The group has also been accused of cherry-picking results that support new particles while discarding null results. The ATOMKI group had claimed to find various other new particles earlier in 2016 but abandoned these claims later, without an explanation of what caused the spurious signals. Efforts by CERN and other groups to independently detect the particle have been unsuccessful so far. In late 2019, a follow-up paper was published in Acta Physica Polonica B. Skepticism Īs of December 2019, the ATOMKI paper describing the particle has not been peer reviewed and should therefore be considered preliminary. This was covered in science journalism, focusing largely on the implications that the existence of the X17 particle and a corresponding fifth force would have in the search for dark matter. Krasznahorkay (2019) posted a preprint announcing that he and his team at ATOMKI had successfully observed the same anomalies in the decay of stable helium atoms as had been observed in beryllium-8, strengthening the case for the existence of the X17 particle. As of 2019, several research experiments are underway to attempt to validate or refute these results. The force may explain the g − 2 muon anomaly and provide a dark matter candidate. (2016) proposed that a "protophobic" X boson, with a mass of 16.7 MeV, suppressed couplings to protons relative to neutrons and electrons at femtometer range, could explain the data. The result was successfully repeated by the team. This indicated that a small fraction of beryllium-8 might shed its excess energy in the form of a new particle. Particles and a combined energy of approximately 17 MeV. Excess decays were observed at an opening angle of 140° between the In an effort to find a dark photon, the team fired protons at thin targets of lithium-7, which created unstable beryllium-8 nuclei that then decayed and produced pairs of electrons and positrons. In 2015, Krasznahorkay and his colleagues at ATOMKI, the Hungarian Institute for Nuclear Research, posited the existence of a new, light boson with a mass of about 17 MeV (i.e., 34 times heavier than the electron).
The NA64 experiment at CERN looks for the proposed X17 particle by striking the electron beams from the Super Proton Synchrotron on fixed target nuclei. The X17 particle could be the force carrier for a postulated fifth force, possibly connected with dark matter, and has been described as a protophobic (i.e., ignoring protons) vector boson with a mass near 17 MeV. The particle has been proposed to explain wide angles observed in the trajectory paths of particles produced during a nuclear transition of beryllium-8 atoms and in stable helium atoms. The X17 particle is a hypothetical subatomic particle proposed by Attila Krasznahorkay and his colleagues to explain certain anomalous measurement results. "Search for New Physics via a Precision Measurement of the Ke2/Kmu2 branching ratio at J-PARC", .Hypothetical subatomic particle as the cause of anomalous measurement results near 17 MeV X17 particle Composition "A spiral fiber tracker for the J-PARC E36 Experiment", POS PhotoDetector 2015 (2016) 069. "Precise measurement of the Ke2/Kmu2 branching ratio and search for new physics beyond the Standard Model." arXiv:1611.02719 nucl-ex. ECT* Workshop, Trento, Italy, June 2016. "TREK/E36 J-PARC: Investigating Lepton Universality with stopped kaon decays". "TREK J-PARC: Beyond the Standard Model with Stopped Positive Kaons.
"The design and basic performance of a Spiral Fiber Tracker for the J-PARC E36 experiment".
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