Positron emission tomography (PET) is an in-vivo method for imaging of biological processes via detection of pairs of 511 keV annihilation gamma rays. A recent paradigm shift in medicine from the treatment of obvious diseases to an early diagnosis and prevention is leading to more stringent requirements on PET sensitivity, while the advances in the targeted radionuclide therapy and theranostics require a need for more widespread and accurate PET. Promising advances in the instrumentation required for this evolution come again from particle physics. In the seminar we will discuss two innovation areas, flexible limited angle PET scanners and scanners based on Cherenkov radiation.

FASER実験はLHCの衝突点前方の480 m地点に検出器を配置し、MeVからGeV領域の未知粒子探索とTeV領域のニュートリノ研究を目的とする。 原子核分野や宇宙線分野へも新たな知見が得られることが期待されている。 LHCはRun 3を開始し、FASER実験はデータ取得を開始した。本セミナーではその最新状況を紹介する。

Long-lived particles are predicted by many extensions of the standard model. Particles that fly a measurable distance before decaying inside the detector produce a clear experimental signature that provides very efficient background suppression. In this talk I will describe recent work in this area. This will include a search for a heavy neutral lepton (HNL) at ATLAS, an HNL search at Belle that covers a different mass range, and several proposed searches of long lived particles in additional scenarios.

Recently it has been proposed to search for dark matter using mechanical sensors, exploiting the fact that all dark matter candidates couple to the size or position of atoms. While focus has been directed towards analyzing signal from gravitational wave detectors and equivalence principle tests, a unique opportunity has emerged to develop compact detectors based on cavity optomechanical systems, which have recently achieved force measurements at the quantum limit. I'll discuss this concept from an experimentalist's perspective, highlighting a proposal to search for vector dark matter with optomechanical accelerometers. In this context, our lab is developing a new generation of ultra-sensitive accelerometers based on centimeter-scale silicon nitride membranes.

When properly engineered, simple quantum systems such as harmonic oscillators or spins can be excellent detectors of feeble forces and fields. Following a general introduction to this fast growing area of research I will focus on using optomechanical systems as sensors of weak acceleration and strain fields. Ultralight dark matter coupling to standard model fields and particles would produce a coherent strain or acceleration signal in an elastic solid. I will discuss the feasibility of searching for this signal using various optomechanical systems. I will also show that current mechanical systems have the sensitivity to set new constraints on scalar field candidates for dark energy. Finally, I will briefly overview the promise of quantum noise limited detectors in the search for beyond the standard model physics.

Detection machanisms for low mass bosonic dark matter candidates, such the axion or hidden photon, leverage potential interactions with electromagnetic fields, whereby the dark matter (of unknown mass) on rare occasion converts into a single photon. Current dark matter searches operating at microwave frequencies use a resonant cavity to coherently accumulate the field sourced by the dark matter and a near standard quantum limited (SQL) linear amplifier to read out the cavity signal. To further increase sensitivity to the dark matter signal, sub-SQL detection techniques are required. Here we report the development of a novel microwave photon counting technique and a new exclusion limit on hidden photon dark mater. We operate a superconducting qubit to make repeated quantum non-demolition measurements of cavity photons and apply a hidden Markov model analysis to reduce the noise to 15.7 dB below the quantum limit, with overall detector performance limited by a residual background of real photons. With the present device, we perform a hidden photon search and constrain the kinetic mixing angle to epsilon < 1.68×10^-15 in a band aroudn 6.011 GHz (24.86 μeV) with an integration time of 8.33 s. This demonstrated noise reduction technique enables future dark matter searches to be sped up by a factor of 1,300. By coupling a qubit to an arbitrary quantum sensor, more general sub-SQL metrology is possible with the techniques presented in this work.

Now that new heavy particles have not been found at the LHC, focusing on light and weakly interacting new particles is one direction to go. Fixed target experiments using accelerators play a part in this. I will explain the basics of the phenomena in fixed target experiments, and how to calculate the number of signal on a target induced by e+ e- beams. Trends in some fixed-target experiments will be introduced. I will discuss some ideas for fixed target experiments at the ILC and KEK.