Optimization of Air Light Guides for New ATLAS and CMS Zero Degree Calorimeters for LHC High Luminosity Operations*

The transition to High Luminosity (HL) operations of the CERN LHC requires the upgrade of several detector systems. One of these systems are the Zero Degree Calorimeters (ZDCs) in ATLAS and CMS, which are used for triggering and event geometry characterization in Heavy Ion (HI) collisions.

The University of Illinois at Urbana-Champaign leads the joint upgrade effort for the next generation of ATLAS and CMS ZDCs. The ZDC is a sampling calorimeter using tungsten absorbers, radiation hard fused-silica Cherenkov radiators, and photomultiplier tubes (PMTs) for light conversion into analog electric signals. The detector uses reflective air Light Guides (LG) to transport Cherenkov light from the fused silica radiators to the PMT entrance windows. Optimizing the efficiency and acceptance uniformity for the light transport is an important goal for the final HL-ZDC design. 

In this contribution, we study different LG designs for use in the Electromagnetic and Hadronic sections of the HL-ZDC. We will present the results for light transport efficiency and acceptance uniformity for LGs of different geometries both from simulations and measurements. Experiments are being carried out using a simple test setup for light guides as well a light guides installed in detector prototypes.