Measurements of wavelength-dependent double photoelectron emission from single photons in VUV-sensitive photomultiplier tubes

TL;DR

This study measures how the probability of double photoelectron emission from VUV-sensitive photomultiplier tubes varies with wavelength, affecting photon detection accuracy in liquid xenon detectors.

Contribution

It provides the first detailed wavelength-dependent measurements of DPE probabilities for specific PMTs used in xenon-based detectors.

Findings

DPE probability varies with wavelength, especially below 250 nm.

At 175 nm, DPE probability ranges from 18% to 24%.

Results impact energy calibration in liquid xenon detectors.

Abstract

Measurements of double photoelectron emission (DPE) probabilities as a function of wavelength are reported for Hamamatsu R8778, R8520, and R11410 VUV-sensitive photomultiplier tubes (PMTs). In DPE, a single photon strikes the PMT photocathode and produces two photoelectrons instead of a single one. It was found that the fraction of detected photons that result in DPE emission is a function of the incident photon wavelength, and manifests itself below $\sim$250 nm. For the xenon scintillation wavelength of 175 nm, a DPE probability of 18--24\% was measured depending on the tube and measurement method. This wavelength-dependent single photon response has implications for the energy calibration and photon counting of current and future liquid xenon detectors such as LUX, LZ, XENON100/1T, Panda-X and XMASS.