Particle physics with tabletop-sized Experiments

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Our group (ICEPP + Asai lab.) searches for new physics beyond the standard model with various tabletop-sized experiments.

If the dark matter in the universe is SUSY particle, the dark matter particles would concentrate in centers of galaxies and annihilate. We try to observe radio-waves and gamma-rays emitted from the annihilation processes.

Search for Photon-Photon scattering with XFEL

Observation of photon-photon elastic scattering is one of the ultimate tests of QED. We search for this phenomenon by using the X-ray free electron laser, SACLA.

Search for WISPs in various wavelengths with high-power light sources

Various searches for Weekly Interacting sub-eV particles (WISPs) are  under way. We use SPring-8 (in X-ray region) or a Gyrotron (in sub-THz region) as a high-power light source to do the `light shining through a wall’ type experiments.

Basic study for Bose-Einstein condensation of positronium

Since positronium is a particle of  integer spin, cooled positronium should create an exotic state, a Bose-Einstein condensate(BEC). However, the BEC of positronium has not been observed yet because of its short lifetime and the difficulty of its cooling. The basic study for the BEC is now under way.

Search for vacuum birefringence

The theory of Quantum Electro-Dynamics predicts a strange behavior of vacuum. It will show birefringence under strong magnetic field. Our group tries to observe this with a high finesse cavity and strong pulse magnets.

A focused high power laser can create a strong electro-magnetic field. Under this field, X-rays are predicted to be bent. We search this phenomena, X-ray diffraction in vacuum, at an XFEL site, SACLA.

Precision measurement of the energy spectrum in the orthopositronium decay

The decay spectrum of orthopositronium has rich information on fundamental physics. We try to measure its shape in ~0.1% accuracy.

Measurement of Positronium Hyper-fine splitting

Measurement of the energy level difference between ortho-positronium and para-positronium (0.84meV) at the ppm level.

Search for weakly coupling neutral particles with ortho-positronium

A search for the exotic decay mode (gamma + X0) of the ortho-positronium. X0 is a weakly coupling neutral particles like the axion, dilation, unparticle, , etc. We are now designing a detector.

Search for CP violation with ortho-positronium

A search for CP violation in the lepton sector by measuring the angular correlation of ortho-positronium spin and its decay gamma rays was done. No CP violation was found, and we obtained the most stringent limit.

Search for the invisible decay of ortho-positronium

Search for the exotic decay of the positronium, in particular for decay to very weakly interacting particles. This search has sensitivity for TeV scale extra dimensions, paraphotons, milli-charged particles, and so on.

Lifetime measurement of ortho-positronium

Test of bound state QED by measuring the lifetime of ortho-positronium. The highest precision to date for this measurement was obtained (150ppm) which confirmed the α2 correction term.

Search for solar axions with Fe-57 resonant absorption

Experimental search for an undiscovered particle, the axion, coming from the sun. For the detection of the axion, the resonant absorption of 57Fe nuclei is used. Unfortunately the axion was not discovered but the strongest experimental limit to date of experiments searching via axion nuclei coupling was obtained, m < 216 eV.

Contact: T. Namba (