J. Y. Li

High altitude test of RPCs for the Argo YBJ experiment

Abstract A 50 m 2 RPC carpet was operated at the YanBaJin Cosmic Ray Laboratory (Tibet) located 4300 m a.s.l. The performance of RPCs in detecting Extensive Air Showers was studied. Efficiency and time-resolution measurements at the pressure and temperature conditions typical of high mountain laboratories, are reported.A 50 m**2 RPC carpet was operated at the YangBaJing Cosmic Ray Laboratory (Tibet) located 4300 m a.s.l. The performance of RPCs in detecting Extensive Air Showers was studied. Efficiency and time resolution measurements at the pressure and temperature conditions typical of high mountain laboratories, are reported.

Observation of multi-TeV gamma rays from the Crab Nebula using the Tibet air shower array

The Tibet experiment, operating at Yangbajing (4300 m above sea level), is the lowest energy air shower array, and the new high-density array constructed in 1996 is sensitive to gamma-ray air showers at energies as low as 3 TeV. With this new array, the Crab Nebula was observed in multi-TeV gamma-rays and a signal was detected at the 5.5 sigma level. We also obtained the energy spectrum of gamma-rays in the energy region above 3 TeV which partially overlaps those observed with imaging atmospheric Cerenkov telescopes. The Crab spectrum observed in this energy region can be represented by the power-law fit dJ&parl0;E&parr0;&solm0;dE=&parl0;4.61+/-0.90&parr0;x10-12&parl0;E&solm0;3 TeV&parr0;-2.62+/-0.17 cm-2 s-1 TeV-1. This is the first observation of gamma-ray signals from point sources with a conventional air shower array using scintillation detectors.

On temporal variations of the multi-tev cosmic ray anisotropy using the tibet iii air shower array

We analyze the large-scale two-dimensional sidereal anisotropy of multi-TeV cosmic rays (CRs) by the Tibet Air Shower Array, with the data taken from 1999 November to 2008 December. To explore temporal variations of the anisotropy, the data set is divided into nine intervals, each with a time span of about one year. The sidereal anisotropy of magnitude, about 0.1%, appears fairly stable from year to year over the entire observation period of nine years. This indicates that the anisotropy of TeV Galactic CRs remains insensitive to solar activities since the observation period covers more than half of the 23rd solar cycle.

Results from the ARGO-YBJ test experiment

Abstract A resistive plate counters (RPCs) carpet of ∼50 m 2 has been put in operation in the Yangbajing Laboratory (Tibet, P.R. China) at 4300 m a.s.l., in order to study the RPCs performance at high altitude and the detector capability of imaging the EAS disc. This test has been performed in view of an enlarged use of RPCs for the ARGO-YBJ experiment. This experiment will be devoted to a wide range of fundamental issues in cosmic rays and astroparticle physics, including in particular γ-ray astronomy and γ-ray bursts physics at energies ⩾100 GeV. In this paper we present and discuss the procedures adopted to calibrate the detector and reconstruct the shower direction. Results concerning many shower features as the angular distribution, the density spectrum, the time profile of the shower front, are found well consistent with the expectation.

Observation of TeV gamma rays from the fermi bright galactic sources with the tibet air shower array

Using the Tibet-III air shower array, we search for TeV γ-rays from 27 potential Galactic sources in the early list of bright sources obtained by the Fermi Large Area Telescope at energies above 100 MeV. Among them, we observe seven sources instead of the expected 0.61 sources at a significance of 2σ or more excess. The chance probability from Poisson statistics would be estimated to be 3.8 × 10–6. If the excess distribution observed by the Tibet-III array has a density gradient toward the Galactic plane, the expected number of sources may be enhanced in chance association. Then, the chance probability rises slightly, to 1.2 × 10–5, based on a simple Monte Carlo simulation. These low chance probabilities clearly show that the Fermi bright Galactic sources have statistically significant correlations with TeV γ-ray excesses. We also find that all seven sources are associated with pulsars, and six of them are coincident with sources detected by the Milagro experiment at a significance of 3σ or more at the representative energy of 35 TeV. The significance maps observed by the Tibet-III air shower array around the Fermi sources, which are coincident with the Milagro ≥3σ sources, are consistent with the Milagro observations. This is the first result of the northern sky survey of the Fermi bright Galactic sources in the TeV region.

Implication of the sidereal anisotropy of ∼5 TeV cosmic ray intensity observed with the Tibet III air shower array

We show that the large‐scale anisotropy of ∼5 TeV galactic cosmic ray (GCR) intensity observed by Tibet Air Shower experiment can be reproduced by the superposition of a bi‐directional and uni‐directional flows (UDF and BDF) of GCRs. The heliosphere is located inside the local interstellar cloud (LIC) very close to the inner edge of the LIC. If the GCR population is lower inside the LIC than outside, the BDF flow is expected from the parallel diffusion of GCRs into LIC along the local interstellar magnetic field (LISMF) connecting the heliosphere with the region outside the LIC, where the GCR population is higher. A type of the UDF, on the other hand, is expected from the B×∇n drift flux driven by a gradient of GCR density (n) in the LISMF (B). The LISMF orientation deduced from the best‐fit direction of the BDF is almost parallel to the galactic plane and more consistent with the suggestion of Frisch (1996) than that of Lallement et al. (2005). We note that the model, if holds, yields the LISMF polarity ...

The use of RPC in the ARGO-YBJ project

We present the ARGO-YBJ experiment, a full coverage detector placed at high altitude (∼4300 m a.s.l.) that exploits the RPC technique. Results of a test experiment performed at Yanbajing site, with a full coverage RPC carpet of 50 m2 are also presented.

Performance of the RPCs for the ARGO detector operated at the YangBaJing laboratory (4300 m a.s.l.)

Bakelite RPCs, assembled according to the ARGO design, have been operated in the high altitude Laboratory of YBJ using dedicated electronics to pick-up the streamer signal. Here we report on the results concerning absorbed current, single counting rate, efficiency and time resolution. Environmental data concerning the operating temperature inside the ARGO experimental hall are also reported.

Tibet air shower array: results and future plan

The Tibet air shower array, which has an effective area of 36,900 m2, has been in operation at Yangbajing in Tibet, China at an altitude of 4,300 m above sea level. In this paper, we will briefly introduce the recent gamma-ray observation with the present Tibet air shower array and our future plan which is called the Tibet muon detector (MD) project.

Results from the analysis of data collected with a 50m(2) RPC carpet at YangBaJing

An RPC carpet covering similar to 10(4) m(2) (ARGO-YBJ experiment) will be installed in the YangBaJing Laboratory (Tibet, Peoples Republic of China) at an altitude of 4300 m a.s.l. A test-module of similar to 50 m(2) has been put in operation in this laboratory and about 10(6) air shower events have been collected. The RPC performance at high altitude and the carpet capability of reconstructing the shower features are presented