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 $\mathcal{O}(10\%)$.
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 \,{\rm{(stat)}} \pm 10.0 \,{\rm{(syst)}}
)\times 10^{10}\, $$\rm{s}^{-1} \rm{cm}^{-2}$, consistent with Standard Solar
Model and existing measurements, corresponding to a flux upper limit of
$23.3\times 10^{10}\, $$\rm{s}^{-1} \rm{cm}^{-2}$ at 90\% C.L..
The PandaX-II experiment employed a 580kg liquid xenon detector to search for the interactions between dark matter particles and the target xenon atoms. The accidental coincidences of isolated ...signals result in a dangerous background which mimic the signature of the dark matter. We performed a detailed study on the accidental coincidence background in PandaX-II, including the possible origin of the isolated signals, the background level and corresponding background suppression method. With a boosted-decision-tree algorithm, the accidental coincidence background is reduced by 70% in the dark matter signal region, thus the sensitivity of dark matter search at PandaX-II is improved.
Precise measurement of two-neutrino double beta decay (DBD) half-life is an important step for the searches of Majorana neutrinos with neutrinoless double beta decay. We report the measurement of DBD ...half-life of \(^{136}\)Xe using the PandaX-4T dual-phase Time Projection Chamber (TPC) with 3.7-tonne natural xenon and the first 94.9-day physics data release. The background model in the fiducial volume is well constrained in situ by events in the outer active region. With a \(^{136}\)Xe exposure of 15.5 kg-year, we establish the half-life as \(2.27 \pm 0.03 (stat.)\pm 0.10 (syst.)\times 10^{21}\) years. This is the first DBD half-life measurement with natural xenon and demonstrates the physics capability of a large-scale liquid xenon TPC in the field of rare event searches.
Compared with the signature of dark matter elastic scattering off nuclei, the absorption of fermionic dark matter by nuclei opens up a new searching channel for light dark matter with a ...characteristic monoenergetic signal. In this Letter, we explore the \(95.0\)-day data from the PandaX-4T commissioning run and report the first dedicated searching results of the fermionic dark matter absorption signal through a neutral current process. No significant signal was found, and the lowest limit on the dark matter-nucleon interaction cross section is set to be \(1.5\times10^{-50}\) cm\(^2\) for a fermionic dark matter mass of \(40\) MeV/\(c^2\) with 90\% confidence level.
We report a search for new physics signals using the low energy electron recoil events in the complete data set from PandaX-II, in light of the recent event excess reported by XENON1T. The data ...correspond to a total exposure of 100.7 ton-day with liquid xenon. With robust estimates of the dominant background spectra, we perform sensitive searches on solar axions and neutrinos with enhanced magnetic moment. We find that the axion-electron coupling \(g_{Ae}<4.6\times 10^{-12}\) for an axion mass less than \(\rm 0.1~keV/c^2\) and the neutrino magnetic moment \(\mu_{\nu}<4.9\times 10^{-11}\mu_{B}\) at 90% confidence level. The observed excess from XENON1T is within our experimental constraints.
Self-interacting Dark Matter (SIDM) is a leading candidate proposed to solve discrepancies between predictions of the prevailing cold dark matter theory and observations of galaxies. Many SIDM models ...predict the existence of a light force carrier that mediate strong dark matter self-interactions. If the mediator couples to the standard model particles, it could produce characteristic signals in dark matter direct detection experiments. We report searches for SIDM models with a light mediator using the full dataset of the PandaX-II experiment, based on a total exposure of 132 tonne-days. No significant excess over background is found, and our likelihood analysis leads to a strong upper limit on the dark matter-nucleon coupling strength. We further combine the PandaX-II constraints and those from observations of the light element abundances in the early universe, and show that direct detection and cosmological probes can provide complementary constraints on dark matter models with a light mediator.
Dual-phase noble-gas time projection chambers (TPCs) have improved the sensitivities for dark matter direct search in past decades. The capability of TPCs to reconstruct 3-D vertexes of keV scale ...recoilings is one of the most advantageous features. In this work, we develop two horizontal position reconstruction algorithms for the PandaX-II dark matter search experiment using the dual-phase liquid xenon TPC. Both algorithms are optimized by the \(^{83m}\)Kr calibration events and use photon distribution of ionization signals among photomultiplier tubes to infer the positions. According to the events coming from the gate electrode, the uncertainties in the horizontal positions are 3.4 mm (3.9 mm) in the analytical (simulation-based) algorithm for an ionization signal with several thousand photon electrons in the center of the TPC
Neutron-induced nuclear recoil background is critical to the dark matter searches in the PandaX-4T liquid xenon experiment. This paper studies the feature of neutron background in liquid xenon and ...evaluates their contribution in the single scattering nuclear recoil events through three methods. The first method is fully Monte Carlo simulation based. The last two are data-driven methods that also use the multiple scattering signals and high energy signals in the data, respectively. In the PandaX-4T commissioning data with an exposure of 0.63 tonne-year, all these methods give a consistent result that there are \(1.15\pm0.57\) neutron-induced background in dark matter signal region within an approximated nuclear recoil energy window between 5 and 100 keV.
Physical Review Letters 130, 021802 (2023) A search for interactions from solar $^8$B neutrinos elastically scattering
off xenon nuclei using PandaX-4T commissioning data is reported. The energy
...threshold of this search is further lowered compared with the previous search
for dark matter, with various techniques utilized to suppress the background
that emerges from data with the lowered threshold. A blind analysis is
performed on the data with an effective exposure of 0.48 tonne$\cdot$year, and
no significant excess of events is observed. Among results obtained using the
neutrino-nucleus coherent scattering, our results give the best constraint on
the solar $^8$B neutrino flux. We further provide a more stringent limit on the
cross section between dark matter and nucleon in the mass range from 3 to 9
GeV/c$^2$.
