Abstract
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 × 1010 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 ∼40σ 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.
Original language | English |
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Pages (from-to) | 137-142 |
Number of pages | 6 |
Journal | Astroparticle Physics |
Volume | 28 |
Issue number | 1 |
DOIs | |
Publication status | Published - 2007 Sept |
Keywords
- Air shower
- Anti-matter
- Cosmic rays
- Observation and data analysis
- Simulations
ASJC Scopus subject areas
- Nuclear and High Energy Physics
- Astronomy and Astrophysics
- Atomic and Molecular Physics, and Optics