Narrow vector resonances widths

Aside from its large mass (3097 MeV/c ), the most remarkable property of the J/ is its extreme narrowness (long lifetime) as compared with ordinary strong interaction resonances. In fact, while the latter tjrpically have widths of the order of few hundred MeV, and the widths seem to grow (linearly ) with mass, the J/ I (3097) while having a large mass, has a total width of only 86 6 keV The leptonic width, on the other hand, into the e+e channel is about 5.36 0.29 keV which is typical of vector mesons. 

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