Yugang Ma

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 × 10−44 cm2, for the spin-independent isoscalar DM-particle-nucleon scattering cross section is obtained at a DM-particle mass of 49GeV/c2 at 90% confidence level.

Low-mass dark matter search results from full exposure of the 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 events were found above the expected background. A profile likelihood ratio 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 a low-mass WIMP is set at a WIMP mass below 10 GeV=c(2), demonstrating that liquid xenon detectors can be competitive for low-mass WIMP searches.

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

The PandaX-4T experiment, a 4-ton scale dark matter direct detection experiment, is being planned at the China Jinping Un- derground 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−1d−1keV−1. The nuclear recoil background in the same region is 2:8 × 10−7 kg−1d−1keV−1. With an exposure of 5.6 ton-years, the sensitivity of PandaX-4T could reach a minimum spin-independent dark matter-nucleon cross section of 6 × 10−48 cm2 at a dark matter mass of 40 GeV/c2.

Neutron time-of-flight spectroscopy measurement using a waveform digitizer

The photoneutron source (PNS, phase 1), an electron linear accelerator (linac)-based pulsed neutron facility that uses the time-of-flight (TOF) technique, was constructed for the acquisition of nuclear data from the Thorium Molten Salt Reactor (TMSR) at the Shanghai Institute of Applied Physics (SINAP). The neutron detector signal used for TOF calculation, with information on the pulse arrival time, pulse shape, and pulse height, was recorded by using a waveform digitizer (WFD). By using the pulse height and pulse-shape discrimination (PSD) analysis to identify neutrons and γ-rays, the neutron TOF spectrum was obtained by employing a simple electronic design, and a new WFD-based DAQ system was developed and tested in this commissioning experiment. The DAQ system developed is characterized by a very high efficiency with respect to millisecond neutron TOF spectroscopy.The photoneutron source(PNS, phase 1), an electron linear accelerator(linac)-based pulsed neutron facility that uses the time-of-flight(TOF) technique, was constructed for the acquisition of nuclear data from the Thorium Molten Salt Reactor(TMSR) at the Shanghai Institute of Applied Physics(SINAP). The neutron detector signal used for TOF calculation, with information on the pulse arrival time, pulse shape, and pulse height, was recorded by using a waveform digitizer(WFD). By using the pulse height and pulse-shape discrimination(PSD)analysis to identify neutrons and γ-rays, the neutron TOF spectrum was obtained by employing a simple electronic design, and a new WFD-based DAQ system was developed and tested in this commissioning experiment. The DAQ system developed is characterized by a very high efficiency with respect to millisecond neutron TOF spectroscopy.

Detector calibration by Monte Carlo simulation based on the energy-range relationship of energetic ions

The experimental measurement of the total interaction cross sections of N, C, B, and Be isotopes on C-12 target at medium energies is described. A new formula that gives a good description of the energy-range relationship of energetic ions over a wide energy range is presented. The energy calibration of detectors is made by a Monte Carlo simulation method based on this new formula.

Isospin Effects of Critical Behavior in Lattice Gas Model

Isopin effects of the critical phenomena were studied via Xe isotopes in the frame of the lattice gas model. All the critical temperatures for four Xe isotopes are close to 5.5 MeV at the same freeze-out density of about 0.39 rho(0). The critical values of power law parameter of mass distribution, mean multiplicity of intermediate mass fragments, information entropy and Campis second moment show minor dependence on the isospin at the critical point.

TOF spectroscopy measurement using waveform digitizer

The photoneutron source (PNS, phase 1), an electron linear accelerator (linac)-based pulsed neutron facility that uses the time-of-flight (TOF) technique, was constructed for the acquisition of nuclear data from the Thorium Molten Salt Reactor (TMSR) at the Shanghai Institute of Applied Physics (SINAP). The neutron detector signal used for TOF calculation, with information on the pulse arrival time, pulse shape, and pulse height, was recorded by using a waveform digitizer (WFD). By using the pulse height and pulse-shape discrimination (PSD) analysis to identify neutrons and γ-rays, the neutron TOF spectrum was obtained by employing a simple electronic design, and a new WFD-based DAQ system was developed and tested in this commissioning experiment. The DAQ system developed is characterized by a very high efficiency with respect to millisecond neutron TOF spectroscopy.The photoneutron source(PNS, phase 1), an electron linear accelerator(linac)-based pulsed neutron facility that uses the time-of-flight(TOF) technique, was constructed for the acquisition of nuclear data from the Thorium Molten Salt Reactor(TMSR) at the Shanghai Institute of Applied Physics(SINAP). The neutron detector signal used for TOF calculation, with information on the pulse arrival time, pulse shape, and pulse height, was recorded by using a waveform digitizer(WFD). By using the pulse height and pulse-shape discrimination(PSD)analysis to identify neutrons and γ-rays, the neutron TOF spectrum was obtained by employing a simple electronic design, and a new WFD-based DAQ system was developed and tested in this commissioning experiment. The DAQ system developed is characterized by a very high efficiency with respect to millisecond neutron TOF spectroscopy.

Possible proton halo and skin in light proton-rich nucleus

Measurements of reaction cross section (sigma(R)) for some proton-rich nuclei (N = 8, 10, 12 isotones) on carbon target at intermediate energies have been performed on RIBLL of HIRFL by a transmission method. The experimental sigma(R) values for Al-23 and P-27 are abnormally large compared with its neighboring nuclei and that of F-17 has an enhancement compared with neighboring isotopes. The calculation of relativistic density-dependent Hartree (RDDH) approach shows there is proton-halo structure in Al-23 and P-27 and there is a proton-skin in F-17. The significance of these measurements was discussed.

Study of Giant Dipole Resonance of Super Heavy Compound System

A microscopic semi-classical approach, i.e., the linearized Vlasov equation with a collision term treated by the relaxation time approximation, is simply described and is used to investigate the giant dipole resonance (GDR) from hot super heavy compound system. The possibility of such GDR γ rays emission is described also according to the fission delay. For Au+Au system (A = 392) and Xe+U system (A = 374), the temperature dependence of strength distribution of GDR γ rays and the deformation effect on GDR γ rays are discussed in framework of this approach.