Star-tpc-l mailing list

[James Dunlop <dunlop AT bnl.gov>]

The delta between east and west vertices is a very good indicator of axis misalignment between

the magnetic field and the TPC electric field.

Just as an FYI after the major magnet bus short in the 2000's we saw

evidence of a shift in the axis of the magnetic field by something close to that level.  

We interpreted that as a catastrophic shift of the coils within their placement

in the iron.

--J

On Apr 10, 2025, at 4:57 PM, Fisyak, Yuri V <fisyak AT bnl.gov> wrote:

Hi Flemming, 

I assumed during the TPC alignment that the STAR magnet axis has defined by the magnet survey measurements and TWIST distortion are taken into account by TPC survey measurement.

But:

1. From comparison 2021 RF and FF I saw TPC rotation around vertical axis by ~ 1 mrad.
2. Multiple Alexei’s measurement of TPC position with respect to magnet do NOT show any movement of TPC with swapping of magnet current.
3. In 2025 Cosmic data I see ~2 mm (~1 mrad) movement with FF of GMT with respect to cosmics tracks obtained with RF alignment.
4. Comparison of X and Y of primary vertex reconstructed with West only and East only hits shows ~1 mm differences which are differed for RF and FF.  

Thus:

1. My guess is that there is a rotation of the STAR magnet axis (~0.5 mrad) with respect to the STAR magnet survey position which could explain all 4 but’s.
2. The problem is to measure this rotation.

1. I am going to use West and East only reconstruction of primary vertex in collision data, and
2. Use δ-electrons average directions, assuming that they are flow along the magnetic field. EandB program which Grigory used in ~2014 to correct West magnetic field  distortion due to EEMC.

After measuring magnetic field direction it will be necessary to revisit results of the last TPC alignment.

 

                                                              Yuri Fisyak

STAR                                           Phone: +1 631 344 3913
Brookhaven National Laboratory  Fax:    +1 631 344 4206
510A/1-161
http://www.star.bnl.gov/~fisyak       E-mail: fisyak AT bnl.gov

 

 

 

From: star-tpc-l-request AT lists.bnl.gov <star-tpc-l-request AT lists.bnl.gov> on behalf of videbaek <videbaek AT bnl.gov>
Date: Thursday, April 10, 2025 at 3:34 PM
To: Witt, Richard CIV USNA Annapolis <witt AT usna.edu>
Cc: Star-tpc L <Star-tpc-l AT lists.bnl.gov>
Subject: Re: [[Star-tpc-l] ] TPC Meeting Minutes

Hi Richard,
Sorry I was busy at the time of the meeting.
At the ops meeting we also learned that the 3 weeks repair time is most 
likely an underestimte more info to come soon.

Q: Does the statement that must be from Yuri on the FF vs RFF come from 
the track to GMT matching which is showed last week? I like some more 
explanation of this since I learned the TOF trays and the thus the GMT 
is
is mounted to the TPC. Thus I would not expect a shift in the matching 
observable, if the geometry is otherwise the same. Of course the B-field 
is changed. Are there any Lorentz effect in the GMT (3 layer GEM)  
itself. Or is the geometry different, and if so what was used.

best Flemming




On 2025-04-10 12:12, Richard Witt wrote:
> Present: Alexei, Jim, Flemming, Yuri, Gene, and myself
> 
> == Hardware
>  — Nothing new reported this week
> 
> == Electronics
>  — Tonko said he will begin to repair electronics next week
> 
> == Software
>  — looking for STAR magnet access
>  — no shifts of TPC found from Alexei’s work
>  — cosmics from Run2025, FF vs RFF seems to show something that
> still looks like a shift
>  — want to better understand actual position of STAR magnet
>  — Work on SC
>  — BESII Run 23 and 24 work
>  — cluster of runs in Run23 that would note produce a calibration
> result
>  — pileup cut was vertex match between TPC and VPD vertices
>  — VPD issue and 1/4 of ToF in first weeks of Run23 (due to clock
> issues) was culprit
>  — somewhat of a sidetrack to look into timing there
> 
> == AOB
>  — Nothing new reported this week
> 
> Best Regards,
>   Richard
> 
> Sent from my iPad
> --
> "Education is the most powerful weapon which you can use to change
> the world."
> 
> --Nelson Mandela
> 
> ~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~
>  Richard Witt, Professor of Physics     Phone (USNA): 410-293-6675 [1]
>     United States Naval Academy         Email: witt AT usna.edu
> ~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~~~***~
> 
> Links:
> ------
> [1] tel:410-293-6675

-- 
Flemming Videbaek
senior scientist, emeritus
videbaek @ bnl.gov
Brookhaven National Lab
Physics Department
Bldg 510D
Upton, NY 11973

phone: 631-344-4106
cell     :  631-681-1596