While we all cheer for New Horizons on its historic day, there’s also big science happening on Earth. The Large Hadron Collider is back online and running at the highest power yet. Yesterday, it made its first notable discovery since firing back up. The LHCb experiment at CERN’s Large Hadron Collider reported the discovery of a class of particles called pentaquarks.
Let’s back up for a second. What is a quark?
Quarks are the building blocks of matter. They combine to form larger particles like protons and neutrons, which are made up of three fractionally charged quarks.
In 1964, American physicist Murray Gell-Mann changed how we think of matter when he proposed the quark model. Five years later he won the Nobel Prize in physics for his work on elementary particles (which quarks are). This model also theorized the existence of other quarks such as the pentaquark (made up of four quarks and one antiquark).
I’ll let LHCb spokesperson Guy Wilkinson explain the pentaquark discovery.
“The pentaquark is not just any new particle,” said Wilkinson in a press release. “It represents a way to aggregate quarks, namely the fundamental constituents of ordinary protons and neutrons, in a pattern that has never been observed before in over fifty years of experimental searches. Studying its properties may allow us to understand better how ordinary matter, the protons and neutrons from which we’re all made, is constituted.”
LHCb researchers spotted the pentaquark by observing the decay of a baryon known as Lambda b. During the decay, it split into three other particles: a J-spi, a proton and a charged kaon. The researchers also observed a transition state where two more particles could be identified.
“Benefitting from the large data set provided by the LHC, and the excellent precision of our detector, we have examined all possibilities for these signals, and conclude that they can only be explained by pentaquark states”, says LHCb physicist Tomasz Skwarnicki of Syracuse University.
“More precisely the states must be formed of two up quarks, one down quark, one charm quark and one anti-charm quark.”
Now, researchers want to understand the exact structure of the pentaquark.
LHCb physicist Liming Zhang describes what the pentaquark may look like. “The quarks could be tightly bound,” says Zhang. “Or they could be loosely bound in a sort of meson-baryon molecule, in which the meson and baryon feel a residual strong force similar to the one binding protons and neutrons to form nuclei.”
Here’s what a loosely bound pentaquark may look like.
LHCb researchers will dive further into the pentaquark structure as the LHC run 2 continues.
Large Hadron Collider back online
On June 3, the Large Hadron Collider began delivering the first physics data in 27 months. The massive machine had been offline for more than two years for maintenance and upgrades.
Today, the LHC is smashing particles together at 13 TeV, nearly double the energy from its first run.
The LHC’s second run is expected to last three years. We are just one month into it, and researchers are already making new discoveries. The future is looking bright for the Large Hadron Collider.