sPHENIX EMCal discussion

[John Haggerty <haggerty AT bnl.gov>]

Bill,

We discussed this at the EMCAL meeting this morning.  Here's my long 
answer, others can check my work, but skip to the end for the short 
answer.

The gain is imagined to give 30 GeV full scale in each tower.  That 
would give an ADC gain of about 1.8 MeV/ADU in normal gain.  If you're 
setting a threshold, 10 ADC units sounds in the ballpark of the 
achievable, so that would be 18 MeV.

As an aside, the MIP peak we measure in cosmics is about 300 ADU, and 
Jingyu's GEANT shown this morning is consistent with the 
back-of-the-envelope calculation of about 30 MeV/MIP with the 
orientation of the blocks we use in our cosmic data, so that comes to 
0.1 MeV/ADC in high gain, so that comes to 1.6 MeV/ADU in normal gain.  
Close enough.

The zero suppression algorithm used in the MPC with the HBD electronics 
boils down to

sample(sample1) - sample(sample0) > threshold

where sample0 is the first sample and sample1 is a fixed sample number 
near the peak.  I can imagine a number of variants on this algorithm 
which could be implemented fairly easily with digital logic that might 
be a little better, for example, averaging the first two samples 
(assuming they both come before the signal starts to rise), since you 
can do that just by adding them and shifting.  The fixed sample number 
for sample1 is not ideal, but probably good enough.  I think this is all 
done on raw ADC data not rescaled, but I might not be right about that.

So the short answer... sure, 30 MeV is reasonable.  It wouldn't be a bad 
idea to study zero suppression at 20,30,40 MeV thresholds.

On 2022-06-24 05:13, W.A. Zajc wrote:
> Dear Chris, Jamie and John (push-down stack order):
>
> Thanks for the detailed and very informative replies that address many
> of my questions. The remaining curiosity I have is one for the
> card-carrying EMCal people: What is an “acceptable” tower energy
> threshold for zero suppression?
>
> I realize this may be a physics-dependent question, and in the end
> will depend on a variety of real-world conditions (noise, luminosity,
> backgrounds, actual bandwidth, etc.). To make the question a bit more
> crisp, Jamie’s study used 30 MeV. Does anyone object to this value?
>
> Best regards,
>
> Bill
>
> —————————————————
> W.A. Zajc
> I.I. Rabi Professor of Physics
> Columbia University
> New York, NY 10027
>
> https://blogs.cuit.columbia.edu/waz1/ [3]
> —————————————————
>
> > On Jun 23, 2022, at 2:06 PM, pinkenburg <pinkenburg AT bnl.gov> wrote:
> >
> > Hello Jamie, Bill
> >
> > so far we have been working with 300kB/event for "non tpc" data:
> https://indico.bnl.gov/event/15770/contributions/63203/attachments/40979/68555/Soltz_computing_plan.pdf
> > From the offline point of view, if this changes within reason (not
> > by an order of magnitude), it'll just affect how much tape we need
> > for storage of the raw data. Our available bandwidth and disk i/o
> > should be able to handle increases easily. Technically this would
> > really just mean fewer events in the 20GB calorimeter data files so
> > we just need to read more bytes into the calorimeter reconstruction
> > for the same number of events.
> >
> > Chris
> >
> > On 6/23/2022 1:50 PM, Jamie Nagle wrote:
> >
> > Hello Bill (cc EmCal list and Chi),
> >
> > A couple of years ago, John Haggerty and I did a set of studies on
> > DAQ throughput for the calorimeters.    With 0-20% central HIJING
> > events run through GEANT, the EMCal average tower energy was 37 MeV
> > and with a threshold for zero suppression of 30 MeV, there was a 28%
> > occupancy.
> >
> > At the time, the advice was to have 3 ADC boards/XMIT for the EMCal
> > and 2 ADC boards/XMIT for the Hadronic Calorimeter, and then 1 DCM2
> > / PAR III --> jSEB2d board.    That would enable one to run the
> > EMCal with 16 samples and "light" zero suppression and the Hadronic
> > Calorimeter without zero suppression.   Those numbers did not
> > translate into additional orders.
> >
> > The reality is that at best we will have 3 ADC boards / XMIT for
> > both the EMCal and the HCal and 2 DCM2 / PAR III -> jSEB2d board.
> > Thus, the bandwidth limitations are exactly the same for the EMCal
> > and HCal -- except considering the total final data volume going to
> > RCF.
> >
> > I am glad to re-show my earlier presentation, but the summary is
> > that there is a Dual Port memory on the DCM II that when it gets 75%
> > full, the busy is raised.    The main bandwidth limitation is going
> > to be the 120 MHz x 36 bits on the DCM II token passing to the PAR
> > III.     I have a "leaky pipe" simulation that includes occupancy,
> > centrality fluctuations, and stochastic modeling for the multi-event
> > buffering etc.
> >
> > (1) If you run with 16 samples and try to push 15 kHz Level-1
> > trigger rate through the DAQ, you get the following without zero
> > suppression.
> >
> > <Screen%20Shot%202022-06-23%20at%2011.42.55%20AM.png>
> >
> > Thus you have 33% livetime -- i.e., you keep pushing too hard and
> > the buffers keep filling up, and you get a 5 kHz rate.    I would
> > not call this "grinding to a halt."
> >
> > (2) If you run with 16 samples and try to push 15 kHz Level-1
> > trigger rate through the DAQ with 60% occupancy in central events
> > (overestimating) and scale occupancy with Nch one gets.
> >
> > <Screen%20Shot%202022-06-23%20at%2011.46.54%20AM.png>
> >
> > Also, the zero suppression in the DCM II will be something like one
> > sample minus another sample (over an average of a couple of
> > pre-samples).    There is no bandwidth in the DCM II to do a
> > sophisticated pulse shape / fit.    The algorithm Chi is working on
> > will keep two samples (a pre and on the peak) even if the channel is
> > zero suppressed, and keep all N = 16 (?) samples if it is above the
> > zero suppression.
> >
> > Note that there are a lot of real world problems not included here,
> > but this should capture the basic bandwidth landscape once things
> > are fully working (which may take most of the run).
> >
> > Chris may want to comment on the implications on the total data
> > volume.
> >
> > Sincerely,
> >
> > Jamie
> ||------------------------------------------------------------------------------------------
> > || James L. Nagle
> > || Professor of Physics, University of Colorado Boulder
> > || EMAIL:   jamie.nagle AT colorado.edu
> > || SKYPE:  jamie-nagle
> > || WEB:      http://spot.colorado.edu/~naglej [1]
> ||------------------------------------------------------------------------------------------
> > On Thu, Jun 23, 2022 at 10:47 AM W.A. Zajc <zajc AT nevis.columbia.edu>
> > 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/ [2]
> > —————————————————
> >
> > 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
> > _______________________________________________
> > sPHENIX-EMCal-l mailing list
> > sPHENIX-EMCal-l AT lists.bnl.gov
> > https://lists.bnl.gov/mailman/listinfo/sphenix-emcal-l
>
> _______________________________________________
> sPHENIX-EMCal-l mailing list
> sPHENIX-EMCal-l AT lists.bnl.gov
> https://lists.bnl.gov/mailman/listinfo/sphenix-emcal-l
>
> --
> *************************************************************
>
> Christopher H. Pinkenburg    ;    pinkenburg AT bnl.gov
>                 ;    http://www.phenix.bnl.gov/~pinkenbu
>
> Brookhaven National Laboratory    ;    phone: (631) 344-5692
> Physics Department Bldg 510 C    ;    fax:   (631) 344-3253
> Upton, NY 11973-5000
>
> *************************************************************
>
>  _______________________________________________
> sPHENIX-EMCal-l mailing list
> sPHENIX-EMCal-l AT lists.bnl.gov
> https://lists.bnl.gov/mailman/listinfo/sphenix-emcal-l
>
>
> Links:
> ------
> [1] 
> https://urldefense.com/v3/__http://spot.colorado.edu/*7Enaglej__;JQ!!P4SdNyxKAPE!Ajjq69_QzWMmqXtvNad_ftDQyUb30d0Ko2EZRcx2Bo8s8bEUYGNdsslORA0rayx6Z3YcgzkOVTxfb8uQ0qQtyFVpqAZdPWewqyVEtw$
> [2] 
> https://urldefense.com/v3/__https://blogs.cuit.columbia.edu/waz1/__;!!P4SdNyxKAPE!CqaxWSyqc98bmXf6m_XgGOQGZjx7IN41Z5WYCrC_gs2FI9AUunUQpbQODWKsjiDNF52YHk3yUl0A05lu522ZG6_20lSemyW9LQ$
> [3] 
> https://urldefense.com/v3/__https://blogs.cuit.columbia.edu/waz1/__;!!P4SdNyxKAPE!FX4I1KdBFwxWFTMBD0dtaRWOqX0gxMMDTiBkLtR8v84f-MwOAbP-ICaOrX0YIJe1XLKZRcGDkRZhg1qVWvQJsUZxGIWT_nquiQ$
> _______________________________________________
> sPHENIX-EMCal-l mailing list
> sPHENIX-EMCal-l AT lists.bnl.gov
> https://lists.bnl.gov/mailman/listinfo/sphenix-emcal-l

---
John Haggerty
haggerty AT bnl.gov
cell: 631 741 3358