A beam test of the upgraded calorimeter prototype of the High Energy cosmic Radiation Detection (HERD) facility was conducted at the CERN SPS H2 and H4 beam lines from Oct 2^nd to Nov 1^st.

HERD, a China-led mission with a large international collaboration, is a flagship scientific experiment for China's future Space Station. The main scientific objectives of HERD are indirect dark matter searches with unprecedented sensitivity, precise cosmic ray spectrum and composition measurements up to the knee energy, and gamma-ray monitoring and surveys.

The calorimeter prototype consists of 250 LYSO crystals, and is an upgraded version of the 2015 prototype, with a more advanced camera and a new technique of crystal encapsulation. During the beam test, data on protons, electrons, muons and fragmented ions were taken, to test the performance of the prototype in key areas including energy linearity, energy resolution, particle ID power, off-axis capability and charge measurement capability.

Preliminary results show that the non-uniformity of the crystals is well controlled, around 2:1, which is much better than the previous prototype. The energy resolution is better than 1.3% for 200 GeV/c electrons, and fragmented ions with Z>20 are clearly seen in the spectrum of fragments.

All expected design criteria were achieved in this test. The novel design of the 3D calorimeter with WLS fiber + IsCMOS/ICCD readout is proved to be feasible for broad-band observation with high energy resolution.

Around 30 scientists, from the Institute of High Energy Physics (China), Xi’an Institute of Optics and Precision Mechanics (China), Guangxi University (China), Beijing Hamamatsu (China), the University of Geneva (Switzerland), INFN Perugia (Italy), INFN Bari (Italy) and INFN Lecce (Italy), participated in the beam test.

In between the proton beam run and ion beam run, the 5^th HERD international workshop was held at CERN. Progress on R&D for the instruments, MC simulation, the beam test underway, and future activities were  discussed in depth.

Fig. 1 Left: HERD calorimeter prototype (China) and the trigger and tracking system (Italy & Switzerland) installed on the SPS H2 line. Right: Reconstructed spectrum of 200 GeV/c electron. (Image by IHEP)

Group photo of the 5th HERD international workshop (Image by IHEP)