Analysis of the latest data obtained at the LHC after its restart, once again did not allow physicists to find traces of magnetic monopoles - hypothetical particles with only a positive or only a negative pole, according to an article posted in the arXiv.org electronic library.
“Despite the fact that we did not find monopoles, we managed to give new, most reliable estimates of its minimum mass and magnetic field strength. There are other estimates of these parameters, but they were made on the basis of various kinds of assumptions, not experimental data,”said Arrtu Rajantie from Imperial College London (UK).
Magnetic monopoles are hypothetical particles with one magnetic pole, the possible existence of which was first announced by the English physicist Paul Dirac in 1931. If scientists manage to find them in nature or create them in the laboratory, then this discovery will unambiguously confirm the assumption that the electric charges of all particles are discrete quantities, on which almost all modern physical theories are based.
Physicists have not yet been able to do this for one simple reason - the mass of the monopole, as theorists believe today, is very large. It is at least a third of the mass of a proton and is most likely comparable to the mass of the T-quark, the heaviest elementary particle to date. Modern particle accelerators have only recently begun to reach this level, which is why earlier searches for monopoles in the form in which Dirac imagined them were impossible in practice.
For example, the LHC began looking for monopoles only in 2011, when a MoEDAL detector was installed in its ring, designed to observe the traces of these superheavy particles. It is a set of metal screens and several hundred aluminum blanks installed between them and interacting with flying particles.
As conceived by the creators of MoEDAL, some of the monopoles will "get stuck" inside these rods, so that they can be detected using supersensitive magnetic field sensors based on superconductors.
The last three attempts to find monopoles using such traps - in 2012, 2013 and 2015 - have failed. Despite the increase in the sensitivity of the detectors and the doubling of the power of the LHC itself, physicists have not been able to find any traces of unipolar magnetic particles, which sharply narrowed the field of their possible searches.
Similar results, according to James Pinfold, a project leader at the University of Alberta in Edmonton, Canada, were obtained by analyzing a complete dataset for the entire second cycle of the LHC, during which MoEDAL accumulated six times more information than for all the previous time.
Promotional video:
According to scientists, initially they were able to detect about four dozen potential traces of monopoles, but retesting showed that they were all caused by malfunctions and errors in the operation of superconducting magnetic field sensors, and not by real elementary particles.
Such measurement results, as Pinfold notes, indicate that the minimum mass of a monopole is about 400 billion electron volts, which is about 400 times the mass of a proton and three times the mass of a T quark. Rajanti's group came to similar conclusions, analyzing data from another part of the LHC - the SPS accelerator, in which, as scientists believed, individual monopoles can be combined into pairs.
Such heavy particles, according to physicists, will be extremely difficult to search for at the LHC and even at its successor, the ILC linear collider, continuously observing collisions of nuclei and protons for many years. For this reason, the mystery of the discreteness of electric charges may remain unsolved for several decades, scientists conclude.