84 research outputs found
Measurement of the diffractive structure function in deep inelastic scattering at HERA
This paper presents an analysis of the inclusive properties of diffractive
deep inelastic scattering events produced in 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 \xpom, the momentum fraction lost by the proton, of , the momentum
fraction of the struck quark with respect to \xpom, and of . The \xpom
dependence is consistent with the form \xpoma where
in all bins of and
. In the measured range, the diffractive structure function
approximately scales with at fixed . In an Ingelman-Schlein type
model, where commonly used pomeron flux factor normalisations are assumed, it
is found that the quarks within the pomeron do not saturate the momentum sum
rule.Comment: 36 pages, latex, 11 figures appended as uuencoded fil
Observation of hard scattering in photoproduction events with a large rapidity gap at HERA
Events with a large rapidity gap and total transverse energy greater than 5
GeV have been observed in quasi-real photoproduction at HERA with the ZEUS
detector. The distribution of these events as a function of the
centre of mass energy is consistent with diffractive scattering. For total
transverse energies above 12 GeV, the hadronic final states show predominantly
a two-jet structure with each jet having a transverse energy greater than 4
GeV. For the two-jet events, little energy flow is found outside the jets. This
observation is consistent with the hard scattering of a quasi-real photon with
a colourless object in the proton.Comment: 19 pages, latex, 4 figures appended as uuencoded fil
Observation of Events with an Energetic Forward Neutron in Deep Inelastic Scattering at HERA
In deep inelastic neutral current scattering of positrons and protons at the center of mass energy of 300 GeV, we observe, with the ZEUS detector, events with a high energy neutron produced at very small scattering angles with respect to the proton direction. The events constitute a fixed fraction of the deep inelastic, neutral current event sample independent of Bjorken x and Q2 in the range 3 · 10-4 \u3c xBJ \u3c 6 · 10-3 and 10 \u3c Q2 \u3c 100 GeV2
Measurement of Weak Neutral Current Couplings of Quarks at HERA
: We present methods to determine the Neutral Current (NC) axial and vector couplings of the quarks at HERA. Without beam polarisation, limits on deviations from the Standard Model (SM) value of the axial coupling of the uptype quark to the Z 0 may be obtained using ratios of NC cross sections to Charged Current (CC) cross sections. Assuming an electron (positron) beam polarisation of 70%, ratios of polarised NC and CC cross sections may be used to set limits on deviations of the up-type quark vector coupling from the SM value. We show that with an integrated luminosity of 1000 pb \Gamma1 , divided equally between the left- and right-handed electron and positron beams, fractional errors on v u ; a u ; v d and a d of 13%, 6%, 17% and 17% may be obtained from a full fit, while if the d (u) quark couplings are held fixed while the u (d) quark couplings are allowed to vary then the errors on v u (v d ) and a u (a d ) are 4% (6%) and 4% (10%) respectively. 1 Introduction The Standard..
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