The production dynamics of baryon-antibaryon pairs are investigated using hadronic Z 0 decays, recorded with the OPAL detector, which contain at least two identified Λ baryons. The rapidly difference for Λ Λ pairs shows the correlations expected from models with a chain-like production of baryon-antibaryon pairs. If the baryon number of a Λ is compensated by a Λ , the Λ is found with a probability of 53% in an interval of ±0.6 around the Λ rapidity. This correlation strength is weaker than predicted by the Herwig Monte Carlo and the Jetset Monte Carlo with a production chain of baryon-antibaryon, and stronger than predicted by the UCLA model. The observed rapidity correlations can be described by the Jetset Monte Carlo with a dominant production chain of baryon-meson-antibaryon, the popcorn mechanism. In addition to the short range correlations, one finds an indication of a correlation of Λ Λ pairs in opposite hemispheres if both the Λ and the Λ have large rapidities. Such long range correlations are expected if the primary quark flavours are compensated in opposite hemispheres and if these quarks are found in energetic baryons. Rates for simultaneous baryon and strangeness number compensation for Λ Λ , Ξ − Ξ + and Ξ − Λ ( Λ + Λ ) are measured and compared with different Monte Carlo models.
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Opposite and same baryon number invariant PI P mass distribuition for additional LAMBDA(LAMBDABAR) candidates in events with one identified LAMBDA(LAMBDABAR). CT.= Data read from plot.
Opposite and same baryon number invariant PI P mass distribuition for additional LAMBDA(LAMBDABAR) candidates in events with one identified XI-(XIBAR+). CT.= Data read from plot.
Quark and gluon jets with equal energies are identified in three-jet hadronicZ0 events, using reconstructed secondary vertices from heavy quark decay in conjunction with energy orderi
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A sample of about 1.4 million hadronic Z decays, selected among the data recorded by the DELPHI detector at LEP during 1994, was used to measure for the first time the momentum spectra of K + , K 0 , p , Λ and their antiparticles in gluon and quark jets. As observed for inclusive charged particles, the production spectra of identified particles were found to be softer in gluon jets than in quark jets, with a higher total multiplicity.
Y events.
Mercedes events.
Using the CLEO detector at the Cornell $e~+e~-$ storage ring, CESR, we study the two-photon production of $\Lambda \overline{\Lambda}$, making the first observation of $\gamma \gamma \to \Lambda \overline{\Lambda}$. We present the cross-section for $ \gamma \gamma \to \Lambda \overline{\Lambda}$ as a function of the $\gamma \gamma$ center of mass energy and compare it to that predicted by the quark-diquark model.
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We have searched for first generation scalar leptoquark (LQ) pairs in the enu+jets channel using ppbar collider data (integrated luminosity= 115 pb^-1) collected by the DZero experiment at the Fermilab Tevatron during 1992-96. The analysis yields no candidate events. We combine the results with those from the ee+jets and nunu+jets channels to obtain 95% confidence level (CL) upper limits on the LQ pair production cross section as a function of mass and of beta, the branching fraction to a charged lepton. Comparing with the next-to-leading order theory, we set 95% CL lower limits on the LQ mass of 225, 204, and 79 GeV/c^2 for beta=1, 1/2, and 0, respectively.
The cross section values are extracted with the assumption that BR(LQ --> EQUARK) = 1/2.
We have measured inclusive electron production in multiprong events produced by e+e− annihilation in the center-of-mass energy range 3.9-7.4 GeV. We find the electron momentum spectra are consistent with the electrons coming mainly from decays of charmed particles, with a smaller contribution from decays of the τ lepton. From our data we calculate the average branching ratio for charmed particles to decay into an electron plus additional particles to be (8.2±1.9)%.
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The production of B ∗ mesons in Z decays has been measured at LEP with the L3 detector. A sample of Z → b b events was obtained by tagging muons in 1.6 million hadronic Z decays collected in 1991, 1992 and 1993. A signal with a peak value of E γ = 46.3 ± 1.9 (stat) MeV in the B rest frame energy spectrum was interpreted to come from the decay B ∗ → γB. The inclusive production ratio of B ∗ mesons relative to B mesons was determined from a fit to the spectrum to be N B ∗ (N B ∗ + N B ) = 0.76 ± 0.08 ± 0.06 , where the first error is statistical and the second is systematic.
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Using the 18.8 pb −1 of data accumulated at LEP in 1990 and 1991 with the ALEPH detector, a direct test of neutral current CP -invariance is performed by a search for CP -odd correlations in Z decays to τ pairs where both τ decay modes are identified. No evidence for CP -violation is observed. The weak dipole moment of the τ has been measured to be d τ ( m Z ) = (1.3 ± 1.4 ± 0.1) × 10 −17 e ·cm which results in an upper limit on the weak dipole moment of | d τ ( m Z )| ⩽ 3.7 × 10 −17 e ·cm with 95% confidence level.
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We observe evidence for the production of b-flavoured baryons in decays of the Z 0 boson with the OPAL detector at LEP. We find 68 Λl − , Λ l + candidates in 458 583 hadronic Z 0 decays. We interpret this as a signal of 55 ± 9 +0.3 −3.1 events from the semi-leptonic decays of b baryons. Assuming weakly decaying b baryons produced in Z 0 decays are mostly Λ b particles, we measure the product branching ratio (Γ b b /Γ had ) f ( b →Λ b ) B (Λ b →Λl − v X ) , averaged over the electron and muon channels, to be (6.2±1.0±1.5)×10 −4 .
FD is considered as a quark fragmentation fraction. Charge conjugated state is understood.
Using the CLEO detector at the Cornell Electron Storage Ring, we observe B-meson decays to Λc+ and report on improved measurements of inclusive branching fractions and momentum spectra of other baryons. For the inclusive decay B¯→Λc+X with Λc+→pK−π+, we find that the product branching fraction B(B¯→Λc+X)B(Λc+→pK−π+)=(0.273±0.051±0.039)%. Our measured inclusive branching fractions to noncharmed baryons are B(B→pX)=(8.0±0.5±0.3)%, B(B→ΛX)=(3.8±0.4±0.6)%, and B(B→Ξ−X)=(0.27±0.05±0.04)%. From these rates and studies of baryon-lepton and baryon-antibaryon correlations in B decays, we have estimated the branching fraction B(B¯→Λc+X) to be (6.4±0.8±0.8)%. Combining these results, we calculate B(Λc+→pK−π+) to be (4.3±1.0±0.8)%.
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