Search

J-PARC E16 is an experiment to examine the origin of hadron mass through a systematic measurement of spectral changes of vector mesons in nuclei. The measurement of $e^{+}e^{-}$ pairs from the decay of vector mesons will provide the information of the partial restoration of the chiral symmetry in a normal nuclear density. To resolve a pulse pile-up and achieve good discrimination of $e^{+}$ and $e^{-}$ from the background of a reaction rate of an order of 10 MHz, the data acquisition (DAQ) system uses waveform sampling chips of APV25 and DRS4. The trigger rate and data rate are expected to be 1 kHz and 120–330 MiB/s, respectively. The DAQ system for readout of APV25 and DRS4 were developed, where events were synchronized by common trigger and tag data. The first commissioning in beam, called Run-0a, was performed in June 2020 with about 1/4 of the designed setup. The DAQ worked with a trigger rate of 300 Hz in the Run-0a and the main bottleneck was a large data size of APV25. Further optimization of the DAQ system will improve the performance.

An experiment at J-PARC, E16 experiment, which aims to measure the spectral modification of vector meson in nuclear matter is planned. The experiment will measure light vector mesons (ρ/ω/ϕ mesons) generated in nuclear target through the 30 GeV p+A reactions. The mass spectra can be reconstructed with e^+e^− pairs originating from their decays. The spectral modification in finite baryon density is studied systematically. The detail of the experimental plan and expected results are presented with a particular focus on first physics run.

We constructed a hadron blind detector (HBD) using a finely segmented pad readout. The finely segmented pad readout enabled us to adopt an advanced particle identification method which applies a threshold to the number of pad hits in addition to the total amount of collected charge. The responses of the detector to electrons and pions were evaluated using a negatively charged secondary beam at 1.0 GeV/c containing 20% electrons at the J-PARC K1.1BR beam line. We observed 7.3 photoelectrons per incident electron. Using the advanced particle identification method, an electron detection efficiency of 83% was achieved with a pion rejection factor of 120. The method improved the pion rejection by approximately a factor of five, compared to the one which just applies a threshold to the amount of collected charge. The newly introduced finely segmented pad readout was found to be effective in rejecting pions.

The J-PARC E16 experiment has been proposed to measure the mass spectrum of ϕ mesons in nuclear matter to study the origin of QCD mass. The ϕ mesons are identified in the e + e − decay channel and the mass of these ϕ mesons is reconstructed using the momenta of the e + and e − pairs. A tracking detector for this experiment is composed of a position sensitive device that employs Gas Electron Multipliers (GEMs) with a two-dimensional readout board. The ionization electrons are amplified with a triple-GEM stack. The required position resolution is 100 μ m up to an incidence angle of 30°. Position resolutions and efficiencies of the tracking device are evaluated using a π − beam with a momentum of 1.0 GeV/ c at the J-PARC K1.1BR beam line. A position resolution of better than 100 μ m is obtained by calculating the center of gravity of the charges on the readout strips when tracks arrive perpendicularly at the detector plane. Timing information of charge clusters is essential to improve the position resolutions for the inclined tracks. The arrival times of the charge clusters are derived from the wave forms collected by flash ADC modules. Using the arrival times of the clusters, the obtained position resolution is better than 100 μ m for the track inclinations of 15° and 30°. The detection efficiency is also investigated as a function of the GEM gains, and the operational voltage is optimized.

1 RIKEN Nishina Center, RIKEN, Saitama 351-0198, Japan 2KEK, High Energy Accelerator Research Organization, Ibaraki 305-0801, Japan 3Center for Nuclear Study, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan 4Department of Physics, University of Tokyo, Tokyo 113-0033, Japan 5Japan Synchrotron Radiation Research Institute, Hyogo 679-5198, Japan 6Department of Physics, Kyoto University, Kyoto 113-0033, Japan 7Hiroshima University, Hiroshima 739-8526, Japan 8Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan

The J-PARC E16 experiment was proposed to investigate the restoration of chiral symmetry at the normal nuclear density. E16 will systematically measure in-medium mass of vector mesons at J-PARC Hadron Experimental Facility using a 30-GeV proton beam with an intensity of 2 x 1010 protons per pulse. The E16 spectrometer was designed to detect e+e- from slowly moving vector meson, particularly the meson. The detector system consists of GEM tracker, Gas Cerenkov detector based on GEM and electromagnetic calorimeter made of lead-glass, whose number of channels reaches about 100,000 in total. The readout electronics, trigger system and data acquisition system for the detectors have been developed, for which level-1 trigger rate of 1-2 kHz is required under several 10 MHz interaction rate. The preparation is underway for the first beam time in 2017.

At the J-PARC E16 experiment[1], we measure mass spectra of vector mesons in nuclei from the e+e- decay channel with high precision and high statistics. We have developed the trigger system consisting of newly developed ASD ASICs which can extract signals from the GEM foil used as a cathode plane of the induction gap in a GEM chamber and digital electronics using FPGAs which processes binary signals from the ASIC.