arXiv subjects

Changbo Fu

Publications and source records attributed to Changbo Fu.

71 records · Page 4Linked to original sources

arXiv2017

Dark Matter Results From 54-Ton-Day Exposure of PandaX-II Experiment

We report a new search of weakly interacting massive particles (WIMPs) using the combined low background data sets in 2016 and 2017 from the PandaX-II experiment in China. The latest data set contains a new exposure of 77.1 live day, with the background reduced to a level of 0.8$\times10^{-3}$ evt/kg/day, improved by a factor of 2.5 in comparison to the previous run in 2016. No excess events were found above the expected background. With a total exposure of 5.4$\times10^4$ kg day, the most stringent upper limit on spin-independent WIMP-nucleon cross section was set for a WIMP with mass larger than 100 GeV/c$^2$, with the lowest exclusion at 8.6$\times10^{-47}$ cm$^2$ at 40 GeV/c$^2$.

astro-ph.CO↗

arXiv2017

Demonstration of Laser-produced Neutron Diagnostic by Radiative Capture Gamma-rays

We report a new scenario of time-of-flight (TOF) technique in which fast neutrons and delayed gamma-ray signals were both recorded in a millisecond time window in harsh environments induced by high-intensity lasers. The delayed gamma signals, arriving far later than the original fast neutron and often being ignored previously, were identified to be the results of radiative captures of thermalized neutrons. The linear correlation between gamma photon number and the fast neutron yield shows that these delayed gamma events can be employed for neutron diagnosis. This method can reduce the detecting efficiency dropping problem caused by prompt high-flux gamma radiation, and provides a new way for neutron diagnosing in high-intensity laser-target interaction experiments.

physics.ins-det↗

arXiv2017

Experimentally Study the Deep Dirac Levels with High-Intensity Lasers

Various theories have predicted the deep Dirac levels (DDLs) in atoms for many years. However, the existence of the DDL is still under debating, and need to be confirmed experimentally. With the development of high intensive lasers, nowadays, electrons can been accelerated to relativistic energy by high intensive lasers, electron-positron pairs can be created, and nuclear reactions can been ignited, which provide a new tool to explore the DDL related fields. In this paper, we propose a new experimental method to study the DDL levels by monitoring nuclei's orbital electron capture life time in plasma induced by high intensive lasers. If a DDL exists, a nuclear electron capture rate could be enhanced by factor of over $10^7$, which makes it practically detectable in nowadays high intensive laser environments.

nucl-ex↗

arXiv2017

Spin-Dependent Weakly-Interacting-Massive-Particle--Nucleon Cross Section Limits from First Data of PandaX-II Experiment

New constraints are presented on the spin-dependent WIMP-nucleon interaction from the PandaX-II experiment, using a data set corresponding to a total exposure of 3.3$\times10^4$ kg-days. Assuming a standard axial-vector spin-dependent WIMP interaction with $^{129}$Xe and $^{131}$Xe nuclei, the most stringent upper limits on WIMP-neutron cross sections for WIMPs with masses above 10 GeV/c$^{2}$ are set in all dark matter direct detection experiments. The minimum upper limit of $4.1\times 10^{-41}$ cm$^2$ at 90\% confidence level is obtained for a WIMP mass of 40 GeV/c$^{2}$. This represents more than a factor of two improvement on the best available limits at this and higher masses. These improved cross-section limits provide more stringent constraints on the effective WIMP-proton and WIMP-neutron couplings.

hep-ex↗

arXiv2017

Krypton and radon background in the PandaX-I dark matter experiment

We discuss an in-situ evaluation of the $^{85}$Kr, $^{222}$Rn, and $^{220}$Rn background in PandaX-I, a 120-kg liquid xenon dark matter direct detection experiment. Combining with a simulation, their contributions to the low energy electron-recoil background in the dark matter search region are obtained.

astro-ph.IM↗

arXiv2016

Nuclear Fusion in Laser-Driven Counter-Streaming Collisionless Plasmas

Nuclear fusion reactions are the most important processes in nature to power stars and produce new elements, and lie at the center of the understanding of nucleosynthesis in the universe. It is critically important to study the reactions in full plasma environments that are close to true astrophysical conditions. By using laser-driven counter-streaming collisionless plasmas, we studied the fusion D$+$D$\rightarrow n +^3$He in a Gamow-like window around 27 keV. The results show that astrophysical nuclear reaction yield can be modulated significantly by the self-generated electromagnetic fields and the collective motion of the plasma. This plasma-version mini-collider may provide a novel tool for studies of astrophysics-interested nuclear reactions in plasma with tunable energies in earth-based laboratories.

nucl-ex↗

arXiv2016

Searching for New Spin-Dependent Interactions with SmCo$_5$ Spin Sources and a SERF Comagnetometer

We propose a novel method to search for possible new macro-scale spin- and/or velocity-dependent forces (SVDFs) based on specially designed SmCo$_5$ spin sources and a spin exchange relaxation-free (SERF) comagnetometer. A simulation shows that, by covering a SmCo$_5$ permanent magnet with a layer of pure iron, a high net spin density source of about $1\times 10^{22}$/cm$^3$ could be obtained. Taking advantages of the high spin density of this iron-shielded SmCo$_5$ and the high sensitivity of the SERF, the proposed method could set up new limits of greater than 10 orders of magnitude more sensitive than those from previous experiments or proposals in exploring SVDFs in force ranges larger than 1 cm.

physics.ins-det↗

arXiv2016

PandaX-III: Searching for Neutrinoless Double Beta Decay with High Pressure $^{136}$Xe Gas Time Projection Chambers

Searching for the Neutrinoless Double Beta Decay (NLDBD) is now regarded as the topmost promising technique to explore the nature of neutrinos after the discovery of neutrino masses in oscillation experiments. PandaX-III (Particle And Astrophysical Xenon Experiment III) will search for the NLDBD of $^{136}$Xe at the China Jin Ping underground Laboratory (CJPL). In the first phase of the experiment, a high pressure gas Time Projection Chamber (TPC) will contain 200 kg, 90% $^{136}$Xe enriched gas operated at 10 bar. Fine pitch micro-pattern gas detector (Microbulk Micromegas) will be used at both ends of the TPC for the charge readout with a cathode in the middle. Charge signals can be used to reconstruct tracks of NLDBD events and provide good energy and spatial resolution. The detector will be immersed in a large water tank to ensure $\sim$5 m of water shielding in all directions. The second phase, a ton-scale experiment, will consist of five TPCs in the same water tank, with improved energy resolution and better control over backgrounds.

physics.ins-det↗

arXiv2016

Low Background Stainless Steel for the Pressure Vessel in the PandaX-II Dark Matter Experiment

We report on the custom produced low radiation background stainless steel and the welding rod for the PandaX experiment, one of the deep underground experiments to search for dark matter and neutrinoless double beta decay using xenon. The anthropogenic 60 Co concentration in these samples is at the range of 1 mBq/kg or lower. We also discuss the radioactivity of nuclear-grade stainless steel from TISCO which has a similar background rate. The PandaX-II pressure vessel was thus fabricated using the stainless steel from CISRI and TISCO. Based on the analysis of the radioactivity data, we also made discussions on potential candidate for low background metal materials for future pressure vessel development.

physics.ins-det↗

arXiv2016

Material Screening with HPGe Counting Station for PandaX Experiment

A gamma counting station based on high-purity germanium (HPGe) detector was set up for the material screening of the PandaX dark matter experiments in the China Jinping Underground Laboratory. Low background gamma rate of 2.6 counts/min within the energy range of 20 to 2700 keV is achieved due to the well-designed passive shield. The sentivities of the HPGe detetector reach mBq/kg level for isotopes like K, U, Th, and even better for Co and Cs, resulted from the low-background rate and the high relative detection efficiency of 175%. The structure and performance of the counting station are described in this article. Detailed counting results for the radioactivity in materials used by the PandaX dark-matter experiment are presented. The upgrading plan of the counting station is also discussed.

physics.ins-det↗

arXiv2016

Dark Matter Results from First 98.7-day Data of PandaX-II Experiment

We report the WIMP dark matter search results using the first physics-run data of the PandaX-II 500 kg liquid xenon dual-phase time-projection chamber, operating at the China JinPing Underground Laboratory. No dark matter candidate is identified above background. In combination with the data set during the commissioning run, with a total exposure of 3.3$\times10^4$ kg-day,the most stringent limit to the spin-independent interaction between the ordinary and WIMP dark matter is set for a range of dark matter mass between 3.5 and 1000 GeV/c$^2$. The best upper limit on the scattering cross section is found $2.5\times 10^{-46}$ cm$^2$ for the WIMP mass 40 GeV/c$^2$ at 90% confidence level.

hep-ex↗

arXiv2016

Dark Matter Search Results from the Commissioning Run of PandaX-II

We present the results of a search for WIMPs from the commissioning run of the PandaX-II experiment located at the China Jinping underground Laboratory. A WIMP search data set with an exposure of 306$\times$19.1 kg-day was taken, while its dominant $^{85}$Kr background was used as the electron recoil calibration. No WIMP candidates are identified, and a 90\% upper limit is set on the spin-independent elastic WIMP-nucleon cross section with a lowest excluded cross section of 2.97$\times$10$^{-45}$~cm$^2$ at a WIMP mass of 44.7~GeV/c$^2$.

hep-ex↗

arXiv2015

Low-mass dark matter search results from full exposure of PandaX-I experiment

We report the results of a weakly-interacting massive particle (WIMP) dark matter search using the full 80.1\;live-day exposure of the first stage of the PandaX experiment (PandaX-I) located in the China Jin-Ping Underground Laboratory. The PandaX-I detector has been optimized for detecting low-mass WIMPs, achieving a photon detection efficiency of 9.6\%. With a fiducial liquid xenon target mass of 54.0\,kg, no significant excess event were found above the expected background. A profile likelihood analysis confirms our earlier finding that the PandaX-I data disfavor all positive low-mass WIMP signals reported in the literature under standard assumptions. A stringent bound on the low mass WIMP is set at WIMP mass below 10\,GeV/c$^2$, demonstrating that liquid xenon detectors can be competitive for low-mass WIMP searches.

hep-ex↗

arXiv2014

First dark matter search results from the PandaX-I experiment

We report on the first dark-matter (DM) search results from PandaX-I, a low threshold dual-phase xenon experiment operating at the China Jinping Underground Laboratory. In the 37-kg liquid xenon target with 17.4 live-days of exposure, no DM particle candidate event was found. This result sets a stringent limit for low-mass DM particles and disfavors the interpretation of previously-reported positive experimental results. The minimum upper limit, $3.7\times10^{-44}$\,cm$^2$, for the spin-independent isoscalar DM-particle-nucleon scattering cross section is obtained at a DM-particle mass of 49\,GeV/c$^2$ at 90\% confidence level.

hep-ex↗

arXiv2011

Limits on possible new spin-spin interactions between neutrons from measurements of the Longitudinal Spin Relaxation Rate of Polarized $^{3}$He Gas

New particles with masses in the sub-eV range have been predicted by various theories beyond the Standard Model. Some can induce new spin-spin interactions between fermions. Existing constraints on such interactions between nucleons with mesoscopic ranges (millimeters to nanometers) are quite poor. Polarized $^{3}$He gas is an especially clean system to use to constrain these possible new spin-spin interactions because the spin-independent atomic potential between helium atoms is well-characterized experimentally. The small effects from binary atomic collisions in a polarized gas from magnetic dipole-dipole and other possible weak spin-spin interactions which lead to spin relaxation can be calculated perturbatively. We compare existing measurements of the longitudinal spin relaxation rate $Γ_{1}$ of polarized $^3$He gas with theoretical calculations and set a $1σ$ upper bound on the pseudoscalar coupling strength $g_p$ for possible new neutron-neutron dipole-dipole interactions of $g_p^{(n)}g_p^{(n)}/4π\le 1.7\times 10^{-3}$ for distances larger than 100 nm. We also set new direct limits on possible gravitational torsion interactions between neutrons.

physics.atom-ph↗

arXiv2010

Constraints on Possible Monopole-Dipole Interactions of WISPs from the Transverse Relaxation Time of Polarized $^3$He Gas

Various theories beyond the Standard Model predict new particles with masses in the sub-eV range with very weak couplings to ordinary matter. A $P$-odd, $T$-odd, spin-dependent interaction between polarized and unpolarized matter is one such possibility. Such a monopole-dipole interaction can be induced by the exchange of spin-$0$ particles. The presence of a possible monopole-dipole interaction between fermion spins and unpolarized matter would cause an decreased transverse spin relaxation time $T_{2}$ for a confined gas of polarized nuclei. By reanalyzing previously existing data on the spin relaxation times of polarized $^3$He in gas cells with pressure in the millibar range and applying the well-established theory of spin relaxation for magnetic field gradients to gradients in a possible monopole-dipole field, we present new laboratory constraints on the strength and range of such an interaction. These constraints represent to our knowledge the best limits on such interactions for the neutron with ranges between $0.01$ cm and 1 cm.

hep-ph↗

arXiv2005

Scattering of $^{7}$Be and $^{8}$B and the astrophysical S$_{17}$ factor

Measurements of scattering of $^{7}$Be at 87 MeV on a melamine (C$_{3}$N$ _{6}$H$_{6}$) target and of $^{8}$B at 95 MeV on C were performed. For $^{7}$Be the angular range was extended over previous measurements and monitoring of the intensity of the radioactive beam was improved. The measurements allowed us to check and improve the optical model potentials used in the incoming and outgoing channels for the analysis of existing data on the proton transfer reaction $^{14}$N($^{7}$Be,$^{8}$B)$^{13}$C. The resultslead to an updated determination of the asymptotic normalization coefficient for the virtual decay $^{8}$B $\to$ $^{7}$Be + $p$. We find a slightly larger value, $C_{tot}^{2}(^{8}B)=0.466\pm 0.047$ fm$^{-1}$, for the melamine target. This implies an astrophysical factor, $S_{17}(0)=18.0\pm 1.8$ eV$\cdot$b, for the solar neutrino generating reaction $^{7}$Be($p$,$γ$)$^{8}$B.

nucl-ex↗