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Status of Daya Bay

March 14, 2017

20170316_180634.jpgDmitry Naumov (left) reported on the new results of Daya Bay: the measurement of the antineutrino flux and energy spectrum, the measurements of theta_13 and delta_m^2_32, the search for sterile neutrinos and study of wave packet effects on neutrino oscillations.

He started by stressing the advantages of reactors as a source: it is intense (10^20 neutrinos per GW per second), clean, and a free source. Additionally, there are negligible matter effects in the neutrino propagation.

As explained yesterday, the experiment works with 8 detectors (but one has recently been devoted to R&D studies). The detectors have liquid scintillator in the inner and middle zones (20 tons each), the inner one doped with Gadolinium; and a mineral oil outer veto, 40 tons of it. Each detector is placed in a water tank watched by photomultipliers, and RPCs provide additional veto power from cosmics. Backgrounds at the end are minor. The largest is provided by accidental coincidences, but its uncertainty is very small.

20170314_101510

Above, a slide of the talk discussing the total flux measurement

The flux is measured at 0.943+-0.008+-0.025 with respect to the Huber and Muller model (see Arxiv:1508.04233).

Daya Bay also sees the 5 MeV bump but in general the speaker notes that the spectrum is not very well predicted by models overall, indicating that probably the effect is due to shortcomings of flux models.

The popular explanation of various neutrino anomalies in terms of sterile neutrinos according to the speaker is steadily disappearing.

The Daya Bay experiment conducted an explicit test of the sterile hypothesis by comparing the oscillation pattern in the energy spectrum predicted by the sterile neutrino model. As a result a significant part of possible sterile neutrino oscillation parameters is ruled out.

A combined analysis of data from reactor experiments Daya Bay, Bugey-3 and accelerator experiment MINOS excludes most of the possible sterile neutrino oscillation scenarios that could explain the LSND result – a long standing anomaly in neutrino physics (see Arxiv:1607.01177). These results place strong limits on the existence of the sterile neutrino.

The Daya Bay data is best consistent with three-neutrino oscillation model. The analysis of 1230 days of data provides the most accurate to the date measurements of theta_13 and delta_m^2_32 (see https://arxiv.org/abs/1610.04802). For example, a zero value of theta_13 (the mixing angle whose value was uncertain till 2012) is now excluded at a confidence exceeding 25 standard deviations.

The speaker also reported about first experimental limits on spatial size of the neutrino wave packet sigma_x > 10^{-11} cm (see https://arxiv.org/abs/1608.01661).

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One Comment leave one →
  1. March 14, 2017 6:17 pm

    The statement “The popular explanation of the flux deficit in terms of sterile neutrinos is not favored anymore” is not updated : see ref.

    Updated Global 3+1 Analysis of Short-BaseLine Neutrino Oscillations
    S. Gariazzo, C. Giunti, M. Laveder, Y.F. Li. Mar 2, 2017. 38 pp.
    e-Print: arXiv:1703.00860 [hep-ph] |

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