K.L. Sterner

Evidence for hard scattering of hadronic constituents of photons in photon-photon collisions of TRISTAN

Abstract We present results of an experimental study of e + e − + hadrons in the kinematic regime for which the process is interpreted as hadron production in collisions of almost-real photons. The data sample corresponds to an integrated luminosity of 27.5 pb − and covers center-of-mass energies from 55 to 61.4 GeV. We observe more events than expected from the incoherent sum of quark-parton and vector-meson-dominance models, and we give a quantitative explanation of the excess by including the hard scattering of the hadronic constituents of the photons calculated with QCD.

Measurements of the inclusive jet cross section in photon-photon interactions at TRISTAN

Abstract We present cross section measurements for inclusive jet production in almost-real photon-photon interactions at TRISTAN using the AMY detector. The results are compared with leading-order QCD calculations for different parameterizations of the parton density in the photon.

A measurement of the photon structure function F2

Abstract The photon structure function F2 has been measured at average Q2 values of 73,160 and 390 ( GeV c ) 2 . We compare the x dependence of the Q2 = 73 ( GeV c ) 2 data with theoretical expectations based on QCD. In addition we present results on the Q2 evolution of the structure function for the intermediate x range (0.3⩽ x ⩽0.8). The results are consistent with QCD.

A high-Q2 measurement of the photon structure function F2γ

Abstract The photon structure function F 2 γ has been measured at average Q 2 values of 73 and 390 GeV 2 using data collected by the AMY detector at the TRISTAN e + e − collider. F 2 γ is observed to be increasing as ln Q 2 . The x -dependence of F 2 γ , where x is the momentum fraction carried by the parton inside the photon, is also measured. The measurements are compared with several parton density models.

Measurement of αs from the moment of particle momenta within jets from e+e- annihilation

We present a study of the third moment of the inclusive momentum distribution of particles within jets produced by e+e- annihilation at TRISTAN. In this analysis, the QCD coupling strength alpha(s) is determined by fits to the prediction of the Next-to-Leading Logarithm Parton-Shower model. The measured value of alpha(s) (57.9 GeV) = 0.134(-0.005)+0.006.

A search for leptoquark and colored lepton pair production in e+e- annihilations at TRISTAN

Abstract We report on a search for the pair production of leptoquarks and colored leptons in e + e − annihilations t center-of-mass energies from 50 to 60.8 GeV, using the AMY detector at TRISTAN. No evidence for such particles is found and 95% CL mass limits are given.

A measurement of Bose-Einstein correlations in e+e− annihilation at TRISTAN

Abstract Using e+e− annihilation events accumulated with the AMY detector at the TRISTAN collider, we have studied the Bose-Einstein correlations in the distributions of like-sign charged tracks. As reference samples we used the opposite-sign charged track pairs and mixed pairs, which are like-sign pairs synthesized from tracks belonging to different events. The results of the different reference samples give approximately 0.45 for the correlation strength and approximately 0.65 fm for the source size. Previous measurements of these parameters in e+e− annihilation at energies from CESR to LEP show remarkably flat dependence on s . Our results conform well with this picture.

Measurements of cross section and charge asymmetry for e+e− → μ+μ− and e+e− → τ+τ− at s = 57.8 GeV

Abstract With data corresponding to 142 pb−1 accumulated at s = 57.8 GeV by the AMY detector at TRISTAN we measure the cross section of the reactions e+e− → μ+μ− and e+e− → τ+τ− and the symmetry in the angular distributions. For the lowest order cross section we obtain σμμ = 27.54 ± 0.65 ± 0.95 pb and σττ = 28.27 ± 0.87 ± 0.69 pb, and for the forward-backward asymmetry, Aμμ = 0.303 ± 0.027 ± 0.008 and Aττ = −0.291 ± 0.040 ± 0.019. These measurements agree with the standard model. Assuming e−μ−τ univrsality we extract the vector and axial coupling constants | gν| = 0.00 ± 0.09 and |gA| = 0.476 ± 0.024. A fit of data to composite models places lower bounds (95% confidence level) on the compositeness scale of 2–4 TeV.

Measurement of e+e-†bb forward-backward charge asymmetry between ss =52 and 57 GeV

Using 123 multihadronic inclusive muon-production {ital e}{sup +}{ital e}{sup {minus}} annihilation events at an average c.m. energy of 55.2 GeV, we extracted the forward-backward charge asymmetry of the {ital e}{sup +}{ital e}{sup {minus}}{r arrow}b{bar b} process and the {ital R} ratio for {ital b{bar b}} production. We used an analysis method in which the behavior of the {ital c} quark and lighter quarks is assumed, with only that of the {ital b} quark left indeterminate. The results, {ital A}{sub {ital b}}={minus}0.72{plus minus}0.28(stat){plus minus}0.13(syst) and {ital R}{sub {ital b}}=0.57{plus minus}0.16{plus minus}0.10, are consistent with the standard model.

Search for anomalous γγ production at TRISTAN

We report on measurements of the total cross section for e+e- --> gammagamma for center-of-mass energies between 57.4 and 59.5 GeV, using the AMY detector at the TRISTAN collider. We set new limits on the production of a possible new s-channel resonance decaying into photon pairs.