Results are presented of an untagged e + e − → e + e − + π + π − experiment performed at PEP with the DELCO detector. In the invariant-mass range 0.7 ⩽ W ππ < 2.0 GeV/ c 2 , the QED e + e − background is identified and eliminated, and both the π + π − predictions and the μ + μ − and K + K − background substractions are normalized to the measurement of the e e + e − events. The results agree with a simple model of superposition and interference of the f 0 (1270) resonance, produced with helicity 2, with a Born-term continuum. From a fit of the model to the data, the radiative width of the f 0 is determined to be Γ f 0 → γγ = 2.70 ± 0.21 keV.
Data read from graph.
In the analysis of the reactione+e−→e+e−KS0Ks0 clear evidence for exclusive γγ→f2′ resonance production is observed. The productΓγγ ·B(f2′→K\(\bar K\)) is measured to be 0.10−0.03−0.02+0.04+0.03 keV independent of ana priori assumption on the helicity structure. Our data are consistent with a pure helicity 2 contribution and we derive an upper limit for the ratioΓγγ(0)/Γγγ. The absence of events in the mass region around 1.3 GeV clearly proves destructivef2−a2 interference and allows to measure the relative phases betweenf2,a2 andf2′. Upper limits on the production of the glueball candidate statesf2(1720) andX(2230) as well as theKS0KS0-continuum are given.
Data read from graph.
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We investigate the four-photon final state produced in γγ colissions. In the π 0 π 0 channel we observe f(1270) production with predominantly helicity 2 and measure a partial width Γ γγ 2.9 +0.6 −0.4 ± keV (independent of assumptions on the helicity). We observe A 2 (1310) production in the π 0 η channel and find a partial width Γ γγ = 0.77 ± 0.18 ± 0.27 KeV (assuming helicity 2). We give an upper limit for f ≈ ηη .
Data read from graph. Systematic error on M is of order of 2% or less.
Data read from graph.
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We have observed exclusive production of K + K − and K S O K S O pairs and the excitation of the f′(1515) tensor meson in photon-photon collisions. Assuming the f′ to be production in a helicity 2 state, we determine Λ( f ′ → γγ) B( f ′ → K K ) = 0.11 ± 0.02 ± 0.04 keV . The non-strange quark of the f′ is found to be less than 3% (95% CL). For the θ(1640) we derive an upper limit for the product Λ(θ rarr; γγ K K ) < 0.03 keV (95% CL ) .
Data read from graph.. Errors are the square roots of the number of events.
Data read from graph.. Errors are the square roots of the number of events.
The process γγ→π+π− was measured using the detector MD-1 at VEPP-4. The two-photon reactionse+e−, μ+ μ− and π+ π− pair production were separated using scintillation counters, Cherenkov counters and shower-range chambers. A radiation widthГγγ(f2(1270))=3.1±0.35±0.35 keV was obtained.
Data read from graph.
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 production of charged kaon pairs in two-photon interactions has been studied with the ARGUS detector and the topological cross section has been measured. The γγ-widths and interference parameters have been determined for the tensor mesonsf2 (1270),a2 (1318) andf′2 (1525). The helicity structure assumed for the continuum contribution has a significant effect on the result. Upper limits have been obtained for the γγ-widths of the glueball candidate statesf2 (1720) andX (2230).
Data read from graph.. Errors are the square roots of the number of events.
Cross section allowing for spin components JM = 22,20,00. Data read from graph.. Additional overall systematic error 8.4%.
Cross section allowing for spin components JM = 22,00. Data read from graph.. Additional overall systematic error 8.4%.
Results of the first experiments with the Neutral Detector at the electron-positron storage ring VEPP-2M are presented. Branching ratios of the ø-meson radiative decays have been measured: B ( ø → ηγ )=(1.30±0.06)%, B ( ø → π 0 γ )=(0.130±0.013)%, their accuracy being several times higher than the world average. The width ratio is Γ(ø→ηγ) Γ(ø→π 0 γ)=(10±1) . Using the abovementioned quantities, the ω − ø mixing angle θ v =(38.3±0.2) ° , as well as the ratio between the effective magnetic moments of the s- and u-quarks, μ s μ u =(0.57±0.03) have been calculated.
CROSS SECTIONS IN THE PHI MESON PEAK (CORRECTED FOR RADIATIVE EFFECTS).
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SAME AS FIG 2A, BUT KINEMATICAL RECONSTRUCTION ARE APPLIED. I.E. THE ENERGY- MOMENTUM CONSERVATIONS ARE USED TO IMPROVE THE ACCURACY OF PARTICLE ENERGIES AND ANGLES MEASURED IN DETECTOR.
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