Last Update: October 2000

ROG ( LNF, Roma1, Roma2 )

P.Astone1, D. Babusci2, M. Bassan3, P. Bonifazi4,1, P. Carelli5,3, M.G. Castellano4,3, E. Coccia3, C. Cosmelli1, S. D'Antonio2, V. Fafone2, G. Giordano2, A. Marini2, Y. Minenkov3, I. Modena3, G. Modestino2, A. Moleti3, G.V. Pallottino1, G. Pizzella2,3, L. Quintieri2, F. Ronga2, R. Terenzi4,3, R. Torrioli4,3, M. Visco4,3, L. Votano2

1 INFN Rome1 and University of Rome "La Sapienza"; 2 INFN LNF, Frascati; 3 INFN Roma2 and University of Rome "Tor Vergata"; 4 CNR IFSI and IESS Roma; 5 University of L'Aquila

Laboratory: CERN and LNF

1. Goal of the experiment

> ROG (the acronym stands for Ricerca Onde Gravitazionali — Gravitational Wave Research ) is a collaboration which has designed and constructed two massive (M=2.3 tons) cryogenic resonant bar detectors: EXPLORER, cooled at 2 K, in operation at CERN since 1990, and NAUTILUS, cooled at the record temperature (for such massive bodies) of 0.1 K, in operation at LNF since 1995.

> The goal is the detection and study of gravitational wave signals emitted by high frequency (kHz) cosmic sources, such as gravitational collapses with formation of neutron stars and black holes, coalescing binaries, fast pulsars and a stochastic background.

> The principle of operation is based on the assumption that any vibrational mode of a resonant body that has a mass quadrupole moment, such as the fundamental longitudinal mode of a cylindrical bar, can be excited by GW.

> The performances of the present cryogenic detectors are the consequence of many years of development. The use of cryogenics and superconducting techniques for noise reduction and signal transduction led to a 105 fold improvement in energy sensitivity over Weber’s original bars. The sensitivity is now good enough so that a serious search for gravitational wave bursts is underway using the international network of 5 resonant bar detectors (IGEC).

> The duty cycle for EXPLORER and NAUTILUS is of about 75%, and the strain sensitivity, of the order of 10-22 Hz-1/2 at the resonance, should allow the detection of the strongest sources in our Galaxy and in the Local Group.

> In parallel to the data taking, two intense R&Ds are conducted, with the goals of enlarging the bandwidth (using high coupling capacitive transducer and low noise dcSQUID amplifier) and of reducing the spuria (cryogenic suspension with sphere prototype).

2. Physics achievements

> In 1999 EXPLORER has been up-graded with a new capacitive transducer and new suspensions. The results obtained this year 2000 are very good: the bandwith is increased of almost a factor 10, being now of about 40 Hz at a strain level of 10-20 Hz-1/2 . This result demonstrates that the banwidth of resonant detectors can be increased.

> NAUTILUS, which is equipped with a cosmic ray veto system, has been capable to detect signals due to the interaction of EAS on the bar. In the words of our PRL 84, 14 (2000) paper referee: "The possibility of detecting cosmic rays represents a significant test of the whole system. So, the results of this paper are a milestone in empirically demonstrating the sensitivity of these detectors. The detection of cosmic rays in such a detector brings together many areas of physics at the limit of our knowledge and that is perhaps the most interesting aspect of this work scientifically."

> We remind the reader that the detection of cosmic rays with NAUTILUS means being able to measure impulsive signals exciting the mode of vibration to an energy of 10-7 eV.

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

> 24 physiscists (14 FTE). Financial support in the year 2000: 930 Mlire.

4. Number of publications in refereed journals: 10

5. Number of talks to conferences: 9

6. Number of undergraduate and doctoral thesis:

> 2 Laurea diplomas.

7. Leadership role in the experiment

> Spokeperson: Eugenio Coccia.

> Other leading roles: Guido Pizzella and Francesco Ronga at LNF, Giovanni Vittorio Pallottino at Roma1, Ivo Modena at Roma2.

8. Innovative instruments

- High coupling capacitive transducer for the measurements of small mechanical vibrations.
- Dc SQUIDs of very low noise. Record energy resolution of 5.5 hbar.
- Largest 3He- 4He dilution refrigerator in the world, developed in collaboration with Oxford Instruments.

9. Competing experiment

- Operating detectors (resonant bars): AURIGA at INFN-LNL, ALLEGRO at Louisiana State University (USA) and NIOBE at University of Western Australia (Australia). Formal collaboration agreement for joint coincidences analysis has been established with these groups (IGEC = International Gravitational Events Collaboration).
- Interferometric detectors: TAMA (in Japan, just starting the data taking). Others detectors will start operating in the next years: GEO (Germany), LIGO (USA), VIRGO (Italy).

10. International committee which has reviewed the experiment

> EXPLORER is a CERN Recognized Experiment (RE5) and follows the CERN policy.

> NAUTILUS results are reported regularly to the LNF Scientific Committee.