The Belle II experiment has published its first result to Physical Review Letters using data from the pilot run in 2018. This paper is also selected for an “Editor’s suggestion” as one of the most important results to provide new knowledge for additional bosons interacting with dark matter.
The Belle II experiment performed the search for a hypothetical neutral boson, Z’ boson, which is predicted by models that explain the remaining puzzle in the Standard Model. For this analysis, Z’ boson is modeled as a new “portal” particle which mediates the interaction between the normal particles in the Standard Model and dark matter according to the Lμ—Lτ model. Such new particles could explain the disagreement of magnetic anomalous moment of the muon, (g—2)μ, between the measurement and the prediction based on the Standard Model.
One of the candidate events of the Z' boson
decaying into two invisible particles (yellow lines)
associated with two muons (light blue lines).
Other markers (red, pink, green, and blue) display detectors' hits.
No sign of Z’ boson is observed within the collected data, but this study successfully sets the most stringent constraints for the strength of the Z’ boson’s coupling to second- and third-generation leptons. They have revealed the properties of the Z’ boson more explicitly.
In addition, this result shows the Belle II experiment is functioning from the early stage of data taking with the upgraded accelerator, SuperKEKB, and the new detectors.
Staff and graduate students from our laboratory (N-lab) are strongly promoting the Belle II experiment. We have continuously been working to develop and operate a new type of particle detector called the TOP counter and to build grid computing for the Belle II experiment. In parallel, we have actively been searching for new physics beyond the Standard Model and new hadron states using the data acquired by Belle II detector. We have provided many achievements in a wide range of activities on both detector development and physics analysis from the start of the experiment. They have ceratinly led to this first results.
We have steadily accumulated the data of more than 30 fb-1 so far,
which is over 100 times larger than that used for this analysis.
The Belle II experiment will release more and more interesting results as well as more precise results for Z’ boson.
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KEK Press Release:
"Belle II explores new "portal" into dark matter - First results from the Belle II Experiment"
Link to the Paper:
"Search for an Invisibly Decaying Z′ Boson at Belle II
in e+e−→μ+μ−(e±μ±)
Plus Missing Energy Final States"
(PRL 124 141801)
Synopsis by Erika K. Carlson, a Corresponding Editor:
"Closing in on the Z′Boson"
