Correcting Dynamic Distortions in the sPHENIX TPC using a Patterned Central Membrane

At the Relativistic Heavy Ion Collider located at Brookhaven National Laboratory, the sPHENIX experiment integrates both tracking and calorimetric detectors to investigate particle interactions in ultrarelativistic heavy-ion collisions, which result in the formation of Quark-Gluon Plasma (QGP). Among these detectors at sPHENIX, the Time Projection Chamber (TPC) is crucial to accurately track the charged particles produced from the collisions. The TPC is a gaseous chamber, in which electron-ion pairs are created when charged particles pass through it. As a side-effect of its operation, there is a buildup of electric charge in the volume, which distorts the apparent trajectories of those particles. These effects cause event-by-event fluctuations which must be accounted for to properly reconstruct the trajectory of the charged particles.

As part of the distortion correction scheme, a diffuse laser system is used to illuminate the metallized central membrane to produce sheets of photoelectrons. These patterns include small pads and long radial stripes with well known positions. By comparing the difference between the measured electron phi positions associated with the stripes to their nominal phi positions, the space charge distortion effects can be corrected. In this talk, I will give a general overview of how the sPHENIX TPC central membrane is used to correct for various distortions using the diffuse laser system.