PandaX-II

PandaX-II PandaX-II was a deep underground particle physics experiment searching for dark matter using a dual-phase liquid xenon time projection chamber located at the China Jinping Underground Laboratory. It aimed to detect Weakly Interacting Massive Particles through nuclear recoil signals and contributed to the global effort alongside experiments such as XENON1T, LUX-ZEPLIN, and DARWIN (project). The project interfaced with institutions including Shanghai Jiao Tong University, Peking University, and the Institute of High Energy Physics, Chinese Academy of Sciences.

Introduction

The experiment built on earlier efforts at the Jiangmen Underground Neutrino Observatory-era infrastructure and the first-generation PandaX-I program to scale up target mass and background suppression. It operated in the China Jinping Underground Laboratory to exploit the overburden provided by the Jinping Mountain complex and reduce cosmic-ray muon flux similar to strategies used by SNOLAB and Gran Sasso National Laboratory. Scientific aims linked to searches pursued by collaborations like AMEGO and SuperCDMS while informing theoretical models developed by groups associated with CERN, Fermilab, and the Perimeter Institute.

Detector Design and Operation

The core detector was a dual-phase time projection chamber (TPC) containing several hundred kilograms of liquid xenon, using photomultiplier tubes from vendors comparable to devices used in KamLAND and Borexino. The TPC design followed principles refined in experiments such as ZEPLIN and XENON100, employing prompt scintillation (S1) and ionization-electroluminescence (S2) signals to reconstruct event energy and position, techniques also used in DarkSide. Cryogenic systems and xenon purification were managed with processes analogous to protocols at LUX and facilities tied to the European Organization for Nuclear Research specialist suppliers. Shielding and passive vetoes incorporated materials vetted by groups from Los Alamos National Laboratory and Oak Ridge National Laboratory to minimize radioactive backgrounds from isotopes studied at institutions like the Nuclear Science Division, Lawrence Berkeley National Laboratory.

Calibration and Data Analysis

Calibration employed external gamma sources and internal injections similar to methods from XENON1T and DEAP-3600, referencing nuclear recoil response measurements made at accelerator facilities such as TRIUMF and RIKEN. Data acquisition systems were influenced by designs from ATLAS and CMS readout electronics, while event selection criteria used statistical frameworks akin to those in analyses from IceCube and Super-Kamiokande. Background modeling incorporated radioassay results from collaboration partners and techniques developed at the Max Planck Institute for Nuclear Physics, using Monte Carlo toolkits like those used by Geant4 teams and computational resources comparable to NERSC and Tianhe (supercomputer). Blind analysis protocols followed standards promoted by the Particle Data Group and methodology echoes in publications from Belle II and BaBar.

Results and Scientific Impact

PandaX-II set competitive limits on spin-independent and spin-dependent WIMP-nucleon cross sections, constraining parameter space explored by phenomenologists at Institute for Advanced Study and Perimeter Institute. Its null results for certain WIMP mass ranges complemented positive and null signals discussed in the context of DAMA/LIBRA and CoGeNT and influenced model building at IPMU (Kavli Institute for the Physics and Mathematics of the Universe). The experiment's background mitigation and material screening efforts impacted material-assay programs at facilities including European XFEL-linked labs and informed design choices for successors like PandaX-4T and competitors such as XENONnT. Results were presented at conferences like the International Conference on High Energy Physics and the Cosmology and Particle Astrophysics (CosPA) meetings.

Collaboration and Timeline

The collaboration comprised scientists from Shanghai Jiao Tong University, Tsinghua University, Peking University, Zhejiang University, and the Institute of High Energy Physics, CAS, with international partners connected to groups at University of California, Berkeley, University of Oxford, and University of Chicago. PandaX-II began commissioning in the mid-2010s, accumulated science runs across multiple campaigns, and transitioned knowledge and hardware to future projects by the early 2020s. The project engaged with funding agencies and oversight bodies similar to those collaborating with National Natural Science Foundation of China and engaged in community coordination alongside collaborations such as Global Argon Dark Matter Collaboration.

Category:Dark matter experiments Category:Particle detectors Category:Chinese experiments