T. J. Brodbeck

A new method of carrier trapping time measurement

Abstract A new method of measuring carrier trapping time by a simple analysis of the current pulse shape is proposed and demonstrated for irradiated silicon detectors. This method which we call Exponentiated Charge Crossing (ECC) requires no knowledge of either the electric field profile in the detector or of the relation between the carrier drift velocity and the electric field. It is general enough to be valid not only for solid-state particle detectors but also for other devices such as some gaseous and liquid detectors. The results obtained by the proposed method are consistent with those obtained by an earlier method.

The electric field in irradiated silicon detectors

The electric field distribution inside heavily irradiated silicon particle detectors is deduced using observations of α particle and minimum ionising particle signals. In these detectors α particle signals are observed for both p+ and n+ side illumination even when the detector is only partially depleted. The observations indicate that the electric field distribution within the partially depleted detector has the contribution expected from a uniform space charge, as in unirradiated detectors, together with a strong, short range, local electric field in the vicinity of the p+ electrode and a non-zero electric field in the remaining part of the detector.

A spin-parity analysis of the ωπ0 enhancement photoproduced in the energy range 20 to 70 GeV

Abstract A study is made of the ωπ 0 system produced near threshold in the reaction γ p→ π + π − π 0 π 0 p. A spin-parity analysis shows that the ωπ 0 enhancement is consistent with predominant 1 + B(1235) production, with ∼20% J P = 1 − background.

Photoproduction of π+π−π0 on hydrogen with linearly polarized photons of energy 20–70 GeV

Results on photoproduction of π+π−π0 in the photon energy range 20–70 GeV are presented. For the ω meson, the production cross-section is found to be 1010±15 (statistical)±290 (systematic) nb and is constant over the incident photon energy range. Spin-density matrix elements are evaluated for ω meson production. The φ meson is observed with a total photoproduction cross section (corrected for branching ratio to π+π−π0) of 610±35±170 nb. A third resonance, at 1.67 GeV, is seen in the mass spectrum and its interpretation is discussed. The production of a broad π+π−π0 continuum, mainly via ϱπ, and peaking at 1.2 GeV, contributes with a cross section of about 2.5 ωb. The spin-parity content is analysed by the moments of the π+π−π0 decay angular distribution in the helicity frame and by maximum likelihood fits to the π+π−π0 Dalitz plot. It is found that production of JP = 1− states accounts for less than half of the total mass spectrum above 900 MeV. There is a broad enhancement in the 1+ wave around 1.15 GeV indicating photoproduction of the H(1190) meson.

e+-e− pair creation by 40–150 GeV photons incident near the 〈110〈 axis in a germanium crystal

Experimental results are presented on the pair production from high-energy photons (40–150 GeV) incident on a 0.5 mm Ge single crystal around the 〈110〉 axis. The observed enhancement increases from around 1 at threshold (40 GeV) to 7 at 1 50 GeV for photons aligned with the axis. Also the angilar dependence and the differential e+/e− spectra have been studied. For photons aligned with the axis, the results are in good agreement with calculations based on the constant field approximation.

Simulation of charge collection and sharing in microstrip detectors

Abstract The various mechanisms which can cause broadening of the signal distribution in a microstrip detector are discussed, in turn, via a simple simulation. Some analytic results for calculating the effect of dead areas are also presented. A comparison is made of GaAs test beam data with the results of the simulation.

Photoproduction of KK̄π final states in the photon energy range from 20 to 70 GeV

The reactions γp→K+K−π0(p) and γp→ Ks0K± π±(p) have been measured using tagged photons in the energy range 20 to 70 GeV. No resonance structure is observed in either of the KKπ invariant mass distributions, which range from threshold up to ∼ 3 GeV. The photoproduction cross sections for φπ0 and K∗(892)K are presented and are compared with theoretical predictions. No evidence has been found for the photoproduction of φ′ (1680).

A study of elastic photoproduction of low massK+K− pairs from hydrogen in the energy range 2.8–4.8 GeV

The results of an experiment to study elasticK+K− photoproduction are presented. Differential cross sections and spin density matrix elements for ϕ(1.019) production are stddied as a function of incident photon energy and over a wide range of momentum transfer,t (tmin>t>−1.5(GeV/c)2). Helicity conserving amplitudes are observed to dominate ϕ production throughout this range and the differential cross sections exhibit a forward diffractive peak which cannot be understood in terms of a simple exponential dependence. A new value of the photon ϕ coupling constant is determined and shown to be consistent withe+e− annihilation measurements. A detailed study of the energy dependence of the differential cross sections is made, including other experimental data, and the extracted effective Regge trajectory compared with other diffractive processes. A study of the dependence of theK+K− decay angular distribution on invariant mass reveals evidence for ans wave contribution interfering with thep wave ϕ which may be attributable to theS* meson.

Strangeness exchange in the photoproduction ofK+ Λ(1520) between 2.8 and 4.8 GeV

A tagged photon beam (2.8<Eγ<4.8 GeV) and multiparticle spectrometer have been used to study the photoproduction in hydrogen ofK+Λ(1520). Precise values for the mass and width of the Λ(1520) are given. The total cross-section is found to fall with increasing photon energy like (6.5±0.7)Eγ−(2.1±0.2) μb. The differential cross sectiondσ/dt indicates peripheral forward production and exhibits no evidence for shrinkage when compared with higher energy data. The Λ(1520) spin density matrix shows thatK exchange alone cannot account for the production mechanism. The reaction is found to resemble the process γp→K+ Λ(1115) in all measurable respects.

Inclusive photoproduction of single charged particles at highp T

Single charged-particle inclusive cross sections for photon, pion and kaon beams on hydrogen at the CERN-SPS are presented as functions ofpT andxF. Data cover the range 0.0<pT<5.0 GeV/c and 0.0<xF<1.0 at incident momenta from 70 to 170 GeV/c. The comparison between photon- and hadron-induced data indicates a relative excess of particles withpT>1.6 GeV/c for the photon-induced data. Using the hadron-induced data to estimate the hadronic behaviour of the photon, the difference distributions and ratios of cross sections are a measure of the contribution of the point-like photon interactions. The data are compared with QCD calculations and show broadly similar features.