Observation of CR Anisotropy with ARGO-YBJ

The measurement of the anisotropies of cosmic ray arrival direction provides important informations on the propagation mechanisms and on the identification of their sources. In this paper we report the observation of anisotropy regions at different angular scales. In particular, the observation of a possible anisotropy on scales between $\sim$ 10 $^{\circ}$ and $\sim$ 30 $^{\circ}$ suggests the presence of unknown features of the magnetic fields the charged cosmic rays propagate through, as well as potential contributions of nearby sources to the total flux of cosmic rays. Evidence of new weaker few-degree excesses throughout the sky region $195^{\circ}\leq$ R.A. $\leq 315^{\circ}$ is reported for the first time.Comment: Talk given at 12th TAUP Conference 2011, 5-9 September 2011, Munich, German

Observation of the cosmic ray moon shadowing effect with the ARGO-YBJ experiment

Cosmic rays are hampered by the Moon and a deficit in its direction is expected (the so-called Moon shadow). The Moon shadow is an important tool to determine the performance of an air shower array. Indeed, the westward displacement of the shadow center, due to the bending effect of the geomagnetic field on the propagation of cosmic rays, allows the setting of the absolute rigidity scale of the primary particles inducing the showers recorded by the detector. In addition, the shape of the shadow permits to determine the detector point spread function, while the position of the deficit at high energies allows the evaluation of its absolute pointing accuracy. In this paper we present the observation of the cosmic ray Moon shadowing effect carried out by the ARGO-YBJ experiment in the multi-TeV energy region with high statistical significance (55 standard deviations). By means of an accurate Monte Carlo simulation of the cosmic rays propagation in the Earth-Moon system, we have studied separately the effect of the geomagnetic field and of the detector point spread function on the observed shadow. The angular resolution as a function of the particle multiplicity and the pointing accuracy have been obtained. The primary energy of detected showers has been estimated by measuring the westward displacement as a function of the particle multiplicity, thus calibrating the relation between shower size and cosmic ray energy. The stability of the detector on a monthly basis has been checked by monitoring the position and the deficit of the Moon shadow. Finally, we have studied with high statistical accuracy the shadowing effect in the ''day/night’’ time looking for possible effect induced by the solar wind

Highlights from the ARGO-YBJ experiment

The ARGO-YBJ experiment at YangBaJing in Tibet (4300 m a.s.l.) has been taking data with its full layout since October 2007. Here we present a few significant results obtained in gamma-ray astronomy and cosmic-ray physics. Emphasis is placed on the analysis of gamma-ray emission from point-like sources (Crab Nebula, MRK 421), on the preliminary limit on the antiproton/proton flux ratio, on the large-scale cosmic-ray anisotropy and on the proton–air cross-section. The performance of the detector is also discussed, and the perspectives of the experiment are outlined

Measurement of the antiproton/proton ratio in the few-TeV energy range with ARGO-YBJ

Cosmic ray antiprotons provide an important probe for the study of cosmic ray propagation in the interstellar space and to investigate the existence of Galactic dark matter. The ARGO-YBJ experiment is observing the Moon shadow with high statistical significance at an energy threshold of a few hundred GeV. Using all the data collected until November 2009, we set two upper limits on the antip/p flux ratio: 5% at an energy of 1.4 TeV and 6% at 5 TeV with a confidence level of 90%. In the few-TeV range the ARGO-YBJ results are the lowest available, useful to constrain models for antiproton production in antimatter domains.Comment: Talk given at the CRIS 2010 Conference, September 2010, Catania - Italy, 6 page

THE STATUS OF THE ARGO EXPERIMENT AT YBJ

The ARGO-YBJ experiment, located at Yangbajing, Tibet, China, performed by a wide Sino-Italian collaboration, is designed to study cosmic rays, sub-TeV gamma ray sources and GeV Gamma Ray Burst (GRB) emission in the northern hemisphere, by means of detecting small size EAS (Extensive Air Shower) using a full coverage RPC (Resistive Plate Chamber) carpet. The central carpet of the detector is installed and put into operation to date, with 1900m2 of the carpet already operating since December 2004. With a trigger multiplicity of ≥60 hits, corresponding to a primary mode energy of 2 TeV, the angular resolution of EAS measurements is < 1° for showers with more than 500 recorded hits. We report the preliminary results of data taking performed during 2005: the all-sky survey for gamma ray sources and the search for GRBs, as well as the cosmic ray spectrum up to about 100TeV. The Forbush decrease of the cosmic ray flux during January, 2005 is observed using the ARGO data

Highlights from the ARGO-YBJ experiment

""The ARGO-YBJ experiment at YangBaJing in Tibet (4300m a.s.l.) has been taking data with its full layout since October 2007. Here we present a few significant results obtained in gamma-ray astronomy and cosmic-ray physics. Emphasis is placed on the analysis of gamma-ray emission from point-like sources (Crab Nebula, MRK 421), on the preliminary limit on the antiproton\\\/proton flux ratio, on the large-scale cosmic-ray anisotropy and on the proton-air cross-section. The performance of the detector is also discussed, and the perspectives of the experiment are outlined."

Measurement of the antiproton/proton ratio at TeV energies with the ARGO-YBJ detector

""Cosmic ray antiprotons provide an important probe for the study of cosmic-ray propagation in the interstellar space and to investigate the existence of Galactic dark matter. Cosmic rays are hampered by the Moon, therefore a deficit of cosmic rays in its direction is expected (the so-called Moon shadow). The EarthMoon system acts as a magnetic spectrometer. In fact, due to the geomagnetic field the center of the Moon shifts westward by an amount depending on the primary cosmic ray energy. Paths of primary antiprotons are therefore deflected in an opposite sense in their way to the Earth. This effect allows, in principle, the search of antiparticles in the opposite direction of the observed Moon shadow. The ARGO-YBJ experiment, in stable data taking since November 2007 with an energy threshold of a few 100s of GeV, is observing the Moon shadow with high statistical significance. Using about 1 year data, an upper limit of the p\\\/p flux ratio in the few-TeV energy region is set to a few percent with a confidence level of 90%."

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 calibratin of the detector pixels is crucial in ordere to get the best angular resolution abd pointing accuracy. Because of the large number of pixels a hardware timing calibration is practically impossible. Therefore, an off-line software calibration. Here, the details of the procedure and the results are presented

The ARGO-YBJ contribution to the cosmic ray physics

""The ARGO-YBJ experiment is in stable data taking since November 2007 at the YangBaJing Cosmic Ray. Laboratory (Tibet, P.R.China, 4300 m a.s.l.). It exploits a full coverage and high altitude approach to the. small air showers detection. The detector is made of a single layer of RPCs operated in streamer mode, fully. instrumenting a central carpet of about 5700 m2, then a guard ring extends the partially instrumented area to. about 11,000 m2. The large field of view (∼ 2 sr) and the high duty cycle (≥ 85%) allow a continuous monitoring. of the sky in the declination band from -10. ◦. to 70. ◦. ; the detector operates with an energy threshold of a few. hundred GeV. Recent achieved results will be reported"