Extracting QCD Vacuum Parameters from Exclusive J/ψ Photoproduction at HERA

by Tobias Toll (IIT Delhi)

Tuesday 22 Sept 2026, 11:00 → 13:00 US/Eastern

In the dual superconductor picture, the QCD vacuum is a condensate of chromomagnetic monopoles characterised by two lengths: the penetration depth λ of the chromoelectric field and the coherence length ξ of the condensate. These have previously been accessible only through lattice calculations of static flux tubes. However, they can instead be measured in exclusive diffraction, where the transverse profile of a gluonic hotspot is the vacuum’s response to a localised colour source and obeys the same Ginzburg–Landau boundary-value problem. Fitting Clem’s vortex profile to all 104 available H1 and ZEUS exclusive J/ψ photoproduction points, spanning |t| < 30 GeV2 and 40 ≤ W ≤ 251 GeV, we obtain χ2/ndf = 0.77 and extract λ = 0.21(2) fm, ξv = 0.109(9) fm, and a Ginzburg–Landau parameter κ = 2.1(4), placing the QCD vacuum in the type-II regime. The corresponding vector and scalar masses, 1/λ = 0.94(9) GeV and 1/ξv = 1.81(14) GeV, agree with lattice determinations of the lightest gluelump and glueball respectively, and the Ginzburg–Landau line tension implied by (λ, κ) directly reproduces the QCD string tension.