Properties of the hadronic final state in photoproduction events with large transverse energy are studied at the electron-proton collider HERA. Distributions of the transverse energy, jets and underlying event energy are compared to\(\bar pp\) data and QCD calculations. The comparisons show that theγp events can be consistently described by QCD models including — in addition to the primary hard scattering process — interactions between the two beam remnants. The differential jet cross sectionsdσ/dE T jet anddσ/dη jet are measured.

The H1 detector at HERA at DESY presently undergoes a major upgrade. In this context silicon strip detectors have been installed at the beginning of 1995. The high bunch crossing frequency of HERA (10.4 MHz) demands a novel readout architecture which includes pipelining, signal processing and data reduction at a very early stage. The front end readout is hierarchically organized. The detector elements are read out by the APC chip which contains an analog pipeline and performs first background subtraction. Up to five readout chips are controlled by a Decoder Chip. The readout processor module (OnSiRoC) operates the detectors, controls the Decoder Chips and performs a first level data reduction. The paper describes the readout architecture of the H1 silicon detectors and performance data of the complete readout chain.

The cross sections for the charged current processes {ie566-1} and, for the first time, {ie566-2} are measured at HERA for transverse momenta larger than 25 GeV.

We present a new measurement of the total photoproduction cross section performed with the H1 detector at HERA. For an average centre of mass energy of 200 GeV a value of σ tot λp =165±2±11µb has been obtained. A detailed analysis of the data in adequate kinematic regions enabled a decomposition of the total cross section in its elastic, single diffractive dissociation and remaining non-diffractive parts, based on safe assumptions on the double diffractive dissociation contribution.

A leading order determination of the gluon density in the proton has been performed in the fractional momentum range 1.9 · 10−3 < xg/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.