In the first millionths of a second after the Big Bang, the universe was a conglomerate of turbulent plasma of quarks and gluons over a trillion degrees. These elementary particles came together in endless combinations before cooling and settling into more stable forms that gave rise to the particles of ordinary matter we know as neutrons and protons.
But, before they cooled down and gave us these particles that make up our conventional matter, a small fraction of these gluons and quarks randomly collided, forming short-lived “X” particles.
These X particles are very rare
And, despite the rarity of these mysterious and unknown particle structures, scientists at the Massachusetts Institute of Technology (MIT) working with CERN in Geneva have found evidence of X particles in the plasma of quarks and gluons generated by the Large Hadron Collider (LHC), according to a recent study published in the journal Physical Review Letters.
Using machine learning techniques, the physicists analyzed more than 13 billion heavy ion collisions. Each of these collisions had generated tens of thousands of charged particles. In this ultra-dense, high-energy soup of particles, the MIT researchers found 100 X particles of a type known as X(3872) , named for the particle’s estimated mass.
How? Although the X particles are very short-lived, when they decay, they produce a shower of lower-mass particles . Thanks to an algorithm to recognize the characteristic patterns of X-particle decay and data from the 2018 LHC in its software (where positively charged lead atoms collided with each other at high speeds generating these billions of collisions and particles), the algorithm identified a signal at a specific mass indicating the presence of about 100 X particles in the data.
A signal that would modify our vision of the universe
“This is just the beginning of the story,” says lead author Yen-Jie Lee, an associate professor of physics at MIT. “We have shown that we can find a signal. In the next few years we want to use the quark-gluon plasma to probe the internal structure of the X particle, which could change our view of what kind of material the universe should produce.”
In theory, these particles could appear in the tiny flashes of quark-gluon plasma that scientists have been creating in particle accelerators for a few years. Unlocking the structure of the X particles will give us a better picture of the birth of the universe.
This could be the first chance physicists have to examine X particles in precise detail , building a better picture of the Big Bang.
For now, a few more years of research will be needed to distinguish between the different scenarios that arise and “expand our view of the types of particles that were abundantly produced in the early universe.”
Referencia: A. M. Sirunyan et al, Evidence for X(3872) in Pb-Pb Collisions and Studies of its Prompt Production at sNN=5.02 TeV, Physical Review Letters (2022). DOI: 10.1103/PhysRevLett.128.032001
