High Energy Physics Programme

Programme Director Heimo Saarikko

The Large Electron-Positron collider (LEP) at CERN represents, together with the electron-proton (HERA) and electron-positron (SLC) machines at DESY and SLAC, one of the most important accelerator facilities presently available for investigating the innermost structure of matter. With its wide range of physics capabilities LEP continues to serve as a leading user facility of today’s high energy physics. The second phase of LEP, LEP2, paves the way for the large e+e-linear collider, an integral part of the high energy physics planning of world accelerator centers that will complement the proton-proton machine (LHC) to be built at CERN.

SEFT high energy physicists have participated in the CERN LEP program since its beginning by designing, constructing and maintaining parts of the LEP-DELPHI detector, preparing tools for data handling and physics analysis and completing a number of physics research analyses published in international series. Supported by the Academy of Finland and the R&D funding agencies of the Ministry of Education & Science and Trade & Industry the group has been able to build up a competitive experimental group, first within the Department of High Energy Physics, then expand it to a complete detector laboratory within the Research Institute of High Energy Physics (SEFT), now part of the Helsinki Institute of Physics (HIP). In close co-operation with the State Research Center’s (VTT) semiconductor laboratory, the group developed the first Finnish single- and double sided silicon strip, pixel, and limited streamer tube (LSM) detectors, now integral parts of the DELPHI experiment. Twelve Ph.D. dissertations, a large number of M.Sc. theses and training programs both in physics and in instrumentation have been completed during the course of LEP activities in the 1990's.

The SEFT theory group has produced new results on the extensions of the Standard Model. Both supersymmetric and non-super-symmetric extensions have been investigated by the group and tests at the future colliders have been proposed.

The main goal of the high energy physics program is to make significant contributions in physics. To succeed, the following prerequisites are to be fulfilled: (1) thorough knowledge of detector technology, (2) mastery of data handling and physics analysis techniques and (3) understanding of the phenomenology relevant to the experiment.

The main goal of the electron-positron physics project is to contribute in solving one of the most burning problems of today's high energy physics, namely the origin of electroweak symmetry breaking.

For this, efficient tools for heavy quark identification and their reconstruction are required. In identifying heavy quarks the previous work on semiconductor strip- and pixel detectors becomes an essential element and in reconstructing the quark jets all the earlier studies on calorimetry and gas detectors are needed.

The particle physics theory project concentrates on the framework of electroweak symmetry breaking as described by supersymmetric and non-supersymmetric models. The theory group provides the experimental group with a relevant phenomenological testing ground of these models in e+e- interactions at LEP2 and linear collider energies and participates in a European network of physicists preparing the design criteria for the next e+e- collider. The theory group also contributes to the phenomenology of high energy proton-proton reactions which will become available at LHC.

There are three major goals for the detector laboratory: 1) maintain and upgrade the gas and semiconductor based LEP-DELPHI hadron calorimeter and microvertex detector systems, 2) carry out basic research on detector ageing and radiation hardness, and 3) provide support for applications of advanced detectors in research and industry.