Center for particle physics

The main purpose of the Center is to provide necessary conditions for efficient participation of the working groups of the Institute of Physics of the Academy of Sciences of the Czech Republic (IP ASCR) and of the Faculty of Mathematics and Physics of the Charles University (FMP) in collaborations carrying out experimental and theoretical research in main international centers of particle physics, where the structure of basic building blocks of matter is investigated and fundamental physical laws of the microworld are studied at subnuclear level. Broad international cooperation is a typical feature of the research in this field and Europen Centre for Particle Physics CERN, Fermi National Laboratory FERMILAB and German laboratory DESY are its main centres. The fact that the Czech Republic is a member state of CERN since 1992 has provided a basic framework for the participation of Czech institutions in particle physics research, but both our institutions participate in research projects in FERMILAB and DESY as well.

The Center builds upon the Joint Laboratory for Subnuclear Physics (JLSP) of FMP and IP ASCR, existing since 1987 and encompassing common scientific activities of both institutions in the field of particle physics. Judged by its program and capacity, the JSLP covers the dominant part of the research in this field in the Czech Republic. The Center is conceived as a joint laboratory of the FMP and IP ASCR, because the organization and functioning of the existing JLSP has proved to be very successful.

The next decade will be of key importance for the research in the area of elementary particle physics (subnuclear physics). The results of experimental and theoretical research obtained in particle physics in the last 30 years have led to the formulation of the so-called Standard Model (SM) of particle physics, which is based on the principle of the local internal symmetry. SM has proved to be an extraordinarily successful framework for the description of the structure of matter at distances between 10^-13 to 10^-17 cm. According to the SM the basic building blocks of matter are leptons and quarks. Leptons encompass e.g. the electron and its neutrino and quarks combine to form nucleons and other so called hadrons. There are four fundamental forces acting between quarks and leptons: gravitational, electromagnetic, weak and strong. Except for the gravitation, the other three forces are quantitatively very well described within the SM. It has been verified experimentally that these forces are mediated by vector bosons: the photon (for electromagnetic interactions), particles W and Z (for weak interactions, responsible e.g. for radioactive decays) and gluons (for the strong interactions, responsible for the binding of quarks inside hadrons). The electromagnetic and weak interactions can be viewed as particular manifestations of a unified electroweak force and some aspects of this partial unification have been tested experimentally. The SM is based on quantum field theory, which on the one hand provides efficient techniques for calculations of measurable quantities in the microworld and on the other hand has a rich mathematical structure that is a subject of a research in its own right. Despite its obvious phenomenological success, the SM has also a number of shortcomings. It involves too many free parameters, the individual forces are not fully unified and, moreover, the origin of the particle masses is not clear. It is precisely the issue of the origin of quark and lepton masses, as well as those of the vector bosons W and Z (in other words, the essence of the electroweak symmetry breaking mechanism), which is the most important open question of the present-day particle physics. Answering it will undoubtedly provide decisive impetus for further development in this area. This problem is closely related to a possible existence the so-called Higgs boson, which is currently the last missing ingredient of the SM. The second basic direction of the research in particle physics aims at unification of all known forces, i.e. understanding them as manifestations of a single fundamental force. In this context, the unification of gravity with other elementary forces provides particularly challenging problem. According to a prevailing opinion, such a goal can be achieved only by means of a radical change of our basic ideas about space-time and matter. To this end, many new ideas have been developed in recent years that go beyond the framework of quantum field theory and are based on the concepts of string theory. However, even within the conservative approach based on the quantum field theory one may ask whether the known quarks and leptons represent, indeed, the deepest level of the structure of the matter, or whether they themselves are composite objects. All the above-mentioned open questions will be subject of an intense experimental and theoretical research in the forthcoming decade.

Because the duration of experimental research in particle physics, from detector design, its development and construction, to running an experiment itself, is typically 10-20 years, efficient participation in international collaborations requires a long-term, stable financing. The admission into such international collaborations gives, on the one hand, a possibility to participate in a fundamental research at a top level, but, on the other hand, represents a commitment to support the involvement of the working groups for the whole period of duration of an experiment and at the level comparable to that of other countries. The basic aim and organizational scheme of the program of research centers, the part of which our Center is, represent a suitable framework for the support of the research in particle physics in the Czech Republic.

In view of the membership of the Czech Republic in CERN, the basic long-term aim of the Center is ensuring appropriate conditions for efficient participation of Czech researchers in the program of this largest world laboratory for particle physics, specifically taking into account that the Large Hadron Collider (LHC), the most powerful proton accelerator in the world to be commissioned at CERN in 2005, will remain for a long time the main tool for the experimental investigation of the fundamental laws of the microworld. Because of the enormous complexity of the relevant detectors, the work on their development and construction has already been going on for several years. The existing JLSP has taken part in the preparation of the experiment ATLAS, one of the three approved experiments at the LHC, which brings together researchers from 150 laboratories around the world. The contribution of the Czech Republic to the construction of this detector is realized within the project of the Ministry of Industry and Trade "The International Collaboration ATLAS-CERN" which ends in 2003. To ensure the participation in the experimental research itself, another long-term source of funding has to be found. The creation of the Center provides an optimal solution of this problem. At the same time, the participation in the LHC experiments offers a clear perspective for the activities of the Center in the next two decades.

During its first stage (roughly until the end of 2003), the main efforts of the Center will be devoted to participating in the operation, processing and physical analysis of the data acquired in the experiments H1 at DESY and D0 at FERMILAB as well as in the construction of the Pierre Auger Observatory. The first two mentioned experiments represent (together with the experiment DELPHI, which ended its running period in 2000) the backbone of the experimental particle physics research in the Czech Republic, while the Pierre Auger Observatory is an important project for the next two decades. Most PhD students of the JLSP are involved in one of these experiments.

The experiment H1 at DESY, in which physicists, technicians and PhD students of the JLSP are involved, investigates electron-proton collisions, which provide a basic information about the short-distance structure of matter. The JLSP has contributed to this experiment since 1987 by constructing a part of the detector, participating in its operation, software equipment and data processing as well as physical analysis of the data. By the end of 2000 an upgrade of the accelerator has begun and eventually the number of particle collisions will increase four times. This will open the possibility to study rare phenomena, in which one will look for signals of new physics. At the same time, an upgrade of the H1 detector will improve considerably its detection capabilities. The JLSP contributes to this upgrade by the development and construction of the forward and backward silicon detector and by the development of the software for processing the experimental data. After completion of this upgrade at the beginning of 2001, the H1 experiment will continue to operate for about 4 years; during this period the main attention will be devoted to physical analyses of the collected data.

The experiment D0 at FERMILAB, where the structure of matter is investigated in the high-energy proton-antiproton collisions, participated on the discovery of the top quark in 1995. A group of physicists, technicians and PhD students from JLSP has taken part in this experiment since 1996. They have concentrated on the analysis of the so-called multi-jet events, including the study of the top quark. The participation in this experiment is very important not only because of the direct access to unique data, but also as an invaluable preparation of young physicists for future LHC experiments, where the detector and the methods of data processing will be quite similar. At present, a communication and computing system for processing and physical analysis of the D0 data is being built in JLSP and our technicians collaborate on the upgrade of the D0 detector (muon detector, vertex silicon detector). In March 2001 the upgraded TEVATRON accelerator will restart operation and with its energy of 2 TeV it will remain the world's most powerful facility with large discovery potential (the Higgs boson and other new particles) until the start-up of LHC at CERN in 2005.

One of the most remarkable results of modern physics is an intimate connection between the laws of the microworld (traditionally the domain of particle physics) and the laws governing the creation and evolution of the Universe (usually associated with astrophysics and cosmology). Although these areas are seemingly rather remote, differing in typical distances by many orders of magnitude, it turns out that the knowledge of the laws of the microworld is a key for understanding of the Universe. On the other hand, the astrophysical observations can bring answers to a number of questions concerning the microworld that cannot be obtained even in the most powerful terrestrial facilities. Physicist from the JLSP participate since 1999 in the international project called Pierre Auger Observatory. This project aims at determination of the origin and composition of the cosmic rays with energies around 10²⁰ eV. The construction of the basic array of detection elements has begun this year. Its first part, serving as a prototype, will be completed in 2001 and the whole detector in 2003. The measurements are expected to start in 2004 and should last for about 20 years. For the first stage of the detector construction the JLSP will build equipment for testing the optical components of the detector and later for producing the components themselves. Participation in the Project Auger follows the involvement of several physicists from JLSP in experiments CAT and CELESTE, which investigate the origin and properties of the photonic component of cosmic rays.

An important part of the Center is the laboratory for research and development of semiconductor detectors. These detectors, which provide precise measurement of spatial coordinates of the ionizing particle, constitute basic components of modern experimental facilities employed in the particle physics and contribute substantially to their discovery potential. Moreover, they can also be used in other fields of science and in practical applications in medicine, defectoscopy, etc. Clean rooms for testing and production of the detectors have recently been set up in the laboratory. The instrumental and software equipment of the laboratory meets high quality standards. Costly equipment for double-sided lithography purchased last year is now being used in collaboration with Tesla Sezam in Roznov. Physicists and technicians with extensive experience from previous stays in foreign institutes work in this laboratory. Research program for the next 5 years is determined primarily by the needs of the D0 experiment.

After completion of the detector ATLAS appropriate material and personal infrastructure for its operation will have to be established, since each of the participating laboratories will be responsible for the reliable operation of the component it supplied. It will also be necessary to set up a laboratory for processing and analysis of the data, since their amount and complexity will exceed considerably the parameters of all previous experiments. This stage, which would be the focus of the activities of the Center in 2003-2004, will be followed by the running of the experiment that will take about 15 years. The first physical results are expected in 2005-2006.

Theoretical research at the Center is pursued in three broad directions. First, the accessible experimental data are being used for testing of the current SM. These efforts will extend previous activities of some of our theorists involved directly in experiments at DESY and CERN. In the next few years, this phenomenological research will concentrate on analyses of physical quantities characterizing structure of the proton and photon, detailed testing of the interactions of intermediate vector bosons of electroweak interactions and investigation of the properties of the top quark. Later on, the research will focus on detailed tests of the electroweak symmetry breaking mechanism and the related physics of the hypothetical Higgs boson. For purposes of these practical tests of the SM the available data from experiments at CERN, FERMILAB and DESY are used. Secondly, theoretical research aimes at the investigation of physical phenomena beyond the SM. Here we envisage applications of the model-independent method of effective Lagrangians, which will draw on the previous experience of some of our theorists from the work on electroweak interactions and low-energy interactions of mesons (within the framework of the so-called chiral perturbation theory). Another aspect of this second theoretical direction are specific models for physics beyond SM, among them first of all the supersymmetric models predicting rich spectra of new particles with clear signatures which make them interesting for experimentalists. Also here we shall build on the previous activities of our theorists and PhD students. The third direction of the theoretical research is devoted to studies of modern mathematical methods of theoretical physics (quantum field theory in particular) and to the development of entirely novel ideas (such as the string theory). The methods of quantum field theory (in particular, symmetries and theory of the so-called quantum anomalies) have been for a long time in a forefront of interest of some of our theorists and one of our PhD students is currently writing a Thesis on this subject. We would like to strengthen this dynamically developing direction by attracting young researchers since we expect its intense development in the coming years and are aware of its attraction to students. At present, two Czech PhD students work on these topics abroad and their return to the home institutions is highly desirable.

Time schedule of the project:

2000: The upgrade of the experiments H1 and D0, work on the prototype of the mirrors for AUGER, completion of the laboratory for development and testing of detectors.

2001 – 2002: Operation of the upgraded experiments H1 and D0, data processing, the construction of the detector AUGER.

2002: Operation and processing of data of the H1 and D0, completion of the detector AUGER, building of the laboratory for processing the data from LHC experiments.

2004: Beginning of the operation of the Observatory Pierre Auger, completion of the operation of the experiments H1 and D0, finalizing the preparations for operation and data procession of the experiment ATLAS.

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