CERN, the European Organization for Nuclear Research, continues to pump out fascinating results relating to the structure of the universe. The latest in a line of big breakthroughs is the discovery of not one but two new subatomic particles, -Xi_b’- and Xi_b*- , whose existence was first predicted by Canadians Randy Lewis and Richard Woolshyn in 2009. This follows the discovery of a related particle Xi_b*0 in 2012. These new particles are bound to make the particle physicist as well as the casual science enthusiast rather excited since it is hoped that these particles will help us to understand how things work at an atomic scale. The particles join the baryon family of which the more familiar protons and neutrons are already a part of.
The structure of these new baryons certainly fits in well with the writer Bill Bryson’s observation in his book A Short History of Nearly Everything. “Physics is really nothing more than a search for ultimate simplicity, but so far all we have is a kind of elegant messiness,” he said . Xi_b’- and Xi_b*- are made up of three types of quarks which are called beauty, strange and down which are held together by a strong force. Due to the beauty quark, the heaviest of the three, these two new particles have are six times as bigger than the proton. Their mass also depends on their configuration. Each of the quarks has an attribute called “spin”. In Xi_b’- the spins of the two lighter quarks point in the opposite direction to the beauty quark, whereas in Xi_b*- , they are aligned.
Quarks are elementary or fundamental particles, which are believed to be the building blocks of subatomic particles such as neutrons. The more famous Higgs boson, which made waves across the scientific community when it was first discovered also at CERN in 2012 after years of research, is another example of an elementary particle. The elementary particles’ internal structure cannot be measured so it is unknown if they themselves are made up of further structural particles. So, taking a neutron as an example, quarks will make up the neutron. The neutron itself makes up the atom and the atom itself is the basic building block of matter or in other words, everything that we see around us.
The promising thing is that the results for both baryons Xi_b’- and Xi_b*- are matching up with predictions made before the experiments began at CERN. One of the predictions that the results have matched up to predictions based on the theory of Quantum Chromodynamics (QCD). QCD is a theory that describes the nature of the strong force, which sounds like it could be something out of Star Wars, but is actually a force that acts between elementary particles and holds together quarks. QCD is a part of the Standard Model of particle physics. The Standard Model describes the fundamental particles (such as the quarks described earlier), how they interact and the forces between. In addition to this, both Xi_b’- and Xi_b*- are also fitting in with the quark model, which is a classification of hadrons, of which the baryons are one of the subdivisions.
This exciting discovery was made by a team working on the Large Hadron Collider beauty (LHCb) experiment at CERN which seeks to find out why the universe that we live in is made up entirely of matter and not antimatter, a material which is exactly like matter except that it instead has an opposite charge. It focuses on the heavy beauty quark. When matter and antimatter collide, they destroy each other, creating an enormous amount of energy. Since the Big Bang should have created equal amount of matter and antimatter, the LHCb experiment is trying to find the explanation why antimatter is practically non-existent in our universe. It does this by using the 27 km long ring that is the Large Hadron Collider (LHC) to accelerate particles which creates an abundance of quarks. The beauty quarks are then captured by the LHCb detector. And so, the Xi_b’- and Xi_b*- subatomic particles, which may help towards explaining some fundamental questions in physics, were first detected one hundred metres below the small and picturesque French village of Ferney-Voltaire near the Swiss border.
The measurements for this experiment that lead to the discovery of the subatomic particles -Xi_b’- and Xi_b*- were made in 2011-2012. Currently, the LHC is in shutdown mode and is now being prepared to work at higher energies and intense beams. “If we want to find new physics beyond the Standard Model, we need first to have a sharp picture,” said Patrick Koppenburg, LHCb’s physics coordinator. “Such high precision studies will help us to differentiate between Standard Model effects and anything new or unexpected in the future.”
Image credit: cern.org