38 research outputs found
Energy Flow in the Hadronic Final State of Diffractive and Non-Diffractive Deep-Inelastic Scattering at HERA
An investigation of the hadronic final state in diffractive and
non--diffractive deep--inelastic electron--proton scattering at HERA is
presented, where diffractive data are selected experimentally by demanding a
large gap in pseudo --rapidity around the proton remnant direction. The
transverse energy flow in the hadronic final state is evaluated using a set of
estimators which quantify topological properties. Using available Monte Carlo
QCD calculations, it is demonstrated that the final state in diffractive DIS
exhibits the features expected if the interaction is interpreted as the
scattering of an electron off a current quark with associated effects of
perturbative QCD. A model in which deep--inelastic diffraction is taken to be
the exchange of a pomeron with partonic structure is found to reproduce the
measurements well. Models for deep--inelastic scattering, in which a
sizeable diffractive contribution is present because of non--perturbative
effects in the production of the hadronic final state, reproduce the general
tendencies of the data but in all give a worse description.Comment: 22 pages, latex, 6 Figures appended as uuencoded fil
A Search for Selectrons and Squarks at HERA
Data from electron-proton collisions at a center-of-mass energy of 300 GeV
are used for a search for selectrons and squarks within the framework of the
minimal supersymmetric model. The decays of selectrons and squarks into the
lightest supersymmetric particle lead to final states with an electron and
hadrons accompanied by large missing energy and transverse momentum. No signal
is found and new bounds on the existence of these particles are derived. At 95%
confidence level the excluded region extends to 65 GeV for selectron and squark
masses, and to 40 GeV for the mass of the lightest supersymmetric particle.Comment: 13 pages, latex, 6 Figure
Scale influence on the energy dependence of photon - proton cross-sections
The scale dependence of the evolution of photoproduction cross sections with the photon-proton centre of mass energy W is studied using low Q 2 < 0.01 GeV 2 e + p interactions collected by the H1 experiment at HERA. The value of the largest transverse momentum of a charged particle in the photon fragmentation region is used to define the hard scale. The slope of the W dependence of the cross section is observed to increase steeply with increasing transverse momentum. The result is compared to measurements of the Q 2 evolution of the W dependence of the virtual photon-proton cross section. Interpretations in terms of QCD and in terms of Regge phenomenology are discussed
Evolution of e p fragmentation and multiplicity distributions in the Breit frame
Low x deep-inelastic ep scattering data, taken in 1994 at the H1 detector at
HERA, are analysed in the Breit frame of reference. The evolution of the peak
and width of the current hemisphere fragmentation function is presented as a
function of Q and compared with e+e- results at equivalent centre of mass
energies. Differences between the average charged multiplicity and the
multiplicity of e+e- annihilations at low energies are analysed. Invariant
energy spectra are compared with MLLA predictions. Distributions of
multiplicity are presented as functions of Bjorken-x and Q^2, and KNO scaling
is discussed.Comment: 24 pages, 9 Figures, figure 2 correcte
Search for excited fermions with the H1 detector
We present a search for excited electrons, neutrinos and quarks using the H1
detector at the collider HERA, based on data taken in 1994 with an
integrated luminosity of 2.75 pb. Radiative decays of excited quarks and
neutrinos have been investigated as well as decays of excited electrons into
all possible electroweak gauge bosons. No evidence for new particle production
is found and exclusion limits are derived.Comment: 20 pages, latex, 6 Figure