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CERN’s Large Hadron Collider Reveals Hints Of A New Particle

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Particle theorist Ben Allanach gives his reaction to yesterday’s seminar, where ATLAS and CMS reported on what we have (and have not yet) learned from a year of the highest-energy particle collisions ever achieved.

“Forget the Higgs, there’s a new boson in town. At least, this is what is hinted at by the latest data coming from the Large Hadron Collider (LHC). The potential discovery has sent theoretical physicists into a frenzy, with nine papers explaining the data already uploaded on arXiv hours after the results were presented.

The LHC experiments ATLAS and CMS have both detected a bump in the data from the events following the proton-proton collisions. Among the particles produced by the collisions, the experiments saw an excess of photon pairs; this is usually an indication that there is a new particle.

The bump was seen in 50 photon pairs (40 in ATLAS and 10 in CMS) and each photon had an energy of 750 gigaelectronvolts (GeV). This indicates that the potential new particle is a boson (but not necessarily like the Higgs) and it weighs 1500 GeV, which is equivalent to almost 1,600 protons. Physicists are intrigued as they weren’t expecting anything with that mass.

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Although this is very exciting, there is a lot more to do before this hint is proven to be a particle or just a coincidence. The low number of detections corresponds to a low statistical certainty. The ATLAS experiment has a confidence level of 99.99 percent (3.9 sigmas) and CMS has a confidence level of 98.9 percent (2.6 sigmas). These values seem really high, but you can see them as one in 10,000 and a bit more than one in 100, respectively. You wouldn’t get in a plane if those were the odds that it would come crashing down.” said iflscience.com

“New particles can only be confirmed if the confidence level has reached 5 sigmas (99.9999 percent), meaning the detection has only a one in 3.5 million chance of being a fluke. The LHC has finished operations for the year, so reaching the 5 sigma level will be the goal of the machine in 2016.

Several theoretical explanations have been put forward to explain the potential new particle. From dark matter to string theory to some exotic version of the standard model of physics, the explanations are squeezing anything possible from the limited data available.” said iflscience.com

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However, the physicists working on ATLAS and CMS are being level-headed when it comes to the bump. Speaking to IFLScience, Professor Dave Charlton, spokesperson for ATLAS, said: “It is too early yet to think that we are seeing anything more than a statistical fluctuation, which is not unlikely.”

He continued: “I would rather not speculate on what it might be, if it is not just a chance coincidence – in the experiments, our job is rather to look hard at the data to see if there is more we can learn, and most especially to prepare for the new data samples coming next year. This is what we are doing!”

If these hints turn out to be a discovery, the world of particle physics might not be the same. The LHC will be back online in March and physicists expect 10 times as much data next year. “If there is an actual natural phenomenon behind these fluctuations, we will know,” Tiziano Camporesi, a CERN physicist and spokesperson for the CMS team, told Nature.

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“CERN’s Large Hadron Collider Reveals Hints Of A New Particle”