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Space and Physics

Unidentified "Bump" In LHC Data May Be Yet Another Brand New Particle

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Caroline Reid

Guest Author

clockJul 20 2015, 18:58 UTC
1211 Unidentified "Bump" In LHC Data May Be Yet Another Brand New Particle
The Large Hadron Collider finds new particles by smashing protons together, illustrated. sakkmesterke/Shutterstock.

New particles at the Large Hadron Collider (LHC) often boldly assert themselves in data as an out-of-place "bump." This is how the Higgs boson, the particle responsible for giving everything else mass, was discovered. Now, the LHC has produced a new blip in the data that could be another brand new particle - but scientists aren't entirely sure what they're seeing yet.

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It's been a busy few days for the world of particle physics: last week the pentaquark and massless Weyl fermion were discovered. This new bump in the data isn't conclusive evidence of a newly discovered particle just yet, but the data so far is promising, and it might be something to watch out for.

The data for this new particle is from the LHC before it received its upgrade. The collisions in the older version of the LHC went up to 8 teraelectron Volts (TeV) but thanks to the recent upgrade, the machine can smash particles together at energies of 13 TeV. The LHC produces so much data that discoveries from the first run at 8 TeV take some time to process, though, which is why we're only seeing some results now, despite them being collected in 2012.

The signal was first seen at the Compact Muon Solenoid (CMS) experiment in July 2014. However, it was discarded as an anomaly. ATLAS has more recently confirmed that they too have seen this signal, and their result is bigger and stronger than the CMS result.

The actual result looks like a tiny blip positioned at roughly 2 TeV. This is an eye-watering energy value; it dwarfs the heaviest elementary particle, the top quark, which is around 173 GeV.

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The following graph might look overwhelming, but it's fairly easy to spot the possible new particle when you know what you're looking for. The black dots follow a blue line as the energy of the collision increases (x-axis). There is one black dot, at 2 TeV, that doesn't seem to be obeying the same rules as all the other black dots. It's sitting much higher than the rest of the dots. 

Graph of the Energy of particles (x-axis) against The number of particle produced or events (y-axis). ATLAS/CERN.

This small deviation from the data is all that's needed to cause a stir amongst particle physicists. If a particle at this energy isn't behaving like other particles do, that means it's probably a particle we don't know about yet. 

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Current speculation has suggested that this may be a new interaction particle known as a gauge boson. The most well known gauge boson is the massless photon, which constitutes light. This new particle is speculated to be a partner of the W gauge boson: one of the mediators of the weak nuclear force. The weak nuclear force is essential for things like radioactive decay. This new particle could be the W prime (or W') particle, the heavier partner particle of the W boson. 

A lot of blips can appear in data when working with such a sensitive machine such as the LHC. However, excitement is building for this new bump because two different groups have seen it: ATLAS and CMS. It seems that the more we look at it, the more promising it becomes.

This region of energy will have to be probed further with the more powerful LHC to identify whether physicists have a new particle on their hands.

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(H/T: Symmetry Magazine)


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