arXiv subjects

Taku Yamanaka

Publications and source records attributed to Taku Yamanaka.

6 recordsLinked to original sources

arXiv2024

Kaon Experiments

After $CP$ violation was discovered in the $K_L \to π^+π^-$ decay, many theories were proposed to explain it, and the Kobayashi-Maskawa model and the Superweak model lasted for many years as strong candidates. High-precision kaon experiments with many new techniques and improvements rejected the Superweak model and supported the Kobayashi-Maskawa model in 1990's. After then, rare kaon decay experiments are studying $K_L \to π^0ν\overlineν$ decays to search for $CP$ violation caused by new physics beyond the Standard Model. Various techniques have been developed to increase the sensitivity and to suppress backgrounds.

hep-ex↗

arXiv2014

CP Violation in Kaon Decays (II)

Major progress has been made in kaon physics in the past 50 years. The number of KL->pi+pi- events has increased by 6 orders of magnitude, and the observed CP violation was experimentally proven to be caused by a complex phase in the CKM matrix. Recent kaon experiments are now searching for new physics beyond the standard model with the K->pi nu nu-bar decays. The branching ratio of K->pi nu nu-bar decays are 7-8 orders of magnitude smaller than the branching ratio of KL->pi+ pi-. This paper reviews the progress of kaon experiments in the US and Japan, and how the 6-7 orders of magnitude improvements were possible in the past 50 years.

hep-ex↗

arXiv2014

Current and Future Kaon Experiments

Kaon experiments are now focusing on searching for new physics beyond the standard model. For example, CERN NA62, J-PARC KOTO and J-PARC TREK-E36 experiments are starting up to study K->pi nu nu-bar decay modes, a lepton flavor violation, and lepton universality.

hep-ex↗

arXiv2014

The Data Acquisition System for the KOTO Experiment

We developed and built a new system of readout and trigger electronics, based on the waveform digitization and pipeline readout, for the KOTO experiment at J-PARC, Japan. KOTO aims at observing the rare kaon decay $K_{L}\rightarrowπ^{0}ν\barν$. A total of 4000 readout channels from various detector subsystems are digitized by 14-bit 125-MHz ADC modules equipped with a 10-pole Bessel filter in order to reduce the pile-up effects. The trigger decision is made every 8-ns using the digitized waveform information. To avoid dead time, the ADC and trigger modules have pipelines in their FPGA chips to store data while waiting for the trigger decision. The KOTO experiment performed the first physics run in May 2013. The data acquisition system worked stably during the run.

physics.ins-det↗

arXiv2008

Review on epsilon'/epsilon

Experiments at CERN and Fermilab have been competing each other to improve the measurement of a CP violation parameter, epsilon'/epsilon. Fermilab KTeV-E832 recently announced their final result, Re(epsilon'/epsilon) = [19.2 +- 2.1] x 10^{-4}. The new world average shows the existence of direct CP violation in the decay process itself with 12 standard deviations.

hep-ex↗

arXiv2004

Measurement of positron lifetime to probe the mixed molecular states of liquid water

Positron lifetime spectra were measured in liquid water at temperatures between 0c and 50c. The long lifetime of ortho-positronium atoms (o-Ps) determined by electron pick-off in molecular substances decreases smoothly by 10% as the temperature is raised. This lifetime temperature dependence can be explained by combining the Ps-bubble model and the mixture state model of liquid water.

cond-mat.other↗