Light mixer proposal Arjan Heering, Anton Karneyeu HCAL Phase 1 Upgrades Meeting / 28 Apr 2016

The problem Original design: fiber attached directly to the surface of the input window SiPM operates best (linearity of response) if the light distributed uniformly over the input window Solution: introduce light mixer Light input fibers SiPM SiPM input window

Setup LED pulse is 25 ns APD for light reference, connected to QADC SiPM connected to QIE11 readout LED APD 4 input channels: Y11 -> 4 meter clear fiber -> ODU -> MIXER -> SiPM

Configurations Connected fibers: 1 fiber 4 fibers Mixer diameter: 2.5 mm 2.6 mm 2.7 mm 2.8 mm Mixer thickness: No mixer 1 mm 1.6 mm

All measurements / RAW

SiPM Gain calculation Low-light runs: resolution is enough to resolve single electron (pixel) peaks Average gain over all channels / runs: 52 fC / pixel

SiPM charge -> pixels

Light yield efficiency, % Diam\Thickness 1fib 1 mm 4fib 1 mm 1 fib 1.6 mm 4 fib 1.6 mm 2.5 85 77 75 2.6 78 76 2.7 88 83 73 2.8 70 61 65 Normalized to the baseline (no mixer) Extracted from low-light region (linear behavior) => Diameter 2.6 mm / thickness 1.6 mm looks best

APD Gain calculation At low light SiMP expected to demonstrate linear behavior Fit 5 low-light points with line, the slope gives qadc counts to effective photo- electrons conversion

APD qadc counts -> effective photo electrons APD effective p.e. = Input Nph * PDE * mixer_efficiency From TB: 15k p.e. ~ 300 GeV

Linear correction factor Mixer improves linearity Thickness 1.6 mm and 1 mm perform similar

Linearity of mixer t = 1 mm / d = 2.6 mm

Conclusions Mixer thickness 1 mm, diameter 2.6 mm

Backup

Correction factor (vs. real light)

Correction factor (vs. real light) of the mixer t = 1 mm / d = 2.6 mm

Shunt factor 11.5 (design)

Shunt factor 10.9