Sphenix-calibration-l mailing list

[Aaron Angerami <angerami AT cern.ch>]

Hi,

I think Takao’s draft input sent to the whole calibration TF list pretty well 
summarizes my point of view.

What I didn’t see in Jamie’s draft slides was the motivation for taking Au+Au 
in year 1 (2023) and only Au+Au. Does anyone know either a physics/political 
reason or RHIC technical constraint of why this needs to be? Is this an item 
that is even open for discussion?

In the current plan we have 11.5 weeks of commissioning + 9 weeks of physics 
data taking w/ Au+Au in 2023. What do we plan to achieve with that data, 
specifically what measurements do we plan to perform? I don’t see how we can 
establish a jet energy scale without pp data— this may be possible but no one 
has come up with an idea on how to do it. So this would mean that either 

-We use the 2023 Au+Au data, but cannot publish any measurements using fully 
reconstructed jets until after we have taken the pp data in 2024 (and had 
time to analyze it). 

-We do jet measurements using the 2023 data with no control over the energy 
scale, not because its particularly valuable to the field, but because its 
the only thing we can do. As I tried to say in the meeting, I think this is 
not a good idea. I also see a scenario in which people generally agree this 
is a bad idea, but that goes out the window when the data actually comes or a 
major conference is on the horizon. 

A good example is something like a jet R_CP. It is true that if you do this 
properly, a large component of the JES uncertainty (and also the JER) is 
correlated between central and peripheral collisions, and will partially 
cancel in the ratio. However, the cancelation is not exact and properly 
evaluating it requires knowledge of the absolute JES uncertainty. For 
example, in measurements at the LHC, even though there is cancellation, this 
is still the largest source of systematic uncertainty. It’s probably fine to 
show a result at a conference with these caveats, but I think it would be 
poor form to compare directly to a theory calculation or other experimental 
data. 

So to try to answer Justin’s question, I think taking only Au+Au data in 2023 
could “work” if there are some protocols of how the data is interpreted for 
cases like this would be established and enforced by the spokespersons, and I 
think the calibration TF has a role in helping craft those protocols. This 
has to be a pretty common issues in experiments with the how people use data 
taken during commissioning. The Au+Au data of course will be real physics 
data, but some of those basic ideas should still apply.

Best,
Aaron




> On Aug 13, 2020, at 9:58 AM, Frantz, Justin <frantz AT ohio.edu> wrote:
> 
> Hi guys,  I would be willing to write it up.   Perhaps though it's easiest 
> to just attend Jamie's open meeting tomorrow on this (I was planning to) 
> and express it there--- if we can come to a bit more of  a conclusion about 
> it.  
> 
> Cause I think I knew where the general conclusion was headed but we did 
> table the discussion before we had quite reached the end.   Perhaps we 
> could just by email see if we can just make some statements concerning our 
> areas that would form the basis of such a response, then I can try to 
> integrate them essentially, and already bring up whatever fraction is 
> appropriate by tomorrow's meeting.    
> 
> I had a couple questions though based on the discussion we did have:  First 
> for Aaron, if I understood your point of view, you do think it could work 
> for the JETS to get the p+p calibration data 0.75yr to 1 yr  afterwards,  
> ie and essentially finalize calibration after the fact, but you are more 
> concerned with the pressure to come up with first results before that (like 
> R_CP), managing expectations (more internal or external?)?
> 
> Here's a crazier idea:  what about commissioning with deuteron+deuteron or 
> if there is another small system that has a more similar e/m  so that the 
> magnet's don't need moved or as far?   (this was the original motivation in 
> my understanding why Rhic did d+Au in the first decade rather than p+Au.)  
> If this is at all a possibility I assume d+d would be virtually be the same 
> as p+p even for jets UE event etc (OK there's a little difference).  Is 
> something as large as d+Au still "OK" ie quite better than peripheral AuAu? 
>   How big could it go if this would work? 
> 
> 
> ----------------------------------------------
> 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  
> PERSONAL ZOOM MEETING:  369-910-7530   Password:  1
> 
> 
>> -----Original Message-----
>> From: Christof E Roland [mailto:cer AT mit.edu]
>> Sent: Thursday, August 13, 2020 4:30 AM
>> To: Christof Roland via sPHENIX-calibration-l
>> Cc: Frantz, Justin; Megan Connors; Aaron Angerami; Takao Sakaguchi
>> Subject: BUR input from Calibration TF
>> 
>> Hi Everybody,
>> 
>> in the last TF meeting we mentioned writing a few lines as input to the 
>> next
>> BUR meeting on Friday.
>> Would anybody voluteer to prepare a draft?
>> 
>> Thanks
>> 
>>   Takao & Christof