Water Cherenkov Detector Array Research Articles

Design of the photomultiplier tube bases for high dynamic range readout in WCDA

The photomultiplier tube (PMT) used in the water Cherenkov detector array (WCDA) of the Large High Altitude Air Shower Observatory (LHAASO) requires a good single photoelectron (SPE) spectrum and a charge dynamic range from 1 to 4000 photoelectrons. In this paper, the bases design and improvement of the photomultiplier tube R5912 are presented. The results show that at the gain of 2.6 × 106, the anode output has a good single photoelectron spectrum, and its charge non-linearity is within 5% when the number of photoelectrons (nPE) is 3500. The charge non-linearity of the 8th dynode output is within 2% when the number of nPE is 4000, which satisfies the dynamic range requirement.

Disentangling the air shower components using scintillator and water Cherenkov detectors

We consider a ground array of scintillation and water Cherenkov detectors with the purpose of determining the muon content of air showers. The different response characteristics of these two types of detectors to the components of the air shower provide a way to infer their relative contributions. We use a detailed simulation to estimate the impact of parameters, such as scintillation detector size, in the determination of the size of the muon component.

Performance of a prototype water Cherenkov detector for LHAASO project

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.

Study of capabilities of the HAWC observatory to detect GRBs

We describe the simulation of atmospheric air showers originated by gamma rays with energies in the 0.1-1 TeV range. We study the properties of the secondary particles at a height above level of 4100 m corresponding to the height of the array of water Cherenkov detectors (WCDs) of the HAWC (High Altitude Water Cherenkov) Observatory. In particular we study the pile-up effect of the secondary particles as they arrive at the HAWC Observatory to discern the way in which the PMTs of the WCDs of HAWC can distinguish isolated secondary particles as a function of their signal thresholds. This study is relevant to the application of the single-particle counting technique often used to try to detect gamma ray bursts (GRBs) with ground-based experiments.

R&D of Lhaaso-Wcda

As one of the important parts of the LHAASO Project, the Water Cherenkov Detector Array (WCDA) is planned to be built in Yangbajing, Tibet, China soon. In order to fully understand the engineering issues and the basic performance of the water Cherenkov detection technique, a prototype water Cherenkov detector has been built and operat- ed in Beijing, and an engineering array has been constructed on site. With the help of the prototype detector, performance related to cosmic muon signals and water quality maintenance has been studied and acquired. Studies of the engineering array are also progressing smoothly: nine 8-in PMTs and their electronics and DAQ systems have been deployed; an optical calibration system, a water recycling and purification system, and a slow control system, have been installed; the data taking started, and the data analysis is going on. These studies will offer a great help to the future work of the full array.

Limit on the diffuse flux of ultra high energy neutrinos using the Pierre Auger Observatory

The surface array of water-Cherenkov detectors of the Pierre Auger Observatory is sensitive to neutrinos of energies around or above 1 EeV. All flavours interact through charged and neutral current interactions in the atmosphere (down-going), and tau neutrinos may also induce the "earth skimming" mechanism (up-going or crossing mountains). Both types of interaction may produce nearly horizontal atmospheric showers close to the ground, triggering the surface array; they may be distinguished from normal showers thanks to the broad time structure of the signals in the water tanks. Using data collected from january 2004 to february 2009, we use an analysis based on down-going neutrinos to obtain a limit on the all-flavour diffuse neutrino flux. We also update the previous limit for up-going tau neutrinos. Sources of possible backgrounds and systematic uncertainties are discussed.

Instrumentation development for an array of water Cherenkov detectors for extensive air shower experiments

A new small array of Cherenkov detectors has been deployed in Tehran, 1200 m above sea level. This array contains four tanks of distilled water with a diameter of 64 cm and a height of 130 cm. The effective area of each tank is about 1382 cm2. They are used to detect air showers and to record the arrival time of the secondary particles. We have collected about 640 000 extensive air showers (EAS) in 8298 h of observation time from November 2006 to October 2007. The distribution of air showers in zenith and azimuth angles has been studied and a cosnθ distribution with n = 6.02 ± 0.01 was obtained for the zenith angle distribution. An asymmetry has been observed in the azimuthal distribution of EAS of cosmic rays due to geomagnetic field. The first and second amplitudes of the asymmetry are AI = 0.183 ± 0.001 and AII = 0.038 ± 0.001. Since the recent results are in good agreement with our previous results of scintillation detectors, and tanks of distilled water are cheaper, we prefer to use them instead of scintillators in a future larger array. By simulation, we have improved the size of the detectors to yield the highest efficiency. The best dimensions for each tank with a photomultiplier tube in the center of its lid are 40 cm in diameter and 60 cm in height.

Testing of photomultiplier tubes for use in the surface detector of the Pierre Auger observatory

In the array of water Cherenkov detectors of the Pierre Auger Observatory, 4800 large photomultiplier tubes (PMTs) will be used. Before being deployed, each PMT is evaluated to check that various parameters, such as the linearity, dark noise, and gain, fall within a specified range. The large scale test system, designed and constructed for this purpose, is capable of testing multiple large PMTs simultaneously. The test system and the results of the tests for the first 3964 PMTs are presented in this paper.

Study on anisotropy of cosmic ray distribution with a small array of water Cherenkov detectors

The study of the anisotropy of the arrival directions is an essential tool to investigate the origin and propagation of cosmic ray primaries. A simple way of recording many cosmic rays is to record coincidences between a number of detectors. We have monitored multi-TeV cosmic rays by a small array of water Cherenkov detectors in Tehran ($35\ifmmode^\circ\else\textdegree\fi{}{43}^{\ensuremath{'}}\text{ }\mathrm{N}$, $51\ifmmode^\circ\else\textdegree\fi{}{20}^{\ensuremath{'}}\text{ }\mathrm{E}$, 1200 m above sea level). More than $1.1\ifmmode\times\else\texttimes\fi{}{10}^{6}$ extensive air shower events were recorded. In addition to the Compton-Getting effect due to the motion of the Earth in the Galaxy, an anisotropy has been observed which is due to a unidirectional anisotropy of cosmic ray flow along the Galactic arms.

The water Cherenkov detector array for studies of cosmic rays at the University of Puebla

We describe the design and performance of a hybrid extensive air shower detector array built on the Campus of the University of Puebla ( 19 ∘ N , 90 ∘ W , 800 g / cm 2 ) to measure the energy, arrival direction and composition of primary cosmic rays with energies around 1 PeV, i.e., around the knee of the cosmic ray spectrum. The array consists of 3 water Cherenkov detectors of 1.86 m 2 cross-section and 12 liquid scintillator detectors of 1 m 2 distributed in a square grid with a detector spacing of 20 m over an area of 4000 m 2 . We discuss the calibration and stability of the array for both sets of detectors and report on preliminary measurements and reconstruction of the lateral distributions for the electromagnetic (EM) and muonic components of extensive air showers. We also discuss how the hybrid character of the array can be used to measure mass composition of the primary cosmic rays by estimating the relative contents of muons with respect to the EM component of extensive air showers. This facility is also used to train students interested in the field of cosmic rays.