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The Belle II experiment

On the track of the antimatter puzzle

Model of the Belle II detector. The MPP has a leading role in developing the inner pixel detector. (Photo: MPP)

Why is there matter in the universe, but hardly any antimatter? Researchers are pursuing this question at the Belle II experiment in Japan. In the particle accelerator SuperKEKB, matter (electrons) and antimatter (positrons) are brought into collision. Among the particles produced as a result, the researchers are searching for indications that could explain the surplus of matter.

According to present-day knowledge, this imbalance came to be because a fundamental symmetry property of particles was violated. The physicists hope for new insights from B mesons, with which they already have been able to provide evidence for a violation of this symmetry. This type of particle is created together with its antiparticle when electrons and their antiparticles, positrons, crash into each other.

The SuperKEKB accelerator serves as a "factory" for B mesons. B mesons only live a short time; after the tiniest fractions of a second, they decay into other particles. These decay tracks are recorded by the Belle II detector and analyzed. So that the differences in the decay patterns of the B mesons and their antiparticles can be seen, the detector must exactly measure the locations where they decay. That's why, in the innermost area of Belle II, there sits a high-resolution pixel vertex detector – a type of precision camera – that the MPP took a leading role in developing.

Matter and antimatter

Stars and galaxies are the visible proof that matter dominates the universe.
Stars and galaxies are the visible proof that matter dominates the universe. (Photo: ESO)

After the Big Bang there came into being heavy particles of matter and antimatter that have yet to be identified. These primordial particles decayed into the particles and antiparticles familiar today: quarks and antiquarks, electrons and postrons, muons and antimuons, and so on.

If a particle and its corresponding antiparticle meet, they transform themselves into energy; they mutually annihilate each other. Therefore no material should have been able to form in the universe – at least not permanently.

Admittedly, atoms, molecules, stars, planets, and galaxies provide us with conclusive evidence for the existence of matter. Physicists suspect that the heavy primordial particles decayed differently: Somewhat more matter particles formed than antimatter particles – that is, more quarks than antiquarks, more electrons than positrons, and so on. As matter and antimatter mutually annihilate each other, all that remained in the universe was the small excess of matter.

The Belle II detector

The former Bell detector is currently being upgraded to Belle II. The first fully functional sensors of the central pixel vertex detector were completed in November 2015. The entire Belle II detector is expected to go into service in 2018.

The SuperKEKB accelerator

In order to improve the measurements, the ring accelerator SuperKEKB (circumference: 3 km) is currently being updated: In the future, B - anti-B meson pairs will be produced at the rate of 1,000 per second, which corresponds to roughly 40 times the production rate of its predecessor, KEKB. The first electron and positron packets successfully circulated through the accelerator in 2016. The first measurements are expected to be taken in 2018.


More information on the Belle II group

News releases


Preparations for the new Belle II detector at the modernized SuperKEKB accelerator in Japan are in full swing. A few months ago, Belle II was rolled into position in the accelerator ring. Individual detector system tests will now follow: on November 18, 2017, physicists and engineers installed the...

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The High Energy Accelerator Research Organization (KEK) successfully completed the "roll-in" of the Belle II detector. This is an important milestone for the international Belle II collaboration and the SuperKEKB accelerator.

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The SuperKEKB accelerator in Japan is still “awaiting” the arrival of “its” detector: Belle II. In a few months, the detector is to be inserted into the accelerator ring for the first time – the first measurements are planned for 2018. The MPP projects for Belle II continue to make good progress: At...

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Prof. Johanna Wanka, federal minister for education and research, recently toured the Belle II experiment at the Japanese accelerator facility KEK. The Belle detector is currently being modernized to analyze particle tracks more accurately in the future. The Max Planck Institute for Physics (MPP)...

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First signs of life for the particle accelerator SuperKEKB: Lately electrons and positrons have begun making their rounds in the modernized facility of the Japanese research center KEK. The first collisions electrons and positron beams are expected in the year 2017. Studies of the particles these...

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Researchers in Munich have presented a highly sensitive sensor for precise measurement of particle tracks. This is the first module for the Vertex Detector of the Belle II experiment at the Japanese accelerator center KEK. The detector is expected to start operation in 2017, recording collisions...

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It’s all about high-energy and astroparticle physics at Wildbad Kreuth from Oct. 4 to 9, 2015, when the Max Planck Institute for Physics hosts this year’s International Symposium on Multiparticle Dynamics (ISMD). Held annually since 1970, the ISMD conference rotates from year to year among different...

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On this year's IEEE Nuclear Science Symposium in Seattle on 15 November Jelena Ninković received the 2014 Radiation Instrumentation Early Career Award.

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Group members

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Abudinen, Fernando

PhD Student 554

Albalawi, Mohammed

Student 550

Bös, Gregor

Student 389

Chekelian, Vladimir, Dr.

Scientist 219

Kiesling, Christian, Prof. Dr.

Scientist 258

Leis, Ulrich

Engineering 550

Leitl, Philipp

PhD Student 380

Li Gioi, Luigi, Dr.

Scientist 356

Moser, Hans-Günther, Dr.

Scientist 248

Müller, Felix Benjamin, Dr.

Scientist 372

Pohl, Sara

PhD Student 555

Skambraks, Sebastian

PhD Student 389

Windel, Hendrik

PhD Student 556

Events and meetings

Currently, there are no events or meetings.

Key publications

Study of B0->ρ+ρ−decays and implications for the CKM angle φ2
P. Vanhoefer, J. Dalseno, C. Kiesling et al.
Phys. Rev. D 93, 032010 (2016)

First Observation of the Decay B0->psi(2S)pi0
V. Chobanova, J. Dalseno, C. Kiesling et al.
Phys. Rev. D 93, 031101 (2016)

Measurement of Branching Fractions and CP Asymmetries in B -> wK Decays and First Evidence of CP Violation in B0 -> wKS
V. Chobanova, J. Dalseno, C. Kiesling et al.
Phys. Rev. D 90, 012002 (2014)

Measurement of the CP Violation Parameters in B0 -> pi+ pi- Decays
J. Dalseno, K. Prothmann, C. Kiesling et al.
Phys. Rev. D 88, 092003 (2013)