Giacomo Bruno

Academic staff


Centre for Cosmology, Particle Physics and Phenomenology - CP3
Université catholique de Louvain
2, Chemin du Cyclotron - Box L7.01.05
B-1348 Louvain-la-Neuve

+32 10 47 3215


UCL member card
People responsibilities
Claudio Caputo (FNRS) (member since April 2017)
I am an experimental particle physicist, member of the CMS collaboration. I am particularly interested in precision measurements of the Higgs boson and searches for new physics.
Andrew Miller (member since January 2020)
I work as part of the LIGO/Virgo collaborations to develop data analysis techniques to detect gravitational waves from isolated neutron stars, depleting boson clouds around black holes, inspiraling primordial black holes, and the stochastic gravitational-wave background. I am also interested in searches for dark matter that interacts directly with gravitational-wave interferometers. In my spare time, I enjoy playing volleyball, travelling, reading, and hiking.
Magdalena Sieniawska (IISN - Virgo) (member since June 2021)
I work on the continuous gravitational wave data analysis for the Virgo Project. My scientific interests cover gravitational radiation theory, detection methods and the neutron stars' equation of state.
Jishnu Suresh (IISN - VIRGO) (member since October 2021)
My primary research focuses on the searches for stochastic gravitational-wave background -SGWB (origin of such a background could be cosmological or astrophysical) using the data from LIGO, Virgo, and KAGRA (LVK) detectors. We have placed the most stringent bounds on the energy density of SGWBs using the latest observational data along with the (first) upper limit maps of the gravitational-wave sky at every frequency bin. We expect that the current efforts will make significant progress in the coming years and result in the first detection of SGWBs. I am also interested in understanding some aspects of the alternative theories of gravity. In the past, I have worked on black hole thermodynamic aspects of these theories in a newly developed framework called Geometrothermodynamics.

PhD students
Federico De Lillo (member since April 2019)
Involved in the search for a stochastic gravitational wave background (SGWB), with particular interest in anisotropies and cosmological components, within the LIGO-Virgo-KAGRA (LVK) collaboration as a Virgo member.
Antoine Depasse (UCL-assistants) (member since September 2019)
Searches for gravitational waves signal emitted by ultralight boson clouds around rotating black holes with the LIGO-Virgo laser interferometers.
Paola Mastrapasqua (member since December 2021)
Stavros Venikoudis (ARC) (member since October 2022)
My research is focused on Stochastic Gravitational Wave Backgrounds with the LIGO-Virgo laser interferometric detectors. Specifically, I work on the development of techniques aimed to disentangle, in case of detection of an SGWB signal, the different contributions to the SGWB and determine their distributions on the sky. Also, I work on the investigation of possible correlations in time and frequency of SGWBs from cosmological sources, such as cosmic strings after relaxing the assumption of stationarity.

Yves Felix (member since September 1981)
topologie algébrique, homotopie rationnelle.
Michel Willem (member since September 2009)
nonlinear partial differential equations, global analysis, calculus of variations, functional analysis, real analysis, history of mathematics.

Former members
Research statement
Giacomo Bruno is an experimental physicist doing research in fundamental interactions with the laser interferometric antenna for gravitational wave (GW) detection Virgo at the EGO observatory and with the CMS experiment at the LHC collider of the CERN laboratory. He is also involved in the preparation of the future terrestrial laser interferometer Einstein Telescope.

His interests in GW physics, which are the core of his current research activity, are related to the stochastic GW background and the detection of quasi-monochromatic GW signals. He is also contributing to the development of Virgo instrumentation and its computing and core software infrastructure.

His current interests in particle physics are searches for signals of physics beyond the Standard Model and measurements related to the 125 GeV Higgs boson: di-tau Higgs decay (associated production of standard model Higgs and exotic Higgs particles). He is also involved in the development of an algorithm for muon momentum measurement. He is responsible for the Belgian "Tier2" computing project in the context of the World LHC Computing Grid.

Before 2018 Giacomo Bruno contributed over several years to the construction of the CMS detector and its related infrastructure. The main contributions were in the following areas: research and development of the RPC gaseous detectors, design of the CMS muon trigger, development of CMS software for online data acquisition, physics data analysis, and configuration/monitoring/calibration of the silicon strip tracker detector.
Research directions:
Cosmology and General Relativity
Data analysis in HEP, astroparticle and GW experiments
Detector commissioning, operation and data processing
Phenomenology of elementary particles
Research and development of new detectors

Experiments and collaborations:

Active projects
E-TEST - Cryogenic inertial sensor development
Giacomo Bruno, Joris van Heijningen, Morgane Zeoli

On Feb 1, 2020 the R&D EU Interreg project E-TEST officially started. It involves 11 institutes from Belgium, Germany and Netherlands and will carry on crucial detector developments for the Einstein Telescope (ET) - a 3rd generation antenna of gravitational waves, related mostly to cryogenic operations of large mass mirrors and their suspensions, ultra-precise metrology and sensing, as well as to advanced geological studies in the region (the ET is a deep-underground detector). The CP3 group is a partner in this project and is working on work package 1 : "Ultra-cold vibration control" and in particular on a cryogenic superconducting inertial sensor.

Gravitational wave signals below a frequency of about 10 Hz are obscured by thermal noise in current detectors. Because temperature is the vibration of atoms in some respect, making the distance measurement between the mirror surfaces more challenging, the mirrors of future detectors will need to be cooled down to temperatures around 10 K. We need to control the motion of some of the cold objects, for which we develop inertial sensors that can survive this harsh environment. The interferometric readout of the inertial sensor also serves as to monitor a ringdown or the E-TEST mirror. After it is excited by a tiny hammer strike, the interferometer follows the ringdown and can determine the quality factor. Additionally, we are investigating an alternative suspension technique, where instead of long fibres under tension, we use short flexures under compression in combination with long, fat rods so we obtain good thermal conductivity and low stiffness suspension.

CP3 members collaborate mostly with KU Leuven (we are collaborating to develop cryogenic readout electronics for the sensor) and ULiège (we align our sensor efforts), RWTH Aachen (they are preparing a cryostat where we will test the inertial sensor).

External collaborators: C. Collette (Liege), S. Hild (Maastricht), A. Bertolini (Nikhef), A. Gatto (KULeuven) and E-TEST collaboration.
ETpathfinder - Bench top suspension design and fabrication
Giacomo Bruno, Nicolas Szilasi, Joris van Heijningen

The ETpathfinder is an R&D infrastructure for testing and prototyping innovative concepts and enabling technologies for the Einstein Telescope, the European concept for a new class of future gravitational wave observatories. ETpathfinder is funded by the interreg program of the EU. The ETpathfinder project broadly consists of six vacuum towers. Four towers are cryogenic and hold suspensions for the mirrors (or test masses) of the experiment. Two towers are operated at room temperature. They hold suspensions for optical tables which hold smaller optics that prepare the beams to be shot into both arms (mode cleaning, frequency stabilisation etc.) and hold the beamsplitters and detection optics.

Many of these optics are suspended individually with small bench top suspensions so they can be steered and additionally seismically isolated. This project concerns the design, prototyping and partial fabrication of >10 suspensions of order 75cm high.

External collaborators: S. Hild (Maastricht), A. Bertolini (Nikhef), Conor Mow-Lowry (Nikhef), Ken Strain (and other LIGO HRTS designers) and ETpathfinder collaboration.
Multi-messenger studies of transient sources
Giacomo Bruno, Karlijn Kruiswijk, Andrew Miller, Magdalena Sieniawska, Jishnu Suresh, Gwenhaël Wilberts Dewasseige

This project aims at studying astrophysical phenomena combining different messengers, mainly neutrinos and gravitational waves.
Search for Higgs bosons in the ll tau tau final state with the CMS experiment at the LHC
Giacomo Bruno, Claudio Caputo, Paola Mastrapasqua

A resonance consistent with the stanadard model Higgs boson with mass of about 125 GeV was discovered in 2012 by the CMS and ATLAS experiments at the LHC. Using the available dataset (2011+2012 LHC runs) evidence was later found of the existence of the SM-predicted decay into a pair of tau leptons. The CP3 Louvain group has been involved in the channel where the Higgs boson is produced in association with the Z boson and decays into a pair of tau leptons.

A search for additional Higgs bosons in the general framework of models with two Higgs doublets (2HDM) was then performed by the same CP3 group using the same final state and the full Run-1 data. Models with two Higgs doublets feature a pseudoscalar boson, A, two charged scalars (H+-) and two neutral (h0 and H0) scalars, one of which is identified with the 125 GeV SM-like Higgs resonance. In some scenarios the most favored decay chain for the discovery of the additional neutral bosons is H0-->ZA-->llττ (or llbb). The search was carried out in collaboration with another group in CP3 who looks at the llbb final state.

An update of both the SM search and the exotic one is expected using the Run-2 dataset using more advanced techniques and by adding the llee and llmumu channels.
Virgo - computing
Giacomo Bruno, Andres Tanasijczuk

The existing UCLouvain/CP3 computing cluster has been augmented with GW-dedicated computing and storage resources. The cluster is integrated into the International Gravitational-Wave Observatory Network (IGWN) Computing Grid, leveraging on the infrastructure CP3 has in place for serving the cluster to the World LHC GRID (WLCG). The UCLouvain GW group has also taken up the responsibility of maintaining at the UCLouvain cluster a service that hosts and serves Virgo data to GW analysis codes submitted over the GRID by the entire LIGO/Virgo/KAGRA international Collaborations.
Virgo - data analysis - search for a stochastic gravitational wave background
Giacomo Bruno, Federico De Lillo, Jishnu Suresh

The stochastic gravitational wave background (SGWB) originates from the superposition of GWs emitted by a large number of
unresolved and uncorrelated sources. Its detection is considered to be one of the ”holy grails” of
GW astronomy, because of its possible cosmological origin and consequently its impact on our
comprehension of the Universe.

The Louvain GW group has been contributing a major effort to the search
for an anisotropic SGWB and the publication of its results. The group is esponsible for one
of the three data analysis algorithms of the LIGO/Virgo/KAGRA (LVK) Collaboration, called broadband radiometer analysis.
Dr J. Suresh has been acting as the anisotropic sub-group chair for the LVK SGWB
group. Not having found any evidence for an SGWB signal, upper limits have been set as a
function of the sky direction.

Millisecond pulsars are one of the potential candidates contributing to the anisotropic stochastic
gravitational-wave background observable in the ground-based gravitational-wave detectors.
We have been contributing to a project aiming to estimate and detect the
stochastic gravitational-wave background produced by millisecond pulsars in the Milky Way.

We have contributed significantly to the published results of a search that looks for
persistent stochastic gravitational-wave sources in all directions of the sky at all frequencies at
which the detectors are sensitive.

Our group has also published a search that is capable of setting constraints on the
ensemble properties of neutron stars, like their average ellipticity, from cross-correlation-based
stochastic gravitational-wave background measurements.
Virgo - data analysis - searches with continuous gravitational waves
Giacomo Bruno, Federico De Lillo, Antoine Depasse, Andrew Miller, Magdalena Sieniawska

Asymmetrically rotating neutron stars (NS) are the canonical sources of continuous gravitational
waves, which is the name given to long-duration, almost monochromatic GW signals. There has
been a growing number of other sources of similar signals, which are in general very weak, but
because they are almost monochromatic and of very long duration, they can be integrated over
observation periods lasting up to years and become observable. Sophisticated corrections need to be devised
in order to capture these long and weak signals. These corrections
take into account the deviation from perfect mono-chromaticity of the signal frequency spectrum, which are caused either
by the source dynamics of by the relative movement of the source and the detector.

Our group has been setting up a search for new ultra-light bosons, which could be dark matter (DM) candidates and could accumulate around spinning black holes (BH) via superradiance. In particular, we have been
focusing on the search for vector boson accumulating in known X-ray binaries in our galaxy.
In addition to the movement of the earth, the signal will be modulated by the Doppler effect due to the motion of the source black hole (BH)
around its barycenter.

Our group is also active on studies aiming to detect planetary-mass (10^-7 to 10^-2 M⊙) primordial BHs (PBH) with continuous-wave
methods. The method applies to binary
systems that are still far from the merger and has allowed to constrain the rates and abundance of PBHs in the universe. Limits on the
fraction of DM made of such PBHs (in the galactic halo, in the galactic centre, and in the solar
system vicinity) have also been calculated, for LIGO/Virgo as well as ET.

Ultra-light (10^-13 - 10^-11 eV) bosons could interact with the baryons and leptons in the LIGO/Virgo
mirrors, causing a constant, narrowband signal in the instruments, very similar to a quasi-monochromatic GW.
This project displays synergy between particle physics and GW physics and shows that we can
now directly look for DM candidates with GW instruments. Both short-author list and Collaboration-wide publications have resulted from this project.
World LHC Computing Grid: the Belgian Tier2 project
Giacomo Bruno, Jérôme de Favereau, Pavel Demin, Vincent Lemaitre, Andres Tanasijczuk

The World LHC Computing GRID (WLCG) is the worldwide distributed computing infrastructure controlled by software middleware that allows a seamless usage of shared storage and computing resources.

About 10 PBytes of data are produced every year by the experiments running at the LHC collider. This data must be processed (iterative and refined calibration and analysis) by a large scientific community that is widely distributed geographically.

Instead of concentrating all necessary computing resources in a single location, the LHC experiments have decided to set-up a network of computing centres distributed all over the world.

The overall WLCG computing resources needed by the CMS experiment alone in 2016 amount to about 1500 kHepSpec06 of computing power, 90 PB of disk storage and 150 PB of tape storage. Working in the context of the WLCG translates into seamless access to shared computing and storage resources. End users do not need to know where their applications run. The choice is made by the underlying WLCG software on the basis of availability of resources, demands of the user application (CPU, input and output data,..) and privileges owned by the user.

Back in 2005 UCL proposed the WLCG Belgian Tier2 project that would involve the 6 Belgian Universities involved in CMS. The Tier2 project consists of contributing to the WLCG by building two computing centres, one at UCL and one at the IIHE (ULB/VUB).

The UCL site of the WLCG Belgian Tier2 is deployed in a dedicated room close to the cyclotron control room of the IRMP Institute and is currently a fully functional component of the WLCG.

The UCL Belgian Tier2 project also aims to integrate, bring on the GRID, and share resources with other scientific computing projects. The projects currently integrated in the UCL computing cluster are the following: MadGraph/MadEvent, NA62 and Cosmology.

External collaborators: CISM (UCL), Pascal Vanlaer (Belgium, ULB), Lyon computing centre, CERN computing centre.

Non-active projects
Publications in IRMP
All my publications on Inspire

Number of publications as IRMP member: 77
Last 5 publications


IRMP-CP3-22-53: Probing Ensemble Properties of Vortex-avalanche Pulsar Glitches with a Stochastic Gravitational-Wave Background Search
De Lillo, Federico and Suresh, Jishnu and Depasse, Antoine and Sieniawska, Magdalena and Miller, Andrew L. and Bruno, Giacomo

[Abstract] [PDF]
Available on arXiv, submitted to Physical Review D.
Refereed paper. December 1.
CP3-22-38: Strategies and performance of the CMS silicon tracker alignment during LHC Run~2
Tumasyan, Armen and others

[Abstract] [PDF] [Local file] [Journal] [Dial] [Full text]
Published in Nucl. Instrum. Meth. A
Refereed paper. August 12.


CP3-21-37: Constraints on cosmic strings using data from the third Advanced LIGO-Virgo observing run
Abbott, R. and others

[Abstract] [PDF] [Journal] [Dial]
Refereed paper. June 18.
CP3-21-36: Upper Limits on the Isotropic Gravitational-Wave Background from Advanced LIGO's and Advanced Virgo's Third Observing Run
Abbott, R. and others

[Abstract] [PDF] [Journal] [Dial]
Refereed paper. June 18.
CP3-21-35: Diving below the spin-down limit: Constraints on gravitational waves from the energetic young pulsar PSR J0537-6910
Abbott, R. and others

[Abstract] [PDF] [Journal] [Dial]
Refereed paper. June 18.

More publications