sPHENIX EMCal discussion

[John Haggerty <haggerty AT bnl.gov>]

Bill,

I gave that some thought some time ago in DAQ meetings:

https://indico.bnl.gov/event/8349/

and I believe Jamie checked my work and came to similar conclusions, but 
I don't have his reference handy.  Neither of us did it with a realistic 
zero suppression algorithm, we just took link speeds and figured out 
what fraction of the raw data has to be eliminated.  As far as I know, 
we don't have a complete proposal for a packed and zero suppressed data 
format, although having worked with Chi for some time, I imagine he 
could sketch out what he has in mind so that it could be implemented in 
simulation and tested, because as you say, the details matter when 
you're trying to squeeze the last Gbit/s out.  Another thing that comes 
into it is the DCM/PM ratio as discussed in the slides above--I 
concluded that 1 is the best value, but we are short PM's due to the 
difficulty of getting the Altera Stratix 3.

One other thing to keep in mind is when we want to activate 
this--according to the commissioning plan, we ramp up rather slowly in 
luminosity, and it makes life easier to have a lot of samples, so it 
would be towards the end of the 3 months of commissioning where we would 
want to push the event and data rate.

On 2022-06-23 09:45, W.A. Zajc wrote:
> Hello all:
>
> I have conflicts that prevent attendance to the EmCal meetings, so
> call me an interested non-observer.
>
> I have a question about the EMCal plans for zero suppression in
> Year-1. This was sparked by a statement from Chris Pinkenburg at
> Tuesday’s Calibrations meeting that always reading out
> non-suppressed calorimeters will slow the readout to a crawl (Chris,
> please correct if I am misquoting you).
>
> A back-of-the-iPad calculation shows that in central Au+Au, the
> average energy in a delta-eta x delta-phi = 0.025 x 0.025 is about 50
> MeV. Divide this by ~4 for MB. These numbers immediately raise the
> question of what energy threshold is being considered for zero
> suppression, and how do various physics signals depend on this
> threshold?
>
> 1) Yes, I know the threshold will be on an ADC value, not an energy.
> But I think its still useful to phrase the question in terms of truth
> values.
>
> 2) Yes, I know that a central collision does not uniformly illuminate
> the EmCal with 50 MeV hits; it will be much more granular and
> concentrated with the average energy per *hit* tower ~ 0.3-0.4 (??)
> GeV.
>
> Chi has reminded me that when zero suppressing you are not just
> throwing away empty words but you are also adding bits to specify the
> tower ID. So real zero suppression gains have to be determined with
> non-trivial simulations. Perhaps this has already been done for the
> EMCal?
>
> Best regards,
>
> Bill
>
> —————————————————
> W.A. Zajc
> I.I. Rabi Professor of Physics
> Columbia University
> New York, NY 10027
>
> https://blogs.cuit.columbia.edu/waz1/ [1]
> —————————————————
>
> > On Jun 23, 2022, at 8:22 AM, Craig Woody <woody AT bnl.gov> wrote:
> >
> > Dear All,
> > Just a reminder that we will have our regular EMCAL meeting
> > tomorrow, Friday June 24th starting at 9:00 am EDT. Here's the
> > Indico link: https://indico.bnl.gov/event/16262/
> >
> > Cheers,
> > Craig
> > _______________________________________________
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>
>
>
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John Haggerty
haggerty AT bnl.gov
cell: 631 741 3358