We report the first search for the elastic scatterings between cosmic-ray boosted sub-MeV dark matter (DM) and electrons in the PandaX-4T liquid xenon experiment. Sub-MeV DM particles can be accelerated by scattering with electrons in the cosmic rays and produce detectable electron recoil signals in the detector. Using the commissioning data from PandaX-4T of <math><mrow><mn>0.63</mn><mtext> </mtext><mtext> </mtext><mi>tonne</mi><mo>·</mo><mi>year</mi></mrow></math> exposure, we set new constraints on DM-electron scattering cross sections for DM masses ranging from <math><mn>10</mn><mtext> </mtext><mtext> </mtext><mi>eV</mi><mo>/</mo><msup><mi>c</mi><mn>2</mn></msup></math> to <math><mn>3</mn><mtext> </mtext><mtext> </mtext><mi>keV</mi><mo>/</mo><msup><mi>c</mi><mn>2</mn></msup></math>.

China

Xiaofeng Shang

Abdusalam Abdukerim

Zihao Bo

Wei Chen

Xun Chen

Yunhua Chen

Chen Cheng

Zhaokan Cheng

Xiangyi Cui

Yingjie Fan

Deqing Fang

Lisheng Geng

Karl Giboni

Xuyuan Guo

Chencheng Han

Ke Han

Changda He

Jinrong He

Di Huang

Junting Huang

Zhou Huang

Ruquan Hou

Yu Hou

United States

Xiangdong Ji

Xiangpan Ji

Yonglin Ju

Chenxiang Li

Jiafu Li

Mingchuan Li

Shuaijie Li

Tao Li

Qing Lin

Jianglai Liu

Congcong Lu

Xiaoying Lu

Lingyin Luo

Yunyang Luo

Wenbo Ma

Yugang Ma

Yajun Mao

Yue Meng

Xuyang Ning

Binyu Pang

Ningchun Qi

Zhicheng Qian

Xiangxiang Ren

Nasir Shaheed

Xiyuan Shao

Guofang Shen

Manbin Shen

Lin Si

Wenliang Sun

Yi Tao

Anqing Wang

Meng Wang

Qiuhong Wang

Shaobo Wang

Siguang Wang

Wei Wang

Xiuli Wang

Xu Wang

Zhou Wang

Yuehuan Wei

Mengmeng Wu

Weihao Wu

Yuan Wu

Mengjiao Xiao

Xiang Xiao

Kaizhi Xiong

Binbin Yan

Xiyu Yan

Yong Yang

Chunxu Yu

Ying Yuan

Zhe Yuan

Youhui Yun

Xinning Zeng

Minzhen Zhang

Peng Zhang

Shibo Zhang

Shu Zhang

Tao Zhang

Wei Zhang

Yang Zhang

Yingxin Zhang

Yuanyuan Zhang

Li Zhao

Jifang Zhou

Ning Zhou

Xiaopeng Zhou

Yubo Zhou

Zhizhen Zhou

Shao-Feng Ge

Chen Xia

Search for Cosmic-Ray Boosted Sub-MeV Dark-Matter–Electron Scattering in PandaX-4T

The proton-proton (  $ pp $  ) fusion chain dominates the neutrino production in the Sun. The uncertainty of the predicted   $ pp $   neutrino flux is at the sub-percent level, whereas that of the best measurement is   $ pp $  (10%). In this study, for the first time, we measure solar   $ pp $   neutrinos in the electron recoil energy range from 24 to 144 keV using the PandaX-4T commissioning data with 0.63 tonne   $ pp $   year exposure. The   $ pp $   neutrino flux is determined as   $ pp $     $ pp $  , which is consistent with the Standard Solar Model and existing measurements, corresponding to an upper flux limit of   $ pp $     $ pp $   at 90% C.L..

 (PandaX Collaboration)

Measurement of solar neutrino flux using electron recoil data from PandaX-4T commissioning run  

Neutrinos from core-collapse supernovae are essential for understanding neutrino physics and stellar evolution. Dual-phase xenon dark matter detectors can be used to track explosions of galactic supernovae by detecting neutrinos through coherent elastic neutrino-nucleus scatterings. In this study, a variation of progenitor masses and explosion models are assumed to predict neutrino fluxes and spectra, which result in the number of expected neutrino events ranging from 6.6 to 13.7 at a distance of 10 kpc over a 10-s duration with negligible backgrounds at PandaX-4T. Two specialized triggering alarms for monitoring supernova burst neutrinos are built. The efficiency of detecting supernova explosions at various distances in the Milky Way is estimated. These alarms will be implemented in the real-time supernova monitoring system at PandaX-4T in the near future, which will provide supernova early warnings for the astronomical community.

Changbo Fu

Mengting Fu

Linhui Gu

Yanlin Huang

QiJianglaing Liu

Andi Tan

Jingkai Xia

Pengwei Xie

Jijun Yang

Yukun Yao

Dan Zhang

Qibin Zheng

Yong Zhou

Detecting neutrinos from supernova bursts in PandaX-4T  

Signal reconstruction through software processing is a crucial component of the background and signal models in the PandaX-4T experiment, which is a multi-tonne dark matter direct search experiment. The accuracy of signal reconstruction is influenced by various detector artifacts, including noise, dark count of photomultiplier, photoionization of impurities in the detector, and other relevant considerations. In this study, we presented a detailed description of a semi-data-driven approach designed to simulate a signal waveform. This work provides a reliable model for the efficiency and bias of the signal reconstruction in the data analysis of PandaX-4T. By comparing critical variables that relate to the temporal shape and hit pattern of the signals, we found good agreement between the simulation and data.

Waveform simulation in PandaX-4T  

We present the constraints on the axial-vector and pseudo-scalar mediated WIMP-nucleus interactions from the PandaX-4T experiment, using the data set corresponding to a total exposure of 0.63 tonne⋅year. No significant signal excess is observed, and the most stringent constraints to date on the mediator mass are set for the axial-vector and pseudo-scalar simplified models. The maximum excluded mass of an axial-vector mediator is <math altimg='si1.svg'><mn>825</mn><mtext>&#160;GeV</mtext><mo stretchy='false'>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></math> and that of a pseudo-scalar mediator is <math altimg='si2.svg'><mn>106</mn><mtext>&#160;GeV</mtext><mo stretchy='false'>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></math>. In addition, the upper limits on the spin-dependent WIMP-nucleon scattering cross-section for conventional neutron-only and proton-only interactions are derived.

Shu Li

Changsong Shang

Jumin Yuan

Constraints on the axial-vector and pseudo-scalar mediated WIMP-nucleus interactions from PandaX-4T experiment

We report results of a search for dark-matter–nucleon interactions via a dark mediator using optimized low-energy data from the PandaX-4T liquid xenon experiment. With the ionization-signal-only data and utilizing the Migdal effect, we set the most stringent limits on the cross section for dark matter masses ranging from <math><mrow><mn>30</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> to <math><mrow><mn>2</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math>. Under the assumption that the dark mediator is a dark photon that decays into scalar dark matter pairs in the early Universe, we rule out significant parameter space of such thermal relic dark-matter model.

Ran Huo

Haibo Yu

Search for Dark-Matter–Nucleon Interactions with a Dark Mediator in PandaX-4T

We report a search for light dark matter produced through the cascading decay of <math><mi>η</mi></math> mesons, which are created as a result of inelastic collisions between cosmic rays and Earth’s atmosphere. We introduce a new and general framework, publicly accessible, designed to address boosted dark matter specifically, with which a full and dedicated simulation including both elastic and quasielastic processes of Earth attenuation effect on the dark matter particles arriving at the detector is performed. In the PandaX-4T commissioning data of <math><mrow><mn>0.63</mn><mtext> </mtext><mtext> </mtext><mi>tonne</mi><mo>·</mo><mi>year</mi></mrow></math> exposure, no significant excess over background is observed. The first constraints on the interaction between light dark matter generated in the atmosphere and nucleus through a light scalar mediator are obtained. The lowest excluded cross section is set at <math><mrow><mn>5.9</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>37</mn></mrow></msup><mtext> </mtext><mtext> </mtext><msup><mrow><mi>cm</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> for a dark matter mass of <math><mrow><mn>0.1</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> and mediator mass of <math><mrow><mn>300</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math>. The lowest upper limit of <math><mi>η</mi></math> to the dark matter decay branching ratio is <math><mn>1.6</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>7</mn></mrow></msup></math>.

Liangliang Su

Lei Wu

Search for Light Dark Matter from the Atmosphere in PandaX-4T

We report the search results of light dark matter through its interactions with shell electrons and nuclei, using the commissioning data from the PandaX-4T liquid xenon detector. Low energy events are selected to have an ionization-only signal between 60 to 200 photoelectrons, corresponding to a mean nuclear recoil energy from 0.77 to 2.54 keV and electronic recoil energy from 0.07 to 0.23 keV. With an effective exposure of <math><mrow><mn>0.55</mn><mtext> </mtext><mtext> </mtext><mi>tonne</mi><mo>·</mo><mi>year</mi></mrow></math>, we set the most stringent limits within a mass range from <math><mrow><mn>40</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> to <math><mrow><mn>10</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> for pointlike dark matter-electron interaction, <math><mrow><mn>100</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> to <math><mrow><mn>10</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>/</mo><mrow><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></mrow></math> for dark matter-electron interaction via a light mediator, and 3.2 to <math><mrow><mn>4</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>/</mo><mrow><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></mrow></math> for dark matter-nucleon spin-independent interaction. For DM interaction with electrons, our limits are closing in on the parameter space predicted by the freeze-in and freeze-out mechanisms in the early Universe.

Zhengyun You

Search for Light Dark Matter with Ionization Signals in the PandaX-4T Experiment

A search for interactions from solar <math><mrow><mmultiscripts><mrow><mi>B</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>8</mn></mrow></mmultiscripts></mrow></math> 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 <math><mrow><mn>0.48</mn><mtext> </mtext><mtext> </mtext><mi>tonne</mi><mtext> </mtext><mi>year</mi></mrow></math>, and no significant excess of events is observed. Among the results obtained using the neutrino-nucleus coherent scattering, our results give the best constraint on the solar <math><mrow><mmultiscripts><mrow><mi>B</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>8</mn></mrow></mmultiscripts></mrow></math> 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 <math><mrow><mn>9</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math>.

Search for Solar <math><mrow><mmultiscripts><mrow><mi>B</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>8</mn></mrow></mmultiscripts></mrow></math> Neutrinos in the PandaX-4T Experiment Using Neutrino-Nucleus Coherent Scattering

Neutron-induced nuclear recoil background is critical to dark matter searches in the PandaX-4T liquid xenon experiment. In this study, we investigate the features of neutron background in liquid xenon and evaluate its contribution in single scattering nuclear recoil events using three methods. The first method is fully based on Monte Carlo simulations. The last two are data-driven methods that also use multiple scattering signals and high energy signals in the data. In the PandaX-4T commissioning data with an exposure of 0.63 tonne-year, all these methods give a consistent result, i.e., there are   $ 1.15\pm0.57 $   neutron-induced backgrounds in the dark matter signal region within an approximated nuclear recoil energy window between 5 and 100 keV.

Yunshan Cheng

Neutron-induced nuclear recoil background in the PandaX-4T experiment  