Results on hyperon production are reported for data accumulated at 10 GeV centre-of-mass energy with the ARGUS detector. Signals for both the octet states Λ, Σ 0 and Ξ − and the decuplet states Σ ± (1385), Ξ 0 (1530) and Ω − are observed 1 (references to a specific state are to be interpreted as also implying the charge conjugate state), some for the first time in e + e − annihilation. Baryon rates from γ dir (1S) decays are enhanced by a factor of about 3 over the continuum.
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We have measured the total normalized cross section R for the process e + e − → hadrons at centre-of-mass energies between 14.0 and 46.8 GeV based on an integrated luminosity of 60.3 pb −1 . The data are well described by the standard SU(3) c ⊗SU(2) L ⊗U(1) model with the production of the five known quarks. No open production of a sixth quark with charge 2/3 or 1/3 occurs below a centre-of-mass energy of 46.6 or 46.3 GeV, respectively. A fitting procedure which takes the correlations between measurements into account was used to determine the electroweak mixing angle sin 2 θ w and the strong coupling constant α s ( S ) in second-order QCD. We applied this procedure to the CELLO data and in addition included the data from other experiments at PETRA and PEP. Both fits give consistent results. The fit to the combined data yields α s (34 2 GeV 2 ) = 0.165±0.030, and sin 2 θ w = 0.236±0.020. Fixing sin 2 θ w at the world average value of 0.23 yields α s (34 2 GeV 2 ) = 0.169±0.025.
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We report measurements of two-particle correlations in rapidity space between a p¯ or Λ¯ and an additional p, p¯, Λ, or Λ¯. We find evidence for local conservation of baryon number, and for the first time observe a pronounced anticorrelation between baryons with the same value of baryon number. Such an anticorrelation is expected in fragmentation models where the rapidity order of particles closely reflects their ‘‘color order,’’ as is the case, for example, in recent versions of the Lund string model.
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New data are presented on charged particle pseudorapidity distributions for inelastic events produced at c.m. energies\(\sqrt s \)=200 and 900 GeV. The data were obtained at the CERN antiproton-proton Collider operated in a new pulsed mode. The rise of the central density ρ(0) at energies up to\(\sqrt s \)=900 GeV has been studied. A new form of central region scaling is found involving the densityρn(0) for charged multiplicityn, namely that the scaled central densityρn(0)/ρ(0) expressed as a function ofz=n/〈n〉 is independent ofs. Scaling in the fragmentation region holds to 10–20%, and the small amount of scalebreaking observed here could be accommodated within the framework suggested by Wdowcyk and Wolfendale to account for both accelerator and cosmic ray data.
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We report a measurement of the inclusive D/D̄ production cross section in 800 GeV/ c proton-proton interactions. The experiment used the high resolution bubble chamber LEBC exposed to an 800 GeV/ c proton beam at the Fermilab MPS. We obtain σ( D/ D ̄ )=59 −15 +22 μ b (statistical errors), having analysed 25% of the total data sample. Comparison with 400 GeV/ c pp dat a obtained with LEBC at CERN shows a D/D̄ cross section increase by a factor of 1.7 −0.5 +0.7 . This is in good agreement with fusion model calculations.
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A narrow meson which decays into ηη is observed in 38 GeV/ c π − p collisions at large momentum transfer. The experiment has been performed at the Serpukhov accelerator with the GAMS-2000 spectrometer. The mass of this new meson is (1755 ± 8) MeV, its width is less than 50 MeV. Its spin-parity is J PC =0 ++ or less probably 2 ++ .
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A search for stableH-dibaryon ofI=0,Y=0,JP=0+ was undertaken in negative pion-, neutron-,12C-nucleus- and proton-propane interactions at 4.0, 7.0, 50.4 and 10 GeV/c, respectively, using 55 cm and 2 m propane bubble chambers. This technique permite one to examine the whole range of possibleH-mass value. In the range ofMH>2MΛ=2231.2 MeV/c2 an enhancement ofMΛΛ=(2365.3±9.6) MeV/c2, ΓΛΛ=(47.2±15.1) MeV/c2 with production cross section σ=(24.2±7.0) μb per carbon nucleus was found. The mass rangeMΣ−p<MH<2MΛ was explored via the search for a weak decay modeH→Σ−+p. AV0-particle was found pointing to a two-prong interaction and satisfying the kinematics of the above two-body decay mode with a high confidence level. The possibility of imitation of the observed event by background processes was investigated for a series of two-step strong reactions and weak decays. We succeeded to show the significance of theH-production hypothesis on a deuteron-mass nuclear fluctuon via thepd→HpK+K0 reaction. The mass of the event treated as aH→Σ−+p weak decay appeared to be (2173.94±1.32) MeV/c2, its life-time being 0.668·10−10 s. Both are in agreement with predictions of the MIT Bag Model for the so-calledH-dihyperon. The formally determined production cross section of theH in proton-propane interactions at 10 GeV/c is estimated to be 40 nb. Perhaps, this event can be considered as a first evidence for a six-quark bound state-H-dihyperon. An independent way for the search for theH-particle, based on a specific conversion processHN→YYN, peculiar to its intranuclear strong interactions was proposed and tried. For this purpose all events with two Λ-hyperons and identified protons were tested for the hypothesesHp→ΛΛp at three fixed masses:MH=1880.00, 2173.94 MeV/c2 and the ΛΛ invariant mass for the event in question. The kinematics of this reaction fits successfully only one event and only atMH=2173.94 MeV/c2. It seems worthy of note that the final state ΛΛ invariant massMΛΛ=2344 MeV/c2 is rather close to the observed peak at 2365 MeV/c2. It is shown that the intranuclear conversion processes Ξ−p→ΛΛ and Ξ0n→ΛΛ fail to imitate the observed event. The ΛΛp invariant mass of this event equal to 3363 MeV/c2 is out of a 3568 MeV/c2 peak region of the ΛΛp invariant mass spectrum observed earlier. TheH conversion cross section exceeds the production one. Thus, we consider this event as providing a new evidence for the stableH-dibaryon ofMH=(2173.94±1.32) MeV/c2.
Claime of DIBARYON(S=-2) with mass M=(2365.3+-9.6) MeV and width G=(47.2+-15.1) MeV.
A comparison is made between the properties of the final state hadrons produced in 280 GeV μp interactions and ine+e− annihilation. The Lund model of hadroproduction is used as an aid in understanding the differences observed. The hadron distributions from μp ande+e− interactions are consistent with the quark parton model assumption of environmental independence, provided that the differences in heavy quark production and hard QCD effects in the two processes are taken into account. A comparison with aK+p experiment is also made. Values are also determined for the Lund model parameters σq = 0.410 ± 0.002 ± 0.020 GeV and σ′ = 0.29−0.15 −0.13+0.09+0.10 GeV, controlling the transverse momenta in fragmentation and intrinsic transverse momenta of the struck quark respectively.
With respect to the virtual photon axis.
With respect to the sphericity axis.
With respect to the thrust axis.
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