AURIGA

Collaboration:

- Ferrara, Firenze, LNL, Padova e Trento

Laboratory: Legnaro National Laboratory of INFN

National Responsible: M. Cerdonio (Padova)

1. Goal of the experiment

The AURIGA experiment (the acronym stands for Ultracryogenic Resonant Antenna for the Gravitational Astronomical Investigation) aims to the direct detection of impulsive gravitational waves originating in astrophysical phenomena (supernovae explosion, final part of coalescing of Neutron Star or Black Hole binary systems) in our and nearest galaxies.

More on the experiment…

2.

Activities during 2001

The scientific program of AURIGA runs on 4 different, but interlinked routes, levels: main detector hardware developement, data analysis , R&D of transduction chains (resonant capacitive with SQUID read-out and resonant optical Fabry-Perot cavity read-out).

Main detector: after the cryogenic failure in October ’99, we have modified fully the cryogenic component of suspension system and a lot of cryogenic component linked to the dilution refrigerator with the aim to increase the duty cicle of the detector. The systems are in the assembling stage, after a demonstration of a mechanical suspension system for a gw detector working in the 600 Hz-1600 Hz band free of spurious frequencies. The restart of the operation of the detector has been postponed, to allow to incorporate all the upgrades, including the new suspensions, not originally planned.

Data analysis: complete validation of the data with the delta like filter for the analisys in coincidence with other detector, using a tested new acquisition and analysis data based on "frames"; this allows complete compatibility with the data format of interferometers .

R&D transduction chain: The ultracryogenic test facility is operating. The development on test of the new capacitive transducer equipped by a double stage SQUID amplifier is almost concluded. Test has been performed within the temperature range 1,5-4,2 K demonstrating a energy sensitivity of about 300 quanta at the transducer resonance frequency.

The double SQUID system has operated, coupled to a resonator, with noise <200 h-bar.

The optomechanical transduction chain: a laser system was implemented with deep phase modulation and quantum-limited intensity stabilization in the kHz range. Two stable Fabry-Perot cavities have been developed which show a minimum relative frequency noise of 4x10-3Hz/sqrt(Hz) at about 900 Hz. A servo loop has been developed that locks the above mentioned laser system to one of these cavities: this apparatus has been integrated into a complete optical readout for the room temperature bar. The room temperature bar, read by the optical transduction chain, has run for few weeks: the achieved sensitivity has a minimum of equivalent input strain spectral density of 8x10-20/sqrt(Hz) and the useful bandwidth is about 20 Hz. The sensitivity is limited by thermal noise and we were able to show that due to the inhomogeneous losses the normal mode expansion fails. The laser system and the two stable cavities have also been employed for testing the model of photothermal effect, which we have recently proposed (M.Cerdonio et al, PRD 63 (2001) 082003).

Delays with the optomechanical transducer are mainly induced by difficulties in actually receiving optical fibers with the predicted specifications. The rubber suspensions for the room temperature test bar make impossible the use of higher finesse mirrors.

We have proposed a new gravitational wave resonant detector based on two nested concentric spheres, which would be competitive and complementary with the advanced version of the long interferometers which are now under construction (M.Cerdonio et al, PRL 87 (2001) 031101).

As a summary, the following achievements have been obtained:

Double SQUID system in operation , coupled to a resonator, with noise <200 h-bar (fulfilled)

Completion of the analysis of all the available IGEC data (fulfilled)

Optimization of the capacitive transduction chain with a <200h-bar double SQUID (85% fulfilled)

Room temperature test of the optomechanical transducer; cryogenic tests on parts (75% fulfilled)

Milestones 2002

New data analysis for both on-line and off-line data. | 31-03-2002
Start of the operation of an ultracryogenic test facility for coupled dc SQUIDs in Trento. | 31-05-2002
Data taking of the detector at T=2K with pulse sensitivity of 0.1 mK and bandwidth of 10 Hz. | 30-06-2002
Noise measurements of the new optical transducer operating at cryogenic temperatures. | 31-12-2002
Data taking at T=0.2 K with pulse sensitività of 0.01 mK and bandwidth of 30 Hz. | 31-12-2002

3. INFN contribution to the experiment in terms of manpower and financial support

Manpower: 20 researchers (16 FTE), 5 technicians (1.5 FTE) and the support from the mechanics workshop of LNL and the electronic workshops of the Padova Section.

Budget for the Year 2002: 342.5 kEuro

4. P ublications in refereed journals (Year 2001): 7

5. Number of conference talks (Year 2001): 7

6. Number of undergraduate and doctoral thesis on the experiment:

- n.1 Ph.D
- n.2 Laurea diplomas.

7. Leadership roles and primary responsibilities in the experiment

- Spokesperson: member of GWIC and PANAGIC
- Padova section leading about up-grading of the main detector and R&D transduction chains in the room temperature bar and ultracryogenic test facility
- LNL and Trento leading in the acquisition and analisys data, G.A.Prodi had a propulsive role in the IGEC "task force" for the joint coincidence analysis.
- Trento and CEFSA collaboration SQUID and LC resonantors;
- Florence Section optical read-out
- Ferrara Section astrophysical sources.

8. Innovative instruments

- The Auriga group develops specific technologies:
- Characterization of ultrasensitive SQUID (below 100 quanta).
- Compact mechanical attenuation system for ultracryogenic enviroments
- Fast data acquisition and analisys on line, data validation against non-stationary and non-modeled noise.
- Ultracryogenic test facility for studies on quanta behaviour of amplifier and mechanical oscillators.
- Optical read-out at shot noise level at 1 kHz.

9. Competing experiments.

The challenge towards the first detection of g.w. has produced between all the project world wide a friendly competition and extensive exchange of scientific information for the methods and the technologies and, most important, collaboration for the data analysis and for the long-term strategies (no single detector would be able to perform significant searches). IGEC is in fact the collaboration effort of all the "bar" project. As for the interferometers detectors, the acknowledged view is that the initial interferometers and "bar" will work complementary togeteher. "Advanced" resonant detectors (hollow spheres, dual systems etc.) will as well complement "advanced" interferometers. The Gravitational Wave International Collaboration GWIC (Cerdonio is a memebrs as Auriga spokesperson) promotes coordination and collaboration among all the project to ensure maximal chances or early first detection and continuing observation.

10. International committee which has reviewed the experiment