Orion Nebula
Orion Nebula (Image Credit: Patrick Gilliland)

Scientists working with ALICE (A Large Ion Collider Experiment), a heavy-ion detector on the Large Hadron Collider (LHC), have made precise measurements of particle’s mass and electric charge. While many may not see this as exciting as, say, discovering a new particle, it is still a remarkable physics find, as it offers new insights related to the fundamental symmetry in nature and heralds a new age in STEM science.

The findings were published in Nature Physics recently, and they confirm that there is a fundamental symmetry between the nuclei of the particles and their antiparticles in terms of charge, parity, and time (which is known as CPT).

The data comes thanks to the measurements of particles that were produced in high-energy collisions at CERN’s LHC. And in the end, the LHC is all about collisions – it whips bunches of protons around a 16 mile (27 km) track at speeds nearing the speed of light. In each bunch, there are some 100 billion protons. 

At it’s best, it can run 2808 bunches per beam, allowing the LHC to produce up to 1 billion collisions every second.

The Experiment

Specifically, the ALICE experiment records high-energy collisions of lead ions, enabling the study of matter at extremely high temperatures and densities.

The lead-ion collisions produce nuclei and antinuclei at nearly equal rates, allowing the ALICE team to juxtapose the properties of both. Notably, the experiment precisely measures the curvature of particle tracks in the detector’s magnetic field and the particles’ time of flight. It then uses this information to determine the mass-to-charge ratios for nuclei and antinuclei.

lhc cern
LHC image via CERN

The ALICE experiment’s high-precision tracking and identification capabilities measured the results of the collisions as part of an investigation meant to measure the differences between the ways in which protons and neutrons join in nuclei while their antiparticles form antinuclei.

The Significance

If you aren’t aware, Antimatter is not just the fictional fuel of the Enterprise and its journeys on Star Trek; quite the contrary, antimatter is something that scientists are currently utilizing. In fact, antihydrogen was created in 1995 (although it didn’t last long).

Antimatter, simply, is matter with its electrical charge reversed. For example, antiprotons are like protons but with a negative charge. Primordial antimatter has never been observed in the universe…yet. However, antiparticles are being created in particle accelerator labs (like the LHC) for a number of reasons.

“After the Big Bang, for every particle of matter an antiparticle was created. In particle physics, a very important question is whether all the laws of physics display a specific kind of symmetry known as CPT, and these measurements suggest that there is indeed a fundamental symmetry between nuclei and antinuclei,” said Marcelo Gameiro Munhoz, a professor at USP’s Physics Institute (IF) and a member of the Brazilian team working on ALICE.

Now, this doesn’t mean that literally everything in our universe is symmetrical, but is does help us better understand the fundamental nature of the universe and the basic physics that guides it.

According to Munhoz, these measurements may help physicists determine which theory of the Fundamental Laws of the universe is most plausible.

“These laws describe the nature of all matter interactions,” he said, “so it’s important to know that physical interactions aren’t changed by particle charge reversal, parity transformation, reflections of spatial coordinates and time inversion. The key question is whether the laws of physics remain the same under such conditions.”

In particular, in this instance, the researchers measured the mass-over-charge ratio differences for deuterons, consisting of a proton and a neutron, and antideuterons, as well as for nuclei of helium-3, comprising two protons and one neutron, and antihelium-3.

Of course, the ALICE team’s investigation into symmetry does not stop with how protons and neutrons join; rather, they are also looking at the production of heavy quarks (charm and bottom quarks) based on the measurement of electrons, and they also study rare phenomena arising from heavy-ion collisions taking place in the LHC.

It is a bold new era in particle physics.