T. Arima

A study of the charm and bottom quark production in e+e− annihilation at s = 58 GeV using prompt electrons

Abstract We have studied c (charm) and b (bottom) quark production at the TRISTAN energy region by tagging prompt electrons from the semileptonic decays. Electrons were identified over a wide momentum range between 1 and 29 GeV/c by a transition-radiation-detector in addition to a lead-glass calorimeter. The production cross sections of c and b quarks and the mean values of the fragmentation functions for c and b quarks were obtained as σc = 55.9±8.8(stat.)±7.9(syst.) pb, σb = 13.1±2.9(stat.)±1.0(syst.) pb, 〈xc〉 = 0.44±0.08(stat.)±0.04(syst.) and 〈xb〉 = 0.72±0.12(stat.)±0.08(syst.), respectively. The forward-backward asymmetries of the c and b quarks were also measured to be −0.57±0.16(stat.)±0.06(syst.) and −0.64±0.26(stat.)± 0.07(syst.), respectively. Both the cross sections and the forward-backward asymmetries of the c and b quarks are consistent with the standard model.

A Study of charged D* production in e+ e- annihilation at an average center-of-mass energy of 58-GeV

Abstract We have studied the production of charged D ∗ mesons in e + e − annihilation at an average center-of-mass energy of 58.0 GeV. Charged D ∗ mesons were identified using two independent methods; the mass-difference method and the detection of the low transverse-momentum pion. The forward-backward asymmetry of the charm quark production was measured to be A c = −0.61±0.13(stat.)±0.08(syst.). The cross section of inclusive D ∗ production was found to be σ(e + e − →D ∗ ± +X) = 24.5 ± 5.3 ( stat. )±3.0( syst. ) pb. If we assume the standard model prediction for the charm quark production, we obtain the branching ratio for the charm quark to produce a charged D ∗ meson to be Br (c→D ∗+ + X) = (22±5( stat. )±3( syst. ))% .

Measurement of open charm production in two-photon processes with detection of electron-inclusive events

Experimental studies of open charm production in two-photon processes have been performed. In the measurement, charmed hadrons were identified by electrons from their semi-leptonic decays. The result was compared with calculations based on the direct process and photon-gluon fusion process by resolved photons. We found that the effect of the gluon component in a photon is substantial in the observed events.

A study of single photon production in e+e− annihilation at √s=58 GeV

Abstract We have studied single photon production in e + e − annihilation based on a data sample corresponding to an integrated luminosity of 164.1 pb −1 at s =58 GeV . The single photon yield is consistent with the prediction of the standard model with three light neutrino species. No anomalous signal has been observed. From this result left- and right-handed scalar electrons in the mass degenerate case are excluded at 90% CL below 44.4 GeV/ c 2 for the massless photino.

Search for heavy neutral spinless particles using e+e− → e+e− and e+e− → γγ reactions in the CM energy range between 54 and 64 GeV

Abstract Heavy neutral spinless particles are searched for using e + e − collision data of CM energies between 54 and 64 GeV, collected with the VENUS detector at TRISTAN. The existence of such a particle might explain the anomalous e + e − → l + l − γγ reaction recently reported by a LEP experiment. Negative results lead to constraints on the partial decay width of such particles to electrons: in narrow resonance cases, Γ ee Γ ee ΓB γγ c 2 .

Measurement of τ polarization in e+e- annihilation at √s = 58 GeV

Abstract The polarization of τ leptons in the reaction e+e− → τ+τ− has been measured using a e+e− collider, TRISTAN, at the center-of-mass energy of 58 GeV. From the kinematical distributions of daughter particles in τ → eν ν , μν ν , ϱν or π(K)ν decays, the average polarization of τ− and its forward-backward asymmetry have been evaluated to be 0.012±0.058 and 0.029±0.057, respectively.

Study of inclusive baryon-antibaryon pair production ofp orΛ in two-photon processes

Inclusive baryon-antibaryon pair production was studied in two-photon events which were collected at thee+e− collider TRISTAN, and correspond to an integrated luminosity of 303 pb−1. Correlations between a baryon and an antibaryon were studied for their flavors (p orΛ) and their momentum vectors. The experimental results were compared with the expectations from a jet-fragmentation Monte Carlo simulation. We have found that although the ratios of the cross sections of different baryon-flavor combinations are consistent with the Monte Carlo expectations, the cross section shows an excess over the Monte Carlo expectation in a low invariant-mass region of final-state particles at large angles, that indicates a significant contribution from higher-order QCD or non-perturbative effects. The experimental data show no narrow azimuthal-angle correlation, which is expected from a jet-fragmentation Monte Carlo. A search for exclusiveΛ pair production has also been made. We have no candidates and have obtained the upper limit for the cross section.

Search for a light scalar top squark in [ital e][sup +][ital e][sup [minus]] reactions at [ital E][sub c. m. ]=58 GeV

A search has been made for a light scalar top squark ([ital [tilde t]][sub 1]), which has remained unexcluded by previous [ital e][sup +][ital e][sup [minus]] experiments up to the [ital Z][sup 0] pole. By assuming the decay [ital [tilde t]][sub 1][r arrow][ital c]+[ital [tilde Z]][sub 1] (lightest neutralino), [ital e][sup +][ital e][sup [minus]] annihilation data at [ital E][sub c.m.]=58 GeV have been analyzed. The number of events comprising large-acoplanarity particle groups is consistent with that expected from known processes. We excluded [ital [tilde t]][sub 1] in the mass range 7.6--28.0 GeV/[ital c][sup 2] and [ital [tilde Z]][sub 1] with a mass very close to the kinematical limit at the 95% C.L.

Search for a light scalar top in e+ e- reaction at E(cm) = 58-GeV

A search has been made for a light scalar top squark ([ital [tilde t]][sub 1]), which has remained unexcluded by previous [ital e][sup +][ital e][sup [minus]] experiments up to the [ital Z][sup 0] pole. By assuming the decay [ital [tilde t]][sub 1][r arrow][ital c]+[ital [tilde Z]][sub 1] (lightest neutralino), [ital e][sup +][ital e][sup [minus]] annihilation data at [ital E][sub c.m.]=58 GeV have been analyzed. The number of events comprising large-acoplanarity particle groups is consistent with that expected from known processes. We excluded [ital [tilde t]][sub 1] in the mass range 7.6--28.0 GeV/[ital c][sup 2] and [ital [tilde Z]][sub 1] with a mass very close to the kinematical limit at the 95% C.L.

SEARCH FOR A LIGHT SCALAR TOP SQUARK IN E+E- REACTIONS AT EC.. ) 58 GEV

A search has been made for a light scalar top squark ([ital [tilde t]][sub 1]), which has remained unexcluded by previous [ital e][sup +][ital e][sup [minus]] experiments up to the [ital Z][sup 0] pole. By assuming the decay [ital [tilde t]][sub 1][r arrow][ital c]+[ital [tilde Z]][sub 1] (lightest neutralino), [ital e][sup +][ital e][sup [minus]] annihilation data at [ital E][sub c.m.]=58 GeV have been analyzed. The number of events comprising large-acoplanarity particle groups is consistent with that expected from known processes. We excluded [ital [tilde t]][sub 1] in the mass range 7.6--28.0 GeV/[ital c][sup 2] and [ital [tilde Z]][sub 1] with a mass very close to the kinematical limit at the 95% C.L.