STAR task force for tuning PYTHIA

["Chang, Zilong" <zchang AT bnl.gov>]

Hi Yuanjing,

I see why you used pythia cross-section over STAR MB cross-section. In this 
ways it is effectively comparing the differential cross-section of the 
particle yield. The difference between pythia MB cross-section and STAR MB 
cross-section will be reflected in the comparison. However because the 
invariant yield is a normalized quantity, not an absolute quantity, what I 
have in mind is you can just compare d^2N/(2pi p_T dp_T dy) 1/N_event from 
PYTHIA directly to the measured invariant yield not worrying about 
cross-sections.

This would be different for hardQCD event. For each p_T hat bin, you need 
apply the PYTHIA cross-section and the number of events in that bin to get 
the correct weight. When you combine the spectrum from all the p_T hat bin, 
you end up with a differential cross-section. To get the PYTHIA invariant 
yield, you would just need to normalize the differential cross-section by the 
sum of PYTHIA cross-section from all p_T hat bins. You don’t need the STAR 
measured MB cross-section in this case.

Does this make sense?

Zilong

> On Mar 24, 2021, at 7:18 PM, Yuanjing Ji via Star-tf-tunepy-l 
> <star-tf-tunepy-l AT lists.bnl.gov> wrote:
> 
> Hi all,
> 
> Please find my response to today's discussion on whether we need a 
> cross-section scale factor for  invariant yield calculation at the 
> following link:
> https://drupal.star.bnl.gov/STAR/system/files/rivet_0324.pdf
> 
> Best
> Yuanjing
> 
> On 2021-03-23 14:24, Matthew Kelsey via Star-tf-tunepy-l wrote:
>> Hi all,
>> Just a friendly reminder of our weekly pythia 8 tuning task-force
>> meeting tomorrow at 3 PM BNL time. I’ve copied the connection details
>> below.
>> Cheers,
>> Matt
>> ——————————
>> Matthew Kelsey
>> Postdoctoral Fellow
>> Wayne State University
>> <he/him/his>
>> Topic: STAR PYTHIA 8 Tune Task Force
>> Time: Mar 24, 2021 03:00 PM Eastern Time (US and Canada)
>> Join Zoom Meeting
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