Grégory Hammad

University of Liège | ulg · GIGA-CRC in vivo imaging

Background Light exposure significantly impacts human health, regulating our circadian clock, sleep–wake cycle and other physiological processes. With the emergence of wearable light loggers and dosimeters, research on real-world light exposure effects is growing. There is a critical need to standardize data collection and documentation across stud...

Rapid eye movement sleep (REMS) is increasingly suggested as a discriminant sleep state for subtle signs of age-related neurodegeneration. While REMS expression is under strong circadian control and circadian dysregulation increases with age, the association between brain aging and circadian REMS regulation has not yet been assessed. Here, we measu...

Light exposure fundamentally influences human physiology and behavior, with light being the most important zeitgeber of the circadian system. Throughout the day, people are exposed to various scenes differing in light level, spectral composition and spatio-temporal properties. Personalized light exposure can be measured through wearable light logge...

Background Circadian dysfunction increases with age, leading to changes in the circadian regulation of physiological and biological rhythms, including sleep. Actigraphy studies demonstrated that altered 24‐h rest‐activity patterns, an estimate of circadian sleep‐wake regulation, is related to cognitive decline and tightly linked to Alzheimer’s dise...

Study objectives Daytime napping is frequently reported among the older population and has attracted increasing attention due to its association with multiple health conditions. Here, we tested whether napping in the aged is associated with altered circadian regulation of sleep, sleepiness and vigilance performance. Methods Sixty healthy older ind...

This article introduces a comprehensive metadata descriptor aimed at capturing crucial metadata information within personalized light exposure datasets. This metadata descriptor fills a critical gap in the field of personalized light exposure research by promoting standardized documentation of light exposure metadata. Light exposure profoundly impa...

Study objectives Daytime napping is frequently reported among the older population and has attracted increasing attention due to its association with multiple health conditions. Here, we tested whether napping in the aged is associated with altered circadian regulation of sleep, sleepiness and vigilance performance. Methods Sixty healthy older ind...

The circadian system orchestrates sleep timing and structure and is altered with increasing age. Sleep propensity, and particularly REM sleep is under strong circadian control and has been suggested to play an important role in brain plasticity. In this exploratory study, we assessed whether surface-based brain morphometry indices are associated wi...

Sleep has been suggested to contribute to myelinogenesis and associated structural changes in the brain. As a principal hallmark of sleep, slow-wave activity (SWA) is homeostatically regulated but also differs between individuals. Besides its homeostatic function, SWA topography is suggested to reflect processes of brain maturation. Here, we assess...

Light exposure fundamentally influences human physiology and behavior, with light being the most important zeitgeber of the circadian system. Throughout the day, people are exposed to a variety of different scenes differing in light level, spectral composition and spatio-temporal properties. Personalized light exposure can be measured through weara...

Growing epidemiological evidence points towards an association between fragmented 24‐h rest‐activity cycles and cognition in the aged. Alterations in the circadian timing system might at least partially account for these observations. Here, we tested whether daytime rest is associated with changes in concomitant 24‐h rest probability profiles, circ...

Context Cognitive fatigue (CF) is a disabling symptom frequently reported by patients with multiple sclerosis (pwMS). Whether pwMS in the early disease stages present an increased sensitivity to fatigue induction remains debated. Objective measures of CF have been validated neither for clinical nor research purposes. This study aimed at (i) assessi...

Over the past 40 years, actigraphy has been used to study rest-activity patterns in circadian rhythm and sleep research. Furthermore, considering its simplicity of use, there is a growing interest in the analysis of large population-based samples, using actigraphy. Here, we introduce pyActigraphy, a comprehensive toolbox for data visualization and...

Over the past 40 years, actigraphy has been used to study rest-activity patterns in circadian rhythm and sleep research. Furthermore, considering its simplicity of use, there is a growing interest in the analysis of large population-based samples, using actigraphy. Here, we introduce pyActigraphy , a comprehensive toolbox for data visualization and...

Study Objectives Sleep disturbances and genetic variants have been identified as risk factors for Alzheimer’s disease. Our goal was to assess whether genome-wide polygenic risk scores (PRS) for AD associate with sleep phenotypes in young adults, decades before typical AD symptom onset. Methods We computed whole-genome Polygenic Risk Scores (PRS) f...

Study Objectives Sleep disturbances and genetic variants have been identified as risk factors for Alzheimer’s disease. Our goal was to assess whether genome-wide polygenic risk scores (PRS) for AD associate with sleep phenotypes in young adults, decades before typical AD symptom onset. Methods We computed whole-genome Polygenic Risk Scores (PRS) f...

We investigated whether cognitive fitness in late midlife is associated with physiological and psychological factors linked to increased risk of age-related cognitive decline. Eighty-one healthy late middle-aged participants (mean age: 59.4 y; range: 50-69 y) were included. Cognitive fitness consisted of a composite score known to be sensitive to e...

Objectif La fragmentation du cycle veille-sommeil augmente avec l’âge. Ici, nous explorons la sieste comme indicateur de cette fragmentation et son impact sur les performances cognitives. Méthodes Des données d’actimétrie ont été collectées chez 35 personnes âgées (57–85 ans, 18 femmes, 19 siesteurs [sieste > 20 min/jour, > 3 fois/semaine, depuis...

The structure of the CMS inner tracking system has been studied using nuclear interactions of hadrons striking its material. Data from proton-proton collisions at a center-of-mass energy of 13 TeV recorded in 2015 at the LHC are used to reconstruct millions of secondary vertices from these nuclear interactions. Precise positions of the beam pipe an...

A new CMS Tracker is under development for operation at the High Luminosity LHC from 2026 onwards. It includes an outer tracker based on dedicated modules that will reconstruct short track segments, called stubs, using spatially coincident clusters in two closely spaced silicon sensor layers. These modules allow the rejection of low transverse mome...

Measurements of the associated production of a \(\mathrm{Z}\) boson with at least one jet originating from a b quark in proton–proton collisions at \(\sqrt{s} = 8\,\text {TeV} \) are presented. Differential cross sections are measured with data collected by the CMS experiment corresponding to an integrated luminosity of 19.8\(\,\text {fb}^{-1}\). \...

The cross section for coherent J/ψ photoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, Xn0n, is measured with the CMS experiment in ultra-peripheral PbPb collisions at √sN N = 2.76 TeV. The analysis is based on a data sample corresponding to an integrated luminosity of...

The high luminosity upgrade of the Large Hadron Collider, foreseen for 2026, necessitates the replacement of the CMS experiment’s silicon tracker. The innermost layer of the new pixel detector will be exposed to severe radiation, corresponding to a 1 MeV neutron equivalent fluence of up to \(\Phi _{eq} = 2 \times 10^{16}\) cm\(^{-2}\), and an ionis...

Two-particle correlations in pPb collisions at a nucleon-nucleon center-of-mass energy of 5.02TeV are studied as a function of the pseudorapidity separation (Δη) of the particle pair at small relative azimuthal angle (|Δϕ|<π/3). The correlations are decomposed into a jet component that dominates the short-range correlations (|Δη|<1), and a componen...

Two-particle correlations in p Pb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV are studied as a function of the pseudorapidity separation ( Δ η ) of the particle pair at small relative azimuthal angle ( | Δ ϕ | < π / 3 ). The correlations are decomposed into a jet component that dominates the short-range correlations ( | Δ η |...

The cross section for coherent photoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, , is measured with the CMS experiment in ultra-peripheral PbPb collisions at . The analysis is based on a data sample corresponding to an integrated luminosity of 159 , collected during t...

The upgrade of the LHC to the High-Luminosity LHC (HL-LHC) is expected to increase the LHC design luminosity by an order of magnitude. This will require silicon tracking detectors with a significantly higher radiation hardness. The CMS Tracker Collaboration has conducted an irradiation and measurement campaign to identify suitable silicon sensor ma...

An inclusive search is performed for supersymmetry in final states containing jets and an apparent imbalance in transverse momentum, p→Tmiss, due to the production of unobserved weakly interacting particles in pp collisions at a centre-of-mass energy of 8 TeV. The data, recorded with the CMS detector at the CERN LHC, correspond to an integrated lum...

The invariance of the standard model (SM) under the CPT transformation predicts equality of particle and antiparticle masses. This prediction is tested by measuring the mass difference between the top quark and antiquark (Δmt=mt−mt‾) that are produced in pp collisions at a center-of-mass energy of 8 TeV, using events with a muon or an electron and...

Measurements of strange hadron (KS0, Λ+Λ‾, and Ξ−+Ξ‾+) transverse momentum spectra in pp, pPb, and PbPb collisions are presented over a wide range of rapidity and event charged-particle multiplicity. The data were collected with the CMS detector at the CERN LHC in pp collisions at s=7TeV, pPb collisions at sNN=5.02TeV, and PbPb collisions at sNN=2....

Improved jet energy scale corrections, based on a data sample corresponding to an integrated luminosity of 19.7 fb−1 collected by the CMS experiment in proton-proton collisions at a center-of-mass energy of 8 TeV, are presented. The corrections as a function of pseudorapidity η and transverse momentum pT are extracted from data and simulated events...

This paper describes the CMS trigger system and its performance during Run 1 of the LHC. The trigger system consists of two levels designed to select events of potential physics interest from a GHz (MHz) interaction rate of proton-proton (heavy ion) collisions. The first level of the trigger is implemented in hardware, and selects events containing...

This paper describes the CMS trigger system and its performance during Run 1 of the LHC. The trigger system consists of two levels designed to select events of potential physics interest from a GHz (MHz) interaction rate of proton-proton (heavy ion) collisions. The first level of the trigger is implemented in hardware, and selects events containing...

A measurement of the top quark pair production (\(\mathrm{t}\overline{\mathrm{t}} \)) cross section in proton–proton collisions at the centre-of-mass energy of 8\(\,\text {TeV}\) is presented using data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.6\(\,\text {fb}^{-\text {1}}\). This analysis is perfor...

Results are presented from searches for R-parity-violating supersymmetry in events produced in pp collisions at √s = 8 TeV at the LHC. Final states with 0, 1, 2, or multiple leptons are considered independently. The analysis is performed on data collected by the CMS experiment corresponding to an integrated luminosity of 19.5 fb^(−1). No excesses o...

A search for dark matter particles directly produced in proton-proton collisions recorded by the CMS experiment at the LHC is presented. The data correspond to an integrated luminosity of 18.8 fb−1, at a center-of-mass energy of 8 TeV. The event selection requires at least two jets and no isolated leptons. The razor variables are used to quantify t...

A measurement is presented of the cross section for the electroweak production of a W boson in association with two jets in proton-proton collisions at a center-of-mass energy of 8 TeV. The data set was collected with the CMS detector and corresponds to an integrated luminosity of 19.3 fb−1 . The measured fiducial cross section for W bosons decayin...

A search for pair production of third-generation scalar leptoquarks decaying to top quark and τ lepton pairs is presented using proton-proton collision data at a center-of-mass energy of s √ =8 s=8 TeV collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 19.7 fb−1. The search is performed using events that co...

A measurement is presented of the cross section for the electroweak production of a W boson in association with two jets in proton-proton collisions at a center-of-mass energy of 8 TeV. The data set was collected with the CMS detector and corresponds to an integrated luminosity of 19.3 fb−1. The measured fiducial cross section for W bosons decaying...

The cross section for pair production of top quarks (tt) with high transverse momenta is measured in pp collisions, collected with the CMS detector at the LHC with s=8 TeV in data corresponding to an integrated luminosity of 19.7 fb-1. The measurement is performed using lepton+jets events, where one top quark decays semileptonically, while the seco...

The polarizations of the ϒ(1S), ϒ(2S), and ϒ(3S) mesons are measured as a function of the charged particle multiplicity in proton–proton collisions at √s = 7 TeV. The measurements are performed with a dimuon data sample collected in 2011 by the CMS experiment, corresponding to an integrated luminosity of 4.9 fb−1. The results are extracted from the...

A direct search for lepton flavour violating decays of the Higgs boson (H) in the H→eτ and H→eμ channels is described. The data sample used in the search was collected in proton–proton collisions at s=8 TeV with the CMS detector at the LHC and corresponds to an integrated luminosity of 19.7 fb−1. No evidence is found for lepton flavour violating de...

A measurement of the decorrelation of azimuthal angles between the two jets with the largest transverse momenta is presented for seven regions of leading jet transverse momentum up to 2.2\(\,\mathrm{TeV}\). The analysis is based on the proton-proton collision data collected with the CMS experiment at a centre-of-mass energy of 8\(\,\mathrm{TeV}\) c...

Searches for new physics by the CMS collaboration are interpreted in the framework of the phenomenological minimal supersymmetric standard model (pMSSM). The data samples used in this study were collected at \( \sqrt{s}=7 \) and 8 TeV and have integrated luminosities of 5.0 fb−1 and 19.5 fb−1, respectively. A global Bayesian analysis is performed,...

A search is presented for the production of two Higgs bosons in final states containing two photons and two bottom quarks. Both resonant and nonresonant hypotheses are investigated. The analyzed data correspond to an integrated luminosity of 19.7 fb-1 of proton-proton collisions at s=8 TeV collected with the CMS detector. Good agreement is observed...

Measurements are reported of the normalized differential cross sections for top quark pair production with respect to four kinematic event variables: the missing transverse energy; the scalar sum of the jet transverse momentum (pT); the scalar sum of the pT of all objects in the event; and the pT of leptonically decaying W bosons from top quark dec...

Measurements are reported of the normalized differential cross sections for top quark pair production with respect to four kinematic event variables: the missing transverse energy; the scalar sum of the jet transverse momentum (pT); the scalar sum of the pT of all objects in the event; and the pT of leptonically decaying W bosons from top quark dec...

A search is presented for single top quark production in the s channel in proton-proton collisions with the CMS detector at the CERN LHC in decay modes of the top quark containing a muon or an electron in the final state. The signal is extracted through a maximum-likelihood fit to the distribution of a multivariate discriminant defined using booste...

A search is presented for the Higgs boson off-shell production in gluon fusion and vector boson fusion processes with the Higgs boson decaying into a W+W− pair and the W bosons decaying leptonically. The data observed in this analysis are used to constrain the Higgs boson total decay width. The analysis is based on the data collected by the CMS exp...

The polarizations of the , , and mesons are measured as a function of the charged particle multiplicity in proton-proton collisions at . The measurements are performed with a dimuon data sample collected in 2011 by the CMS experiment, corresponding to an integrated luminosity of 4.9 fb−1. The results are extracted from the dimuon decay angular dist...

The inclusive cross section for top quark pair production is measured in proton-proton collisions at \( \sqrt{s}=7 \) and 8 TeV, corresponding to 5.0 and 19.7 fb−1, respectively, with the CMS experiment at the LHC. The cross sections are measured in the electron-muon channel using a binned likelihood fit to multi-differential final state distributi...

Results are reported from a search for the pair production of top squarks, the supersymmetric partners of top quarks, in final states with jets and missing transverse momentum. The data sample used in this search was collected by the CMS detector and corresponds to an integrated luminosity of 18.9\(\,\text {fb}^\text {-1}\) of proton-proton collisi...

The differential cross section and charge asymmetry for inclusive \(\mathrm {p}\mathrm {p}\rightarrow \mathrm {W}^{\pm }+X \rightarrow \mu ^{\pm }\nu +X\) production at \(\sqrt{s}=8\,\mathrm{TeV} \) are measured as a function of muon pseudorapidity. The data sample corresponds to an integrated luminosity of 18.8\(\,\text {fb}^{-1}\) recorded with t...

A search for exclusive or quasi-exclusive γγ → W+W− production, via pp → p(*)W+W−p(*) → p(*)μ±e∓p(*) at \( \sqrt{s}=8 \) TeV, is reported using data corresponding to an integrated luminosity of 19.7 fb−1. Events are selected by requiring the presence of an electron-muon pair with large transverse momentum pT(μ±e∓) > 30 GeV, and no associated charge...

The decorrelation in the azimuthal angle between the most forward and the most backward jets (Mueller-Navelet jets) is measured in data collected in pp collisions with the CMS detector at the LHC at \( \sqrt{s}=7 \) TeV. The measurement is presented in the form of distributions of azimuthal-angle differences, Δϕ, between the Mueller-Navelet jets, t...

The consistency of the spin correlation strength in top quark pair production with the standard model (SM) prediction is tested in the muon+jets final state. The events are selected from pp collisions, collected by the CMS detector, at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 fb−1. The data are compared wi...

A search is reported for a light pseudoscalar Higgs boson decaying to a pair of τ leptons, produced in association with a bb pair, in the context of two-Higgs-doublet models. The results are based on pp collision data at a centre-of-mass energy of 8 TeV collected by the CMS experiment at the LHC and corresponding to an integrated luminosity of 19.7...

An inclusive measurement of the Zγ→νν‾γ production cross section in pp collisions at s=8TeV is presented, using data corresponding to an integrated luminosity of 19.6 fb−1 collected with the CMS detector at the LHC. This measurement is based on the observation of events with large missing energy and with a single photon with transverse momentum abo...

The charge asymmetry in tt‾ events is measured using dilepton final states produced in pp collisions at the LHC at s=8TeV. The data sample, collected with the CMS detector, corresponds to an integrated luminosity of 19.5fb−1. The measurements are performed using events with two oppositely charged leptons (electrons or muons) and two or more jets, w...

Inclusive jet production in pPb collisions at a nucleon–nucleon (NN) center-of-mass energy of \(\sqrt{s_{_\mathrm {NN}}} =5.02\,\mathrm{TeV} \) is studied with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 30.1 nb\(^{-1}\) is analyzed. The jet transverse momentum spectra are studied in seven pseudorapidity...

A search is presented for narrow heavy resonances X decaying into pairs of Higgs bosons (\({\mathrm{H}}\)) in proton-proton collisions collected by the CMS experiment at the LHC at \(\sqrt{s}=8\,\text {TeV} \). The data correspond to an integrated luminosity of 19.7\(\,\text {fb}^{-1}\). The search considers \({\mathrm{H}} {\mathrm{H}} \) resonance...

Jet multiplicity distributions in top quark pair (t t ¯) events are measured in pp collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC using a data set corresponding to an integrated luminosity of 19.7fb-1. The measurement is performed in the dilepton decay channels (e +e -, μ+μ-, and e ±μ∓). The absolute and normalized...