N.W. Tanner

A radium assay technique using hydrous titanium oxide adsorbent for the Sudbury Neutrino Observatory

Abstract As photodisintegration of deuterons mimics the disintegration of deuterons by neutrinos, the accurate measurement of the radioactivity from thorium and uranium decay chains in the heavy water in the Sudbury Neutrino Observatory (SNO) is essential for the determination of the total solar neutrino flux. A radium assay technique of the required sensitivity is described that uses hydrous titanium oxide adsorbent on a filtration membrane together with a β−α delayed coincidence counting system. For a 200 tonne assay the detection limit for 232 Th is a concentration of ∼3×10 −16 g Th/g water and for 238 U of ∼3×10 −16 g U/g water. Results of assays of both the heavy and light water carried out during the first 2 years of data collection of SNO are presented.

Cross section measurement of the π−p→π−π+n reaction near threshold

Abstract Result of cross section measurements for the reaction π − p → π − π + n are presented. They cover a range of incident pion momenta between 295 and 450 MeV/ c . It is the first time that the cross section has been measured so close to threshold. The experiment was performed with Omicron, a large-solid-angle spectrometer, which enables a measurement of the full set of kinematic variables. In the region of overlap there is a good agreement with other experiments. The extracted value for the chiral-symmetry-breaking parameter ξ is seen to be largely extrapolition dependent but the measured value of -0.5±0.8 leaves Weinbergs prediction of ξ =0 the only remaining choice.

Optical properties of an EMI K2CsSb bialkali photocathode

Abstract A measurement of the angular and polarisation dependence of the reflectance of an EMI 9124B K 2 CsSb bialkali photocathode, with the photomultiplier immersed in water, has allowed an unambiguous determination of the K 2 CsSb complex refractive index (2.7 ± 0.1 + i(1.5 ± 0.1) at 442 nm wavelength) and thickness (23 ± 2 nm). The wavelength dependence of the refractive index has been obtained from a re-analysis of “three intensities” data from Timan [H. Timan, Optical characteristics and constants of high efficiency photoemitters, Revue Technique Thomson-CSF 8 (1976) 49]. A detailed study of K 2 CsSb optical properties (absorptance, reflectance and transmittance) has been performed using the above results as reference points.

Measurement of π−p→π−pπ0 reaction near threshold and breaking of chiral symmetry

Abstract A full-kinematics measurement of the π − p→ π − p π 0 reaction in the incident π − momentum region from 295 to 450 MeV/ c is presented. The measurement was performed with the OMICRON spectrometer at the CERN synchrocyclotron. An incident-momentum dependent number of π − p→ π − p π 0 events, ranging from 6 to 430 has been extracted from collected data. Differential cross sections are found to be consistent with phase-space distributions. Integrated cross-sections are used to determine the value of the chiral symmetry breaking parameter ξ. The measured value of ξ =0.1 −0.7 +0.5 is obtained in a model-independent way, strongly favouring Weinbergs choice of ξ =0.

Light concentrators for the Sudbury Neutrino Observatory

Abstract There is an important and growing class of elementary particle detectors which are characterized by a large sensitive volume (thousands of tonnes), very low radioactive backgrounds, and rely on the emission of light for particle detection. Water Cherenkov detectors come into this category; they have a large mass of water as the sensitive medium. Particles are detected when they interact with the water and produce Cherenkov light, so detection efficiency relies on having a huge light sensitive area at the periphery of the detector. The most cost-effective way of achieving this is by placing light concentrators on large photomultiplier tubes (PMTs). This paper describes the work carried out on light concentrators for the PMTs in the Sudbury Neutrino Observatory, a 1000 tonne heavy water Cherenkov detector. We discuss the advantages of using light concentrators, summarize the optical theory of non-imaging light concentration, and describe in detail the development and manufacture of the concentrators themselves.

Measurement of the reaction π+p→π+π+n near threshold

The reaction π+p→π+π+n was studied in the vicinity of the reaction threshold at ten incident pion beam momenta from 297 MeV/c to 480 MeV/c. From data angular distributions, invariant mass spectra and integrated cross-sections were deduced. The chiral symmetry breaking parameter as determined by this reaction equals to ξ=1.56±0.26±0.39, where the first error is experimental, while the latter reflects the uncertainty in the ansatz used in the extrapolation to the reaction threshold. A comparison with the other reaction channels of the reaction πp→ππN indicates that a single parameter (ξ) is not sufficient to describe low energy ππ interactions.

Design and performance of a magnetic spectrometer for the study of πp → ππN reactions near threshold

Abstract A measurement of the cross sections of several π p → ππ N reaction channels in the region of incident pion momenta of 300 to 460 MeV/ c has been performed with Omicron, a multi-arm magnetic spectrometer of large solid angle. This paper describes the apparatus, the trigger, the readout and data-acquisition systems and the off-line analysis. Sample data illustrating the operation of the apparatus are also presented.

A long liquid Cherenkov counter for 300 to 460 MeV/c pion beams

Abstract A long liquid Cherenkov counter has been used to measure the proportion of muons in positive and negative pion beams in the momentum range between 300 and 460 MeV/ c . A nine-parameter function fits all the spectra well. The data show a smooth dependence on incident momenta and agree with calculations of pion and muon pulse heights.

A Cherenkov radiation source for photomultiplier calibration

Abstract The Sudbury Neutrino Observatory (SNO) will detect the Cherenkov radiation from relativistic electrons produced from neutrino interactions in a heavy water (D 2 O) target. A Cherenkov radiation source is required that will enable the efficiency of the photomultipliers to detect this radiation to be calibrated in situ. We discuss such a source based upon the encapsulation of a 90 Sr solution in a glass bulb, and describe its construction. The Cherenkov light output of this source is computed using the theory of Frank and Tamm and an EGS4 Monte Carlo code is used to propagate the beta decay electrons. As an example of the use of this source, the single photoelectron counting efficiency of an EMI 9350 photomultiplier was measured as a function of the applied voltages, given that the quantum efficiency of its photocathode was known. The single photoelectron counting efficiencies obtained were in the range 73–87% and these are consistent with the measurements of other authors using photomultipliers of a broadly similar design.

π − p → π 0 π 0 n near threshold and chiral symmetry breaking

Total cross sections, angular, and mass distributions for the reaction {pi}{sup {minus}}{ital p}{r arrow}{pi}{sup 0}{pi}{sup 0}{ital n} have been measured for {ital p}{sub {pi}}{sup {minus}}(lab)=7--140 MeV/{ital c} above threshold. The threshold amplitude was used to determine a value for the chiral-symmetry-breaking parameter, {xi}, of {minus}0.98{plus minus}0.52. The {pi}{pi} scattering lengths {ital a}{sub {ital I}} for isospin {ital I}=0 and 2 are derived from this result, together with a current-algebra sum rule. The results are {ital a}{sub 0}=(0.207{plus minus}0.028){ital m}{sub {pi}}{sup {minus}1} and {ital a}{sub 2}=({minus}0.022{plus minus}0.011){ital m}{sub {pi}}{sup {minus}1}. These values are consistent with chiral symmetry broken by the Weinberg {pi}{pi} interaction and the effects of the {ital f}{sub 0}(975) scalar meson.