The generation of top quark pairs is observed This process of interaction between atomic nuclei was observed for the first time in lead-lead collisions at CERN's Large Hadron Collider (LHC) and the ATLAS detector.
We show lead-lead collisions at 5.02 TeV per nucleon pair, resulting in the production of candidate pairs of top quarks that decay into other particles. This event contains four particle jets (yellow cone), one electron (green line), and one muon (red line). The inlay shows an axial view of the event. Image credit: ATLAS/CERN.
In quark-gluon plasma, quarks (matter particles) and gluons (strong force transmitters), which are the basic constituents of protons and neutrons, are not bound within particles and exist in an unconfined state of matter, and almost It forms a complete dense fluid.
Physicists believe that quark-gluon plasma filled the universe shortly after the Big Bang, and their study provides a glimpse into conditions at earlier times in the universe's history.
However, the lifespan of quark-gluon plasma produced by heavy ion collisions is extremely short, approximately 10 years.-twenty three Seconds — means not directly observable.
Instead, physicists study the particles produced in these collisions that pass through the quark-gluon plasma and use them as probes of the plasma's properties.
In particular, the top quark is a very promising probe of the evolution of quark-gluon plasmas over time.
The top quark, the heaviest elementary particle known, decays into other particles an order of magnitude faster than the time required to form a quark-gluon plasma.
The delay between the collision and the decay products of the top quark interacting with the quark-gluon plasma may serve as a “time marker” and provide a unique opportunity to study the temporal dynamics of the plasma.
In addition, physicists could potentially extract new information about the nuclear parton distribution function, which describes how the momentum of a nucleon (proton or neutron) is distributed among its constituent quarks and gluons.
In the new study, physicists from the ATLAS collaboration studied lead ion collisions that occurred during LHC Experiment 2 at a collision energy of 5.02 teraelectronvolts (TeV) per nucleon pair.
They observed the production of a top quark in a dilepton channel, where the top quark decays into a bottom quark and a W boson, which then decays into an electron or muon and its associated neutrino.
This result has statistical significance with a standard deviation of 5.0, and is the first observation of the production of a top quark pair in a nucleus-nucleus collision.
“We measured the production rate, or cross section, of the top quark pair with a relative uncertainty of 35%,” the physicists said.
“The overall uncertainty is primarily driven by the size of the dataset, which means new heavy ion data from the ongoing Experiment 3 will improve the accuracy of the measurements.”
“The new results open the door to the study of quark-gluon plasmas,” the researchers added.
“Future studies will also consider semi-leptonic decay channels for top quark pairs in heavy ion collisions. This may provide the first glimpse of the evolution of quark-gluon plasmas over time.” ”
Source: www.sci.news
