135 research outputs found
Formalism for dilepton production via virtual photon bremsstrahlung in hadronic reactions
We derive a set of new formulas for various distributions in dilepton
production via virtual photon bremsstrahlung from pseudoscalar mesons and
unpolarized spin-one-half fermions. These formulas correspond to the leading
and sub-leading terms in the Low-Burnett-Kroll expansion for real photon
bremsstrahlung. The relation of our leading-term formulas to previous works is
also shown. Existing formulas are examined in the light of Lorentz covariance
and gauge invariance. Numerical comparison is made in a simple example, where
an "exact" formula and real photon data exist. The results reveal large
discrepancies among different bremsstrahlung formulas. Of all the leading-term
bremsstrahlung formulas, the one derived in this work agrees best with the
exact formula. The issues of M_T-scaling and event generators are also
addressed.Comment: 37 pages, RevTeX, epsf.sty, 10 embedded figure
Measurement of the D 0 → K - Π + Branching Fraction a
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72296/1/j.1749-6632.1988.tb51529.x.pd
Charged particle multiplicity distributions in e + e − annihilation at 29 GeV: a comparison with hadronic data
The charged particle multiplicity distributions for two-jet events in e + e − annihilation at 29 GeV have been measured using the High Resolution Spectrometer at PEP. A Poisson distribution describes the data for both the complete event and for the single jets. In addition, no correlation is observed between the multiplicities in the two jets of an event. For fixed values of the prong number of the complete event, the multiplicity sharing between the two jets is in good agreement with a binomial distribution. The rapidity gap distribution is exponential with a slope equal to the mean rapidity density. These observations, which are consistent with a picture of independent emission of single particles, are contrasted to the results from soft hadronic collisions and conclusions are drawn about the nature of clusters.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47881/1/10052_2005_Article_BF01570767.pd
Experimental limits on monojet production in e+e- annihilation at 29 GeV
A search was made for e+e--->X1X2 where X1 consists of one or more light unobservable particles and X2 decays promptly to a visible jet of particles. One event was found for an integrated luminosity of 176 pb-1, a rate consistent with known backgrounds. This result places a significant constraint on a number of theoretical models.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25641/3/0000191.pd
Studies of jet production rates in e + e − annihilation at E cm =29 GeV
Production rates of multijet hadronic final states are studied in e + e − annihilation at 29 GeV center of mass energy. QCD shower model calculations with exact first order matrix element weighting at the first gluon vertex are capable of reproducing the observed multijet event rates over a large range of jet pair masses. The method used to reconstruct jets is well suited for directly comparing experimental jet rates with parton rates calculated in perturbative QCD. Evidence for the energy dependene of α s is obtained by comparing the observed production rates of 3-jet events with results of similar studies performed at higher center of mass energies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47886/1/10052_2005_Article_BF01506527.pd
Measurements of Z-boson resonance parameters in e+e- annihilation
We have measured the mass of the Z boson to be 91.14±0.12 GeV/c^2, and its width to be 2.42-0.35+0.45 GeV. If we constrain the visible width to its standard-model value, we find the partial width to invisible decay modes to be 0.46±0.10 GeV, corresponding to 2.8±0.6 neutrino species, with a 95%-confidence-level upper limit of 3.9
First measurements of hadronic decays of the Z boson
We have observed hadronic final states produced in the decays of Z bosons. In order to study the parton structure of these events, we compare the distributions in sphericity, thurst, aplanarity, and number of jets to the predictions of several QCD-based models and to data from lower energies. The data and models agree within the present statistical precision
Initial measurements of Z-boson resonance parameters in e+e- annihilation
We have measured the mass of the Z boson to be 91.11±0.23 GeV/c^2, and its width to be 1.61-0.43+0.60 GeV. If we constrain the visible width to its standard-model value, we find the partial width to invisible decay modes to be 0.62±0.23 GeV, corresponding to 3.8±1.4 neutrino species
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