Hopes for revolutionary new LHC particle dashed

From Nature:

Stefano Dal Pozzolo/Contrasto/eyevine

  The CMS (pictured) was one of two experiments that saw a potential new particle late last year.

It would have been bigger than finding the Higgs boson and marked the beginning of a new era in particle physics. But new data has squashed the hope that the hints of a new particle detected by the Large Hadron Collider (LHC) would solidify with time. Instead, the intriguing data ‘bump’ — first reported in December — turns out to be nothing more than a statistical fluctuation.

Representatives from ATLAS and CMS — two independent experiments at the LHC — presented the news at the International Conference on High Energy Physics (ICHEP) in Chicago on 5 August. Analyses incorporating almost five times the amount of data used in December show that the signal has faded to almost nothing. 

“There is no significant excess seen in the 2016 data” says Bruno Lenzi, a CERN physicist and part of the ATLAS collaboration, presenting to a standing-room only session at ICHEP.

Presenting directly after Lenzi, Chiara Ilaria Rovelli, a physicist at the National Institute of Nuclear Physics in Rome, piled on the bad news. Additional data from CMS also failed to produce a significant signal. “The modest excess presented in 2015, is unfortunately not confirmed by 2016 data,” she said.

While the announcement was a disappointment to researchers, it wasn’t completely unexpected. The ATLAS collaboration’s most recent update in June put the significance of the signal — a measure of how likely random fluctuations in the data would produce such a bump without a particle — at 2.1 sigma. That was well below the 5 sigma threshold for determining whether a signal is a discovery or just noise.

But because both ATLAS and CMS experiments independently saw the signal — which consisted of slightly …

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