sPHENIX HCal discussion

["Lajoie, John G [PHYSA]" <lajoie AT iastate.edu>]

John,

    I think there is some confusion on a number of points here; let me try to sort it out. The main point of what follows is that at the engineering meeting we decided there would be no major changes to the inner HCAL prototype for this year.

    To start with some background, at the engineering meeting last week we discussed additional value engineering for the inner HCAL.  The main reason for this is that the current price quotes are coming in well above what we had budgeted, and additional work is necessary to try to come up with a design we can afford.  The major thing that we can do is try to reduce the machining in a number of ways, and a reasonable way to do this is to reduce the number of plates that need to be machined. One way to do this is to go from 5 scintillators per tower to 4/tower.

    As John H. has pointed out in the past, this is a natural change as the sampling fraction in the inner HCAL is quite large (compared to the outer HCAL) and we can afford some light loss.  I would say that there have been a little more than some studies; at the beginning of the year I did simulations of energy resolution and e/pi rejection with the 4/tower EMCAL.  This was not just discussed in the engineering meetings, but the last presentation was at a simulations meeting (3/29/2016):

https://indico.bnl.gov/conferenceDisplay.py?confId=1903

The bottom line of this is that there is essentially no difference between the 4/tower and 5/tower design in simulations. The next step, of course, would be to have the ToG's evaluate this design with more sophisticated simulations, but it seems unlikely to make much of a difference.

    In order to proceed with obtaining price quotes with a 4/tower design we need a new set of drawings, and this is what was discussed at the engineering meeting.  We need to have this done before the next cost & schedule review in November, so we need the drawings much earlier than that.  I don't interpret this (at this point) as a decision on the design, but we need a set of drawings we can get quoted.  In the end the budget (combined with the fact that the simulations show no real effect) may make the decision for us. 

    Now, at the meeting the impact on the prototype was discussed for quite a while, as this potentially has a large impact.  For example, the tilt angle changes when you go to 4/tower if you still want to maintain 4 crossings, so the scintillator tile length changes.  Rich *just* finished the drawings for the 5/tower scintillators and those need to be sent to Uniplast soon if they are to get us the finished high-eta scintillators in time.  For reasons of time alone I think it is too late to say you want to build a completely new inner hcal prototype for the next test beam.

    The stated goal of the next prototype run is to test the high-eta configuration and compare it to the central configuration, and that is muddied quite a bit if you change the design of the inner HCAL at the same time.  (One big change will be the sPHENIX electronics.) It was my understanding from our discussion at last week's engineering meeting that we would *not* try to modify the physical design of the inner HCAL.  One could consider just recabling the SiPMs from 5/tower to 4/tower for a set of special runs, which would get you most of the way there and be a partial test.  (Again, we can compare data to simulations.)

    *If* we decide ultimately to go to 4/tower for sPHENIX, that (final) design would be tested in 2018 when we do a beam test of the pre-production prototype.  Given that the 2016 test beam has given us some confidence in our simulations, I think this is a very reasonable approach.

    Sorry for the long email, I probably should have sent around a set of notes from this engineering meeting earlier.

Regards,
John

On 6/30/2016 12:55 PM, John Haggerty wrote:

Very soon, we need to agree to changes in the "reference design" of the 
calorimeters engendered by the descoping exercise.

In particular, I think the next prototypes we test should be as close to 
the final design as possible.  In the case of the HCAL, there are not 
that many changes to the reference design.  The main one, which I 
believe has only been discussed in engineering meetings, is that the 
Inner HCAL would be made of 4 flat plates per tower instead of 5 tapered 
plates.  There have already been some studies of this design by John 
Lajoie and others, but we should all agree that this is how we wish to 
proceed.

If we can agree on this design change in the next week or so, it should 
be possible to build a new Inner HCAL prototype in time for the next 
beam test.

Since not everyone attends every meeting, I think it's important that we 
discuss this with a wide audience on the lists.  So fire away.

John Lajoie

Professor of Physics

Iowa State University

 

(515) 294-6952

lajoie AT iastate.edu

Contact me: john.lajoie