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II. Institute for Theoretical Physics |
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Elementary Particle Phenomenology
In the center of our research work is located the theoretical investigation of the characteristics (e.g. masses, couplings, discrete symmetry characteristics, total and partial decay widths etc..) of elementary particles and their connection conditions (e.g. Positronium, corpse, D and b-b-Mesonen, Charmonium, Bottomonium etc..) as well as their reciprocal effects during impact processes with high energies (e.g. electron positron destruction, lepton nucleon -, nucleon nucleon and photon photon dispersion etc..) in the context of the standard model and its extensions (e.g. fourth fermion generation, supersymmetry, models with Majorananeutrinos or other exotic leptons, scenarios without Higgsbosonen, effective theories with abnormal couplings etc.). The high accuracy of final, current and planned experiments of particle physics makes the inclusion of quantum corrections indispensable in many cases into the theoretical forecasts.
The Higgssektor of the electricalweak reciprocal effect is so far almost unexplored from experimental view. The production of reliable forecasts for production and decay processes of Higgsbosonen forms therefore an emphasis of our research work. The treatment more easily Higgsbosonen can be simplified with the help of suitable low energy theorems. On the other hand the gold clay/tone boson equivalence theorem offers a useful aid to the description of heavy Higgsbosonen.
The Hadronisierung of quarks and gluons takes place in the energy region below approximately 1 GeV and is therefore a not-disturbance-theoretical phenomenon, which is described in the context of the QCD Partonmodells by phenomenological fragmenting functions. These know for example by global Fits to precise e + e - data with different energies to be determined. From the scale injury occurring here here the strong coupling constant αs can be extracted. The fragmenting functions are universal due to the factorizing theorem of the QCD and find therefore various applications within the range of the inclusive hadron production.
The possibility opens recently in the context of the nonrelativistic QCD (NRQCD) a suggested factorizing theorem of describing Charmonium and Bottomonium by means of a formal separation from disturbance-theoretical and not-disturbance-theoretical phenomena systematically. A spectacular success of this entrance was the fact that the production rate of J/-Mesonen, measured atthe Tevatron, which more than one order of magnitude lay over earlier theoretical expectation in the color singlet model, now by the inclusion of so-called Farboktettprozesse could be explained. On the other hand the inelastic J/Photoproduktion in the quasi-elasticborder line a significant discrepancy between the HERA data and the theoretical forecast in prominent order in the case, which is called occasionally Tevatron HERA anomaly , resulted. Experimentum crucis for the factorizing hypothesis of the NRQCD the measurement of the polarization of J/-Mesonenis in the direct Hadroproduktion, which should be completely transverse for sufficient large transverse impulses.
Since the Topquark disintegrates because of its large measures, before it can hadronisieren, the production can be described by Topquark pairs in the threshold region in the context of the NRQCD completely without not-disturbance-theoretical parameters and thus in principle arbitrarily exactly. However the appropriate disturbance row seems to converge only very slowly, so that now also the consideration of corrections of the order αs^3 lines up.
Apart from the treatment of concrete particle-physical processes we concern ourselves also with a set of conceptional questions of the quantenfeldtheorie, e.g. subtraction regulations for dispersionsrelationen for the computation lepton sector extended amended by ultraviolet divergenten Feynman amplitudes, low energy theorems for scalar fields, calibrationindependent definition of the mass, the partial and total decay width and the Cabibbo Kobayashi Maskawa matrix and/or its counterpart in theories with and/or.
Our future plans include among other things the following research project:
* The scale behavior of αs is to be examined for third order in the impulse subtraction pattern and be compared with the appropriate behavior in the ms pattern.
* The production of loaded Higgsbosonen as well as Top and Bottomquarks with TESLA is to be treated in the super+symmetrical standard model with consideration of strong quantum effects.
* The production of Charmonium and Bottomonium by Hadroproduktion at the Tevaton and at the LHC, by photo production and low-inelastic dispersion with HERA and by two-photon dispersion with LEP 200 and with TESLA is to be treated in the context of the Partonmodells using the factorizing theorem of the NRQCD in next-prominent order. In particular the Tevatron HERA anomaly is to be cleared up and the existence of the Farboktettmechanismus in nature to be examined.
* The excitation curve of the Topquark pair creation with TESLA is to be predicted in the NRQCD for third order in αs
