Showing papers by "Hermann Kolanoski published in 1999"

Diffractive dijet production at HERA

Abstract: Interactions of the type ep → eXY are studied, where the component X of the hadronic final state contains two jets and is well separated in rapidity from a leading baryonic system Y. Analyses are performed of both resolved and direct photoproduction and of deep-inelastic scattering with photon virtualities in the range 7.5 < Q 2 < 80 GeV2. Cross sections are presented where Y has mass M Y < 1.6 GeV, the squared four-momentum transferred at the proton vertex satisfies |t| < 1 GeV2 and the two jets each have transverse momentum p T jet > 5 GeV relative to the photon direction in the rest frame of X. Models based on a factorisable diffractive exchange with a gluon dominated structure, evolved to a scale set by the transverse momentum $$\hat p_T $$ of the outgoing partons from the hard interaction, give good descriptions of the data. Exclusive $$q\bar q$$ production, as calculated in perturbative QCD using the squared proton gluon density, represents at most a small fraction of the measured cross section. The compatibility of the data with a breaking of diffractive factorisation due to spectator interactions in resolved photoproduction is investigated.

The electronics of the H1 lead/scintillating-fibre calorimeters-H1 SpaCal Group

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.

Charmonium spectroscopy from inclusive $’ and j/$ radiative decays*

Abstract: Results from a detailed study using the Crystal Ball detector at SPEAR of the inclusive photon spectra from 1.8. lo6 $J’ and 2.2. lo6 J/lc, decays are presented. Radiative transitions from the 9’ to the x2,1,0 states are observed with photon energies of (126.0 f 0.2 f 4) MeV, (169.6 f 0.3 f 4) MeV and (258.4 f 0.4 f 4) MeV and branching ratios B($’ -+ 7 x,,,,,) = (8.0 f 0.5 f 0.7)%, (9.0 f 0.5 f 0.7)%, and (9.9 It 0.5 f 0.8)‘?’ 0, respectively. Values for the natural line widths of the x states are obtained: I’(x,,,,,) = (0.8 4.9) MeV, (< 3.8) MeV and (1321) MeV, respectively (90% C.L.). I m roved values are found for the branching p ratios B(~!J’ + 7r],) = (0.28 f 0.06)?’ o and B(J/$ + 7~~) = (1.27 kO.36)%, and forthe natural width I’(r],) = (11.5 f 4.5) MeV. 1. SPECTROSCOPY OF THE 4 FAMILY Since the discovery of the resonances of the ci~ charmonium family more than a decade ago, the T/J’ and J/+ h ave continued to stimulate considerable theoretical and experimental interest to explore the spectrum of states accessible via radiative photon decays. Potential models’ and dispersion relation models2 have predicted the spectrum of states, radiative transition rates, and natural line widths, in lowest order quantum chromodynamics (&CD). Calculations of relativistic and higher order QCD corrections3 have also been made. Two early experiments measured the inclusive photon spectra in J/$J and $’ decays. Ten years ago the Mark I magnetic detector, sensitive to converted photons above 200 MeV, discovered the $’ + 7x,, transition4 at the SPEAR e+ecolliding ring. In a short run at SPEAR the SP-27 experiment5 used a moderately segmented NaI(T1) detector to obtain a highly structured photon spectrum in $’ decays. The $’ radiative decay branching ratios to each of the triplet 1 3P2,1,~ (XJ) states6 were measured and found to be significantly below the naive potential model predictions. In a more recent work7 at the CERN-ISR and using a very different technique, the x2,1 states have also been measured. Furthermore a candidate for the 1 lS’0 ground state, the r],(2980) was observed in the inclusive photon spectra from G’ and J/$ decays by the Crystal Ball experiment.8 This state was confirmed in exclusive decays of the $J’ by the Mark II experiment9 and has recently been well measured by the Mark III experiment” which also determined the spin and parity to be O+. The Crystal Ball also reported existence of a 2 lS0 candidate,ll the vL(3590) seen in the $J’ inclusive photon spectrum. A candidate for the lP1 state has not been observed so far.12 In this paper we present final results of a detailed study of the radiative tran-

Large-System Experience with the ASD-8 Chip in the HERA-B Experiment

Abstract: The ampliier-shaper-discriminator chip ASD-8, developed by the University o f P ennsylvania for drift chamber applications in high rate environments, is used in large detector systems in the HERA-B experiment. We report on the results of tests performed on some 25 000 chips and on the design and tests of the PC-boards. The so far largest system employing ASD-8 chips is the HERA-B Outer Tracker with about 120 000 drift chamberchannels. We present rst experience with the grounding scheme, noise suppression and the slow c o n trol system as well as rst measurements with the full readout chain in the HERA-B experiment.