11 research outputs found
The energy spectrum of all-particle cosmic rays around the knee region observed with the Tibet-III air-shower array
We have already reported the first result on the all-particle spectrum around
the knee region based on data from 2000 November to 2001 October observed by
the Tibet-III air-shower array. In this paper, we present an updated result
using data set collected in the period from 2000 November through 2004 October
in a wide range over 3 decades between eV and eV, in which
the position of the knee is clearly seen at around 4 PeV. The spectral index is
-2.68 0.02(stat.) below 1PeV, while it is -3.12 0.01(stat.) above 4
PeV in the case of QGSJET+HD model, and various systematic errors are under
study now.Comment: 12 pages, 7 figures, accepted by Advances in space researc
Moon Shadow by Cosmic Rays under the Influence of Geomagnetic Field and Search for Antiprotons at Multi-TeV Energies
We have observed the shadowing of galactic cosmic ray flux in the direction
of the moon, the so-called moon shadow, using the Tibet-III air shower array
operating at Yangbajing (4300 m a.s.l.) in Tibet since 1999. Almost all cosmic
rays are positively charged; for that reason, they are bent by the geomagnetic
field, thereby shifting the moon shadow westward. The cosmic rays will also
produce an additional shadow in the eastward direction of the moon if cosmic
rays contain negatively charged particles, such as antiprotons, with some
fraction. We selected 1.5 x10^{10} air shower events with energy beyond about 3
TeV from the dataset observed by the Tibet-III air shower array and detected
the moon shadow at level. The center of the moon was detected
in the direction away from the apparent center of the moon by 0.23 to
the west. Based on these data and a full Monte Carlo simulation, we searched
for the existence of the shadow produced by antiprotons at the multi-TeV energy
region. No evidence of the existence of antiprotons was found in this energy
region. We obtained the 90% confidence level upper limit of the flux ratio of
antiprotons to protons as 7% at multi-TeV energies.Comment: 13pages,4figures; Accepted for publication in Astroparticle Physic
Are protons still dominant at the knee of the cosmic-ray energy spectrum?
A hybrid experiment consisting of emulsion chambers, burst detectors and the
Tibet II air-shower array was carried out at Yangbajing (4,300 m a.s.l., 606
g/cm) in Tibet to obtain the energy spectra of primary protons and heliums.
From three-year operation, these energy spectra are deduced between
and eV by triggering the air showers associated with a high energy
core and using a neural network method in the primary mass separation. The
proton spectrum can be expressed by a single power-law function with a
differential index of and based on the
QGSJET+HD and SIBYLL+HD models, respectively, which are steeper than that
extrapolated from the direct observations of in the energy
range below eV. The absolute fluxes of protons and heliums are
derived within 30% systematic errors depending on the hadronic interaction
models used in Monte Carlo simulation. The result of our experiment suggests
that the main component responsible for the change of the power index of the
all-particle spectrum around eV, so-called ``knee'', is
composed of nuclei heavier than helium. This is the first measurement of the
differential energy spectra of primary protons and heliums by selecting them
event by event at the knee energy region.Comment: This paper has been accepted for publication Physics Letters B on
October 19th, 2005. This paper has been accepted for publication Physics
Letters B on October 19th, 200
Sensitivity of ARGO-YBJ to different composition models in the energy range 10 ÷ 500 TeV
The ARGO-YBJ experiment is currently under construction at the Yangbajing Cosmic Ray Laboratory (4300 m a.s.l.).The detector consists of a central carpet, 74 × 78 m2, made of a single layer of Resistive Plate Counters (RPCs), and surrounded by a partially instrumented guard ring for a total instrumented area of about 6700 m2. The digital read-out, performed by means of pick-up electrodes 6.7 × 62 cm2 (strip), allows to measure the charged particle number of small size air showers. The technique of counting the number of fired strips on the ARGO carpet corresponds to operate in the 10÷500 TeV energy region where both direct and indirect measurements on the primary cosmic radiation have been performed. Many composition models have been proposed by different experiments. In this work we discuss the ability of the ARGO detector to discriminate among some models
Results of the ARGO-YBJ test experiment
A resistive plate counters (RPCs) carpet of ∼50 m2 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
Results from the Analysis of data collected with a 50m2 RPC carpet at Yangbajing
An RPC carpet covering View the MathML source (ARGO-YBJ experiment) will be installed in the YangBaJing Laboratory (Tibet, People's Republic of China) at an altitude of 4300 m a.s.l. A test-module of View the MathML source has been put in operation in this laboratory and about 106 air shower events have been collected. The RPC performance at high altitude and the carpet capability of reconstructing the shower features are 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