Re: BCAL Dark Hits

[Blake Leverington <leverinb@uregina.ca>]

Hi Matt,

Has this been included in the latest release, release-2009-02-24 or in 
the main trunk only?

Cheers,
-Blake

Matthew Shepherd wrote:
>
> Hi all,
>
> I've just committed code to the repository that generates dark hits on 
> the BCAL sensors.
>
> Briefly, the algorithm is:
>
> For each of sensor in the inner layers only ( N_sensors = 2 * N_cells ):
>
> - determine the number of dark pulses from random poisson with mean = 
> ( dark rate ) * ( ADC integration window )
> - generate additional cross talk pulses from random poisson with mean 
> =  ( number from above ) * ( cross talk probability )
> - convert sum of both of these to an energy based on the photoelectron 
> < - > energy conversion
>
> If either of the sensors of a cell already has a hit, then add this 
> extra energy to the hit.  Otherwise, create a new hit with this energy 
> and a time that is randomly picked uniformly between -25% and +75% of 
> the ADC integration window.
>
> A few notes:
>
> The relevant parameter to adjust the dark rate is 
> BCALRESPONSE:DARK_RATE_GHZ.  The nominal value is 0.041 (41 Mhz), i.e. 
> to get back to the rosy response do -PBCALRESPONSE:DARK_RATE_GHZ=0.
>
> Hits for upstream and downstream sensors are handled independently.  
> The reconstruction code requires a hit in both ends in order for a 
> cell to be used in reconstruction -- this requirement provides some 
> suppression for spurious cells since one must have a dark pulse above 
> threshold in both the upstream and downstream readouts.
>
> The algorithm for determining the threshold depends on dark rate (see 
> the GlueX-doc 1231).  This means that as the dark rate is turned up, 
> the relative number of cells with spurious hits should stay constant 
> at the fraction set by:  BCALRESPONSE:OCCUPANCY_FRACTION_LIMIT.  
> However, the energy spectrum of these spurious hits (because the now 
> contain more dark pulses) is higher.
>
> Attached is a plot of "hybrid" pi0s -- one photon in BCAL and one in 
> FCAL taken from a small sample of 10k PYTHIA events.  There are no 
> cuts on this sample.  You can see what the peak looks like for three 
> different dark rates.  Clearly this is only the tip of the iceberg.  
> There is energy dependence to study as well as how can the 
> reconstruction be tuned (minimum cell energy cut) etc. to accommodate 
> various dark rates.  My goal was to get some working code into the 
> repository so we can begin to explore this.
>
> -Matt
>
>
>
>