Performance of the wavelength-shifting fiber upgrade for the Mu2e cosmic-ray veto detector

TL;DR

This paper evaluates the performance of larger diameter wavelength-shifting fibers in the Mu2e cosmic-ray veto detector to enhance light yield and background rejection, including testing procedures, light properties, and aging effects.

Contribution

It introduces the use of 1.8 mm diameter fibers in critical detector regions and compares their performance with previous 1.4 mm fibers, including aging assessments.

Findings

1.8 mm fibers provide higher light yield than 1.4 mm fibers.

The testing procedure using a custom scanner was successful.

Fiber aging measurements indicate stability over time.

Abstract

The Cosmic-Ray Veto detector for the muon-to-electron conversion experiment at Fermilab consists of four plastic scintillating counter layers read out by silicon photo-multipliers through embedded wavelength-shifting fibers. In order to increase the light yield in the most critical regions of the Cosmic-Ray Veto detector for improved background rejection, a 1.8 mm diameter fiber is being used in many of the detector's critical modules instead of the previously planned 1.4 mm diameter fiber. This paper reports the testing procedure and light properties of thirty-four 1.8 mm fiber spools, with measurements performed using a custom-built scanner. We compare these new results with previously published data from the 1.4 mm diameter fiber used for regions of the cosmic-ray veto where the increased light yield is not required. In addition, measurements of fiber aging were performed.