Researchers and Research Professors

• Georges Aad
• Marlon Barbero
• Arnaud Duperrin (Team Leader)
• Emmanuel Monnier
• Elemer Nagy
• Elisabeth Petit
• Alexandre Rozanov
• Thomas Strebler
• Mossadek Talby
• Timothée Theveneaux-Pelzer

Engineers and Technicians

• Ahmaidi Myriam, service mécanique
• Kevin Arnaud, service électronique
• Pierre Barrillon, service détecteurs et données
• Amira Bouzourene, service détecteurs et données (Apprenti)
• Patrick Breugnon, service électronique
• Laurence Caillat, cellule qualité
• Bernard Dinkespiler, service électronique
• Farès Djama, service détecteurs et données
• Denis Fougeron, service électronique
• Fabrice Gallo, service mécanique
• Fabrice Gensolen, service électronique
• Pierre Karst, service mécanique
• Edith Knoops, service détecteurs et données
• Paul Lacroix, cellule qualité
• Danièle Laugier, service détecteurs et données
• Jean-Philippe Logier, service mécanique
• Mohsine Menouni, service électronique
• Mathieu Niclas, service mécanique
• Patrick Pangaud, service électronique
• Théo Pariset, service détecteurs et données (Apprenti)
• Françoise Riviere, service mécanique
• Franck Salomon, service électronique
• Léa Trouillet, service mécanique
• Felipe Vaccari, service électronique
• Eric Vigeolas, service mécanique
• Teo Weicherding, service électronique

PhD students

• Raphaël Bertrand
• Christian Mavungu Tsava
• Leonardo Splendori
• Grigorii Tolkachev
• Vincenzo Triglione
• Katarina Kazakova

Post-doctoral fellows

• Zhibo Wu (2025-2027)

• March 2026:

• March 2026: Supersymmetry (SUSY) is an elegant theory that predicts new particles by offering a possible explanation for electroweak symmetry breaking. But if these particles exist, why haven’t we seen them? One possibility is that a rule called “R-parity” is violated (RPV), leading to unusual signatures that are harder to detect. For the Rencontres de Moriond, the ATLAS collaboration has reinterpreted its Run 2 SUSY searches with this idea in mind. The results significantly extend constraints on RPV SUSY models and highlight the untapped discovery potential of existing LHC data. This work builds on a joint experimental–theoretical effort supported by the Labex OCEVU. The resulting publication has been led within ATLAS by the CPPM group.

• December 2025: A year-end brochure providing an overview of the ATLAS Experiment in 2025, highlighting major milestones in operations, physics results, upgrade progress, and collaboration activities.

• December 20, 2025: The ATLAS electronics group at CPPM is responsible for the design and production of the new high-speed readout electronics board, LASP (Liquid Argon Signal Processor), dedicated to processing data from the liquid argon calorimeter. This board will be deployed during the second phase of the ATLAS detector upgrade for the High-Luminosity LHC, scheduled for commissioning in 2030. A true concentration of hardware engineering, this high-density board integrates 5,000 components interconnected by more than 20,000 links distributed over a 20-layer multilayer PCB. The team finalized the electronic schematics of this board and launched the production of the first prototype during the summer of 2025. The first boards, received in October and November, are currently under test, and preliminary results show no major issues, thereby validating the design of the first prototype. This milestone represents a decisive step ahead of the mass production of the 364 boards to be delivered to the ATLAS collaboration.

• December 15, 2025: The ATLAS internal track detector will be replaced for the HL-LHC phase, and the CPPM will play an active role in its construction, in particular in assembling the pixel modules onto the support structures. Nearly 1,000 modules will need to be assembled over two years. 2025 was the year of pre-production, during which team members were trained and procedures were drafted; methods and equipment were validated. An important first step was taken this summer with an initial Production Readiness Review (PRR), which qualified the site for part of the assembly work. A second important milestone was reached this week with the first assembly of modules on a support structure populated with 28 modules, the largest assembly in the collaboration to date. Patience and meticulousness are required! The next step, at the beginning of next year, will be to test the complete system in preparation for the second PRR.

• October 13, 2025: The ATLAS group at CPPM develops neural networks for the reconstruction of the energy deposited in the cells of the ATLAS liquid argon calorimeters, under the high pile-up conditions expected at the HL-LHC. These networks are designed to run on the calorimeter readout electronics, which are FPGA-based, and must satisfy strict constraints on size and latency. Several architectures - including Dense networks, RNNs (recurrent neural networks), and CNNs (convolutional neural networks) - are developed and optimized using a Bayesian procedure that balances energy resolution and network size. The optimized architectures achieve a transverse energy resolution of about 80 MeV, outperforming the optimal filtering (OF) method currently in use. The “Deep Evidential” regression method is implemented within the Dense architecture to address the need for reliable event-by-event uncertainties. This approach provides predictive uncertainty estimates with a minimal increase in network size. These modern algorithms improve the performance of the liquid argon calorimeter and offer new handles for clustering and object reconstruction algorithms in the exploitation of ATLAS data at the HL-LHC. This new study has been submitted for publication in EPJC.

• September 13, 2025: Although the main focus of the LHC has been constraining TeV-scale physics, new physics could still be hiding below the electroweak scale: well-motivated dark matter (DM) models predict light scalars, such as axion-like particles (ALPs), as mediators between the Standard Model (SM) and DM. The experimental-theoretical HEP working group Low@LHC, a collaboration fostered through the years by Amidex/OCEVU/IPhU, has recently focused on the exploration of the ALP parameter space. The current direct and indirect searches already constrain strongly the coupling between ALPs and the top quark. By considering models where the ALP dominantly couples to down-type fermions, such as b-quarks, the derived constraints turn out to be weaker, and the prospects to discover ALPs at the High-Luminosity LHC become more compelling. In particular, the recent publication (just accepted by Physical Review D) focuses on the prospects for discovering ALPs at the HL-LHC in events where a photon and two b-quarks are produced. The identification of photons and b-quarks are at the core of the CPPM-ATLAS group expertise.

• July 31, 2025: News Letter CNRS Nucléaire & Particules #256 (in French): The constraints on the Higgs boson self-coupling are tightening

• July 8, 2025: Many theories beyond the Standard Model predict the existence of several types of Higgs boson. Just over a year ago, the ATLAS collaboration unveiled the results of a new study on the search for additional Higgs bosons in the final state with two photons and two b-quarks. The CPPM team was the driving force behind this analysis, and a small excess was found in the LHC Run 2 data. An update was presented at the EPS-HEP2025 conference in Marseille, this time including a partial dataset from the Run 3 of the LHC (2022 and 2023). Once again, the CPPM was at the helm of coordination, analysis and writing. Unfortunately, the small excess seems to have disappeared, mainly thanks to a better identification of the b-quark jets, a re-optimisation of the analysis and the inclusion of the new data. The Higgs boson remains the only one in its family, but the search continues!

• 7 to 11 July 2025: The EPS-HEP2025 conference is one of the largest international conference for the particle physics, astroparticle physics, gravitation, and cosmology communities. It took place from 7 to 11 July 2025 at the Palais du Pharo in Marseille. Thomas Strebler, a researcher in the ATLAS group at CPPM, led the organization of the conference, which brought together more than 700 participants.

• May 26, 2025: ATLAS has submitted in Nature Communications a paper that presents a novel transformer-based flavour tagging algorithm (GN2) which is a paradigm shift from previous approaches. The CPPM team is among the institute which contributed to this important result designed to classify jets based on the flavour of their constituent particles. Its performance is validated in both simulation and collision data. The GN2 algorithm provides substantial benefits for physics analyses involving heavy-flavour jets, such as measurements of Higgs boson pair production in which the group is strongly involved, and demonstrates the impact of advanced machine learning methods in experimental particle physics.

• May 16, 2025: A new ATLAS result result presented at the recent Higgs Pair workshop marks a significant step forward in the search for di-Higgs production. The study introduces a powerful algorithm to identify boosted Higgs bosons decaying into pairs of hadronically decaying τ-leptons — a crucial signature for the HH→bbττ channel. Building on previous developments for identifying Higgs decays into b and c-quark pairs, the new method leverages detailed information from both charged and neutral jet constituents, achieving remarkable background rejection while maintaining high signal efficiency. This breakthrough benefits directly from the strong involvement of the CPPM group through the ANR-funded DIVE project, which focuses on advanced reconstruction techniques for boosted objects — a cornerstone of Run 3 and HL-LHC Higgs pair analyses.

• May 12, 2025: The ATLAS experiment has set a new limit on the production of a pair of Higgs bosons decaying to a pair of b-quarks and a pair of photons with data collected in 2022, 2023, and 2024 combined with Run 2 data. This represents the first result from ATLAS with a record integrated luminosity of 308 fb-1. The upper limit is observed to be 3.8 times the Standard Model cross-section at 95% confidence level. The computed cross-section ratio to the predicted cross-section is measured to be 0.9+1.4-1.1, in complete agreement with the Standard Model. This is an important result for ATLAS, setting the stage for more stringent constraints on the Higgs self-coupling with Run 3 data. The results are presented at the Higgs Pairs Workshop this week. The ATLAS group at CPPM contributed significantly to this analysis with involvement in analysis framework development, analysis data production, validation of di-Higgs reconstruction techniques, and the statistical analysis. The group also contributed to the preparation of photon identification efficiency corrections, which are mandatory for this analysis. This result is an achievement for the ATLAS CPPM group after a long-lasting contribution to the main ingredients of this analysis. The CPPM has led the upgrade of the trigger readout path of the liquid argon calorimeter with significant improvements to the photon triggers used in this analysis. Additionally, the group's contribution to the identification of b-jets with ever more powerful algorithms based on state-of-the-art machine learning techniques had a significant impact on the increasing efficiency of selecting the rare HH->bbγγ signal.

• April 5, 2025: the ALICE, ATLAS, CMS, and LHCb collaborations at CERN’s Large Hadron Collider (LHC) were awarded the Special Breakthrough Prize in Fundamental Physics by the Breakthrough Prize Foundation. These four collaborations, bringing together thousands of researchers from over 70 countries, were recognized for their work based on data collected during the LHC’s second run, up to July 2024. The prize was presented to the spokespersons who led the collaborations during this period, in recognition of their detailed measurements of the Higgs boson’s properties confirming the mechanism of spontaneous symmetry breaking responsible for mass generation, the discovery of new strongly interacting particles, the study of rare processes and matter–antimatter asymmetry, and the exploration of nature at the smallest distance scales and under the most extreme physical conditions made accessible by the LHC. This award highlights the scientific excellence and international leadership of CPPM, through the major contribution of its ATLAS team to the recognized results. It also acknowledges the long-term commitment of many CPPM members, over several decades, to the design, construction, and operation of these experiments. In particular, it underlines the laboratory’s involvement in the construction and operation of the ATLAS liquid argon calorimeter and pixel detector, as well as in scientific computing activities—each being essential contributions to the discoveries honored by this award. These projects, currently undergoing major developments, are pillars of the laboratory’s scientific and technological strategy, with a view toward the Phase 2 upgrades and the High-Luminosity LHC program for at least the next two decades.

• March 31, 2025: Publication of the Feasibility Study of the FCC: in 2020, the CERN Councel asked for a feasibility report of a Future Circular Collider (FCC) at CERN. This study is also a summary of last years achievements towards FCC project, including not only forseen measurements and searches at FCC, but also accelerators, civil engineering and sustainability. Volume 1 is about physics and detectors. The other volumes concern accelarators and civil engineering.

• Januray 20, 2025: In the first years of Run 3 data-taking, the new neural network-based b-tagging algorithms led to a significant increase in the ATLAS trigger performance compared to Run 2. This is detailed in a paper recently released by the ATLAS collaboration and co-written by one CPPM-ATLAS member, which also sheds light on the CPPM's key role in the success of b-tagging at trigger level since Run 1: its integration into the trigger software infrastructure, calibration, monitoring, and commissioning studies. A new set of improvements allowed ATLAS to collect di-Higgs events in a final state with b-anti-b quarks and tau-lepton pairs with a signal efficiency increase of ~50% compared to Run 2. The CPPM is part of the ATLAS HH team responsible for analyzing this data.

• December 19, 2024: The transition to the High-Luminosity phase of the LHC (HL-LHC), with up to 200 interactions per beam crossing, presents unprecedented challenges for the reconstruction of charged particle trajectories, which is essential for the ATLAS physics program. The new Inner Tracker (ITk), made entirely of silicon, will replace the current Inner Detector (ID) during Long Shutdown 3 (2026-2030). The latest paper submitted by the ATLAS collaboration details the expected performance of the ITk in terms of track reconstruction. The ATLAS group at CPPM has played a central role in these performance studies. By combining its expertise in track reconstruction with its significant involvement in the design and construction of the ITk, the group contributes to pushing the boundaries of instrumentation and data analysis. These efforts highlight CPPM’s leading role in enhancing ATLAS’s performance for the years to come, paving the way for new discoveries in high-energy particle physics during the LHC’s high-luminosity phase, which will begin in 2030.

• July 22nd, 2024: The ATLAS group in CPPM has been involved for many years on the search, the observation and then the study of Higgs production in association with a top quark pair (ttH). The very heavy mass of the quark top (as heavy as a gold atom!) could hint to the fact that it plays a peculiar role with respect to the Higgs boson. The ATLAS collaboration has published its final study on the whole Run 2 sample (2015-2018), in which the Higgs boson decays to 2 b-quarks. This measurement, with a precision of about 25%, is in agreement with the Standard Model prediction, and also at high transverse momentum of the Higgs boson. The results of this analysis could hence not prove the existence of a deviation with respect to standard model predictions, that still resists our attempts to put it in default. The CPPM team was a major contributor to this analysis, in particular with supervised learning technique developments and deep neural networks. Ziyu Guo (PhD defended in 2019) had introduced recurrent neural networks and the use of low level variables. Neelam Kumari had followed and developped deep sets (PhD defended in 2022). This underlines the time needed to pursue this type of complex analysis. This publication concludes CPPM implication on ttH analysis, to focus on di-Higgs analysis at Run 3 and at HL-LHC.

• June 24th, 2024: Study of the production of two Higgs boson, known as "di-Higgs" production, allows to measure the Higgs boson "self-coupling" strength - a fundamental aspect of the Standard Model linking the Higgs mechanisms and the stability of our universe. But the measure of the di-Higgs production is a particularly difficult one. This process is very rare, approx. 1000 times less frequent that the single Higgs production. To maximize their chances, ATLAS researchers study the most promizing desintegration of the two Higgs boson: H(→bb)H(→ττ), H(→bb)H(→γγ), H(→bb)H(→bb), H(→bb)H(→ll+ETmiss), HH→leptons+X, all having its advantages and drawbacks. Combining these 5 studies to enhance their statistical significance, the ATLAS collaboration has obtained the most sensitive probe to the di-Higgs production and to the Higgs self-coupling. This analysis, submitted to the PRL journal this week, excludes di-Higgs production cross-section that are more than 2.9 times above the Standard Model prediction. Researchers have also constrained the magnitude of the Higgs boson self-coupling with respect to the Standard Model prediction, which stays for now compatible with the predictions. LHC Run 3 is now on-going and could more than double the data sample collected, opening new perspectives for these searches.

• June, 2024: The CPPM team is continuing the development of the new LASP (Liquid Argon Signal Processor) electronic board for data processing from the Liquid Argon Calorimeter (LAr). This board will be installed during the second phase of the ATLAS detector upgrade. The CPPM LAr team has completed the electronic schematics for the LASP board, which successfully passed an ATLAS preliminary design review, validating the construction of the board’s first prototype. This marks the beginning of the final stage of the board's design, focusing on routing before building the initial prototypes.

• May 20th, 2024: Important progresses have been done these last weeks concerning the ITk-Pixel project, both at the collaboration level and at the local level. The "global mechanics" Final Design Report concerning all assembly procedures of the mechanical structures sheltering the modules with the goal to construct the whole detector, has been "passed successfully with recommandations". At the local level, pre-production is advancing : The team members learn the complex procedures enabling to mount modules on mechanical structures (photo) with the help of the "itinerant stave" that contains all the necessary elements and travels between the various labs of the collaboration. The module test system (photo) has passed its qualification phase and first digital modules could be tested. These progresses will be shown and discussed next week in Clermont-Ferrand at the fourth "Journées Upgrade ATLAS-France". In the end, our team will be in charge to mount approximately 1000 modules on structures the next years that will form the future ATLAS tracker for the high luminosity phase of the LHC.

• May 6th, 2024: 12 years after the Higgs boson discovery, most of its properties have been measured, but the Higgs boson self-coupling measurement remains a priority of the ATLAS collaboration and the CPPM team, in particular in the final state with two photons and two b-quarks. Numerous theories also predict the existence of multiple Higgs bosons that we could find following the same final state. A new article was thus recently submitted for publication and presented at the Moriond EW conference. This anaylsis, derived from the one on Higgs self-coupling and using the complete data sample from LHC Run 2, was done by CPPM group members and collaborators (with contribution of a visiting student from Shanghai Jiao Tong university), L2IT in Toulouse and the KTH institute from Stockholm university. A small excess has been recorded with a local significance of 3.5 standard deviations, but only 2.0 standard deviations if one corrects for the fact that a large number of masses were tested. This gives an extra motivation to follow this analysis with the Run 3 data!

• May, 2024: The start of the LHC in 2024 is marked by the implementation of the new digital trigger system for the Liquid Argon Calorimeter (LAr), which has become the default trigger for all physics objects. The CPPM team has played a major role in the hardware, firmware, and software development of this trigger, as well as in its commissioning. This achievement represents the successful completion of a significant project in which the CPPM held critical responsibilities. The LAr system is operating exceptionally well (see this link), with an efficiency of 99.9%. The CPPM also contributes significantly to the operation and data quality control of this system.

• December 2023: Publication of the final di-Higgs results with Run 2 data, and start of the Run 3 data analysis. Two ATLAS CPPM group members (Thomas Strebler and Timothée Theveneaux-Pelzer) become coordinators within the di-Higgs group.

• October 24th, 2023: The CNRS crystal medal was awarded today to Eric Vigeolas, research engineer in mecanics and mecatronics, and project leader on the ATLAS ITk tracker, for the ATLAS CPPM team.

• October 2023: The ITkPixV2 ASIC for the ATLAS ITk detector (HL-LHC project) is back from the foundry. On top of many tests to be performed in laboratories, several testing campains under proton or ion flux are already planned for beginning of 2024, to test the circuit in harsh conditions close to those of HL-LHC (under our team supervision).

• April 2023: The new higher granularity e-gamma digital trigger based on the Liquid Argon Calorimeter, whose deployment was the goal of the Phase-I Calorimeter upgrade and put in place with large contributions from our team, has now become the new default trigger system for ATLAS, outperforming the performances of the old analog trigger system.

• March 27^th, 2023: A large number of new ATLAS physics results have been presented during the winter conferences: Observation of the
  four-top-quark production, measurement of the ttW production, most precise single measurement of the strong interaction "alpha_s" coupling, improvement on the W mass measurement W... Some beautiful results from the ATLAS experiment in a context of restart of the Run 3 phase of the LHC.

• March 22^nd, 2023: A major milestone of the ATLAS ITk project has been reached today. The very complex ITkPixV2 Integrated Circuit (IC), production version for the ATLAS pixel detector has been submitted for production. The IC will be used for the Run 4 of the ATLAS experiment in the new pixel detector (High Luminosity LHC phase, post-2028). It is the result of the effort of an almost 10-year long development by teams from more than 20 institutes worldwide, in the framework of the CERN RD53 project, among which the ATLAS CPPM team.

• March 14^th-15^th 2023: The first DRD7 workshop (ECFA process) "Electronics and On-Detector Processing" has taken place in CERN with implication from the team members for our activities in micro-electronics, as well as 250-300 participants over the two days. The ECFA process will structure R&D developments for particle physics at the european level for the next decade.

• October 11^th, 2022: Elisabeth Petit, researcher in the CPPM team, receives the CNRS bronze medal, a reward that underlines her implication in Higgs boson studies but also in the upgrade project of the pixel detector of ATLAS Inner Tracker for the High Luminosity LHC phase.

• August 22^nd, 2022: Intensity of the Higgs boson coupling as a function of the Z and W boson masses, as well of the masses of the muons, taus, and charm, bottom and top quarks. This summary plot shows the excellent agreement of the experimental data with the theory developed by Brout-Englert-Higgs to account for the electroweak symmetry breaking mechanism and the generation of the masses of bosons and fermions.

• July 6^th, 2022: At the occasion of the 10-year anniversary of the Higgs boson discovery, a colloquium was organized by the national institute IN2P3 with a contribution of Elisabeth Petit, researcher in the CPPM team.

• July 5^th, 2022: Today, the LHC has seen its first proton-proton collisions at the unprecedented center of mass energy of 13.6 TeV. After three years of stop for upgrade and maintenance work, it is the official kick-off of the Run 3 phase of operation for the LHC, during which further test of the Standard Model (SM) will be pursued in the Higgs sector and with searches for extensions to the SM of particles.

• June 28^th, 2022: Elisabeth Petit, researcher in the ATLAS CPPM team, is invited in « la méthode scientifique », the french radio program of France Culture.

• June the 2^nd, 2022: Georges Aad, researcher in the CPPMATLAS team, has received an « Outstanding Achievement Award 2022 », a prize given by the ATLAS collaboration for «exceptional contribution to the digital electronic system of the ATLAS Liquid Argon calorimeter trigger», a phase 1 upgrade installed and starting operation for the LHC Run 3, to efficiently treat increased event pile-up related to the higher luminosity of LHC. This prize acknowledges and rewards the importance and the quality of the CPPM ATLAS team work in this project. The finalization of this upgrade is on-going and the CPPM, with engineers, students and physicists is responsible for several key aspects. The new system is operational and collects the first collision data that the LHC has just started producing on May 28th, 2022 as Run 3 is now starting.

• April 18^th, 2022: To prepare the production phase of the future ATLAS pixel detector for HL-LHC (ITK Pixel Detector project), the « mechanics and production » team has developed an automated glue deposition method, for the cells that shelter the modules before integration in the mechanical structures of the detector. This highly reliable method allows to deposit a quantity of glue with a 4% accuracy for 400 mg of glue used. This is important in order not to degrade the detector’s performance and guaranty a lifetime above 10 years in-situ. The production phase for the detector will take place from 2024 to 2026 and our team will handle the integration of about 50 modules per month during this phase.

• March, 2022: The ATLAS and CMS Collaborations have released as an input for the US Snowmass prospective exercise a common White Paper summarizing the most recent physics projection results for the High-Luminosity phase of the LHC (HL-LHC). The CPPM group was in particular directly involved in the prospect result related to the search for di-Higgs production at HL-LHC, which is one of the main cornerstones of the ATLAS HL-LHC physics program. Those results have confirmed that a 3-sigma evidence with ATLAS data and a 5-sigma observation combining with CMS is definitely by the end of HL-LHC data-taking.

• December 13^th-16^th, 2021: 13^th FCPPL “France-China Particle Physics laboratory” workshop, in which the group was represented with presentations giving status reports of activities in the framework of several collaborations between our team and partner teams in China.

• November 22^nd, 2021: The CPPM ATLAS team has been involved for many years in the search, the observation, and then the study of theHiggs boson production with a top quark pair. The ATLAS collaboration has just published a new study in which the Higgs boson decays to a b quark pair. The Higgs field gives mass to elementary particles by means of its interaction. The very heavy mass of the top quark (almost as heavy as a gold atom!) hints to the top quark having a special relation to the Higgs, and the study of this relation is the topic of these analyses. For the first time in this channel, the analysis is performed as a function of the Higgs boson transverse momentum. The CPPM team has deeply contributed to this study, in particular with the development of machine learning techniques.

• November 2021: Beam circulation has started in the LHC at the injection energy (2x450 GeV) in stable mode. The ATLAS detector registers new data and in particular with its Liquid Argon (LAr) Calorimeter. The LAr calorimeter has seen a major update during the recent long shutdown, for which the CPPM team was extremely active.The LAr system has started transmitting data for the first time with its new updated readout systemand in particular in direction of the calorimeter first level trigger. This is an important milestone towards Run 3, which starts in spring 2022.

• October 21^st 2021: Publication of the ECFA document(European Committee for Future Accelerators) concerning detector R&D perspectives and organization « Detector Research and Development Roadmap ». This document will structure detector R&D at colliders for the years to come.

• End of October, 2021:Protons are back in the LHC !After more than two years of maintenance and updating of the collider and the detectors, LHC pilot runs are currently ongoing. The ATLAS detector recorded “Splash” events (a flux of particles resulting from the interaction between the beams and a collimator located before the detector). The first proton frictions happened at the LHC injection energy (450 GeV per beam) in stable mode in the last week of October. This has allowed ATLAS to register these first data and to validate its good functioning. In June 2022 this will be the start of Run 3, for which the LHC will raise its center of mass energy from 13 to 13.6 TeV.

• June 2021: Publication on the configuration and the performances of the Run 2 b-jet trigger. The Run 2 High Level Trigger (HLT) reduces the data rate from 100 kHz at the level 1 trigger output to save events on disk at a rate of about 1 kHz. The hadronic jets containing b-quarks are identified (b-tagged) in the HLT by exploiting the properties of b-hadrons, which have a relatively long lifetime, of the order of 1.5 ps, to reconstruct secondary vertices typically located few mm away from the hard-scatter interaction. The b-jet trigger software was redesigned to improve stability under increasingly harsh pile-up conditions. These changes, together with improved tracking performance in the trigger, the installation of the insertable B-layer for Run 2, and the usage of the most advanced algorithms lead to significantly improved performance compared to Run 1. The CPPM group has contributed to the success of the Run 2 b-jet trigger with multiples responsibilities (monitoring, software development and validation, calibration).

• February 2021:Probing for Single Event Effects (SEE) at the GANIL accelerator. The structures that were tested are memory blocks conceived to be SEE-resistant. They use hardening methods such as data and control line redundancy, memory triplication, DICE cells, physical layout level separation…. The tested memories are implemented in three different technologies (TJ180, AMS180 and LF150). This work is done in the framework of the DICE master project and of the RD50 collaboration.

• End march 2021: The ATLAS collaboration has released anew result on the Higgs boson self-interaction, looking for events containing a Higgs boson pair. This process is very rare, about 1000 times rarer than the production of a Higgs boson alone. Events where one Higgs boson decays to two photons and the other Higgs bosons to two bottom quarks are a powerful handle to search for Higgs boson pair production. New analysis technics were developed to search for this rare process (only 12 such events would have been produced at the LHC so far) by several teams, including the ATLAS team of CPPM. Limits were set on how often pairs of Higgs bosons are produced, at 4.1 times the Standard Model prediction. This result sets the world's best limits on the Higgs self-coupling. But we will need much more data to precisely measure the Higgs self-coupling and to see whether it agrees with the Standard Model prediction. The High-Luminosity upgrade of the LHC plans to deliver a dataset 20 times larger than the one we used for this study. The ATLAS group at CPPM is deeply involved in the upgrade of the detectors for this new phase.

• February 2021:Emmanuel Monnier has been re-elected as ATLAS Liquid Argon Calorimeter Project Leader for two years, with his new terms starting on March 1st 2021.

• October, 29^th 2020: New results concerning the production of the Higgs boson in association to a top quark pair (ttH) were shown at the Higgs 2020 conference. This analysis concerns the complete ATLAS Run 2 set (139 fb-1) and benefited from the strong work from several members of our group.

• October, 8^th 2020: Submission to the European Physical Journal C of the paper "Search for phenomena beyond the Standard Model in events with large b-jet multiplicity using the ATLAS detector at the LHC". This analysis, to which our group is a strong contributor, allows to establish model-independent limits to the presence of new physics in events with high b-jet multiplicity and, at the same time, to constrain natural supersymmetric models violating the R-Parity.

• End of March 2020: While the virus’ proliferation is spreading rapidly in different parts of the world, theresearchers mobilize international action in response to the new coronavirus. The grid computing infrastructure at CPPM that is mainly used during normal time by the LHC experiments ATLAS and LHCb in the context of WLCG collaboration (Worldwide LHC Computing Grid) is now ready to receive more jobs from biomedical research projects related to Covid-19 research studies. We work in coordination with the virtual organisation biomed and INSERM computing for researchers to have access to our ressources.

• March, 30^th 2020: TheCPPM grid computing infrastructure for ATLAS is now considered as a Nucleus. The Nucleus sites are the main processing sites receiving data directly staged at CC-IN2P3 (Tier-1) but processed outside CC-IN2P3. To have this Tier-1 like status, the grid site needs to have enough storage, very good availability and processing efficiency for data in addition to a good network bandwidth. So far, only the LAPP Tier-2 had this status in France. It is therefore a recognition for the CPPM Tier 2.

• March, 17^th 2020: On March 17 2020,the ITkPixV1 chip was submitted to the TSMC foundry for production. With a surface area of more than 4 cm², this chip has been designed in the 65 nm CMOS process and will tolerate an ionizing dose of more than 500 Mrad. It contains more than 1/2 billion transistors and 153600 pixels of 50x50 µm² organized in 2400 regions of 8x8 pixels. This is the culmination of nearly 8 years of work by CERN's RD53 collaboration, to which the CPPM's ATLAS team has been a major contributor since its foundation. This is the pre-production version of the chip which will equip, in more than 33,000 units, the 5 internal pixel layers of the future ATLAS post-2026 trajectograph. This is a major step towards improving the ATLAS detector for the High Luminosity phase of CERN's Large Hadron Collider, which has now been completed.

• January 2020: TheCERN Yellow Report "Physics of the HL-LHC, and perspectives at the HE-LHC"is now published. This report summarizes the outcome of five working groups that have studied the physics potential of the High-Luminosity phase of the LHC (14 TeV HL-LHC) as well as perspectives for a future possible High Energy LHC (27 TeV HE-LHC), and covers topics such as: Standard Model measurements, Higgs boson properties, flavor physics with heavy quarks, QCD at high density and temperature, and searches for phenomena Beyond the Standard Model. The ~1400 pages report can be found at CERN Yellow Report: Physics of the HL-LHC, and HE-LHC perspectives.

• July 2019: 64 ATLAS contributions given at the European Physics Society High Energy Physics 2019 conference in Ghent, Belgium. ATLAS highlights can be found at http://atlas.cern/updates/atlas-news/eps-2019-highlights .

• Spring 2019: Success of the AAP (Call for Project) of the Aix-Marseille AMIDEX fundation forthe AIDAQ project: This project deals with the implementation of artificial intelligence algorithms on FPGAs (in particular of neural networks) for the real time computation of the energies deposited in the ATLAS Liquid Argon Calorimeter.

• January 2019 - now:LHC Long Shutdown 2 and on-going ATLAS detector Phase I Upgrade targetting Run 3 data taking. Our group is a strong contributor to the installation of the new readout electronics for the electromagnetic calorimeter.

• December 2018: End of proton-proton data taking (Run 2 Phase), with a record collected luminosity of 139 fb^-1 which will lead to precision analysis of the Higgs boson properties, as well as searches for New Physics in an extended mass range.

• 13^th November 2018:Aix-Marseille Thesis award 2017 given to Thomas Calvet. This work comes in recognition of his excellent research work on the assocatied Higgs production with a quark top pair where the Higgs decays to two bottom quarks (so-called ttH(bb) channel), and the b jet tagging with the ATLAS experiment at the LHC. https://hal-amu.archives-ouvertes.fr/tel-01681700/

• 4^th June 2018: publication of theproduction of the Higgs boson with a pair of top quarks (ttH) by the ATLAS experiment, with a significant contribution by the CPPM group. https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2018-13/

• 24^th December 2017:evidence seen by ATLAS of the ttH associate production. https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2017-02/

• 2017:finalization of the Phase 2 Upgrade TDRs, including those on calorimetry and ITk pixels.

• April 2016:first proton collisions in ATLAS for 2016

• 3^rd June 2015: stable beams in the LHC, first collisions at 13 TeV and first signals in the new IBL layer!The beginning of Run 2...

• 9^th December 9, 2014:A first LHC magnet reaches the current needed to communicate an energy of 6.5 TeV to protons, paving the way for the LHC Run 2 data taking to begin in spring 2015.

• June 2014: Thefirst 3D pixel circuit for ATLAS, designed at CPPM, is qualified to withstand the radiation dose expected at HL-LHC.

• 7^th May 2014:insertion of the fourth layer of IBL pixels in ATLASfor which the CPPM made major contributions to the FE-I4 electronic readout chip and to mechanics.

• October 2013:Nobel Prize in Physics awarded to F. Englert and P. Higgs.

• 4^th July 2012: announcement of thediscovery of the Higgs boson by ATLAS (and CMS).

• 17^th December 2012:end of the LHC Run 1 data collection period.

• 30^th March 2010:first high-energy proton collisions (7 TeV) in the LHC.

Researchers and Research professors

• Justine Serrano (Team responsible)
• Vitalii Lisovskyi
• Giampiero Mancinelli
• Karim Trabelsi
• Vidya Sagar Vobbilisetti

PHD students and post-doctoral fellows

• Isaac Consigny
• Mattia Marfoli

Engineers and Technicians

March 2026:

Two new results from the CPPM team have recently been to Physical Review Letters (PRL). The first concerns the search for decays that violate lepton flavor conservation of the $\chi_bJ(1P)$ into two leptons ($e\mu$ , $e\tau$ , or $\mu\tau$ ). This analysis uses a data sample of $\Upsilon(2S)$ collected by the Belle experiment, in which the $\Upsilon(2S)$ decays into a photon and a $\chi_bJ(1P)$ , with J=0,1,2. The upper limits obtained, on the order of $10^{-5}$ − $10^{-6}$ , are the first ever established for this type of decay and allow constraints to be placed on Wilson coefficients in new physics models involving a scalar operator that induces lepton flavor-violating processes. The second result concerns the search for the decay $B^+ \to K^+ \tau^+ \tau^-$ . According to the Standard Model, the expected branching fraction is very small ($10^{-7}$ ), but it could be higher in new physics models consistent with the flavor anomalies observed. This analysis, based on Belle and Belle II Run 1 data, uses hadronic tagging to fully reconstruct the events. The upper limit obtained, at 90% confidence level, is 5.6×$10^{-4}$ , improving the previous result from BaBar by a factor of four.

October 2025:

Around 80 international experts in tau lepton physics gathered for a week-long workshop at Le Pharo. The presentations are available on the TAU workshop 2025 website. Researchers from the Belle II, LHCb, KM3Net and CPT teams participated in the local organising committee.

September 2025:

The CPPM team obtained new limits on lepton flavour violating modes $\tau\to e\ell \ell$ , where $\ell$ is a muon or an electron, improving four existing limits previously obtained by Belle. This analysis formed the core of Arthur Thaller's thesis and was accepted by JHEP

July 2025 Two new results obtained by the Belle II team have been accepted for publication by JHEP. These are the search for modes violating the lepton flavour $\tau\to\ell K_S^0$ (led by Klemens Lautenbach and Laura Zani) and $B\to K^*tau\ell$ (led by Clotilde Lemettais and Valerio Bertacchi), where $\ell$ is a muon or an electron. These analyses use all the data collected by Belle as well as Run 1 of Belle II. The limits obtained on the $\tau\to\ell K_S^0$ branching ratios are the world's best, while those obtained on $B\to K^*\tau\ell$ are the first results from a B factory.

February 2025:

The Belle II thesis award has been atributed to Robin Leboucher.

Decembre 2024:

The SuperKEKB accelerator reached a new record of instantaneous luminosity at $5.1\times 10^{34}$ cm$^{-2}$ s$^{-1}$ .

February 2024:

After a technical break of one year and half, the data taking has restarted at Belle II ! This first 'long shutdown' allowed to upgrade the SuperKEKB accelerator, with the aim of improving the injection and reduce the beam backgrounds, as well as the Belle II experiment that has now a complete vertex detector. The first Run2 collisions took place on the 20th of February 2024. The machine parameters will be tuned to improved the previous world record of instantaneous luminosity, and exceed 10^35/cm2/s.

December 2023:

Belle II obtains the best experimental upper limit on the lepton flavour violating decay $\tau\to\mu\mu\mu$ . This result, presented at the TAU 2023 conference, has been the PhD topic of Robin Leboucher.

March 2023:

New Belle II results presented at Moriond 2023

The Belle II experiment presented 14 new results at the Moriond conference, among which two were obtained by the CPPM team:

• The measurement of the B->D(*)KKs branching fractions, with a precision improved by a factor 3 for the B- -> D0K0Ks decays and three new decay modes observed. This will allow to improve the simulation and B tagging algorithm. This result was presented by Valerio Bertacchi, post doc at CPPM.
• The search for the lepton flavour violating decays tau -> ephi and tau ->muphi. This analysis was the subject of Leonard Polat's PhD and was presented by Laura Zani, former post doc of the CPPM team. The statistic used (190 fb-1) does not yet allow to improve the existing limits but this will possibly be achieved with the 424 fb-1 already recorded before the long shutdown.

May 2022:

Organisation of the Belle II face to face tracking workshop, 11-13 May.

October 2021:

Laura Zani has been awarded the first annual Belle II thesis prize, together with Giacomo De Pietro, for her thesis: "Search for an invisible Z’ in μ⁺μ⁻ plus missing energy events at Belle II” (thesis submitted to University of Pisa).

March 2021:

Organisation of first Belle II Masterclass at CPPM.

June 2020:

SuperKEKB reached a peak luminosiy of 2.226 x $10^{34}$ cm$^{-2}$ s$^{-1}$ , breaking the world record!

March 2020:

The Belle II international collaboration has published its first results in a paper selected as an Editors’ Suggestion in Physical Review Letters The paper reports the first search for a new type of elementary particle that may act as a “portal” between ordinary matter and dark matter, which is understood to make up some 85% of the matter in the universe.

This search has been the thesis work of Laura Zani, who recently joined the CPPM group.

Researchers and Research professors

• Julien Cogan
• Renaud Le Gac
• Olivier Leroy (team responsible)
• Anton Poluektov
• Dorothea Vom Bruch

PHD students and post-doctoral fellows

• Ching-Hua Li
• Léa Dreyfus
• Tommaso Fulghesu
• Anna Heyn

Engineers and Technicians

• Andrew Morris
• Kevin Arnaud, electronic department
• Julien Langouët, electronic department
• Fredéric Hachon electronic department
• Costy Nassif electronic department
• Andreï Tsaregorodtsev, Detectors and Data department