Comparing to the Huber-Mueller model, there is a $\sim6$% deficit, consistent with the past 19 short baseline ($<100$ m) measurements.

With the nonlinearity model described in Sec. \[signal\], Daya Bay has measured the prompt-energy spectrum with a precision ranging from 1.0% at 3.5 MeV to 6.7% at 7 MeV. An excess of about 10% at $\sim 5$ MeV compared with expectations is observed, leading to a discrepancy of up to $4~\sigma$.

Such a deviation shows the importance of the direct measurement of the reactor antineutrino spectrum, particularly for next-generation reactor experiments such as JUNO [@JUNO], and may indicate the need to revisit the models underlying the calculations. The prompt-energy spectrum is unfolded, i.e. removing the detector response effect, to an antineutrino spectrum, as shown in Fig. \[fig:generic\].

Daya Bay will improve the measurement with much larger statistics and better energy nonlinearity. Recently a Flash Analog-to-Digital Converter (FADC) system has been installed on one AD to pin down the nonlinearity from the electronics. Another calibration and systematic study campaign is being planned. We expect to measure the reactor antineutrino spectrum to 1% precision in a large energy range, and improve the precision especially for the very high- and very low-energy regions 