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Neutrinos that go bump in the night

Tripple bump: The 5 MeV bump data presented by K. Joo at Neutrino 2016 conference (Courtesy: RENO collaboration)

Triple bump: the 5 MeV bump data presented by K Joo at the Neutrino 2016 conference. (Courtesy: RENO Collaboration)


By Tushna Commissariat

A final mystery that was mentioned at the Neutrino 2016 I attended in London this week was yet another unexpected “bump” in data at 5 MeV, measured while monitoring the neutrino flux from nuclear power plants. Starting with the RENO experiment in 2012, it was spotted by the Double Chooz experiment in 2014 and finally by the Daya Bay neutrino experiment earlier this year. While the initial signal was not of high enough statistical significance, it has now held up over time and more measurements.

Kyung Kwang Joo from the Chonnam National University in South Korea, who presented the latest results from RENO, revealed that the significance of the excess is now at a whopping 9σ for RENO data. Joo also said that RENO found that the excess was clearly linked to reactor thermal power as it was immediately visible when all six reactors at the plant were running, but dropped off when two or three reactors were switched off.

The 9 σ data from RENO on the 5 MeV excess

High significance: the 9σ data from RENO on the 5 MeV excess. (Courtesy: RENO Collaboration)

After all of this neutrino talk, in case you would like to remind yourself about the exciting story that led to the discovery of these particles, take a look at the Institute of Physics blog, where editor Christopher White has written a five-part series on the history of neutrinos.

Suffice to say that although we know a fair bit about neutrinos today, there seems to be as much, if not more, that we still do not fully understand. These “little neutral ones” (as they were christened by Enrico Fermi) still hold some big secrets and I’m looking forward to the big reveal.

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  1. Soo-Bong Kim

    Dear Tushna Commissariat,

    Thank you for the nice article.

    I am a spokesperson of the RENO experiment. I see some of your statements are not really true, and would rephrase them as follows if I were you:
    “Starting with the RENO experiment in 2012, where only the disagreement
    between data and expectation is mentioned for the first time,
    it was finally spotted by the same RENO experiment with 3.5 sigma in 2014,
    where the excess is identified as reactor neutrinos for the first time,
    by the Double Chooz experiment with much smaller significance in 2014,
    and finally by the Daya Bay experiment with 4 sigma earlier this year.”

    I may provide some slides for you if necessary. They are presented in Neutrino 2012, Kyoto and 2014, Boston.

    Thanks again for your interest in the 5 MeV excess.

    Best wishes,

    • Tushna Commissariat

      Hi Soo-Bong,

      Thank you for your comment. I have edited the text to reflect the fact that RENO first spotted the excess in 2012.

      Tushna Commissariat


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