3 Theories About LHC’s Mysterious “New Particle” Explained

January 18, 2016 | Joanne Kennell

The ALICE Time Projection Chamber used for particle tracking and identification.
Photo credit: CERN (CC BY-SA 3.0)

Ideas started pouring in immediately after its announcement.

If you remember back on December 15, 2015, CERN announced that researchers may have discovered a new particle using the Large Hadron Collider (LHC) — marking the first set of significant results since upgrades were completed at the LHC earlier that year.

What happened was that researchers observed large spikes in energy that could have been the result of particle collisions between a new boson that is even larger than the Higgs Boson.  More specifically, the LHC saw unexpected, excess pairs of photons, each carrying 750 gigaelectronvolts (GeV) of energy, as the result of proton-proton collisions.  They believe this could have come from the decay of a new 1,500 GeV particle.

Since the collision could not be explained by the Standard Model — the theoretical foundation of particle physics — theories on what this spike in energy could be started pouring in.   However, experts have narrowed it down to what they believe are the most likely explanations.

1. Heavier Cousin of the Higgs Boson

This is by far the most popular explanation.  This unexplained signal could be the sign of a new particle that resembles a Higgs boson — only it would be about 12 times heavier, with a mass of 1,500 GeV.

Scientists are nowhere near calling this a discovery, and the teams that analyze the data at CERN do not have enough evidence of a new particle for it to be even worth presenting.  For it to be deemed a discovery, the evidence has to have a statistical value of 5 sigma, while evidence currently sits between 1.2 and 3.6.  Definitely significant, but more data needs to be collected.

2. Graviton

Some theories have also pointed to the particle being a graviton — the hypothetical, elementary, quantum particle carrier of gravity — similar to the way in which photons carry the electromagnetic force (light).

But why have we never been able to detect a graviton?  The problem with gravitons is that gravity is really not actually a force according to general relativity — it is a warp in spacetime.  Even though scientists have never detected gravitons, they still know a little bit about them.

Since gravity is a force with an infinite reach, gravitons would have to be massless, carry a lot of energy, and have a spin of two — a very unique property among particles.  Therefore, if a particle was detected with no mass and a spin of two, scientists would instantly know it was a graviton.

To complicate things, the discovery of a graviton could imply the existence of extra dimensions of spacetime, which could explain why they have never been seen, possibly until now.

3. Fluke

Or maybe it was a complete fluke — a random spike in data with no meaning whatsoever.  That is definitely not exciting nor what anyone wants to hear.  However, it is far more likely than this excess energy being discovered as a new particle.

“When all the statistical effects are taken into consideration ... the bump in the Atlas data had about a 1-in-93 chance of being a fluke — far stronger than the 1-in-3.5-million odds of mere chance, known as five-sigma, considered the gold standard for a discovery,” Dennis Overbye writes for The New York Times.  “That might not be enough to bother presenting in a talk, except for the fact that the competing CERN team, named CMS, found a bump in the same place.”

So what do you think?  Will researchers soon announce the discovery of a new particle, or will we be disappointed?

Cross your fingers for a new particle!

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