Reducing the Virgo site infrastructure noise in preparation of the O4 observing run

TL;DR

This paper details the identification and mitigation of low-frequency infrastructure noise sources in the Virgo gravitational wave detector to enhance sensitivity for the upcoming O4 observing run.

Contribution

It presents a comprehensive noise characterization and mitigation strategy for infrastructure-induced disturbances in gravitational wave detectors.

Findings

Identification of critical noise sources affecting Virgo sensitivity

Implementation of targeted mitigation measures

Development of operational best practices for low-noise environments

Abstract

The heating, ventilation and air conditioning systems serving the experimental halls of the Virgo gravitational wave interferometer generate low-frequency noise - namely below 100 Hz - of seismic, acoustic, and electromagnetic origin. Such disturbances have repeatedly affected the interferometer sensitivity throughout its operational history, with particularly notable impacts during the third observing run. In preparation for the fourth run, a comprehensive investigation was carried out to identify the most critical noise sources within this infrastructure and to trace their transmission paths into the experimental areas. This manuscript presents the methodology and results of the noise characterization campaign, together with the design, implementation and assessment of targeted mitigation measures. The technical solutions adopted, along with the operational best practices developed, provide valuable guidance for the design of low-noise environments in future gravitational-wave observatories.