The international collaboration operating the ATLAS experiment at CERN’s Large Hadron Collider (LHC) has reported the observation of toponium, a junction of the heavier elementary particles or 'top quark'. For decades this state was thought to be impossible to detect. A group from the Institute of Corpuscular Physics (IFIC), located in the UV Science Park, has played an important role in the detection of this new quantum system
The international collaboration operating the ATLAS experiment at CERN’s Large Hadron Collider (LHC) reported early in July the observation of toponium, a junction of the heavier elementary particles, the top quark. In physics, it is known as a 'quasi-bound state', a temporary bond between particles that is unstable and eventually disintegrates. For decades this state was thought to be impossible to detect. Now, the ATLAS experiment confirms the observation of the toponium carried out by the CMS experiment also in the LHC. A group of the Institute of Corpuscular Physics (IFIC), located in the scientific-academic area of the University of Valencia Science Park (PCUV) and joint research centre of the Higher Council for Scientific Research (CSIC) and the University of Valencia (UV), has played an important role in detecting this new quantum system.
Everything we see in the universe, including ourselves, is made up of quarks. Among them, the top quark is by nature a solitary particle. Unlike other quarks, which can combine to form hadrons (like the protons that make up the nucleus of the atom), the top quark disintegrates almost instantly, with no time to form bound states. In physics, a bound state is one where a particle is trapped in a region of space with other particles because it does not have enough energy to escape. It is stable, unlike the quasi-bound state where the particle can escape and is temporary and unstable. Quantum mechanics, the physics that explains the behavior of atoms and particles, allows, under exceptional conditions, a top quark and its antiparticle, an antiquark top, to survive long enough to interact and form the toponium, an almost bound state of extremely short life. However, for decades it had been considered virtually impossible to detect at the LHC, the world’s largest particle accelerator where scientists collide protons at near-light speeds to recreate the conditions in which the universe emerged.
New quasi-bound quantum state
Some time ago, in one of the large experiments of the LHC called CMS something unusual was observed with the data recorded between 2016 and 2018: an excess of quark pairs and antiquark top (its antiparticle, identical in everything except its electric charge). Although this type of excess can be interpreted as a sign of new particles, the exact location of the phenomenon led the team to consider a different possibility: the formation of toponium. On 8 July, the ATLAS collaboration, which involves more than 5,000 scientists and technicians from around the world, independently announced to CMS the observation of the same phenomenon, analyzing data taken between 2015 and 2018. The results are in close agreement with the results obtained by the CMS collaboration, reinforcing the interpretation that it is a new quasi-bound quantum state called toponium.
"For years it was believed that a bound state such as toponium would be undetectable, since the effects of this binding were too subtle. But ATLAS and CMS analyses show that the LHC has been able to detect this short-lived junction between a top quark and an antiquark top, which would result in this new quasi-bound state already predicted in 1990, even before the discovery of the top quark", IFIC researcher Marcel Vos
Participation of IFIC
The Institute of Corpuscular Physics has been involved in the ATLAS experiment at the LHC since its inception and has had a prominent presence in the top quark physics group. CSIC researcher at the IFIC Marcel Vos has contributed to the review process of this result. Vos also coordinates the LHC Top Working Group, the team in charge of all results related to the top quark at the LHC.
"Since the detection of the top quark in 1995, the production and properties of this particle and its antiparticle have been studied in great detail," explains Marcel Vos. "For years it was believed that a bound state such as toponium would be undetectable, since the effects of this binding were too subtle. But the ATLAS and CMS analyses show that the LHC has been able to detect this short-lived junction between a top quark and an antiquark top, which would result in this new quasi-bound state already predicted in 1990, even before the discovery of the top quark," says the PCUV scientist.
Despite clear evidence of an unexpected phenomenon, the ultimate origin of toponium has yet to be clarified. A possible alternative explanation would be the existence of a new particle with a mass close to twice that of the top quark. These results show that there is still much to explore in the Standard Model of particle physics, the theory that best describes the visible universe. If the toponium observation is confirmed, the finding will mark a new milestone in our understanding of the most fundamental constituents of the universe.
Don’t miss the interview with Marcel Vos (IFIC) in our EuroPark section
Source: UV News
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