Sen Qian

Test of high time resolution MRPC with different readout modes for the BESIII upgrade

In order to further enhance the particle identification capability of the Beijing Spectrometer (BESIII), it is proposed to upgrade the current end-cap time-of-flight (eTOF) detector with multi-gap resistive plate chamber (MRPC). The prototypes, together with the front end electronics (FEE) and time digitizer (TDIG) module have been tested at the E3 line of Beijing Electron Positron Collider (BEPCII) to study the difference between the single and double-end readout MRPC designs. The time resolutions (sigma) of the single-end readout MRPC are 47/53 ps obtained by 600 MeV/c proton/pion beam, while that of the double-end readout MRPC is 40 Ps (proton beam). The efficiencies of three MRPC modules tested by both proton and pion beam are better than 98%. For the double-end readout MRPC, no incident position dependence is observed

A performance evaluation system for photomultiplier tubes

A comprehensive performance evaluation system for Photomultiplier tubes has been built up. The system is able to review diverse cathode and anode properties for PMTs with different sizes and dimensions. Relative and direct methods were developed for the quantum efficiency measurement and the results are consistent with each other. Two-dimensional and three-dimensional scanning platforms were built to test both the cathode and anode uniformity for either the plane type or spherical type photocathode. A Flash Analog-to-Digital Convertor module is utilized to achieve high speed waveforms sampling. The entire system is highly automatic and flexible. Details of the system and some typical experimental results are presented in this paper.

A method for calibrating PMTs in T0 system for beam test

In order to study the performance of MRPC, which will be used for the upgrade of the Endcap TOF in BES III, a T0 system is composed of high speed response PMTs H6533 coupling with BC420 plastic scintillators. Because the T0 system should offer a toughly strict timing start, the high precision electronics based on VME system were used to test the SPS (single-photoelectron spectrum) of H6533 PMT. A suitable operation voltage for optimal performance is confirmed by researching the dependence relationship between the PMT gain and energy resolution of SPS (single-photoelectron spectrum). At the end, the timing resolution of this type of T0 system was 41.6 ps in the cosmic ray test and 39.1 ps in the proto beam test.

PMT overshoot study for the JUNO prototype detector

The quality of PMT signals is crucial for large-size and high-precision neutrino experiments, but most of these experiments are affected by the overshoot of PMT signals from the positive HV-single cable scheme. Overshoot affects the trigger, dead time and charge measurement from a detector. For the JUNO prototype detector, we have performed a detailed study and calculation on PMT signal overshoot to control the ratio of overshoot to signal amplitude to ~1%, with no effect on other PMT parameters.

Evaluation of new large area PMT with high quantum efficiency

The neutrino detector of the Jiangmen Underground Neutrino Observatory (JUNO) is designed to use 20 kilotons of liquid scintillator and approximately 16 000 20 inch photomultipliers (PMTs). One of the options is to use the 20 inch R12860 PMT with high quantum efficiency which has recently been developed by Hamamatsu Photonics. The performance of the newly developed PMT preproduction samples is evaluated. The results show that its quantum efficiency is 30% at 400 nm. Its Peak/Valley (P/V) ratio for the single photoelectron is 4.75 and the dark count rate is 27 kHz at the threshold of 3 mV while the gain is at 1 × 107. The transit time spread of a single photoelectron is 2.86 ns. Generally the performances of this new 20 inch PMT are improved over the old one of R3600.

Performance of the 8-in. R5912 photomultiplier tube with super bialkali photocathode

An enhanced R5912 family photomultiplier (8-inch.) model with super bialkali photocathode was developed by Hamamatsu. The spectral responses of the standard and enhanced photocathode were compared and a relative increase of 39% at 400 nm was found for the enhanced one. Additional measurements on the relative detection efficiency at a gain of 1E7 showed a consistent improvement of the quantum efficiency. Good uniformity was observed on the super bialkali photocathode. Additional tests proved that both the charge resolution and time properties were not affected by the new cathode technology. Dark count rate and dark current values were found larger in the super bialkali model compared to the standard one.

Developments of oil-free Bakelite resistive plate chambers for particle physics experiments

In this paper, we sumarized a Bakelite Resistive Plate Chamber (RPC) with non-oil surface treatment. This type of RPC has been installed and run smoothly in BESIII Muon identification system and Daya Bay cosmic Muon veto system. Based on its good performances, it has been futher studied as the sensitive detector of a digital hadron calorimeter for measuring the energies of particles in a hadron jet and as a thermal neutron detector. In addition, since the bulk resistivity of Bakelite plates can be controlled, futher developments with low bulk resistivity are being undertaken to guarantee high rate capability in experiments.

Development of the large area MCP-PMT

To adapt the specific demands of photomultiplier tubes (PMTs) in the Jiangmen Underground Neutrino Observatory, we design and manufacture a new type of micro-channel plate PMT (MCP-PMT) with the following performance indicators: the PMTs’ glass shell adopts the formula of GG-17 which have no K2O, and very low background (the contents of 232Th, 238U and 40K in the raw materials are less than 40 ppb, 20 ppb and10 ppb, respectively). Its main body is sphere with 500 mm external diameter, 4 mm wall thickness and the tails that using a gradual transition of kinds of low radiation background glasses, then sealing with the Kovar. The photocathode material with lowest dark noise is bi-alkali photocathode which spectral region matches the liquid scintillator emission spectral (400~440 nm). The front and back hemisphere is transmission and reflective photocathode separately. Two sets of double-stack micro-channel plates replacing the dynode chain are used to detect the photoelectrons from both sites. The focusing system makes the photoelectrons hit into the inside of MCPs to the uttermost. The anode and lead make sure charge signal is no distortion. No matter made by transfer equipment or not, the peak value of quantum efficiency of the PMT should reach 30%, and the peak-to-valley ratio of single photoelectron spectrum has surpassed 2.5:1. In a word, the MCP-PMT’s reliability and other characteristics meet the need of Jiangmen Underground Neutrino Observatory.

The high timing resolution T0 system in IHEP E3 beam line

The designed aim of the multi-gap resistive plate chamber module (MRPC) for the BESIII endcap TOF upgrade project is less than 50 ps, so a Time-zero (T0) system is required to achieve the timing resolution at 30 ps level. After study the scintillator, the PMT, the DAQ subsystem, the assemblage form and the distributing position, the timing resolution of this type of T0 detector composed of scintillator BC420 coupling with PMT H6533 could achieve 30 ps level. Further more, the T0 could also perform the particle identification (proton and pion) just as the beam TOF and EMC detectors during the beam test process for the compelling result. For this type of T0 system, the MRPC beam test was finished and achieved a compelling result.

Status of the 20 inch MCP-PMT prototype development for JUNO experiment

A new concept of large area photomultiplier based on MCPs was conceived for JUNO by the scientists in IHEP, Beijing. In the past 5 years by collaborative work of the MCP-PMT collaboration in China, 8 inch and 20 inch prototypes were produced. Test results show that this type of MCP-PMT can have similar photon counting performance as the traditional dynode type PMTs. With the better collection efficiency, low after pulse rate, low Low-Potassium Glass, the JUNO ordered 75% about 15,000 20 inch MCP-PMT from NNVT at the end of 2015. This manuscript just give the overview this type of MCP-PMT, the R&D process and the main characteristics.