F. Vetrano

Is it possible to detect gravitational waves with atom interferometers

We investigate the possibility of using atom interferometers to detect gravitational waves. We discuss the interaction of gravitational waves with an atom interferometer and analyse possible schemes.

Upper limit on the prompt muon flux derived from the LVD underground experiment

We present the analysis of the muon events with all muon multiplicities collected during 21804 hours of operation of the first LVD tower. The measured depth-angular distribution of muon intensities has been used to obtain the normalization factor, A, the power index, gamma, of the primary all-nucleon spectrum and the ratio, R_c, of prompt muon flux to that of pi-mesons - the main parameters which determine the spectrum of cosmic ray muons at the sea level. The value of gamma = 2.77 +/- 0.05 (68% C.L.) and R_c<2.0 x 10^-3 (95% C.L.) have been obtained. The upper limit to the prompt muon flux favours the models of charm production based on QGSM and the dual parton model.

LISA test-mass charging process due to cosmic-ray nuclei and electrons

Solar energetic particles and galactic cosmic rays with energies larger than 100 MeV cause progressive charging of the LISA experiment test masses. Consequently, Coulomb forces occur between the test masses and the surrounding conducting surfaces generating spurious signals that might be mistaken for gravitational wave signals. We have parametrized the energy spectra of galactic cosmic-ray nuclei and electrons near the LISA orbit in order to evaluate their role in the test-mass charging relative to the most abundant proton component. This work has been carried out using the FLUKA Monte Carlo program.

Silicate bonding properties: Investigation through thermal conductivity measurements

A direct approach to reduce the thermal noise contribution to the sensitivity limit of a GW interferometric detector is the cryogenic cooling of the mirrors and mirrors suspensions. Future generations of detectors are foreseen to implement this solution. Silicon has been proposed as a candidate material, thanks to its very low intrinsic loss angle at low temperatures and due to its very high thermal conductivity, allowing the heat deposited in the mirrors by high power lasers to be efficiently extracted. To accomplish such a scheme, both mirror masses and suspension elements must be made of silicon, then bonded together forming a quasi-monolithic stage. Elements can be assembled using hydroxide-catalysis silicate bonding, as for silica monolithic joints. The effect of Si to Si bonding on suspension thermal conductance has therefore to be experimentally studied. A measurement of the effect of silicate bonding on thermal conductance carried out on 1 inch thick silicon bonded samples, from room temperature down to 77 K, is reported. In the explored temperature range, the silicate bonding does not seem to affect in a relevant way the sample conductance.

The dynamics of monolithic suspensions for advanced detectors: A 3-segment model

In order to reduce the suspension thermal noise, the second generation GW interferometric detectors will employ monolithic suspensions in fused silica to hold the mirrors. The fibres are produced by melting and pulling apart a fused silica rod, obtaining a long thin wire with two thicker heads. The dynamics of such a fibre is in principle different from that of a cylindrical, regular fibre, because most of the deformation energy is stored in the neck region where the diameter is variable. This is an advantage, since adjusting the neck tapering, a thermoelastic noise cancellation effect can be obtained. Therefore, a careful study of the suspensions behavior is necessary to estimate the overall noise and to optimize the control strategy. To simplify the control design, a simple three segment model for the silica fibres has been developed, fully equivalent to the beam equation at low frequencies. The model, analytically proved for a regular cylindrical fibre, can be extended to a fibre with tapered necks, provided that the equivalent bending length is suitably measured. We developed a tool to measure the position of the bending point for each fibre, thus allowing to experimentally check the validity of the model. A numerical code has been written to solve the beam equation for wires with varying diameter. This code confirms the validity of the three segment model. Moreover, it is possible to extend the solution to higher frequencies thus computing the transfer function and the energy distribution of the suspension system and estimating the thermal noise contribution.

Experimental upper limit on the estimated thermal noise at low frequencies in a gravitational wave detector

A. Di Virgilio, L. Barsotti, S. Braccini, C. Bradaschia, G. Cella, V. Dattilo , M. Del Prete, I. Ferrante, F. Fidecaro, I. Fiori, F. Frasconi, A. Gennai, A. Giazotto, P. La Penna, G.Losurdo , E. Majorana, M. Mantovani , F. Paoletti, R. Passaquieti, D. Passuello, F. Piergiovanni, A. Porzio, P. Puppo, F. Raffaelli, P. Rapagnani, F. Ricci, S. Solimeno, G. Vajente, F. Vetrano INFN, Sez. di Pisa, Pisa, Italy 2 EGO, European Gravitational Observatory, Cascina (Pi) 3 Universita’ di Pisa, Italy 4 INFN Sezione di Firenze, Sesto Fiorentino, Italy 5 Università di Roma1, and INFN-Roma1, Roma Italy 6 Universita’ di Siena, Italy 7 Università di Urbino, Urbino, Italy 8 Coherentia, CNR-INFM, and CNISM Unitá di Napoli 9 INFN, Sez. di Napoli, Università di Napoli 10 Scuola Normale Superiore, Pisa

Measurement of the thermoelastic properties of crystalline Si fibres

In order to reduce the thermal noise in future interferometers for gravitational wave (GW) detectors, new suspension materials with low thermal noise are under investigation. Crystalline silicon seems to be a promising material mainly at low temperature. A new technology to produce crystalline silicon fibres has been realized. Measurements of mechanical and thermal properties of the fibres at room temperature have been performed. Preliminary measurements at low temperature are presented.

Ground based 2DoF test for LISA and LISA PF

On-ground tests are required to study the couplings between LISA test masses and the spacecraft that host them. Very interesting and useful results have already been obtained with a 1 DoF torsion pendulum. In order to study couplings that might act between two or more degrees of freedom in measuring the position and acting on the position of each test mass, a many degrees of freedom facility is needed. Here we present a new 2 DoF double torsion pendulum that will be used to test LISA Gravitational Reference Sensor (GRS) on the ground. The facility will be located at INFN Laboratory at Gran Sasso (LNGS), in order to reduce the local ambient noise that limits the sensitivity of the system.

A tool for measuring the bending length in thin wires

Great effort is currently being put into the development and construction of the second generation, advanced gravitational wave detectors, Advanced Virgo and Advanced LIGO. The development of new low thermal noise suspensions of mirrors, based on the experience gained in the previous experiments, is part of this task. Quasi-monolithic suspensions with fused silica wires avoid the problem of rubbing friction introduced by steel cradle arrangements by directly welding the wires to silica blocks bonded to the mirror. Moreover, the mechanical loss level introduced by silica (φfs ∼ 10(-7) in thin fused silica wires) is by far less than the one associated with steel. The low frequency dynamical behaviour of the suspension can be computed and optimized, provided that the wire bending shape under pendulum motion is known. Due to the production process, fused silica wires are thicker near the two ends (necks), so that analytical bending computations are very complicated. We developed a tool to directly measure the low frequency bending parameters of fused silica wires, and we tested it on the wires produced for the Virgo+ monolithic suspensions. The working principle and a set of test measurements are presented and explained.

Ground Based 2 DoF Test For LISA And LISA Pathfinder: A Status Report

On‐ground tests are required to study the couplings between LISA test masses and the spacecraft that host them. In order to study couplings that might act between two ore more degrees of freedom in measuring the position and acting on the position of each test mass, a many degrees of freedom facility is needed. Here we present the status of our new 2 DoF double torsion pendulum, that will be used to test LISA Gravitational Reference Sensor (GRS) on the ground.