P. A. Dorsaz

Production of high transverse momentum prompt photons and neutral pions in proton-proton interactions at 280 GeV/c

The inclusive cross sections for production of prompt photons and π0s by 280 GeV/c protons incident on a liquid hydrogen target, have been measured forpT in the range 4.0 to 6.5 GeV/c and for |xF|<0.45. A quantitative comparison of the prompt photon cross section with next-to-leading order QCD predictions using Duke and Owens structure functions is performed. Phenomenological fits to the π0 and prompt photon cross sections are given.

High transverse momentum prompt photon production by π− and π+ on protons at 280 GeV/c

The inclusive cross sections for prompt photon production by π− and π+ on protons have been measured with a beam momentum of 280 GeV/c using a fine grained electromagnetic calorimeter and the CERN Omega spectrometer. The transverse momentum and FeynmanxF ranges covered are 4.0<pT<7.0GeV/c and −0.45<xF<0.55 respectively. A quantitative comparison of the prompt photon cross section with next-to-leading order QCD predictions using Duke and Owens structure functions is performed.

A lead-liquid scintillator electromagnetic calorimeter for direct photon physics

Abstract A fine-grained sampling electromagnetic calorimeter using liquid scintillator contained in teflon tubes, its associated electronics and reconstruction programs, as used in an experiment on direct photons at CERN, are described. The performance of the system based on three years of operation is discussed.

Double prompt photon production at high transverse momentum byπ− on protons at 280 GeV/c

A search for pairs of highpT prompt photons produced in hydrogen by a 280 GeV/c incidentπ- beam has been carried out using a fine-grained electromagnetic calorimeter and the Omega spectrometer at the CERN SPS. Clear evidence for the existence of such events is found with a six standard deviation signal forpT>3.0 GeV/c. The cross-sections are consistent with beyond leading order QCD calculations. A discussion on the determination of αs is also presented.

A 1152 channel timing system for an electromagnetic calorimeter readout

Abstract A 1152 channel timing system used with a large electromagnetic calorimeter is described. Analysis of the timing information from the vertical and horizontal elements of the calorimeter yielded values for the position coordinates of the showers. This information was used to resolve ambiguities in the pattern recognition arising from multiple showers. A resolution of better than 0.25 ns for all channels was achieved. The calibration methods employed to maintain this resolution over several years are discussed.

High transverse momentum π0 production by π− and π+ on protons at 280 GeV/c

The inclusive cross sections for π0 production by π− and π+ on protons have been measured with a beam momentum of 280 GeV/c using a fine grained electromagnetic calorimeter and the CERN Omega spectrometer. The transverse momentum and FeynmanxF ranges covered are 4.0<pT<7.0 GeV/c and −0.45<xF<0.6 respectively. The data are compared with leading order QCD calculations.

Study of the performance of a large sample of Philips photomultipliers type XP2972

Abstract The gain of the Philips XP2972 phototube was measured as a function of time and anode current using 3456 tubes in conditions simulating the experimental situation at the CERN SPS. After an initial ageing period of 35 h, the mean gain variation was measured to be 0.7% with an rms of 0.5% over 12 h at constant anode current ( I a =1.6 μ A). At an approximately constant gain of 2.2×10 5 , the majority (88%) of the tubes show an increase in gain with an average of 1.6% and an rms of 1.1% when the anode current rises from about 10 nA to 1.6 μA. These characteristics were used to select and distribute the tubes on the electromagnetic calorimeter of the CERN WA70 experiment. Short term instability and photocathode homogeneity were studied on a reduced sample.

High pT trigger electronics for a large orthogonal readout electromagnetic calorimeter

Abstract A trigger system has been designed and built to select events containing high p T electromagnetic showers detected in a large calorimeter with orthogonal readout. The electronics include analog adders with up to 123 inputs, pulse shapers with 20 ns integration time, 100 MHz flash ADCs and ECL loop-up tables. The total number of input channels is 3072 and the trigger decision is made in about 120 ns.

Calibration of an electromagnetic calorimeter for direct photon physics

Abstract A large lead-liquid scintillator electromagnetic calorimeter has been built for a “direct photon” experiment at CERN. Gain equalisation and monitoring of the calorimeter were achieved by two complementary computer-controlled calibration systems, a laser system connected by optical fibres and a system of moveable radioactive sources. Final corrections to the equalisation were made using the physics data recorded during the experiment.

High transverse momentumη production in π−p, π+p, andpp interactions at 280 GeV/c

The inclusive cross sections for η production by the interactions of 280 GeV/c momentum π−, π+, and proton beams in hydrogen have been measured. The kinematical range covered is −0.45<xF<0.45, and 4.0<PT<7.0 GeV/c for FeynmanxF and transverse momentum respectively. The η to π0 cross section ratios are given for the three reactions. The ratio of π−p to π+p cross sections for η production in the above kinematic ranges is 1.22±0.08±0.11.