Observation of coherent elastic neutrino-nucleus scattering

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Science  15 Sep 2017:
Vol. 357, Issue 6356, pp. 1123-1126
DOI: 10.1126/science.aao0990
  • Fig. 1 Neutrino interactions.

    (A) Coherent elastic neutrino-nucleus scattering. For a sufficiently small momentum exchange (q) during neutral-current neutrino scattering (qR < 1, where R is the nuclear radius in natural units), a long-wavelength Z boson can probe the entire nucleus and interact with it as a whole. An inconspicuous low-energy nuclear recoil is the only observable. However, the probability of neutrino interaction increases substantially with the square of the number of neutrons in the target nucleus. In scintillating materials, the ensuing dense cascade of secondary recoils dissipates a fraction of its energy as detectable light. (B) Total cross sections from CEνNS and some known neutrino couplings. Included are neutrino-electron scattering, charged-current (CC) interaction with iodine, and inverse beta decay (IBD). Because of their similar nuclear masses, cesium and iodine respond to CEνNS almost identically. The present CEνNS measurement involves neutrino energies in the range ~16 to 53 MeV, with the lower bound defined by the lowest nuclear recoil energy measured (fig. S9) and the upper bound by SNS neutrino emissions (fig. S2). The cross section for neutrino-induced neutron (NIN) generation following 208Pb(νe, e xn) is also shown, for single and double neutron production. This reaction, originating in lead shielding around the detectors, can generate a potential beam-related background affecting CEνNS searches. The cross section for CEνNS is more than two orders of magnitude larger than for IBD, the mechanism used for neutrino discovery (35).

  • Fig. 2 COHERENT detectors populating the “neutrino alley” at the SNS.

    Locations in this basement corridor profit from more than 19 m of continuous shielding against beam-related neutrons and a modest 8 m.w.e. overburden able to reduce cosmic ray–induced backgrounds, while sustaining an instantaneous neutrino flux as high as 1.7 × 1011 νμ cm–2 s–1.

  • Fig. 3 Observation of coherent elastic neutrino-nucleus scattering.

    (A and B) Residual differences (data points) between CsI[Na] signals in the 12 μs after POT triggers and those in a 12-μs window before, as a function of (A) their energy (number of photoelectrons detected) and (B) event arrival time (onset of scintillation). Steady-state environmental backgrounds contribute to both groups of signals equally, vanishing in the subtraction. Error bars denote SD. These residuals are shown for 153.5 live days of SNS inactivity (“Beam OFF”) and 308.1 live days of neutrino production (“Beam ON”), over which 7.48 GWh of energy (~1.76 × 1023 protons) was delivered to the mercury target. Approximately 1.17 photoelectrons are expected per keV of cesium or iodine nuclear recoil energy (34). Characteristic excesses closely following the standard model CEνNS prediction (histograms) are observed for periods of neutrino production only, with a rate correlated to instantaneous beam power (fig. S14).

  • Fig. 4 Constraints on nonstandard neutrino-quark interactions.

    The blue region represents values allowed by our data set at 90% confidence level (Embedded Image < 4.6) in Embedded Image space. These quantities parameterize a subset of possible nonstandard interactions between neutrinos and quarks, where Embedded Image = 0,0 corresponds to the standard model of weak interactions, and indices denote quark flavor and type of coupling. The gray region shows an existing constraint from the CHARM experiment (34).

Supplementary Materials

  • Observation of coherent elastic neutrino-nucleus scattering

    D. Akimov, J. B. Albert, P. An, C. Awe, P. S. Barbeau, B. Becker, V. Belov, A. Brown, A. Bolozdynya, B. Cabrera-Palmer, M. Cervantes, J. I. Collar, R. J. Cooper, R. L. Cooper, C. Cuesta, D. J. Dean, J. A. Detwiler, A. Eberhardt, Y. Efremenko, S. R. Elliott, E. M. Erkela, L. Fabris, M. Febbraro, N. E. Fields, W. Fox, Z. Fu, A. Galindo-Uribarri, M. P. Green, M. Hai, M. R. Heath, S. Hedges, D. Hornback, T. W. Hossbach, E. B. Iverson, L. J. Kaufman, S. Ki, S. R. Klein, A. Khromov, A. Konovalov, M. Kremer, A. Kumpan, C. Leadbetter, L. Li, W. Lu, K. Mann, D. M. Markoff, K. Miller, H. Moreno, P. E. Mueller, J. Newby, J. L. Orrell, C. T. Overman, D. S. Parno, S. Penttila, G. Perumpilly, H. Ray, J. Raybern, D. Reyna, G. C. Rich, D. Rimal, D. Rudik, K. Scholberg, B. J. Scholz, G. Sinev, W. M. Snow, V. Sosnovtsev, A. Shakirov, S. Suchyta, B. Suh, R. Tayloe, R. T. Thornton, I. Tolstukhin, J. Vanderwerp, R. L. Varner, C. J. Virtue, Z. Wan, J. Yoo, C.-H. Yu, A.

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