Calibration of the Air Shower Energy Scale of the Water and Air Cherenkov Techniques in the LHAASO experiment

TL;DR

This paper presents a method to calibrate the energy scale of water and air Cherenkov detectors in the LHAASO experiment using Moon shadow measurements, enabling accurate cosmic ray energy spectrum analysis from TeV to PeV energies.

Contribution

It demonstrates the feasibility of cross-calibrating water and air Cherenkov detectors using Moon shadow measurements in LHAASO data.

Findings

WCDA energy scale calibrated up to 35 TeV

Cross calibration of WFCTA with WCDA established

Feasibility confirmed with real data from 2019-2020

Abstract

The Wide Field-of-View Cherenkov Telescope Array (WFCTA) and the Water Cherenkov Detector Arrays (WCDA) of LHAASO are designed to work in combination for measuring the energy spectra of various cosmic ray species over a very wide energy range from a few TeV to 10 PeV. The energy calibration of WCDA can be achieved with a proven technique of measuring the westward shift of the Moon shadow of galactic cosmic rays due to the geomagnetic field. This deflection angle $\Delta$ is inversely proportional to the energy of the cosmic rays. The precise measurements of the shifts by WCDA allows us to calibrate its energy scale for energies as high as 35 TeV. The energy scale measured by WCDA can be used to cross calibrate the energy reconstructed by WFCTA, which spans the whole energy range up to 10 PeV. In this work, we will demonstrate the feasibility of the method using the data collected from April 2019 to January 2020 by the WFCTA array and WCDA-1 detector, the first of the three water Cherenkov ponds, already commissioned at LHAASO site.