(Some of) recent $γγ$ measurements from LEP

TL;DR

The paper surveys LEP two-photon processes by reporting DELPHI's measurement of inclusive J/Ψ production in γγ events, ALEPH's η_b search in γγ final states, and ALEPH's double-tagged hadronic γγ cross section. It applies sequential event selections to isolate heavy-quark production, sets upper limits on η_b decays, and contrasts cross sections with LO/NLO QCD and BFKL expectations. Key findings include a dominant resolved-photon contribution to J/Ψ production, no η_b signal with corresponding branching limits, and a double-tagged γγ cross section that challenges NLO QCD and LL BFKL predictions. These results advance understanding of photon structure and QCD dynamics in two-photon processes at LEP energies.

Abstract

Inclusive measurement of $J/Ψ$ (DELPHI), search for $η_b$ (ALEPH) and measurement of the cross-section of the double-tagged $γγ$ events (ALEPH) are briefly overviewed.

Figures (6)

• Figure 1: Left: Reconstructed mass spectrum of identified muon pairs. Right: The best fit of the transverse momentum of the reconstructed $J/\Psi$ with a mixture of resolved and diffractive events simulated with Pythia 6.1.
• Figure 2: Invariant mass spectrum of selected events.
• Figure 3: Pseudorapidity disribution at the detector level. MC predictions are scaled to match the observed number of events.
• Figure 4: Björken x distribution of the corrected data, compared to the MC predictions (scaled to match the observed number of events) and NLO QCD calculations.
• Figure 5: Y distribution of the corrected data, compared to the MC predictions (scaled to match the observed number of events) and NLO QCD calculations.