41 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
Low Q^2 Jet Production at HERA and Virtual Photon Structure
The transition between photoproduction and deep-inelastic scattering is
investigated in jet production at the HERA ep collider, using data collected by
the H1 experiment. Measurements of the differential inclusive jet
cross-sections dsigep/dEt* and dsigmep/deta*, where Et* and eta* are the
transverse energy and the pseudorapidity of the jets in the virtual
photon-proton centre of mass frame, are presented for 0 < Q2 < 49 GeV2 and 0.3
< y < 0.6. The interpretation of the results in terms of the structure of the
virtual photon is discussed. The data are best described by QCD calculations
which include a partonic structure of the virtual photon that evolves with Q2.Comment: 20 pages, 5 Figure
Hadron Production in Diffractive Deep-Inelastic Scattering
Characteristics of hadron production in diffractive deep-inelastic
positron-proton scattering are studied using data collected in 1994 by the H1
experiment at HERA. The following distributions are measured in the
centre-of-mass frame of the photon dissociation system: the hadronic energy
flow, the Feynman-x (x_F) variable for charged particles, the squared
transverse momentum of charged particles (p_T^{*2}), and the mean p_T^{*2} as a
function of x_F. These distributions are compared with results in the gamma^* p
centre-of-mass frame from inclusive deep-inelastic scattering in the
fixed-target experiment EMC, and also with the predictions of several Monte
Carlo calculations. The data are consistent with a picture in which the
partonic structure of the diffractive exchange is dominated at low Q^2 by hard
gluons.Comment: 16 pages, 6 figures, submitted to Phys. Lett.
Measurement of D* Meson Cross Sections at HERA and Determination of the Gluon Density in the Proton using NLO QCD
With the H1 detector at the ep collider HERA, D* meson production cross
sections have been measured in deep inelastic scattering with four-momentum
transfers Q^2>2 GeV2 and in photoproduction at energies around W(gamma p)~ 88
GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe
the differential cross sections within theoretical and experimental
uncertainties. Using these calculations, the NLO gluon momentum distribution in
the proton, x_g g(x_g), has been extracted in the momentum fraction range
7.5x10^{-4}< x_g <4x10^{-2} at average scales mu^2 =25 to 50 GeV2. The gluon
momentum fraction x_g has been obtained from the measured kinematics of the
scattered electron and the D* meson in the final state. The results compare
well with the gluon distribution obtained from the analysis of scaling
violations of the proton structure function F_2.Comment: 27 pages, 9 figures, 2 tables, submitted to Nucl. Phys.
The Gluon density of the proton at low x from a QCD analysis of F2
We present a QCD analysis of the proton structure function measured by
the H1 experiment at HERA, combined with data from previous fixed target
experiments. The gluon density is extracted from the scaling violations of
in the range and compared with an
approximate solution of the QCD evolution equations. The gluon density is found
to rise steeply with decreasing .Comment: 17 pages, latex2e, 5 figures appended as uuencoded file, hep number
include
Transverse energy and forward jet production in the low x regime at HERA
The production of transverse energy in deep inelastic scattering is measured
as a function of the kinematic variables and using the H1 detector at
the ep collider HERA. The results are compared to the different predictions
based upon two alternative QCD evolution equations, namely the
Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) and the
Balitsky-Fadin-Kuraev-Lipatov (BFKL) equations. In a pseudorapidity interval
which is central in the hadronic centre of mass system between the current and
the proton remnant fragmentation region the produced transverse energy
increases with decreasing for constant . Such a behaviour can be
explained with a QCD calculation based upon the BFKL ansatz. The rate of
forward jets, proposed as a signature for BFKL dynamics, has been measured.Comment: 16 pages, latex, 4 figures appended as uuencoded fil
Comparison of deep inelastic scattering with photoproduction interactions at HERA
Photon-proton () interactions with~~GeV and
deep-inelastic scattering () interactions with photon virtualities
~GeV are studied at the high energy electron-proton collider HERA.
The transverse energy flow and relative rates of large rapidity gap events are
compared in the two event samples. The observed similarity between
and interactions can be understood in a picture where the photon
develops as a hadronic object. The transverse energy density measured in the
central region of the collision, at in the centre of
mass frame, is compared with data from hadron-hadron interactions as function
of the CMS energy of the collision.Comment: 15 pages, latex, 4 figures appended as uuencoded fil
A Direct determination of the gluon density in the proton at low x
A leading order determination of the gluon density in the proton has been performed in the fractional momentum range 1.9 · 10 −3 < x g / p < 0.18 by measuring multi-jet events from boson-gluon fusion in deep-inelastic scattering with the H1 detector at the electron-proton collider HERA. This direct determination of the gluon density was performed in a kinematic region previously not accessible. The data show a considerable increase of the gluon density with decreasing fractional momenta of the gluons
Measurement of the e+ and e- induced charged current cross-sections at HERA
The cross sections for the charged current processes
and, for the first time,
are measured at HERA for
transverse momenta larger than 25 GeV.Comment: 21 pages, latex, 10 figures appended as uuencoded fil