Search for an H-dibaryon with mass near 2m_Lambda in Y(1S) and Y(2S) decays

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We report the results of a high-statistics search for H-dibaryon production in inclusive Y(1S) and Y(2S) decays.

• No indication of an H-dibaryon with mass near the M_H=2m_Lambda threshold is seen in either the H-> Lambda p pi- or Lambda-Lambda decay channels and 90% confidence level branching-fraction upper limits are set that are between one and two orders of magnitude below the measured branching fractions for inclusive Y(1S) and Y(2S) decays to antideuterons.
• Since Y(1,2S) decays produce flavor-SU(3)-symmetric final states, these results put stringent constraints on H-dibaryon properties.
• The results are based on analyses of 102 million Y(1S) and 158 million Y(2S) events collected with the Belle detector at the KEKB electron-positron collider.