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) followed by 15 cm air (X0=30420cm)
  • 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)
    • 0.02inches of Aluminum
  • 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 17 micron mylar and 3 micron aluminum. Filled with helium ( Radlen = 754560 cm).
  • Drift through air until drift chamber 1
  • 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)
no wire chamber smearing, no multiple scattering in material	0.08	0.01	.014	.002
wire chamber smearing, no multiple scattering in material	0.36	0.26	.038	.084
wire chamber smearing, multiple scattering in all materials with Kevlar exit window, vacuum pipe	1.00	0.94	.072	.12
wire chamber smearing, multiple scattering in all materials with Kevlar exit window,helium bag	1.04	0.96	.092	.14
wire chamber smearing, multiple scattering in all materials with Al exit window, vacuum pipe	1.15	1.05	.102	.14
wire chamber smearing, multiple scattering in all materials with Al exit window,helium bag	1.10	1.02	.134	.16

• Plots of [xptar] , [yptar], [ytar] and [delta] resolutions versus the thrown delta, xptar and yptar comparing the four different sets of MC flags listed in the above table.