Physics · the experiment
Count the invisible nudges
A 3.6-gigawatt reactor, 5.6 kilograms of germanium, 1,555 nuclei nudged by antineutrinos. Four questions, from beginner to expert, on a measurement moving from detection to precision.
1 · Describe the impact
Beginner
What does the antineutrino do in the collision measured by CONUS+?
2 · Work out an impostor's signal
With the reactor running, the exposure is 1,296 kilogram-days and the fit finds 1,555 events. With the reactor stopped, the exposure is only 86 kilogram-days.
Imagine those 1,555 events came from a constant background, unrelated to the reactor.
Intermediate
How many events would that background give with the reactor stopped?
3 · Weigh the protons
In the Standard Model, the collision rate grows with the square of the nucleus's weak charge: Q_W = N − (1 − 4 sin²θ_W) Z, with N neutrons and Z protons. The expected value of sin²θ_W is 0.2387.
Expert
How much do the protons weigh in this weak charge?
4 · Predict the effect of the conversion
A reactor antineutrino gives the germanium nucleus a few thousand electronvolts at most, of which only 15 to 20% becomes an electric signal. The events pile up just above the detector's threshold.
Expert
If germanium turned a larger share of the recoil energy into signal, the number of events above the threshold would be:
Nudges counted
—