First collisions in the upgraded SuperKEKB accelerator

Belle II starts its research programme

Cheers in the control room: the Belle II detector has recorded first collisions. Image: KEK

Event display from a collision in the Belle II detector. Image: KEK / Belle II collaboration

After eight years of refurbishing, particles collided for the first time in the SuperKEKB accelerator on 26 April 2018. SuperKEKB is located at the KEK research facility in the Japanese town of Tsukuba and is meant to produce more particle collisions during its operating life than any other particle accelerator ever before. These collisions between electrons and their anti-particles, known as positrons, will take place inside the particle detector Belle II, which has also been completely redesigned, a process in which DESY and other German research groups have been integrally involved.

Belle II is specifically designed to look for physical phenomena extending beyond the previously explored realms of physics. It specialises in measuring rare particle decays, for example that of so-called beauty quarks, charm quarks or tauons. Scientists hope that this will help the to unravel the mysteries of dark matter and the imbalance between matter and antimatter in the universe, and to track down new phenomena.

“We would like to convey our heartiest congratulations to our colleagues at KEK and to the Belle II team on their success. Starting up a new particle accelerator is a huge challenge. The particle physics community is very excited to see the results SuperKEKB and Belle II will produce,” says DESY’s Research Director for Particle and Astroparticle Physics, Joachim Mnich. DESY’s Carsten Niebuhr, the scientist who heads the Belle II group at DESY, adds: “It is extremely exciting to see the detectors that we have been developing and building for years coming to life bit by bit. And we hope that the scientific discoveries that we get from the generated data will be even more exciting and ground-breaking.”

The first collisions are a key milestone on the way to launching the research programme at Belle II. For about a month, particles have once again been circling inside the accelerator, which has been fitted with a new system of focusing magnets and a new damping ring. Both of these ensure that the particle beam is extremely narrow and compressed, so that as many particles as possible collide with each other, leading to a high luminosity or collision rate. An important prerequisite was achieved in January when the DESY-designed and built remote vacuum system RVC that makes a crucial connection between focus magnets and the detector was installed.

Putting a new particle accelerator into operation is a laborious and complicated process, in which each system has to be tested and adjusted in innumerable small steps. The particle detector too must be set up very carefully before the actual research programme can begin. The international Belle II Collaboration consisting of more than 750 scientists from around the world has even gone so far as to initially install a test detector inside Belle II, where the highest partcile background is expected. The data from this detector help accelerator physicists at KEK in adjusting the operation of the accelerator in such a way that the highly sensitive vertex detector, which is currently being assembled by the German groups involved in Belle II, can be safely installed at the end of the year.

Over a period of some ten years, the accelerator is to produce some 50 billion pairs of B- and anti‑B mesons. When the Belle II detector goes into full-scale operation in early 2019, it will generate huge amounts of data, which need to be stored, reconstructed and analysed. To this end, DESY and GridKa in Karlsruhe will be contributing significant storage and computing capacities towards the experiment.