Geant3 Simulation of Shielding for “sheet of flame” Background Kalyan Allada Jefferson Lab 26th May 2012

Hit distribution on GEM (with target field) What we know: 1. High-rate background on narrow regions of the detectors (due to 5 T target field) Two solutions to deal with this background: 1. Switch off certain sectors of the detectors 2. Add local shielding at the target I have tried to explore the second option in this simulation y(cm) X (cm)

Shielding at the Target Pb shielding Target chamber Beam pipe Beam Pb shielding NH3 target 1. Shielding is a rectangular box made of lead. 2. Dimensions: +/- 1.8cm in X (left-right) +/- 5 cm in Y (up-down) +/- 3 cm in Z (beam dir.) 3. Shielding was put at Z= +20cm 4. I chose about 12 radiation lengths of Pb 5. I generated same no. of events for both cases (with and without shielding) See next slides for comparison... Event display (rastered beam)

With Pb shielding No Pb shielding Lot more photons generated

Comparison of Hits Y (cm) Y (cm) X(cm) X(cm) Y (cm) Y (cm) X(cm) X(cm) GEM 1 (with shielding) GEM 1 (no shielding) Y (cm) Y (cm) X(cm) X(cm) Shower (no shielding) Shower (with shielding) Y (cm) Y (cm) X(cm) X(cm)

Continued ... Momentum dist. Momentum dist. (no shielding) (with shielding) Type of particles (no shielding) Type of particles (with shielding)

Chamber rate No Shielding Shielding Number of hits on GEM (with shielding) Number of hits in GEM (no shielding) Chamber rate No Shielding Shielding

Summary A shielding block (made of lead) at the target region was introduced in the geant3 model to study the effect on sheet-of-flame background The hits on the GEM chamber and calorimeter are compared with no shielding case The sheet of flame background seems to disappear resulting in more uniform hit distribution The momentum distribution of particles hit on GEM chamber are around ~0.2 GeV (compared to 0.5-1 GeV without shielding) Trigger threshold can get rid of these events ( trigger threshold > 0.8 GeV?) With shielding, photon events increase by more than 2 order of magnitude Number of e- remain same, however number of e+ decreases by factor of 2 Rate on chamber is slightly better with shielding (maybe due to decrease in e+ events) Shielding option looks promising, but need more thorough study is required Question is whether it is possible to add any shielding in the target region? Is it okay to present these results to the PAC or is it being too optimistic?