[Show abstract][Hide abstract] ABSTRACT: Single particles and jets in deeply inelastic scattering at low x are measured with the H1 detector in the region away from the current jet and towards the proton remnant, known as the forward region. Hadronic final state measurements in this region are expected to be particularly sensitive to QCD evolution effects. Jet cross sections are presented as a function of Bjorken-x for forward jets produced with a polar angle to the proton direction, θjet, in the range 7° < θjet < 20°. Azimuthal correlations are studied between the forward jet and the scattered lepton. Charged and neutral single particle production in the forward region are measured as a function of Bjorken-x, in the range 5° < θ < 25°, for particle transverse momenta larger than 1 GeV. QCD based Monte Carlo predictions and analytical calculations based on BFKL, CCFM and DGLAP evolution are compared to the data. Predictions based on the DGLAP approach fail to describe the data, except for those which allow for a resolved photon contribution.
[Show abstract][Hide abstract] ABSTRACT: The electronic system developed for the SpaCal lead/scintillating-fibre calorimeters of the H1 detector in operation at the HERA ep collider is described in detail and the performance achieved during H1 data taking is presented. The 10 MHz bunch crossing rate of HERA puts severe constraints on the requirements of the electronics. The energy and time readout are performed, respectively, with a 14-bit dynamic range and with a resolution of ∼0.4 ns. The trigger branch consists of a nanosecond-resolution calorimetric time of flight for background rejection and an electron trigger based on analog ‘sliding windows’. The on-line background rejection currently achieved is ∼106. The electron trigger allows a low-energy trigger threshold to be set at ∼0.50±0.08 (RMS) GeV with an efficiency ⩾99.9%. The energy and time performance of the readout and trigger electronics is based on a newly developed low noise (σnoise∼0.4 MeV) wideband (f⩽200 mHz) preamplifier located at the output of the photomultipliers which are used for the fibre light readout in the ∼1 T magnetic field of H1.
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment - NUCL INSTRUM METH PHYS RES A. 01/1999; 426(2):518-537.
[Show abstract][Hide abstract] ABSTRACT: Quasi-elastic (z>0.95) photo-production of ψ(2S) mesons has been observed at HERA for photon-proton centre-of-mass energies in the range 40 to 160 GeV. The ψ(2S) mesons were identified through their decays to ℓ+ℓ−, and to J/ψπ+π−, where the J/ψ subsequently decays to ℓ+ℓ−, the lepton ℓ being either a muon or an electron. The cross-section for quasi-elastic photoproduction was measured to be (18.0±2.8(stat)±3.0(syst)) nb at a photon-proton centre-of-mass energy of 80 GeV. The ratio of the ψ(2S) to J/ψ quasi-elastic cross-sections is (0.150±0.027(stat)±0.022(syst)).
Physics Letters B - PHYS LETT B. 01/1998; 421(1):385-394.
[Show abstract][Hide abstract] ABSTRACT: The new lead/scintillating-fibre calorimeter (“SpaCal”) for the backward region of the H1 experiment at HERA (DESY) is equipped with fine mesh phototubes which operate in a magnetic field close to 1 T. A large sample of these tubes of the types Hamamatsu R5505 and R5506, and Hamamatsu R2490-05, have been tested in fields of up to 1.2T. We have investigated the cathode homogeneity with and without magnetic field, the gain loss under the influence of the magnetic field, and stability with time. For a subsample of tubes, we have performed additional studies on stability with respect to temperature changes, variation of gain as a function of the magnetic field, high voltage discharges, single photo-electron response, and linearity. We finally summarize the experience with these tubes after one year of operation in the experiment.
[Show abstract][Hide abstract] ABSTRACT: 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 (xF) variable for charged particles, the squared transverse momentum of charged particles (pT∗2), and the mean pT∗2 as a function of xF. These distributions are compared with results in the γ∗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 Q2 by hard gluons.
[Show abstract][Hide abstract] ABSTRACT: The scale dependence of the evolution of photoproduction cross sections with the photon-proton centre of mass energy W is studied using low Q2 < 0.01 GeV2e+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 Q2 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.