[en] The aim of our work was to investigate the production of top-antitop pairs and the spin correlations when the top (antitop) quark decays to a b-quark and two leptons. The effect of spin correlations was studied in the case of proton-proton collisions at the energy of 14 TeV for the ATLAS detector. A full density matrix was used at the generation level. We also investigated the influence of heavy Higgs boson on spin correlations. We can conclude that spin correlations could be observed in the ATLAS experiment and the ATLAS detector enables the study of the dynamics of heavy quark production and decay. (author)

[en] An apparatus developed for the measurement of radon diffusion through thin foils for the SuperNEMO project is presented. The goal of the SuperNEMO collaboration is to construct a new generation detector for the search for neutrinoless double-beta decay (0νββ) with 100 kg of enriched isotope as the source. At present, the collaboration is carrying out R and D in order to suppress significantly intrinsic background including that caused by radon. The description of the apparatus, data analysis method, as well as the results obtained in the measurement of radon diffusion through several types of thin foils, glue and sealant suitable for shielding in the SuperNEMO detector are discussed.

[en] The SuperNEMO experiment is devoted to neutrinoless double beta decay detection and main R and D of the detector design is already finished. The crucial role in such low background experiments plays the suppression of background. One of the most important sources of radioactivity is the radon gas and its daughter products. The radon activity in the volume of the detector will be reduced significantly using the antiradon facility already installed in the Modane underground laboratory which provides air with a radon volume activity at the order of ∼ mBq/m³. To be able to measure low radon activities at the output of this antiradon facility in reasonable time of measurement the develoment of new ultra-sensitive radon detector is currently carried out. The detection is based on electrostatic collection of radon progenies (²¹⁴Po, ²¹⁸Po) on a Si PIN diode. Our idea is to increase the volume of the detector up to 1 m³ divided into smaller subdetectors (50–100 l) to improve the detection effectiveness and consequently the sensitivity. Two prototypes of sensitive radon detectors were constructed (50 l and 300 l). Preliminary results of the detection efficiency and the background measurement for the first prototype are also presented.

[en] The application of the CdTe Timepix detector for the measurement of the activity of radon progenies (²¹⁴Po and ²¹⁸Po) in the air is briefly described. The result of the background test and the comparison of efficiencies of the CdTe Timepix detector and the Si detector for the detection of radon progenies are presented.

[en] Stringent tests on top quark production and decay mechanisms are provided by the measurement of the top quark and W boson polarization. This paper presents a detailed study of these two measurements with the ATLAS detector, in the semileptonic (tt→WWbb→lνj₁j₂bb) and dileptonic (tt→WWbb→lνlνbb) t anti t channels. It is based on leading-order Monte Carlo generators and on a fast simulation of the detector. A particular attention is paid to the systematic uncertainties, which dominate the statistical errors after one LHC year at low luminosity (10 fb^-1), and to the background estimate. Combining results from both channel studies, the longitudinal component of the W polarization (F₀) can be measured with a 2% accuracy and the right-handed component (F_R, which is zero in the Standard Model) with a 1% precision with 10 fb^-1. Even though the top quarks in t anti t pairs are not polarized, a large asymmetry is expected within the Standard Model in the like-spin versus unlike-spin pair production. A 4% precision on this asymmetry measurement is possible with 10 fb^-1, after combining results from both channel studies. These promising results are converted in a sensitivity to new physics, such as tWb anomalous couplings, top decay to charged Higgs boson, or new s-channels (heavy resonance, gravitons) in t anti t production. (orig.)

[en] A nuclear power reactor is the most intense man-controlled source of electron antineutrinos. An installation of a neutrino detector in close vicinity to a reactor core ($\sim <!--\; ???\; -->$10 m) enables the study of neutrino properties with a higher efficiency, for example an investigation of short-baseline neutrino oscillations and a verification of sterile neutrino hypothesis. A knowledge of the antineutrino flux enables us to determine the reactor power in real time. Measurement of the antineutrino energy spectrum gives the possibility to investigate the isotopic composition of the reactor fuel and to monitor illegal manipulation of ${}^{239}$Pu. The S${}^3$ detector was developed as a common effort between IEAP CTU in Prague and JINR (Dubna). The high segmentation of the detector enables identification of the antineutrino interaction which has a specific time, energy and spatial pattern. The software for the data acquisition and visualization is under development in IEAP CTU in Prague. Since the detector does not contain any flammable, toxic, caustic and dangerous materials, it is safe to be installed under the industrial power reactor. The S${}^3$ detector has applications in fundamental physics, an applied research as well as nuclear safety.

[en] Suppression of radon background is one of main tasks in ultra-low background experiments. The most promising technique for suppression of radon is its adsorption on charcoal. Within the frame of the NEMO-3 experiment, radon trapping facility (RTF) was installed in Modane underground laboratory in 2004. Based on long-term experience with this facility a new compact transportable anti-radon facility was constructed in cooperation among IEAP CTU, SÚRO and ATEKO company. The device provides 20m"3/h of purified air (air radon activity at the output ∼10mBq/m"3). The basic features and preliminary results of anti-radon device testing are presented

[en] In theories with large extra dimensions, we study the top spin correlations at the Large Hadron Collider. The s-channel process mediated by graviton Kaluza-Klein modes contributes to the top-antitop pair production in addition to the Standard Model processes, and affects the resultant top spin correlations. With the fundamental scale of the extra dimensional theory below 2 TeV, we find a sizable deviation of the top spin correlations from the Standard Model one

[en] We study top-antitop pair production and top spin correlations in a model with an electrically neutral massive gauge boson, Z', at the Large Hadron Collider. In addition to the Standard Model processes, the Z' contributes to the top-antitop pair production process in the s-channel. Choosing a kinematical region of top invariant mass around the Z' resonance pole, we find sizable deviations of the top-antitop pair production cross-section and the top spin correlations from those of the Standard Model. (author)

[en] We examine the top quark production in the brane world scenario. We study two typical models - the model proposed by Arkani-Hamed, Dimopoulos and Dvali (ADD) and the model of Randall and Sundrum (RS). In addition to the Standard Model processes, there is a new contribution to the top-antitop pair production process mediated by graviton Kaluza-Klein modes in the s-channel. We calculated the density matrix for the top-antitop pair production including the new contribution. With a reasonable parameter choice, we find a sizable deviation of the top-antitop quark spin correlations from those in the Standard Model