Geant4 Simulation for the EIC Light Guides

Program evaluates the best length of a lightguide required to obtain maximum light yield from a scintillation-based detector. These studies are rested by the EIC barrel calorimeter engineering group (Rolf Ent, Elke Aschenauer).

Key Geometry Features

• Trapezoidal scintillation crystals. SciGlass material, size 4×4 → 6×6 cm. Length is 40 cm.
• Trapezoidal light guides made from PMMA material.
• Light guide material is PMMA, properties found online.
• Crystal and light guide are wrapped in 65 micron ESR reflector.
• SciGlass material parameters taken from the Glass Prototype simulation.
• Sensitive detector part is 6x6 array of S13360_6025CS SiPMs with silicone resin window.

Detector geometry. Top: 5 cm light guide. Bottom: no light guide.

Validating Photon Trajectories

Test simulation visualizing thee Optical Photon (OP) trajectories is carried out to ensure reasonable detector geometry and data output.

• 500 OP emitted from the center of the crystal (1 event).
• OP energy distribution histogram for the General Particle Source (GPS) is generated from the SciGlass emission spectrum.
• Number of Photo-electrons (PE) obtained from detector Quantum Efficiency curve.
• OP emitted from a single point inside the crystal (approximately center).

Left: Visual validation of the detector geometry, 500 OP emitted. Right: Obtaining number of PE per run via the efficienct curve.

Data Analysis

Series of simulations for a set of different light guide length are carried out.

• 4 GeV electrons are injected into the scintillation crystal in longitudinal direction (500 events).
• Following light guide length are studies: 0, 5, ...(step 5 mm), … 60, 80, and 100 mm.
• Crystal Ball function used to fit distributions of registered PE/event.
• Optical resolutions are calculated for each simulation run.

Distributions of registered number of PE/Event • 500 events per run • 8 out of 15 length presented

Cumulative graphs of registered number of PE along with the optical resolution for each light guide length are presented below:

Registered number of PE/Event and corresponding optical resolution • 500 injection events per point.

Results

Optical simulations on the Farm for 0, 5, ...(step 5 mm), … 60, 80, and 100 mm light guide length are finished. 4 GeV electrons, trapezoidal SciGlass scintillation crystal, 6x6 SiPM matrix with 36x36 mm² surface area. ROOT plotting scripts are added to the Light Guides repository.

Registered PE/Event and corresponding energy resolutions are plotted. Minimum reasonable light guide length is estimated to be 30 mm.