In new experiments at the Large Hadron Collider (LHC) in Switzerland, researchers work to recreate the first microseconds after the Big Bang. They want to see how the energy of particles are distributed around the universe. These particles make all matter we see – from the solar system to deli sandwiches.
UC Davis professors Daniel Cebra and Manuel Calderon de la Barca Sánchez from the Heavy Ion Group in the UC Davis physics department will be taking part in experiments to collide lead ions and create an extremely hot “particle soup.”
Until recently the LHC had been accelerating small particles called protons in hopes of finding the elusive Higgs Boson particle, which physicists theorize is the particle that gives matter mass. While the Higgs Boson particle remains unconfirmed, experiments conducted with Cebra and Calderon will smash together lead ions at energies higher than ever used before at the LHC.
The lead ion will reveal different results than the previous collisions of smaller particles.
In order to conduct the experiments, large particles have to be broken down into their smaller ingredients. Lead ions are made of a lot of protons and neutrons. Protons and neutrons belong to a group called nucleons. Protons are positively charged and made of smaller particles called quarks and gluons.
“The lead ion collisions have so much energy that the nucleons which make up the lead nuclei are completely vaporized,” Cebra said. “These collisions create a hot dense plasma of quarks and gluons.”
Cebra hopes to find out the mechanism for energy loss as the plasma cools; physicists predict that the plasma loses energy. This is similar to the loss of energy seen when a light bulb radiates light.
Calderon’s experiments will also focus on the quark-gluon plasma and how the strong nuclear force affects these particles. The strong nuclear force is the force that keeps protons and neutrons attached in nuclei.
“Without [the strong nuclear force], protons, neutrons and the nuclei that make up all the matter we are familiar with would not exist,” Calderon said on his UC Davis website.
Running the LHC with positively charged lead ions is different than with protons, but the transition has so far gone smoothly.
“It’s been very impressive to see how well the LHC has adapted to lead ions,” said Spokesperson Jürgen Schukraft, in a press release for the LHC facility.
The LHC consists of a 27 kilometers long ring of highly efficient magnets. Charged particles are forced into a stream by the magnets and accelerated over several revolutions around the ring until a stream starts in the opposite direction. The particles collide and highly sensitive equipment detects the particles that emerge.
The LHC experiments are working to validate The Standard Model of Particles and Forces. The Standard Model states that everything in the universe is made of 12 basic particles and four fundamental forces. Physicists have conducted experiments over the past century that show how the Standard Model is the best explanation of how the Universe works. Cebra and Calderon’s project could help expand on the behavior of forces around us.
“We experimentalists always want to push the limits to find the region where the model no longer works,” Cebra said.
However, gaps still remain in our understanding of the Standard Model. The model predicts that four forces keep the Universe together: gravity, electromagnetism, the strong nuclear force and the weak nuclear force. These forces are all related somehow. The problem is that no one has yet figured out how gravity is related to the other three forces.
Another issue is that the Standard Model also predicts the presence of the mysterious Higgs Boson particle that gives matter the property of mass. Such a particle has yet to be found.
Physicists at the LHC have studied protons for the past two years, but they hope that the new round of lead ion experiments will give new knowledge into the model of forces and particles. They want to understand why our universe looks the way it does.
AMY STEWART can be reached at firstname.lastname@example.org.