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Abstract
Evidence for the production of charged D* mesons has been obtained in proton-antiproton collisions at center of mass energy 540 GeV with the UA1 detector at the CERN collider. The search was confined to the charged particle fragments of hadronic jets, which are expected to be predominantly gluon jets in this experiment.
The data used for the analysis was a subset of the same triggers which revealed the electronic decays of the W('(+OR-)) and Z('o) bosons. The integrated luminosity of this sample is 113 nb('vs1). The D* was found using the decay mode D*('+) (--->) D('o)(pi)('+) (--->) K('-)(pi)('+)(pi)('+) plus the charge conjugate. Particle identification was not employed to distinguish K from (pi). Clear peaks of over 7 standard deviation significance were found in the mass distributions for M(,k(pi)) and (DELTA)M = M(,K(pi)(pi) ) - M(,K(pi)). The mean of the M(,K(pi)) peak was 1.870 (+OR-) 0.005 GeV/c('2), consistent with the known D('o) mass. The (DELTA)M peak was centered at 147.0 MeV/c('2) with error 0.1 MeV/c('2). This value for (DELTA)M is shifted by about 1.5 MeV/c('2) from the known D*('+)-D('o) mass difference. This deviation is thought to be due to detector systematics. The number of events in the peaks above background was about 20.(')
The observed D* decays were used to form a fragmentation distribution in the variable z, which is the fraction of the jet momentum carried by the D*. This mean of this distribution is a z = 0.2, suggesting that the charm quark of the D* is not the initiator of the jet. The production rate of charged D* relative to jets was found to be 0.65 (+OR-) 0.19 (+OR-) 0.33. This large rate, coupled with the soft fragmentation distribution, lead to the conclusion that the most likely source of the charm particles is the fragmentation of gluon jets into cc pairs. This result is probably reflective of the QCD prediction for flavor independence of gluon-quark couplings.
