Study of SHMS resolution

Using the following setup for SHMS single arm MC

• 2 GeV , 20 deg scattered electrons
  • Reconstruction of tracks in the focal plane assumed 200 microns resolution.
  • LH2 target with 20cm length. Assume beer can with radius of 3.37cm and wall thickness in 0.005in Al.
  • 16 mil Al scattering chamber window (X0=8.89cm, frac rad len = 0.46%) followed by 15 cm air (X0=30420cm, frac rad len =0.05%)
  • Spectrometer entrance window 15 mil Kevlar (X0=74.6cm) and 5 mil Mylar (X0=28.7cm)
  • Two options for spectrometer exit window,
    • 15 mil Kevlar, 5 mil Mylar (use 20 mil,X0=53.3, Frac Rad len = 0.095%)
    • 0.02inches of Aluminum (Frac Rad len = 0.57%)
  • Two options in Hut when AR/Neon Cerenkov is removed
    • Vacuum pipe so the the spectrometer exit window is moved to location of Cerenkov exit window
    • Helium bag. The spectrometer exit window is located in front of Cerenkov entrance, but the Cerenkov is replaced by a helium bag. Assume the entrance and exit of helium bag is aluminized mylar.
      • Each window is 0.010 inches mylar (Frac Rad len = 0.089%) and 3x10-4 cm aluminum (Frac Rad len = 0.03%).
      • Filled with helium ( Radlen = 754560 cm, Frac Rad len = 0.03%).
  • Drift through air until drift chamber 1 (Frac Rad len = 0.06%).
  • Chamber 1 entrance foil, 1 mil of Mylar
  • Scattering in drift chamber, for each plane
    • Effective cathode plane, Be/Cu with Rad Len = 28.7cm , 0.0005 in
    • Drift through Chamber gas, 50/50 ethane/argon with Rad Len = 16700.0cm
    • Effective wire plane, 25 micron W+Be/Cu
    • Fill hit position for plane
    • Drift through Chamber gas, 50/50 ethane/argon with Rad Len = 16700.0cm
  • Chamber 1 exit foil, 1 mil of Mylar
  • Drift through air until drift chamber 2
  • Chamber 2 entrance foil, 1 mil of Mylar
  • Scattering in drift chamber, for each plane
    • Effective cathode plane, Be/Cu with Rad Len = 28.7cm , 0.0005 in
    • Drift through Chamber gas, 50/50 ethane/argon with Rad Len = 16700.0cm
    • Effective wire plane, 25 micron W+Be/Cu
    • Fill hit position for plane
    • Drift through Chamber gas, 50/50 ethane/argon with Rad Len = 16700.0cm
  • Chamber 2 exit foil, 1 mil of Mylar

Comparing resolutions with vaccuum pipe versus helium bag

• Monte Carlo run for 2 GeV electrons for 20cm LH2 target with spectrometer at 20 degs.
• Table with the resolution for xptar, yptar, ytar and delta for all events

	Single arm Monte Carlo Flags	Xptar (mr)	Yptar (mr)	Delta %	Ytar (cm)
1	no wire chamber smearing, no multiple scattering in material	0.17	0.09	.031	.037
2	wire chamber smearing, no multiple scattering in material	0.30	0.35	.041	.010
3	wire chamber smearing, multiple scattering in all materials with Kevlar exit window, vacuum pipe	0.86	0.87	.058	.15
4	wire chamber smearing, multiple scattering in all materials with Kevlar exit window,helium bag	0.86	0.89	.077	.15
5	wire chamber smearing, multiple scattering in all materials with Al exit window, vacuum pipe	0.94	0.94	.077	.15
6	wire chamber smearing, multiple scattering in all materials with Al exit window,helium bag	0.86	0.92	.113	.18

• Plots of [xptar] , [yptar], [ytar] and [delta] resolutions versus the thrown delta, xptar and yptar comparing the first four different sets of MC flags listed in the above table.
• Plots of [xptar] , [yptar], [ytar] and [delta] resolutions versus the thrown delta, xptar and yptar comparing the sets 1,2,5 and 6 listed in the above table.
• Plot of [xptar],[yptar], [delta] versus the thrown delta, xptar and yptar comparing sets 3,4,5 and 6 listed in the above table.