To investigate the dependence of large gradual solar energetic particle (SEP) events on the associated flares and coronal mass ejections (CMEs), the correlation coefficients (CCs) between peak intensities of E > 10 MeV ( I ₁₀ ), E > 30 MeV ( I ₃₀ ) and E > 50 MeV ( I ₅₀ ) protons and soft X-ray (SXR) emission of associated flares and the speeds of associated CMEs in the three longitudinal areas W0–W39, W40–W70 (hereafter the well connected region) and W71–W90 have been calculated. Classical correlation analysis shows that CCs between SXR emission and peak intensities of SEP events always reach their largest value in the well connected region and then decline dramatically in the longitudinal area outside the well connected region, suggesting that they may contribute to the production of SEPs in large SEP events. Both classical and partial correlation analyses show that SXR fluence is a better parameter describing the relationship between flares and SEP events. For large SEP events with source location in the well connected region, the CCs between SXR fluence and I ₁₀ , I ₃₀ and I ₅₀ are 0.58±0.12, 0.80±0.06 and 0.83±0.06 respectively, while the CCs between CME speed and I ₁₀ , I ₃₀ and I ₅₀ are 0.56±0.12, 0.52±0.13 and 0.48±0.13 respectively. The partial correlation analyses show that in the well connected region, both CME shock and SXR fluence can significantly affect I ₁₀ , but SXR peak flux makes no additional contribution. For E > 30 MeV protons with source location in the well connected region, only SXR fluence can significantly affect I ₃₀ , and the CME shock makes a small contribution to I ₃₀ , but SXR peak flux makes no additional contribution. For E > 50 MeV protons with source location in the well connected region, only SXR fluence can significantly affect I ₅₀ , but both CME shock and SXR peak flux make no additional contribution. We conclude that these findings provide statistical evidence that for SEP events with source locations in the well connected region, a CME shock is only an effective accelerator for E < 30 MeV protons. However, flares are not only effective accelerators for E < 30 MeV protons, but also for E > 30 MeV protons, and E > 30 MeV protons may be mainly accelerated by concurrent flares.

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 $\sim 40 \sigma$ level. The center of the moon was detected in the direction away from the apparent center of the moon by 0.23$^\circ$ 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