sPHENIX EMCal discussion

[Edward Kistenev <kistenev AT bnl.gov>]

Craig, I briefly talked to Jin, linearity curve is made with proton 
calibration and I always was skeptical of it. I can’t be 100% positive 
without proper simulation (protons with ionization and/or nuclear 
interactions OFF) but on the back of the envelope nonlinearity may simply 
reflect problem existing in proton calibration and beam position variations 
which are momentum dependent. Let me briefly explain what I think. 

- I suspect that at low momenta beam is on the laser mark, at 16 GeV/c - 
maximum energy we used with E864 module - it is found ~1/2” below that mark 
(see Andrei’s picture for beam position in silicon);

- Your “tower number” “MIP (proton)” peak position dependence (and probably 
peak width dependence)  may reflect contribution of comovers due to 
ionization losses in the air (absorbed very early in W), interplay between 
momentum loss of a proton in nuclear interactions in W and dE/dx of a proton 
(relativistic rise effect is ~x1.5 in the range 3-100 GeV/c) and additional 
losses from extra particles in nuclear shower (probability for second 
interaction is really small);

- If 6cm wide beam moves down with momentum its tower selection moves from 
tower with high calib. peak to tower with low calib. peak (see above) 
effectively pushing its measured energy up or (in Jin parlance) developing 
shoulder of showers with enhanced energies.  


I suggest to redo that picture in electron calibration (checked with Jin, he 
used old GAMS recursive algorithm with minimal modifications to control tails 
and that one I believe). Or use only showers with peak position in the same 
tower at all energies and center of gravity within +-7mm of the center of 
peak tower. Hopefully it will help.

                        Edward

PS. Using cosmic muons should help too.

  
On May 11, 2016, at 12:22 PM, Craig Woody <woody AT bnl.gov> wrote:

Hi Edward,
 Yes, I agree. That bothered me too, even though it seems to be a small 
effect and may just be an artifact of not knowing the absolute energy scale 
well enough. I'll talk with Jin about it and see what we can come up with.

Thanks,
Craig

On 5/11/2016 12:04 PM, Edward Kistenev wrote:
> Craig, nice talk. One caveat - I would be very much worried showing the 
> picture with positive second derivative as EMCal  linearity plot. There 
> can't be any explanation to this behavior except misrepresentation of 
> unknown (artifact of analysis). You need a very short attenuation length in 
> the calorimeter and certainly above 18X0 depth of the calorimeter to even 
> start thinking of such picture. It is absolutely inconsistent with measured 
> att. length of 200cm. In fact - I would include that picture (at least have 
> it as a backup) - this will be the first question asked when people will 
> see this linearity plot.
> 
>                       Edward
> 
> 
> On May 11, 2016, at 11:31 AM, Craig Woody <woody AT bnl.gov> wrote:
> 
> Dear All,
>  Here is a draft of my talk for the CALOR 2016 conference coming up next 
> week. I've included some plots on the results of our recent beam test at 
> Fermilab which we discussed at our EMCAL meeting yesterday, but of course 
> not everybody was there for that discussion. The results certainly look 
> very encouraging and I think we can definitely claim that they achieve our 
> design goals for sPHENIX, but we clearly don't want to overstate any of 
> these results yet since we're still at a very early stage of the analysis. 
> I think we came up with a reasonable way to present them during our meeting 
> yesterday, but please have a look at the slides and let me know if you have 
> any comments.
> 
> Many thanks,
> Craig
> <CALOR_2016_sPHENIX_draft.pdf>_______________________________________________
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