Researchers from ALICE international experiment at the Large Hadron Collider have determined the mass of free charmed quark. Thus, they confirmed the findings of the theory describing 1/4 of the world. The research resulted in publication in "Nature", and its authors include employees and doctoral students from the Warsaw University of Technology.

The charmed quark is an extremely small elementary particle that loves company. Already a fraction of a second since its birth (in this case, it is one hundred thousand billionth of a billionth of a second – 10^-23), it is trying to find a partner or partners.

We already know quite a lot about the properties of hadrons, or the compounds of quarks, however, we still lack data on how quarks behave when they are completely alone. Researchers from ALICE experiment decided to investigate this. They designed an experiment to determine the properties of the charmed quark in the short time it is looking for a partner. The publication on this subject was published in „Nature”.

What is the mass of the charmed quark?

The challenge was to identify charmed quarks looking for a partner in the abundant shower of particles that are formed in the Large Hadron Collider.

– ALICE experiment makes it possible to measure and identify these particles – to the extent that we were interested in the study of charmed quarks – explains prof. Adam Kisiel from the Faculty of Physics of the Warsaw University of Technology, a participant in the experiment.

The so-called dead cone effect helped to search the data from detectors and find information about charmed quarks released for a while there. The theory was that a charmed quark looking for a partner will lose energy by emitting particles (gluons) in a characteristic way: no particle escaping from this losing quark's energy leaves it in the direction of its flight, so a so-called dead cone is formed, not observed for lighter quarks. It is an observation of one of the fundamental effects of strong interactions.

The publication in „Nature” confirms the experimental observation of such dead cones and the fact that owing to them one can gain insight into the moment of a lonely life of a charmed quark.

– Our research is the most direct confirmation that a free charmed quark has a mass, says Łukasz Graczykowski, PhD, from the Faculty of Physics of the WUT. – This weight is approx.1.28 GeV/c2, so approx. 2.29x10^-24 g. So one could say that about half a million billion billion of these lonely quarks would weigh one gram.

Description of 1/4 of the world

Polish participants of the experiment explain that these studies are important because they confirm the findings of the so-called quantum chromodynamics. Prof. Adam Kisiel reminds that in order to describe the operation of the world, it is necessary to understand four interactions: electromagnetic, strong, weak and gravity.

– And quantum chromodynamics is a theory describing strong interactions – so 1/4 of the world – reminds a researcher from the WUT. – Therefore, the fundamental question is whether this description that we use is actually correct.

In order to confirm in practice how strong interaction works, it is good to have experiments in which you can observe quarks in a free state for a moment. Like the one we ran in ALICE detector.

20 years of cooperation

Four Polish scientific institutions take part in ALICE experiment: Warsaw University of Technology, the National Centre for Nuclear Research, the Institute of Nuclear Physics of the Polish Academy of Sciences and the AGH University of Science and Technology in Krakow.

For almost two decades, employees, doctoral students and students from several WUT faculties have participated in the experiment. They deal with data analysis, development of key elements of the software and the ALICE collision visualization system.

The final analysis, which leads to a specific discovery – as in this case, is carried out by a small group of researchers. However, their work is the culmination of the efforts of many people involved in the research in ALICE, which is why the list of authors of the publication always lists, in alphabetical order, all people participating in the experiment.

– Researchers from Polish institutions were not directly involved in the final analysis presented in the latest work, but we are proud of the obtained result, because it shows how comprehensive an experiment ALICE is and how high quality research is possible thanks to multilateral international cooperation in a joint scientific project – notes Łukasz Graczykowski, PhD, from the Faculty of Physics.

Co-authors of publications in "Nature" from the Warsaw University of Technology:

Kamil Deja, MSc., (Faculty of Electronics and Information Technology), Łukasz Graczykowski, PhD, (Faculty of Physics), Rihan Haque, PhD, (Faculty of Physics), Monika Jakubowska, PhD, (Faculty of Electrical Engineering), Małgorzata Janik, PhD, (Faculty of Physics), Przemysław Karczmarczyk, MSc., (Faculty of Physics), Associate Professor Eng. Adam Kisiel, PhD, (Faculty of Physics), Georgy Kornakov, PhD, (Faculty of Physics), Julian Myrcha, MSc., (Faculty of Electronics and Information Technology), Piotr Nowakowski, MSc., (Faculty of Electronics and Information Technology), Janusz Oleniacz, PhD, (Faculty of Physics), Prof. Przemysław Rokita, PhD, DSc, (Faculty of Electronics and Information Technology), Wioleta Rzęsa, MSc., (Faculty of Physics), Associate Professor Tomasz Trzciński, PhD, DSc., (Faculty of Electronics and Information Technology), Assistant Professor Hanna Zbroszczyk, PhD DSc Eng. (Faculty of Physics).

More information about the latest discovery of ALICE experiment in the text on naukawpolsce.pl and in the article „Nature”