A Review of the Tension between the T2K and NOνA Appearance Data and Hints to New Physics

Ushak Rahaman, Soebur Razzaque, Sankagiri Uma Sankar

Research output: Contribution to journalReview articlepeer-review

6 Citations (Scopus)


In this article, we review the status of the tension between the long-baseline accelerator neutrino experiments T2K and NOνA. The tension arises mostly due to the mismatch in the appearance data of the two experiments. We explain how this tension arises based on νµ → νe and ¯νµ → ¯νe oscillation probabilities. We define the reference point of vacuum oscillation, maximal θ23, and δCP = 0 and compute the νe / ¯νe appearance events for each experiment. We then study the effects of deviating the unknown parameters from the reference point and the compatibility of any given set of values of unknown parameters with the data from T2K and NOνA. T2K observes a large excess in the νe appearance event sample compared to the expected νe events at the reference point, whereas NOνA observes a moderate excess. The large excess in T2K dictates that δCP be anchored at −90 and that θ23 > π/4 with a preference for normal hierarchy. The moderate excess at NOνA leads to two degenerate solutions: (a) NH, 0 < δCP < 180, and θ23 > π/4; (b) IH, −180 < δCP < 0, and θ23 > π/4. This is the main cause of tension between the two experiments. We review the status of three beyond standard model (BSM) physics scenarios, (a) non-unitary mixing, (b) Lorentz invariance violation, and (c) non-standard neutrino interactions, to resolve the tension.

Original languageEnglish
Article number109
Issue number2
Publication statusPublished - Feb 2022


  • Long-baseline experiments
  • Neutrino mass hierarchy

ASJC Scopus subject areas

  • General Physics and Astronomy


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