Dezso Varga

Energy dependence of pion and kaon production in central Pb¿Pb collisions

Measurements of charged pion and kaon production in central Pb+Pb collisions at 40, 80 and 158 AGeV are presented. These are compared with data at lower and higher energies as well as with results from p+p interactions. The mean pion multiplicity per wounded nucleon increases approximately linearly with s_NN^1/4 with a change of slope starting in the region 15-40 AGeV. The change from pion suppression with respect to p+p interactions, as observed at low collision energies, to pion enhancement at high energies occurs at about 40 AGeV. A non-monotonic energy dependence of the ratio of K^+ to pi^+ yields is observed, with a maximum close to 40 AGeV and an indication of a nearly constant value at higher energies.The measured dependences may be related to an increase of the entropy production and a decrease of the strangeness to entropy ratio in central Pb+Pb collisions in the low SPS energy range, which is consistent with the hypothesis that a transient state of deconfined matter is created above these energies. Other interpretations of the data are also discussed.

Evidence for an Exotic S = -2, Q = -2 Baryon Resonance in Proton-Proton Collisions at the CERN SPS

Results of resonance searches in the Xi- pi-, Xi- pi+, antiXi+ pi- and antiXi+ pi+ invariant mass spectra in proton-proton collisions at sqrt{s}=17.2 GeV are presented. Evidence is shown for the existence of a narrow Xi- pi- baryon resonance with mass of 1.862+/-0.002 GeV/c^2 and width below the detector resolution of about 0.018 GeV/c^2. The significance is estimated to be 4.0 sigma. This state is a candidate for the hypothetical exotic Xi_(3/2)^-- baryon with S = -2, I = 3/2 and a quark content of (d s d s ubar). At the same mass a peak is observed in the Xi- pi+ spectrum which is a candidate for the Xi_(3/2)^0 member of this isospin quartet with a quark content of (d s u s dbar). The corresponding antibaryon spectra also show enhancements at the same invariant mass.

Electrostatic spectrometer for measurement of internal conversion electrons in the 0.1–20 keV region

Abstract A new second order focusing, n = 1.5 cylindrical mirror electron spectrometer has been built. It enables us to measure the electrons emitted from the radioactive sources in the 0.1–20 keV region with an instrumental energy resolution of 0.1-1%. The ring-shaped input slit serving as a virtual electron optical object together with the large dimensions of the analyser (the total focal length equals 525 mm) allow us to utilize sources up to 1.5 cm 2 area. The spectrometer was adjusted using electron guns and tested also by 57 Co and 169 Yb radioactive sources prepared by vacuum evaporation and mass separation. The instrument operates automatically at oil-free vacuum of 4 × 10 −6 Pa and the electron spectra are scanned in cycles. The background of the channeltron is about 1.5 counts/min.

System-size dependence of Λ and Ξ production in nucleus-nucleus collisions at 40A and 158A GeV measured at the CERN Super Proton Synchrotron

T. Anticic, B. Baatar, D. Barna, J. Bartke, H. Beck, L. Betev, H. Bia lkowska, C. Blume, B. Boimska, J. Book, M. Botje, J. Bracinik, P. Bunčić, V. Cerny, P. Christakoglou, P. Chung, O. Chvala, J.G. Cramer, P. Csató, P. Dinkelaker, V. Eckardt, Z. Fodor, P. Foka, V. Friese, J. Gál, M. Gaździcki, 11 V. Genchev, K. Grebieszkow, S. Hegyi, C. Höhne, K. Kadija, A. Karev, D. Kresan, V.I. Kolesnikov, M. Kowalski, I. Kraus, M. Kreps, A. Laszlo, R. Lacey, M. van Leeuwen, P. Lévai, L. Litov, B. Lungwitz, M. Makariev, A.I. Malakhov, M. Mateev, G.L. Melkumov, C. Meurer, A. Mischke, M. Mitrovski, J. Molnár, St. Mrówczyński, V. Nicolic, G. Pálla, A.D. Panagiotou, D. Panayotov, A. Petridis, ∗ W. Peryt, M. Pikna, J. Pluta, D. Prindle, F. Pühlhofer, R. Renfordt, C. Roland, G. Roland, M. Rybczyński, A. Rybicki, A. Sandoval, N. Schmitz, T. Schuster, P. Seyboth, F. Siklér, B. Sitar, E. Skrzypczak, M. Slodkowski, G. Stefanek, R. Stock, C. Strabel, H. Ströbele, T. Susa, I. Szentpétery, J. Sziklai, M. Szuba, P. Szymanski, M. Utvić, D. Varga, 10 M. Vassiliou, G.I. Veres, 5 G. Vesztergombi, D. Vranić, Z. W lodarczyk, A. Wojtaszek, and I.K. Yoo

Search for positons in the decay of 143Pm, 144Pm and 146Pm

Abstract A coincidence method was used for detecting annihilation radiation in the research for positons in the decay of 143 Pm, 144 Pm and 146 Pm nucleides. The activities of these three isotopes contained in the source were determined from an analysis of the gamma spectrum. The source was obtained by chromatography separation from Ta, Er and Gd targets irradiated by 660–680 MeV protons. The number of positons per decay was determined to be −6 for 143 Pm , −5 for 144 Pm and −4 for 146 Pm . These limits are lower by several orders of magnitude for the first two nucleides than previously published data. No data have been published for 146 Pm. From these values the upper limits for the total disintegration energies are 1122, 2635 and 1982 keV for 143 Pm, 144 Pm and 146 Pm, respectively.

Results on correlations and fluctuations from NA49

The large acceptance and high momentum resolution as well as the significant particle identification capabilities of the NA49 experiment at the CERN SPS allow for a broad study of fluctuations and correlations in hadronic interactions. In the first part recent results on event-by-event charge and p_t fluctuations are presented. Charge fluctuations in central Pb+Pb reactions are investigated at three different beam energies (40, 80, and 158 AGeV), while for the p_t fluctuations the focus is put on the system size dependence at 158 AGeV. In the second part recent results on Bose Einstein correlations of h-h- pairs in minimum bias Pb+Pb reactions at 40 and 158 AGeV, as well as of K+K+ and K-K- pairs in central Pb+Pb collisions at 158 AGeV are shown. Additionally, other types of two particle correlations, namely pi p, Lambda p, and Lambda Lambda correlations, have been measured by the NA49 experiment. Finally, results on the energy and system size dependence of deuteron coalescence are discussed.

A distorted field cylindrical mirror electron spectrometer: I. Calculation of the analyzer

Abstract A new “box” type cylindrical mirror electrostatic analyzer (CMA) with second order focusing properties is presented. The effect of the fringing field was taken into consideration in the design, resulting in some advantage (e.g. better dispersion) compared to the classical CMA.

Measurement of the ϵ/β+ ratio in the decay of 22Na and 74As

Abstract The ϵ/β+ ratios of the transitions from 22Na and 74As to the first excited state of 22Ne and 74Ge were measured as 0.1042±0.0010 and 1.288±0.018, respectively. The coincidence method was applied, using a 4π β-scintillation detector and NaI and Ge(Li) gamma-ray detectors.

X-ray photoelectron spectroscopic investigation of electrochemically oxidised and reduced platinum surfaces

Abstract The growing of oxide layer with the time of anodic oxidation in 1M, 3.5M and 8.8M perchloric acid solutions has been investigated by XPS on smooth and platinised Pt surfaces. Pure metallic Pt surfaces were prepared by acidic digestion, ignition and cathodic reduction, and their electron spectra have been compared. The presence of a single species, probably PtO, can be evaluated from the XPS measurements. Calculated values of PtO film thickness for different time intervals of electrolytic oxidation are given at various concentrations of HClO 4 .

Line shape analysis of high energy X-ray induced Auger- and photoelectron spectra of thin Cu and Ni films

Abstract A detailed study of the line shape of high energy Cu X-rays excited Auger- and photoelectron spectra of layered samples is presented. The samples consisted of polycrystalline Cu and Ni overlayers of various thicknesses deposited on a Si substrate. The raw data show that the contribution caused by bulk inelastic scattering in the spectra increases significantly with overlayer thickness. Employing a general deconvolution procedure, the contribution of bulk inelastic scattering was consistently eliminated. The resulting spectra are in excellent agreement. The contribution caused by surface excitations has a very moderate effect at these high energies, while intrinsic losses were estimated to make up ∼30–50% of the total intensity. The true energy distribution at the source as seen by the spectrometer was established by elimination of the features due to surface excitations and the contribution from intrinsic excitations of the delocalized electronic states was determined.