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 (IISN) (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.
Wang Yi
My research focuses on optical instrumentations for gravitational wave detectors. I especially have interest in thermal noise suppression in cryogenic gravitational wave detectors.

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 (member since September 2019)
Searches for gravitational waves signal emitted by ultralight boson clouds around rotating black holes with the LIGO-Virgo laser interferometers.
Angela Taliercio (member since December 2018)

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

His interests in GW physics are the search for a stochastic GW background and the search for dark matter in relation to (primordial) black holes. 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 recently discovered, Higgs-like, 125 GeV boson: di-tau Higgs decay (associated production of standard model Higgs and exotic Higgs particles), long-lived particles. He is also involved in the development of some of the basic tools necessary for these physics data analyses like muon momentum measurement. He is responsible for the Belgian "Tier2" computing project in the context of the World LHC Computing Grid.

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
Phenomenology of elementary particles
Data analysis in HEP and GW experiments
Detector commissioning, operation and data processing
Research and development of new detectors

Experiments and collaborations:

Active projects
E-TEST - Cryogenic inertial sensor development
Giacomo Bruno, Krzysztof Piotrzkowski, Joris van Heijningen

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.

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

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.
Search for Higgs bosons in the ll tau tau final state with the CMS experiment at the LHC
Giacomo Bruno, Claudio Caputo, Angela Taliercio

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.
Search for long-lived heavy neutral leptons with CMS
Giacomo Bruno, Claudio Caputo, Angela Taliercio

Many well motivated new physics extensions of the SM include new particles whose decay width is very small and hence have a decay length which is macroscopic. One very attractive and minimal extension of the standard model is one with right-handed neutrinos with Majorana masses below the electroweak scale (low scale see-saw). This addition is able to generate both the light neutrino masses and the baryon asymmetry of the universe via low scale leptogenesis. In what is probably the most studied model that invokes the low scale seesaw, the Neutrino Minimal Standard Model [2], one of the three right-handed neutrinos is a dark matter candidate. A large allowed region of phase space for right handed neutrinos spans masses between 1 and 50 GeV with corresponding lifetimes (cτ) ranging from 10^3 to 10^-4 m. For higher masses the right handed neutrino basically decays promptly and for lower masses the probability that it decays within the detector volume is virtually zero thus giving rise to missing transverse momentum in the detector. These latter two extreme cases can be captured experimentally by standard searches at the general purpose LHC experiments, while the intermediate case is the natural target of the so-called “displaced” searches, which are highly peculiar and challenging analyses at the LHC in high demand for dedicated data reconstruction tools in order to extend their sensitivity. We intend to search for long-lived sterile neutrinos decaying at displaced vertices into a charged light lepton and hadrons. A fundamental ingredient of this search is the identification of charged tracks emerging from highly displaced vertices.
Search for massive long-lived charged particles with the CMS detector at the LHC
Giacomo Bruno, Claudio Caputo, Angela Taliercio

The CMS detector at the LHC is used to search for yet unobserved heavy (mass >100 GeV/c$^2$), long-lived (lifetime > 1 ns), electrically charged particles, called generically HSCPs.
HSCPs can be distinguished from Standard Model particles by exploiting their unique signature: very high momentum and low velocity. These features are a consequence of their high mass and the relatively limited LHC collision energy. Two experimental techniques are used to identify such hypothetical heavy and low-velocity particles: the measurement of the ionization energy loss rate using the all-silicon tracker detector and the time-of-flight measurement with the muon detectors.

UCL members have developed the ionization energy loss identification technique and have lead the CMS HSCP search since 2010, when the first HSCP paper became one of the first published LHC search papers. Updated results, using the 2011 dataset, were then published followed by a comprehensive paper including also searches for fractional and multiply-charged particles published using the full CMS Run-1 dataset. The results obtained by analysing the 2015 Run 2 data at 13 TeV have also been published.

The analysis, which is very inclusive, doesn't find evidence of HSCP. It currently excludes, among various models, the existence of quasi-stable gluinos, predicted by certain realizations of supersymmetry, and Drell-Yan-produced staus with masses lower than about 1.3 TeV and 350 GeV, respectively. These and the other limits set by the analysis are the most stringent to date. The CMS HSCP papers total to date more than 300 citations.
Virgo - computing
Giacomo Bruno, Andres Tanasijczuk

The CP3 computing cluster has been enabled to receive and run LIGO/Virgo jobs over the GRID. The CP3 cluster is being developed to host the so-called StashCash service that serves Virgo data to any job running on the GRID.
Virgo - data analysis - direct search for ultra-light dark matter with gw detectors
Giacomo Bruno, Andrew Miller

We know that a lot of matter we cannot see affects the motion of the stars around the center of the galaxy. This matter is present on earth, and in theory can interact directly with the mirrors in LIGO-Virgo in a specific way depending on the mass of the constituent particles. Since the dark matter is always present, the signal is at a fixed frequency that impinges on the detector. We are developing methods that search for this unique signature of dark matter.
Virgo - data analysis - search for a stochastic gravitational wave background
Giacomo Bruno, Federico De Lillo

The stochastic gravitational wave background (SGWB) originates from the superposition of gravitational waves of many astrophysical and cosmological sources. The variety of possible sources is huge, ranging from binary coalescences to cosmic strings or even gravitational waves produced during inflation or phase transitions. A detection of the SGWB would have a large impact on our understanding of black hole populations or cosmological models. Observing gravitational waves of inflation would be at least as revolutionary as the first observation of the cosmic microwave background. CP3 members are responsible for one of the three official directional searches conducted by LIGO and Virgo.
Virgo - data analysis - searches for inspiralling primordial black holes
Giacomo Bruno, Federico De Lillo, Andrew Miller

The detection of gravitational waves from the merger of heavy binary black hole and neutron star systems has driven the worldwide interest in gravitational wave physics. However, we have only seen the last second or less of these systems’ lives. If the black holes were less massive, we could actually have seen them as they were slowly moving towards each other. Lighter black holes imply different physics and formation mechanisms for them in the universe, hence a detection of these so-called primordial black holes would be a major breakthrough in physics.

External collaborators: Sebastien Clesse (ULB).
Virgo - data analysis - ultra-light dark matter around black holes
Giacomo Bruno, Antoine Depasse, Andrew Miller

If ultralight dark matter exists and is composed of bosons, dark matter clouds can form around black holes after their birth and grow exponentially in size by extracting energy and spin from the black holes. Once the cloud has fully formed, the bosons will couple to each other and annihilate, emitting almost monochromatic (fixed energy) gravitational waves for extremely long periods of time. The boson can be treated as a scalar, vector or tensor field, which all imply different timescales for growth and deletion, and gravitational wave signal strength. Additionally, the implications of a detection of differ for each of these fields.
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 CP3
All my publications on Inspire

Number of publications as CP3 member: 57 Download BibTeX

Last 5 publications


CP3-21-06: Search for anisotropic gravitational-wave backgrounds using data from Advanced LIGO's and Advanced Virgo's first three observing runs
The LIGO Scientific Collaboration and the Virgo Collaboration and the KAGRA Collaboration

[Abstract] [PDF]
Submitted to PRD.
Refereed paper. March 16.


CP3-20-65: Adapting a semi-coherent method to directly detect dark photon dark matter interacting with gravitational-wave interferometers
Miller, Andrew L. and others

[Abstract] [PDF]
Submitted to PRD
Refereed paper. December 26.
CP3-20-64: Probing planetary-mass primordial black holes with continuous gravitational waves
Miller, Andrew L. and Clesse, S\'ebastien and De Lillo, Federico and Bruno, Giacomo and Depasse, Antoine and Tanasijczuk, Andres

[Abstract] [PDF]
Submitted to Phys. Dark Univ.
Refereed paper. December 26.
CP3-20-40: Search for nonresonant Higgs boson pair production in the 4 leptons plus 2 b jets final state in proton-proton collisions at √s = 13 TeV
CMS Collaboration

[Full text]
Public experimental note. August 2.
CP3-20-33: Test beam demonstration of silicon microstrip modules with transverse momentum discrimination for the future CMS tracking detector
CMS Tracker Collaboration

[Journal] [Full text]
Published in: JINST 13 (2018) 03, P03003, Report number: FERMILAB-PUB-18-385-CMS, CERN-CMS-NOTE-2017-010

O. Bondu5, S. Brochet5, A. Caudron5, S. De Visscher5, B. Francois5, A. Jafari5, J. Cabrera Jamoulle5, M. Komm5, G. Krintiras5, A. Magitteri5, A. Mertens5, D. Michotte5, M. Musich5,, L. Quertenmont5, M. Vidal Marono5,
Refereed paper. July 2.

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