NSF-BSF: Irradiation Studies of Cherenkov Radiators for Use in Zero Degree Calorimeters and Reaction Plane Detectors During the High Luminosity LHC Era

Collisions of heavy ions, typically lead nuclei, create small droplets of nuclear matter at extremely high temperatures at the Large Hadron Collider (LHC) of the European Laboratory for Nuclear and Particle Physics (CERN) in Geneva, Switzerland. The temperatures of those collisions and those droplet-like pieces of nuclear matter mimic the early Universe about one microsecond after the Big Bang.

The scientific interpretation of heavy ion collisions at the LHC requires the experimental characterization of the geometry of the collisions: Do the colliding lead nuclei fully overlap or only partially during the collision? In addition, the orientation of the particles created in the collision with regard to the collision plane needs to be determined experimentally.

This information can be measured for individual lead-lead collisions by Reaction Plane Detectors (RPDs) that will be located in the LHC accelerator tunnel and will be exposed to extremely high radiation doses. Current technology used for the active components of RPDs cannot withstand the radiation levels that will result from LHC upgrades aiming at higher beam intensities.

This award supports the exploration of new materials that can withstand the increased radiation levels at the LHC. The research will study the behavior of advanced fused silica materials under extremely high radiation levels. The work will consist of material studies as well as the design, construction, and beam tests of RPD detector prototypes.

This award will develop new radiation hard Reaction Plane Detectors, RPDs, for the ATLAS and CMS experiments in the High Luminosity LHC era. The detectors will be used together with the Zero Degree Calorimeters (ZDC) to characterize the event geometry in Heavy Ion collisions. The current RPD in CMS is not sufficiently tolerant of radiation for the upcoming high luminosity LHC operations, while ATLAS currently does not have an RPD.

The new RPD design will have to be compatible with the modifications planned for the LHC tunnels in 2024, which will reduce considerably the transverse space available to the detector. The basic problem is devising a robust two-dimensional Cherenkov light detector that is radiation hard to an unprecedented degree. A comprehensive regimen of radiation testing of each detector component using neutron and gamma sources at the Soreq Nuclear Research Center will proceed in parallel with tests of light production and transmission measurements at the Frederick Seitz Materials Research Laboratory at the University of Illinois.

These data will guide the construction of prototypes that will be checked in beam tests. The project will culminate with a final radiation hard RPD design integrated into the ZDC for both ATLAS and CMS. With the installation of an RPD in both ATLAS and CMS it will be possible to determine the reaction plane angle of individual heavy collisions by measuring the correlated deflection of spectator neutrons.

A measured reaction plane will enable studies of key features of heavy ion collisions pertinent to a deeper understanding of the dynamical evolution of the Quark Gluon Plasma. By measuring the initial deflection of the neutrons, it will also be possible to characterize with precision the directed flow relative to the spectator plane, which is sensitive to the three-dimensional spatial profile of the initial system and the pre-equilibrium early time dynamics in the evolution of the heavy ion collision.

The R&D to produce such a highly radiation-tolerant device will be a significant contribution to the field of instrumentation in high radiation environments.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.