Resolution of a long standing discrepancy in R with spin zero quarks

Abstract

A previously successful dispersive method has been applied to understand different values for $R(\sqrt{s} = 5 ÷7.5 GeV)$ obtained by MARK I and Crystal Ball collaborations. We compute $R$ in the disputed region with data from outside this region and asymptotic behavior given by the standard model with 5 quark flavors, and find agreement with the Crystal Ball result. On the other hand, the MARK I data are reproduced if we augment the asymptotic behavior with contributions from a single spin zero quark of charge ($ -1/3$). The visible hadronic fragments from such scalar quarks are not likely to produce predominantly pure 2-jet events at such low energies. Hence, such decay modes may have been removed by the Crystal Ball energy imbalance cuts in their definition of hadronic events but not in MARK I events, thus accounting for the discrepancy in the two results. Upper bounds on spin zero quark production at LEP through $Z$ decay data are used to estimate the mixing angle between $T_3\ = -1/2$ and $T_3 = 0$ scalar quarks. Recent negative results about spin zero quarks from CLEO are critically examined. We briefly discuss diquark production hypothesis and find it very unlikely to explain the discrepancy.