HAL : Dernières publications

[tel-05642082] Search on the production of Higgs boson pairs in the bbγγ final state with the ATLAS detector, using data from Run 2 and partial data from Run 3, and characterization of the timing performance and irradiation tolerance of the High Granularity Temporal Detector

ano.nymous@ccsd.cnrs.fr.invalid (Arthur Lafarge) — Wed, 03 Jun 2026 08:45:07 +0000

This thesis presents joint advances on (i) the search for Higgs boson pair production in the bbγγ final state, (ii) the first ATLAS study dedicated to associated ttHH production in this channel, and (iii) the experimental validation of the timing performance and radiation robustness of the High-Granularity Timing Detector (HGTD) readout electronics in preparation for the HL-LHC.The combined gluon-gluon fusion (ggF) and vector-boson fusion (VBF) HH → bbγγ search, exploiting 308 inverse femtobarns of Run 2 data at a center-of-mass energy of 13 TeV, supplemented with early Run 3 data at 13.6 TeV, achieves the highest single-channel sensitivity in this final state for ATLAS. A unified strategy, incorporating a kinematic fit to improve the bb invariant mass resolution, a low-/high-mass separation to preserve discrimination on the self-coupling, and an optimized categorization using boosted decision trees (BDTs), maximizes the signal-to-background ratio. No significant deviation is observed (0.84 sigma), and an upper limit of μ_HH < 3.8 at 95% confidence level is set. The corresponding interval on the Higgs self-coupling modifier is -1.7 < κ_lambda < 6.6.The first ATLAS analysis targeting tt(HH → bbγγ) is developed with a multi-BDT strategy tailored to the high object multiplicity. With 199 inverse femtobarns, a 95% confidence level observed limit on μ_ttHH of 76 is obtained. This topology, roughly 38 times rarer than ggF, provides a complementary probe of the Higgs coupling structure, specifically the double top-Higgs vertex.HL-LHC projections at 3 inverse attobarns indicate that evidence could be reached in this single channel alone, with an expected significance of 2.4 sigma (2.7 sigma without systematics) and a projected tightening of the interval to κ_lambda in [-0.1, 3.4], representing a reduction of about 60% compared to current constraints. Further gains are anticipated and discussed.On the instrumental side, HGTD hybrid components tested under beam conditions achieve per-hit timing resolutions down to 36 picoseconds, close to design targets. Single-event upset (SEE) studies quantify total rates on the order of 10^-5 percent per bunch crossing per pixel channel under HL-LHC fluxes and validate mitigation mechanisms, including a triplication system and measures to handle rare stuck timing frames.These results strengthen ATLAS's capability to probe the shape of the Higgs potential and constrain the Higgs self-coupling λ (via the modifier κ_lambda), an essential step toward a dynamic understanding of electroweak symmetry breaking and scenarios beyond the Standard Model.

[tel-05627316] Modulation des réponses cellulaires aux irradiations X : approche bio-inspirée sur le modèle de l'ours brun hibernant

ano.nymous@ccsd.cnrs.fr.invalid (Jade Sutter) — Wed, 20 May 2026 09:19:05 +0000

La torpeur est caractérisée par un ralentissement métabolique profond, qui peut se prolonger sur plusieurs jours à plusieurs mois en cas d'hibernation. Cet état physiologique a été associé à une protection naturelle contre les radiations ionisantes chez des petits mammifères hibernants. La compréhension des mécanismes sous-jacents à cette tolérance pourrait permettre de développer de nouvelles stratégies de radioprotection chez l'être humain, en particulier pour les personnels travaillant en contexte radiatif. En outre, il a été démontré que le sérum d'ours brun prélevé pendant la période d'hibernation exerçait des effets anti-protéolytiques sur des cellules musculaires humaines en culture, reproduisant ainsi certaines caractéristiques de l'hibernation in vitro. Dans cette thèse, nous avons donc évalué la capacité du sérum d'ours hibernant ou non, à moduler la réponse cellulaire aux radiations ionisantes.Une première approche à large échelle sur des cellules fibroblastiques humaines saines (HFF-1) irradiées ou non a révélé qu'une incubation avec le sérum d'ours induit un profond remodelage du protéome cellulaire, avec des signes d'un phénotype anti-fibrotique. De plus, nos résultats suggèrent que cette réponse met en jeu une grande diversité de protéines plutôt qu'une voie métabolique unique. L'analyse fonctionnelle, après exposition aux rayons X, a montré un effet radiosensibilisant associé au sérum d'ours hibernant sur la lignée HFF-1. L'exploration des mécanismes impliqués a mis en évidence des modifications du cycle cellulaire, des perturbations de la réparation des cassures double brin de l'ADN, et des altérations mitochondriales. Lorsque les expériences ont été étendues à une lignée tumorale humaine (PC3), l'effet radiosensibilisant n'a pas été observé, en condition d'incubation en présence de sérum d'ours hibernant soulignant une forte dépendance à la lignée cellulaire et ouvrant la voie à de nouvelles hypothèses sur les mécanismes de radiosensibilisation. En conclusion, l'étude des effets du sérum d'ours hibernant sur des cellules humaines a révélé des mécanismes potentiels de radiosensibilisation. Ces observations ouvrent des pistes intéressantes pour la recherche radiothérapeutique, mais leur pertinence clinique reste à confirmer, notamment au regard des différences de sensibilité entre cellules normales et cellules tumorales.

[hal-05612554] Formation of dilute versus concentrated pyroclastic density currents in the impact zone of eruptive fountains: an experimental study

ano.nymous@ccsd.cnrs.fr.invalid (Baptiste Penlou) — Thu, 07 May 2026 11:21:04 +0000

We study the physical mechanisms that operate in impact zones of collapsing fountains during explosive volcanic eruptions. To this end, we simulate the formation of pyroclastic density currents in analogue laboratory experiments by releasing a mixture of glass particles of different sizes from a hopper, which impact the base of a horizontal channel. Acoustic attenuation measurements and high-speed imaging are used to monitor the particle concentration and velocity of falling mixtures just before impact. Over the course of the experiments, we identify two successive distinct regimes primarily governed by the particle concentration of the falling mixtures, which decreases over time. The first is an early decoupled regime, where particles settle in the impact zone to form a concentrated granular flow overlain by a dilute particle cloud. The second is a late coupled regime, in which particles remain entrained with the carrier air, resulting in a dilute suspension. At the transition between the regimes, we find a power-law relationship between particle concentration and the Stokes number, suggesting that these two parameters play an important role in controlling impact zone processes. We compare our results to recent numerical simulations on pyroclastic fountains and discuss relevant parameters that control the impact dynamics of pyroclastic mixtures.

[hal-04845851] Precision calibration of calorimeter signals in the ATLAS experiment using an uncertainty-aware neural network

ano.nymous@ccsd.cnrs.fr.invalid (Georges Aad) — Wed, 22 Apr 2026 15:34:25 +0000

The ATLAS experiment at the Large Hadron Collider explores the use of modern neural networks for a multi-dimensional calibration of its calorimeter signal defined by clusters of topologically connected cells (topo-clusters). The Bayesian neural network (BNN) approach not only yields a continuous and smooth calibration function that improves performance relative to the standard calibration but also provides uncertainties on the calibrated energies for each topo-cluster. The results obtained by using a trained BNN are compared to the standard local hadronic calibration and to a calibration provided by training a deep neural network. The uncertainties predicted by the BNN are interpreted in the context of a fractional contribution to the systematic uncertainties of the trained calibration. They are also compared to uncertainty predictions obtained from an alternative estimator employing repulsive ensembles.

[hal-05038157] Measurement of substructure-dependent suppression of large-radius jets with charged particles in Pb+Pb collisions with ATLAS

ano.nymous@ccsd.cnrs.fr.invalid (Georges Aad) — Wed, 22 Apr 2026 15:33:57 +0000

Measurements of jet substructure in Pb+Pb collisions provide key insights into the mechanism of jet quenching in the hot and dense QCD medium created in these collisions. This Letter presents a measurement of the suppression of large-radius jets with a radius parameter of $R = 1.0$ and its dependence on the jet substructure. The measurement uses 1.72 nb$^{-1}$ of Pb+Pb data and 255 pb$^{-1}$ of $pp$ data, both at $\sqrt{s_{_\mathrm{NN}}} = 5.02$ TeV, recorded with the ATLAS detector at the Large Hadron Collider. Large-radius jets are reconstructed by reclustering $R = 0.2$ calorimetric jets and are measured for transverse momentum above $200$ GeV. Jet substructure is evaluated using charged-particle tracks, and the overall level of jet suppression is quantified using the jet nuclear modification factor ($R_\mathrm{AA}$). The jet $R_\mathrm{AA}$ is measured as a function of jet $p_{\mathrm{T}}$, the charged $k_t$ splitting scale ($\sqrt{d_{12}}$), and the angular separation ($dR_{12}$) of two leading sub-jets. The jet $R_\mathrm{AA}$ gradually decreases with increasing $\sqrt{d_{12}}$, implying significantly stronger suppression of large-radius jets with larger $k_t$ splitting scale. The jet $R_\mathrm{AA}$ gradually decreases for $dR_{12}$ in the range $0.01{-}0.2$ and then remains consistent with a constant for $dR_{12} \gtrsim 0.2$. The observed significant dependence of jet suppression on the jet substructure will provide new insights into its role in the quenching process.