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 750 meson pairs will be produced, i.e. 30 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.

Belle II at the MPP

Installation of the complete version of the Pixel Vertex Detector in the Belle II experiment (Photo: B. Paschen/University of Bonn)

Made in Germany and big in Japan: Pixel Vertex Detector installed in Belle II experiment

The Pixel Vertex Detector (PXD), at the size of just a soda can, forms the innermost detector layer of the international Belle II experiment. It has now been installed at its destination, the SuperKEKB electron-positron accelerator in Japan. The…

Read more
The Belle II detector records and analyses particle collisions produced by SuperKEKB. (Photo: Shota Takahashi/KEK)

Belle II catches up with predecessor experiment

Since March 2019, the Belle II detector has been measuring decays of B mesons, a particular type of quark pair. Previous experiments had shown that B and anti-B mesons decay at different rates, i.e., exhibit CP violation. Belle II is intended to…

Read more

Belle II: Picking the best data cherries with neural networks

The Belle II detector records about 5,000 collision events per second. However, only a fraction of these are of interest for physical questions. In order to distinguish the real signals from unusable data, the experiment uses “triggers”. Since the…

Read more
The SuperKEKB tunnel during reconstruction (Photo: KEK/Shota Takahashi)

Belle II: World record in the accelerator ring

Tailwind for the search for rare particle decays in the Belle II experiment: The SuperKEKB accelerator ring has now achieved the highest luminosity ever measured. The electron-positron accelerator beats not only its predecessor KEKB but also the…

Read more
The Belle II detector searches for the Z’ boson. This particle could reveal itself by an unexpected high number of muon pairs with opposite charges, as shown here. (Image: Belle II)

Belle II yields the first results: In search of the Z′ boson

The Belle II experiment has been collecting data from physical measurements for about one year. After several years of rebuilding work, both the SuperKEKB electron–positron accelerator and the Belle II detector have been improved compared with their…

Read more
Artistic view of collisions in Belle II

Searching for disappeared anti-matter: A successful start to measurements with Belle II

The Belle II detector got off to a successful start in Japan. Since March 25, 2019, the instrument has been measuring the first particle collisions, which are generated in the modernized SuperKEKB accelerator. The new duo produces more than 50 times…

Read more
The Vertex Detector on its way into the core of the Belle II Detector

Belle II detector completed

A few days ago, the final components were installed in Belle II. With the aid of special tracks, technicians very gently pushed the highly sensitive vertex detector into the correct position inside the Belle II detector. Over the coming weeks, the…

Read more
The PXD-half-shell delivered to the Tsukuba Hall of KEK in Japan by Carsten Niebuhr (Photo: H.-G. Moser/MPP)

At the finishing line: vertex detector ready for installation in Belle II

Everything is ready for the installation of the innermost detector for the Belle II experiment. Following successful measurements with a test instrument, the actual pixel detector (PXD) has now reached the KEK research institute. Together with one…

Read more
The Belle II detector records and analyses particle collisions produced by SuperKEKB.

Belle II measures first particle collisions

The particle physics community has been waiting for this moment for a long time: On 26 April 2018 0:38, GMT+09:00 at KEK in Tsukuba, Japan matter and anti-matter particles collided for the first time in the new SuperKEKB accelerator. News of this…

Read more
The Belle II detector records and analyses particle collisions produced by SuperKEKB.

Search for antimatter: SuperKEKB accelerator kicks into new gear

Following an eight year conversion period, the SuperKEKB particle accelerator in Japan is almost ready to restart: soon, electrons and positrons will be brought to collision in the completely modernized accelerator ring. In future, the Belle II…

Read more

E-mail address: e-mail@mpp.mpg.de
Phone number: +49 89 32354-extension
name function e-mail extension office
Ay, Ceren Student cerenay 356 A.2.63
Bartl, Martin PhD Student bartl 380 A.2.67
Bierwirth, Lukas PhD Student brwrth 554 A.2.53
Caldwell, Allen, Prof. Dr. Director caldwell 529 A.2.51
Dugic, Katarina PhD Student dugic 219 A.2.65
Eren, Okan Student okaneren 554 A.2.53
Fausch, Yannik Student fausch 555 A.2.63
Grußbach, Lukas PhD Student grussbac 207 A.2.59
Hamurcu, Simeon Student hamurcu 554 A.2.53
Hattenbach, Maximilian Kei Student maxkeiha 554 A.2.53
Hiesl, Simon Student hiesl 555 A.2.63
Jackl, Franz Student jackl 555 A.2.63
Katscho, Arina Student akatscho 555 A.2.63
Kiesling, Christian, Prof. Dr. Emeritus cmk 258 A.1.15
Kurten, Godo Student kurten 555 A.2.63
Leis, Ulrich Engineering leis 550 A.1.67
Leitl, Philipp PhD Student phleitl 555 A.2.63
Moser, Hans-Günther, Dr. Senior Scientist moser 248 A.2.59
Paul, Stephan Senior Scientist spaul 356 A.2.59
Perez-Orive, Claudia Student perezori 356 A.2.63
Reif, Markus PhD Student mreif 389 A.2.67
Skorupa, Justin PhD Student jskorupa 554 A.2.53
Tittel, Oskar PhD Student otittel 380 A.2.67
Wach, Benedikt, Dr. PhD Student wach 554 A.2.63
Wacker, Ina Secretary ina 207 A.2.49
Wallner, Stefan, Dr. Postdoc swallner 219 A.2.65
Werth, Lars van der Student vdwerth 555 A.2.63

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)
arXiv:1510.01245

First Observation of the Decay B0->psi(2S)pi0
V. Chobanova, J. Dalseno, C. Kiesling et al.
Phys. Rev. D 93, 031101 (2016)
arXiv:1512.06895

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)
arXiv:1311.6666

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)
arXiv:1302.0551