arXiv subjects

Xun Chen

Publications and source records attributed to Xun Chen.

214 records · Page 12Linked to original sources

arXiv2017

Current status of direct dark matter detection experiments

Much like ordinary matter, dark matter might consist of elementary particles, and weakly interacting massive particles are one of the prime suspects. During the past decade, the sensitivity of experiments trying to directly detect them has improved by three to four orders of magnitude, but solid evidence for their existence is yet to come. We overview the recent progress in direct dark matter detection experiments and discuss future directions.

astro-ph.CO↗

arXiv2017

Update of the trigger system of the PandaX-II experiment

PandaX-II experiment is a dark matter direct detection experiment using about half-ton of liquid xenon as the sensitive target. The electrical pulses detected by photomultiplier tubes from scintillation photons of xenon are recorded by waveform digitizers. The data acquisition of Pandax-II relies on a trigger system that generates common trigger signals for all waveform digitizers. Previously an analog device-based trigger system was used for the data acquisition system. In this paper we present a new FPGA-based trigger system. The design of this system and trigger algorithms are described. The performance of this system on real data is presented.

physics.ins-det↗

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

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

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↗

arXiv2016

The Electronics and Data Acquisition System for the PandaX-I Dark Matter Experiment

We describe the electronics and data acquisition system used in the first phase of the PandaX experiment -- a 120 kg dual-phase liquid xenon dark matter direct detection experiment in the China Jin-Ping Underground Laboratory. This system utilized 180 channels of commercial flash ADC waveform digitizers. This system achieved low trigger threshold ($<$1 keV electron-equivalent energy) and low deadtime data acquistion during the entire experimental run.

physics.ins-det↗

arXiv2016

Performance of Photosensors in the PandaX-I Experiment

We report the long term performance of the photosensors, 143 one-inch R8520-406 and 37 three-inch R11410-MOD photomultipliers from Hamamatsu, in the first phase of the PandaX dual-phase xenon dark matter experiment. This is the first time that a significant number of R11410 photomultiplier tubes were operated in liquid xenon for an extended period, providing important guidance to the future large xenon-based dark matter experiments.

physics.ins-det↗

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↗

arXiv2014

Performance of General STCs over Spatially Correlated MIMO Single-keyhole Channels

For MIMO Rayleigh channels, it has been shown that transmitter correlations always degrade the performance of general space-time codes (STCs) in high SNR regimes. In this correspondence, however, we show that when MIMO channels experience single-keyhole conditions, the effect of spatial correlations between transmission antennas is more sophisticated for general STCs: when $M>N$ (i.e., the number of transmission antennas is greater than the number of receiving antennas), depending on how the correlation matrix $\mathbf{P}$ beamforms the code word difference matrix $\mathbfΔ$, the PEP performance of general STCs can be either degraded or improved in high SNR regimes. We provide a new measure, which is based on the eigenvalues of $\mathbfΔ$ and the numbers of transmission and receiving antennas, to exam if there exists certain correlation matrices that can improve the performance of general STCs in high SNR regimes. Previous studies on the effect of spatial correlations over single-keyhole channels only concentrated on orthogonal STCs, while our study here is for general STCs and can also be used to explain previous findings for orthogonal STCs.

cs.IT↗

arXiv2012

Understanding Polarization Correlation of Entangled Vector Meson Pairs

We propose an experimental test of local hidden variable theories against quantum mechanics by measuring the polarization correlation of entangled vector meson pairs. In our study, the form of the polarization correlation probability is reproduced in a natural way by interpreting the two-body decay of the meson as a measurement of its polarization vector within the framework of quantum mechanics. This provides more detailed information on the quantum entanglement, thus a new Monte Carlo method to simulate the quantum correlation is introduced. We discuss the feasibility of carrying out such a test at experiments in operation currently and expect that the measured correlated distribution may provide us with deeper insight into the fundamental question about locality and reality.

hep-ph↗

arXiv2005

Parity-violating asymmetry of $W$ bosons produced in $p$-$p$ collisions

The parity-violating asymmetry is an ideal tool to study the quark helicity distribution in the proton. We study the parity-violating asymmetry of $W^{\pm}$ bosons produced by longitudinally polarized $p$-$p$ collision in RHIC, based on predictions of quark distributions of the proton in the SU(6) quark-spectator-diquark model and a perturbative QCD based counting rule analysis. We find that the two models give nearly equal asymmetry for $W^+$ but that for $W^-$ quite different. Therefore future experiments on such quantity can help to clarify different predictions of the value $Δd(x)/d(x)$ at $x \to 1$ in the proton.

hep-ph↗

arXiv2004

Decay Probability Ratio of Pentaquark Theta^+ State

The pentaquark state of $Θ^{+}(uudd\bar{s})$ has been observed to decay with two decay modes: $Θ^+\to n K^+$ and $Θ^+ \to p K^0$. The decay probability ratio of the two decay modes is studied with general symmetry consideration of isospin, spin, and parity. We arrive at a result of the ratio $\frac{Γ(Θ^+\to nK^+)}{Γ(Θ^+\to pK^0)} =\frac{(α-β)^2}{(α+β)^2}(\frac{k_1}{k_2})^{2L+1}$, which is valid for the $Θ^+$ state to be a pure isoscalar or isovector state, or an isoscalar and isovector mixing state, or an isotensor state with mixture of isoscalar and isovector components with coefficients $α$ and $β$. The dependence on spin and parity of the pentaquark $Θ^+$ state is found to be small due to small difference between the center of mass decay momenta $k_1$ and $k_2$ of the two decay modes. We also provide an analysis on the constraint of the isospin of $Θ^+$ from the absence of a peak in the $pK^+$ invariant mass distribution in the $γp \to pK^+K^-$ process. Future experimental results about the decay probability ratio may provide information about the properties of the pentaquark $Θ^+$ state.

hep-ph↗