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The Belle II experiment

On the track of the antimatter puzzle

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.


Ready for future measurements

Starting in 2011, the research plant was completely overhauld too improve its physics measurements. In the future, about 1,000 meson pairs will be produced, i.e. 40 times the production rate achieved by the KEKB predecessor. In parallel, also the former Belle detector was modernized to the new version Belle II. The first measure run started in March 2019.

Matter and antimatter

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.

More information on the Belle II group

News releases

Two detector modules are bonded together “head to head”.

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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Bierwirth, Lukas

PhD-Student 554 126C

Caldwell, Allen, Prof. Dr.

Director 529 212

Chekelian, Vladimir, Dr.

Scientist 219 124C

Humair, Thibaud

Postdoc 307 118C

Kiesling, Christian, Prof. Dr.

Emeritus 258 113C

Krinner, Fabian

Postdoc 356 112C

Krätzschmar, Thomas

PhD-Student 557 117C

Leis, Ulrich

Engineering 550 122C

Leitl, Philipp

PhD-Student 380 115C

Luger, Paul

Student 389 115c

Meggendorfer, Felix

PhD-Student 555 128C

Moser, Hans-Günther, Dr.

Scientist 248 114C

Nemeth-Csoku, Marton

Student 554 126C

Paul, Stephan

Scientist 356 112c

Pawar, Anirvddh

Student 389 115c

Popov, Ivan

Student 393 116C

Reif, Markus

PhD-Student 389 115C

Schmitt, Caspar

Student 552 125c

Simon, Frank, Dr.

Scientist 535 121C

Skorupa, Justin

Student 557 117C

Tittel, Oskar

Student 372 127

Wach, Benedikt

PhD-Student 554 126C

Wacker, Ina

Secretary 207 213

Wang, Boqun, Dr.

Postdoc KEK (372) KEK (127C)

Windel, Hendrik

PhD-Student 556 120C

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)