Measurement of isolated photons accompanied by jets in deep inelastic ep scattering
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 715:1-3 (2012) 88-97
Abstract:
The production of isolated high-energy photons accompanied by jets has been measured in deep inelastic ep scattering with the ZEUS detector at HERA, using an integrated luminosity of 326pb -1. Measurements were made for exchanged photon virtualities, Q 2, in the range 10 to 350GeV 2. The photons were measured in the transverse-energy and pseudorapidity ranges 4Search for first-generation leptoquarks at HERA
Physical Review D - Particles, Fields, Gravitation and Cosmology 86:1 (2012)
Abstract:
A search for first-generation leptoquarks was performed in electron-proton and positron-proton collisions recorded with the ZEUS detector at HERA in 2003-2007 using an integrated luminosity of 366pb-1. Final states with an electron and jets or with missing transverse momentum and jets were analyzed, searching for resonances or other deviations from the standard model predictions. No evidence for any leptoquark signal was found. The data were combined with data previously taken at HERA, resulting in a total integrated luminosity of 498pb-1. Limits on the Yukawa coupling, λ, of leptoquarks were set as a function of the leptoquark mass for different leptoquark types within the Buchmüller-Rückl-Wyler model. Leptoquarks with a coupling λ=0.3 are excluded for masses up to 699 GeV. © 2012 American Physical Society.Scaled momentum distributions for K S 0 and ∧/∧ in DIS at HERA
Journal of High Energy Physics 2012:3 (2012)
Abstract:
Scaled momentum distributions for the strange hadrons K S0 and ∧/∧were measured in deep inelastic ep scattering with the ZEUS detector at HERA using an integrated luminosity of 330 pb -1. The evolution of these distributions with the photon virtuality, Q 2, was studied in the kinematic region 10 < Q 2 < 40000 GeV 2 and 0.001 < x < 0.75, where x is the Bjorken scaling variable. Clear scaling violations are observed. Predictions based on different approaches to fragmentation were compared to the measurements. Leading-logarithm parton-shower Monte Carlo calculations interfaced to the Lund string fragmentation model describe the data reasonably well in the whole range measured. Nextto-leading-order QCD calculations based on fragmentation functions, FFs, extracted from e +e - data alone, fail to describe the measurements. The calculations based on FFs extracted from a global analysis including e +e -, ep and pp data give an improved description. The measurements presented in this paper have the potential to further constrain the FFs of quarks, anti-quarks and gluons yielding K S0 and ∧/∧ strange hadrons. © SISSA 2012.Angular correlations in three-jet events in ep collisions at HERA
Physical Review D - Particles, Fields, Gravitation and Cosmology 85:5 (2012)
Abstract:
Three-jet production in deep inelastic ep scattering and photoproduction was investigated with the ZEUS detector at HERA using an integrated luminosity of up to 127pb-1. Measurements of differential cross sections are presented as functions of angular correlations between the three jets in the final state and the proton-beam direction. These correlations provide a stringent test of perturbative QCD and show sensitivity to the contributions from different color configurations. Fixed-order perturbative calculations assuming the values of the color factors CF, CA, and TF as derived from a variety of gauge groups were compared to the measurements to study the underlying gauge group symmetry. The measured angular correlations in the deep inelastic ep scattering and photoproduction regimes are consistent with the admixture of color configurations as predicted by SU(3) and disfavour other symmetry groups, such as SU(N) in the limit of large N. © 2012 American Physical Society.Measurement of the t dependence in exclusive photoproduction of Υ{hooked} (1S) mesons at HERA
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 708:1-2 (2012) 14-20