5 research outputs found
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 the reaction gamma* p --> phi p in deep inelastic e+ p scattering at HERA
The production of mesons in the reaction (), for GeV and for
virtual photon-proton centre of mass energies () in the range 42-134 GeV,
has been studied with the ZEUS detector at HERA. When compared to lower energy
data at similar , the results show that the \gamma^*p \rightarrow \phid
p cross section rises strongly with . This behaviour is similar to that
previously found for the cross section. This
strong dependence cannot be explained by production through soft pomeron
exchange. It is, however, consistent with perturbative QCD expectations, where
it reflects the rise of the gluon momentum density in the proton at small .
The ratio of , which has previously been
determined by ZEUS to be 0.065 0.013 (stat.) in photoproduction at a mean
of 70 GeV, is measured to be 0.18 0.05 (stat.) 0.03 (syst.) at
a mean of 12.3 GeV and mean of 100 GeV and is thus
approaching at large the value of 2/9 predicted from the quark charges of
the vector mesons and a flavour independent production mechanism.Comment: 22 pages, including 4 figures. Includes some minor editorial change
Dijet angular distributions in direct and resolved photoproduction at HERA
Jet photoproduction, where the two highest transverse energy (\ETJ) jets
have \ETJ above 6 GeV and a jet-jet invariant mass above 23~GeV, has been
studied with the ZEUS detector at the HERA collider. Resolved and direct
photoproduction samples have been separated. The cross section as a function of
the angle between the jet-jet axis and the beam direction in the dijet rest
frame has been measured for the two samples. The measured angular distributions
differ markedly from each other. They agree with the predictions of QCD
calculations, where the different angular distributions reflect the different
spins of the quark and gluon exchanged in the hard subprocess.Comment: 20 pages including 4 figure
Measurement of alpha-s from jet rates in deep inelastic scattering at HERA
Jet production in deep inelastic scattering for ~GeV has
been studied using data from an integrated luminosity of 3.2~pb
collected with the ZEUS detector at HERA. Jets are identified with the JADE
algorithm. A cut on the angular distribution of parton emission in the
-parton centre-of-mass system minimises the experimental and
theoretical uncertainties in the determination of the jet rates. The jet rates,
when compared to (^2\alpha_{s}(Q)Q^2\alpha_{s}(Q)Q=M_{Z^0}\alpha_{s}(M_{Z^0}) =
0.117~\pm~0.005~(stat)~^{+0.004}_{-0.005}~(syst_{exp})~
~{\pm~0.007}~(syst_{theory})$.Comment: 22 pages, latex, 4 figures appended as uuencoded fil