publications

2023

1. PPN

   Ultra-Peripheral Physics with ATLAS

   H. Hamdaoui

   Physics of Particles and Nuclei, Aug 2023

   Abs DOI

   An overview of the latest ultra-peripheral physics measurements performed with the ATLAS detector at the LHC is presented. These include measurements of light-by-light scattering, which result in an observation of this elusive Standard Model process and set competitive limits on the parameter space for axion-like particles, differential measurements of the exclusive di-muon production cross-section, which are crucial for setting constraints on the initial photon spectrum for all ultra-peripheral collision measurements at the LHC and measurements of collective behavior in high-multiplicity photo-nuclear collisions.

2022

1. JHEP

   Search for invisible Higgs-boson decays in events with vector-boson fusion signatures using 139 fb−1 of proton-proton data recorded by the ATLAS experiment

   G. Aad, B. Abbott, D. C. Abbott, and 296 more authors

   Journal of High Energy Physics, Aug 2022

   Abs DOI

   A direct search for Higgs bosons produced via vector-boson fusion and subsequently decaying into invisible particles is reported. The analysis uses 139 fb−1 of pp collision data at a centre-of-mass energy of }} \backslashsqrt{s} }}= 13 TeV recorded by the ATLAS detector at the LHC. The observed numbers of events are found to be in agreement with the background expectation from Standard Model processes. For a scalar Higgs boson with a mass of 125 GeV and a Standard Model production cross section, an observed upper limit of 0.145 is placed on the branching fraction of its decay into invisible particles at 95% confidence level, with an expected limit of 0.103. These results are interpreted in the context of models where the Higgs boson acts as a portal to dark matter, and limits are set on the scattering cross section of weakly interacting massive particles and nucleons. Invisible decays of additional scalar bosons with masses from 50 GeV to 2 TeV are also studied, and the derived upper limits on the cross section times branching fraction decrease with increasing mass from 1.0 pb for a scalar boson mass of 50 GeV to 0.1 pb at a mass of 2 TeV.

2. JINST

   The KM3NeT multi-PMT optical module

   S. Aiello, A. Albert, M. Alshamsi, and 271 more authors

   Journal of Instrumentation, Jul 2022

   Abs DOI

   The optical module of the KM3NeT neutrino telescope is an innovative multi-faceted large area photodetection module. It contains 31 three-inch photomultiplier tubes in a single 0.44 m diameter pressure-resistant glass sphere. The module is a sensory device also comprising calibration instruments and electronics for power, readout and data acquisition. It is capped with a breakout-box with electronics for connection to an electro-optical cable for power and long-distance communication to the onshore control station. The design of the module was qualified for the first time in the deep sea in 2013. Since then, the technology has been further improved to meet requirements of scalability, cost-effectiveness and high reliability. The module features a sub-nanosecond timing accuracy and a dynamic range allowing the measurement of a single photon up to a cascade of thousands of photons, suited for the measurement of the Cherenkov radiation induced in water by secondary particles from interactions of neutrinos with energies in the range of GeV to PeV. A distributed production model has been implemented for the delivery of more than 6000 modules in the coming few years with an average production rate of more than 100 modules per month. In this paper a review is presented of the design of the multi-PMT KM3NeT optical module with a proven effective background suppression and signal recognition and sensitivity to the incoming direction of photons.

2021

1. JHEP

   Measurement of light-by-light scattering and search for axion-like particles with 2.2 nb−1 of Pb+Pb data with the ATLAS detector

   G. Aad, B. Abbott, D. C. Abbott, and 297 more authors

   Journal of High Energy Physics, Mar 2021

   Abs DOI

   This paper describes a measurement of light-by-light scattering based on Pb+Pb collision data recorded by the ATLAS experiment during Run 2 of the LHC. The study uses 2.2 nb−1 of integrated luminosity collected in 2015 and 2018 at }} \backslashsqrt{s_{\backslashmathrm{NN}}} }}= 5.02 TeV. Light-by-light scattering candidates are selected in events with two photons produced exclusively, each with transverse energy }} {E}_{\backslashmathrm{T}}^{\backslashgamma } }}> 2.5 GeV, pseudorapidity |ηγ| < 2.37, diphoton invariant mass mγγ> 5 GeV, and with small diphoton transverse momentum and diphoton acoplanarity. The integrated and differential fiducial cross sections are measured and compared with theoretical predictions. The diphoton invariant mass distribution is used to set limits on the production of axion-like particles. This result provides the most stringent limits to date on axion-like particle production for masses in the range 6–100 GeV. Cross sections above 2 to 70 nb are excluded at the 95% CL in that mass interval.

2. PPNP

   Photon–photon physics at the LHC and laser beam experiments, present and future

   L. Schoeffel, C. Baldenegro, H. Hamdaoui, and 3 more authors

   Progress in Particle and Nuclear Physics, Mar 2021

   Abs DOI

   Under certain running conditions, the CERN Large Hadron Collider (LHC) can be considered as a photon–photon collider. Indeed, in proton–proton, proton–ion, ion–ion collisions, when incoming particles pass very close to each other in very peripheral collisions, the incoming protons or ions remain almost intact and continue their path along the beam axis. Then, only the electromagnetic (EM) fields of these ultra-relativistic charged particles (protons or ions) interact to leave a signature in the central detectors of the LHC experiments. The interest is that the photon–photon interactions happen at unprecedented energies (a few TeV per nucleon pairs) where the quantum electrodynamics (QED) theory can be tested in extreme conditions and unforeseen laws of nature could be discovered. In this report, we propose a focus on a particular reaction, called light-by-light scattering in which two incoming photons interact, producing another pair of photons. We describe how experimental results have been obtained at the LHC. In addition, we discuss prospects for on-shell photon–photon interactions in dedicated laser beam facilities. Potential signatures of new physics might manifest as resonant deviations in the refractive index, induced by anomalous light-by-light scattering effects. Importantly, we explain how this process can be used to probe the physics beyond the standard model such as theories that include large extra dimensions. Finally, some perspectives and ideas are given for future data taking or experiments.

2020

1. CPC

   The Control Unit of the KM3NeT Data Acquisition System

   S. Aiello, F. Ameli, M. Andre, and 221 more authors

   Computer Physics Communications, Mar 2020

   Abs DOI

   The KM3NeT Collaboration runs a multi-site neutrino observatory in the Mediterranean Sea. Water Cherenkov particle detectors, deep in the sea and far off the coasts of France and Italy, are already taking data while incremental construction progresses. Data Acquisition Control software is operating off-shore detectors as well as testing and qualification stations for their components. The software, named Control Unit, is highly modular. It can undergo upgrades and reconfiguration with the acquisition running. Interplay with the central database of the Collaboration is obtained in a way that allows for data taking even if Internet links fail. In order to simplify the management of computing resources in the long term, and to cope with possible hardware failures of one or more computers, the KM3NeT Control Unit software features a custom dynamic resource provisioning and failover technology, which is especially important for ensuring continuity in case of rare transient events in multi-messenger astronomy. The software architecture relies on ubiquitous tools and broadly adopted technologies and has been successfully tested on several operating systems.

2019

1. PRL

   Observation of Light-by-Light Scattering in Ultraperipheral \mathrmPb+\mathrmPb Collisions with the ATLAS Detector

   G. Aad, B. Abbott, D. C. Abbott, and 2945 more authors

   Phys. Rev. Lett., Jul 2019

   DOI