Machine learning techniques for detecting topological avatars of new physics
Dr Adrian Bevan, Queen Mary University of London, UK
The search for highly ionising particles in nuclear track detectors (NTDs) traditionally requires experts to manually search through samples in order to identify regions of interest that could be a hint of physics beyond the Standard Model (SM). The advent of automated image acquisition and modern data science, including machine learning-based processing of data, presents an interesting opportunity to accelerate the process of searching for anomalies in NTDs that could be a hint of a new physics avatar.
The potential for modern data science to be applied to this topic is discussed, in the context of the MoEDAL experiment at the Large Hadron Collider (LHC) at the European Centre for Nuclear Research, CERN. Polymer chains in the NTDs are damaged by ionising particles traversing the plastic. Subsequent chemical etching of the plastic results in nanoscopic damage being transformed into microscopic damage – visible under a microscope or on a modern scanner system. Featuring finding algorithms can be developed, ranging from traditional clustering algorithms to modern deep-learning methods, in order to address the issue of identifying holes in the plastic. A heavily ionising avatar will differ from a SM particle as it will traverse a stack of NTDs inflicting damage to many adjacent foils, whereas the SM particle will range out only affecting a few foils as that particle comes to rest. The potential for modern data science to be applied to this area is explored.
The inevitability of sphalerons in field theory
Professor Nicholas Manton FRS, University of Cambridge, UK
Many field theories have nonlinear equations, but more interesting is when the nonlinearity is geometrically essential, and independent of the details of the theory. This can happen through constraints on the fields, as in sigma models, through the geometry of the vacuum manifold, or through the need to quotient out by gauge transformations. When the Higgs mechanism operates, a nontrivial vacuum manifold and gauge transformations combine. In many such field theories, the field potential energy function inevitably has saddle-points in the infinite-dimensional field configuration space, and these are sphalerons. Sphalerons are smooth, spatially localised solutions of the static field equations, so they are rather like solitons, but unlike solitons they are unstable [ancient Greek: sphaleros = unstable]. Examples of sphalerons are kink-antikink and monopole-antimonopole solutions. Also, the electroweak sector of the Standard Model has no monopoles, but it has sphaleron solutions. The Skyrme model of baryons and nuclei has stable solitons, and also higher energy sphaleron-type solutions. Sphalerons can set the energy scale where perturbation theory breaks down, and control the energy scale for tunnelling, analogous to the transition state controlling a chemical reaction. Tunnelling processes in electroweak theory are accompanied by violations of baryon and lepton number, and could have been important in the early universe.
Searches for cosmic magnetic monopoles: past, present and future
Dr Laura Patrizii, Istituto Nazionale di Fisica Nucleare, Italy
In 1931 Dirac introduced the magnetic monopole in order to explain the quantization of the electric charge. Grand Unification Theories (GUT) of the basic interactions imply the existence of monopoles of extremely large mass, O(1016 GeV/c2 ). Larger masses are expected if gravity is brought into the unification picture. Intermediate mass magnetic monopoles (105 – 1012 GeV/c2) are predicted by theories with an intermediate energy scale between the GUT and the electroweak scales and would appear in the early universe at a considerably later time than the GUT epoch. The lowest mass magnetic monopoles should be stable, therefore they should still exist as cosmic relics from the early universe and be a component of the cold dark matter.
Significant efforts have been made over several decades searching for magnetic monopoles whose discovery would represent a breakthrough in particle physics, astrophysics and cosmology. Supermassive poles should have low velocities and relatively large energy losses; they are best searched for underground in the penetrating cosmic radiation. Lower mass monopoles could be relativistic reaching high altitude laboratories.
In this talk the status of the searches for classical, super-heavy, and intermediate mass monopoles with experiments in space, at high altitudes, underground and underwater/ice is reviewed, emphasizing the most recent results and future perspectives.
Monopole-antimonopole pair production by magnetic fields
Professor Arttu Rajantie, Imperial College London, UK
It is a well-known prediction of quantum electrodynamics that in a strong electric field, electron-positron pairs are produced through the Schwinger process, which can be interpreted as quantum tunnelling through the Coulomb potential barrier. If magnetic monopoles exist, the monopole-antimonopole pairs would be produced by strong magnetic fields through the electromagnetic dual of this process. The production rate can be computed using semiclassical techniques without relying on perturbation theory, and therefore it can be done reliably in spite of monopoles’ strong coupling to the electromagnetic field. This talk explains this process and discusses the bounds on monopole masses arising from the strongest magnetic fields in the universe, which are in neutron stars known as magnetars and in heavy ion collision experiments such as lead-lead collisions carried out in November 2018 in Large Hadron Collider at CERN. The talk will also discuss open theoretical questions affecting the calculation.
The MoEDAL experiment at the LHC - a new light on the high energy frontier
Professor James Pinfold, University of Alberta, Canada
MoEDAL is a pioneering LHC experiment designed to search for anomalously ionizing messengers of new physics such as magnetic monopoles or massive (pseudo-)stable charged particles, which are predicted to existing in a plethora of models beyond the Standard Model. It started data taking at the LHC at a centre-of-mass energy of 13 TeV in 2015. Its ground breaking physics program defines a number of scenarios that yield potentially revolutionary insights into such foundational questions as: are there extra dimensions or new symmetries; what is the mechanism for the generation of mass; does magnetic charge exist; and what is the nature of dark matter. MoEDAL's purpose is to meet such far-reaching challenges at the frontier of the field. We will present the results from the MoEDAL detector on Magnetic Monopole and highly ionizing electrically charged particle production that are the world’s best. In conclusion, progress on the installation of MoEDAL’s MAPP (MoEDAL Apparatus for the detection of Penetrating Particles) sub-detector prototype will be very briefly be discussed.