New Rare Particle Decay Spotted
by Caroline Reid
Photo credit: Particle Collision in LHC (Large Hadron Collider) by general-fmv via Shutterstock
The Large Hadron Collider (LHC) is closed for refurbishment until later this year. But that doesn’t stop the discoveries from flooding in. While sifting through data from 2011 and 2012, particle physicists have found compelling data for a new, previously unseen decay channel. The pre-published article can be found in Nature.
The LHC accelerates protons, typically located at the center of an atom, and sends them zooming around its circular chamber deep underground. When the protons collide, they annihilate—transforming from matter into pure energy. Then, amongst the cacophony of crazy energy that’s fizzling in and out of existence all around the reaction chamber, particles start to appear, disappear and manifest themselves again. This pathway that the proton’s energy takes through particles is called a decay channel.
It might seem random, but the channels that go from proton to new particle are dictated heavily by mathematics. Physicists can even predict how likely a decay channel is. Some are much less probable than others, which is why it can take a long time to detect them. Just like this newly discovered decay.
The decay in question starts with two protons obliterating each other. From the remnant energy, a particle called a strange B meson pops into existence. This strange B meson is unstable, so it then transforms into two muons: a negative muon and a positive muon. Muons are the slightly heavier cousin of the electron.
The physicists also tentatively suggest that they have observed an even rarer decay: a proton decaying into a B meson (instead of a strange B meson), which then decays into a positive muon and negative muon pair. However, their certainty is lower for this interaction.
This exciting discovery was made from a collaboration of two previous CERN experiments: The Large Hadron Collider Beauty experiment (LHCb) and the Compact Muon Solenoid experiment (CMS), which are both published in the Physical Review Letters.
Both of these papers noticed the strange B to muon pair decay, but individually the results weren’t significant enough. However, when combined, the discovery became apparent.
“Both experiments on their own have published their measurements before, so in that sense it’s not a surprise,” says Philip Burrows, a professor of physics at the University of Oxford who was not involved in the CERN research. “But it’s the combined precision of the measurements which is the important thing.”
LHCb spokesperson Guy Wilkinson added: “It is testament to the excellent performance of the LHC, and the sensitivity of our experiments, that we have been finally able to observe this extremely rare but important decay.”
Particle physics is a unique field where hundreds of scientists have to cooperate and share to make progress. It’s beautiful to witness this teamwork in physics, and maybe other fields can learn from this.
Via Nature, Physical Review Letters LHCb, Physical Review Letters CMS