We report a measurement of the production of antideuterons d in e + e − annihilation at centre-of-mass energies around 10 GeV using the ARGUS detector at the DORIS II storage ring. We observe an enhancement of d production in direct hadronic ϒ (1S) and ϒ (2S) resonance decays. From 21 events width a d candidate the inclusive cross section 1 σ dir had · d σ d p and the production rate of antideuterons are determined. A production rate of (6.0±2.0±0.6) × 10 -5 d per direct hadronic ϒ decay and a 90% CL upper limit of 1.7 × 10 −5 d per e + e − →q q continuum event are obtained. These results are related to antiproton production through a simple model.
We report on the first observation of Δ(1232) ++ and Δ(1232)++¯ baryons in e + e − annihilation at energies around 10 GeV, using the ARGUS detector at DORIS II. The sum of the rates of Δ ++ and Δ++¯ per hadronic event in the continuum is measured to be 0.040±0.008±0.006, and the rate in direct ϒ(1S) decays is 0.124±0.016±0.015. The momentum spectrum of Δ ++ baryons in direct ϒ(1S) decays has been measured.
Using the ARGUS detector at the DORIS II storage ring, we have observed the charmed baryons Σ c ++ and Σ c 0 , through their decays to Λ c + π ± . We have measured the mean Σ c −Λ c + mass difference as 167.6±0.3±1.6 MeV/ c 2 . The isospin mass splitting between the Σ c ++ and the Σ c 0 was found to be 1.2±0.7±0.3 MeV/ c 2 . The rate of Λ c + production from Σ c decays was found to be (36±12±11)% of the total rate of Λ c + production. The Σ c χ p spectrum was observed to be similar to that of the Λ c + , with a Peterson function parameter ϵ of 0.29±0.06.
Using the ARGUS detector at the DORIS II e + e − storage ring we have measured direct photons from the decay ???(1 S )→ γgg . The ratio R γ = Γ (???(1S)→ γgg )/ Γ (???(1S)→ ggg )=(3.00±0.13±0.18)% has been determined, from which we deduce values of the strong coupling constant α s =0.225±0.011±0.019 and the QCD scale parameter Λ MS =115±17±28 MeV defined in the modified minimal-subtraction scheme. The shape of the measured spectrum clearly rules out the predictions of the lowest order QCD calculations.
The production cross sections for the Λ, Σ0, Ξ−, Σ0 (1385), Ξ0 (1530) and Ω− hyperons have been measured, both in the continuum and in direct ϒ decays. Baryon rates in direct ϒ decays are enhanced by a factor of 2.5 or more compared to the continuum. Such a large baryon enhancement cannot be explained by standard fragmentation models. The strangeness suppression for baryons and mesons turns out to be the same. A strong suppression of spin 3/2 states is observed.
We report on a high statistics study of π0 and η production in continuum events and in direct decays of the Γ(1S) and Γ(2S) resonances. The measured production rates per event are\(\left\langle {n_{\pi ^0 } } \right\rangle\)=3.22 ± 0.07 ± 0.31 (3.97 ± 0.23 ± 0.38) and 〈nη〉=0.19 ± 0.04 ± 0.04 (0.40 ± 0.14 ± 0.09) for continuum events (direct Γ(1S) decays).
Using data collected with the ARGUS detector, we have performed a decay angular analysis of the enhancement, previously known as the D ∗ (2420), seen in the final state D ∗ (2010) + π − . We thereby exhibit that the observed broad structure is actually due to two relatively narrow resonances, one of which is identified as the D ∗ (2459) 0 , while the massof the other is measured to be (2414±2±5) MeV/ c 2 . The results of the analysis are in good agreement with the interpretation of the two states as L =1 D mesons of spin-parities 2 + and 1 + respectively.
Using the ARGUS detector at the DORIS II e + e − storage ring at DESY, we have obtained evidence for a new charmed-strange meson which decays into D *+ K 0 . Its mass is observed to be 2535.9±0.6±2.0 MeV/ c 2 and its width to be less than 4.6 MeV/ c 2 at the 90% confidence level. No structure is observed at this mass in the D + K 0 invariant mass spectrum, which suggests that an unnatural spin-parity is preferred.
Using the ARGUS detector at the DORIS II storage ring at DESY, we have observed a charmed meson of mass (2455±3±5) MeV/c2, decaying to D + π − . The natural width of this state is determined to be (15 +13+5 −10−10 ) MeV c 2 . The fragmentation function is hard, as expected for a leading charmed particle from nonresonant e + e − annihilation. Analysis of the decay angular distribution supports the hypothesis that the observed state is an L =1 excited charmed meson with spin-parity 2 + .
We report the first observation of an orbitally excited baryon, the Λ(1520), in quark and gluon fragmentation. The production rate is found to be (1.15±0.21±0.16)×10 −2 and (0.80±0.17 −0.13 +0.10 )×10 −2 Λ (1520) hyperons per event in direct ϒ decays and in the continuum, respectively. In contrast to the observed situation for ground state baryons, the production of the Λ(1520) in direct ϒ decays shows little or no enhancement with respect to continuum production.
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