[en] The Omega spectrometer has been utilised for experiments with relativistic heavy ion collisions. With the aid of the WA97 experiment (lead-lead at 167 GeV/c per nucleon) data were accumulated during three periods and almost 300 millions of triggers being recorded. To study the quark-gluon plasma (QGP) we have utilised the analysis of the strange particles and the following results were obtained for the ratios of the production rates: 0.54 ± 0.13 for Ωbar/Ω and 0.16 ± 0.1 for (Ω + Ωbar)/(Ξ + Ξ-bar). In order that the anti-strange/strange ratio be the presence signature of the quark-gluon plasma it must reach a value of the order of unity. The results of the West Hall and North Hall experiments gave hints in favor of QGP. However, these hints are not formally solid even for the lead beam at 160 GeV/nucleon. Work developed for the program of the data acquisition as well as for the particle track reconstruction are also mentioned

[en] This report presents the activity of the Laboratory of Particle Physics and Cosmology of College de France on the years 1996-1997 in the fields of Cosmic Physics, Observational Cosmology, Neutrino Experiments, HELLAZ Project, Instrumentation, DELPHI Experiment, Research of Quark-Gluon Plasma, Research on Dark Matter, Theory, Parallel Processing. Also, are mentioned the activities in computer software, electronics, mechanics, general service, publications, external relations, seminars and collaborations. In the field of Cosmic Physics there are described the current experiments on cosmic gamma rays, the work with AUGER observatory and simulations. In the field of observational cosmology there are mentioned the search for baryonic dark matter and studies on type Ia supernovae. In the field of neutrino studies there are described the searches on neutrino oscillations on a 1 km base, while in the framework of HELLAZ project there is reported the work on solar neutrinos. In the field of instrumentation there are mentioned the work on Hybrid Photon Detector and the contribution of the laboratory to the LHC-B Experiment at CERN and on long-base RICH experiment. In the framework of DELPHI experiment at LEP there are reported investigations on beauty particles, new particles and detector performances. There are given results obtained in the field of Quark-Gluon Plasma studies. There are described the research and development works with the dark matter detectors. In the field of theory there are reported studies on the proton structure, photon-photon collisions, the physics of the excited leptons and studies on neutron stars. Also, in this field there is reported the studies in Quantum Chromodynamics and physics of top quark. In the section devoted to parallel processing there are mentioned the research activities related to actinide burning by accelerators and simulations in nuclear medicine issues, electron channelling in crystals and beam-beam effect in colliders. The report also, presents the activities in the field of computer net infrastructures as well as in electronics

[en] The report presents results concerning the methods of bolometric and scintillation crystal detection of dark matter as well as the work on very low-temperature detectors. In the frame of the laboratory and EDELWEISS collaboration pioneering work was developed aiming at the direct detection of the particles which could constitute a major part of this matter as an exotic form of matter. In the frame of this experiment installed at LSM it was reached a detection threshold of 3 keV (as nucleus recoil energy) and a background noise as low as 15 count/kg.day.KeV at energies above 10 keV. As part of the project a 10 mK dilution cryostat was developed. The work performed with scintillating crystals and analyses with pulse shape discriminators for search of the hypothetical weak interacting massive particles (WIMPs) showed the existence of a third population not clearly identified but definitely consisting not of neutrons. So, the research for WIMPs with scintillating crystals is limited by this third population. Finally, in the field of very low temperature detectors the functioning and characterization of the tunnel junctions operating at 20 mK (with the Orange cryostat) are reported

[en] The work in the field of parallel processing has developed as research activities using several numerical Monte Carlo simulations related to basic or applied current problems of nuclear and particle physics. For the applications utilizing the GEANT code development or improvement works were done on parts simulating low energy physical phenomena like radiation, transport and interaction. The problem of actinide burning by means of accelerators was approached using a simulation with the GEANT code. A program of neutron tracking in the range of low energies up to the thermal region has been developed. It is coupled to the GEANT code and permits in a single pass the simulation of a hybrid reactor core receiving a proton burst. Other works in this field refers to simulations for nuclear medicine applications like, for instance, development of biological probes, evaluation and characterization of the gamma cameras (collimators, crystal thickness) as well as the method for dosimetric calculations. Particularly, these calculations are suited for a geometrical parallelization approach especially adapted to parallel machines of the TN310 type. Other works mentioned in the same field refer to simulation of the electron channelling in crystals and simulation of the beam-beam interaction effect in colliders. The GEANT code was also used to simulate the operation of germanium detectors designed for natural and artificial radioactivity monitoring of environment

[en] In the theoretical physics section of the report works concerning the particle structure, the Quantum Chromodynamics and the physics of the top quark are mentioned. As a way of investigation of the proton structure a study of the exclusive photoproduction of a Φ meson on protons was carried out. In the field of photon-photon collisions a study concerning the event generators is mentioned. The physics of excited leptons is approached by a study of the neutrino-production of neutrinos or excited muons via processes of the type ν + nucleus → ν^* + X at very high energies (of the order of 10 TeV). In the same field works were done concerning the excited leptons production in heavy ion collisions at very high energy, the contribution of a heavy Majorana neutrino to the 0ν2β decay and the muon pair production at very high energy in cosmic rays. Also, a paper using the diquark model in the study of neutron stars is reminded. In the field of the quark physics efforts were undertaken to solve a numerical disagreement between two different approaches of the semi-weak production of the top quark in hadronic colliders. Also reported is the the supersymmetric extension of the Eurojet event generator seemingly useful as a supersymmetric entrance, on one hand and permitting to tackle the problem of inclusion of R-parity violation, on the other hand

[en] In the framework of DELPHI collaboration at LEP collider after six years of operation at Z⁰ energy and a first upgrade in energy at 135 GeV it was possible to study the threshold pair production of W at 161 GeV. The installation of 28 new superconducting cavities allowed achieving a 10 pb^-1 sensitivity at 172 GeV. The performances of the silicon vertex detector and RICH Cherenkov counter allowed a profound study of the B mesons properties due to the efficient signature of the Z⁰ → bb-bar reaction. The lifetime of the B mesons was determined as well as the beauty-implying Cabibbo-Kobayashi-Maskawa matrix elements. The number of 4.1 x 10⁶ hadronic Z⁰ events recorded after 1990 allowed the observation and the measurement of the B_d in-flight oscillations. The study of B_s oscillations is underway. Any energy upgrading by installation of additional cavities at an electron collider re-opens the field of the search for new particles (Higgs, supersymmetric particles). The development and performances of the new silicon vertex detectors are mentioned. A second pixel shell has been installed, which will improve significantly the track recognition and thus will give to DELPHI a homogeneous angular covering, indispensable for the new particle search. Also, are mentioned the simulations carried out on the farm working station BASTA at Lyon

[en] A Hybrid Photon Detector (HPD) is currently manufactured in the framework of the tests of LHC-B collaboration. These extremely fast and sensible detectors (95% efficiency and 1 ns time accuracy for a single electron) could be utilized in many other applications: long base neutrino oscillations and possibly, HELLAZ. The model consists of an array of 2,048 1 x 1 mm² on Si strips of 50 mm thickness placed in glass cylinders of 127 mm diameter provided with Si windows and containing focalization electrodes. The electron circuits on 16 VA3 readout ceramic chips where designed, realized and tested. The stainless steel base card provided with 40 vacuum holes was already realised. The first production tests of visible light bi-alkali photocathodes operating in high vacuum will be performed soon. The design of the RICH2 counter (covering polar angles from 12 to 120 mrad) has been modified by turning the 120 mrad mirror to increase the spectrometer luminosity, i.e. to increase the length of the radiation path in gas by a factor of two. A second mirror sends the image in a region behind the magnetic field return, a region well-shielded from the LHC interaction zone. This design will provided 28 points for a β = 1 tracks and an angular uncertainty of 0.34 mrad per point. To cover the entire image 115 HPD will be necessary. The reconstruction of the complex systems of rings has been recently accomplished for events typical for RICH2, downstream, to discriminate between pions and kaons between 16 and 180 GeV/c. A simulation of 3,068 tracks has produced only 19 erroneous identifications, i.e. 0.6%. Another, simulation of 1,989 tracks with the RICH upstream resulted in 39 erroneous π/K identification, i.e. 2%. The report presents also the long base RICH experiment for detecting neutrino oscillations. A new version of 100 m length and 18.6 m diameter (27 kt of water) provided with HPDs of 250 mm diameter with 85 6 x 6 mm² arrays has been designed. Fifty such detectors will be manufactured for the in-been tests and 5,000 for the detector operated at Gran Sasso in the year 2001

[en] After participating in a several experiments near the reactor at Bugey, at distances from 15 to 100 m from the reactor the laboratory joined a collaboration for search of effect of neutrino oscillations at longer distances (1 km) from the neutrinos' point of origin. The zone covered by this experiment raises a particular interest because the results of several underground experiments on the atmospheric neutrinos indicated that oscillation could appear in this zone. The Chooz collaboration, reported here, joined three American universities (Philadelphia, New Mexico and Irvine), two Italian universities (Pisa and Trieste), the Kurchatov Institute in Moscow and two French laboratories (the LAPP in Annecy and the College de France). The first data have been recorded during the autumn of 1996 prior to the commissioning of the reactors (2 x 4200 MW_th), to measure the background noise. The detector is a target of 6 t liquid scintillator doped with Gd, sunk in 120 t non-doped liquid scintillator separated by thin transparent wall. The target is viewed by 192 photomultipliers. The scintillator liquids are carried up to the detector and then to the exterior tanks by a tunnel of 200 m length and a height gradient of 15 m. The fragility of the detector imposes a simultaneous filling of its components, with an accuracy of the order of 1 cm. A 200 MHz sampling system of the photomultiplier pulses signing the neutrino interaction was developed in order to obtain simultaneously information on the pulse-height, timing and shape. This experiment could serve as a prototype for heavier experiments conceived in US, in Russia at Rovno and Krasnoyarsk, and in France, at 15 km from the Perry reactor, at 500 m underground. Still more ambitious is the Japan project at Kamioka, at 160 m distance from a nuclear reactor. The experiment at Perry will push the electron neutrino upper mass estimates down to 0.01 eV

[en] The HELLAZ experiment aims at obtaining the solar neutrino spectra as well as their angular correlation with the sun. The recoil electrons from the collision ν-e are detected in a time projection chamber (TPC) serving as target. The choice of helium as gas target lowers the electron energy threshold down to 100 keV i.e. to 200 keV for the neutrino energy. HELLAZ will be thus sensible to ν_pp, their flux being practically independent of the sun model, as well as to the ⁷Be neutrinos. To obtain a good energy resolution for neutrinos, namely a good separation between the pp neutrinos and the ⁷Be neutrinos a precise measurement of the emission angle of the recoil electron is necessary. In order to achieve this aim the TPC will be operated in the digital mode by individual measurement in the space of the each electron forming the recoil electron track and precise determination of the main axes of inertia ellipsoid of the cloud formed at the track beginning. The measuring error in the direction of recoil electron is thus low (∼ 35 mrad) leading to an uncertainty in the value of neutrino energy lower than 10%. Additionally, HELLAZ will be capable to identify the neutrino flavor from the angular distribution of the ν-e collision. The HELLAZ experiment will thus measure with high precision the pp neutrino spectrum which is thought to be determined by the sun luminosity and the current measurement of helioseismology. Thus, any deformation of this spectrum can be interpreted in physical terms. For instance, the HELLAZ precision will be high enough to measure the effect of the deformation due to the vacuum oscillations. A schedule of the 5 stages experiment is presented starting from HELLAZ 0 (0.5 l) to the final version of HELLAZ (2000 m³) which will measure the solar neutrinos at Gran Sasso. Two simulation programs where developed. The first, simulating the creation and the shift of ionisation electrons in a track, will serve as starting point in the analysis program, while, the second is dealing with subtraction of the radioactive background noise, specific to the HELLAZ experiment