Measurement of Solar $pp$ Neutrino Flux using Electron Recoil Data from PandaX-4T Commissioning Run

The proton-proton ($pp$) fusion chain dominates the neutrino production from the Sun. The uncertainty of the predicted $pp$ neutrino flux is at the sub-percent level, whereas that of the best measurement is $\mathcal{O}(10\mathrm{\%})$. In this paper, we present the first result to measure the solar $pp$ neutrinos in the electron recoil energy range from 24 to 144 keV, using the PandaX-4T commissioning data with 0.63 tonne$\times$year exposure. The $pp$ neutrino flux is determined to be $(8.0\pm 3.9(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 10.0(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}))\times {10}^{10}$${\mathrm{s}}^{-1}{\mathrm{c}\mathrm{m}}^{-2}$, consistent with Standard Solar Model and existing measurements, corresponding to a flux upper limit of $23.3\times {10}^{10}$${\mathrm{s}}^{-1}{\mathrm{c}\mathrm{m}}^{-2}$ at 90% C.L…