA-B vs 4 Tm in LHCb. HERA-B also needs more tracking stations in the magnet to keep the K0 efficiency high. Therefore they have more multiple scattering. The resolution of the tracking devices in mircometers in indeed very similar in the two experiments. * What is an effective thickness of one outer tracker station? Anwser by B.Koene: TP, p.58, near bottom of left column, gives 1.6 % of X_0 for "standard stations" (y u v y views). For stations T2 and T10 with 6 planes it is (6/4) x 1.6 %. Depending on the final choice of cathode material, the final number may be slightly different (range of 1.4 % - 1.8 % per standard station). There are 2 mm wide joints between detector modules of 4 or 5 % X_0 per view, which cover about 0.5 % of the acceptance area. (Their placement in consecutive views is not projective, so roughly speaking one must multiply their area, not their thickness, to get the situation per station; i.e. about 2 % of the acceptance area of a standard station has an effective thickness of 4 % - 5 % instead of 1.6 %. * When do you plan to have a prototype of outer tracker station for the beam tests this year? Anwser by B.Koene: Test at beam T7 of the PS is to take place in October/November 1998. It concerns a telescope of two stations, one inside a 1 Tesla magnet, the other a few meters behind it. The stations are of reduced lateral dimensions (each detection plane is only one module wide, and the module length of the first station is restricted by the magnet bore), but otherwise they correspond to the design given in the TP. We will use the preamps (ASD/BLR chips) that are foreseen as our final choice, but the rest of the readout chain differs from the final truth in LHCB. The first module is ready and undergoing acceptance tests, the others should be available before June (total of 2 x 4 modules). It should be noted that these prototype stations are still built with Pokalon as cathode material. Materials research (essentially: aging tests) is performed with small prototypes as a parallel R&D line.
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