[Frost] Scale factors and dilution factors

[Michael Dugger]

Franz,

I understand and appreciate what you wrote, but worry that it might be 
a bit confusing.

In what I wrote previously, I assumed that the momentum is correct for 
each target after eloss is applied. We know this is not true, the momentum 
vertex resolution will cause the eloss corrected momentum to be smeared 
about the true value. As you stated, the vertex resolution will be worse 
for the events with a single charged particle, and this smearing of the 
eloss corrected momentum is inherent to the detector and can not be 
solved.

My hope is that when we study the effects of the single particle momentum 
smearing, it turns out that we don't have to compensate for this. If we do 
have to compensate for the smearing, I am confident that we can get that 
problem under control. The main point is not to try and solve a resolution 
issue for events coming from butanol, but to make sure that the momentum 
smearing from the carbon events look like that of the butanol events. This 
could be accomplished by randomly smearing the carbon event momentum to 
match that of the butanol. Finding the correct smearing parameters would 
be a tedious task, but one that is within our ability to perform.

Currently my goal is to figured out what I want to do about the TOF 
paddles. Perhaps after this, I'll try and study how the momentum smearing 
effects the scale factors.

This bound nucleon problem is not anywhere as easy as I thought it would 
be :(

Take care,
Michael

On Thu, 24 Feb 2011, Franz Klein wrote:

>
> 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
>> _______________________________________________
>> Frost mailing list
>> Frost at jlab.org
>> https://mailman.jlab.org/mailman/listinfo/frost
>> 
>
> ===============================================================
>                  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
> ---------------------------------------------------------------
>