First observation of hadron production in e+e− collisions at 13 and 17 GeV CMS energy with the pluto detector at petra

Abstract

First results from the magnetic detector PLUTO at the new e+e− storage ring PETRA are shown. The ratio R of the cross section for hadron production to that for μ-pair production has been measured to be R = 5.0 ± 0.5 at 13 GeV and 4.3 ±0.5 at 17 GeV. Both values have an additional systematic error of 20%. The events show a typical 2-jet structure. The mean transverse momentum approaches a constant value with increasing energy implying a shrinkage of the jet opening angle.