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| KEK E371 | |
|---|---|
| Name | KEK E371 |
| Facility | High Energy Accelerator Research Organization |
| Place | Tsukuba |
| Country | Japan |
| Period | 1994–1999 |
| Type | Kaon decay experiment |
| Spokesperson | Toshio Nakano |
KEK E371 was a fixed-target particle physics experiment at the High Energy Accelerator Research Organization facility in Tsukuba, Ibaraki. The experiment focused on rare decays of charged and neutral kaons with sensitivity to processes predicted by extensions of the Standard Model and tests of CP violation and lepton flavor violation. It combined high-intensity secondary beams, precision tracking, and calorimetry to search for decay modes with extremely small branching fractions.
The collaboration designed the program to probe rare decay channels motivated by theoretical work from groups at CERN, Fermilab, Brookhaven National Laboratory, SLAC National Accelerator Laboratory, and DESY. Primary objectives included searches for forbidden or suppressed decays predicted in frameworks such as Supersymmetry, Left–Right Symmetric Model, and models incorporating Heavy Neutral Leptons. Secondary goals targeted precision measurements of branching ratios relevant to constraints from the Cabibbo–Kobayashi–Maskawa matrix, comparisons with results from experiments like KTeV, NA48, E787, and cross-checks with lattice-QCD-informed predictions from groups at RIKEN, KEK Theory Center, and Brookhaven National Laboratory theorists.
The apparatus combined magnetic analysis from spectrometers inspired by designs at CERN SPS and Fermilab Main Injector experiments with calorimetric systems used at Crystal Ball and KLOE. Tracking employed multiwire proportional chambers and drift chambers similar to those developed at KEK, DESY, and SLAC beamlines. Particle identification integrated Cherenkov counters modeled after detectors at CERES and time-of-flight systems following implementations at Paul Scherrer Institute experiments. Electromagnetic calorimetry used lead glass blocks akin to assemblies from WA89 and photomultiplier technology refined by vendors supplying Super-Kamiokande and Hyper-Kamiokande collaborations.
The experiment used a secondary beam produced by proton pulses from the KEK Proton Synchrotron striking a fixed production target similar to configurations at CERN PS and Fermilab Booster. The target station and optics were influenced by design studies from TRIUMF and Los Alamos National Laboratory groups to maximize kaon yield while minimizing contamination from pions and protons. Momentum selection utilized magnetic elements comparable to those in the AGS and PSI beamlines, with collimation schemes informed by work at IHEP and JINR to shape the phase space and reduce background from upstream interactions.
Signal reconstruction relied on fast front-end electronics and trigger logic architectures inspired by systems at CERN LHC prototype projects and Fermilab experiments. The data acquisition chain combined waveform digitizers and time-to-digital converters developed in collaboration with instrumentation groups at University of Tokyo and Tohoku University. Trigger tiers included hardware-level vetoes patterned after NA62 and software-level selections analogous to frameworks used by BaBar and Belle for online event filtering. Calibration procedures involved radioactive sources and cosmic-ray muon campaigns similar to those employed by MINOS and T2K.
Analysis techniques incorporated blind analysis strategies promoted by the Particle Data Group and statistical methods from likelihood frameworks used by ATLAS and CMS. Background estimation combined sideband interpolation and Monte Carlo simulations using toolkits developed at CERN and validated against control channels measured by collaborations at Fermilab and KEK. Results set upper limits on branching fractions for several rare decay modes, constraining parameter space in models discussed by researchers at Princeton University, Harvard University, MIT, and Caltech. Comparative studies referenced complementary bounds from MEG and SINDRUM searches and influenced global fits performed by groups at CERN Theory and Perimeter Institute.
Systematics were evaluated following best practices from experiments like KLOE and KTeV, including uncertainties from detector alignment procedures developed at CERN Alignment Group and time calibration studies informed by work at IEEE instrumentation conferences. Sources included beam flux normalization tied to measurements at KEK Proton Synchrotron, particle identification efficiencies benchmarked against samples used by NA48 and tracking resolution terms characterized with cosmic-ray and test-beam data from CERN SPS. The collaboration reported dominant uncertainties arising from residual background modeling, acceptance corrections cross-checked with simulations produced by computing centers at KEK and RIKEN.
Limits and measurements from the experiment informed theoretical constraints adopted by authors at Institute for Advanced Study, Max Planck Institute for Physics, University of California, Berkeley, and Stanford University. The techniques influenced detector design choices in later projects such as J-PARC kaon experiments, NA62 upgrades, and proposals from Hyper-Kamiokande collaborators. Personnel and technology transfers contributed to instrumentation efforts at T2K, Belle II, and accelerator studies at J-PARC Main Ring, while results fed into global analyses by consortia including the Particle Data Group and model-builders at CERN and Perimeter Institute.