M. Valdata-Nappi

Measurement of elastic scattering in antiproton-proton collisions at 52.8 GeV centre-of-mass energy

We measured the differential cross section for pp and pp elastic scattering in the momentum-transfer range 0.01 0.09 GeV2, bpp = 10.68 ± 0.26 GeV−2. Using the optical theorem, we obtained for the total cross section σtot(pp)= 44.86 ± 0.78 mb and, by integrating the differential cross section, we obtained for the total elastic cross section σel(pp) = 7.89 ± 0.28 mb. Calculations of σtot combining elastic-rate and total-rate measurements are also given. All of these measurements were also performed for pp scattering at the same energy, and the results for both reactions are compared.

Precision measurement of proton-proton total cross section at the CERN intersecting storage rings

Abstract The measurement of the proton-proton total cross section performed by the CERN-Pisa-Rome-Stony Brook Collaboration at the CERN ISR is discussed in detail. The total interaction rate, the elastic scattering rate in the forward direction, and the machine luminosity were measured simultaneously to obtain three different determinations of the total cross section. Consistent results were found, which made it possible to prove the reliability of the Van der Meer luminosity calibration within +-0.9% and to achieve a precision of +-0.6% in the measurement of the total cross section.

The electromagnetic calorimeter of the NOMAD experiment

Abstract A description is given of the NOMAD electromagnetic calorimeter, consisting of 875 lead-glass counters read out by two-stage photomultipliers and a low noise electronic chain. The detector operates in a 0.4 T magnetic field transverse to the counter axis. The paper discusses the design criteria, the lead-glass characteristics, the properties of the read out chain and provides a summary of the calorimeter performance.

A study of the transverse fluctuations of hadronic showers in the NOMAD electromagnetic calorimeter

Abstract The transverse shower shape of the energy deposition of hadrons in the NOMAD lead glass calorimeter has been studied by exposing a prototype of this calorimeter to pion test beams of various momenta and incident angles. Large event-to-event fluctuations in the shower shape and significant energy depositions far from the incident hadron were observed making it difficult to associate all the deposited energy to the incident hadron that caused it. Since in the NOMAD detector the momenta of charged hadrons are measured by a magnetic spectrometer, such an association is necessary to be able to subtract from the calorimeter all the energy caused by the observed charged hadrons in order to avoid double counting. Probability functions based on the measurements have been developed to describe fluctuations of the lateral shower shape. Starting from these functions, an algorithm is developed for identifying the energy deposition associated to a charged hadron. The identification and separation of overlapping showers based on these functions is also discussed. The Monte Carlo simulation of the calorimeter reproduces the test beam data well therefore allowing the application of the algorithm at angles and momenta not studied in the test beam.

Precise measurements of proton-antiproton and proton-proton total cross sections at the CERN intersecting storage rings

Abstract A detailed account is given of high-precision measurements of the total hadronic cross sections of proton-antiproton and proton-proton interactions at centre-of-mass energies of 30.6, 52.8 and 62.7 GeV. The experiment was performed at the CERN Intersecting Storage Rings (ISR) using the total interaction-rate method, in which additive correction terms for trigger losses were held to less than 6% of the final result. An experimental determination of the vertical beam-displacement scale permitted luminosity-monitor calibrations to be made with high intrinsic accuracy. The overall precision (systematic and statistical errors combined) achieved in the total cross sections was ± 1.1% for proton-antiproton reactions and 0.7% for proton-proton reactions. In the proton-proton case the measurement was the most precise such measurement made at the ISR.

Test beam performance of the electromagnetic calorimeter of the NOMAD experiment

Abstract Test beam results of the NOMAD electromagnetic calorimeter are presented showing linearity, signal uniformity, energy and position resolution measured in an electron beam. Tests were also performed placing the calorimeter in a magnetic field of 0.4 T. Results on the π rejection obtained using a combined measurement of preshower/electromagnetic calorimeter are found to be in good agreement with the project expectations. Finally the calorimeter response to the muons is discussed.

A HIGH STABILITY LIGHT EMITTING DIODE SYSTEM FOR MONITORING LEAD GLASS ELECTROMAGNETIC CALORIMETERS

Abstract We have designed, built and tested a high stability system based on blue light emitting diodes (LED) and current pulse generators for calibration and monitoring of lead-glass calorimeters. This apparatus is presently being used for the electromagnetic calorimeter of the WA96 (NOMAD) experiment at CERN. The system was developed to minimize the sensitivity to temperature variations, different loadings, and ageing effects. Tests performed both in the laboratory and in the experiment showed that the response of the lead-glass calorimeter modules to LED light pulses could be kept within the precision of ±1% for periods of several months.

Performance of the UA2 jet vertex detector at the CERN collider

Abstract The UA2 jet vertex detector, a drift chamber with jet geometry, was successfully operated during the 1987 and 1988 CERN pp Collider runs. A description of the chamber and a comparison between test-beam results and the chambers performance during the Collider runs are given.

Measurement of the antiproton-proton total cross section and elastic scattering at the CERN intersecting storage rings

Abstract We measured the total cross section for p p scattering at √s = 53 GeV at the CERN ISR. The method was based on the measurement of the total interaction rate and of the ISR luminosity. The result obtained, σtot = 44.1 ± 2.0 mb, suggests that σ tot ( p p) starts increasing at ISR energies. A measurement of the p p differential cross section was also performed: the results show a change in the slope at |t| ≈ 0.1 GeV2, similar to that observed in pp scattering.

Evidence of a rise in the antiproton-proton total cross section at the CERN intersecting storage rings

Abstract We measured the total cross section for p p scattering at s = 52.8 GeV at the CERN ISR, using the direct, total-rate method. The result obtained, σ tot ( p p ) = 44.70 ± 0.53 mb , shows that, in common with σtot(pp), this cross section also starts to rise in the ISR energy range. We remeasured the total cross section for pp scattering at the same energy, obtaining σtot(pp) = 43.26 ± 0.33 mb, and found for the difference, Δσ tot = σ tot ( p p ) − σ tot ( pp ) , a value of 1.44±0.45 mb.