The process e + e − →e + e − μ + μ − has been studied in single-tag and double-tag configurations using the TOPAZ detector at TRISTAN. The data correspond to the integrated luminosity of 45.3pb − at center-of-mass energies ranging from 52 to 61.4 GeV. The observed events in both configurations have shown a good agreement with QED predictions in order α 4 . Although the AMY group reported an excess of e + e − →e + e − μ + μ − events in double-tag mode at low muon invariant mass region less than 1.0 GeV/c 2 , we did not observed such excess in our data.
No description provided.
Using the CELLO detector, we have measured cross sections for the processγγ→π+π− in the mass range 0.75–1.9 GeV/c2. A partial wave fit to the data indicates the presence of a sizeableS-wave amplitude with signs of resonant behaviour. Values for the γγ width of thef2(1270) are given, showing the model-dependence of this quantity. At higher dipion masses, the model of Brodsky and Lepage is found to give an order of magnitude description of the data.
No description provided.
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We have collected 122 multi-hadronic inclusive muon events with the TOPAZ detector at 〈 s 〉 = 58.27 GeV with ∫ L d t=40.61 pb −1 . From this event sample we derived the differential cross section for B-hadron productions and determined B-hadron forward-backward asymmetry (A b b ) to be A b b = −0.71 ± 0.34 ( stat ) +0.07 −0.08 ( syst ) . A fit to the differential cross section, after correcting for the effect of B 0 B 0 mixing, yielded the axial-vector coupling constant of the b-quark ( a b ): a b = −1.79 +0.34 −0.32 (stat) +0.15 −0.14 (syst). We also set a 90% confidence level limit of χ <0.37 on the B 0 B 0 mixing parameter.
Observed differential cross section.
No description provided.
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Data at Parton level.
Ratio data/(Monte Carlo) at Parton level.
Data at Parton level.. Distribution of Ellis-Karliner angle.
We have measured the partial width and forward-backward charge asymmetry for the reaction e + e - →Z 0 →μ + μ - (γ). We obtain a partial width Γ μμ of 83.3±1.3(stat)±0.9(sys) MeV and the following values for the vector and axial vector couplings: g v =−0.062 −0.015 +0.020 and g A =−0.497 −0.005 +0.005 . From our measurement of the partial width and the mass of the Z 0 boson we determine the effective electroweak mixing angle, sin 2 θ w =0.232±0.005, and the neutral current coupling strength parameter, ϱ =0.998±0.016.
No description provided.
Forward backward charge asymmetry.
No description provided.
We have studied the properties of pion production in the reaction γ →3 π + 3 π − in the energy range 1.6⩽ W γγ ⩽7.5 GeV with the CELLO detector at PETRA. We present the topological cross section both for Q 2 ≈0 (anti-tag) and Q 2 ≈0 (single-tag). The Q 2 dependence of the cross section is flatter than the GVDM prediction. The distribution of the production angle of the pions in the CMS peaks at small angles, indicating a peripheral process. In accordance with the VDM picture the p T distribution of the pions manifests an exponential fall-off. Like sign pion pairs were found to be Bose-Einstein correlated. We use this correlation to estimate the spatial dimensions of the interaction region.
No description provided.
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Resonance production in the γγ reactionse+e−→e+e+e−π0π0 ande+e−π0η has been studied with the JADE detector at PETRA. The decay widths into γγ of thef2(1270),a0(980) anda2(1320) were measured to be\(\Gamma _{\gamma \gamma } (f_2 (1270)) = 3.19 \pm 0.09_{ - 0.38}^{ + 0.22} \) Kev,Γλλ(a0(980))=0.28±0.04±0.10 KeV/BR(a0(980)→π0η) andΓλλ(a2(1320))=1.01±0.14±0.22KeV. For thef0(975) andf4(2050) upper limits of the widths were obtained,Γλλ(f0(975))<0.6 KeV, andΓλλ(f4(2050))<1.1 KeV, both at the 95% C.L. Assuming that the spin 0 background under thef2(1270) is small, thef2(1270) was found to be produced exclusively in a helicity 2 state. The helicity 0 contribution is <15% at the 95% C.L. The cross section forλλ→π0π0 in the mass range 2.0–3.5 GeV/c2 was measured for the first time. Since the cross section forλλ→π+π− is a factor ∼2 larger, ππ production in this range can be interpreted as taking place via isospin 0 production.
Cross section for ABS(COS(THETA*)) < 0.3.
Cross section under assumptions of spin 2, helicity 2 production.
Cross section under assumption of spin 0 production.
The reaction e+e−→e+e−π0π0 has been analyzed using 97 pb−1 of data taken with the Crystal Ball detector at the DESY e−e+ storage ring DORIS II at beam energies around 5.3 GeV. For the first time we have measured the cross section for γγ→π0π0 for π0π0 mvariant masses ranging from threshold to about 2 GeV. We measure an approximately flat cross section of about 10 nb for W=mπ0π0<0.8 GeV, which is below 0.6 GeV, in good agreement with a theoretical prediction based on an unitarized Born-term model. At higher invariant masses we observe formation of the f2(1270) resonance and a hint of the f0(975). We deduce the following two-photon widths: Γγγ(f2(1270))=3.19±0.16±0.280.29 keV and Γγγ(f0(975))<0.53 keV at 90% C.L. The decay-angular distributions show the π0π0 system to be dominantly spin 0 for W<0.7 GeV and spin 2, helicity 2 in the f2(1270) region, with helicity 0 contributing at most 22% (90% C.L.).
Statistical errors only.
Statistical errors only.
We present the general properties of multihadron final states produced by e+e− annihilation at center-of-mass energies from 52 to 57 GeV in the AMY detector at the KEK collider TRISTAN. Global shape, inclusive charged-particle, and particle-flow distributions are presented. Our measurements are compared with QCD+fragmentation models that use either leading-logarithmic parton-shower evolution or QCD matrix elements at the parton level, and either string or cluster fragmentation for hadronization.
Rapidity distribution with respect to the Thrust axis.
Charged particle X distribution.
Charged particle PL distribution.
The full TASSO data have been used to study the orientation of three-jet events ine+e− annihilation. The polar angle distributions of the normal to the three-jet plane as well as the polar angle distribution of the most energetic jet have been measured as a function of the thrust cut-off used to select the three-jet sample. The data corrected for radiation and detector effects are compared to QCD predictions and fair agreement is found. As a consistency check we also present measurements of the azimuthal correlations between the lepton and hadron planes. A significant azimuthal dependence is found, consistent again with the QCD predictions.
No description provided.
Forum