G. Cella

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.

QCD corrections to the weak radiative B-meson decay

Abstract The B → X s γ decay, which is sensitive to the top-quark mass, has become now particularly interesting as we expect a t-mass greater than 80 GeV. The QCD corrections play a relevant role, enhancing the GIM suppressed vertex: their computation presents many technical difficulties, which have led to different results in the previous literature. We have performed the calculation off-shell, in all gauges, in the leading logarithmic approximation; we confirm the strong enhancement of the QCD corrected branching ratios.

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.

Mirror suspension system for the TAMA SAS

Several R&D programmes are ongoing to develop the next generation of interferometric gravitational wave detectors providing the superior sensitivity desired for refined astronomical observations. In order to obtain a wide observation band at low frequencies, the optics need to be isolated from the seismic noise. The TAMA SAS (seismic attenuation system) has been developed within an international collaboration between TAMA, LIGO, and some European institutes, with the main objective of achieving sufficient low-frequency seismic attenuation (−180 dB at 10 HZ). The system suppresses seismic noise well below the other noise levels starting at very low frequencies above 10 Hz. It also includes an active inertial damping system to decrease the residual motion of the optics enough to allow a stable operation of the interferometer. The TAMA SAS also comprises a sophisticated mirror suspension subsystem (SUS). The SUS provides support for the optics and vibration isolation complementing the SAS performance. The SUS is equipped with a totally passive magnetic damper to suppress internal resonances without degrading the thermal noise performance. In this paper we discuss the SUS details and present prototype results.

Seismic attenuation performance of the first prototype of a geometric anti-spring filter

Abstract Next generation gravitational wave detectors, such as an advanced LIGO, will generally require improved sensitivity at low frequency. One of the principal challenges for low-frequency sensitivity is isolation from seismic motion. A mechanical seismic isolation filter specifically studied for the next generation of the LIGO detectors, based on a geometric anti-spring concept, has been developed with the aim to provide thermal noise limited sensitivity to frequencies of 10 Hz . The design and the performance of the isolation filter, mainly for the vertical degree of freedom are discussed.

THE CREEP PROBLEM IN THE VIRGO SUSPENSIONS : A POSSIBLE SOLUTION USING MARAGING STEEL

Abstract Each optical component of the interferometric gravitational wave detector VIRGO is suspended from a cascade of mechanical filters designed to suppress the transmission of seismic vibrations. Each mechanical filter supports the weight of the filters below it by means of a set of steel cantilever blade springs. The stress from the load acting on the blades was found to induce a drooping of the blade tips of several microns per day due to a series of microscopic yielding events (micro-creep). This process induces a mechanical displacement shot-noise on the optical component which can dominate the small displacements produced by gravitational waves. The use of a special precipitation hardened steel (Maraging C250), instead of common spring steel, allows the construction of blades that show an acceptable stability under stress.

QCD corrections to electroweak processes in an unconventional scheme: application to the b → sγ decay

Abstract In this work we give a detailed description of a method for the calculation of QCD corrections to electroweak processes in dimensional regularization that does not require any definition of the γ 5 matrix in d dimensions. This method appears particularly convenient to limit the algebraic complexity of higher order calculations. As an example, we compute the leading logarithmic corrections to the b → sγ decay.

SEISMIC NOISE FILTERS, VERTICAL RESONANCE FREQUENCY REDUCTION WITH GEOMETRIC ANTI-SPRINGS : A FEASIBILITY STUDY

Abstract The achievement of low resonance frequency in vertical action oscillators is the most difficult of the basic ingredients for seismic noise attenuation filters. These oscillations are achieved by means of “anti-springs” systems coupled with more classical suspension springs. Magnetic anti-springs have been used so far. Geometric anti-springs have been studied and the concept tested in this work, opening the way to a simpler and better performance seismic attenuation filters.

QCD corrections to the B→Xse+e− decay

Abstract We have evaluated the short distance QCD corrections to the B→X s e + e − process in a quark spectator model within an effective hamiltonian framework. The dependence of the rate on the top-quark mass is examined in the minimal standard model. We have found a light suppression of the differential width for a large invariant mass of the e + e − pair; the integrated width is slightly enhanced.

Anatomy of the TAMA SAS seismic attenuation system

The TAMA SAS seismic attenuation system was developed to provide the extremely high level of seismic isolation required by the next generation of interferometric gravitational wave detectors to achieve the desired sensitivity at low frequencies. Our aim was to provide good performance at frequencies above ~10 Hz, while utilizing only passive subsystems in the sensitive frequency band of the TAMA interferometric gravitational wave detectors. The only active feedback is relegated below 6 Hz and it is used to damp the rigid body resonances of the attenuation chain. Simulations, based on subsystem performance characterizations, indicate that the system can achieve rms mirror residual motion measured in a few tens of nanometres. We will give a brief overview of the subsystems and point out some of the characterization results, supporting our claims of achieved performance. SAS is a passive, UHV compatible and low cost system. It is likely that extremely sensitive experiments in other fields will also profit from our study.