K. Pretzl

Review of the development of diamond radiation sensors

Abstract Diamond radiation sensors produced by chemical vapour deposition are studied for the application as tracking detectors in high luminosity experiments. Sensors with a charge collection distance up to 250 μm have been manufactured. Their radiation hardness has been studied with pions, proton and neutrons up to fluences of 1.9×10 15 π cm −2 , 5×10 15 p cm −2 and 1.35×10 15 n cm −2 , respectively. Diamond micro-strip detectors with 50 μm pitch have been exposed in a high-energy test beam in order to investigate their charge collection properties. The measured spatial resolution using a centre-of-gravity position finding algorithm corresponds to the digital resolution for this strip pitch. First results from a strip tracker with a 2×4 cm 2 surface area are reported as well as the performance of a diamond tracker read out by radiation-hard electronics with 25 ns shaping time. Diamond pixel sensors have been prepared to match the geometries of the recently available read-out chip prototypes for ATLAS and CMS. Beam test results are shown from a diamond detector bump-bonded to an ATLAS prototype read-out. They demonstrate a 98% bump-bonding efficiency and a digital resolution in both dimensions.

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.

Tracking with CVD diamond radiation sensors at high luminosity colliders

Recent progress on developing diamond-based sensors for vertex detection at high luminosity hadron colliders is described. Measurements of the performance of diamond sensors after irradiation to fluences of up to 5/spl times/10/sup 15/ hadrons/cm/sup 2/ are shown. These indicate that diamond sensors will operate at distances as close as 5 cm from the interaction point at the Large Hadron Collider (LHC) for many years at full luminosity without significant degradation in performance. Measurements of the quality of the signals from diamond sensors as well as spatial uniformity are presented. Test beam results on measurements of diamond-based microstrip and pixels devices are described.

Review on the development of cryogenic silicon detectors

Abstract In this paper, we report on the performance of heavily irradiated silicon detectors operated at cryogenic temperatures. The results discussed here show that cryogenic operation indeed represents a reliable method to increase the radiation tolerance of standard silicon detectors by more than one order of magnitude. In particular, a 400xa0μm thick “double-p” silicon detector irradiated up to 1×10 15 xa0n/cm 2 delivers a mip signal of about 27xa0000 electrons when operated at 130xa0K and 500xa0V bias. The position resolution of an irradiated microstrip detector, and “in situ” irradiation of a pad detector during operation in the cold are also discussed.

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.

Superheated superconducting granule device: detection of minimum ionizing particles

We present the first efficiency measurement of a superheated superconducting granule (SSG) detector irradiated with minimum ionizing particles (mips). The SSG device is a solenoid readout coil filled with tin granules (22 μm average diameter) embedded (16% volume filling factor) in a good thermal conductor varnish cooled down to T = 490 mK. n nIt is shown that a 2 mm thick detector is close to 100% efficient (1σ over the electronic noise) to mips. The probability of a mip to hit at least one granule, sensitive to an energy deposition of 16 keV or more over the detector length, is approximately 100%. Only 10% of the granules in the detector were sensitive to mips because of the finite granule size distribution and the phase transition smearing observed with this sample.

Radiation hard cryogenic silicon detectors

It has been recently observed that heavily irradiated silicon detectors, no longer functional at room temperature, resuscitate when operated at temperatures below 130 K. This is often referred to as the Lazarus effect. The results presented here show that cryogenic operation represents a new and reliable solution to the problem of radiation tolerance of silicon detectors.

Feasibility study of a Superheated Superconducting Granule detector for cold dark matter search

The presented results are part of a feasibility study of a Superheated Superconducting Granule (SSG) device for weakly interacting massive particles (WIMPs) detection. The sensitivity of SSG to nuclear recoils has been explored irradiating SSG detectors with a 70MeV neutron beam proving that energy thresholds of ∼1keV can be reached in 30µm Zn and 17µm Sn granules. The successful irradiation experiments with neutrons encouraged us to plan a prototype SSG dark matter detector. The status of the project will be presented and the expected counting rate for spin-independent WIMP interactions in SSG detectors will be discussed.

First results with the ORPHEUS dark matter detector

Abstract The ORPHEUS dark matter detector is operating at our underground laboratory in Bern (70 m.w.e.). The detector relies on measuring the magnetic flux variation produced by weakly interacting massive particles (WIMPs) as they heat micron-sized superheated superconducting tin granules (SSG) and induce superconducting-to-normal phase transitions. In an initial phase, 0.45xa0kg of tin granules in a segmented detector volume have been used. In this paper a general description of the experimental setup, overall performance of the detector, and first results are presented.

Phase transition study of superheated planar arrays of tin cylinders

Abstract We have investigated the superheating and the supercooling fields of a planar array of tin cylinders with diameters ranging from 40 to 80 μm and thickness 8.3 μm evaporated onto a glass substrate and onto a kapton foil. Experimental values of the Ginzburg–Landau parameter have been obtained and compared with results from tin spheres. The spread of the superheating curves is below 5%.