The MoEDAL experiment
(Monopole & Exotics Detector at the LHC)
Magnetic monopoles are the counterpart to electric charge in Maxwell equations. But, while the are distinct particles with positive or negative electric charge, it’s impossible to isolate a define magnetic pole. Infact, if we take a magnet and break it, we’ll always have two magnets, each one with is own south pole and north pole. The existence of magnetic monopoles was hypothesized by Paul Dirac in 1931 to explain electric charge quantization. Their search has continued over the decades with experiments at accelerators and in the cosmic radiation.
Pioneer and leader in the search for magnetic monopoles was Giorgio Giacomelli to whom the MoEDAL collaboration dedicated his first article. Under the guidance of Giacomelli, the Bologna Section played a fundamental role in the main experiments in the sector. Among all, it is worth mentioning the MACRO experiment (Monopole, Astrophysics and Cosmic Ray Observatory) leaded at Laboratori Nazionali del Gran Sasso from 1988 to 2000.
MoEDAL is installed near the LHCb experiment, at Point 8 on the LHC ring. It uses two detection systems, both passive: sheets of CR39 and Makrofol as nuclear track detectors (NTD) and Alluminun bars as Monopole Trapping Detector (MTD). MoEDAL’s radiation environment is monitored by the TimePix Radiation Monitoring System.
Layout of the MoEDAL experiment
In the nuclear track detectors, electrically and/or magnetically charged particles produce permanent damage in the structure of the materials. After a chemical etching this damage appears as conical hole under an optical microscope, whose dimensions are related to the properties of the particle.
In MTD aluminum bars act as a trap for magnetic charge. The unmistakable signal of a trapped monopole is sought by scanning the detectors with a magnetometer of very high sensitivity and stability
The Bologna team has full responsability of the nuclear track detector, that is its calibration, construction, chemical etching and analysis. As no signal was found compatible with what was expected for a magnetic monopole, new lower limits were placed on the mass of these particles. The first publication based on NTD analysis is in progress.