C. Cosmelli

The gravitational wave detector NAUTILUS operating at T = 0.1 K

Abstract We report on the ultralow-temperature resonant-mass gravitational-wave detector NAUTILUS, operating at the Frascati INFN Laboratories. The present aim of this detector is to achieve a sensitivity sufficient to detect bursts of gravitational radiation from sources located in our Galaxy and in the local group. Progress in transducer technology is likely to lead to sensitivities that will enable us to observe events from sources as far away as the Virgo cluster of galaxies. We describe the cryogenic apparatus, readout system, cosmic-ray veto system, and give first results obtained during one year of continuous operation at T = 0.1 K. In particular the Brownian noise of the detector at T = 0.1 K was measured. The measured strain sensitivity was h ≈ 6 · 10 −22 Hz − 1 2 at the frequencies of the two modes, 908 Hz and 924 Hz, with bandwidths of about 1 Hz.

Study of the coincidences between the gravitational wave detectors EXPLORER and NAUTILUS in 2001

We report the result from a search for bursts of gravitational waves using data collected by the cryogenic resonant detectors EXPLORER and NAUTILUS during 2001 for a total measuring time of 90 days. With these data we repeated the coincidence search performed on the 1998 data (which showed a small coincidence excess) applying data analysis algorithms based on known physical characteristics of the detectors. With the 2001 data, a new interesting coincidence excess is found when the detectors are favourably oriented with respect to the galactic disc.

Energy resolution and efficiency of phonon-mediated kinetic inductance detectors for light detection

The development of sensitive cryogenic light detectors is of primary interest for bolometric experiments searching for rare events like dark matter interactions or neutrino-less double beta decay. Thanks to their good energy resolution and the natural multiplexed read-out, Kinetic Inductance Detectors (KIDs) are particularly suitable for this purpose. To efficiently couple KIDs-based light detectors to the large crystals used by the most advanced bolometric detectors, active surfaces of several cm2 are needed. For this reason, we are developing phonon-mediated detectors. In this paper, we present the results obtained with a prototype consisting of four 40 nm thick aluminum resonators patterned on a 2 × 2 cm2 silicon chip, and calibrated with optical pulses and X-rays. The detector features a noise resolution σE = 154 ± 7 eV and an (18 ± 2)% efficiency.

Increasing the Bandwidth of Resonant Gravitational Antennas: The Case of Explorer

Resonant gravitational wave detectors with an observation bandwidth of tens of hertz are a reality: the antenna Explorer, operated at CERN by the ROG Collaboration, has been upgraded with a new readout. In this new configuration, it exhibits an unprecedented useful bandwidth: in over 55 Hz about its center operating frequency of 919 Hz the spectral sensitivity is better than 10(-20) Hz(-1/2). We describe the detector and its sensitivity and discuss the foreseeable upgrades to even larger bandwidths.

Search for coincident excitation of the widely spaced resonant gravitational wave detectors EXPLORER, NAUTILUS and NIOBE

We report the search for coincidences among three resonant mass detectors: EXPLORER at CERN and NAUTILUS in Frascati of the Rome group and NIOBE in Perth of the UWA group. The three detectors have a sensitivity for short bursts of GW in the h ≈ 10−18 range, about one thousand times better in energy than Webers original detectors. The analysis is based on the comparison of candidate event lists recorded by the detectors in the period December 1994 through October 1996. The events have been obtained by applying a pulse detection filter to the raw data and using a predetermined threshold. Due to the different periods of data taking it was not possible to search for triple coincidences. We searched for coincidences between EXPLORER and NAUTILUS during the years 1995 and 1996 for a total time coverage of 1372 hours and between EXPLORER and NIOBE in 1995 for a coverage of 1362 hours. The results have been: a weak indication of a coincidence excess with respect to the accidental ones between EXPLORER and NAUTILUS and no coincidence excess between EXPLORER and NIOBE.

Return current in hysteretic Josephson junctions: Experimental distribution in the thermal activation regime

We present an experimental study on the retrapping process of a hysteretic, high-quality Josephson junction; namely, we have measured the distribution of the values at which the junction switches back from the voltage state to the zero-voltage state, as a function of the applied magnetic field. While the opposite process (escape from the zero-voltage state) has been extensively studied in the past, both from the theoretical and the experimental point of view, little is found in the literature on the retrapping process. In terms of the tilted washboard potential, the process corresponds to the retrapping from the running state to a locked state in a potential well. The interest of the measurements is in the fact that the value of the return current can be directly related to the dissipation in the junction. While the deterministic behavior, experimentally measured through the I–V curve, appears to be in agreement with the theoretical predictions, even in minor details, the statistical behavior is strongly ...

The low radioactivity link of the CUORE experiment

CUORE will be an array of 988 TeO2 bolometers (5 5 5 cm 3 ) held at about 10 mK. It will study the very rare double b decay process from 130 Te. The electrical connections of the array to the room temperature electronics will consist in about 2000 wires. We will describe the design and characterization of the 3 interconnection sectors going from the detectors to the mixing chamber, the coldest stage at which the array is thermally and mechanically anchored, and from the mixing chamber to room temperature. The lower part consists of a set of 2.3 m long, 50mm thick, Cu-insulator tapes having PEN (Polyethylene 2.6 Naphthalate) substrate, on which a pattern of copper tracks are etched. The differential layout pattern chosen allows obtaining a signal cross talk between adjacent channels of about 0.024%, together with a capacitance of about 26 pF/m and a resistance larger than 200 GW/m. On the top of the mixing chamber, Cu-Kapton boards are used to join the tapes to the second upward-going 2 m long links, implemented with twisted NbTi wires, interwoven in a NOMEX R texture. NbTi-NOMEX link features about 100 pF/m and negligible level of cross-talk. The radioactivity content of Cu-PEN tapes, Cu-Kapton boards, NbTi-NOMEX ribbons and connectors has been investigated and found to be compliant with the experimental requirements. A mechanical study has been done to quote the vibration transmission properties of the highly packaged tapes.

High sensitivity phonon-mediated kinetic inductance detector with combined amplitude and phase read-out

Developing wide-area cryogenic light detectors with baseline resolution better than 20 eV is one of the priorities of next generation bolometric experiments searching for rare interactions, as the simultaneous read-out of the light and heat signals enables background suppression through particle identification. Among the proposed technological approaches for the phonon sensor, the naturally multiplexed Kinetic Inductance Detectors (KIDs) stand out for their excellent intrinsic energy resolution and reproducibility. The potential of this technique was proved by the CALDER project that reached a baseline resolution of 154 ± 7 eV RMS by sampling a 2 × 2 cm2 Silicon substrate with 4 Aluminum KIDs. In this paper, we present a prototype of Aluminum KID with improved geometry and quality factor. The design improvement, as well as the combined analysis of amplitude and phase signals, allowed to reach a baseline resolution of 82 ± 4 eV by sampling the same substrate with a single Aluminum KID.

CUORE EXPERIMENT: THE SEARCH FOR NEUTRINOLESS DOUBLE BETA DECAY

The main purpose of the Cryogenic Underground Observatory for Rare Events (CUORE) experiment is the search for the Neutrinoless Double Beta Decay (0νDBD) of 130Te reaching a sensitivity on Majorana mass better than 50 meV. Cuoricino represents not only the first stage of CUORE, but also the most massive 0νDBD experiment presently running. Present results and future planning of these experiments will be described in the paper.

Study of coincidences between resonant gravitational wave detectors

Coincidences are searched for with the cryogenic resonant gravitational wave detectors EXPLORER and NAUTILUS, during a period of about six months (2 June-14 December 1998) for a total measuring time of 94.5 d, with the purpose of studying new analysis algorithms, based on the physical characteristics of the detectors.