DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS 2025
Cancelled/Postponed: Tuesday 14 January 2025 at 10:15 in A315 and using Zoom: Michael Campbell (CERN) Hybrid pixel detectors Abstract: Hybrid pixel detectors were first developed for the LHC as they provide noise hit free imaging of particle collisions even at extremely high event rates. The same feature can be used to provide detection and imaging solutions in numerous other fields. The Medipix Collaborations, which are coordinated at CERN, have pioneered the spread of hybrid pixel detector technology to fields as far apart as space-based dosimetry, industrial X-ray analysis and inspection, homeland security, molecular biology, medical imaging and classroom experiments. This presentation will explain how hybrid pixel detectors work and cover how the Medipix and Timepix readout chips can provide unique imaging solutions to many different fields. The recent introduction of sub-ns timing at the pixel level combined with novel interconnect technologies permitting almost seamless coverage of large detection areas should further extend the reach of the technology.
Cancelled/Postponed: Thursday 16 January 2025 at 10:15 in A315 and using Zoom: Michal Heller (Gent) New looks at nonequilibrium phenomena at high and low energies Abstract: I will discuss recent insights into nonequilibrium dynamics at high and low energies originating from the interplay of slow and fast processes. These theoretical developments are motivated, on one hand, by ultrarelativistic nuclear collisions at RHIC and LHC and neutron star mergers, and on the other, by cold atom experiments.
Tuesday 21 January 2025 at 10:15 using Zoom: Emidio Gabrielli (Trieste) Quantum Entanglement and Bell Inequality Violation at High Energies Abstract: I will present pioneering results demonstrating, for the first time, quantum entanglement and non-locality at high energies and in the presence of strong and weak interactions. Central to this discussion is Bell’s inequality relating the probabilities of different measurements on a given system. It is satisfied by local, deterministic theories and violated by quantum mechanics in the presence of entangled states. I will review the potential for detecting entanglement and testing Bell inequalities in collider experiments, focusing on diverse final states such as top-quark and tau-lepton pairs, Lambda baryons, massive gauge bosons, and vector mesons. Additionally, I will explore how entanglement offers a novel approach for constraining physics beyond the Standard Model, highlighting its most promising implications for future researches.
Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=363a6d95-fdf1-4b51-9ba4-452e7675bb5d
Link to pdf slides: Talk_Entanglement-Bell .
Tuesday 4 February 2025 at 10:15 in A315 and using Zoom: Laurids Jeppe (DESY) Searching for new scalars, pseudoscalars and top quark pair bound states at CMS Abstract: I will present a search for heavy pseudoscalar or scalar bosons decaying to a top quark pair ($t\bar{t}$) in final states with one or two charged leptons, using 138 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} = 13$ TeV recorded by the CMS experiment. The invariant mass of the reconstructed $t\bar{t}$ system and variables sensitive to its spin state are used to discriminate against the standard model $t\bar{t}$ background and to infer spin quantum numbers. An excess of the data above the background prediction, as modeled using perturbative quantum chromodynamics (QCD) only, is observed with a significance of above five standard deviations. I will discuss three possible hypotheses to interpret the excess, which is located close to the $t\bar{t}$ production threshold: by production of an additional scalar or pseudoscalar boson, or by the existence of a color singlet pseudoscalar $t\bar{t}$ bound state, as predicted in a simplified model of nonrelativistic QCD. For the first two hypotheses, I will outline upper limits on the coupling of pseudoscalar or scalar bosons to top quarks in a mass range of 365-1000 GeV and relative widths of 0.5-25%. For the third scenario, I will present and discuss an extracted cross section of 7.1 pb with an uncertainty of 11%.
Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=10f833b4-012e-489c-8d92-0f6013c485fd
Thursday 20 February 2025 at 10:15 in A315 and using Zoom: Oleg Komoltsev (Stavanger) QCD in the cores of neutron stars Abstract:Rapid advancements in neutron-star (NS) observations allow unprecedented empirical access to cold, ultra-dense Quantum Chromodynamics (QCD) matter. The combination of these observations with theoretical calculations reveals previously inaccessible features of the equation of state and the phase diagram of QCD. In this talk, I demonstrate how perturbative-QCD calculations at asymptotically high baryon density provide robust constraints on the equation of state at neutron-star densities, based solely on causality and stability. By comparing the calculations to multimessenger neutron-star observations using a Bayesian framework, I show that QCD input softens the equation of state at neutron-star densities, supporting the hypothesis of a first-order phase transition or a crossover to quark matter cores in the most massive neutron stars.
Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=45c5502a-fa88-40df-9a52-45a1321ddb78
Tuesday 25 February 2025 at 10:15 in A315 and using Zoom: Samuli Autti (Lancaster) From a universe in a helium droplet to that droplet observing the Universe Abstract: Superfluid 3He is perhaps the most versatile macroscopic quantum system in the laboratory. It has touching points with seemingly distant fields such as particle physics and cosmology and supports practical realisations of many exotic theoretical concepts. In this presentation, I discuss some striking phenomena recently discovered in this system, for example time crystals and their interactions and a superfluid that behaves as if it is two dimensional. Superfluid 3He is also increasingly being used to observe and model the behaviour of our Universe. I will show the first results from a dark matter detector using 3He as the collision target and explain how this sheds light on the yet-unresolved homogeneous nucleation problem with possible implications for a first-order phase transition in the early Universe.
Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=f60519ab-e971-4833-b4d4-0e7b813175e5
Thursday 27 February 2025 at 10:15 in A315 and using Zoom: Adrita Chakraborty (Krakow) Holographic study of confining QCD-like theory on non-SUSY D2 brane and partial deconfinement Abstract: We elucidate the nonperturbative aspects of non-conformal 2+1D Yang-Mills-like gauge theories on the worldvolume of isotropic and anisotropic
non-supersymmetric D2 brane solutions of type IIA supergravity. Because of the lack of conformal invariance, these theories possess energy scale-dependent running coupling similar to the pure QCDs. We implement the holographic approach to study some salient QCD-like confining properties, e.g., flux-tube tension and glueball masses in the low-energy nonperturbative sector of these non-SUSY theories. For anisotropic D2 brane, the variation of the above QCD features with the anisotropy parameter in low-energy limit manifests a duality between Hawking-Page transition and QCD confinement-deconfinement phase transition. We also discuss the same from an empirical finite temperature scenario. The smooth crossover found at this transition point has been countered as the appearance of “partially deconfined” mixed QCD phases where glueballs and quark-gluon plasma coexist. As the transition from a black brane to large black hole occurs at the Gregory-Laflamme transition point, one can comprehend it as the dual of complete confinement/deconfinement phase transition in a confining gauge theory. In this context, we make some remark upon a possible holographic duality between the mixed phases and the small evaporating black holes.
Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=d451c33a-5d60-4d43-bb6d-0a9a219c00b9
Tuesday 4 March 2025 at 10:15 in A315 and using Zoom: Michael Campbell (CERN) Hybrid pixel detectors Abstract: Hybrid pixel detectors were first developed for the LHC as they provide noise hit free imaging of particle collisions even at extremely high event rates. The same feature can be used to provide detection and imaging solutions in numerous other fields. The Medipix Collaborations, which are coordinated at CERN, have pioneered the spread of hybrid pixel detector technology to fields as far apart as space-based dosimetry, industrial X-ray analysis and inspection, homeland security, molecular biology, medical imaging and classroom experiments. This presentation will explain how hybrid pixel detectors work and cover how the Medipix and Timepix readout chips can provide unique imaging solutions to many different fields. The recent introduction of sub-ns timing at the pixel level combined with novel interconnect technologies permitting almost seamless coverage of large detection areas should further extend the reach of the technology.
