Minutes SHMS MC 7

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Minutes of SHMS MC working group meeting 11/15/2011

Participants: Dave, Dipangkar, Mark and Peter

1. Mark showed plots that demonstrated why the delta acceptance in the SNAKE and COSY model looked different as observed during the previous meeting. The reason for the difference was the cuts in the detector HUT which were not being applied in the SNAKE model. Once those cuts are in place, the COSY and SNAKE distributions agree very well. The x at the focal plane agree remarkably well, although at different intermediate apertures in the dipole they can look somewhat different. The y distribution at the FP agree but has an offset of few cm. (see https://hallcweb.jlab.org/wiki/images/4/4c/Comp_snake_cosy.gif)

2. Dipangkar showed the plots of focal plane x vs y distributions where the current apertures were compared with the apertures from mid-2006 model. In the mid-2006 model there were no HB apertures, no mechanical entrance and exit for the Quads and dipole apertures were also different. It seems the largest effect is from the Quad mechanical apertures. Without the quad mechanical apertures, the focal plane distributions resemble the distributions on the 12 GeV webpage that we have been trying to reproduce. However, the acceptance is still only about 4.6 msr, i.e. smaller than the 5 msr reported in the 12 GeV webpage. (See for example https://hallcweb.jlab.org/wiki/images/f/fa/Aperture3.png)

3. Next we looked at studies of the x-y distributions in the detector HUT. It seems that for the Dipole offset of 26 cm, the center of the drift-chambers do not have to be offset by 5 cm with respect to the central ray (as in the current design). Making the DCs symmetric about the central ray increases the delta acceptance at the lower deltas with almost no effect at the higher delta and increases the average acceptance by ~5%. Even larger gains are mitigated by the dimensions of the Calorimeter. Both COSY and SNAKE model suggest that it would be better to make the DCs symmetric about the central axis. Mark and Howard will inform the the designers about this change. (see https://hallcweb.jlab.org/wiki/images/7/7f/Comp_det_xy.gif and https://hallcweb.jlab.org/wiki/images/0/08/Comp_det2_xy.gif for SNAKE and https://hallcweb.jlab.org/wiki/images/2/2e/Det_pos_nc.png , https://hallcweb.jlab.org/wiki/images/f/f3/Det_pos_center.png for COSY distributions