A search for excited fermions in electron-proton collisions at HERA
Zeitschrift für Physik C Particles and Fields 65:4 (1995) 627-647
Abstract:
A search for excited states of the standard model fermions was performed using the ZEUS detector at the HERA electron-proton collider, operating at a centre of mass energy of 296 GeV. In a sample corresponding to an integrated luminosity of 0.55 pb-1, no evidence was found for any resonant state decaying into final states composed of a fermion and a gauge boson. Limits on the coupling strength times branching ratio of excited fermions are presented for masses between 50 GeV and 250 GeV, extending previous search regions significantly. © 1995 Springer-Verlag.Measurement of elastic ρ 0 photoproduction at HERA
Zeitschrift für Physik C: Particles and Fields 69:1 (1995) 39-54
Abstract:
Elastic ρ 0 photoproduction has been measured using the ZEUS detector at HERA. Untagged photoproduction events from ep interactions were used to measure the reaction γp→ρ 0 p(ρ 0)→π +π-) at photon-proton centre-of-mass energies between 60 and 80 GeV and |t|<0.5 GeV2, where t is the square of the four-momentum transferred at the proton vertex. The differential cross section dσ/d M ππ where M ππ is the invariant mass of the two pions, and the integrated cross section, σγp→ρ{variant}0ρ{variant}, are presented; the latter was measured to be 14.7±0.4 (stat.) ±2.4 (syst.)μb. The differential cross section dσ/dt has an approximately exponential shape; a fit of the type A t ′ exp(-b t ′ |t|+c t ′ t 2) yields a t-slope b t ′ =9.9±1.2 (stat.) ±1.4 (syst.) GeV-2. The results, when compared to low energy data, show a weak energy dependence of both σγp→ρ{variant}0p and of the t-slope. The ρ 0 is produced predominantly with transverse polarisation, demostrating that s-channel helicity conservation holds at these energies. © 1996 Springer-Verlag.Measurement of the diffractive structure function in deep inelastic scattering at HERA
Zeitschrift für Physik C Particles and Fields 68:4 (1995) 569-584
Abstract:
This paper presents an analysis of the inclusive properties of diffractive deep inelastic scattering events produced in ep interactions at HERA. The events are characterised by a rapidity gap between the outgoing proton system and the remaining hadronic system. Inclusive distributions are presented and compared with Monte Carlo models for diffractive processes. The data are consistent with models where the pomeron structure function has a hard and a soft contribution. The diffractive structure function is measured as a function of xℙ, the momentum fraction lost by the proton, of β, the momentum fraction of the struck quark with respect to xℙ, and of Q2 in the range 6.3·10-4Measurement of the proton structure function F 2 at low x and low Q 2 at HERA
Zeitschrift fur Physik C-Particles and Fields 69:1 (1995) 607-620
Abstract:
We report on a measurement of the proton structure function F 2 in the range 3.5×10-5≤x≤4×10-3 and 1.5 GeV2≤Q 2≤15GeV2 at the ep collider HERA operating at a centre-of-mass energy of √s=300GeV. The rise of F 2 with decreasing x observed in the previous HERA measurements persists in this lower x and Q 2 range. The Q 2 evolution of F 2, even at the lowest Q 2 and x measured, is consistent with perturbative QCD. © 1996 Springer-Verlag.Measurement of αs from jet rates in deep inelastic scattering at HERA
Physics Letters B 363:3 (1995) 201-216