[Halld-offline] CKOV light collection efficiency and PMT quantum efficiency

[Richard Jones]

Nathan,

Ok.  My comment in the svn log is below.
>    - set the default value of TOP_CERENKOV_EFFICIENCY to 1.  This is not a good
>      choice for production, but ok for testing.  For efficient production, you
>      will need to set this back to the maximum value of the photodetector PE
>      vs wavelength, and then divide this value out from the PE tables in
>      Materials_HDDS.xml to save wasted time in tracking all of the undetected
>      Cerenkov photons.  Probably should implement a less error-prone mechanism
>      at some point, so that the same constant is divided out of the efficiency
>      tables as is being used to reduce Cereknov production in the radiators.

-Richard J.


On 8/2/2012 3:24 PM, Nathan Sparks wrote:
> Hi Richard,
>
> Recall that the current CKOV simulation is giving a smaller average numbers of photoelectrons (around 7-10 at high momentum) than expected based on Eugene's simulations.  I found that the differences in PMT quantum efficiencies can not fully account for this. However, I found something else that appears to. Before the Cherenkov light makes it to the photocathode, there is a 25% inefficiency factor applied to the CKOV photons in gustep.F. This factor is presumably the light collection efficiency of the PMTs; the number of photoelectrons depends on two efficiencies, the PMT quantum efficiency and the CKOV light collection efficiency, which is geometrical. The problem is that this geometrical factor is already built into the simulation because the PMT photocathode is simulated. After removing the 25% inefficiency factor, the average number of photoelectrons is about 40 at 7.5 GeV/c, which is reasonable.  Could you please remove this factor from gustep.F (or I can do it if you prefer)?
>
> Best Regards,
> -Nathan


-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 3103 bytes
Desc: S/MIME Cryptographic Signature
URL: <https://mailman.jlab.org/pipermail/halld-offline/attachments/20120803/7fa7f3f8/attachment.p7s>