No Arabic abstract
In any EAS array, the rejection of events with shower cores outside the detector boundaries is of great importance. A large difference between the true and the reconstructed shower core positions may lead to a systematic miscalculation of some shower characteristics. Moreover, an accurate determination of the shower core position for selected internal events is important to reconstruct the primary direction using conical fits to the shower front, improving the detector angular resolution, or to performe an efficient gamma/hadron discrimination. In this paper we present a procedure able to identify and reject showers with cores outside the ARGO-YBJ carpet boundaries. A comparison of the results for gamma and proton induced showers is reported.
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.
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, P.R. China) and the full ground plane coverage. The lower energy limit of the detector (E $sim$ 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.
The ARGO-YBJ experiment is a full coverage EAS-array installed at the YangBaJing Cosmic Ray Laboratory (4300 m a.s.l., Tibet, P.R. China). We present the results on the angular resolution measured with different methods with the full central carpet. The comparison of experimental results with MC simulations is discussed.
We report on a measurement of thermal neutrons, generated by the hadronic component of extensive air showers (EAS), by means of a small array of EN-detectors developed for the PRISMA project (PRImary Spectrum Measurement Array), novel devices based on a compound alloy of ZnS(Ag) and $^{6}$LiF. This array has been operated within the ARGO-YBJ experiment at the high altitude Cosmic Ray Observatory in Yangbajing (Tibet, 4300 m a.s.l.). Due to the tight correlation between the air shower hadrons and thermal neutrons, this technique can be envisaged as a simple way to estimate the number of high energy hadrons in EAS. Coincident events generated by primary cosmic rays of energies greater than 100 TeV have been selected and analyzed. The EN-detectors have been used to record simultaneously thermal neutrons and the air shower electromagnetic component. The density distributions of both components and the total number of thermal neutrons have been measured. The correlation of these data with the measurements carried out by ARGO-YBJ confirms the excellent performance of the EN-detector.
The ARGO-YBJ experiment has been in stable data taking from November 2007 till February 2013 at the YangBaJing Cosmic Ray Observatory (4300 m a.s.l.). The detector consists of a single layer of Resistive Plate Chambers (RPCs) ( about 6700 m^2}) operated in streamer mode. The signal pick-up is obtained by means of strips facing one side of the gas volume. The digital readout of the signals, while allows a high space-time resolution in the shower front reconstruction, limits the measurable energy to a few hundred TeV. In order to fully investigate the 1-10 PeV region, an analog readout has been implemented by instrumenting each RPC with two large size electrodes facing the other side of the gas volume. Since December 2009 the RPC charge readout has been in operation on the entire central carpet (about 5800 m^2). In this configuration the detector is able to measure the particle density at the core position where it ranges from tens to many thousands of particles per m^2. Thus ARGO-YBJ provides a highly detailed image of the charge component at the core of air showers. In this paper we describe the analog readout of RPCs in ARGO-YBJ and discuss both the performance of the system and the physical impact on the EAS measurements.