Leptoquark
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Leptoquarks are hypothetical color-triplet bosons that carry both lepton and baryon numbers. They are encountered in various extensions of the Standard Model, such as technicolor theories or GUTs based on Pati-Salam model, SU(5) or E6, etc. Their quantum numbers like spin, (fractional) electric charge and weak isospin vary among theories.
In 1997 an excess of events at the HERA accelerator created a stir in the particle physics community, because one possible explanation of the excess was the involvement of leptoquarks. However, more recent studies performed both at HERA and at the Tevatron with larger samples of data ruled out this possibility for masses of the leptoquark up to 275-325 GeV [1].