Characterisation of NEXT-DEMO using xenon K$_{\alpha}$ X-rays

TL;DR

This paper characterizes the NEXT-DEMO xenon TPC detector using xenon K$_{ ext{α}}$ X-ray emissions to understand its response and improve energy measurement accuracy for neutrinoless double beta decay searches.

Contribution

It introduces a method to use xenon K$_{ ext{α}}$ X-ray signals for detector calibration and response equalization in a high-pressure xenon TPC.

Findings

Measured electron drift properties in the TPC.

Analyzed effects of electroluminescence production region.

Derived position-dependent correction constants for detector response.

Abstract

The NEXT experiment aims to observe the neutrinoless double beta decay of $^{136}$Xe in a high pressure gas TPC using electroluminescence (EL) to amplify the signal from ionization. Understanding the response of the detector is imperative in achieving a consistent and well understood energy measurement. The abundance of xenon k-shell x-ray emission during data taking has been identified as a multitool for the characterisation of the fundamental parameters of the gas as well as the equalisation of the response of the detector. The NEXT-DEMO prototype is a ~1.5 kg volume TPC filled with natural xenon. It employs an array of 19 PMTs as an energy plane and of 256 SiPMs as a tracking plane with the TPC light tube and SiPM surfaces being coated with tetraphenyl butadiene (TPB) which acts as a wavelength shifter for the VUV scintillation light produced by xenon. This paper presents the measurement of the properties of the drift of electrons in the TPC, the effects of the EL production region, and the extraction of position dependent correction constants using K$_{\alpha}$ X-ray deposits. These constants were used to equalise the response of the detector to deposits left by gammas from $^{22}$Na.