17 research outputs found
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
A collection of modelling problems carried out in the academic year 1995-1996 by the ECMI-students at the Eindhoven University of Technology
A collection of modelling problems carried out in the academic year 1995-1996 by the ECMI-students at the Eindhoven University of Technology
Current perspectives on in vitro maturation and its effects on oocyte genetic and epigenetic profiles
Study of D*(2010)+- Production in ep Collisions at HERA
We report the first observation of charmed mesons with the ZEUS detector at HERA using the decay channel D*(+) --> (D-0 --> K(-)pi(+)) pi(+) (+ c.c.). Clear signals in the mass difference Delta M=M(D*)-M(D-0) as well as in the M(K pi) distribution at the D-0 mass are found. The ep cross section for inclusive D*(+/-) production with Q(2) c ) over bar cX)=(0.45+/-0.11(-0.22)(+0.37)) mu b at root s=296 GeV and [W]=198 GeV. The average gamma p charm cross section sigma(gamma p --> c $($) over bar cX) is found to be (6.3+/-2.2(-3.0)(+6.3)) mu b at [W]=163 GeV and (16.9+/-5.2(-8.5)(+13.9)) mu b at [W]=243 GeV. The increase of the total charm photoproduction cross section by one order of magnitude with respect to low energy data experiments is well described by QCD NLO calculations using singular gluon distributions in the proton
Diffractive hard photoproduction at HERA and evidence for the gluon content of the pomeron
Inclusive jet cross sections for events with a large rapidity gap with
respect to the proton direction from the reaction with quasi-real photons have been measured with the ZEUS detector. The cross
sections refer to jets with transverse energies ~GeV. The data
show the characteristics of a diffractive process mediated by pomeron exchange.
Assuming that the events are due to the exchange of a pomeron with partonic
structure, the quark and gluon content of the pomeron is probed at a scale
. A comparison of the measurements with model predictions
based on QCD plus Regge phenomenology requires a contribution of partons with a
hard momentum density in the pomeron. A combined analysis of the jet cross
sections and recent ZEUS measurements of the diffractive structure function in
deep inelastic scattering gives the first experimental evidence for the gluon
content of the pomeron in diffractive hard scattering processes. The data
indicate that between 30\% and 80\% of the momentum of the pomeron carried by
partons is due to hard gluons.Comment: 25 pages, latex, 4 figures appended as uuencoded file. No change
w.r.t. previous version (just avoiding warning latex messages while
processing
Inclusive jet differential cross-sections in photoproduction at HERA
Inclusive jet differential cross sections for the reaction ep --> jet + X at Q(2) below 4 GeV2 have been measured with the ZEUS detector at HERA using an integrated luminosity of 0.55 pb(-1). These cross sections are given in the kinematic region 0.2 < y < 0.85, for jet pseudorapidities in the ep-laboratory range -1 < eta(jet) < 2 and refer to jets at the hadron level with a cone radius of one unit in the eta - phi plane. These results correspond to quasi-real photoproduction at centre-of-mass energies in the range 130-270 GeV and, approximately, for jet pseudorapidities in the interval -3 < eta(jet)(gamma p CMS) < 0. These measurements cover a new kinematic regime of the partonic structure of the photon, at typical scales up to similar to 300 GeV2 and photon fractional momenta down to x(y) similar to 10(-2). Leading logarithm parton shower Monte Carlo calculations, which include both resolved and direct processes and use the predictions of currently available parametrisations of the photon parton distributions, describe in general the shape and magnitude of the measured eta(jet) and E(T)(jet) distributions