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By accurately measuring composition and energy spectrum of cosmic ray, the origin problem of so called "knee" region (energy >one PeV) can be solved. However, up to the present, the results of the spectrum in the knee region obtained by several previous experiments have shown obvious differences, so they cannot give effective evidence for judging the theoretical models on the origin of the knee. Recently, the Large High Altitude Air Shower Observatory (LHAASO) has reported several major breakthroughs and important results in astro-particle physics field. Relying on its advantages of wide-sky survey, high altitude location and large area detector arrays, the research content of LHAASO experiment mainly includes ultra high-energy gamma-ray astronomy, measurement of cosmic ray spectra in the knee region, searching for dark matter and new phenomena of particle physics at higher energy. The electron and thermal neutron detector (EN-Detector) is a new scintillator detector which applies thermal neutron detection technology to measure cosmic ray extensive air shower (EAS). This technology is an extension of LHAASO. The EN-Detector Array (ENDA) can highly efficiently measure thermal neutrons generated by secondary hadrons so called "skeleton" of EAS. In this paper, we perform the optimization of ENDA configuration, and obtain expectations on the ENDA results, including thermal neutron distribution, trigger efficiency and capability of cosmic ray composition separation. The obtained real data results are consistent with those by the Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

Ultra-high-energy (UHE, >0.1 PeV) γ-ray astronomy is rapidly evolving into an expanding branch of γ-ray astronomy with the surprising discovery of 12 PeVatrons and the detection of a handful of photons above 1 PeV. Nearly all known celestial object types that have emissions in the TeV band are found also to emit UHE photons. UHE γ-rays have a well-defined horizon inside our Galaxy due to the absorption of infrared and cosmic microwave backgrounds in the Universe. In the last 30 years, traditional cosmic ray (CR) measurement techniques have enabled the detection of UHE γ-rays and opened the last observation window. For leptonic sources, UHE radiation is in the deep Klein–Nishina regime, which is largely suppressed. Therefore, UHE γ-ray detection will be helpful in locating and identifying hadronic radiation sources, tracing the historic pursuit for the origin of CRs around the knee of the spectrum. The Crab Nebula is the focus of attention with measured photon emissions up to 1 PeV. In the absence of hadronic processes, these emissions may indicate the existence of an extreme accelerator of e+e−. Use of CR extensive air shower detection techniques broadens the field of view of the source observations, enabling measurement of UHE radiation surrounding the sources. These observations can probe the particle propagation inside and outside the accelerators and the subsequent injection/escape into the interstellar medium. [ABSTRACT FROM AUTHOR]

The measurement of shower muons on an event-by-event basis offers a potent tool for conducting ground-based experiments on gamma rays and cosmic rays due to its sensitivity to primary mass and interaction models. In recent years, underground water Cherenkov detectors as large-area muon counters provide the most powerful way of rejecting cosmic ray background when searching for TeV–PeV gamma rays and cosmic ray electrons, an unprecedented rejection power of 1 0 4 – 1 0 5 is achieved. Unburied water Cherenkov detectors are widely used in ground-based gamma astronomy experiments, e.g, Milagro, HAWC, LHAASO-WCDA, etc. However, due to the presence of electromagnetic components, their deployment as event-by-event muon counters has encountered considerable challenges. All the experiments mentioned above reconstruct lateral-distribution-function related parameters to tell a gamma from hadrons. In this work, we first developed a method to utilize the WCDA, to specify muon content in each shower with LHAASO KM2A-WCDA synergy and help LHAASO to gain approximately a 37,650-meter-square effective area as a muon counter. [ABSTRACT FROM AUTHOR]

The Wide Field of view Cherenkov Telescope Array (WFCTA) of the Large High Altitude Air Shower Observatory (LHAASO), located in Haizishan National Natural Reserve, Sichuan Province, China, is designed to perform nearly calorimetric measurements of extensive air showers induced by cosmic rays with energies between 10 13 eV –10 18 eV. The end-to-end calibration method will be employed in the WFCTA and nitrogen lasers have been proven to work properly in our application at the altitude of 4410 m a.s.l. for the first time. Due to extremely harsh environment, especially outdoor temperature as low as about −30 ° C during operation of WFCTA, a high-stability thermotank for lasers was designed to stabilize temperature and humidity, with a thermal stability of 1 ° C. In order to precisely control the beam pointing, a high-precision 3D Lifting Rotating Platform (HiRoP) with a home-made standard zero monitoring system is developed. To eliminate the error of the beam pointing by manual controls, an automatic scanning program was adopted to control the beam pointing when scanning the full field-of-view (FOV) of WFCTA. Both the on-site and remote controls are applied for the nitrogen laser systems and ∼ 13 million laser shots have been recorded by WFCTA from Sept. 2020 to May 2022. In this paper, the design, properties, operation and the on-site performance of the nitrogen laser systems at LHAASO are reported. [ABSTRACT FROM AUTHOR]

Abstract The Wide Field of View Cherenkov Telescope Array (WFCTA) is an important part of the Large High Altitude Air Shower Observatory (LHAASO) project. A high-resolution and low-relative deviation charge measurement is required over a dynamic range of 10 photoelectrons (p.e.) to 32,000 p.e. in the electronics readout system of the WFCTA. The analog circuit is one of the crucial parts in the electronics readout system. Because of the large dynamic range of the signals, a dual-gain electronics channel has been designed. In other words, for the signals from a SiPM, we designed two channels with the similar structures and different gains When these two kinds of channels are placed on two different Printed Circuit Boards (PCBs), it reduces the crosstalk between the large gain channels and the small gain channels. Tests have been conducted to evaluate the performance of the electronics readout system under different temperature conditions. Results indicate that accurate charge measurements can be achieved, ranging from 10 p.e. to 32,000 p.e., and that the system is capable of adapting to the temperature environment of the plateau where the altitude is more than 4000 m. [ABSTRACT FROM AUTHOR]

Abstract In the Large High Altitude Air Shower Observatory (LHAASO), the Water Cherenkov Detector Array (WCDA) and Muon Detector (MD) employ a large number of photomultiplier tubes for cosmic ray detection. In order to explore the cosmic ray sources at very high energy level, these photomultiplier tubes require not only good single photoelectron resolution, but also large linear dynamic range: up to 4000 photoelectrons for WCDA and over 10000 muons for MD. In order to meet these requirements, we design a high dynamic range base for three photomultiplier tube candidates (R5912, CR365 and XP1805) for WCDA and R5912 for MD, and test their performance. The results show that the characteristics of all three candidates with a charge dynamic range up to 1–4000 photoelectrons satisfy the demands of WCDA. For R5912 of MD, the equivalent current non-linearity of DY7 within 5% is up to 1.87A, satisfying the dynamic range requirement of MD. [ABSTRACT FROM AUTHOR]

The Wide Field of View Cherenkov Telescope Array (WFCTA), a main component of the Large High Altitude Air Shower Observatory (LHAASO), is designed for cosmic rays spectrum measurement from 30 TeV to several EeV. Silicon photomultipliers (SiPMs) have been adopted for the telescope cameras as they do not suffer any aging even with strong light exposure and thus they can be operated with moonlight. The physics of WFCTA requires a dynamic range of SiPMs to be within 10 p.e. (photoelectrons) to 32, 000 p.e. at any energy range. And the dynamic range of SiPMs is proportional to the total number of APDs and depends on the distribution of light hitting on the active area. This light distribution is affected by the use of light concentrator and also by the use of spherical mirrors of the telescope. The effect of these two factors on the Cherenkov light distribution has to be taken into account to evaluate the dynamic range and in this work they have been simulated with a ray-tracing software. The non-uniform light distribution caused by the light concentrator and the spherical mirror will be below 2% for 32, 000 p.e. at the condition if the SiPM has 360, 000 cells. The characteristics of SiPMs from three different producers – Hamamatsu, FBK, and SensL – are measured in laboratory, and the dynamic range of them has also been measured using a uniform light flux. The results of dynamic range correspond with the calculation by the function which describes the relationship between the number of fired APDs and the total number of APDs in the SiPM. The performance of the SiPMs and PMTs under long time duration light pulses up to 3 μ s are compared, in order to investigate the stability of the gain of the SiPMs for the fluorescence mode. [ABSTRACT FROM AUTHOR]

The electromagnetic particle detectors (EDs) for one square kilometer detector array (KM2A) of large high altitude air shower observation (LHAASO) are designed to measure the densities and arrival times of secondary particles in extensive air showers (EASs). ED is a type of plastic scintillator detector with an active area of 1 m 2 . This study investigates the design and performance of prototype ED. Approximately 20 photoelectrons are collected by the 1st dynode of a photomultiplier tube (PMT). The prototype ED exhibited good detection efficiency and time resolution. The detection for the wide dynamic particle density varying from 1 to 10 000 particles/m 2 is realized with the design of the PMT divider for the readout of both the anode and 6th dynode. [ABSTRACT FROM AUTHOR]

The detectability of active galactic nuclei (AGN), a major class of -ray emitters in the sky, by the newly planned Chinese project, Large High Altitude Air Shower Observatory (LHAASO), is investigated. The expectation is primarily based on the AGN catalog of Fermi Large Area Telescope (Fermi-LAT), with an extrapolation to the very high energy (VHE) range taking into account the absorption effect by the extragalactic background light (EBL). It is found that LHAASO may have the potential to detect more than several tens of the Fermi detected AGN, basically BL Lacertaes, with one-year sky survey. The capability of measuring the energy spectrum and light curve are also discussed. [ABSTRACT FROM AUTHOR]

The Water Cherenkov Detector Array (WCDA) is one of the key parts in the Large High Altitude Air Shower Observatory (LHAASO). In the WCDA, 3600 Photomultiplier Tubes (PMTs) and the Front End Electronics (FEEs) are scattered within a 90000~\m^2 area, while a time measurement resolution better than 0.5 ns is required in the readout electronics. To achieve such time measurement precision, high quality clock distribution and synchronization among the 400 FEEs (each FEE for 9 PMTs readout) is required. To simplify the electronics system architecture, data, commands, and clock are transmitted simultaneously through fibers over a 400-m distance between FEEs and the Clock and Data Transfer Modules (CDTMs). In this article, we propose a new method based on the White Rabbit (WR) to achieve completely automatic clock phase alignment between different FEEs. The original WR is enhanced to overcome the clock delay fluctuations due to ambient temperature variations. This paper presents the general scheme, the design of prototype electronics, and initial test results. These indicate that a clock synchronization precision better than 50 ps is achieved over 1 km fibers, which is well beyond the application requirement. [ABSTRACT FROM AUTHOR]

Abstract: LHAASO (Large High Altitude Air Shower Observatory) is a large project to research on high energy gamma ray astronomy and cosmic ray physics. KM2A (one KM 2 Array), one main part of the LHAASO project, using a 1km 2 array composed of electron detectors (ED) and muon detectors (MD), focuses on gamma ray astronomy above 30TeV and cosmic ray physics in the “knee” region. Accurate measurement of gamma ray energy spectra above 30TeV is crucial to identify the sources as the galactic cosmic ray accelerators. Monte Carlo simulation indicates that cosmic gamma rays can be distinguished from cosmic nuclei background by using muon content in extensive air showers (EAS). With the sensitivity of about 1% of the integral flux of Crab Nebula, the high duty cycle of at least 90 and the full sky survey, the KM2A array would be very useful in discovering the galactic gamma ray sources and identifying the cosmic ray sources with gamma-ray emission. A detailed simulation is carried out for studying performance and expectation of the KM2A array in gamma ray astronomy above 30TeV. [Copyright &y& Elsevier]

Ultra-high-energy (> 100 TeV) gamma-ray detection benefits from the use of muon detectors (MDs) thanks to their capability of suppressing the cosmic-ray background. More than 1100 8-inch photomultiplier tubes (PMTs), CR365-02-2 from Beijing Hamamatsu Photon Techniques INC. (BHP), will be deployed for the LHAASO-MD experiment. In this paper, the design of the photomultiplier base for CR365-02-2 is presented. Signals are extracted from two outputs: the anode and the 7th dynode. This design ensures a high dynamic range, from single photoelectron (SPE, peak-to-valley ratio > 2), up to bunches of 7 × 1 0 5 photoelectrons, with an equivalent anode peak current of up to 1600 mA. The anode-to-dynode amplitude ratio (A/D) is below 160 in order to ensure enough overlap between the two outputs. Test results of 4 PMTs, including the SPE response, A/D, linearity, dark count rate, and afterpulse rate, are reported. [ABSTRACT FROM AUTHOR]

Over 5000 1.5-inch photomultiplier tubes (PMTs) are deployed in the electromagnetic particle detectors (EDs) of the Large High Altitude Air Shower Observatory (LHAASO). The PMTs are developed as two outputs devices (the anode and the 6th dynode) to measure the large dynamic ranges of particle densities within the extensive air shower. Before assembly, the PMTs must be fully tested to ensure the products meet the performance requirements. A dedicated test bench has been designed for this purpose, capable of testing multiple PMTs simultaneously. The major performances such as single photoelectron spectrum, gain versus high voltage, pulse linearity, dark noise rate and temperature coefficient are measured for each PMT, and transit time spread (TTS) is measured from a 5% sample. The PMTs that comply with the requirements are used in the EDs construction. The design of the PMT voltage divider and the test results of 5366 PMTs are presented in this paper. [ABSTRACT FROM AUTHOR]

Abstract: A large high-altitude air-shower observatory (LHAASO) is to be built at Shangri-La, Yunnan Province, China. This observatory is intended to conduct sub-TeV gamma astronomy, and as an important component of the LHAASO project, a water Cherenkov detector array (WCDA) is proposed. To investigate engineering issues and fully understand the water Cherenkov technique for detecting air showers, a prototype array at 1% scale of the LHAASO-WCDA has been built at Yang-Ba-Jing, Tibet, China. This paper introduces the prototype array setup and studies its performance by counting rate of each photomultiplier tube (PMT), trigger rates at different PMT multiplicities, and responses to air showers. Finally, the reconstructed shower directions and angular resolutions of the detected showers for the prototype array are given. [Copyright &y& Elsevier]

Abstract: A large high-altitude air shower observatory is to be built at Yang-Ba-Jing, Tibet, China. One of its main purposes is to survey the northern sky for very-high-energy (above 100GeV) gamma ray sources via its ground-based water Cherenkov detector array. To gain full knowledge of water Cherenkov technique in detecting air showers, a prototype water Cherenkov detector is built at the Institute of High Energy Physics, Beijing. The performance of the prototype water Cherenkov detector is studied by measuring its response to cosmic muons. The results are compared with those from a full Monte Carlo simulation to provide a series of information regarding the prototype detector in guiding electronics design and detector optimization. [Copyright &y& Elsevier]

The Large High Altitude Air Shower Observatory (LHAASO) is a new generation hybrid cosmic ray observatory which is expected to reveal the mystery of the origin of cosmic rays. The one square kilometer array (KM2A) consisting of 5195 Electromagnetic particle Detectors (ED) and 1188 Muon Detectors (MD) is a sub-array of LHAASO. The EDs are designed to measure the density and arriving time of the secondary particles of extensive air showers. The performance of the EDs is tested for the quality control after construction in the laboratory at sea level. In this paper, the performance of more than four thousands EDs is summarized. The performance of all tested EDs meets the design requirements with the time resolution of 1.6 ns, the detection efficiency of 97.8%, charge resolution for single particle of 18.5% and count rate around 480 Hz. Furthermore, one ED is singled out for monitoring of the long-term stability over a period of nearly two years from December 2018 to November 2020. [ABSTRACT FROM AUTHOR]

The Large High-Altitude Air Shower Observatory (LHAASO) is being built at Haizi Mountain, Sichuan province of China at an altitude of 4410 m. One of its main goals is to survey the northern sky for very-high-energy gamma ray sources via its ground-based water Cherenkov detector array (WCDA). 900 8-inch photomultiplier tubes (PMTs) CR365-02-1 from Beijing Hamamatsu Photon Techniques INC. (BHP) are installed in the WCDA, collecting Cherenkov photons produced by air shower particles crossing water. The design of the PMT base with a high dynamic range for CR365-02-1, the PMT batch test system, and the test results of 997 PMTs are presented in this paper. [ABSTRACT FROM AUTHOR]

In the Large High Altitude Air Shower Observatory (LHAASO), the main physics objective of the water Cherenkov detector array (WCDA) is to survey the sky for gamma-ray sources in the energy range of 100 GeV to 30 TeV. In order to extend the dynamic range of the WCDA, a 1.5-inch photomultiplier tube (PMT) is placed aside the 8-inch PMT in each cell of the WCDA. All of these 1.5-inch PMTs (900 in total) consist of the WCDA dynamic extended system (WCDA++). These PMTs are required to maintain linearity within four orders of magnitude. The performance of the 1.5-inch PMTs with a specially designed bi-readout voltage divider is tested with a PMT test system. Accordingly, the effects of the working high voltage and signal width on the dynamic range of the PMTs are studied. The test results show that the dynamic range with a 5% non-linearity for a driven signal width of 5.5 ns is more than 200 kPEs (photoelectrons). The dark noise count rate is less than 200 Hz for a 1 mV threshold at a PMT gain of 2 × 1 0 5. These results confirm that the PMT performance meets the WCDA++ requirements. • Photomultiplier tube performance of the WCDA++ experiment is presented. • A bi-readout divider circuit maintains linearity within four orders of magnitude. • The pulse signal width affects the linear maximum number of photoelectrons. • The light intensity does not affect the relation between gain and voltage. [ABSTRACT FROM AUTHOR]