A Toroidal LHC ApparatuS (ATLAS) is a general-purpose particle physics experiment, one of the four major experiments at the Large Hadron Collider (LHC) at CERN. It is run by an international collaboration and is designed to exploit the full discovery potential and the huge range of physics opportunities that the LHC provides.

A Toroidal LHC ApparatuS (ATLAS) is a general-purpose particle physics experiment, one of the four major experiments at the Large Hadron Collider (LHC) at CERN. It is run by an international collaboration and is designed to exploit the full discovery potential and the huge range of physics opportunities that the LHC provides.

ATLAS has the dimensions of a cylinder: 46 meters long and 25 meters in diameter is the largest volume detector ever constructed for a particle collider - it weighs 7000 tonnes, similar to the weight of the Eiffel Tower. It sits in a cavern 100 meters below ground. It consists of six different detecting subsystems wrapped concentrically in layers around the collision point to record the trajectory, momentum, and energy of particles, allowing them to be individually identified and measured. A huge magnet system bends the paths of the charged particles so that their momenta can be measured as precisely as possible.

The four major components of the ATLAS detector are the Inner Detector, the Calorimeter, the Muon Spectrometer and the Magnet System. Integrated with the detector components are: the Trigger and Data Acquisition System, a specialized multi-level computing system, which selects physics events with distinguishing characteristics; and the Computing System, which develops and improves computing software used to store, process and analyse vast amounts of collision data at 130 computing centres worldwide.

Over a billion particle interactions take place in the ATLAS detector every second, a data rate equivalent to 20 simultaneous telephone conversations held by every person on the earth. Only one in a million collisions are flagged as potentially interesting and recorded for further study. The detector tracks and identifies particles to investigate a wide range of physics, from the study of the Higgs boson and top quark to the search for extra dimensions and particles that could make up dark matter.

 

ATLAS explores a range of physics topics, with the primary focus of improving our understanding of the fundamental constituents of matter. Some of the key questions that ATLAS addresses are:

1. What are the basic building blocks of matter? The Standard Model describes the elementary subatomic particles of the universe which have been experimentally seen. ATLAS studies these particles and searches for others to determine if the particles we know are indeed elementary or if they are in fact composed of other more fundamental ones.

2. What are the forces that govern their interactions? The Standard Model also describes the fundamental forces of Nature and how they act between fundamental particles. Possible discoveries at the LHC could validate models, such as those incorporating Supersymmetry, where the forces unify at very high energies.

3. What happened to antimatter? By searching for imbalances in the production of matter and antimatter, we seek to understand why our universe appears to comprise only matter.

4. What is “dark matter”? Astronomical measurements support the existence of matter that cannot be directly seen. The hermetic construction of ATLAS, however, makes it possible to search for this “dark matter”.

5. What was the early universe like and how will it evolve? Proton-proton and heavy-ion collisions delivered by the LHC recreate the conditions immediately following the Big Bang when the Universe was governed by high-energy particle physics and later by a primordial soup of quarks and gluons, and allow ATLAS to study fundamental questions such as the Brout-Englert-Higgs field or Dark Matter.

6. How does gravity fit in? Gravity is extremely weak when compared to the other forces. To explain the difference we look for such exotic phenomena as extra dimensions, gravitons, and microscopic black holes.

7. Anything else? Perhaps the most exciting aspect of the ATLAS physics programme is our ability to explore and discover new phenomena beyond existing theoretical predictions: the search for the unknown.

Testing the predictions of the Standard Model can lead to ground-breaking discoveries, such as that of the Higgs boson (below), physics beyond the Standard Model and the development of new theories to better describe our universe.

ATLAS comprises about 3000 scientific authors from 181 institutions around the world, representing 38 countries from all the world’s populated continents. It is one of the largest collaborative efforts ever attempted in science. Around 1200 doctoral students are involved in detector development, data collection and analysis. The collaboration depends on the efforts of countless engineers, technicians and administrative staff.

Scientists usually work in small groups, choosing the research areas and data that interest them most. Any output from the collaboration is shared by all members. The success of the collaboration is bound by individual commitment to physics and the prospect of exciting new results that can only be achieved with a complete and coherent collaborative effort.

The countries participating in ATLAS provide investment through project funds, with contributions also coming from CERN, and some resources from individual universities.

Members of the ATLAS group from Jagiellonian University are at present participating in development and optimisation of the High Level Trigger software for preparation of Run 3 (years 2022 - 2025).

Members of the ATLAS group from the Jagiellonian University:

• prof. dr hab. Elżbieta Richter-Wąs,

• dr hab. Witold Przygoda,

• dr Damian Gil,

• dr Marek Pałka,

• dr Kacper Topolnicki,

• mgr Tomasz Przedziński,

• Patryk Czudak,

• Adrianna Frydrowicz.