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Overview of ATLAS SH/HH resonant results
No full textThe talk presents a summary of recent ATLAS searches for heavy resonances decaying into pairs of Higgs bosons (X→HH) or a Higgs boson and a new scalar (X→SH), based on the full Run-2 proton-proton collision dataset at √s = 13 TeV. These searches cover a wide range of final states—including b\bar{b}b\bar{b}, b\bar{b}\gamma\gamma, VV\tau\tau⁻, VV\gamma\gamma⁻, and multi-b-jet final states—targeting various beyond-the-Standard Model scenarios such as the 2HDM, NMSSM, and the Two Real Scalar Model. No significant excess above the Standard Model expectation is observed, and limits are set on the production cross sections for a variety of signal models. Improvements in analysis techniques, including the use of machine learning-based discriminants and data-driven background estimations, play a key role in enhancing the sensitivity of these searches
ATLAS Highlights
No full textATLAS Experimental Highlights for the opening plenary of Quark Matter 202
Top-quark pair production in Pb+Pb collisions in the ATLAS experiment
No full textIn relativistic heavy-ion collisions, top quarks are expected to be attractive candidates for probing the quark-gluon plasma as well as to bring unique information about the time evolution of strongly interacting matter. We report the first study of top-quark pair production in lead-lead collisions at the centre-of-mass energy of 5.02 TeV with the ATLAS experiment at the LHC. The dataset was recorded in 2015 and 2018, amounting to an integrated luminosity of 1.9 nb. Top-quark pair production cross section is studied in the eµ channel. The result is compared to theory predictions based on different nuclear PDF sets
Recent flow and correlation measurements from ATLAS in pp, p+Pb and Pb+Pb collisions
No full textThis talk presents multiple recent ATLAS measurements of azimuthal-anisotropy and multi-particle correlations in , +Pb, and Pb+Pb collisions. Measurements of the coefficient -- the correlation between and mean transverse-momentum () -- in and +Pb colisions are presented. The results, show striking similarity in the evolution of with multiplicity across both collision systems. These results aim to clarify whether initial-state saturation effects and collective evolution contribute to trends or if they are purely driven by collective interactions. Correlations between soft particles and jets are examined in collisions. It is shown that excluding jet-associated particles does not affect the ridge, and no significant azimuthal correlations are found between jet-associated particles and the soft underlying event, ruling out hard-process contributions to the ridge. New measurements extending this analysis to +Pb collisions are also presented. Prior +Pb flow measurements show a small but significant high- . In contrast, suppression measurements indicate no clear suppression of high- hadrons. These jet-tagged measurements can give further insight into the origin of the high- observed in +Pb collisions. Finally, measurements of high- azimuthal anisotropy in 5.02~TeV Pb+Pb colisions measured over wide ranges of (1--400~GeV), pseudorapidity (), and centrality (0--60\%) are presented. The measurements are done using the scalar-product as well as four-particle cumulant methods. These results probe the path-length dependence of jet energy loss in the quark-gluon plasma, revealing that high- is more sensitive to event-by-event fluctuations than . Together, these measurements offer a comprehensive understanding of the interplay between initial-state effects, collectivity, and jet-medium interactions across collision systems of different sizes
Recent highlights of top-quark cross section and mass measurements at the LHC with ATLAS and CMS
No full textThe exceptionally large dataset collected by the ATLAS and CMS detectors at the highest proton-proton collision energies provided by the LHC enables precision testing of theoretical predictions using an extensive sample of top quark events. The top-quark mass is one of the key fundamental parameters of the Standard Model that must be determined experimentally. Its value has an important effect on many precision measurements and tests of the Standard Model. The Tevatron and LHC experiments have developed an extensive program to determine the top quark mass using a variety of methods. In this contribution, the top quark mass measurements by the ATLAS experiment are reviewed. This wealth of data has also opened the door to new measurements of top quark properties, such as quantum entanglement, which were previously beyond reach. Recent measurements include total and differential top quark cross sections, as well as detailed studies of top quark production at various center-of-mass energies. This contribution presents the latest highlights from the ATLAS and CMS top quark physics program, including key measurements from Run II, and new results using Run III data
Comparison between a Two-Wavelength Absolute Distance Meter and a GNSS-Based Distance Meter at CERN Geodetic Network
No full textAbsolute distance determination, which is the determination of distances consistent with the International System of Units (SI)definition of meter, is a current challenge for distances of several kilometers in the open air and with submillimetric accuracies, which is beingincreasingly demanded for scientific and technological applications. We present the first comparison of two techniques recently developedfor this purpose: the Arpent Absolute Distance Meter and the improved Global Navigation Satellite System (GNSS)-based distance meter.Both techniques have been tested and compared on the European Organization for Nuclear Research (CERN) geodetic network during a2-week observation campaign. The results obtained include the rigorous determination of the uncertainties for both methodologies. In the end,four baselines of 2.2, 4.8, 6.0, and 6.5 km were measured, and for three of them, the differences between the two systems were less than0.7 mm. The baseline of 4.8 km showed a difference of 2.7 mm, i.e., about 0.6 parts per million (ppm): in the case of conventional opticaltelemetry, such an agreement would require refractivity correction with knowledge of the air temperature and pressure at better than 0.6 K and0.15 hPa, respectively
FASER tracker performance
No full textFASER is located 480 meters from the ATLAS interaction point, along the collision axis. The tracking system of the FASER detector consists of four identical tracker stations made from silicon microstrip detectors. It is designed to measure the trajectories of charged particles to search for long-lived particles such as dark photons and axion-like particles, as well as to study collider neutrinos, which are the highest-energy human-made neutrinos. This talk covers the basic performance of the tracker detector over three years of LHC operational experience, focusing on its efficiency, long-term stability and results from track alignment study
Jet cross-section and sub-structure measurements in ATLAS
No full textThis talk reports recent measurements of jet production cross-sections and the sub-structure properties inside jets in ATLAS. These measurements provide important inputs to understand Quantum Chromodynamics at the high energy regime