Measurement of proton-dissociative diffractive photoproduction of vector mesons at large momentum transfer at HERA: The ZEUS collaboration
European Physical Journal C 26:3 (2003) 389-409
Abstract:
Diffractive photoproduction of vector mesons, γp → VY, where Y is a proton-dissociative system, has been measured in e+p interactions with the ZEUS detector at HERA using an integrated luminosity of 25 pb-1. The differential cross section, dσ/dt, is presented for 1.2 < -t < 12 GeV2, where t is the square of the four-momentum transferred to the vector meson. The data span the range in photon-proton centre-of-mass energy, W, from 80 GeV to 120 GeV. The t distributions are well fit by a power law, dσ/dt ∝ (-t)-n. The slope of the effective Pomeron trajectory, measured from the W dependence of the ρ0 and φ cross sections in bins of t, is consistent with zero. The ratios dσγp→φY/dt to dσγp→ρ0Y/dt and dσγp→J/ψY/dt to dσγp→ρ0Y/dt increase with increasing -t. Decay-angle analyses for ρ0, φ and J/ψ mesons have been carried out. For the ρ0 and φ mesons, contributions from single and double helicity flip are observed. The results are compared to expectations of theoretical models.Search for resonance decays to lepton+jet at DESY HERA and limits on leptoquarks
Physical Review D - Particles, Fields, Gravitation and Cosmology 68:5 (2003) 520041-5200415
Abstract:
A search for narrow-width resonances that decay into electron+jet or neutrino+jet has been performed with the ZEUS detector at the DESY ep collider HERA operating at center-of-mass energies of 300 and 318 GeV. An integrated e+p luminosity of 114.8 pb-1 and e-p luminosity of 16.7 pb-1 were used. No evidence for any resonance was found. Limits were derived on the Yukawa coupling λ as a function of the mass of a hypothetical resonance that has arbitrary decay branching ratios into eq or vq. These limits also apply to squarks predicted by R-parity-violating supersymmetry. Limits for the production of leptoquarks described by the Buchmüller-Rückl-Wyler model were also derived for masses up to 400 GeV. For λ = 0.1, leptoquark masses up to 290 GeV are excluded.Demonstration of lasing at 41.8 nm in Xe8+ driven in a plasma waveguide
P SOC PHOTO-OPT INS 5197 (2003) 105-118
Abstract:
We describe the first demonstration of a collisionally-excited optical field ionisation laser driven within a gas-filled capillary waveguide. Lasing on the 4d(9)5d-4d(9)5p transition at 41.8 nm in Xe8+ was observed to be closely-correlated to conditions under which the pump laser pulses were guided well by the waveguide. Simulations of the propagation of the pump laser radiation show that gain was achieved over essentially the whole 30 mm length of the waveguide.Measurement of high-Q2 e-p neutral current cross sections at HERA and the extraction of xF3
EUROPEAN PHYSICAL JOURNAL C 28:2 (2003) 175-201
Measurement of proton-dissociative diffractive photoproduction of vector mesons at large momentum transfer at HERA
EUROPEAN PHYSICAL JOURNAL C 26:3 (2003) 389-409