Legals | Data Protection | Login | Home

Topic 1: "Fundamental Particles and Forces"

Physics at electron–positron colliders

After the discovery of a Higgs boson at the LHC, the need for the ILC is pressing: the necessary percent precision for example in the model-independent measurements of the Higgs couplings will be reached only by an e+e collider; the precision will typically improve on that of the LHC by an order of magnitude. Absolute measurements of couplings, branching ratios and the total decay width are possible at the ILC without additional theoretical assumptions and so complement the measurements of the LHC in a crucial way. Likewise, accurate investigations of signals of New Physics at high masses and scales — which may be invisible at the LHC — will require the ILC. The simplicity of its initial state means that the ILC has intrinsically a high discovery potential for New Physics. In a complementary fashion, Belle II has the potential to unravel New Physics in rare processes at lower energy.



Preparatory phase for the ILC

The next funding period will be a period of preparation for the ILC. There is every indication that the Japanese government intends, if there is an international consensus, to propose that the ILC be constructed in Japan. This opportunity dominates the strategy to be pursued during the coming funding period, namely to form a world-wide consensus to build the ILC in Japan and, for the experimental community, to organise itself to plan and build the experiments. While the initiative originates from Japan, the project is entirely conceived as a global one which requires major high-tech components to be fabricated and tested outside of Japan. As the approval of the project realistically will take some time, the retention of the current expert community, particularly on the accelerator, is essential; after approval the necessary additional expert personnel has to be recruited.


On the technical side, the natural challenge for the accelerator is to further improve the maximum energy gradient for industrially produced cavities and to ensure that sufficient qualified industrial capacity exists in the Americas, Asia and Europe to produce the required number of ILC cavities – 18,000 in total. The selection of the Kitakami site in Japan means that site-dependent design work can already begin. At the same time the planning also has to take into account the emerging LHC results, in particular at the highest energy, which will lead to an optimisation of the machine parameters and may have an effect on future staging scenarios. Additional R&D that could result in cost savings should be carried out.


For the ILC experiments, the challenge lies in the selection of detector technologies, in the completion of the detector technical designs, and in the validation of the assembly scheme and the ability to swap detectors in the beam line via the so-called "push-pull" technology.



A complementary example of precision: Belle II

As for the ILC, precision is the guiding principle at Belle II. The aim here is to make use of high-precision measurements of phenomena such as CP violation or of interference effects at lower energies in e+e collisions. These measurements will elucidate the puzzle of the matter{antimatter asymmetry observed in the Universe, which is not understood at a fundamental level. High-precision measurements of rare decays and CP violation in processes involving heavy quarks and leptons provide a unique probe of New Physics at the TeV scale and even higher mass scales through the effects of new particles in higher-order loop processes. While the LHCb experiment at the LHC addresses these aspects starting from a hadronic initial state, Belle II complements these investigations using the highly-constrained decays of the ϒ (4S) in the clean environment of an e+e collider.


Belle II and the upgrade of the KEKB accelerator (SuperKEKB) are well under way. Their completion is ambitiously scheduled for mid 2015 with detector commissioning foreseen for 2016. The upgrade of the machine entails the new nano-beam concept which still needs to be validated. If successful, this operation mode provides a constant luminosity of L = 8x1035 cm2 s-1 and a total integrated luminosity of 50 ab-1 by 2023 — a factor 50 more than the original Belle experiment.


Challenges lie also in the development and construction of the detectors for Belle II in time for data taking. A German consortium in Belle II has taken over the complete construction of the novel pixel detector based on DEPFET (DEPleted Field Effect Transistor) technology.