[Frost] Scale factors and dilution factors

[Franz Klein]

Mike,
you brought up an important point. The energy loss difference is obvious 
and partly not solvable for single track events (since a photon beam of 
about 0.7-1.0cm width causes a smearing of the corrected momentum by ~ 
20-30 MeV for those 500 MeV protons). The TOF (and partly start counter)
dependence can (in principle) be accounted for by determining the 
efficiency of each TOF paddle ... I hope it works for frost too!

Greetings
Franz

On Thu, 24 Feb 2011, Michael Dugger wrote:

>
> Hi,
>
> At today's meeting I was not able to describe why the trigger issue might
> be important with regards to scale factors and dilution factors. I think I
> can do a better job in this email.
>
> One thing that we are probably all aware of is that the scale factors are
> dependent upon angle and momentum. One of the reasons for this phase
> space dependence is that charged particles will typically lose more energy
> swimming through the butanol target than for the carbon target. The
> difference in eloss between the targets can be fairly large. As a
> test, I ran a few events looking at the momentum differences at fixed
> eloss corrected momentum and lab angle, and found that a 500 MeV/c proton
> at 27 degrees can lose from about 14 to 57 MeV/c in momentum when
> originating from butanol, whereas the same proton event originating from
> the carbon target will lose about 19 MeV. This means that the CLAS seen
> kinematics will be different dependent upon which target the event comes
> from. From the small number of test events, I found that the proton events
> (500 MeV/c protons at 27 degrees) coming from the carbon target hit TOF
> paddle 22, but the events originating from butanol ranged between TOF
> paddles 21 through 23. It then follows that the efficiency for a proton
> with fixed lab angle and eloss corrected momentum will depend upon the
> target of origination.
>
> The important thing to keep in mind is that the scale factors do not
> represent the ratio of butanol bound nucleons to that of carbon. The scale
> factors also include the ratio of efficiencies. If the efficiency ratios
> were equal to one (no z-vertex dependence on particle efficiency) than we
> would not see any structure in the scale factor phase space and the scale
> factors would just represent the ratio of bound nucleons between
> the butanol and carbon targets.
>
> Since the scale factors contain the ratio of efficiency between events
> that originate in the butanol to those coming from the carbon (not always
> = 1), then events that have TOF trigger problems may very well have a
> different efficiency ratio than for events without TOF trigger issues.
> This means that if the scale factors are measured using the reactions with
> pi+ pi- p in the final state, then these scale factors may not be correct
> for the single proton or single pion events.
>
> Thanks for your time.
>
> I hope this makes sense. If I got something wrong, please let me know.
>
> Take care,
> Michael
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>

===============================================================
                   Franz J. Klein, Associate Professor
                   CUA, Department of Physics
                   Washington, DC 20064
   office: Hannan Hall 206          phone: 202-319-6190
   or: Jefferson Lab,CC F-243       phone: 757-269-6672
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