sPHENIX is a new detector at RHIC.

[John Lajoie <lajoie AT iastate.edu>]

Hi Gunther,

This one, in particular, has always bothered me:

As an example, the Jet resolution UPP in my notes is "Jet resolution of < 150%/sqrt(E)" (did we specify at which E, as the resolution does not go as sqrt(E), but has a constant term from the AuAu underlying event?). Our simulations however show a resolution that is much better than that. E.g. 15% at 50GeV from simulations vs 150%/sqrt(50) = 21% from the UPP. 

Forgive me if this gets a bit long...I'm kind of walking through things in detail...

First, the statement above was originally (before UPP's) that we require a " jet energy resolution from the combined calorimetry system of < 100%/sqrt(E) in quadrature with a small constant term."  In subsequent presentations I have "defined" small as < 15%, but the important point is the stochastic term as this dominates the energy resolution for low energy jets.  

The origin of this statement, as noted, is that we want the intrinsic energy resolution of the calorimeter system to be smaller than the fluctuations introduced by the subtraction of the underlying event in heavy ions.  In this sense it really is some sort of a limit - it is either smaller or it isn't - so the fact that this has been blown up to 150%/sqrt(E) confuses the issue a bit. If I Iook at the plots Dennis and the CO group sent around on 4/24 (especially the lefthand plot on slide 3) according to simulations we're clearly in that limit, as evidenced by the fact that the energy resolution in p+p is substantially smaller than for jets of the same energy embedded in HI's.

In previous reviews the committee hasn't really understand/concentrated on the subtraction of the underlying events in heavy ions. They tend to focus on the performance specification in terms of the jet energy resolution and ask if we can achieve that, especially with the inner HCAL replaced with an Al frame.  Songkyo has approached this by asking what is the jet energy resolution we could achieve in p+p using a semi-realistic calibration procedure that uses sample of gamma+jet events (with the expected statistics).  With the CDR configuration she can get ~19% at 25GeV (just making the 100%/sqrt(E) spec) for R=0.4 jets and closer to ~14% @ 25GeV with an instrumented SS310 inner HCAL. So, approaching the specification from this direction, given the original 100%/sqrt(E) specification the CDR configuration barely makes it and it is comfortably better than the expanded 150%/sqrt(E) spec.

(for Songkyo's plots see https://indico.bnl.gov/event/4012/ , slide 7 shows the resolutions)

However, if I Iook at the plots Dennis sent around on 4/24, on slide 3 he shows a resolution in p+p for R=0.4 jets that is about 0.14 at 25GeV for the CDR configuration, while Songkyo has an energy resolution of ~0.19. 

Question to Dennis/Rosi - This makes me worried. Shouldn't these numbers be very similar for p+p jets between these two approches?  I'm concerned that what might be shown in the HI plots is the instrumented SS310 instead of the uninstrumented Al frame?  Is that possible?

I realize that what the CO group and Songkyo are showing approach similar things from different directions, but I would like to better understand the difference before CD-1. The plots from the CO group would seem to argue that even with the inner HCAL replaced by a frame we are still in a regime where we are dominated by the fluctuations in the underlying event.  Songkyo's work would seem to seem to argue that we are closer to the edge.  If the combination of the calorimetry and our ability to calibrate it in the end results in worse performance, we should acknowledge that, especially it is close to what we have previously stated as "the limit".

John

On 4/27/2018 8:39 AM, Gunther M Roland wrote:

Friends,,

Maria just reminded us that we will have a dry-run of the CD-1 review plenary talks next Wednesday. I am not sure we will quite have the final plots at that time, but we need to figure out what the line of argument is going to be.

We have a nice set of new simulations for the MIE configuration for e.g. jet energy resolution and various physics plots. I'm now thinking of how to make the connection to the UPPs for the OPA talk, and I'm finding that not so easy. 

As an example, the Jet resolution UPP in my notes is "Jet resolution of < 150%/sqrt(E)" (did we specify at which E, as the resolution does not go as sqrt(E), but has a constant term from the AuAu underlying event?). Our simulations however show a resolution that is much better than that. E.g. 15% at 50GeV from simulations vs 150%/sqrt(50) = 21% from the UPP. 

So, my questions/suggestions:
- I assume it is ok if the UPP is somewhat relaxed compared to the performance in simulations?
- We probably should add a line on the performance plots reflecting the UPP performance
- We should add a set of points corresponding to the UPP performance to the physics plots
- for the physics plots, one needs some to provide some scale of why we want to reach a certain performance. I'm planning to argue that we want comparable performance to that at LHC (e.g. gamma-jet balance uncertainties, Upsilon resolution). Any better ideas?
- for the t-shirt plot, it would be nice to have for comparison also the current RHIC status (applies only to jets/hadron RAA) and a backup plot of how much the MIE vs reference acceptance costs us

Question to Dennis/Rosi: Any chance of getting a photon resolution plot from simulation to compare to the photon UPP of <15%/sqrt(E) photon resolution? I think it would be good to fold this into the physics plot. 

Question to Tony: Where can I find the latest Upsilon mass plot for pp? The UPP (Y(1s) mass resolution < 100MeV) probably needs to refer not just to the system, but also specific running conditions: single central Au+Auevent, max pileup, average pileup? It would be good to have a comparison of the resolution for pp, single central Au+Au and central Au+Au at max pileup (beginning of store) to see where we stand.

Cheers,

Gunther

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John Lajoie

Professor of Physics

Iowa State University

 

(515) 294-6952

lajoie AT iastate.edu