C. Joram

Operation of a Fast-RICH Prototype with VLSI readout electronics

Abstract We discuss the first test results, obtained with cosmic rays, of a full-scale Fast-RICH Prototype with proximity-focused 10 mm thick LiF (CaF2) solid radiators, TEA as photosensor in CH4, and readout of 12 × 103 cathode pads (5.334 × 6.604 mm2) using dedicated VLSI electronics we have developed. The number of detected photoelectrons is 7.7 (6.9) for the CaF2 (LiF) radiator, very near to the expected values 6.4 (7.5) from Monte Carlo simulations. The single-photon Cherenkov angle resolution σθ = 19.1 (15.2) mrad for the CaF2 (LiF) radiator, to be compared with 19.3 (13.2) mrad predicted by the Monte Carlo calculations. These first results have shown that the Fast-RICH Prototype works well and that the technique is well-suited for the next generation of high luminosity e+e− or hadron colliders.

Measurement of pion induced double charge exchange on 34S and 56Fe at Tπ = 50 MeV☆

Abstract Measurements of double charge exchange cross sections at an incident π + energy of 50 MeV in the angular range 10°–90° are reported for analog and non-analog transitions on 34 S and 56 Fe. In the case of 56 Fe several individual non-analog transitions have been observed and their angular distributions measured. A state 1.5 MeV below the double isobaric analog state in 56 Ni, which recently has been observed at high incident pion energies as well, shows a peculiar backward peaked angular distribution.

Evidence for a dibaryon resonance in the pionic double charge exchange

New measurements of the pionic double charge exchange on56Fe exhibit a pronounced energy dependence of this reaction at low energies in accordance with similar observations on other nuclei. We show that this peculiar energy dependence finds its natural explanation by a resonance in theπNN subsystem withJp=0−,T=0 and a mass of 2.065 GeV.

Isospin mixing of the 1+ doublet in 12C determined by low-energy pion scattering☆

With the Low Energy Pion Spectrometer (LEPS) at PSI the inelastic scattering of 50 MeV positive and negative pions to the 1+ excitations at 12.71 MeV (T = 0) and 15.11 MeV (T = 1) in 12C has been measured in the angular range 35°−105°. The angular distributions are in good agreement with impulse approximation calcculations. From the double ratio of the 1+ cross sections for π+ and π− scattering an isospin mixing matrix element of H01 = 157 ± 35 keV is derived. In contrast to a previous study of this reaction these results do not question the validity of the impulse approximation at low energies.

Measurement of the π + p→ analyzing power at 68.3 MeV

The analyzing power {ital A}{sub {ital y}} for {pi}{sup +}{ital p{searrow}} scattering at 68.3 MeV has been measured at the Paul Scherrer Institut with the magnetic spectrometer LEPS. The measurements cover the angular range 40{degree}{le}{theta}{sub lab}{le}70{degree}. The protons have been polarized in a butanol target, operated in frozen spin mode. The {ital S}31 phase shift comes out by about 1{degree} smaller than the Koch-Pietarinen [Nucl. Phys. A {bold 336}, 331 (1980)] phase shift analysis, supporting the necessity of an alternative dispersion analysis of {pi}{ital N} scattering to determine the {sigma} term and the {pi}{ital N} coupling constant. {copyright} {ital 1996 The American Physical Society.}

CaF2 single crystals as entrance windows of a fast photosensitive MWPC for a RICH detector

Abstract CaF2 single crystals (162 × 170 × 3.5 mm3) are used as entrance windows for a photosensitive multiwire proportional chamber (MWPC) being the main component of a Fast RICH detector. Thin silver traces (100 μm wide with a pitch of 1.5 mm) have been vacuum evaporated onto the surface of the crystals. Thus the windows can be used as the cathode of the MWPC which is operating with a TEA/methane gas mixture at room temperature. VUV measurements of the optical transmissivity before and after the evaporation reveal a reduction of 7% which is consistent with the geometry of the evaporation mask.

Normalisation of scattering cross sections for low-energy pions☆

Abstract Reliable cross section normalisation of the low-energy scattering of pions has been the source of one of the great weaknesses in that experimental field. Here we describe techniques used at the Low-Energy Pion Spectrometer (LEPS) at PSI/SIN to provide normalisations with a precision of the order of several percent.

Resonance-like behaviour of the pionic double charge exchange at low energies☆

Abstract All presently available data on pionic double charge exchange on nuclei exhibit a resonance-like energy dependence near T π = 50 MeV, while the angular distributions behave quite regularly. We show that these features find their natural explanation by a narrow resonance in the πNN-subsystym with J p = 0 − and a mass of 2.065 GeV.

Precision measurements of low-energy pion scattering on sulphur isotopes

A precise measurement of the elastic and inelastic π±-scattering from 32S and 34S at Tπ = 50 MeV has been performed with the LEPS spectrometer at PSI. Exploiting the enhanced isospin sensitivity of low-energy pions, we obtain a difference in neutron r.m.s.-radii between isotopes of 34rn - 32rn = 0.06(1) fm from the elastic scattering. Analysis of the angular distributions of inelastic scattering to the 21+- and 22+-excitations in 34S yields a ratio of neutron to proton matrix elements of Mn/Mp = + 1.17(9) and - 0.4(2), respectively. The latter result is at variance with previous investigations, but agrees with recent shell model calculations.

Measurement of pi+ p (polarized) analyzing power at 68.3-MeV

The analyzing power {ital A}{sub {ital y}} for {pi}{sup +}{ital p{searrow}} scattering at 68.3 MeV has been measured at the Paul Scherrer Institut with the magnetic spectrometer LEPS. The measurements cover the angular range 40{degree}{le}{theta}{sub lab}{le}70{degree}. The protons have been polarized in a butanol target, operated in frozen spin mode. The {ital S}31 phase shift comes out by about 1{degree} smaller than the Koch-Pietarinen [Nucl. Phys. A {bold 336}, 331 (1980)] phase shift analysis, supporting the necessity of an alternative dispersion analysis of {pi}{ital N} scattering to determine the {sigma} term and the {pi}{ital N} coupling constant. {copyright} {ital 1996 The American Physical Society.}