Sphenix-calibration-l mailing list

["Perepelitsa, Dennis" <dvp AT bnl.gov>]

Hi Justin,

Yes, this is my understanding as well - in the region >20 GeV, the pi0-level (not decay photon level) is really the appropriate way to think of the background. 

One factoid I like to remember - even though the PHENIX PbSc towers are about twice as big in the transverse dimensions compared to the sPHENIX EMCal, the PHENIX calorimeter was like ~5x further away from the beam pipe. So the decay photon merging in sPHENIX starts a lot earlier.

I definitely agree with you on the need for simulation studies since as you say it’s a smooth transition. As a reminder, we have a user-friendly photon isolation reconstruction which uses all of the calorimeters and can be configured to run on unsubtracted (in p+p) or HI-algorithm-subtracted (in Au+Au) towers: https://github.com/sPHENIX-Collaboration/coresoftware/tree/master/offline/packages/ClusterIso

Dennis

On Aug 15, 2020, at 12:43 PM, Frantz, Justin <frantz AT ohio.edu> wrote:

Probably I spoke too fast, in fact because of sPHENIX’s EMcal segmentation at some point around ~22-25 GeV (probably) most of the pi0’s become indistinguishable from photons due to merging.  So the story will actually be more complicated and between 20-~30 GeV there will be a transition to pi0 itself indeed being the relevant background.      So we will be even more reliant on the isolation effectiveness…which highlights even more the need to quantify it.

 

----------------------------------------------
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

 

From: sPHENIX-jet-structure-l [mailto:sphenix-jet-structure-l-bounces AT lists.bnl.gov] On Behalf Of Frantz, Justin
Sent: Friday, August 14, 2020 6:59 PM
To: Perepelitsa, Dennis; sphenix-calibration-l AT lists.bnl.gov; sphenix-jet-structure-l AT lists.bnl.gov
Subject: Re: [Sphenix-jet-structure-l] short followups to BUR discussion

 

Hi all,

 

One comment to point out Dennis is that gamma_dir/pi0 is not the too relevant quantity and e.g. was not what Jamie was referring to today :  rather that is gamma_dir/(_gamma _from pi0).    Gamma from pi0 is approximately 2/(n-1) of pi0  if I remember correctly so about 1/3, so you can times the S/B by 3 on all those plots for the real background level.   With clean isolation in p+p it should also increase the S/B quite a bit further, further than even was possible in PHENIX since in PHENIX we could not make our cones very big and had some the acceptance effects to deal with.   It would be good to quantify this further though, I will see if I have something around to do it, or if anyone else does already it please chime in.

 

-Justin

----------------------------------------------
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

 

From: sPHENIX-jet-structure-l [mailto:sphenix-jet-structure-l-bounces AT lists.bnl.gov] On Behalf Of Perepelitsa, Dennis
Sent: Friday, August 14, 2020 5:46 PM
To: sphenix-calibration-l AT lists.bnl.gov; sphenix-jet-structure-l AT lists.bnl.gov
Subject: [Sphenix-jet-structure-l] short followups to BUR discussion

 

Dear sPHENIX Calibration and Jet Structure TGs,

 

Here I follow up on two points raised during the BUR discussion this morning ( https://indico.bnl.gov/event/9139/ ).

 

1. Equivalent pp luminosity in peripheral Au+Au events for Year-1 calibrations

 

In the current version of the BUR, we will record 39B in Year-1 Au+Au data-taking. If we consider >60% peripheral events (for example) and ignore any MB trigger inefficiency, those will be 40% of the events. The <Ncoll> for this selection is 12.4 according to MCGlauber v3.2. Thus the equivalent pp luminosity is: 

 

39B * 0.40 * 12.36 / 42 mb = 4.6e+9 mb^-1 = 4.6 pb^-1 .

 

For triggerable events, we could sample 47B in Year-1 running, which in >60% peripheral events is an equivalent p+p luminosity of 5.5 pb^-1. 

 

Either number seems very small for in situ calibration studies, except perhaps for modest pT hadron track->calo (?). 

 

2. Numbers for the Direct Photon / pi0 ratio at RHIC

 

I attach a plot of the expected direct photon / pi0 yield ratio made using our pQCD calculations. Note that there is no isolation or ID requirement, this is just the ratio of expected pQCD rates. You can see that the ratio is >1 starting at perhaps ~20 GeV in Au+Au, but only at ~35 GeV in p+p.

 

However, I also attach Fig 1.50 from the MIE proposal document, which shows that the measured gamma_dir / pi0 ratio by PHENIX is actually somewhat higher than this.

 

Dennis 

 

Dennis V. Perepelitsa

Assistant Professor, Physics Department

University of Colorado Boulder

Dennis V. Perepelitsa

Assistant Professor, Physics Department

University of Colorado Boulder