Identification of low-energy kaons in the ProtoDUNE-SP detector

TL;DR

This work demonstrates the first identification of low-energy kaons in a liquid-argon TPC using ProtoDUNE-SP beam data, addressing proton-decay searches in DUNE, particularly the p -> K+ nubar channel. It develops a robust kaon selection exploiting stopping-kaon topology and the K+ -> mu+ nu_mu decay signature, achieving 522 kaon candidates with 92% purity. A novel Coherent Fit approach characterizes the Ka+ dE/dx energy-loss profile as a function of residual range, enabling precise kaon/background separation and validation against GEANT4-based simulations. The results establish the feasibility of kaon identification in LArTPCs for proton-decay studies and provide groundwork for enhanced DUNE analyses, including potential gains from the Photon Detection System.

Abstract

The Deep Underground Neutrino Experiment (DUNE) is a next-generation neutrino experiment with a rich physics program that includes searches for the hypothetical phenomenon of proton decay. Utilizing liquid-argon time-projection chamber technology, DUNE is expected to achieve world-leading sensitivity in the proton decay channels that involve charged kaons in their final states. The first DUNE demonstrator, ProtoDUNE Single-Phase, was a 0.77 kt detector that operated from 2018 to 2020 at the CERN Neutrino Platform, exposed to a mixed hadron and electron test-beam with momenta ranging from 0.3 to 7 GeV/c. We present a selection of low-energy kaons among the secondary particles produced in hadronic reactions, using data from the 6 and 7 GeV/c beam runs. The selection efficiency is 1\% and the sample purity 92\%. The initial energies of the selected kaon candidates encompass the expected energy range of kaons originating from proton decay events in DUNE (below $\sim$200 MeV). In addition, we demonstrate the capability of this detector technology to discriminate between kaons and other particles such as protons and muons, and provide a comprehensive description of their energy loss in liquid argon, which shows good agreement with the simulation. These results pave the way for future proton decay searches at DUNE.

Figures (9)

• Figure 1: Configuration of ProtoDUNE-SP LArTPC. CPA refers to Cathode Plane Assembly.
• Figure 2: Kaon candidate event display. A beam hadron track can be seen in the left side of the image. It interacts and generates secondary particles. One of these particles propagates in the argon until it interacts again, generating a kaon candidate. The white arrow points to the kaon track, which is followed by a muon track, ultimately followed by a Michel electron. 50 wires correspond approximately to 24 cm.
• Figure 3: Cut on the reduced $\chi^{2}$ distribution under kaon hypothesis to isolate the kaons from the remaining backgrounds. This sample is obtained after applying all but the last cut of the selection. Only statistical uncertainties of the data sample are shown, and the simulation is scaled to the data sample based on the number of candidates.
• Figure 4: $\mathrm{d}E/\mathrm{d}x$ distribution as a function of the residual range for the sample presented in Fig. \ref{['fig:selection_result']} for data (top) and simulation (bottom).
• Figure 5: $\mathrm{d}E/\mathrm{d}x$ distribution for the residual range slice between 17 and 19 cm. Each entry corresponds to a hit of a selected candidate. Data and simulation samples are normalized such that their integrated area is 1. Only data statistical uncertainties are shown.