Discovering CMS, the large detector at CERN in Geneva. An interview with Roberto Carlin
On 1 September 2018, Roberto Carlin became the new Spokesperson for CMS, one of the main experiments at CERN in Geneva, and he also played a significant role in the discovery of the Higgs Boson. Professor at the University of Padua and researcher at INFN, the Italian National Institute for Nuclear Physics, Roberto Carlin will hold this important position until 2020. We met him in the days before he took office in building 40 at CERN, where he welcomed us with the warmth and excitement of someone who is preparing to take on a great challenge for knowledge.
With your appointment, three of the four main experiments at the Large Hadron Collider (LHC) in Geneva are now led by Italian scientists. How did you receive your appointment to the important role of Spokesperson for the CMS experiment?
I am honoured to have been chosen as the Spokesperson for such an important collaboration, which brings together about 3,000 scientists from 45 countries from around the world. My appointment is also confirmation of the excellence of Italian physics, which has a key role in the CMS collaboration as well as in all the other LHC research programmes. As you said, three of the four main LHC experiments are now in the hands of Italian scientists: besides myself, there are Federico Antinori, Spokesperson for ALICE, and Giovanni Passaleva, Spokesperson for LHCb, as well as Simone Giani who coordinates one of the smaller experiments, TOTEM, and obviously Fabiola Gianotti, who is currently Director-General of CERN. But many researchers working at CERN are Italian and some of them are responsible for some sub-projects, such as Francesca Cavallari, Andrea Venturi and Anna Colaleo, who are responsible for the CMS calorimeter, trackers and muon detectors, respectively.
What is CMS all about?
CMS ‒ an acronym for Compact Muon Solenoid ‒ is one of the four main experiments at LHC (the others are ATLAS, ALICE and LHCb, Ed.) and, together with ATLAS, is one of the two big general-purpose experiments, that is, experiments that study any new physical phenomena that may occur following particle collisions. The experiment is a cylindrical particle detector weighing nearly 14,000 tons, 21 metres long and 15 metres in diameter, located at a depth of 100 metres along the LHC tunnel near the village of Cessy, in France. Like all particle detectors, CMS is composed of several concentric layers that allow us to identify and measure the physical characteristics of all the particles generated in LHC collisions. The innermost part, for example, houses a silicon ‘tracker’ for the identification of the characteristics of charged particles; it is followed by the so-called ‘calorimeters’, which measure the energy of electrons, photons and hadrons. Finally, the outermost area detects the most elusive particles, muons, similar to electrons but heavier.
How can we understand the CMS experiment?
What we do is basically try to understand the behaviour of matter at very high energy levels, therefore at very small distance scales. One of our goals is to try to explain all the physics phenomena that occur in nature and provide answers to important scientific questions, such as the nature of dark matter and the properties of the Universe in its earliest moments. An important milestone was reached in 2012 with the discovery of the Higgs Boson and today we are studying in detail the characteristics of this elementary particle, with some interesting discoveries.
What new elements have emerged from the study of the Higgs Boson?
One of the most relevant elements is the measurement of the interaction of the Higgs Boson with fundamental constituents of matter, fermions. This interaction had been predicted by the Standard Model (the model that explains the fundamental interactions of matter, Ed.) but had never been experimentally verified. This is an important step towards understanding the laws of physics governing the Universe.
However, not all the behaviours in nature can be explained through the Standard Model. Is it time to go beyond this theory?
The Standard Model provides an excellent description of the fundamental interactions of matter but today we know that this model is incomplete. For example, it provides no explanation of dark matter, neutrino masses or the Higgs Boson itself. Therefore, any other new theory will have to include or expand the laws of the Standard Model without abandoning them, as was the case with Einstein’s laws, which provided new models and also expanded Newton’s laws, which are still valid today.
New developments could come with HL-LHC, the project designed to upgrade the CERN collider. Can you explain what it is about?
The HL-LHC (High Luminosity LHC) project will increase the LHC’s luminosity by a factor of 10, that is, it will multiply by ten the total number of particle collisions inside the detector. This will allow us to study rare events and explore any new particle interactions, explaining some unknown properties of matter as well as some properties of the Higgs Boson. The project should be operational as from 2026 and includes major upgrades of the particle detectors currently in use, including CMS, with projects in which Italy plays a key role through INFN. Once operational, HL-LHC will provide an important contribution to our scientific knowledge and will open new frontiers in the development of very high-energy particle accelerators.