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Experimental Particle Physics

  • TOJO Junji, Professor
  • OTONO Hidetoshi, Associate Professor
  • YOSHIOKA Tamaki‡, Associate Professor
  • SHIRABE Shohei, Assistant Professor
  • MORITSU Manabu, Assistant Professor
  • ‡ Research Center for Advanced Particle Physics
Our group is conducting experimental research projects using state-of-the-art accelerators for understanding of the fundamental law of the universe. Our current projects are as follows:
  1. The ATLAS experiment at the LHC
  2. The International Linear Collider project
  3. Particle physics experiments using highly intense muon beams at J-PARC
  4. Fundamental physics experiments using low energy neutrons at J-PARC

The ATLAS experiment at the LHC

We participate in the ATLAS experiment at the CERN Large Hadron Collider (LHC), the world largest and most powerful particle collider. You may know that the ATLAS experiment, together with the CMS experiment, discovered the Higgs particle, the origin of particle masses, in proton-proton collisions at center of mass energies of 7-8 TeV (Run 1) in 2012. After a long shutdown, the LHC started its Run 2 operation in 2015, with a center of mass energy of 13 TeV. We contribute the the ATLAS both in the physics analysis (measurement of the Higgs boson properties and searches for new particles) as well as the detector operation and upgrade (the Semiconductor tracker). Currently two faculty members and a graduate student from our group are resident at CERN for the ATLAS experiment. We hope to send more graduate students for the ATLAS experiment in future.

The International Linear Collider project

The International Linear Collider (ILC) is the next generation energy-frontier electron-positron collider being designed by a world-wide collaboration. The ILC can discover news physics beyond the standard model of particle physics with precise measurements the Higgs boson and the top quark properties, as well as direct searches for new particles. The ILC will be operated at center of mass energies of 250-500 GeV, and upgradable to 1 TeV. Japan is now seriously considering to host the ILC project at the governmental level.

Our group is heavily involved in the detector R&D for the ILC experiment, especially for the electromagnetic calorimeter (ECAL) under a framework of the CALICE international collaboration. We are aiming to achieve unprecedented jet energy resolution using a highly granular ECAL. We are developing silicon sensors and readout electronics for the ECAL. We participate in the ILD detector concept group, where we work on the detector optimization and physics simulation studies at the ILC. Prof. Kawagoe is the deputy spokesperson of the ILD group.

Except for the collider experiments using the energy frontier accelerator, our group is also conducting several experiment at Japan Proton Accelerator Research Complex (J-PARC) in Ibaraki prefecture. Thanks to high intense proton beam from J-PARC accelerator, unique experiments can be realized.

Particle physics experiments using high intense muon beams at J-PARC

Search for the lepton flavor violation: the mu-e conversion is a process that violates the lepton flavor conservation and strictly prohibited by the Standard Model (SM).　Discovery of the process is unambiguous evidence for the physics beyond the SM (BSM). We are aiming 100 times and 10000 times better sensitivity than the previous experiment in the first phase and second phase, respectively. We are developing several detector components; electromagnetic calorimeter, trigger counter and straw chamber. (2) Precise measurement of muon anomalous magnetic moment (g-2) and electric dipole moment (EDM): We are also participating to an experiment that is aiming to measure the g-2 and EDM simultaneously with the novel technique. Our group is responsible for the development of the positron tracker using the silicon sensor.

Fundamental physics experiments using low energy neutrons

A neutron is electrically neutral and has a long lifetime compared to other unstable hadrons. In addition, three fundamental interactions, i.e. the gravitational, electromagnetic, and strong interactions, act to neutrons with a same order of magnitude. Combination of these remarkable features enables us to perform various kinds of experiments for fundamental physics. Our group is currently conducting the following experiments at J-PARC: (1) Precise measurement of the neutron lifetime : It is highly desired to precisely determine the neutron lifetime because it is an important input parameter for the Big-Bang Neucleosynthesis. However, there is a 3.9σ disagreement between two historical experiments with different methods. We therefore aim to measure the neutron lifetime with a 0.1% precision by a new experimental method. (2) Search for time reversal violation via the nuclear reaction: Large time reversal violation is theoretically predicted in the compound nucleus resonance. We plan to search for the violation by measuring the neutron scattering cross section in the forward region.