R. Del Fabbro

The VIRGO Project: A wide band antenna for gravitational wave detection

Abstract The status of advancement of the VIRGO Project is presented: the first-generation results from the Pisa seismic noise super attenuator give an upper limit to the noise transfer function of 2 × 10 −8 at 10 Hz. The upper limit to the absolute noise of the 400 kg test mass at 10 Hz has been measured to be 1.5 × 10 −13 m/√Hz. The scheme and the related problems of the VIRGO interferometer, which is supposed to work down to 10 Hz, are also presented. At the 3rd Pisa Meeting in 1986 we presented the idea of what could be a very efficient seismic noise reduction system able to give a sensitivity h ∼ 10 −25 at 10 Hz, in a 3 km interferometer for 1 year integration time. Now we have two new facts to present: the first is that the attenuation has been built, is working in Pisa, and shows remarkable characteristics. The second is the Italian-French interferometer VIRGO [1,2], a 3 km long antenna for low and high frequency (10–1000 Hz) gravitational wave (GW) detection. These two items will be presented in this article.

The Virgo interferometer

The Virgo gravitational wave detector is an interferometer with 3 km long arms in construction near Pisa to be commissioned in the year 2000. Virgo has been designed to achieve a strain sensitivity of a few times at 200 Hz. A large effort has gone into the conception of the mirror suspension system, which is expected to reduce noise to the level of at 10 Hz. The expected signals and main sources of noise are briefly discussed; the choices made are illustrated together with the present status of the experiment.

TOTAL CROSS-SECTION FOR HADRONIC PRODUCTION BY E+E- ANNIHILATION IN THE TOTAL CM ENERGY-RANGE 1.42-3.09 GEV

Abstract We report experimental results on the cross section for the reaction e + e − → hadrons as a function of the total c.m. energy in the range W = 1.42–3.09 GeV. The results, combined with those already existing below the charm threshold, clearly indicate a structure for R ( W ) = α ( e + e − → hadrons)/ α ( e + e − → μ + μ − ) in that energy region.

The CDF Central and Endwall Hadron Calorimeter

Abstract The CDF central and endwall hadron calorimeter covers the polar region between 30° and 150° and a full 2π in azimuth. It consists of 48 steel-scintillator central modules with 2.5 cm sampling and 48 steel-scintillator endwall modules with 5.0 cm sampling. A general description of the detector is given. Calibration techniques and performance are discussed. Some results of the test beam studies are shown.

Extending the VIRGO gravitational wave detection band down to a few Hz: metal blade springs and magnetic antisprings

Abstract The detection band of the interferometric gravitational wave detector VIRGO can be extended down to a few Hz by suspending each optical component of the interferometer from a chain of mechanical filters designed to suppress the transmission of seismic vibrations. Each mechanical filter supports the weight of the stages below it through a set of cantilevered blade springs. A system of permanent magnets, providing an “antispring” force, helps to reduce the highest vertical resonance of the chain from 7 Hz to about 2 Hz. This improvement allows VIRGO to reduce the frequency detection threshold from 10 Hz to about 4 Hz. A characterization of the mechanical filters is provided in this paper.

Air bake-out to reduce hydrogen outgassing from stainless steel

Hydrogen outgassing is the most significant factor limiting the attainment of outgassing rates below 10−12u2009mbaru2009lu2009s−1u2009cm−2 in stainless steel vacuum systems. This limit turns out to be crucial in very large vacuum systems, like the VIRGO vacuum tubes (2 tubes 1.2 mu2009diam, 3000 mu2009length). Heating the raw material at 400u2009°C in air was suggested as a money saving alternative to the classical vacuum heating at 950u2009°C. We report the results of hydrogen content analysis performed on stainless steel samples submitted to different treatments, and also the measurement performed on a prototype tube (1.2-m-diam, 48-m-long). We concluded that air bake-out drives out most of the hydrogen absorbed in the bulk stainless steel, while the presence of an oxide layer does not reduce the hydrogen outgassing.

Three-dimensional seismic super-attenuator for low frequency gravitational wave detection

Abstract We present the study of a passive n -fold pendulum to be used as a three-dimensional seismic noise attenuator. A 7-fold pendulum, under construction at the INFN laboratory in Pisa, is expected to provide a horizontal and vertical attenuation factor of 10 −11 and 10 −9 respectively at 10 Hz and is capable to sustain a 400 kg test mass used in a large base interferometric gravitational wave antenna.

Seismic vibrations mechanical filters for the gravitational waves detector VIRGO

VIRGO is a detector of gravitational waves based on a laser interferometer with 3 km long arms, now under construction. In order to detect gravitational waves down to 10 Hz, the seismic noise has to be reduced by several orders of magnitude. New mechanical filters using cantilever springs as elastic elements have been developed for the VIRGO seismic isolation system. The spring total stiffness is reduced by more than one order of magnitude using magnetic antispring. A control system allows one to keep the spring length constant. The new filters provide an attenuation ≥40 dB each for frequencies above 10 Hz and, compared to the previously adopted solution (gas springs), are much less sensitive to temperature changes.

First results from the pisa seismic noise super-attenuator for low frequency gravitational wave detection

The detection of gravitational wave (GW) signals requires the test masses of an interferometric antenna to be carefully made free from seismic noise coming from the suspension point. In this paper we report the first results coming from the Pisa super-attenuator. We have measured both the test mass absolute noise upper limit to be ⩽10−11/vm/√Hz for 10<v<200 Hz and the transfer functions (TF). These TF applied to the measured seismic noise spectral displacement should allow in a 3 km long interferometric antenna a maximum spectral strain sensitivity h<1.9×10−20Hz−12 at 10 Hz and h<7.5×10−19/v2Hz−12 for v⩾20 Hz; this gives at the Vela (Crab) pulsar frequency the limit h<3×10−25 (h<4×10−26), for 1 year integration time.

Low frequency behaviour of the Pisa seismic noise super-attenuator for gravitational wave detection

The absolute displacements, for frequencies below 20 Hz, of the 400 kg test mass seismically isolated by the Pisa super-attenuator, to be used in long base interferometer for gravitational wave research, are presented. In the region below 6 Hz, the maximum displacement is about 14 μm. The displacements, at 10 and 20 Hz, are ≤ 1.5 × 10-13 and ≤ 4 × 10-14 m/√Hz respectively and represent presumably the lowest ever reached by a suspended mass on earth. The super-attenuator transfer function, which has been measured using the seism as an exciter for 0<υ<6 Hz, shows a remarkable agreement with the theoretical one and demonstrates the necessity of having an attenuating system working in three dimensions.