collim

Correction 07/16/06

There was a bug in my code. hms/mc_hms_coll.f had this function call

call musc(m2,p,coll_radw,thick,dydzs,dxdzs)

whereas, the multiple scatting routine needed a function call like this

call musc(m2,p,coll_radw,dydzs,dxdzs)

As a result, only one of the angles was affected by multiple scattering. With the second line of code above used, the missing mass distributions no longer have the strange peak, here are the missing mass distributions for H(e,e'pi) and C(e,e'pi).

Collimator punch-through 07/02/06

The hsxptar acceptance was changed from +-0.070 to +-0.075. There was minimal effect on the contamination due to collimator punch through events

The fraction of events that come from the collimator BEFORE the change are here: link

The fraction of events that come from the collimator AFTER the change are here: link

Collimator punch-through 06/28/06

This is the missing mass distribution before collimator punch-through was turned on in SIMC
(x-axis is mmx in GeV, Hydrogen runs are shown from Q2=1.1 to 4.8 GeV2)

This is after it was turned on

Collimator punch-through checks 06/28/06

The fraction of events that come from the collimator are at this link. The fraction can be very high (5%) and tend to be worse at the higher Q2. This means that the SIMC yield at higher Q2 was previously too small, and the transparency will be reduced.

The pions typically loose 125 MeV in momentum independent of the kinematic setting when they pass through the collimator material, and approximately 44-47% are lost due to aborption.

Below is a plot of SIMC events projected to the collimator. On the left are those events that do not hit the collimator. On the right are those events that pass through the collimator.