Last Update: October 2000

VIRGO R&D

Collaboration:

# Firenze (Università di Firenze; Università di Urbino), Napoli (Università di Napoli; Università di Salerno), Perugia, Pisa, Roma1

Researchers:

C. Altucci, P. Amico, F. Barone, C. Bradaschia, E. Calloni, C. Cattuto, G. Cella, E. Cuoco, C. De Lisio, R. De Rosa, A. Di Virgilio, A. Eleuteri, S. Frasca, L. Gammaitoni, F. Giammanco, A. Giazotto, F. Marchesoni, L. Milano, C. Palomba, D. Passuello, A. Porzio, P. Puppo, P. Rapagnani, F. Ricci, A. Ruffini, S. Solimeno, R. Stanga, F. Strumia, H. Vocca, F. Vetrano

Technologists:

F. Garufi, P. La Penna, E. Majorana, M. Punturo

Technicians:

E. Babucci, P. Dominici, M. Masi, A. Piluso, C. Ricci

1 – Goal of the experiment

> - Virgo R&D is an experiment constituted by four sub-projects. Each one aims: or to insure that foreseen sensitivity of Virgo detector (the gravitational antenna which is building up in Cascina, near Pisa) will be reached and preserved; or else to improve Virgo sensitivity by reducing noise from sources or by increasing SNR. From this point of view, Virgo R&D is presently the most powerful effort to improve the performances of ground-based interferometric gravitational detectors at short- and medium –time.

> The four activities can be separately described, even though they are obviously strongly related.

> The first one, labelled as UVVV (Ultra Violet Vacuum Virgo), is aiming to monitoring the vacuum level of Virgo arms. A coherent UV beam is generated by a pulsed high-power Nd-YAG laser entering a narrow tube filled by Ar gas. Non linear optical effects generate harmonics of many orders: suitable UV harmonic is extracted and used, by absorption and/or fluorescence, as probe for H2 molecules; sensitivity of this probe is of about 103 molecules/cm3, which is good enough to satisfy requirements by Virgo.

> The second one (LDSW, Low Dissipation Suspension Wires) is an experimental detailed study of the quality factor of the wire suspensions of Virgo. All the Virgo mirrors are suspended by wires which are producing thermal noise: reducing it (by improving Q quality factor) results in proportional improving of Virgo sensitivity in the frequency band from 10 to some hundreds Hz. Many materials have been , and are now being, tested (in Perugia Lab) in order to determine the best solution.

> For it concerns thermal noise, another sub-project has been developed by building up an isolation tower (Superattenuator) equal to standard Virgo towers: this facility (LFF, Low Frequency Facility) is now ready, as concerning mechanical part, in S.Piero (INFN Lab of Pisa Section). The idea is to suspend an optical resonant cavity (Fabry-Pèrot cavity) to the last stage of the Superattenuator. This cavity results in an optical very-sensitive sensor which is able, owing to SA isolation, to determine thermal noise spectra in a large band, out of resonance too. By this we can characterize the noise of the mirrors and to study which are the best substrate for them.

> Lastly, we are now planning to design an approach to Data Analysis for Virgo which is following the idea of distributed calculus (GRID). This idea is presently in its first rising and is under theoretical estimation until now.

2 – Physics achievements during 2000

> - During 2000, UVVV has only studied the overall design for coupled devices (laser+monocromator) for producing desired harmonics, waiting for having the laser ready.

> - LFF has fully characterized the Superattenuator as a complex of mechanical filters, having 90 degrees of freedom; all the transfer functions have been determined, inertial damping of remnant motions has been achieved, control of the last stage (the one supporting the mirror) is now starting to work.

> - In LDSW, comparison of many results on different material was leading to the conclusion that fused silica can reach the best quality factor, because it has simultaneously lower loss angle (for internal friction) and higher breaking strength. Furthermore, techniques to improve clamping of wires and connection to the mirror substrates are now successfully developing, by using the “silicate bonding” technique in which connection can be obtained by reconstruction of chemical bonds.

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

> - Manpower: 5 researchers (1.8 FTE), 4 technologists (1.3 FTE), 2 technicians (0.7 FTE);

> - Financial support (2000): 597 MLit (299 kEuro)

4 – Number of publications in refereed journals: 7

5 – Number of talks to conferences: 10

6 – Number of undergraduate and doctoral thesis on the experiment: 5

7 – Leadership role in the experiment

> - Spokeperson of the Virgo R&D Collaboration is Flavio Vetrano from Urbino University & Florence Section. For each sub-project there are corresponding leading persons: A. Di Virgilio from Pisa for LFF; L. Gammaitoni from Perugia for LDSW; F. Strumia from Pisa for UVVV; F. Ricci from Roma1 for GRID.

8 – Innovative instruments

> - Linear position-transducer of very high sensitivity (LVDT)

9 – Competing experiments

> - For LFF: TNI (Thermal Noise Interferometer) is now starting in Caltech

10 – International committees which has revised the experiment

> - None