Communications | - running smoothly since yesterday, 2 CU positions completed at 2.5Gev, both tagged and full bream photons, 2 position completed at 1GeV tagged, currently running tagged photons at 0.5GeV with CU at 0 angle; 3rd position tagged photon by tonight, 3rd position full-brem at 2.5GeV for the owl shift. Running with 4 spills per supercycle since 1.3PM
- dump position: last night understood that 1GeV beam and 0.5GeV beam have larger divergence and some photons hit the dump; larger statistics for the 1Gev tagged photons was requested to compensate; the same was observed today with straight e in the CU, displaying a clear cut in the beam spot. The effect is larger with photons as the brem - induced divergence (scales as m/p) adds to the larger e beam divergenve. We removed the last pb brick wall from the dump, increasing the dump-beam distance to 11cm still keeping the unradiated beam within 23cm Pb (>6 moliere radii) when the magnet is ON. Online monitor with full AD + CU data proved critical to get this info in real time
- discussion for definition of 4th CU position: current agreement is to simulate albedo gammas by shooting gammas at 145 degrees in the tower 3 CAL; the impact point would be half way in the CAL, as having gammas too close to the TKR would give too poor an energy resolution, while shooting from the bottom of the CAL side would result in very few events making their way to the TKR. Philippe is concerned that we also get some tagged gammas in such configuration to cross-check the energy as the CU energy measurement would be very poor; suggestions were made to evaluate the possibility of placing the ACD tile currently on top on the side of tower 3, to be able to run background rejection cuts similar to the LAT ones. Luca to evaluate time to move ACD tile and contact Bill and Steve to check if this position is ok, or they feel other configurations should come before.
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