Semileptonic decays of charmedD ± meson

Using the ACCMOR spectrometer equipped with a vertex telescope of high resolution silicon microstrip detectors 74 decays \(D^ + \to \bar K^{*0} (892)e^ + v_e \) (andcc.) withx _F <0.4 have been observed in 200 GeV π^? Be interactions. The cross-section forD ^± production, itsx _F -dependence in the central region and theD ^± lifetime have been measured.     

Double parton scattering inpp collisions at\sqrt s = 63 GeV

In a study ofpp collisions at \(\sqrt s = 63\) GeV with more than 29 GeV total transverse energy emitted into 1.8 units of rapidity in the central region, we have extracted a sample of 4-jet events and compared it with models of the two sources of 4-jet production: double bremsstrahlung and double parton scattering. The data cannot be described by bremsstrahlung alone, and we extract the fraction of 4-jet events attributed to double parton scattering for various definitions of the 4-jet sample. We determine the double parton scattering/2-jet yield ratio, and this leads to a determination of the proton radius. We discuss the implications of our observations for the general understanding of high-ΣE _T events.     

Inclusive pion production in 360 GeV/cpp interactions

In a study of proton-proton interactions at \(\sqrt s = 26GeV\) , inclusive distributions of single pions and systems of pions of various charge combinations are presented, as well as the production ratio obtained in association with various trigger particles. The results are compared to current phenomenological models in an attempt to understand multiparticle productions in hadron collisions.     

Nuclear shape transition in neutron-deficient gold isotopes

On-line resonance ionization mass spectrometry has been applied to determine the isotope shift and hyperfine structure of^185–189Au and tne I=11/2 isomer of¹⁸⁹Au in the 6s²S_1/2 6p²P_1/2=268 nm) transition. The Au atoms were obtained as daughters of mass-separated Hg isotopes produced at the ISOLDE facility at CERN, ionized by a three-step resonant photoionization process, detected and mass-selected by time of flight. A drastic change of the nuclear charge radius was observed between¹⁸⁷Au and¹⁸⁶Au, which is interpreted as an onset of strong deformation of ₂ 0.25 in¹⁸⁶Au and¹⁸⁵Au.This work has been supported by the Bundesministerium für Forschung und Technologie. One of us, J. Wood was supported in part by the U.S. Department of Energy, Contract DE-AS05-80 ER 10599.     

\bar \Lambda Production inK − p interactions at 32 GeV/c

Antilambda production is studied inK ^? p interactions at 32 GeV/c. Both total and differential cross sections are presented. The inclusive \(\bar \Lambda \) production cross section amounts to 109±7 μb. A remarkable energy dependence is observed, σ( \(\bar \Lambda \) ) increasing by a factor of four between 14.3 and 32 GeV/c. Thep _⊥ ² distribution exhibits an exponential fall-off with a slope of 3.3±0.2 (GeV/c)^?2. Most of the \(\bar \Lambda \) 's are emitted in the forward hemisphere. The invariantx distribution increases between 14.3 and 32 GeV/c. Data are presented for \(\bar \Lambda \) production inK ^- p→Λ \(\bar \Lambda \) +X K ^- p→ \(\bar \Lambda \) K ⁿ +X, andK ^- p→ \(\bar \Lambda \) p+X.     

Study of longitudinal correlations between pions from fragmentation processes inK − p interactions at 32 GeV/c

Longitudinal correlations between pions inclusively produced in the target and beam fragmentation regions are studied in aK ^? p bubble chamber experiment at 32 GeV/c with a sensitivity of about 6.7 ev/μb. It was found that the \({{\tilde x_2 = x_2 } \mathord{\left/ {\vphantom {{\tilde x_2 = x_2 } {(1 - \left| {x_1 } \right|)}}} \right. \kern-0em} {(1 - \left| {x_1 } \right|)}}\) distributions of charged pions with momentum fraction in the proton hemisphere with respect to a charged “trigger” pion with momentum fraction x₁ do not show scaling, that those of the associated π₁/π₂ do not compare toK ⁺ p interactions and give indications for quark annihilation. The invariant two- and three pion longitudinal C.M. distributions show significant deviations from the naive quark recombination picture. Distinct long-range correlations observed between π^? s from the proton fragmentation region and π⁺ s from theK ^? fragmentation region could imply contributions from quark exchange or quark annihilation mechanisms inK ^? p interactions at 32 GeV/c.     

Mössbauer study of197Au in Zn and Cd single crystals

The 77.3 keV Mössbauer transition of¹⁹⁷Au was used to study the hyperfine interactions and recoilfree fractions of dilute Au impurities in Zn and Cd single crystals at 4 K. Mössbauer sources were prepared by ion implantation of^197mHg/¹⁹⁷Hg at ambient temperature. From the quadrupole splittings the electric field gradients $$\begin{gathered} eq(Au\underline {Cd} ) = + 11.7(6) \times 10^{17} v/cm^2 and \hfill \\ eq(Au\underline {Zn} ) = ( + )15.0(2.5) \times 10^{17} v/cm \hfill \\ \end{gathered} $$ were determined. The electric field gradients as well as the isomer shifts are in good agreement with the systematics of other impurity host systems. The recoilfree fractions agree with estimates using the mass corrected Debye temperatures of the host lattice.     

Differential cross sections for in the CM energy range from 2.0 to 3.1 GeV

Exclusive production of proton-antiproton pairs by two photon scattering at CM energies between 2.0 GeV and 3.1 GeV has been measured with the TASSO detector at the e⁺e⁻ storage ring PETRA. The angular distribution is flat within the accepted CM angular range |cos Θ^*|0.7. The integrated cross section (|cos Θ^*|0.6) drops from about 4 nb at 2 GeV to less than 0.5 nb above 3 GeV. For the two-photon production of the η_c(2984) and its subsequent decay into proton-antiproton the upper limit

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(95% CL) is found.