1. Low mass dimuon acceptance
Shiuan-Hal Shiu

2. Contents Introduction The result of varying M1 current
Dump/Target separation
Conclusion

3. The location of M1 and M2
Configuration file

4. Why varying the magnet current
Original
Want

5. Why varying the magnet current
In low mass region the dimuon events have small opening angle

6. Fix M2 current and vary M1 current
Use the E906 Fast Monte Carlo simulation for study configuration data.
The configuration file is “fe198v5.dat”.
By changing the entry “current and step to scale” we can adjust the M1 or M2 current.
The input to the simulation is decided by Ykick*input/2000 and the tracking plane from #2 to #13 will affected by this factor.

7. The top diagram is the mass distribution of generated dimuon pairs.
The middle diagram is the mass distribution of accepted dimuon pairs.
The bottom diagram “Acceptance” as a function of dimuon mass.

8. The mass range of generated dimuon pairs is from 0.2Gev to 15Gev
Green line is the acceptance value with the original M1 current setting.
By increasing the current we find that the peak of acceptance is shifting to high mass end.
Reducing the M1 current can increase the acceptance in the low- mass region.
/Fastmc/090413/im2 m=2

9. Fix M1 current and vary M2 current
Fix the M1 current, and change the M2 current (Ykick).

10. M2*1.5
M2*1
M2*0.5

11. M2*1.5
M2*1
M2*0.5

12. M2*1.5
M2*1
M2*0.5

13. Dump/Target separation
Cuts conditions
Purple: all events
Green: xF>0 and
M>4.5 GeV
and pz>20 GeV
Blue: Green and
|ytrack|>2.25 in at z=0 (zdump)
Red: Blue and
|ytrack|<10.0 in at z=-60 (zstart)
Target
Dump

14. Dump/Target separation
Runrunscan#dump
Target retrace and dump retrace can be separated
Target retrace and dump retrace can not be separated

15. Dump/Target separation1 3
/anachcurrent/zrtr.kumac exe zrtr#runse 2 4

16. Dump/Target separation1 3
/anachcurrent/zrtr.kumac exe zrtr#runse 2 4
Reducing the M1 current will lead the z resolution bad.

17. Change the target location
/layout/qqq.kumac
The target original location is at -70 to We change it to -150 to -130.

18. Change the target location
M1*0.5 1 3 2 4

19. Change the target location
M1*0.1 1 3 2 4
Changing target location can not improve the z resolution.

20. Moving the cut condition at zdump to Station 1 and change the value.
Cuts conditions
Purple: all events
Green: xF>0 and
M>4.5 GeV
and pz>20 GeV
Blue: Green and
|ytrack|>2.25 in at z=0 (zdump)
Red: Blue and
|ytrack|<10.0 in at z=-60 (zstart)
Moving the cut condition at zdump to Station 1 and change the value.

21. Cutana&cutana#dc
Original
Changed

22. Changed
Original
Try |ytrack|>8 in at z=238 (before station1)

23. M1*0.5 1 3 2 4

24. Changing cut condition can not improve the z resolution.1 3 2 4
Changing cut condition can not improve the z resolution.

25. Check the relations of retrace mass and retrace z
Left diagram is using the original cut condition.
The mass cut is “>4.5Gev” here.
After applied the cut(mass >4.5 Gev) , we can see that the events are almost spread in the region which less than z=0.
Mrtrvszrtr#run

26. Check the relations of retrace mass and retrace z
Left diagram is using the original cut condition but mass cut is “<4.5Gev”.
After applied the cut , we can see that the events are still scattered throughout the x axis.
M1*0.5
M1*0.1

27. Momentum Difference(X) (M1*0.5)
/FastMC/anachcurrent/diffkin#mainc

28. Momentum Difference(Y) (M1*0.5)

29. Momentum Difference(Z) (M1*0.5)
/FastMC/anachcurrent/diffkin#mainc

30. Pt/Pz(positive) (M1*0.5)

31. Pt/Pz(negative) (M1*0.5)

32. Opening angle of muon pairs
fe198v5m101
mrtr.le.4.5
zrtr.le.0
fe198v5m101
mrtr.le.4.5
zrtr.ge.0
fe198v5m101_dump
mrtr.le.4.5
zrtr.le.0
fe198v5m101_dump
mrtr.le.4.5
zrtr.ge.0

33. Momentum Difference(X) (M1*0.1)

34. Momentum Difference(Y) (M1*0.1)

35. Momentum Difference(Z) (M1*0.1)

36. Pt/Pz(positive) (M1*0.1)

37. Pt/Pz(negative) (M1*0.1)

38. Opening angle of muon pairs
fe198v5m101
mrtr.le.4.5
zrtr.le.0
fe198v5m101
mrtr.le.4.5
zrtr.ge.0
fe198v5m101_dump
mrtr.le.4.5
zrtr.le.0
fe198v5m101_dump
mrtr.le.4.5
zrtr.ge.0

39. Conclusion
Reducing the M1 current can increase the acceptance of low mass dimuons.
Adjusting the M2 current does not change the acceptance significantly.
Howerer, decreasing M2 current can enlarge the acceptance.
After reducing the M1 current, the z resolution is become bad.
Changing target location and cut condition can not improve the Dump/Target resolution.
Low mass events are affected by the multiple scattering seriously.

42. backup

43. Theta y distribution of positive muon at zstart

44. Theta y distribution of positive muon at zstart

45. Theta y distribution of negative muon at zstart

46. Theta y distribution of negative muon at zstart

47. Momentum distribution of positive muon at zstart

48. Momentum distribution of positive muon at zstart

49. Momentum distribution of negative muon at zstart

50. Momentum distribution of negative muon at zstart

51. X distribution of positive muon at zstart

52. X distribution of positive muon at zstart

53. X distribution of negative muon at zstart

54. X distribution of negative muon at zstart

55. Theta x distribution of positive muon at zstart

56. Theta x distribution of positive muon at zstart

57. Theta x distribution of negative muon at zstart

58. Theta x distribution of negative muon at zstart

59. Xf distribution of muon at zstart

60. Xf distribution of muon at zstart

61. X1 distribution of muon at zstart

62. X1 distribution of muon at zstart

63. X2 distribution of muon at zstart

64. X2 distribution of muon at zstart

65. Total momentum distribution of muon at zstart

66. Total momentum distribution of muon at zstart

67. Station 1 Chamber Rates Occasionally a muon showers in the absorber
Absorber and B Field
Occasionally a muon showers in the absorber
If this happens in the center of the absorber, no effect is seen as shower is also absorbed
If this happens in the last few inches of the absorber, shower can create extremely large rates in Station 1 (of low momentum particles)
Solution is to have an absorber- free region at the end of the field volume and use field as a sweeper
In Solid Iron magnet, there is no absorber-free sweeper region! (Can we find a wide gap sweeper magnet?)
Requires GEANT MC to see magnitude of effect 
Absorber and B Field
Absorber and B Field 
B Field only