Re: Attenuation length for GEANT

["Kornicer, Mihajlo" <mikornic@indiana.edu>]

Hi all,

just an update regarding the attenuation length in the FCAL:
it does effect photon reconstruction especially for low energy photons
as we all expect. However after smearing hit-energy
to mimic effects of photon statistics, changing attenuation in the block
to 100 cm degrades photon energy resolution by less than 0.5%

Second: Richard pointed in his note

http://www.jlab.org/Hall-D/software/wiki/index.php/Attenuation_Results_from_Radphi

that effective attenuation length does not depend on energy.
Does it depend on incident angle?
I would expect so, but I do not know how fast it changes with angle.
I would argue that 0 deg (Richard studies) and 90 deg (Beni)
represent two extreme cases.
Richard, what are you thoughts on this?

Cheers,
Mihajlo


>
> Hi Elke,
>
> See answers below:
>
> On Jan 29, 2008, at 6:51 PM, Elke-Caroline Aschenauer wrote:
>
>> But I have a question which I have asked several times already if we  run
>> muons through the detector and compare the results we get for the  geant
>> based simulation for energy and timing resolution, do we come close to
>> what was measured in the bcal test beam or for the current cosmic  tests
>> in regina.
>
> Zisis, Alex, or George would probably be best to answer this.  Note
> that in the mainstream simulation we haven't yet incorporated light
> yield and threshold information from the current, most accurate,
> cosmic tests done with SiPMs into the simulation mainly because this
> info is quite fresh.  After the review, we plan to go back and do all
>  of this, but it seems like the changes aren't quite so drastic.
>
>> The attenuation length of the FCal has a big impact on the light  output
>> and such what the lowest energy photons we can see. Can we really  neglect
>> all this issues if we have a final design review and want to show our
>> detector has the performance we need.
>
> Changing attenuation length from 166 cm to 90 cm as suggested by
> Richard's notes according to my estimate corresponds to a degradation
>  in light yield of about 10% for showers that peak in intensity in
> the  middle of the block.  Seeing as how Mihajlo recently changed the
> per  block threshold in the FCAL from 100 MeV to what we think might
> be a  better estimate of 30 MeV (although admittedly still under
> investigation) and noticed only small effects in reconstruction
> efficiency for physics channels such as eta pi0.  I think these
> changes are at the level of other uncertainties in our current
> understanding of the FCAL simulation.  For instance, we are proposing
>  a light coupling that increases the light yield by a factor of 2-3
> from RadPhi, but again, this is based on study and simulation with
> some notable systematic error.  I'm not dismissing the need for a
> better understanding here, but I don't necessarily think that the
> attenuation length itself is the most pressing issue.  In other
> words,  yes, I think it is safe to lump this issue in with others
> that need to  be addressed regarding FCAL performance.  A full scale
> prototype with  the actual proposed light coupling and readout and/or
> a beam test  would be an excellent way to try to address these
> issues.  This is why  we are enthusiastic about pursuing prototype
> and beam test studies.
>
> Cheers,
>
> Matt
>
>
>