A. Stanovnik

Tests of a multianode PMT for the HERA-B RICH

Abstract A new multianode photomultiplier tube, type H6568 manufactured by Hamamatsu company, has been tested in view of using it for measuring Cherenkov rings in the HERA-B experiment. The results of measurements of single-photoelectron pulse-height distributions, uniformity of response, cross-talk, photon detection efficiency, rate dependence of the gain and ageing will be presented and discussed. In addition, the response of the PMT to scintillations of perfluorobutane (C 4 F 10 ), argon and air has been measured.

The HERA-B RICH

Abstract The design issues and tests carried out with the ring imaging Cherenkov detector for the HERA-B experiment are reviewed. Results of on-the-bench tests of the employed photomultiplier tubes are reported together with the early commissioning measurements with the HERA proton beam.

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.

Multianode photomultipliers as position-sensitive detectors of single photons

Tests of 2300 Hamamatsu multianode photomultipliers (1543 pieces of R5900-M16 and 762 pieces of R5900-M4) have been tested on the bench in order to evaluate their performance for use as position-sensitive photon detectors in the ring imaging Cherenkov counter of the HERA-B experiment.1 A weak and stable source of photons has been obtained by Cherenkov radiation of electrons from a 90Sr source in a quartz radiator. From measurements of the count rate versus high voltage, optimal high-voltage values have been obtained as well as a parameter (RQE) corresponding to the relative quantum e

Tests of a solid CsI photocathode in a thin multiwire proportional chamber

ciency. Distributions of the number of photomultipliers as a function of the optimal high voltage and as a function of the relative quantum e

A multiwire chamber with a CsI photocathode as a detector of Cherenkov radiation

ciency are presented. The measured parameters are in good correlation with those provided by the manufacturer. The stability of the photomultipliers has also been followed over two years. The observed count rate decrease is consistent with the radioactive decay of 90Sr. ( 2000 Elsevier Science B.V. All rights reserved.

Measurement of 90Sr activity with Cherenkov radiation in a silica aerogel

A methane filled, 3 mm thick multiwire chamber with CsI photocathode and NaF window as Cherenkov radiator has been tested with electrons from 90Sr and with cosmic rays. Simulation calculations of the measured pulse height distributions show that the quantum efficiency of solid CsI in a MWPC environment could be close to that measured by Seguinot et al. About 30 Cherenkov photons are detected per cosmic particle traversing 1 cm of NaF. The time spread of Cherenkov signals with respect to a scintillation counter trigger has been measured to be 4.5 ns FWHM. Results are also presented for detector performance over a three months period.

PHOTON DETECTORS FOR THE HERA-B RICH

A multiwire chamber with a CsI photocathode and methane gas filling has been used to measure pulse height distributions of Cherenkov radiation emitted by electrons from 90Sr in a NaF radiator. A clear Cherenkov signal is seen. During one month of operation no deterioration of detector performance has been observed. Simulation calculations based on the results of Seguinot et al. for the quantum efficiency of CsI indicate that the measured event rate is half of that expected. Some possible reasons for this discrepancy are mentioned.

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

A method of determination of 90Y (Eβmax = 2.27 MeV, t12 = 64 h), the daughter of 90Sr (Eβmax = 0.546 MeV, t12 = 28.5 yr), on the basis of Cherenkov radiation of the β particles in a silica aerogel has been tested. The relatively high end-point energy of the 90Y β-spectrum, together with a suitably chosen aerogel refractive index and thus electron threshold energy, permits elimination or at least a considerable reduction of the interference of other β emitters with lower end-point energies. The interference of γ emitters is reduced by using a thin, transmission multiwire proportional chamber in coincidence with the aerogel Cherenkov detector. Any possible contribution of other radionuclides to the count rate may be monitored by the shape of the Cherenkov pulse height spectrum, which depends sensitively on the electron energy. With an aerogel refractive index of 1.055, which corresponds to an electron threshold energy of 1.09 MeV, we have obtained an efficiency of 5 × 10−3 for 90Y. The background counting rate of 15 × 10−3 s−1 is stable (σ = 1 × 10−3s−1) and allows the determination of 1 Bq of 90Y activity in a few hours of measurement of a thin sample. If the ratio of 90Y to 90Sr activity is known (e.g. in equilibrium), the activity of 90Sr may be obtained.

Measurements of the quantum efficiency of CsI photocathodes in a multiwire proportional chamber

Abstract Results of tests of different position-sensitive photon detectors for the HERA-B RICH are given. It is observed, that the CsI-MWPC cannot be routinely produced and maintained with sufficiently high quantum efficiency and that the TMAE detector loses anode wire gain too quickly. The third candidate, the H-6568 Hamamatsu multianode PMT, seems to meet all the requirements necessary for photon detection in the HERA-B RICH.