Commissioning and running of sPHENIX

[Jamie Nagle <jamie.nagle AT colorado.edu>]

Hello sPHENIXians,

This week marks the start of cryo-week #11 (out of 19 + 6).     In coordination with C-AD, we have made a major change with the D0 magnet busses swapped by C-AD during last Thursday's Maintenance Day to support a zero crossing angle.    This configuration can also support up to a +2 mrad crossing (as opposed to the -2 mrad crossing before), but not the full range of beta*.     In the last day, sPHENIX has started running with 0 crossing angle which yields a big (potentially x4-5) increase in total collision rate, though with only 16% of collisions within |z| < 10 cm.   This may get us back on track for purely calorimetric jet, dijet, photon-jet, pizero/eta measurements, while maintaining significant data with the INTT and MVTX.     One can see the potential in the plot below, and also everyone should read the detailed presentations from sPHENIX and C-AD at the RHIC Coordination meeting earlier today (linked below).

https://indico.bnl.gov/event/20768/contributions/93375/attachments/55493/94921/sPHENIXRunCoordinator_RHICCoordinationMeeting2024_06252024.pdf

https://indico.bnl.gov/event/20768/contributions/93374/attachments/55481/94904/RHIC_Coordination_Meeting_XXII.pdf

Extra kudos to the shift crews, and Sam in particular on the trigger, for adjusting to the new configuration quickly.    sPHENIX has been running all systems (except the TPC) and sampling the full luminosity.    On the APEX day, Thursday, there will be some trigger changes to hopefully sharpen the photon and jet turn on curves, as well as resolve issues with the MBD Level-1 z-vertex selection (particularly important with the zero crossing angle).    Hard work by the INTT and MBD groups has led to smoother running and critical additional QA checks offline.

The TPC has been running in select periods with 4.1 kV and the nitrogen gas mixture.     Initial offline indications are that this might be a working point delivering important (though not all) physics.     A firm conclusion requires additional analysis and checking.   In parallel, substantial work has converged on the firmware / zero suppression.    A full test without zero suppression and the new beam conditions is underway and later this week a full test with zero suppression is scheduled.  While experts are coordinating a potential change from nitrogen to isobutane, it is critical that we continue to learn with the current working point.

It is another exciting week in sPHENIX-land and we welcome the new shift crew (pictured below) and the continued hard work of Period Coordinator John Lajoie.

Sincerely,

Jamie

sPHENIX Run Coordinator 2024

||------------------------------------------------------------------------------------------
|| James L. Nagle   
|| Professor of Physics, University of Colorado Boulder

|| EMAIL:   jamie.nagle AT colorado.edu
|| SKYPE:  jamie-nagle        
|| WEB:      http://spot.colorado.edu/~naglej 
||------------------------------------------------------------------------------------------