GeV Resonance Research Articles

Hyperon-nucleon final-state interaction in kaon photoproduction on a deuteron

Final state hyperon-nucleon interaction in strangeness photoproduction of the deuteron is investigated making use of the covariant reaction formalism and the P-matrix approach to the YN system. Remarkably simple analytical expression for the amplitude is obtained. Pronounced effects due to final state interaction are predicted including the manifestation of the 2.13 GeV resonance.

Search for anomalous production of high mass photon pairs in e +e − collisions at LEP

A search for events with photon pairs of large invariant mass is described based on a data sample of 43 pb −1 collected with the OPAL detector. This search is motivated by the L3 observation of four events of the type e +e − → l + l − γγ with an invariant mass of the two photons, m γγ , clustering around 60 GeV. In the OPAL data, four ℓ +ℓ −γγ events are found with m γγ above 40 GeV. The number of observed events is consistent with the QED expectation and no obvious resonance structure is seen. Three candidate qq̄γγ events with m γγ above 40 GeV are found and no νν̄nγγ candidate with m γγ > 5 GeV is found. From these searches an upper limit is set on any anomalous production of ℓ +ℓ − γγ (ℓ = e, μ, τ) events, where the ℓ +ℓ − pair comes from a virtual Z 0 and m γγ is near 60 GeV , of B( Z 0 → Z ∗0γγ → ℓ +ℓ −γγ) < 6.0 × 10 −7 at the 95% CL. In a similar search in the reaction e +e − → γγγ, seven events are observed with a photon pairing of mass near 60 GeV compared to an expected background of 2.7 ± 0.4 from QED. In a search for the production of a 60 GeV resonance X in two-photon collisions, an upper limit is set on Γ X B 2(X → γγ) of 2.6 MeV at the 95% CL. A search is also performed for ℓ +ℓ −X (ℓ = e, μ) events in non-γγ decay modes of X. No indication of a 60 GeV resonance is seen. Combining these two searches, Γ X values greater than 110 MeV are excluded at the 95% CL for ℓ +ℓ − γγ (ℓ = e, μ) cross-sections greater than 0.05 pb.

Production characteristics of the F meson

Inclusive cross sections of η production by e +e - annihilation for c.m. energies between 4.0 and 5.0 GeV are presented. The η production is shown to be correlated with the production of a weakly decaying particle, indicating that its main source is F production. At the 4.42 GeV resonance it is correlated with a low energy photon, suggesting F F ∗ or F ∗ F ∗ production. A mass determination of the F is made at 4.42 GeV using the F → ηπ decay channel.

Two-body hadronic decays of the 3.1 GeV resonance

Hadronic two body decays of the 3.1 GeV resonance were measured and the following branching ratios were obtained: Γ π + π −/Γ μ μ <0.0046, Γ K + K −/Γ μ μ <0.0084, and Γ p p/ Γ μ μμ = 0.036 ± 0.010 assuming the p p decay distribution is ≈ + cos 2θ.

Observation of the two photon cascade 3.7 → 3.1 + γγ via an intermediate state P c

The two photon cascade decay of the 3.7 GeV resonance into the 3.1 GeV resonance has been observed in two nearly independent experiments. The clustering of the photon energies around 160 MeV and 420 MeV observed in the channel 3.7 → (3.1 → μ +μ −) + γγ indicates the existence of at least one intermediate state with even charge conjugation at a mass around 3.52 GeV or 3.26 GeV.

Experimental results on the reaction e+e−→photons at the 3.1 GeV resonance

Experimental results on the reaction e+e−→photons at the 3.1 GeV resonance

Dynamical Consequences of a Photon Regge Trajectory

It is argued that the newly discovered narrow resonances are Regge recurrences of the photon Regge trajectory. The widths and masses are calculated using the Anselm-Gribov technique, taking the data on the 3�1 GeV resonance as an input.