22 research outputs found
Limits on the effective quark radius from inclusive scattering at HERA
The high-precision HERA data allows searches up to TeV scales for Beyond the
Standard Model contributions to electron-quark scattering. Combined
measurements of the inclusive deep inelastic cross sections in neutral and
charged current scattering corresponding to a luminosity of around 1
fb have been used in this analysis. A new approach to the beyond the
Standard Model analysis of the inclusive data is presented; simultaneous
fits of parton distribution functions together with contributions of "new
physics" processes were performed. Results are presented considering a finite
radius of quarks within the quark form-factor model. The resulting 95% C.L.
upper limit on the effective quark radius is cm.Comment: 10 pages, 4 figures, accepted by Phys. Lett.
Measurement of the cross-section ratio sigma_{psi(2S)}/sigma_{J/psi(1S)} in deep inelastic exclusive ep scattering at HERA
The exclusive deep inelastic electroproduction of and
at an centre-of-mass energy of 317 GeV has been studied with the ZEUS
detector at HERA in the kinematic range GeV,
GeV and GeV, where is the photon virtuality, is the
photon-proton centre-of-mass energy and is the squared four-momentum
transfer at the proton vertex. The data for GeV were taken in
the HERA I running period and correspond to an integrated luminosity of 114
pb. The data for GeV are from both HERA I and HERA II
periods and correspond to an integrated luminosity of 468 pb. The decay
modes analysed were and for the
and for the . The cross-section ratio
has been measured as a function of
and . The results are compared to predictions of QCD-inspired
models of exclusive vector-meson production.Comment: 24 pages, 8 figure
Combined QCD and electroweak analysis of HERA data
A simultaneous fit of parton distribution functions (PDFs) and electroweak parameters to HERA data on deep inelastic scattering is presented. The input data are the neutral current and charged current inclusive cross sections which were previously used in the QCD analysis leading to the HERAPDF2.0 PDFs. In addition, the polarisation of the electron beam was taken into account for the ZEUS data recorded between 2004 and 2007. Results on the vector and axial-vector couplings of the Z boson to u- and d-type quarks, on the value of the electroweak mixing angle and the mass of the W boson are presented. The values obtained for the electroweak parameters are in agreement with Standard Model predictions
Search for a narrow baryonic state decaying to and in deep inelastic scattering at HERA
A search for a narrow baryonic state in the and system has been performed in collisions at HERA with the ZEUS detector using an integrated luminosity of 358 pb taken in 2003-2007. The search was performed with deep inelastic scattering events at an centre-of-mass energy of 318 GeV for exchanged photon virtuality, , between 20 and 100 . Contrary to evidence presented for such a state around 1.52 GeV in a previous ZEUS analysis using a sample of 121 pb taken in 1996-2000, no resonance peak was found in the invariant-mass distribution in the range 1.45-1.7 GeV. Upper limits on the production cross section are set
Studies of the diffractive photoproduction of isolated photons at HERA
The photoproduction of isolated photons has been measured in diffractive events recorded by the ZEUS detector at HERA. Cross sections are evaluated in the photon transverse-energy and pseudorapidity ranges 5 < ETγ< 15 GeV and -0.7 < ηγ< 0.9, inclusively, and also with a jet with transverse energy and pseudorapidity in the ranges 4 < ETjet< 35 GeV and -1.5 < ηjet< 1.8, using a total integrated electronproton luminosity of 456 pb-1. A number of kinematic variables were studied and compared to predictions from the RAPGAP Monte Carlo model. An excess of data is observed above the RAPGAP predictions for zℙmeas> 0.9, where zℙmeasis the fraction of the longitudinal momentum of the colorless "Pomeron" exchange that is transferred to the photon-jet final state, giving evidence for direct Pomeron interactions
Measurement of the cross-section ratio in deep inelastic exclusive ep scattering at HERA
The exclusive deep inelastic electroproduction of and at an centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range GeV, GeV and GeV, where is the photon virtuality, is the photon-proton centre-of-mass energy and is the squared four-momentum transfer at the proton vertex. The data for GeV were taken in the HERA I running period and correspond to an integrated luminosity of 114 pb. The data for GeV are from both HERA I and HERA II periods and correspond to an integrated luminosity of 468 pb. The decay modes analysed were and for the and for the . The cross-section ratio has been measured as a function of and . The results are compared to predictions of QCD-inspired models of exclusive vector-meson production
Production of exclusive dijets in diffractive deep inelastic scattering at HERA
Production of exclusive dijets in diffractive deep inelastic e(+/-) p scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 372 pb(-1). The measurement was performed for gamma*-p centre-of-mass energies in the range 90 25 GeV2. Energy flows around the jet axis are presented. The cross section is presented as a function of beta and phi, where beta = x/x(P), x is the Bjorken variable and xIP is the proton fractional longitudinal momentum loss. The angle f is defined by the gamma*-dijet plane and the gamma*-e(+/-) plane in the rest frame of the diffractive final state. The f cross section is measured in bins of beta. The results are compared to predictions from models based on different assumptions about the nature of the diffractive exchange