sPHENIX bulk physics topical group

[Ron Belmont <belmonrj AT gmail.com>]

Hi All,

Please see this informative message from Mickey about the average collision z-vertex in Run23.

Cheers,

Ron

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Ron Belmont (he/him/his)
RHIC/AGS Users' Executive Committee
Assistant Professor, Department of Physics & Astronomy
University of North Carolina at Greensboro
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Begin forwarded message:

From: Mickey Chiu <chiu AT bnl.gov>

Subject: Re: [Sphenix-mbd-l] Mean z-vertex position vs. run number ?

Date: November 18, 2023 at 4:24:55 PM EST

To: "sphenix-mbd-l AT lists.bnl.gov" <sphenix-mbd-l AT lists.bnl.gov>

Hi,

The offset is real.  It would be wrong to recenter to 0, and I highly advise against it.  The zvertex distributions across run index was shown at the 10/20 PCM, here:

  https://indico.bnl.gov/event/20893/contributions/82140/attachments/50551/86448/mbd_offline_20231020.pptx

There are three broad groupings, and the <z> and RMS (in cm) by run group are approximately

  20859-20888    -21.4  10.3 

  21199-23019    18.5    11

  >23020              -3.3     8.5

Of course, analyzers should double-check these.  The runs in that plot aren’t consistent with the runs in the official DSTs, since some runs have been added and some taken away from the lists I was told to use.

We aligned the vertex with the INTT using run 20869.  Once that is done, the dependencies in the BBC detector and MBD electronics are stable enough such that we’re confident that the z-vertex measurements are good in the absolute sense.  Right now we would estimate the systematic error in z at around 1 cm.  We need to understand the INTT errors a bit more to finalize this.

Cheers,

Mickey

On Nov 17, 2023, at 6:29 PM, Perepelitsa, Dennis <dvp AT bnl.gov> wrote:

Hi MBD team,

In the PCM earlier today, there was some confusion amongst the analyzers about the need for (or presence of) overall offsets in the calculated z-vertex positions in DSTs, including in the “pre-QM” datasets vs. the new “v3” production, etc. 

For example, I think that for some runs, some analyzers may see a large offset in the reconstructed z-vertex position, and manually re-center it at zero - but that may not be correct if the offset is “real” (i.e. if it was early in Run-23 before we asked C-AD to adjust the overall vertex location).

As an official reference to help analyzers, would you be able to help us out by providing some documentation from the MBD team about the mean z-vertex positions as a function of run number [1]? Or if this already exists, could you help me find a pointer to it?

Is that possible to have before the Thanksgiving holiday - for example by the Software/Simulations meeting on Tuesday, if we have one?

Thanks for any pointers,

Dennis

[1] https://github.com/sPHENIX-Collaboration/macros/blob/master/eventcombine/runnumbers.txt 

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