Measurement of the antiproton to proton ratio in cosmic rays using the Moon shadow with the L3+C detector

The observation of the Moon shadow effect with the L3+C detector is reported. The expected offset and elongation of the Moon shadow due to the geomagnetic field are clearly observed. A determination of the angular resolution and pointing error has beem performed through this observation. A preliminary upper limit of the antiproton to proton ratio in cosmic rays is given in the TeV region.