S. Mango

A compact versatile dilution refrigerator with top-loading capability

Abstract The design and characteristics of a compact versatile 3 He evaporation/ 3 He 4 He dilution refrigerator with central access to the mixing chamber are described. The sample holding device and /or the refrigerator unit can be removed from or inserted into the cryostat at 4 K. The apparatus is reliable and service-friendly. The version with a continuous heat exchanger reaches 50 mK, and at 100 mK its cooling power is 1 mW. A version with two sintered silver heat exchangers reaches around 30 mK.

Detection of nuclear recoils in prototype dark matter detectors, made from Al, Sn and Zn superheated superconducting granules

Abstract This work is part of an ongoing project to develop a superheated superconducting granule (SSG) detector for cold dark matter and neutrinos. The response of SSG devices to nuclear recoils has been explored irradiating SSG detectors with a 70 MeV neutron beam. The aim of the experiment was to test the sensitivity of Sn, Al and Zn SSG detectors to nuclear recoil energies down to a few keV. The detector consisted of a hollow teflon cylinder (0.1 cm 3 inner volume) filled with tiny superconducting metastable granules embedded in a dielectric medium. The nuclear recoil energies deposited in the SSG were determined measuring the neutron scattering angles with a neutron hodoscope. Coincidences in time between the SSG and the hodoscope signals have been clearly established. In this paper the results of the neutron irradiation experiments at different SSG intrinsic thresholds are discussed and compared to Monte Carlo simulations. The results show that SSG are sensitive to recoil energies down to ∼ 1 keV. The limited angular resolution of the neutron hodoscope prevented us from measuring the SSG sensitivity to even lower recoil energies.

Dynamic nuclear polarization in thin polymer foils and tubes

Abstract First results of DNP at 2.5 T and below 0.3 K in thin polymer foils and tubes with the chemical composition (CX 2 ) n , [ X = 1 H, 2 D, 19 F ], doped with TEMPO, are presented. Appreciable polarization of protons, deuterons, and 19 F-nuclei were obtained. The samples can be handled at room temperature for several hours, and therefore they are suitable for new applications.

Polarized scintillator targets

Abstract The hydrogen nuclei in an organic scintillator have been polarized to more than 80% and the deuterons in its fully deuterated version to 24%. The scintillator, doped with TEMPO, has been polarized dynamically in a field of 2.5 T in a vertical dilution refrigerator in which a plastic lightguide transports the scintillation light from the sample in the mixing chamber to a photomultiplier outside the cryostat. Sizeable solid samples with acceptable optical properties and light output have been prepared and successfully operated as “live” polarized targets in nuclear physics experiments.

Full angular distribution of the analysing power in p elastic scattering at 697 MeV/c

Abstract Full angular distributions of the differential cross-section dσ/dμ and of the analysing power Ay in p p elastic scattering have been measured at 697 MeV/c. The results of Ay are compared with the predictions of various theoretical models.

Measurement of ΔσL in pp scattering between 200 and 583 MeV

Abstract The main structure around m = 2.15 GeV first observed by the Argonne group in the spin-dependent total cross section Δσ L is confirmed in the energy range available at SIN. A simultaneous study of the scattered particles at small angles has been carried out with success and gave the spin-correlation parameter A 00 kk for the pp elastic scattering and for the reaction pp → π + d. The contribution of the 3-body reactions to this spin-dependent total cross section has been deduced and found to be lower than the contribution of the π + d reaction even at 583 MeV.

Search for the hypothetical π → μx decay

Abstract The KARMEN collaboration has reported the possible observation of a hitherto unknown neutral and weakly interacting particle x, which is produced in the decay π+ → μ+x with a mass mx = 33.9 MeV. We have searched for this hypothetical decay branch by studying muons from pion decay in flight with the LEPS spectrometer at the πE3 channel at PSI and find branching ratios BR(π − → μ − x ) −7 and BR(π+ → μ+x)

Spin-dependent neutron-proton total cross section differences ΔσL and ΔσT from 140 to 590 MeV

Abstract A polarized neutron beam at PSI has been used to measure the spin-dependent neutron-proton total cross sections Δσ L and Δσ T from 140 to 590 MeV. The results are compared with recent phase-shift calculations.

Low-energy analyzing powers in pion proton elastic scattering

Analyzing powers of pion-proton elastic scattering have been measured at PSI with the Low Energy Pion Spectrometer LEPS as well as a novel polarized scintillator target. Angular distributions between 40 and 120 deg (c.m.) were taken at 45.2, 51.2, 57.2, 68.5, 77.2, and 87.2 MeV incoming pion kinetic energy for � + p scattering,

The ORPHEUS dark matter experiment

Abstract A progress report of the ORPHEUS dark matter experiment in the Bern Underground Laboratory is presented. A description of the ORPHEUS detector and its sensitivity to WIMPs is given. The detector will consist of 1 to 2 kg Sn granules operating in a magnetic field of approximately 320 G and at a temperature of 50 mK. In the first phase, the detector will be read out by conventional pickup coils, followed by a second phase with SQUID loops. Preliminary results on background and radioactivity measurements are shown.