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PETAR ADŽIĆ PH.D., SERBIA’S SCIENTIFIC DELEGATE IN CERN COUNCIL
DECADE AFTER HISTORIC HIGGS BOSON DISCOVERY
To this very day, almost seven decades after its establishment, the European centre for nuclear research that’s known as CERN represents the most prestigious international scientific organisation, the work of which also includes the participation of numerous teams from Serbia
Speaking to CorD Magazine on the occasion of the 10th anniversary of the revolutionary discovery of the Higgs boson, professor Petar Adžić discusses the latest results and upcoming research into the properties of this elementary particle, but also CERN’s importance to Serbia’s scientific community, education system and economy.
■ Precisely 10 years have passed since the discovery of the Higgs boson particle, also known among journalists as the “God particle”. How do you view this turning point in science from today’s perspective?
CMS project control room
- The Higgs boson was probably the longest awaited particle clearly predicted by the prevailing Standard Model (SM) theory of particle physics. During my past lectures at the Faculty of Physics of the University of Belgrade, I very often had to answer the same question posed by students: do I believe the Higgs boson really exists? My answer was always the same: “besides strong physics and mathematical arguments, there is one more convincing argument: with the exception of the Higgs boson, all particles predicted by the Standard Model – the most precise theory in particle physics – have to date been confirmed as existing, and it is thus hard to believe that only the prediction of the Higgs boson, the SM’s last missing particle, was wrong”.
Finally, after more than 60 years of hunting, it was found in 2012, when the two largest experiments in particle physics – ATLAS and CMS – announced this historic discovery on 4th July at CERN. It represents a huge leap in particle physics, the predicting of which was worthy of the Nobel prize in physics for two great physicists, Peter Higgs and Francois Englert. Among the many scientists taking part in this long journey, Serbian scientists were involved in both of these experiments from 2001 and also gave direct contributions. These two largest and most complex experiments in the history of science involve about 9,000 scientists, engineers and experts of various profiles.
■ Was research on the Higgs boson
and the Higgs field concluded back in 2012?
- This discovery represented a turning point in High Energy Physics (HEP) and for particle physicists at the same time also the beginning of new challenges and deeper studies. It firstly confirmed SM as the leading theory of current energies produced at the LHC accelerator complex. This particle also confirms the existence of the complex Higgs field, thus encouraging physicists that they are on the right track in their research endeavours. However, although it is perfectly explained mathematically, we still do not understand the physics behind the Higgs mechanism and how it acts in the creation of particle masses. There are so many phenomena within the Higgs sector that we still need to understand and we are trying to study them in the Higgs boson’s interactions with other particles. Over the last ten years, ATLAS and CMS experiments performed very
■What has been happening at CERN
in the meantime? Has the research of some other teams led to some new discoveries, to new revelations about new particles?
- There are other priorities in particle physics too. Several important results and discoveries have also been reported and published in the meantime by ATLAS, CMS and another two LHC experiments: LHCb and ALICE. Some new exotic particles were discovered and some very rare particle decays were confirmed or discovered, including the Higgs boson rare decay, along with other phenomena. On the occasion of the tenth anniversary of the announcing of the discovery, ATLAS and CMS collaborations published two independent papers in the scientific journal Nature showing that the properties of the Higgs boson are remarkably consistent with those predicted by the SM. Further studies of this particle would represent a powerful tool to search for new and unknown phenomena that may shed more light on some of the biggest mysteries of physics, such as the nature of the mysterious dark matter present in the universe. All these discoveries and new precise measurements of particle properties are in line with SM predictions, but one of the priorities is also to search for indications of possible new physics and phenomena beyond SM predictions. All these will stimulate a more intensive search in the ongoing experiments, particularly after the upgrade of the High Luminosity LHC (HLLHC), the operation of which is planned for 2027-2028, while its programmes are expected to probably conclude by 2040.
■ Serbia has been a full member
of the European Organization for Nuclear Research – CERN since 2019. What has this membership brought us?
- There are several Serbian research teams involved in CERN projects, four of which are larger: two particle physics teams involved in the CMS (since 2001) and ATLAS experiment (2004), then one research team working on ISOLDE (in nuclear physics) experiments and the team involved in LHC GRID computing and SHIP experiment. There are also several smaller research groups and Serbian scientists and engineers contributing independently to different CERN projects. More than 80 people from Serbia have been registered as CERN users since Serbia became a full member of CERN. Apart from organised teams that provide an active research contribution to CERN projects, to date many Serbian summer students, Ph.D. students, postdoctoral and senior researchers have obtained prestigious CERN stipends, fellowships and various forms of financial support. They have spent between several months and several years working at CERN. Most of them returned to their home institutions to share their knowledge and experience with their colleagues, while continuing their close collaboration within CERN projects. ■ Did the engagement of a larger
number of research and technical experts at CERN at least slow down the brain drain of experts and future experts leaving Serbia?
- I don’t have any official information, but the answer is positive as far as HEP physicists are concerned. Most of those who collaborate actively within CERN projects travel from Serbia to CERN when needed. We are grateful for the general support of the Serbian govern-
With Rolf Heuer, former CERN General Director
One of CERN’s important missions is education. Serbia utilised the great opportunity to send pupils from Serbian schools to CERN on several occasions, then students and physics teachers, to attend CERN educational programmes. These programmes included lectures by CERN scientists, active training sessions, visits to CERN laboratories and experiments. Such activities were highly valued by Serbian schools and by the Serbian Ministry of education.
During the construction phase, Serbian industrial companies designed, constructed and delivered some detector parts for ATLAS and CMS detector as an in-kind contribution early in 2000. Some Serbian industrial companies were also active within CERN projects, but we expect the industrial return to improve in the following years.
ment, but what we need is much better financial support. We have been expecting the financial support required for active and comfortable work, including necessary longer stays at CERN, for many years. We hope that financial support will improve in the following years.
I should like to take this opportunity to mention that Belgrade will host the annual international conference “LHCPhysics” (LHCP2023) in the last week of May (22nd-29th) 2023. Serbia and Belgrade will have the honour of welcoming about 500 physicists from all over the world, who will present the latest results of LHC experiments at CERN. During one conference week, there will be also several ongoing events connected with CERN activities.
In front of open CMS detector
■ Does research work or engage-
ments on projects at CERN imply the transferring of part of the activities to the domestic scientific institutions to which researchers belong and, if so, to what extent?
- This is crucial and one of the most important benefits for each CERN member state. New research goals stimulate the development and application of new technologies as an indispensable ingredient of the construction of complex detectors. It is always a great opportunity for industrial companies to get involved in CERN’s scientific and technological projects. The knowledge and experience gained in this work pay off in the best way provided at least part of these activities and experience are transferred to home institutions. The same holds for scientists. Their experience and knowledge gained working on CERN projects represent the great award and may become beneficial for their home institutions. When they return home, they still can continue collaborating within CERN projects, but at the same time they can upgrade and enrich the scientific environment by implementing their knowledge, experience and new methods in research work at home institutions.
■ What are scientists from small
countries like ours most impressed by at CERN?
- The experimental research in HEP projects assumes the period from feasibility studies, construction and then commissioning of complex detectors and it takes usually 10 or more years. All these are dictated by high and ambitious research goals and priorities set by scientists and by technological development. Naturally, scientists and engineers, particularly young ones, are always impressed by unique equipment and the presence of many experts from whom they can usually learn. Even we seniors, with 35 or more years of experience at CERN, are astonished and thrilled each time we find ourselves in - It is estimated that approximately 80% of total particle physics research worldwide is currently being carried out at CERN. It is also one of the leading institutions in accelerator technologies, engineering and IT, along with all activities that necessarily follow the construction of complex detectors. CERN will certainly retain the status of leading HEP laboratory for several more decades and even longer, as all HEP research priorities should receive additional focus in
future CERN experiments at much higher energies. The ongoing LH-LHC programme upgrade has already enabled CERN to take a leading role in the following decades. The concept for building the new Future Circular Collider (FCC), which will be more than three times bigger (100 km circumference) than the existing LHC complex at CERN, has been considered and already adopted by the CERN Council within the scope of the plan of the European Strategy for Particle Physics. It should guarantee CERN’s long domination, as the first stage of FCC would become operational after 2040 and will offer the most advanced particle physics programmes for new generations of scientists worldwide for another 20 years or more.
front of those complex and huge detectors composed of more than 100 million parts surrounded by associated instruments and occupying the space of four- or five-storey buildings. Besides top-class research and the use of all kinds of modern equipment, I would reemphasis that the greatest benefit offered by CERN is education and experience that scientists or engineers can gain and bring back to their home institutions.
■ It is thanks to CERN that Europe
