[Paper Review] The Large High Altitude Air Shower Observatory (LHAASO) Science Book (2021 Edition)

Z. Cao, D. della Volpe+92 more|arXiv (Cornell University)|May 7, 2019

Astrophysics and Cosmic PhenomenaPhysics and Astronomy100 citations

TL;DR

A comprehensive description of LHAASO’s multi-component instrument design (KM2A, WCDA, WFCTA, ENDA) and on-site performance, with projected capabilities for Galactic and extragalactic gamma-ray astronomy, cosmic-ray physics, dark matter, and multimessenger studies.

ABSTRACT

Since the science white paper of the Large High Altitude Air Shower Observatory (LHAASO) published on arXiv in 2019 [e-Print: 1905.02773 (astro-ph.HE)], LHAASO has completed the transition from a project to an operational gamma-ray astronomical observatory LHAASO is a new generation multi-component facility located in Daocheng, Sichuan province of China, at an altitude of 4410 meters. It aims at measuring with unprecedented sensitivity the spectrum, composition, and anisotropy of cosmic rays in the energy range between 10$^{12}$ and 10$^{18}$~eV, and acting simultaneously as a wide aperture (one stereoradiant) continuously operating gamma-ray telescope in the energy range between 10$^{11}$ and $10^{15}$~eV with the designed sensitivity of 1.3\% of the Crab Unit (CU) above 100 TeV. LHAASO's capability of measuring simultaneously different shower components (electrons, muons, and Cherenkov/fluorescence light), will allow it to investigate the origin, acceleration, and propagation of CR through measurement of the energy spectrum, elemental composition, and anisotropy with unprecedented resolution. The remarkable sensitivity of LHAASO will play a key role in CR physics and gamma-ray astronomy for a general and comprehensive exploration of the high energy universe and will allow important studies of fundamental physics (such as indirect dark matter search, Lorentz invariance violation, quantum gravity) and solar and heliospheric physics. The LHAASO Collaboration organized an editorial working group and finished all editorial work of this science book, to summarize the instrumental features and outline the prospects of scientific researches with the LHAASO experiment.

Motivation & Objective

• Summarize the LHAASO instrument complex and its detector technologies (KM2A, WCDA, WFCTA, ENDA) and their performance targets.
• Explain how LHAASO achieves high-sensitivity measurements of gamma rays and cosmic rays up to PeV energies.
• Outline the on-site operational capabilities and synchronization infrastructure enabling multimessenger and fundamental physics studies.

Proposed method

• Describe the detector components and their layouts (ED, MD, WCDA, WFCTA, ENDA) and their integration.
• Present key performance parameters: effective area, angular and core resolution, energy resolution, and sensitivity.
• Explain the clock synchronization (White Rabbit protocol) and DAQ/trigger architecture (front-end digitization, trigger-less scheme).
• Summarize on-site performance metrics from deployment (August 2021) including synchronization accuracy and stability.

Experimental results

Research questions

• RQ1 What are the design performance goals of LHAASO’s KM2A in terms of gamma-ray detection above 30 TeV and cosmic-ray measurements up to 100 PeV?
• RQ2 How does WCDA enable high-sensitivity gamma-ray surveys and extended-source observations in the 100 GeV–30 TeV range?
• RQ3 What are the achievable angular, core, and energy resolutions for the KM2A and WCDA detectors, and how do these drive PeVatron and UHE gamma-ray investigations?
• RQ4 How does the integrated detector suite (KM2A, WCDA, WFCTA, ENDA) support multimessenger and beyond-Standard-Model physics?
• RQ5 What are the on-site performance metrics (synchronization, stability, and trigger performance) achieved after the August 2021 deployment?

Key findings

• KM2A achieves an effective area up to about 0.8 km2 at 30 TeV and an energy resolution of about 28% at 30 TeV.
• KM2A provides angular and core position resolutions suitable for identifying PeVatrons and reconstructing EAS properties (7 m core resolution at 30 TeV; 2 m at 1 PeV).
• The array aims for a Crab-like source sensitivity of about 1% Crab Unit above 100 TeV in one year of observation.
• WCDA covers 78,000 m2 across three pools and provides high-sensitivity gamma-ray surveys from 100 GeV to 30 TeV, with 3 pools and large-area PMT instrumentation.
• On-site performance as of August 2021 shows 5216 EDs installed with synchronization precision within 1 ns, and stable trigger rates and arrays showing moon shadow detections.
• MD detectors (1188 tanks, 36 m2 each) provide muon content measurements with ~25% single-muon energy resolution and ~10 ns time resolution, enabling composition studies at EAS core regions.