ARGO-YBJ Detector Research Articles

ARGO-YBJ detector simulation using GEANT4

‘G4argo’, a GEANT4-based simulation package for the ARGO-YBJ detector, is described in this paper. G4argo incorporates in the simulation the true RPC time resolution and another 0.5 ns time uncertainty which is introduced from the offline calibration of TDC. In addition, the correct RPC geometry and the true materials for the ARGO-YBJ experimental hall are implemented. As a result, G4argo simulation shows a very good agreement with real data.

Temperature effect on RPC performance in the ARGO-YBJ experiment

The ARGO-YBJ experiment has been taking data for nearly 2 years. In order to monitor continuously the performance of the Resistive Plate Chamber detectors and to study the daily temperature effects on the detector performance, a cosmic ray muon telescope was setup near the carpet detector array in the ARGO-YBJ laboratory. Based on the measurements performed using this telescope, it is found that, at the actual operating voltage of 7.2 kV, the temperature effect on the RPC time resolution is about 0.04 ns / ∘ C and on the particle detection efficiency is about 0.03 % / ∘ C . Based on these figures we conclude that the environmental effects do not affect substantially the angular resolution of the ARGO-YBJ detector.

The monitoring system of the ARGO-YBJ data acquisition

The ARGO-YBJ detector has been completely installed at the YangBaJing High Altitude Cosmic Ray Observatory (Tibet, China), at 4300 m a.s.l., and is taking data with a trigger rate of about 4 kHz and a dead time of about 4%. The ARGO-YBJ Data Acquisition System is based on a two-layer readout architecture implementing an event-driven data collection. In order to sustain a high data throughput and have a good readout efficiency or keep the dead time as low as possible, the decoupling FIFOs have been housed on the data packet processing modules. In this paper, the hardware solution to monitor the DAQ system and to track in real-time anomalous data transfers is presented.

Physics and astronomy results with the ARGO-YBJ experiment

The ARGO-YBJ detector, installed at the Yangbajing Cosmic Ray Laboratory (Tibet, China), at 4300m a.s.l., is a full coverage layer of Resistive Plate Counters with an area of about 6.700 m 2 . The high space-time granularity, the full-coverage technique and the high altitude location make this detector a unique device for a detailed study of atmospheric shower characteristics and allow the investigation of a large variety of astrophysical phenomena. In this work a status report on ARGO-YBJ physics and astronomy results will be presented.

Operation and performance of RPCs in the ARGO-YBJ experiment

The ARGO-YBJ array for EAS detection at high altitude (4300 m a.s.l.) is the largest RPC-based detector in operation at present (active area of 6700 m 2 out of a total instrumented surface of about 10 4 m 2 ). The constant monitoring of the main operational and environmental parameters is essential for both keeping the detector status under control and understanding the detector behaviour more deeply. Exploiting the information provided by the ARGO-YBJ Detector Control System, the present status of the detector is described and some correlations between the environmental and the operational parameters of the ARGO-YBJ RPCs are shown. This study was performed using the monitored data from the complete ARGO-YBJ array which has been in operation since October 2007. Preliminary results on the observations of the Moon shadow and of γ -ray point sources are also presented.

Software timing calibration of the ARGO-YBJ detector

The ARGO-YBJ experiment is mainly devoted to search for astronomical gamma sources. The arrival direction of air showers is reconstructed thanks to the times measured by the pixels of the detector. Therefore, the timing calibration of the detector pixels is crucial in order to get the best angular resolution and pointing accuracy. Because of the large number of pixels a hardware timing calibration is practically impossible. Therefore an off-line software calibration has been adopted. Here, the details of the procedure and the results are presented.

Scaler mode technique for the ARGO-YBJ detector

The ARGO-YBJ experiment has been designed to study the extensive air showers with an energy threshold lower than that of the existing arrays by exploiting the high altitude location (4300 m a.s.l. in Tibet, PR China) and the full ground plane coverage. The lower energy limit of the detector ( E ∼ 1 GeV) is reached by the scaler mode technique, i.e. recording the counting rate at fixed time intervals. At these energies, transient signals due to local (e.g. Forbush decreases) and cosmological (e.g. Gamma ray bursts) phenomena are expected as a significant variation of the counting rate compared to the background. In this paper, the performance of the ARGO-YBJ detector operating in scaler mode is described and discussed.

ARGO-YBJ experiment in Tibet

The ARGO-YBJ detector is an extensive air shower array consisting of a carpet of Resistive Plate Chambers (RPCs). The main scientific goal of this Chinese-Italian experiment is the observation of very high energy (VHE) gamma-rays from astrophysical sources. High altitude and full coverage ensure a low energy threshold (few hundreds of GeV for gamma-initiated showers). High duty-cycle and large field of view allow a continuous sky survey. The data collected with the central carpet during the detector debugging have been analysed. First results about detector performance, gamma astronomy and cosmic ray physics are presented.

Search for gamma ray bursts with the ARGO-YBJ detector in scaler mode

The ARGO-YBJ experiment has been designed to decrease the energy threshold of typical Extensive Air Shower arrays by exploiting the high altitude and the full coverage, consisting of a 6700m2 carpet of Resistive Plate Chambers located at Yangbajing (Tibet, PR China, 4300m a.s.l.). The lower energy limit of the detector (∼1GeV) is reached with the “Scaler Mode”, recording the counting rate at fixed time intervals. Here we present results concerning the search for emission from Gamma Ray Bursts (GRBs) in coincidence with satellite detections.

Preliminary results of the Moon shadow using ARGO-YBJ detector

ARGO-YBJ is a “full coverage” air shower detector consisting of Resistive Plate Chambers(RPCs) at the Yangbajing High Altitude Cosmic Ray Laboratory (Tibet, China) at 4300 m a.s.l. (lat=30.11° N, long=90.53° E). Using the data collected with a carpet of RPCs (1900 m 2 , about 1/3 of the whole ARGO-YBJ detector), the cosmic ray shadowing effect due to the Moon was studied. The 50% angular resolution is found to be ∼1.2° with the Chess-board method and the Moon shadow with a significance of 4.9 σ is found displaced by 0.7° westward and 0.5° northward with respect to the expected position by the equi-zenith angle Method.

ARGO-YBJ experiment and TeV gamma astronomy

The ARGO-YBJ detector is an extensive air shower array consisting of a carpet of Resistive Plate Chambers (RPCs). Very high energy (VHE) gamma ray astronomy is the main scientific goal of this Chinese-Italian experiment. High altitude and full coverage ensure a low energy threshold (few hundreds of GeV for primary photons), high duty-cycle and large field of view allow a continuous sky survey in the declination range from −10° to +70°. Also many features of the high energy cosmic rays are studied by ARGO-YBJ exploiting the unprecented shower reconstruction.

The trigger supervisor of the ARGO-YBJ detector

ARGO-YBJ is a full coverage air shower detector under construction at the Yangbajing Laboratory (4300 m a.s.l., Tibet, People Republic of China). Its main fields of research are gamma ray astronomy and cosmic ray studies. The detector covers /spl sim/5800 m/sup 2/ with single layer Resistive Plate Counters (RPCs), surrounded by a partially instrumented guard ring. This paper describes in detail the ARGO-YBJ Trigger Supervisor, which provides the interface between the Data Acquisition and the Trigger System. It is a simple and robust control instrument that monitors continuously the dead time at different levels in the Data Acquisition architecture. We present in this paper the results of the first pilot runs at the Yangbajing laboratory.

ARGO-YBJ: a unique device for the EAS study

The ARGO-YBJ detector, installed at the Yangbajing Cosmic Ray Laboratory (Tibet, China), at 4300m a.s.l., is a full coverage layer of Resistive Plate Counters (RPCs) covering an area of about 5800 m2. The high space-time granularity, the full-coverage technique and the high altitude location will make this detector a unique device for deeply investigating a large variety of astrophysical phenomena. In this work, the capabilities of ARGO-YBJ in imaging and reconstructing in detail some of the main atmospheric shower features will be presented.

Searching for emission from gamma-ray bursts with the ARGO-YBJ detector

The ARGO-YBJ experiment has been designed to decrease the energy threshold of typical Extensive Air Shower arrays by exploiting the high altitude location (Tibet, People's Republic of China, 4300 m a.s.l.) and the full coverage. The lower energy limit of the detector (a few GeV) is reached with the single particle technique, recording the counting rate at fixed time intervals. We present first results concerning the search for emission from Gamma-Ray Bursts in coincidence with satellite detections

First results on the angular resolution of the ARGO-YBJ detector

We present the first results on the angular resolution of the ARGO-YBJ detector in data taking at the Yangbajing Laboratory (Tibet, People's Republic of China, 4300 m a.s.l.).

SELECTION OF THE PRIMARY COSMIC RAY LIGHT COMPONENT WITH ARGO-YBJ

The ARGO-YBJ experiment, currently under construction at the YangBaJing High Altitude Cosmic Ray Laboratory (Tibet, P.R. China, 4300 m a.s.l.), may be upgraded with a large muon detector (~ 2500 m2) both to extend the sensitivity to γ-ray sources to energies ≥ 20 TeV and to perform a cosmic ray primary composition study. In this paper we discuss the capability of the upgraded ARGO-YBJ detector to select the primary cosmic ray light component in the knee energy region.

The trigger system of the ARGO-YBJ experiment

The ARGO-YBJ experiment has been designed to detect air shower events over a large size scale and with an energy threshold of a few hundreds GeV. The building blocks of the ARGO-YBJ detector are single-gap Resistive Plate Counters (RPCs). The trigger logic selects the events on the basis of their hit multiplicity. Inclusive triggers as well as dedicated triggers for specific physics channels or calibration purposes have been developed. This paper describes the architecture and the main features of the trigger system.

Multiscale image analysis applied to γ/h discrimination for VHE gamma-ray astronomy with ARGO-YBJ

Intrinsic differences in the processes involved in the electromagnetic and hadronic shower development in the atmosphere have been evidenced by means of a careful analysis of the event image given by the ARGO-YBJ detector. The images have been analyzed at different length scales and their multifractal nature has been studied. The use of the multiscale approach together with a properly designed and trained Artificial Neural Network, allowed us to obtain a good discrimination power. If confirmed by further studies on different event categories, this result would allow to nearly double the detector sensitivity to gamma-ray sources.