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Physics background
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The standard model in particle physics is extremely successfull in describing a wide spectrum of experimental data, from low-energy phenomena like kaon decay (below 1 GeV) up to high-energy processes (several hundred GeV), like the production of weak gauge bosons (W and Z) and the top quark. Accordingly, there is very little doubt that this standard model is the theory to describe experimental data below some hundred GeV - within their current accuracy - best.
Even though, it should be mentioned there are a number of fundamental questions which cannot be answered by the present standard model. While the gauge sector (charged and neutral weak bosons, photon, gluon) is comparatively well understood, there are several unclear phenomena in the flavor sector (quarks, leptons): The question for the number of quark lepton families, for example, cannot be adressed in the standard model. Where the hierarchies in the masses of quarks and leptons or the mixing angles between the quark families (and, due to neutrino oscillations, between lepton families) originate, is also unclear. Still, the phenomenological model by Kobayashi and Maskawa, honored by the 2008 nobel prize, can explain the quark mixing observed and the violation of the CP invariance for K and B mesons by introducing few parameters, which have to be determined experimentally. The BaBar and Belle experiments at the two "B factories" at SLAC (USA) and KEK (Japan) have impressively proved CP violation for B mesons decays and verified the theory by Kobayashi and Maskawa.
CP violation is the central breaking of symmetry, by which baryon excess (matter-antimatter asymmetry) - to which we owe our existence - can be explained from the Big Bang. In Kobayashi's and Maskawa's theory, CP violation is explained by a single phase factor, which helps to describe correctly all the CP-violationg processes found so far within the current experimental uncertainty. The baryon excess observed, though, - or rather the baryon-photon ratio - cannot be described by the CP violation seen in the K and B system and is forecast as too small by several factors of ten.
Based not only on the asymmetry between matter and antimatter not to be explained by the standard model, the existence of "New Physics" outside the standard model (i.e. at higher energies) is considered inevitable. At the Large Hadron Collider (LHC) the search is on for the Higgs boson, the last missing piece in the standard model. At the same time, there is going to be a concentrated lookout for New Physics which is expected to occurr at energies of about 1 TeV, motivated by solid theoretical explanations concerning the quantum stabilization of the Higgs field.
The high-energy region, defined by ample centroid energy to produce new massive particles, is not the sole possibility to make out New Physics. New Particles can also be traced by virtual effects in the reactions of known particles at low energies. In the history of particle physics, this has happened before: The charm quark was predicted from suppressed decays of the neutral K meson, the existence of the third generation of quarks and leptons has long before their observation been suggested by the Kobayashi-Maskawa theory of CP violation in the K system. The top quark mass has been correctly predicted from LEP data by virtual (quantum-loop) effects. High-precision experiments can indeed search out energy scales for new physics which will not be accessible by the current (and the following) generation of colliders.
Flavor phyics is the best choice for the search for New Physics in quantum loops for several reasons: Firstly, quark-flavor conversion ("violation") is caused by weak charged currents, which are suppressed by small mixing angles. Secondly, quark-flavor conversions with equal charges (e.g. b→s), i.e. flavor-changing neutral currents (FCNCs), meson-antimeson mixing and CP violation, happen exclusively in higher order, that is on the loop level. Both conditions do not have to be realised for the particle states of New Physics. This means potentially large effects, only suppressed by the high mass scale of the new states, could be anticipated. If generic flavor-violating New Physics with O(1) coupling is included in the standard model, present flavor data allows for such additions only on scales above about 10-100 TeV. This shows how sensitive precision experiments can be on high mass-scales. On the other hand, if the mass scale for New Physics is only about 1 TeV, the flavour structure of new states has to be highly non-trivial and a thorough examination of those new flavor-violating couplings is only possible in a „Super“ B Factory.
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