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First study of initial gluonic fluctuations using UPCs with ALICE
No full textIncoherent photoproduction is sensitive to fluctuations in the gluon structure of the target. Thus, the photoproduction measurement off colliding hadrons sheds light on QCD at high energies and provides important constraints on the initial conditions used in hydrodynamical models of heavy-ion collisions. In this contribution, the first measurement of the transverse momentum dependence of both coherent and incoherent photoproduction in ultra-peripheral collisions (UPCs) of lead ions at mid-rapidity is presented. These new results provide, for the first time, an indication of subnucleonic fluctuations in the color structure of lead ions. Recent results on the energy dependence of photoproduction with proton dissociation in proton–lead UPCs are also shown, measured for the first time at a hadron collider
Visit by Princess Maha Chakri Sirindhorn, Kingdom of Thailand
No full textVisit by Her Royal Highness Princess Maha Chakri Sirindhorn, Kingdom of Thailan
Winners of ATLAS Thesis Awards 2024
No full textCeremony for the 2024 ATLAS Thesis Awards held on 20 February 2025
Anomalous dimension of a general effective gauge theory. Part I. Bosonic sector
No full textWe classify the physical operators of the most general bosonic effective gauge theory up to dimension six using on-shell methods. Based on this classification, we compute the complete one-loop anomalous dimension employing both on-shell unitarity-based and geometric techniques. Our analysis fully accounts for the mixing of operators with different dimensions. The results broadly apply to any Effective Field Theory with arbitrary gauge symmetry and bosonic degrees of freedom. To illustrate their utility, we perform a complete cross-check of results on the renormalization of the Standard Model Effective Field Theory (SMEFT), O(n) scalar theory, and the SMEFT extended with an axion-like particle. Additionally, we present new results for axion-like particles with CP-violating interactions.We classify the physical operators of the most general bosonic effective gauge theory up to dimension six using on-shell methods. Based on this classification, we compute the complete one-loop anomalous dimension employing both on-shell unitarity-based and geometric techniques. Our analysis fully accounts for the mixing of operators with different dimensions. The results broadly apply to any Effective Field Theory with arbitrary gauge symmetry and bosonic degrees of freedom. To illustrate their utility, we perform a complete cross-check of results on the renormalization of the Standard Model Effective Field Theory (SMEFT), scalar theory, and the SMEFT extended with an axion-like particle. Additionally, we present new results for axion-like particles with CP-violating interactions
Stability conditions for bound states in antiprotonic atoms
No full textWe study the stability of bound antiprotons in close proximity to the atomic nucleus. Using experimental data from x-ray spectroscopy measurements of antiprotonic atom transitions, we tune a minimal theoretical framework and estimate parameter ranges where the strong or electromagnetic decay channels govern the stability of the deepest bound states. In this way, we present an overview of the dominant decay mechanism of antiprotonic orbits for a given principle quantum number, to assist future spectroscopic experiments on antiprotonic atoms.We study the stability of bound antiprotons in close proximity to the atomic nucleus. Using experimental data from X-ray spectroscopy measurements of antiprotonic atom transitions, we tune a minimal theoretical framework and estimate parameter ranges where the strong or electromagnetic decay channels govern the stability of the deepest bound states. In this way, we present an overview of the dominant decay mechanism of antiprotonic orbits for a given principle quantum number, to assist future spectroscopic experiments on antiprotonic atoms
(Re)interpretation of the LHC results for new physics
No full textThis contribution will describe ongoing efforts to provide event generation output to the broader community. There are a number of advantages that such a project could offer: reduced waste, easier project uptake, better validation, and improved communication between the experimental and phenomenological communities, among others
(Re)interpretation of the LHC results for new physics
No full textThe Rivet framework is widely used for analysis preservation and Monte Carlo validation, featuring around 2000 analysis routines, and is primarily used in BSM reinterpretation through the measurement-focused Contur method and tool. However, it is much less established in preservation of BSM searches, despite possessing the essential features such as detector "smearing" of physics objects, and cutflow computation. In this talk we review the major developments in the new Rivet version 4 and its underlying statistics library YODA2, which provide more coherent statistical breakdowns of MC predictions (including automatic propagation of theory uncertainties) and improvements for high-performance computing deployments. We will also present a new user-facing interface and tools designed to reduce entry barriers for BSM-search physics users, and streamline the preservation of BSM analyses in the Rivet collection
A workshop to introduce children from the Jardin des Particules to prototyping and teamwork at IdeaSquare
No full textFor three mornings, around forty children from the Jardin des Particules came to IdeaSquare, the innovation space at CERN, for an extraordinary workshop! Aged 5 to 7, the children of members of the CERN community were introduced to the basics of prototyping. Their mission: to create a model representing the Jura mountain range and its biodiversity. The project, co-developed with the Jardin des Particules, aims to educate children about their immediate environment in a creative and manual way. The Jura was chosen because it is a great source of biodiversity in addition to being omnipresent in the CERN landscape. The IdeaSquare team first prepared the base of the model, with materials available in the space for low-fidelity prototypes: cardboard, paint, and other recovered and recycled materials. These same materials are sometimes used in educational programmes with older students to teach them rapid prototyping. The children then thought about what they would like to add to complete this landscape. What animals inhabit the Jura? What plants? What other elements? The goal of this exercise is not only to make them aware of their environment but also to stimulate their creativity and invite them to share their creations in a large collective project. With playdough and coloured thread, the children thus completed the landscape collaboratively: each one added and carefully placed at least one element completing the model. The children surprised us all with their creativity and many ideas came to them: a lynx, a Saint Bernard, butterflies, flowers, plants, a river, snowmen, a skier, but also a magic stone hidden in the farm, reflections of the sun, ponds of different colours depending on the time of day, dinosaur footprints... Creating is a fundamental aspect of childhood that does not stop when growing up! Showing them how to use materials to design a collective work related to their environment is a fun way to make them collaborate to better understand nature, just like their parents do. So, when the children have their next outing in the Jura, they may remember this model and the real or imaginary elements that populate the mountain
Overview of ATLAS forward proton detectors: status, performance and new physics results
No full textA key focus of the physics program at the LHC is the study of head-on proton-proton collisions. However, an important class of physics can be studied for cases where the protons narrowly miss one another and remain intact. In such cases, the electromagnetic fields surrounding the protons can interact producing high-energy photon-photon collisions. Alternatively, interactions mediated by the strong force can also result in intact forward scattered protons, providing probes of quantum chromodynamics (QCD). In order to aid identification and provide unique information about these rare interactions, the instrumentation to detect and measure protons scattered through very small angles is installed in the beam pipe far downstream of the interaction point. We describe the ATLAS Forward Proton ‘Roman Pot’ detectors (AFP and ALFA), their performance of Tracking and Time-of-Flight detectors, and first results.A key focus of the physics program at the LHC is the study of head-on proton-proton collisions. However, an important class of physics can be studied for cases where the protons narrowly miss one another and remain intact. In such cases, the electromagnetic fields surrounding the protons can interact producing high-energy photon-photon collisions. Alternatively, interactions mediated by the strong force can also result in intact forward scattered protons, providing probes of quantum chromodynamics (QCD). In order to aid identification and provide unique information about these rare interactions, the instrumentation to detect and measure protons scattered through very small angles is installed in the beam pipe far downstream of the interaction point. We describe the ATLAS Forward Proton `Roman Pot' detectors (AFP and ALFA), their performance of Tracking and Time-of-Flight detectors, and first results
(Re)interpretation of the LHC results for new physics
No full textWe explore the collider phenomenology of the fat-brane realization of the Minimal Universal Extra Dimension (mUED) model, where Standard Model (SM) fields propagate in a small extra dimension while gravity accesses additional large extra dimensions. This configuration allows for gravity-mediated decay (GMD) of Kaluza-Klein (KK) particles, resulting in unique final states with hard photons, jets, massive SM bosons, and large missing transverse energy due to invisible KK gravitons. We derive updated constraints on the model's parameter space by recasting ATLAS mono-photon, di-photon, and multi-jet search results using 139 inverse femtobern of integrated luminosity data