Erratum:A Search for Solar Axions and Anomalous Neutrino Magnetic Moment with the Complete PandaX-Ⅱ Data[CHIN.PHYS.LETT.38(2021)011301]

In our published letter,[1]we have identified a minor error in Figs.2 and 3.Instead,we have 2111 events in these two plots with 646,249,382,and 834 events in Run 9(20.0 ton·day),Run 10(19.4 ton·day),Run 11–1(24.2 ton·day),and Run 11–2(37.1 ton·day).The mistake is due to an incorrect application of a small energy non-linearity(known as the BLS non-linearity)in making plots,but has no impact to the final results.Figures 2 and 3 are now updated in this note.

A Search for Solar Axions and Anomalous Neutrino Magnetic Moment with the Complete Panda X-Ⅱ Data

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 XENON1 T.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.It is found that the axionelectron coupling gAe<4.6×10^(-12) for an axion mass less than 0.1 keV/c^(2) and the neutrino magnetic moment μv<4.9×10^(-11)μB at 90%confidence level.The observed excess from XENON1 T is within our experimental constraints.

The biochemical behavior and mechanism of uranium(Ⅵ)bioreduction induced by natural Bacillus thuringiensis

For a broader understanding of uranium migration affected by microorganisms in natural anaerobic environment,the bioreduction of uranium(Ⅵ)(U(Ⅵ))was revealed in Bacillus thuringiensis,a dominant bacterium strain with potential of uranium-tolerant isolated from uranium contaminated soil.The reduction behavior was systematically investigated by the quantitative analysis of U(Ⅳ)in bacteria,and mechanism was inferred from the pathway of electron transmission.Under anaerobic conditions,appropriate biomass and sodium lactate as electron donor,reduction behavior of U(Ⅵ)induced by B.thuringiensis was restricted by the activity of lactate dehydrogenase,which was directly affected by the initial pH,temperature and initial U(Ⅵ)concentration of bioreduction system.Bioreduction of U(Ⅵ)was driven by the generation of nicotinamide adenine dinucleotide(NADH)from enzymatic reaction of sodium lactate with various dehydrogenase.The transmission of the electrons from bacteria to U(Ⅵ)was mainly supported by the intracellular NADH dehydrogenase-ubiquinone system,this process could maintain the biological activity of cells.

Detecting neutrinos from supernova bursts in PandaX-4T

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.

Dark matter direct search sensitivity of the PandaX-4T experiment

The Panda X-4T experiment, a 4-ton scale dark matter direct detection experiment, is being planned at the China Jinping Underground Laboratory. In this paper we present a simulation study of the expected background in this experiment. In a 2.8-ton fiducial mass and the signal region between 1-10 keV electron equivalent energy, the total electron recoil background is found to be 4.9 × 10^(-5) kg^(-1) d^(-1) keV^(-1). The nuclear recoil background in the same region is 2.8 × 10^(-7) kg^(-1) d^(-1) keV^(-1). With an exposure of 5.6 ton-years, the sensitivity of Panda X-4 T could reach a minimum spin-independent dark matter-nucleon cross section of 6 × 10^(-48) cm^2 at a dark matter mass of 40 Ge V/c^2.

Searching for neutrino-less nouble neta necay of 136Xe with PandaX-Ⅱ liquid xenon detector

We report the Neutrino-less Double Beta Decay（NLDBD） search results from PandaX-Ⅱ dual-phase liquid xenon time projection chamber.The total live time used in this analysis is 403.1 days from June 2016 to August2018.With NLDBD-optimized event selection criteria,we obtain a fiducial mass of 219 kg of natural xenon.The accumulated xenon exposure is 242 kg yr,or equivalently 22.2 kg yr of 136Xe exposure.At the region around 136Xe decay Q-value of 2458 keV,the energy resolution of PandaX-Ⅱ is 4.2%.We find no evidence of NLDBD in PandaX-Ⅱand establish a lower limit for decay half-life of 2.1×1023yr at the 90% confidence level,which corresponds to an effective Majorana neutrino mass mββ <（1.4-3.7） eV.This is the first NLDBD result reported from a dual-phase xenon experiment.

Microbial reduction of uranium(Ⅵ)by Bacillus sp.Dwc-2:A macroscopic and spectroscopic study

The microbial reduction of U（VI） by Bacillus sp. dwc-2, isolated from soil in Southwest China, was explored using transmission electron microscopy （TEIVI）, X-ray photoelectron spectros- copy （XPS） and X-ray absorption near edge spectroscopy （XANES）. Our studies indicated that approximately 16.0% of U（VI） at an initial concentration of 100 mg/L uranium nitrate could be reduced by Bacillus sp. dwc-2 at pH 8.2 under anaerobic conditions at room temperature. Additionally, natural organic matter （NOM） played an important role in enhancing the bioreduction of U（VI） by Bacillus sp. dwc-2. XPS results demonstrated that the uranium presented mixed valence states （U（VI） and U（IV）） after bioreduction, which was subse- quently confirmed by XANES. Furthermore, the TEM and high resolution transmission electron microscopy （HRTEM） analysis suggested that the reduced uranium was bioaccumulated mainly within the cell and as a crystalline structure on the cell wa11. These observations implied that the reduction of uranium may have a significant effect on its fate in the soil environment in which these bacterial strains occur.

An improved evaluation of the neutron background in the PandaX-Ⅱ experiment

In dark matter direct detection experiments,neutron is a serious source of background,which can mimic the dark matter-nucleus scattering signals.In this paper,we present an improved evaluation of the neutron background in the PandaX-II dark matter experiment by a novel approach.Instead of fully relying on the Monte Carlo simulation,the overall neutron background is determined from the neutron-induced high energy signals in the data.In addition,the probability of producing a dark-matter-like background per neutron is evaluated with a complete Monte Carlo generator,where the correlated emission of neutron(s)andγ(s)in the(α,n)reactions and spontaneous fissions is taken into consideration.With this method,the neutron backgrounds in the Run 9(26-ton-day)and Run 10(28-ton-day)data sets of PandaX-II are estimated to be(0.66±0.24)and(0.47±0.25)events,respectively.

Bioaccumulation characterization of uranium by a novel Streptomyces sporoverrucosus dwc-3

The biosorption mechanisms of uranium on an aerobic bacterial strain Streptomyces sporoverrucosus dwc-3,isolated from a potential disposal site for（ultra-）low uraniferous radioactive waste in Southwest China,were evaluated by using transmission electron microscopy（TEM）,energy dispersive X-ray（EDX）analysis,Fourier transform infrared spectroscopy（FT-IR）,X-ray photoelectron spectroscopy（XPS）,proton induced X-ray emission（PIXE）and enhanced proton backscattering spectrometry（EPBS）.Approximately60% of total uranium at an initial concentration of 10 mg/L uranium nitrate solution could be absorbed on 100 mg S.sporoverrucosus dwc-3 with an adsorption capacity of more than3.0 mg/g（wet weight）after 12 hr at room temperature at p H 3.0.The dynamic biosorption process of S.sporoverrucosus dwc-3 for uranyl ions was well described by a pseudo second-order model.S.sporoverrucosus dwc-3 could accumulate uranium on cell walls and within the cell,as revealed by SEM and TEM analysis as well as EDX spectra.XPS and FT-IR analysis further suggested that the absorbed uranium was bound to amino,phosphate and carboxyl groups of the cells.Additionally,PIXE and EPBS results confirmed that ion exchange also contributed to the adsorption process of uranium.

Constraining self-interacting dark matter with the full dataset of PandaX-II

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 mediates 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 signals of SIDM models with a light mediator using the full dataset of the PandaX-II experiment,basing 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.

Results of dark matter search using the full PandaX-Ⅱ exposure

We report the dark matter search results obtained using the full 132 ton·day exposure of the PandaX-II experiment,including all data from March 2016 to August 2018.No significant excess of events is identified above the expected background.Upper limits are set on the spin-independent dark matter-nucleon interactions.The lowest 90%confidence level exclusion on the spin-independent cross section is 2.2×10−46 cm2 at a WIMP mass of 30 GeV/c2.

Determination of responses of liquid xenon to low energy electron and nuclear recoils using a PandaX-Ⅱ detector

We present a systematic determination of the responses of PandaX-Ⅱ,a dual phase xenon time projection chamber detector,to low energy recoils.The electron recoil(ER) and nuclear recoil(NR) responses are calibrated,respectively,with injected tritiated methane or 220Rn source,and with 241Am-Be neutron source,in an energy range from 1-25 keV(ER) and 4-80 keV(NR),under the two drift fields,400 and 317 V/cm.An empirical model is used to fit the light yield and charge yield for both types of recoils.The best fit models can describe the calibration data significantly.The systematic uncertainties of the fitted models are obtained via statistical comparison to the data.

Study of background from accidental coincidence signals in the PandaX-Ⅱexperiment

Ⅰ.INTRODUCTION The direct detection of dark matter particles,especially the weakly interacting massive particles(WIMPs),is being actively carried out by a couple of experiments worldwide[1].In recent years,the PandaX-Ⅱ experiment located in the China Jinping Underground Laboratory(CJPL)[1-3],which uses the technology of dual phase liquid xenon time projection chambers(TPCs),has pushed the limits of the cross section between WIMPs and nucleons to a new level for most of the possible WIMP masses;other experiments of the same type are also being performed[4–10].

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

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±0.57 neutron-induced backgrounds in the dark matter signal region within an approximated nuclear recoil energy window between 5 and 100 keV.

Input Trade Liberalization and Welfare Loss of Manufacturing Enterprises:Based on the Perspective of Efficient Market Power

Considering that upstream monopoly will lead to an exponential increase in the loss of social welfare,this paper investigates the impact of intermediate goods tariff concession on the welfare loss of manufacturing enterprises from the perspective of input trade liberalization and effective market power.It has been discovered that input trade liberalization significantly reduces the welfare loss of manufacturing enterprises.Due to the game condition in which oligopolies check each other and small businesses“gain from fishing”,the inhibitory impact increases as market share decreases.The mechanism test demonstrates that input trade liberalization boosts the effect of technical competition and minimizes welfare loss through promoting market development degree and reducing factor distortion.In addition,this paper also finds that the effect of input trade liberalization on high monopolistic power enterprises is obviously stronger than that of low monopolistic power enterprises.Furthermore,the impact on non-high-tech industries and capital-intensive enterprises is significant,while that on high-tech industries and labor-intensive industries is not.Therefore,the welfare loss should be investigated from the dual perspective of market structure and marker power.Competitiveness has an important effect,while trade liberalization of intermediate inputs has a pivotal effect on promoting market development and improving resource allocation efficiency.