1. New Small Wheel Background Charles Young (SLAC)

2. NEW JD GEOMETRY New Small Wheel Background 2

3. Geometry Description Based on engineering plans from Marco et al –Thinner Disk compared with Runs 1 / 2 –Outside of Hub is not tapered Cutouts in cladding to accommodate chamber supports –“Mismatch” between Disk and Hub cladding Inner radius of Disk cladding is circular Outer radius of Hub and cladding is polygon –Larger gap between Disk and endcap calorimeter with three rings –“L-shaped” polyboron shielding on Hub as in Run 2 Stainless steel bushing not yet implemented Some engineering details ignored, as in all such background simulations New Small Wheel Background 3

4. Side View of Disk and Hub 5-cm front plate 4-cm back plate polygon on outside cylinder on outside tapered cylinder on inside beam line New Small Wheel Background 4

5. Side View Including Disk Cladding 4-cm polyboron cladding on Disk 1-cm lead cladding on Disk New Small Wheel Background 5

6. Side View Including Hub Cladding 5-cm polyboron cladding. Note cutouts for NSW supports. 3-cm thick lead cladding (not shown here) has similar cutouts. New Small Wheel Background 6

7. End View of Disk and Hub Cladding Hub polyboron cladding Hub lead cladding Hub and its cladding have polygonal outer circumference Inner radii of lead and polyboron cladding on Disk Note radial gap between polyboron pieces Note radial gap between lead pieces New Small Wheel Background 7

8. Side View of L-Shaped Cladding “L-shaped” cladding 5-cm polyboron cladding on Hub. Disk and its cladding not shown New Small Wheel Background 8

9. Side View of First Ring Innermost ring between JD and endcap calorimeter, made of steel Disks beam line New Small Wheel Background 9

10. Close-Up Side View of First Ring Innermost ring between JD and endcap calorimeter Note gap between ring and disks. Ring is mounted on JD and spring-loaded so it touches endcap calorimeter Disks New Small Wheel Background 10

11. Side View Including Part of 2 nd Ring Disks Innermost ring between JD and endcap calorimeter Second ring between JD and endcap calorimeter attached to Disk New Small Wheel Background 11

12. Side View of 1 st and 2 nd Rings Second ring made up of three materials: steel, polyboron and lead New Small Wheel Background 12

13. Side View of All Three Rings Note gap between 3 rd ring and JD is larger than gap for 1 st ring 3 rd ring: polyboron + lead New Small Wheel Background 13

14. SIMULATION RESULTS New Small Wheel Background 14

15. Simulation Conditions Three detector geometries –2012 geometry –Run 2 geometry –NSW geometry, as outlined earlier Otherwise identical assumptions: –√s = 14 TeV –  (pp) = 70 mb –Normalized to luminosity = 10 34 cm -2 sec -1 –TGC sensitivities 2012 & Run 2 results from ATL-COM-MUON-2014-027. 2012 corresponds to “I1” in Note. New Small Wheel Background 15

16. 2012 Geometry Red:Photon hits Blue:Neutron hit Green:Charged particle hits except e + /e - Yellow:e + /e - hits New Small Wheel Background 16

17. Run 2 Geometry Red:Photon hits Blue:Neutron hit Green:Charged particle hits except e + /e - Yellow:e + /e - hits New Small Wheel Background 17

18. NSW Geometry Red:Photon hits Blue:Neutron hit Green:Charged particle hits except e + /e - Yellow:e + /e - hits New Small Wheel Background 18

19. Summary of Changes & Explanation 2012 to Run 2 –Reduction by ~2x –Thinner beam pipe –Additional shielding around JD and JT Run 2 to NSW –Increase by ~2x, i.e. rates similar to 2012 –Reduced JD shielding Changes here refer to those due to geometry changes only. New Small Wheel Background 19