Belle II explores new "portal" into dark matter - First results from the Belle II Experiment

April 7, 2020
Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)
 

Figure 1: A computer graphics image of a simulated event in which a Z' boson is produced by e+e- collisions, in association with two muons (green curves and hits) and decays into invisible particles. In this figure, the Z’ boson decays into an invisible neutrino and an anti-neutrino, but it may also decay into a dark matter particle and its anti-particle. In either case, no trace is left is in the detector.／© KEK, Belle II, created using Belle II in Virtual Reality developed by Zachary Duer, Tanner Upthegrove, Leo Piilonen, George Glasson, W. Jesse Barber, Samantha Spytek, Christopher Dobsonat the Virginia Tech Institute for Creativity, Arts and Technology, Virginia Tech Department of Physics, Virginia Tech School of Education.
The first search for a new type of elementary particle that may act as a "portal" between ordinary matter and dark matter by the Belle II international collaboration has been published in this week's Physical Review Letters.

The Belle II experiment, which operates at the SuperKEKB electron-positron collider in Tsukuba, Japan, searched for a hypothetical new particle called the Z’ that may act as a “portal” between ordinary matter and dark matter. Belle II data collected in 2018 shows no evidence of the Z’, setting new limits on the properties of such a particle.

A Z’ boson is one of the proposed theoretical candidates that might connect dark matter with the ordinary world. If it exists, it could be produced in electron-positron collisions at SuperKEKB and subsequently decay to invisible dark matter particles. Discovery of a Z’ boson might solve important open issues in particle physics related to the behavior of dark matter and resolve some anomalies observed in other experiments that cannot be explained by the reigning theory of particle physics (the Standard Model).

Figure 2: Mass of the Z' candidates (data points) compared to the expected background events (histograms) on a semi-logarithmic scale. Although the dark matter particles cannot be directly observed at Belle II, mass of the candidates could be determined from the energies and momenta of the other particles produced in the electron-positron collision simultaneously with the Z' candidate. The presence of a Z' would show up as a sharp excess of data over the background. No such structure is visible here.／This figure is taken from Fig. 2 of the paper: I. Adachi et al, (Belle II Collaboration), Phys. Rev. Lett. 124, 141801 (2020), DOI:10.1103/PhysRevLett.124.141801 published under the Creative Commons Attribution 4.0 International license.

Researchers at the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) have been involved with the Belle II experiment to upgrade the Belle II detector.

"This paper was the result of a collaboration involving many groups, including the Kavli IPMU. Our team will also work on new-particle searches by maximally utilizing the Silicon Vertex Detector that we had produced and delivered to the experiment," said Kavli IPMU Associate Professor Takeo Higuchi.

For more details, please refer to the press release by KEK.

 

 

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Related links
Background information on the science goals of the SuperKEKB/Belle II facility

Belle II explores new "portal" into dark matter - First results from the Belle II Experiment

 

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