SNO Periodicity Analyses

SNO has published two periodicity searches, searching for periodicities in its solar neutrino data down to periods as short as 10 minutes and as long as 10 years. These are detailed in these two publications. Researchers interested in performing their own periodicity searches with the data available on this page are strongly urged to read these carefully for a discussion of important methodological issues.


  1. A Search for Periodicities in the 8B Solar Neutrino Flux Measured by the Sudbury Neutrino Observatory (hep-ex/0507079, Phys.Rev.D72:052010,2005, 10.1103/PhysRevD.72.052010)

  2. Searches for High Frequency Variations in the 8B Solar Neutrino Flux at the Sudbury Neutrino Observatory (arXiv:0910.2433, Astrophys.J.710:540-548,2010, 10.1088/0004-637X/710/1/540)

In addition, SNO has published searches for day-night variability in the solar neutrino flux in a number of publications (see for example and

Publicly released data:

The following data are available for download:

1) Exact run start times and run lengths for D2O and salt phase runs

The data files are in ASCII format, and the header text of each file explains the format.

WARNING #1: The start and stop times of SNO's runs, while irregular, do contain periodic structure (for example, a 7-day modulation associated with SNO's weekly work schedule can be extracted from the run boundary times). Any periodicity analysis that does not take into explicit account the actual start and stop times of each run, and the actual distribution of livetime on each calendar date, may be suspect. These files indicate the exact time intervals over which the SNO detector was taking solar neutrino data, and should be explicitly included in any periodicity analysis. In addition, see Warning #2 below.

WARNING #2: Most SNO solar neutrino analyses apply burst cuts to remove events that come in bursts, or events that are preceded by a muon in the SNO detector. The muon cut in particular removes 20 seconds of livetime after each muon (a few times per hour). The run start times and run length files given above do not list the short periods that are removed by muon or burst cuts during each run. For this reason, they are not sufficient to allow searches for periodicities with periods less than about one minute. The data here is however sufficient for searches at periods longer than a minute. SNO’s periodicity analyses generally model any deadtime within a run as being uniformly distributed over the duration of that run---an assumption that breaks down for shorter periods.

2) Event times for neutrino events, truncated to the second

For each event, the date and time on which that event occurred is given, truncated the the second. The header text of each file explains the format.

WARNING #3: These data sets are those used for SNO’s two published periodicity analyses. As described in those publications, burst cut has been applied to the data to remove short bursts of events, since solar neutrinos are not expected to occur in bursts. Accordingly these data are not appropriate for use in searches for short bursts.

Contact person: Scott Oser
April 15, 2021