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[Carl Gagliardi <c-gagliardi AT tamu.edu>]

Hi Flemming and Gene--  I don’t know what low lumi statistics are required by the TPC group.  But if 50M+ NSD collisions with field on will suffice, then the forward cross sections data could likely serve double duty.

 

A thought…

Carl

 

p.s.  Note:  The statistics estimate above is based on the assumption that a high fraction of the EPDE&&TOFmult0 events will be NSD collisions, with a z_vtx distribution that follows the collision diamond.

     We haven’t been in a position to test that assumption yet.  But the converse has been tested for a mix of semi-hard to hard scattering.  In particular, Bassam finds that EPDE&&TOFmult0 has low-to-mid 90s% efficiency for all of the existing FCS triggers, with only 1~2% variation trigger to trigger.  Also, when running at low lumi, Bassam has found that 98% of the FCS-triggered events that include TPC read-out contain a good vertex.

 

 

From: Carl Gagliardi <c-gagliardi AT tamu.edu>
Sent: Friday, January 14, 2022 10:28 AM
To: 'Aschenauer Elke-Caroline' <elke AT bnl.gov>; 'STAR sTGC upgrade' <star-stgc-l AT lists.bnl.gov>; 'Star-fst L' <star-fst-l AT lists.bnl.gov>; 'Carl Gagliardi' <c-gagliardi AT tamu.edu>; 'Flemming Videbaek' <videbaek AT bnl.gov>; 'Van Buren, Gene' <gene AT bnl.gov>
Subject: RE: low luminosity running

 

Hi Elke—

 

The forward MB cross sections measurement will need 16 hours of beam with magnet on and _very low_ luminosity.  Specifically, the non-singly diffractive collision rate per bunch should be no more than a few percent.  2%/bunch would be great; we should be able to live with 4%/bunch if C-AD can’t get down further.  Under these conditions, there is no value in having more than 6 bunches in the fill.  Motivation:

6 bunch fills at 2%/bunch corresponds to about 9400 NSD collisions per second.  The TPC, which will provide vertexing and measure the in-bunch pile-up, will only be able to record 2 kHz or thereabouts.  (At these very low rates, that might be pushed to 2500 Hz (TBD), but not more.)  6 bunches will easily saturate that; more will only increase the background activity in the TPC with no benefit for the measurement.

Note:  9400 NSD collisions per second correspond to a ZDC coincidence rate of 800-900 Hz.

Side note:  These total and recorded collision rates aren’t “new”.  They are in fact very similar to the values we adopted to optimize the isobar studies in 2018.

 

The beam lifetime might be quite long under these conditions.  If the entire data set can be recorded in one very long fill, that will be fine.  Otherwise, two fills should be more than adequate.

 

To achieve the highest practical final precision, we should request that a Vernier scan be performed in conjunction with the measurement.

 

Finally, a personal concern:  Beginning next week, I will be out of pocket teaching class on Tuesdays and Thursdays from 10:15-12:15 BNL time.  I don’t need to watch the entire running period from Texas, and likely won’t.  But I definitely think it would be useful for me to be online for at least the first hour or two of each fill.  I hope that can be factored into the scheduling.

 

Hope this is clear!

Carl

 

p.s.  If C-AD believes it could reliably deliver the beams with a collision rate of 1%/bunch crossing (even better!), then a 12-bunch fill would be desired.

 

p.p.s.  I only expect us to have two “physics triggers” in the runs, EPDE singles and (EPDE && TOFmult0).  However, there will also be a number of other highly prescaled trigger-detector only triggers to facilitate normalization using the TCU scalers.

 

 

From: Aschenauer Elke-Caroline <elke AT bnl.gov>
Sent: Thursday, January 13, 2022 10:02 PM
To: STAR sTGC upgrade <star-stgc-l AT lists.bnl.gov>; Star-fst L <star-fst-l AT lists.bnl.gov>; Carl Gagliardi <c-gagliardi AT tamu.edu>; Flemming Videbaek <videbaek AT bnl.gov>; Van Buren, Gene <gene AT bnl.gov>
Cc: Aschenauer Elke-Caroline <elke AT bnl.gov>
Subject: low luminosity running

 

Dear All, as you know the next week we will most likely have lower luminosity and polarization as there is an issue with the APS. So this might be the perfect time to take our alignment data for the FST and the sTGC. So the requirement was ZjQcmQRYFpfptBannerStart

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Dear All,

 

as you know the next week we will most likely have lower luminosity and polarization as there is an issue with the APS.

 

So this might be the perfect time to take our alignment data for the FST and the sTGC.

So the requirement was one fill with 28 bunches and low bunch current, with Magnet off. Do we have a luminosity number we want for this.

Is one fill enough.

Are there any measurements we need to do before we are ready for this alignment run.

 

Carl you wanted low luminosity running for the cross section measurement in the forward region, I assume you want it with magnets on.

Can you please remind me about the exact conditions you want.

Are there any measurements we need to do before we are ready for this low lumi run.

 

Flemming and Gene there was also some request for low lumi running for the TPC if I remember correctly, can you remind me what lumi you want and what conditions. 

 

I would appreciate to have all the info by tomorrow CoB Friday 01/14/2022

 

Thanks elke

 

 

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