Novosibirsk Scientists Participate in Large Hadron Collider Experiment

Researchers at the Budker Institute of Nuclear Physics (INP SB RAS) and NSU joint laboratory are continuing their work on the ATLAS Experiment to study the properties of the Higgs boson particle. ATLAS (A Toroidal LHC ApparatuS) is one of the two largest particle detector experiments to acquire and analyze data in collisions of ultra high-energy proton beams at the Large Hardon Collider (LHC). LHC is a particle accelerator located at the “European Organization for Nuclear Research’ (CERN) near Geneva, Switzerland.

The ATLAS Collaboration, founded in 1992, now includes more than 180 institutes and universities fr om 38 countries, more than 3,000 physicists, and approximately 1,000 students. Data on high energy proton collisions (“created by man”) has been collected since 2010. The research program is planned until the end of the 2030’s. The INP SB RAS has been participating in the ATLAS Collaboration since 1995. In 2014, INP SB RAS formed a joint laboratory with NSU.

ATLAS is a large detector of elementary particles. Its length is 44 meters, and its diameter is 25 meters. It contains some of the most modern subsystems for registering various particles and is located in the LHC mine at a depth of about 100 meters. The ATLAS Experiment is devoted to the study of the physical processes occurring during the collision of ultrahigh energy protons. The more energy, the more likely the birth of heavier (and therefore vanishingly rare in our accustomed world) particles - a consequence of Einstein’s famous equation “E = mc2”. The role of these particles was important in the early stages of the emergence and development of our Universe.

Modern physicists believe that all of space is “saturated” with condensates of elementary scalar particles known as “Higgs boson”. It is because of this interaction that other known elementary particles "acquire" a non-zero mass. Theorists predicted the existence of the Higgs boson in the 1960s, but it was not possible to detect it for 50 years. Finally, in 2012, the LHC ATLAS and CMS detectors identified the Higgs boson. In 2013, the Nobel Prize in Physics was awarded to the scientists who predicted it.

Alexey Maslennikov, a Senior Researcher at the NSU Physics Department, talked about this work,

The Higgs boson was the last missing element of the Standard Model of Particle Physics (the modern theory of the microworld). However, the Standard Model is known to be incomplete since it does not include gravity or “dark matter”. So far from astrophysical observations, we only know that it manifests itself through gravity and interacts very weakly with the matter known to us. Therefore, the search for the “new physics” (beyond the Standard Model) and a precise study of the properties and interactions of already known, but rare particles (Higgs bosons, heavy t- and b-quarks, exotic hadrons), which may turn out to be a “window to the new physics ”are priorities for ATLAS physicists, and our friends and competitors in the CMS collaboration. There is not now, and will not be in the next two decades, another experimental installation in the world wh ere these problems can be solved better or faster.

Laboratory physicists analyze physical processes. In particular, the group studying the properties of the Higgs boson in the decay channel into four leptons (fundamental particles with a half-integer spin, not participating in the strong interaction) and searching for heavier Higgs boson as predicted in an expansion of the Standard Model. A journal publication is currently being prepared based on an analysis of all the statistics collected by the ATLAS detector in the course of “Run2” from 2015 to 2018. Novosibirsk researchers also take part in work supporting and developing software code to ensure the performance of ATLAS calorimeters, modeling, reconstruction and identification of particles in them, and preparing for future data collection.

Maslennikov talked about the significance of the Novosibirsk scientist’s work,

Both absorbers and electrodes of electromagnetic calorimeters have a very complex shape, resembling an accordion. Describing their geometry in the software package for modeling GEANT4 detectors and creating efficient algorithms for playing out the energy release and collecting the signal when particles pass through a non-uniform electric and magnetic field is a very difficult task. Andrei Sukharev (Senior Researcher at the NSU Physics Department) has been involved in this since 2001 and is the main expert. Several years ago, he and Dmitry Maximov (Senior Lecturer at the NSU Physics Department) not only eliminated rare errors caused by inaccurate geometry, but also sped up the program by 15%. This saved a significant portion of computer resources that were spent on modeling an additional number of events. Now the issue of reorganizing the program code to ensure its work in a multiprocessor environment is being addressed.

According to specialists, there are more than 182 thousand electronics channels in the calorimeters on liquid argon of the ATLAS detector. For each of them, For each of them, during the collection of statistics, it is necessary to regularly measure, check for reasonableness, and store the parameters of the response to signals from the calibration generator in the database.

Maslennikov summarized the importance of their efforts,

Without this, it is impossible to provide the energy resolution and background suppression necessary for obtaining physical results. Victor Bobrovnikov (Senior Researcher and engineer at the NSU Physics Department) and Olga Rezanova (Senior Teacher at the Physics Department) are developing software to monitor the quality of calibrations of the calorimeter electronics and channel status. Thanks to the qualifications and efforts of experts and overseers in 2018, the share of “unsuitable for processing” data was 2.5%, the average for “Run 2” from 2015 to 2018, was 5%.