B. X. Yu

Luminosity monitoring and calibration of BLM

The BEPC II Luminosity Monitor (BLM) monitors relative luminosity per bunch. The counting rates of gamma photons, which are proportional to the luminosities from the BLM at the center of mass system energy of the psi(3770) resonance, are obtained with a statistical error of 0.01% and a systematic error of 4.1%. Absolute luminosities are also determined by the BESIII End-cap Electro-Magnetic Calorimeter (EEMC) using Bhabha events with a statistical error of 2.3% and a systematic error of 3.5%. The calibration constant between the luminosities obtained with the EEMC and the counting rates of the BLM are found to be 0.84 +/- 0.03 (x10(26) cm(-2).count(-1)). With the calibration constant, the counting rates of the BLM can be scaled up to absolute luminosities.

Measurement of the liquid scintillator nonlinear energy response to electron

Nonlinearity of the liquid scintillator energy response is a key to measuring the neutrino energy spectrum in reactor neutrino-experiments-such as Daya Bay and JUNO. We measured the nonlinearity of the linear alkyl benzene based liquid scintillator in the laboratory, which is used in Daya Bay and will be used in JUNO, via the Compton scattering process. By tagging the scattered gamma from the liquid scintillator sample simultaneously at seven angles, the instability of the system was largely cancelled. The accurately measured nonlinearity will improve the precision of the theta(13), Delta m(2), and reactor neutrino spectrum measurements at Daya Bay.

Temperature dependence of the light yield of the LAB-based and mesitylene-based liquid scintillators

We studied the temperature dependence of the light yield of linear alkyl benzene (LAB)-based and mesitylene-based liquid scintillators. The light yield increases by 23% for both liquid scintillators when the temperature is lowered from 26 degrees C to 40 degrees C, correcting for the temperature response of the photomultiplier tube. The measurements help to understand the energy response of liquid scintillator detectors. Especially, the next generation reactor neutrino experiments for neutrino mass hierarchy, such as the Jiangmen Underground Neutrino Observatory (JUNO), require very high energy resolution. As no apparent degradation on the liquid scintillator transparency was observed, lowering the operation temperature of the detector to similar to 4 degrees C will increase the photoelectron yield of the detector by 13%, combining the light yield increase of the liquid scintillator and the quantum efficiency increase of the photomultiplier tubes.

p/π+ response of single layer THGEM detector in Ar+3% iC4H10*

In this work, we study the response of a single layer Thick Gaseous Electron Multiplier (THGEM) detector to p/pi(+) at the E3 line of the Beijing Test Beam Facility. The THGEM detector drift gap used in this study is 4 mm, and the gain of the detector operated in Ar+3% iC(4)H(10) is about 2000. p/pi(+) particles at momenta between 500 MeV/c and 1000 MeV/c are distinguished by a Time Of Flight system. Our results show that at the measured momenta, detection efficiencies for p are from 93% to 99%, and for pi(+) in the range of 82%-88%. Meanwhile, simple Geant4 simulations also have been done, and are consistent with the amplitude spectra of the beam test results. We preliminarily study the feasibility of the THGEM detector as a sampling element for a Digital Hadronic Calorimeter (DHCAL), which may provide support for the possible application of a THGEM detector in the Circular Electron Positron Collider (CEPC) HCAL.

Simulation of background reduction and Compton suppression in a low-background HPGe spectrometer at a surface laboratory

High-purity germanium (HPGe) detectors are well suited to analyse the radioactivity of samples. In order to reduce the environmental background for an ultra-low background HPGe spectrometer, low-activity lead and oxygen free copper are installed outside the probe to shield from gamma radiation, with an outer plastic scintillator to veto cosmic rays, and an anti-Compton detector to improve the peak-to-Compton ratio. Using Geant4 tools and taking into account a detailed description of the detector, we optimize the sizes of these detectors to reach the design requirements. A set of experimental data from an existing HPGe spectrometer was used to compare with the simulation. For the future low-background HPGe detector simulation, considering different thicknesses of BGO crystals and anti-coincidence efficiency, the simulation results show that the optimal BGO thickness is 5.5 cm, and the peak-to-Compton ratio of (40).K is raised to 1000 when the anti-coincidence efficiency is 0.85. In the background simulation, 15 cm oxygen-free copper plus 10 cm lead can reduce the environmental gamma rays to 0.0024 cps/100 cm(3) Ge (50 keV-2.8 MeV), which is about 10(-5) of the environmental background.

Preliminary study of light yield dependence on LAB liquid scintillator composition

Liquid scintillator (LS) will be adopted as the detector material in JUNO (Jiangmen Underground Neutrino Observatory). The energy resolution requirement of JUNO is 3%, which has never previously been reached. To achieve this energy resolution, the light yield of liquid scintillator is an important factor. PPO (the fluor) and bis-MSB (the wavelength shifter) are the two main materials dissolved in LAB. To study the influence of these two materials on the transmission of scintillation photons in LS, 25 and 12 cm-long quartz vessels were used in a light yield experiment. LS samples with different concentration of PPO and bis-MSB were tested. At these lengths, the light yield growth is not obvious when the concentration of PPO is higher than 4 g/L. The influence from bis-MSB becomes insignificant when its concentration is higher than 8 mg/L. This result could provide some useful suggestions for the JUNO LS.