Last Update: October 2000

AURIGA (LNL, Pd+Gr.Coll. Tn, Fe, Fi)

1.Goal of the experiment

> The Auriga experiment (the acronym stands for Ultracryogenic Resonant Antenna for the Gravitational Astronomical Investigation) aims at the direct detection of impulsive gravitational waves coming by astrophysical phenomena (supernovae explosion, final part of coalescences NS-NS or BH-BH) in our and nearest galaxies. Auriga represents with the similar experiment Nautilus the most sensitive resonant bar detector on the air, thanks to the possibility to cool down the 2,3 tons bar to ultracryogenic temperature with a Dilution Refrigerator He3-He4. Auriga collaborate with the 4 other cryogenic detectors working in the world (Allegro, Explorer, Nautilus and Niobe) within the International Gravitational Event Collaboration, IGEC, with the aim to study the coincidences between the detectors. The present sensitivity allows to detect very strong sources within our Galaxy as NS-NS, BH-BH and BH-BH coalescences, with a false alarm rate below 10-4/year when at least 3 detectors are on the air. The Auriga group is engaged in an aggressive R&D to bring the performances of the transduction chains to an overall energy sensitivity of the detector below 100 quanta of vibration of the resonant bar. This will enable to reach out to the Local Group of Galaxies.

2.Physics achievement during 1999-2000

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

> Main detector: by up-grading the SQUID room temperature electronic a record sensitivity as been achieved with an effective temperature of 1 mK, corresponding to some 10000 quanta of vibration of the bar. Unfortunately in October 1999 a cryogenic failure of the main cryostat has interrupted the acquisition run.

> Data analysis: a robust validation of the data has been implemented to minimize the effect of the no-modeled and no-stationary noise and to prepare with the delta like filter the event list for the coincidence analysis. Result from 1,5 year with up to 4 detectors in coincidence are in press in Phys. Rev. Lett.

> R&D transduction chains: the ultracryogenic test facility has been commissioned, the thermal and mechanical characterization of an optimal energy coupling capacitive transduction chain is done, it is in progress the measurement about the behaviour of the integrated electronics. The prototype of the optical transduction chain is ready for tests on the room temperature bar, where it is possible to characterize the behaviour of the complete optical read-out.

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

> Manpower: 20 researchers (15 FTE), 1 technician and the support from the electronic workshop of the Padova Section, support from the mechanics workshop of LNL.

> Financial support: 600 MLit.

4.Number of publication in refereed journals: 7

5.Number of talks to conferences: >7

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

> -n.3 Ph.D. (2-1999,1-2000)

> -n.6 Laurea Diplomas

7.Leadership role in the experiment

> -Spokesperson: Chairman of Virgo Council, member of GWIC and PANAGIC

> -Padova Section leading about maintenance of the main detector and R&D transduction chain in the room temperature bar an ultracryogenic test facilities.

> -LNL and Trento leading in the acquisition and analysis 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 resonators.

> -Florence and Padova section optical transducer.

> -Ferrara Section astrophysical sources.

8. Innovative Instruments

> The Auriga group develops specific technologies:

> > -Characterization of ultrasensitive SQUID (below 100 quanta)

> > -Compact mechanical attenuation systems for ultracryogenic environments.

> > -Fast data acquisition and analysis on line, data validation against non-stationary and non-modeled noise.

> > -Ultracryogenic test facility for studies on quanta behaviour of amplifiers and mechanical oscillators.

> > -Optical read-out at shot noise level at 1 KHz.

9.Competiting experiments. (Collaboration and Complementarity)

> The challenge towards the first detection of g.w. has induced 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 complementarity together. "Advanced" resonant detectors (hollow spheres, dual systems etc.) will as well complement "advanced" interferometers. The Gravitational Wave International Collaboration GWIC (Cerdonio is a members as Auriga spokesperson) promotes coordination and collaboration among all the project to ensure maximal chances or early first detection and continuing observation.

10.International committees which has reviewed the experiment

> The R&D on transduction chains has been recently positively reviewed by a committee with mostly foreign members.