sPHENIX EMCal discussion

[John Haggerty <haggerty AT bnl.gov>]

Justin,

I just looked at some data that is not only clearly labeled in my 
notebook, but also has the test pulse.  The data I attached was 
certainly normal (a.k.a. low) gain.  The high gain pedestal widths (x16) 
are pretty easily distinguished from these.   I should mention for full 
disclosure that the particular run I looked at was a little different 
(the largest width was maybe 50 instead of 65), but I'd have to dive 
into the temperature data at that level.

On 1/31/20 2:51 PM, Frantz, Justin wrote:
> Hi John, Craig, or anyone....did we ever determine whether John's plot that 
> was attached to this email was for normal gain or high gain?
>
>
> ----------------------------------------------
> Justin Frantz, Ph. D.
> RHIC/AGS User Executive Committee
> Brookhaven National Lab
> Associate Professor
> Ohio University Dept. Of Physics and Astronomy
> frantz AT ohio.edu
> 646-228-2539
>
>
> > -----Original Message-----
> > From: sPHENIX-EMCal-l [mailto:sphenix-emcal-l-bounces AT lists.bnl.gov] On
> > Behalf Of John Haggerty
> > Sent: Saturday, January 18, 2020 11:28 AM
> > To: sphenix-emcal-l AT lists.bnl.gov
> > Subject: Re: [Sphenix-emcal-l] Radiation damage in the EMCAL SiPMs
> >
> > Craig and Justin,
> >
> > On 1/17/20 1:22 PM, woody wrote:
> > > Dear All,
> > >     We had a lively discussion at today's EMCAL meeting about how the
> > > radiation damage in the SiPMs will affect the noise and our ability to
> > > see MIPs in the EMCAL after we start running. While our paper on
> > > radiation damage in the SiPMs doesn't answer this question directly, it
> > > shows the effect we expect to see in the SiPMs currents as a function of
> > > radiation dose, which I think we have now taken as a given. There are
> > > also lots of other slides and talks about this subject, but we have not
> > > really faced how this will affect the EMCAL calibration and performance,
> > > especially after some period of running. I think some simulation of this
> > > would be extremely helpful and I would therefore encourage anyone who
> > is
> > > interested to join in the discussion and help us understand how we will
> > > eventually deal with this problem.
> >
> > For the purposes of the simulation, I think the best information we have
> > about how the detector will behave as it becomes radiation damaged comes
> > from the SiPM boards that we sent to Lowell to be radiation damaged in
> > their reactor:
> >
> > > https://urldefense.com/v3/__https://www.uml.edu/research/radlab/neutron-facilities.aspx__;!!P4SdNyxKAPE!U3rUxW1nDMLfF1NGByTkYWQg7f64iwwNBNa219YmKl7QokEzlXBGLPAcF_0p3N3o$
> >
> > I like that exposure best because a) it's our exact devices, b) the
> > doses were chosen to reflect our best estimate of the dose we expect in
> > sPHENIX based on Jin's radiation maps, and c) Lowell is in the business
> > of radiation exposure, so I think we can trust their dosimetry.  The
> > data we have is limited but consistent; Eric, Sean, and Craig selected 3
> > SiPM boards (== 4 towers == 16 SiPM's) and dosed each to about 1E10,
> > 1E11, and 1E12 1 MeV equivalent n/cm^2.  Some of what we know from that
> > is attached, which is the pedestal widths at the 3 doses taken through
> > the EMCAL electronics.  I think that data can be  codified into the
> > simulation, at least for a first pass.
> >
> > There are some complications we have to account for to put this
> > carefully into our simulations.  [The first is that I should make sure
> > that what I'm showing you is in a normal gain channel and not the
> > switchable high gain channel, but that should be just checking the
> > bookkeeping.]  You need the energy scale in the channel to use it in the
> > Monte Carlo, and there is an additional effect due to the fact that the
> > SiPM's are drawing current which effectively reduces the bias applied
> > unless corrected for; I tried to do that and check it with the LED's,
> > but I had problems with the procedure, which is also a long story, but
> > boils down to the difficulty of making the LED's reproducible over time
> > and temperature and removal and insertion of the daughterboards. The
> > reduced gain due to current draw is not a negligible effect, and it's
> > part of what we have to keep under control to keep the EMCAL calibrated
> > in sPHENIX.
> >
> > I think we can come up with some estimates for everything I've
> > described, and that can be the first pass at adding it to the
> > simulation.  I think we should actually do a second round of this using
> > some sector 0 SiPM's where we dose more SiPM boards and do the
> > calibration and correction more carefully based on what we learned from
> > the first round.  There is yet one more complication I should mention,
> > which are the dose estimates--Jin did a typically great job in his
> > estimates, but estimates are, well, estimates and maybe we should make
> > some measurements at higher doses to be prepared for the worst.
> >
> > Finally, if anyone read this far, I think we do not want to divorce the
> > calibration from the detector group, which is why I encouraged Justin to
> > address the EWMCAL meeting.  We have spent a loooong time developing
> > the
> > calorimeter concepts into a working detector, and the detector groups
> > are the repository of knowledge about how the detectors are built, how
> > they work, and what we know about their characteristics.
> >
> > --
> > John Haggerty
> > email: haggerty AT bnl.gov
> > cell: 631 741 3358


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