"BESS-Polar - A Search for Cosmic Antiprotons and

Antimatter by a Long Duration Balloon Flight in Antarctica"


Tetsuya Yoshida

Associate Professor,

High Energy Accelerator Research Organization (KEK)


The apparent imbalance of matter and antimatter in the Universe is a fundamental puzzle for particle physics and for astronomy. Though Big Bang theory predicts that at the birth of the Universe matter and antimatter had to be present in equal amount, our Galaxy and its neighborhood seem to be matter dominant. This fact has two interpretations. Possibly elementary particle phenomena in the very early Universe broke the matter/antimatter symmetry throughout the entire Universe and the expected antimatter then disappeared. Alternatively, our Galaxy just happens to be in a matter zone, but the Big Bang made antimatter domains which survive somewhere else. In the latter case, antimatter traveling from an antimatter domain might penetrate into our Galaxy and be observed.


Antiprotons in the cosmic radiation might have novel origins in addition to the natural production process by interactions between high-energy cosmic rays and interstellar matter. Antiprotons can be produced by evaporation of primordial black holes, which might be formed by a density fluctuation in the early Universe, or by annihilations of neutralinos, lightest of the hypothesized supersymmetric (SUSY) particles, which are one of the candidates for the dark matter filling our Universe. Precise measurement of cosmic-ray antiprotons can reveal such types of elementary particle phenomena in the early Universe.


Therefore, a series of flights of the Balloon-borne Experiment with a Superconducting Spectrometer (BESS) has been carried out since 1993 as a US-Japan international collaboration, in order to measure precise amount of antiprotons in the cosmic radiation and to search for cosmic antimatter. State-of-the-art particle detector technology developed in high-energy accelerator experiments has been adopted to the balloon payload. Based on the scientific achievements from the past BESS experiments, preparation for the next-generation balloon-borne experiment that will utilize a long-duration ballooning in Antarctica, BESS-Polar, is now underway. BESS-Polar will extend capability for the intensive search for cosmic antimatter and for more precise measurement of cosmic-ray antiprotons. The first scientific observation is scheduled next Austral summer with a 10-day balloon flight from McMurdo base.



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