J.F. Loude

Measurement of the pion axial form factor from radiative decay

Abstract The decay π + → e + νγ has been measured by detecting the positron with a magnetic spectrometer and the photon with an array of NaI scintillators. Using CVC to compute the vector form factor from the π 0 lifetime we use our data to determine the ratio γ of the axial-vector form factor to the vector form factor. With the best present value for the π 0 lifetime (0.897±0.022±0.017)×10 −16 s and F V =(2.55 ±0.05)×10 −2 we obtain two solutions: γ =0.52 ±0.06, favored by a likelihood ratio greater than 8.5 against γ =−2.48±0.06.

Use of a neural network to exploit light division in a triangular scintillating crystal

Abstract This work presents a novel way of exploiting light division in a scintillating crystal to localise the point of interaction using a neural network. Because sensitivity at the centre of a positron tomograph would be significantly increased for a spherical geometry compared to a cylinder with the same area of detection, we explored the possibility of developing a position-sensitive triangular block detector that might be used ultimately as an element of a spherical shell. With 3 PMTs coupled on each side of a triangular BaF 2 crystal of about 8 cm 2 × 1 cm, we obtain spatial resolutions less than 4 mm FWHM over the whole surface of the triangle and energy resolutions of about 14% FWHM for 662 keV impinging photons. Experimental measurements are compared with Monte Carlo simulations and prospects for different configurations are discussed.

A measurement of the inclusive π0 and η production cross sections at high pT in p̄p and pp collisions at s = 24.3 GeV

Abstract Inclusive π 0 and η production at large transverse momentum were studied in both pp and pp interactions at √ s = 24.3 GeV. The experiment was performed using an internal molecular hydrogen gas jet target in the CERN SPS collider. No significant differences between production in pp and pp were observed in the transverse momentum range 2.5 P T c .

Characterisation of arrays of avalanche photodiodes for small animal positron emission tomography

Abstract Characteristics of recently developed arrays of avalanche photodiodes (APDs) are investigated with the perspective of replacing photomultiplier tubes in small animal positron emission tomography. Quantum efficiency of the APDs is measured as a function of wavelength in the VIS–UV region. Gain and capacitance are determined at fixed temperatures as a function of bias voltage. Finally, bulk and surface contributions to the dark current are estimated.

Precise comparison of antiproton-proton and proton-proton forward elastic scattering at √s = 24.3 GeV

Abstract We report results from a measurement of antiproton-proton and proton-proton small-angle elastic scattering at √ s = 24.3 GeV in the range 0.001 ⩽ | t | ⩽ 0.06 (GeV/ c ) 2 . The measurement was performed at the CERN p p Collider by using silicon detectors to observe protons recoiling from a hydrogen cluster-jet target intercepting the stored p and p beams. Fits to the measured differential cross sections yield the ratio of the real to the imaginary part of the forward nuclear scattering amplitude ρ and the nuclear slope parameter b for both p p and pp. We find that the difference Δρ = ρ ( p p ) − ρ( pp ) = 0.031 ± 0.010 agrees with conventional fits and disagrees with the “odderon” fit designed to accommodate the recent UA4 measurement of ρ( p p) at 546 GeV.

Determination of αs and the gluon distribution using direct photon production in pp and pp collisions

Abstract Direct photon cross sections obtained in p p and pp collisions at √s = 24.3 GeV at the CERN SPS, are used in a next-to-leading order QCD analysis. From the cross-section difference σ( p p → γX) − σ (pp → γX) , and quark distributions measured in deep inelastic scattering, a determination of the strong coupling constant, αs, is performed via a measurement of Λ (4) MS . This first measurement of Λ (4) MS using direct photon data yields a value Λ (4) MS = 235 ± 79 (stat.) ± 70 (syst.) MeV. The corresponding value of αs expressed at MZ2 is αs (MZ2) = 0.112±0.006 (stat.)±0.005 (syst.)−0.001+0.009 (theor.). The gluon distribution in the proton for x > 0.2 is determined both from the p p and from the pp data, and the results agree with each other and with previous determinations using the same method.

Measurement of the inclusive J / psi production cross-sections in anti-p p and p p collisions at s**(1/2) = 24.3-GeV

Abstract The inclusive cross section times branching ratio for J/ψ→e + e − has been measured in the forward region in the UA6 experiment for p p and pp collisions at √ s = 24.3 GeV. The ratio of the pp to p p cross sections is found to be 0.76 ± 0.14 ± 0.06. This demonstrates that gluon-gluon fusion dominates over quark-antiquark annihilation in the formation of the c c state.

Direct photon production in pp and pp interactions at √s=24.3 GeV

Abstract Inclusive direct photon invariant cross sections have been measured in both p p and pp collisions at √ s = 24.3 GeV at the CERN SPS, permitting the first measurement of the difference of the p p and pp cross sections. The direct photon cross section in p p collisions has been found to be systematically larger than that in pp collisions, which indicates a significant contribution of the q q annihilation term as predicted by theoretical calculations.

Cathode charge sampling readout system for MWPC

Abstract In order to reach a horizontal spatial resolution of about 0.1 mm in the two arms spectrometer of the CERN UA-6 experiment, it is planned to add to the MWPC an induced charge cathode readout system. The construction of the chambers and the cathode readout electronics are described. Results of preliminary tests are given.

A lead/proportional-tube electromagnetic calorimeter for direct photon detection

Abstract The fine-grained lead/proportional-tube electromagnetic calorimeter used in CERN experiment UA6 is described. Test-beam results demonstrate linear energy response over a wide dynamic range, position resolution for shower localization reaching 1.7 mm for 70 GeV electrons, and good electron/hadron differentiation. Electron shower transverse widths are measured to be less than 9.0 mm for energies between 3 and 70 GeV. This feature allows us to identify neutral-meson decays yielding two close photon showers that constitute the main background to single-photon detection.