D.Y. Kim

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 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 charm production in two-photon processes using inclusive lepton events at TRISTAN

Abstract Measurements of open charm production in photon-photon collisions made with the AMY detector at TRISTAN are reported. Charmed hadrons were identified by detecting the high momentum muons or electrons from their semileptonic decays. The data sample corresponds to an integrated luminosity of 275 pb −1 at an average center of mass energy of 58 GeV. Results are presented in the form of cross sections of inclusive leptons from charm for both muons and electrons. The measured cross section is 1.8 standard deviations higher than theoretical predictions based on the direct and photon-gluon fusion process, where the mass of charm quark is assumed to be 1.6 GeV.

A measurement of the photon structure function F2γ at Q2 = 6.8 GeV2

The photon structure function F-2(gamma) has been measured at an average Q(2) value of 6.8 GeV2 using data collected by the AMY detector at the TRISTAN e(+)e(-) collider. The measured F-2(gamma) is compared with several QCD-based parton density models

New limits on the masses of the selectron and photino

Abstract A study of e + e − annihilations into final states containing a single energetic photon with no accompanying particles is made at a center of mass energy of 57.8 GeV. The measured cross section is consistent with expectations from standard model processes and is used to set limits on the masses of the scalar electron and photino particles predicted by supersymmetry theories. If the photino is assumed to be massless, the 90% confidence level lower limit on the mass of the degenerate scalar electron is 65.5 GeV. If the results of all the single photon experiments are combined, this lower limit increases to 79.3 GeV.

Measurement of D-*+/- production in two-photon processes at TRISTAN

The inclusive cross section for the production of charmed D*(+/-) mesons in two-photon processes is measured with the AMY detector at the TRISTAN e(+)e(-) collider. D*(+/-) mesons ate identified from the distribution of charged-particle transverse momenta relative to the jet axis. A data sample corresponding to an integrated luminosity of 176 pb(-1) at a center-of-mass energy of 58 GeV is used to determine a cross section sigma(e(+)e(-) --> e(+)e(-)D*(+/-)X) = 270 +/- 49(stat) +/- 38(syst) pb. The results are compared with theoretical expectations based on the Vector Meson Dominance, direct quark-parton model, and resolved photon processes.

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.

Observation of exclusive ηc production in two photon interactions at TRISTAN

Abstract We observe η c production in the two photon process e + e − → e + e − η c at an e + e − center-of-mass energy of 58 GeV. We determine the radiative decay width Γ γγ ( η c ) to be 27±16(sta)±10(sys) keV.

Observation of the color coherence effect in sub-jet multiplicity of three-jet and four-jet events in e+e− annihilations

We have measured the ratio of the average sub-jet multiplicity in 3-jet to 2-jet events, R(23), and 4-jet to 2-jet events, R(24), using the e(+)e(-) annihilation data at root s = 58 GeV obtained from the AMY detector. We compare the measured values of R(23) and R(24) With the predictions of coherent and incoherent Monte Carlo models. R(23) is also compared with the NLLA calculations to all-orders. The color coherence effect has been observed to contribute to the suppression of R(23) and R(24) Also, the difference of the behavior between gluon jets in 3-jet and 4-jet events has been studied.