Z. T. He

Northern Sky Galactic Cosmic Ray Anisotropy between 10 and 1000 TeV with the Tibet Air Shower Array

We report on the analysis of the 10−1000 TeV large-scale sidereal anisotropy of Galactic cosmic rays (GCRs) with the data collected by the Tibet Air Shower Array from 1995 October to 2010 February. In this analysis, we improve the energy estimate and extend the decl. range down to −30◦. We find that the anisotropy maps above 100 TeV are distinct from that at a multi-TeV band. The so-called tail-in and loss-cone features identified at low energies get less significant, and a new component appears at ∼ 100 TeV. The spatial distribution of the GCR intensity with an excess (7.2σ pre-trial, 5.2σ post-trial) and a deficit (−5.8σ pre-trial) are observed in the 300 TeV anisotropy map, in close agreement with IceCube’s results at 400 TeV. Combining the Tibet results in the northern sky with IceCube’s results in the southern sky, we establish a full-sky picture of the anisotropy in hundreds of TeV band. We further find that the amplitude of the first order anisotropy increases sharply above ∼ 100 TeV, indicating a new component of the anisotropy. All these results may shed new light on understanding the origin and propagation of GCRs.

Time dependence of loss-cone amplitude measured with the tibet air-shower array

The galactic cosmic-ray anisotropy at TeV energies has a large-scale deficit region distributed around 150 to 240 degrees in right ascension, which is called “Loss-Cone”. The Milagro experiment in the U.S. detected a significant increase in the Loss-Cone amplitude at 6 TeV from July 2000 to July 2007, and argued that it could be due to variations in the heliosphere in relation to solar activities. In this presentation, we report on the time dependence of the Loss-Cone amplitude from November 1999 through December 2008 measured with the Tibet air-shower array. No time dependence was found in the Loss-Cone amplitude at energies of 4.4, 6.2, and 11 TeV. If the increase in the Loss-Cone amplitude Milagro detected were genuine, the same tendency would be seen at sub-TeV energies where the anisotropy is far more sensitive to solar activities. Matsushiro underground muon observation at 0.6 TeV during the corresponding period, however, reported no significant increase of the Loss-Cone amplitude.

Calibration of the Yangbajing air-shower core detector (YAC) using the beam of BEPC

Aiming at the observation of cosmic-ray chemical composition at the knee energy region, a new type airshower-core detector (YAC, Yangbajing Air shower Core array) has been developed and set up at Yangbajing, 4300 m a.s.l. in Tibet, China since August, 1st, 2011. YAC will work together with the Tibet-III array and a large muon detector as a hybrid experiment. Each YAC detector unit consists of lead plates of 3.5 cm thick and a scintillation counter which detects the burst size induced by high energy electromagnetic component in the air-shower cores. The burst size is demanded to be measured from 1 MIP (Minimum Ionization Particles) to 10 MIPs. The linearity and the saturation of the plastic scintillator and PMT used in the YAC detector have been studied with the accelerator beam of the BEPCII (Beijing Electron Positron Collider, IHEP, China). The accelerator-beam experiment shows a good linearity between the incident particle flux and YAC-ADC output below 5×10 MIPs and the saturation effect of the plastic scintillator satisfies YAC detector’s requirement.

Modeling of the galactic cosmic-ray anisotropy at TeV energies

A possible origin of the large-scale anisotropy of TeV galactic cosmic rays is discussed. It can be well modeled by a superposition of the Global Anisotropy and the Midscale Anisotropy. The Global Anisotropy would be generated by galactic cosmic rays interacting with the magnetic field in the local interstellar space of a few parsec scale surrounding the heliosphere. On the other hand, the Midscale Anisotropy would be caused by the modulation of galactic cosmic rays in the heliotail. The Midscale Anisotropy can be expressed as two intensity enhancements placed along the Hydrogen Deflection Plane, each symmetrically centered away from the heliotail direction. It is found that the separation angle between the heliotail direction and each of the two intensity enhancements monotonously decreases as energy increases from 4 TeV to 30 TeV.

Measurement of high energy cosmic rays by the new Tibet hybrid experiment

We have started a new hybrid air shower experiment at Yangbajing (4300 m a.s.l.) in Tibet in February 2014. This new hybrid experiment consists of the YAC-II comprised of 124 core detectors placed in the form of a square grid of 1.9 m spacing covering about 500 m2, the Tibet-III air shower array with the total area of about 50,000 m2 and the underground MD array consisting of 80 cells, with the total area of about 4,200 m2. This hybrid-array system is used to observe air showers of high energy celestial gamma-ray origin and those of nuclear-component origin. In this paper, a short review of the experiment will be followed by an overview on the current results on energy spectrum and chemical composition of CRs and test of hadronic interaction models.

Interplanetary Coronal Mass Ejection and the Sun's Shadow Observed by the Tibet Air Shower Array

We continuously observed the Sun’s shadow in 3 TeV cosmic-ray intensity with the Tibet-III air shower array since 2000. We find a clear solar-cycle variation of the deficit intensity in the Sun’s shadow during the periods between 2000 and 2009. The MC simulation of the Sun’s shadow based on the coronal magnetic field model does not well reproduce the observed deficit intensity around the solar maximum. However, when we exclude the transit periods during ICMEs towards to the Earth, the MC simulation shows better reproducibility. In the present paper, we report on the MC simulation and the analysis method of the Sun’s shadow observed by the Tibet-III array.

The Tibet AS+MD Project; status report 2017

We built a large (approximately 4,000 m**2) water　Cherenkov- type muon detector array under the existing Tibet air shower array at 4,300 m above sea level, to observe 10-1000 TeV gamma rays from cosmic-ray accelerators in our Galaxy with wide field of view at very low background level. A gamma-ray induced air shower has significantly less muons compared with a cosmic-ray induced one. Therefore, we can effectively discriminate between primary gamma rays and cosmic-ray background events by means of counting number of muons in an air shower event by the muon detector array. We make a status report on the experiment.

Solar magnetic field strength and the “Sun's Shadow”

The angular displacement of the center of the observed Suns shadow from the center of the optical solar disc tells us the information of average solar magnetic field strength in the space between the Sun and the Earth. We analyze the displacement of the Suns shadow observed in 5 ~ 240 TeV cosmic-ray intensity with the Tibet-III air shower array during 10 years between 2000 and 2009, and compare with the MC simulations based on the coronal magnetic field model and Parkers spiral interplanetary magnetic field model. We find that the observed North-South displacement is significantly larger than the prediction of simulations. This result uniquely suggests the underestimation of the average field strength between the Sun and the Earth in our model. In this work, we will report the actual solar magnetic field strength evaluated from the observed Suns shadow.

Progress Report on the TIBET AS+MD Project

M. Amenomori1, X. J. Bi2, D. Chen3, T. L. Chen4, W. Y. Chen2, S. W. Cui5, Danzengluobu4, L. K. Ding2, C. F. Feng6, Zhaoyang Feng2, Z. Y. Feng7, Q. B. Gou2, Y. Q. Guo2, H. H. He2, Z. T. He5, K. Hibino8, N. Hotta9, Haibing Hu4, H. B. Hu2, J. Huang2, H. Y. Jia7, L. Jiang2, F. Kajino10, K. Kasahara11, Y. Katayose12, C. Kato13, K. Kawata14, M. Kozai13, Labaciren4, G. M. Le2, A. F. Li15,6,2, H. J. Li4, W. J. Li2,7, C. Liu2, J. S. Liu2, M. Y. Liu4, H. Lu2, X. R. Meng4, K. Mizutani11,16, K. Munakata13, H. Nanjo1, M. Nishizawa17, M. Ohnishi14, I. Ohta18, S. Ozawa11, X. L. Qian6,2, X. B. Qu19,2, T. Saito20, T. Y. Saito21, M. Sakata10, T. K. Sako14, J. Shao2,6, M. Shibata12, A. Shiomi22, T. Shirai8, H. Sugimoto23, M. Takita14, Y. H. Tan2, N. Tateyama8, S. Torii11, H. Tsuchiya24, S. Udo8, H. Wang2, H. R. Wu2, L. Xue6, Y. Yamamoto10, Z. Yang2, S. Yasue25, A. F. Yuan4, T. Yuda14, L. M. Zhai2, H. M. Zhang2, J. L. Zhang2, X. Y. Zhang6, Y. Zhang2, Yi Zhang2, Ying Zhang2, Zhaxisangzhu4, X. X. Zhou7 (The Tibet ASγ Collaboration)

A Monte Carlo study to measure the energy spectra of the primary cosmic-ray components at the knee using a new Tibet AS core detector array

A new hybrid experiment has been started by AS{\gamma} experiment at Tibet, China, since August 2011, which consists of a low threshold burst-detector-grid (YAC-II, Yangbajing Air shower Core array), the Tibet air-shower array (Tibet-III) and a large underground water Cherenkov muon detector (MD). In this paper, the capability of the measurement of the chemical components (proton, helium and iron) with use of the (Tibet-III+YAC-II) is investigated by means of an extensive Monte Carlo simulation in which the secondary particles are propagated through the (Tibet-III+YAC-II) array and an artificial neural network (ANN) method is applied for the primary mass separation. Our simulation shows that the new installation is powerful to study the chemical compositions, in particular, to obtain the primary energy spectrum of the major component at the knee.