Upon further review, suspected new particle vanishes

Hints of discovery fade away with new data from Large Hadron Collider

ATLAS

PARTICLE PERISHES Two experiments at the Large Hadron Collider, ATLAS (shown above) and CMS, have seen no evidence of a new particle in their most recent data, despite previous hints.

CERN

CHICAGO — Particle physicists’ hopes have been dashed. A possible new particle hasn’t been sighted in new data from the Large Hadron Collider, scientists reported August 5 at the International Conference on High Energy Physics.

Physicists from LHC experiments CMS and ATLAS first unveiled hints of the new particle in December 2015 (SN: 1/9/16, p. 7). In the months that followed, enthusiastic physicists published hundreds of papers proposing theoretical explanations (SN: 5/28/16, p. 11).

Evidence of the particle, in the form of a bump on a plot — an excess of events at a particular energy — popped up after the LHC, at the European particle physics laboratory CERN near Geneva, began smashing together protons at a newly boosted energy of 13 trillion electron volts. The hint appeared in collisions that produced two high-energy photons.

LHC physicists had previously cautioned that the bump could be due to a random fluctuation that would disappear with more data. That caution appears to have been warranted: Neither experiment now shows any evidence of a wayward bump.

The bump “unfortunately is not confirmed by the new data,” CMS physicist Chiara Ilaria Rovelli of the National Institute for Nuclear Physics in Rome said in a session at ICHEP. Similarly, in ATLAS data, “there is no significant excess seen,” said CERN physicist Bruno Lenzi of the ATLAS collaboration.

Because the evidence had emerged independently in the two experiments, scientists had been especially hopeful that more data would increase the strength of the signal. Now, said Rovelli, “I would say that was a coincidence.”

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