S. Ozawa

Quadrupole deformation of 12Be studied by proton inelastic scattering

Abstract Inelastic proton scattering exciting the 2 + 1 states in the neutron-rich beryllium isotopes 10,12 Be has been studied in inverse kinematics. From a coupled-channel analysis, the deformation lengths for the 2 + 1 states in 10 Be and 12 Be were determined to be 1.80±0.25 fm and 2.00±0.23 fm respectively, indicating that a tendency towards strong quadrupole deformation is preserved for these nuclei and that the singly-closed shell structure does not prevail in 12 Be. A quantitative analysis based on shell model calculations supports this picture.

Performance of the Tibet II/HD air shower array

Tibet II Air Shower Array consisting of scintillation counters with lattice of 15 m spacing has been operated with very high trigger rate of about 200 Hz. The threshold enegy of this array is estimated to be about 8 TeV for proton induced showers. Tibet High Density (HD) Array with 7.5 m spacing has been operated with the trigger rate of 115 Hz. The Mode energy of this array is estimated to be about 3 TeV for proton showers. Angular resolution of the arrays are estimated to be 0.9 degree above 10 TeV for Tibet II array, and 0.85 degree above TeV for HD array, resepectively. The angular resolution of these arrays and other array performances are examined by observing the Moon shadow resulting from the cosmic ray deficit in the direction of the Moon. Using the deflection of the Moon shadow to the east-west direction, the error of the array can be estimated by observing the displacement of the shadow in the north-south direction, because it is free from the effect of geomagnetic field, especially at Yangbaji...

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.

Search for gamma rays above 100 TeV from the Crab Nebula using the Tibet air shower array and the 100 m

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. Le15, A. F. Li16,6,2, H. J. Li4, W. J. Li2,7, C. Liu2, J. S. Liu2, M. Y. Liu4, H. Lu2, X. R. Meng4, T. Miyazaki13, K. Mizutani11,17, K. Munakata13, T. Nakajima13, Y. Nakamura13, H. Nanjo1, M. Nishizawa18, T. Niwa13, M. Ohnishi14, I. Ohta19, S. Ozawa11, X. L. Qian6,2, X. B. Qu20, T. Saito21, T. Y. Saito22, M. Sakata10, T. K. Sako14, J. Shao2,6, M. Shibata12, A. Shiomi23, T. Shirai8, H. Sugimoto24, M. Takita14, Y. H. Tan2, N. Tateyama8, S. Torii11, H. Tsuchiya25, S. Udo8, H. Wang2, H. R. Wu2, L. Xue6, Y. Yamamoto10, K. Yamauchi12, Z. Yang2, S. Yasue26, 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

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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)

muon detector

We have operated the 500 m Yangbajing air-shower core (YAC-II) detector array near the center of the Tibet air-shower array ( Tibet-III ) to study the cosmic-ray chemical composition at the knee energy region since August, 2011. YAC-II array consists of 124 YAC detector units. Each unit of YAC-II consists of a lead layer 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. Each scintillator has the size 80 cm × 50 cm × 1 cm. 60 WLSFs (Wave Length Shifting Fiber) are installed inside the scintillator, a high-gain PMT and a low-gain PMT are coupled with it. The burst size can be measured from 1 MIP (Minimum Ionization Particles) to 10 MIPs. In this paper, the details of the hybrid experiment and the processes of the data reconstruction are described.

Progress Report on the TIBET AS+MD Project

The Coulomb breakup technique was applied to determine the E1 strength of excited levels in 12N and 13O, which dominate the low-energy cross sections of the 11C(p,γ)12N and 12N(p,γ)13O reactions, respectively. These reactions are important in the hot pp mode nuclear burning in hydrogen-rich massive objects [1]. Under a high-temperature and high-density condition, these capture reactions become faster than the β + decay of 11C and 12N. However, these 11C(p,γ)12N and 12N(p,γ)13O reactions are difficult to study experimentally because the life times of 11C and 12N are too short to prepare them as targets.

Measurement of some properties of EAS-cores using new air-shower core array developed for the Tibet hybrid experiment

In the neutron-rich region around N = 8, experimental evidence is being to accumulate that several neutron-rich nuclei, such as 11Li and 11Be, are strongly influenced by lowlying intruder orbitals [1,2]. In this neighborhood, 12Be is a typical neutron-rich nucleus with N = 8 , where the effects of shell quenching are most likely to be manifested. Since properties of low-lying states in even-even nuclei are sensitive to the modification of the nuclear shell structure, we have studied the low-lying E1 and E2 transitions of 12Be via inelastic scattering.

Coulomb dissociation of 12N and 13O

We searched for multi-TeV counterparts to the gamma–ray bursts (GRBs) at keV energies detected by BATSE during the period from October 2, 1995 to March 18, 1999 using the data of the Tibet Air Shower Array. In the field of view of the array there were 70 GRBs detected by BATSE in this period. The search was done based on the sky survey within error circles of BATSE bursts and with time scales during 10 to several hundred seconds. No significant signals of counterparts were detected.

Studies of low-lying excited states in 12Be via inelastic scattering

The Tibet air-shower array operating at Yangbajing (4300 m above sea level) is sensitive to gamma-ray air showers at energies as low as 3 TeV. The observation of the moon’s shadow has provided a direct check of the angular resolution, the energy estimation and the systematic pointing error of this air-shower array. Using these data, we have searched for multi-TeV gamma-ray emission from 21 SNRs located within 5 kpc distance in the declination band of 0° to +60°. The signal from the Crab Nebula was detected at 5.5 σ level as described another paper. No significant DC excess exceeding 5 σ level was found from any of these SNRs except from the Crab Nebula. The results of nearby eight SNRs piled up gave a flux upper limit slightly lower than the expected values for a simple model of shock acceleration.