The French-Italian interferometric gravitational wave detector VIRGO is currently being commissioned. Its principal instrument is a Michelson interferometer with 3 km long optical cavities in the arms and a powerrecycling mirror. This paper gives an overview of the present status of the system. We report on the presently attained sensitivity and the system’s performance during the recent commissioning runs. Send correspondence to A. Freise, E-mail: andreas.freise@ego-gw.it After a sequence of intermediate stages, the interferometer is now being used in the so-called recombined configuration. The input laser beam is spatially filtered by a 144 m long input mode-cleaner before being injected to the main interferometer. The main optics are suspended from so-called superattenuators, which provide an excellent seismic isolation. The two 3 km long Fabry-Perot arm cavities are kept in resonance with the laser light, and the Michelson interferometer is held on the dark fringe. An automatic mirror alignment system based on the Anderson technique has been implemented for the arm cavities. The light leaving the dark port contains the gravitational wave signal; this light is filtered by an output mode-cleaner before being detected by a photo detector. This setup is the last step on the way to the final configuration, which will include power recycling.

Cross sections, angular distributions and forward-backward asymmetries are presented, of two-fermion events produced in e+e- collisions at centre-of-mass energies from 189 to 209 GeV at LEP, measured with the ALEPH detector. Results for e+e-, mu+mu-, tau+tau-, qq, bb and cc production are in agreement with the Standard Model predictions. Constraints are set on scenarios of new physics such as four-fermion contact interactions, leptoquarks, Z' bosons, TeV-scale quantum gravity and R-parity violating squarks and sneutrinos.

A search for Higgs bosons produced in association with a fermion pair, and decaying to WW, is performed with the data collected by the ALEPH detector at centre-of-mass energies ranging from 191 to 209 GeV. The data correspond to an integrated luminosity of 453.2 pb-1. Thirteen exclusive selections are developed according to the different final state topologies. No statistically significant evidence for a Higgs boson decaying into a WW pair has been found. An upper limit is derived, as a function of the Higgs boson mass, on the product of the e+e-→Hff̄ cross section and the H→WW branching ratio. The data on the search for H→WW are combined with previously published ALEPH results on the search for H→γγ, to significantly extend the limits on the mass of a fermiophobic Higgs boson.

A review of the present status of the W boson mass and width measurements at LEP is presented. The analysis of the data collected in 1998 by the 4 LEP collaborations, corresponding to about 700 pb(-1), allows to reach an experimental uncertainty on the W boson mass measured at LEPII approaching the precision of the indirect results from the high precision electroweak measurements at LEPI.

Hadronic Z decays into three jets are used to test QCD models of colour reconnection (CR). A sensitive quantity is the rate of gluon jets with a gap in the particle rapidity distribution and zero jet charge. Gluon jets are identified by either energy-ordering or by tagging two b-jets. The rates predicted by two string-based tunable CR models, one implemented in JETSET (the GAL model), the other in ARIADNE, are too high and disfavoured by the data, whereas the rates from the corresponding non-CR standard versions of these generators are too low. The data can be described by the GAL model assuming a small value for the R0 parameter in the range 0.01-0.02.

Two-particle correlations in pp, (p) over bar(p) over bar and K-S(0) K-S(0) pairs have been studied in hadronic Z decays recorded at LEP with the ALEPH detector. The correlations were measured as a function of the four-momentum difference Q of the pair. For pp, (p) over bar(p) over bar pairs a depletion of events is observed in the region Q < 3 GeV, and for (KSKS0)-K-0 pairs an enhancement of events is observed in the region Q < 0.5 GeV. These features are consistent with expectations from Fermi-Dirac and Bose-Einstein statistics, respectively. (c) 2004 Elsevier B.V. All rights reserved.

Triple gauge-boson couplings gamma WW and ZWW involving single-photon, single-W and W-pair production are determined using data samples collected at LEP with the ALEPH detector at centre-of-mass energies between 183 and 209 GeV The integrated luminosity used is 700 pb(-1) for the single-photon measurement and 683 pb-1 for the W channels. Restricting the measurement to C- and P-conserving terms and applying local SU(2)(L) x U(1)(Y) gauge invariance, the measured values of the parameters g(1)(Z), kappa(gamma) and lambda(gamma) are:g(1)(Z) = 1.001 +/- 0.027(stat) +/- 0.013(syst),kappa(gamma) = 0.971 +/- 0.055(stat) +/- 0.030(syst),lambda(gamma) = -0.012 +/- 0.027(stat) +/- 0.011(syst)for single-parameter fits, where the two other parameters are fixed to their Standard Model values. Results are also presented for the cases where two or all three couplings are allowed to vary. An additional analysis using W-pair events is performed to measure the unconstrained real and imaginary parts of all 14 triple gauge-boson couplings and to perform an indirect search for a techni-p resonance. No deviations from the Standard Model expectations are observed and the lower limit on the techni-p mass is set to 600 GeV/c(2) at 95% confidence level. (c) 2005 Elsevier B.V. All rights reserved.

Virgo is a French–Italian collaboration for the construction and operation of a 3 km long interferometric gravitational wave antenna. The construction of the detector is already completed and the commissioning is quite advanced, while the data taking is expected to start in 2005. In this paper, we report on the present status of Virgo and on the results of commissioning activity. In particular, we analyse the first four engineering runs (C1–C4) and discuss the sensitivity obtained in C4.

In order to detect gravitational waves, the kilometric interferometer Virgo needs an active control of the positions of the suspended optical components, keeping the detector at its working point. The constraints are about 10-10m RMS for the longitudinal control (“Locking”) and 10-9rad RMS for the angular degrees of freedom (“Alignment”). A dedicated hardware and software named Global Control is in charge of the Locking and the Alignment loops for the Virgo experiment. This system has been designed to match the synchronization constraint and provide a flexible tool in order to easily integrate the various algorithms needed for the control of Virgo. This paper presents the technical requirements to be fulfilled by the Global Control. Then, the dedicated hardware is described and the overall architecture of the Global Control is shown.

Bose-Einstein correlations in W-pair decays are studied using data collected by the ALEPH detector at LEP at e(+)e(-) centre-of-mass energies from 183 to 209 GeV. The analysis is based on the comparison of WW --> q (q) over barq (q) over bar events to "mixed" events constructed with the hadronic part of WW --> q (q) over bar lv events. The data are in agreement with the hypothesis that Bose-Einstein correlations are present only for pions from the same W decay. The JETSET model with Bose-Einstein correlations between pions from different W bosons is disfavoured. (C) 2004 Elsevier B.V. All rights reserved.

The cross sections for single vector boson production in the Wenu and Zee channels are measured from the data collected by AA the ALEPH detector at LEP for centre-of-mass energies between 183 and 209 GeV. These data correspond to a total integrated luminosity of 683 pb(-1). Single-W production is studied in both hadronic and leptonic decay channels. Hadronic and dimuon decays are used for single-Z production. The measured cross sections agree with the Standard Model predictions. (C) 2004 Elsevier B.V. All rights reserved.

The acoplanar photon pairs produced in the reaction e+e−→νν¯γγ are analysed in the 700 pb−1 of data collected by the ALEPH detector at centre-of-mass energies between 183 and 209 GeV. No deviation from the Standard Model predictions is seen in any of the distributions examined. The resulting 95% C.L. limits set on the anomalous QGCs, a0Z, acZ, a0W and acW, are −0.012

We present the results of a study of the major low-frequency sources of seismic activity at the Virgo site. These sources are of natural and human origin: oceanic microseism (below 1 Hz), local traffic and human activity on site (below 10 Hz). Using data collected during the commissioning of the central Virgo interferometer (CITF) we have measured the seismic coupling to the interferometer, demonstrating that seismic noise contributed to the CITF dark fringe noise only below approximately 2 Hz.

The French-Italian interferometric gravitational wave detector VIRGO is currently being commissioned. Its pr incipal instrument is a Michelson laser interferometer with 3 km long optical cavities in the arms and a power-recycling mirror. The interferometer resides in an ultra-high vacuum system a nd the mirrors are suspended from multistage pendulums for sei smic isolation. This type of laser interferometer reaches its maximum sensi tivity only when the optical setup is held actively very accurately at a defined operating point: control systems using the preci se interferometer signals stabilise the longitudinal and angular positions of the optical component. This paper gives an overvi ew of the control system for the angular degrees of freedom; we Send correspondence to A. Freise, E-mail: andreas.freise@ ego-gw.it present the current status of the system and report the first experimental demonstration of the Anderson technique on a l argescale interferometer.

The Virgo interferometer for gravitational wave detection has concluded four months of scientific data acquisition in its final optical configuration (a power-recycled interferometer with Fabry-Perot cavities in the arms). The lock acquisition technique developed to bring and keep the Virgo detector on its working point largely proved to be very efficient and robust. In this paper we describe the variable finesse lock acquisition technique and we discuss the performance of the whole locking system.

Operation of the central portion of Virgo as a simple 6 m Michelson interferometer has given the first demonstration of the possibility to control an interferometer suspended from Virgo full scale multistage seismic attenuators using information derived from the interferometer locking signal. A special role in the control is played by the first stage of these suspensions, an inverted pendulum: besides its seismic preisolation action, this stage has positioning dynamics of several mm, and it allows to exert a very low frequency control at the upper level of the suspension using the interferometer fringe signal. The application of this feedback to the top-stage of the suspension allows corrections of drifts, such as tidal ones, at a stage of the suspension where a large dynamic range in displacements is available, without introducing noise at the level of the mirror, resulting in a significant reduction of the lock keeping force applied directly on the mirror at the lowest stage of the attenuator.

The mirrors of interferometric detectors of gravitational waves (GW) are suspended in order to be isolated from external disturbances. A local control system able to keep them correctly aligned and to damp the angular modes of the suspension is necessary. In this paper we present the solution adopted for Virgo based on a CCD camera sensor and on digital controls. With this solution the mirrors are kept aligned at the level of less than 1 μrad rms, enough to lock the interferometer and start the automatic alignment system.

Most of the known pulsars with frequencies lying in the best sensitivity range of the Virgo/LIGO/TAMA interferometers belong to binary systems. Accordingly their frequencies are Doppler shifted in an unknown way. We investigate a new method to search for and extract the parameters of such pulsars. A first preliminary test of this method, performed on the Virgo data recorded during the E4 engineering run, is presented.

Charginos and neutralinos are searched for in the data collected by the ALEPH experiment at LEP for centre-of-mass energies up to 209 GeV. The negative result of these searches is combined with those from searches for sleptons and Higgs bosons to derive an absolute lower limit of 43.1 GeV/c(2) on the mass of the lightest supersymmetric particle (LSP), assumed to be the,lightest neutralino. This limit is obtained in the framework of the MSSM with R-parity conservation and with gaugino and sfermion mass unification at the GUT scale and assuming no mixing in the stau sector. The LSP limit degrades only slightly to 42.4 GeV/c(2) if stau mixing is considered. Within the more constrained framework of minimal supergravity, the limit is 50 GeV/c(2). (C) 2004 Published by Elsevier B.V.