sPHENIX EMCal discussion

["Frantz, Justin" <frantz AT ohio.edu>]

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!Rz9irEDcifAhNEe8q7262tKqyx221Uk9u04l6qPUZPCDnvXxEW2Y7_RHPNBrCLikvhkx3BWZMQU$
> >  
> 
> 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