Measurement of the b baryon lifetime and branching fractions in Z decays

Using approximately 4 million hadronic Z decays recorded with the aleph detector from 1991 through 1995, the lifetime of the b baryon is measured with three independent methods. From the impact parameter distribution of candidate leptons in 1063 events with combinations, the average b baryon lifetime is measured to be ps. From a sample of 193 fully reconstructed candidates correlated with a lepton and a sample of 46 combinations, the lifetime is measured to be ps. The product branching fractions to these final states are % for the first sample and % for the second and third samples combined. Received: 15 August 1997 / Online publication: March 10, 1998     

Investigation of the splitting of quark and gluon jets

The splitting processes in identified quark and gluon jets are investigated using longitudinal and transverse observables. The jets are selected from symmetric three-jet events measured in Z decays with the Delphi detector in 1991-1994. Gluon jets are identified using heavy quark anti-tagging. Scaling violations in identified gluon jets are observed for the first time. The scale energy dependence of the gluon fragmentation function is found to be about two times larger than for the corresponding quark jets, consistent with the QCD expectation . The primary splitting of gluons and quarks into subjets agrees with fragmentation models and, for specific regions of the jet resolution , with NLLA calculations. The maximum of the ratio of the primary subjet splittings in quark and gluon jets is . Due to non-perturbative effects, the data are below the expectation at small . The transition from the perturbative to the non-perturbative domain appears at smaller for quark jets than for gluon jets. Combined with the observed behaviour of the higher rank splittings, this explains the relatively small multiplicity ratio between gluon and quark jets. Received: 18 February 1998 / Published online: 24 April 1998     

The and transitions in the oxygen isoelectronic sequence

Multiconfiguration Dirac-Fock results are reported for the and transitions in the oxygen-like sequence for Z =9,...,18. Both transition energies and transition rates are included. Received: 29 June 1998 / Accepted: 1st July 1998     

Nuclear fusion in charge-asymmetric muonic molecules

Nuclear fusion reactions in hydrogen-lithium muonic molecules, (where h=p,d,t) are considered and fusion rates from rotational states J=0 of the molecules are presented. Results obtained depend on the isotopic composition of the molecules and range between and . The upper limit for fusion rates from rotational states J=0 of hydrogen-helium muonic molecules, and , equal , is also found. Received: 4 December 1997 / Revised: 30 April 1998 / Accepted: 7 May 1998     

Application of B-splines finite basis sets to relativistic two-photon decay rates of level in hydrogenic ions

A theoretical study of the one- and two-photon spontaneous emission rates from the 2 s1/2 state of one-electron ions is presented. High-precision values of the relativistic emission rates for ions with nuclear charge Z up to 100 are obtained through the use of finite basis sets for the Dirac equation constructed from B-splines. Furthermore, we analyze the influence of the inclusion of quantum electrodynamics corrections in the initial and final state energies. Received: 6 January 1998 / Accepted: 31 March 1998     

CO2 laser-induced plasma CVD synthesis of diamond

2 laser maintenance of a stationary optical discharge in a gas stream, exhausting over a substrate into the air (laser plasmatron). Nano- and polycrystalline-diamond films were deposited on tungsten substrates from atmospheric-pressure Xe(Ar):H₂:CH₄ gas mixtures at flow rates of 2 ?/min. A 2.5-kW CO₂ laser focused beam produced plasma. The deposition area was about 1 cm² and growth rates were up to 30–50 μm/h. Peculiarities and advantages of laser plasmatrons are discussed. Received: 15 January 1998/Accepted: 16 January 1998     

Semiclassical approach to the three-body muon-transfer collisions

Muon-transfer rates in collisions of hydrogen-like atoms or with light nuclei t, ³He, ⁴He, ⁶Li or ⁷Li, are calculated in a semiclassical approximation to the Faddeev-Hahn equations. The two nuclei involved are treated classically, while the motion of the muon in their Coulomb field is considered from the quantum mechanical point of view. The experimentally observed strong dependence on the charge of the nuclei is reproduced. Received: 1st November 1997 / Revised: 26 March 1998 / Accepted: 18 August 1998     

MACRO, a large-area detector at the Gran Sasso Laboratory

Summary MACRO is a large-area detector to be installed in hall B of the Gran Sasso Laboratory. Making use of scintillation counters, plastic streamer tubes, and track-etch detectors, it is designed to search for superheavy magnetic monopoles beyond the Parker bound, high-energy gamma and neutrino cosmic sourcs, and, more in general, exotic phenomena in the cosmic radiation. MACTO is an acronym for Monopole, Astrophysics and Cosmic Ray Observatory. The present collaboration: Bari(**)C. De Marzo, O. Erriquez, N. Giglietto andF. Posa. Bologna(**):M. Attolini, F. Baldetti, G. Giacomelli, F. Grianti, A. Margiotta andP. Serra. Caltech:B. Barish, C. Lane andG. Liu. CERN:P. Musset, G. Poulard andH. Sletten. Drexel:R. Steinberg. Laboratori Nazionali di Frascati dell'INFN:G. Battistoni, H. Bilokon, C. Bloise, P. Campana, V. Chiarella, A. Ciocio, A. Grillo, E. Iarocci, A. Marini, A. Rindi, F. Ronga, L. Satta, M. Spinetti, L. Trasatti andV. Valente. Indiana:S. Ahlen, B. Brabson, R. Heinz, S. Mufson, H. Ogren andP. Smith. Michigan:J. Musser, J. Stone, L. Sulak andG. Tarlé. Pisa(**):C. Angelini, A. Baldini, C. Bemporad, A. Cnops, V. Flaminio, G. Giannini, R. Pazzi andB. Saitta. Roma(**):G. Auriemma, M. De Vincenzi, E. Lamanna, G. Martellotti, S. Petrera, L. Petrillo, P. Pistilli, G. Rosa, A. Sciubba andM. Severi. Texas A&M:R. Webb. Torino:M. Arneodo, G. Borreani, P. Giubellino, F. Marchetto, A. Marzari, S. Palestini andL. Ramello.Virginia Tech:S. Torres andP. Trower. (**) Sezione INFN e Dipartimento di Fisica dell'Università.     

Reaction and inelastic processes in the collision O () + O ()

A reduced dimensionality model is used to study the reaction OO O ₃ ( X1A1 ) + O( ³ P ) by means of time-dependent and time-independent quantum-mechanical methods. State-selected probabilities and rate constants are obtained for the reactive process as well as for the inelastic collision in which the vibrationally excited oxygen loses one or more quanta. It is found that the experimentally observed jump in depletion rates above a critical value of v could be partially explained by the vibrational relaxation rather than reaction. Reaction only becomes important for relatively high translational energies and therefore the calculated rates are too small at the temperatures of interest. It is concluded, however, that the reaction saddle point region in the potential energy surface plays a crucial role in the enhancement of vibrational relaxation. Received: 3 February 1998 / Revised: 27 March 1998 / Accepted: 15 May 1998     

Transition probabilities of forbidden lines in Pb I

Multiconfiguration Dirac-Fock as well as semiempirical calculations of decay rates of forbidden transitions within the ground 6s ² 6p ² configuration of neutral lead are reported and compared with relativistic Hartree-Fock results as well as with available experimental data. Received: 15 July 1998 / Received in final form: 15 October 1998     

Charge transfer from the ground state of muonic hydrogen to at room temperature

The present status of research of muon transfer from the ground state of muonic protium to ⁴He is reviewed. The analysis of a recent measurement in a triple gas mixture of H₂+⁴He+Ne at 15 bar and room temperature is presented and the result is compared to the existing experimental and theoretical rates. The average muon transfer rate from protium to ⁴He determined from all lifetime measurements is . Received: 22 January 1998 / Revised: 4 March 1998 / Accepted: 31 March 1998     

Identified charged particles in quark and gluon jets

A sample of 2.2 million hadronic Z decays, selected from the data recorded by the Delphi detector at Lep during 1994–1995 was used for an improved measurement of inclusive distributions of and p and their antiparticles in gluon and quark jets. The production spectra of the individual identified particles were found to be softer in gluon jets compared to quark jets, with a higher multiplicity in gluon jets as observed for inclusive charged particles. A significant proton enhancement in gluon jets is observed indicating that baryon production proceeds directly from colour objects. The maxima, , of the -distributions for kaons in gluon and quark jets are observed to be different. Received: 24 January 2000 / Revised version: 15 May 2000 / Published online: 8 September 2000     

Mechanism of thermoluminescence in AlN:O

Thermoluminescence of AlN: O in the 80–420 K temperature range is described. Two mechanisms are proposed for its explanation: the release of charges due to thermal ionization of the centres and migration of charges on the impurity centres. The probability of the occurrence of impurity migration is discussed.The authors are indebted to Dr. J.Pastrák, CSc for valuable discussions, stimulating hints and his interest in the present work. They are also grateful to Ing. J.Hejduk and his collaborators for preparation of samples and for chemical analyses.     

“Electron collisional excitation of argon-like Ni XI using the Breit-Pauli R-matrix method”

In a recent paper, Verma et al. [Eur. Phys. J. D 42, 235 (2007)] have reported results for energy levels, radiative rates, collision strengths, and effective collision strengths for transitions among the lowest 17 levels of the (1s²2s²2p⁶)3s²3p⁶, 3s²3p⁵3d and 3s3p⁶3d configurations of Ni xi. They adopted the civ3 and R-matrix codes for the generation of wavefunctions and the scattering process, respectively. In this paper, through two independent calculations performed with the fully relativistic darc (along with grasp) and fac codes, we demonstrate that their results are unreliable. New data are presented and their accuracy is assessed.     

Surface instability of a current carrying plasma under the influence of a high frequency electric field

Surface instability of a collisionless semi-infinite current carrying plasma is studied. The semi-infinite plasma bounded by a plane surface is under the influence of a high frequency (hf) field. There are two classes of surface modes. One is a normal extension of zero high frequency field and the other due entirely to the presence ofhf field. As expected, with the increase in thehf field, the growth rates of the surface instabilities decrease. There are regions defined by the electron drift velocityu where the unstable surface and bulk regions overlap. The interesting result is that unlike the bulk plasma, there is a stable region on theu-axis flanked by two unstable regions. The width of this stable region increases with the increase in the field strength.     

Wet bone ablation with mechanically Q-switched high-repetition-rate CO2 laser

2 laser using a miniature water spray is demonstrated. An ablation threshold of 1.4 J/cm², an optimal energy density of 9–10 J/cm², and a corresponding specific ablation energy of 25–30 J/mm³ are found for pig thighbone compacta at λ=9.57 μm and a beam waist diameter of 0.5 mm. The water spray alleviates tissue carbonization even at high laser pulse repetition rates and increases ablation efficiency. Received: 9 March 1998/Revised version: 6 July 1998     

ac anddc electroluminescence in CaS:Cu,Sm phosphors

Theac anddc electroluminescence in CaS:Cu, Sm have been investigated. The luminescence spectra show three peaks in the visible region. The brightness-voltage dependence satisfies the relationB=B ₀ exp (−b/V ^1/2) with two modes of variation. The nature of this dependence indc andac at different frequencies is discussed. The electroluminescence brightness also depends on the temperature of the phosphors and shows a peak around 80.0;C. The electroluminescence efficiency increases with applied voltage up to 2200 V and this dependence on V is explained on the basis of a transport process of the Schottky emission type.     

Microwave heating of electrons of a dense plasma column at frequencies higher than electron cyclotron frequency

In this experimental study the absorption of plasma waves, excited in a dense plasma column, was investigated and the localization of the regions of efficient heating of electrons were determined in a broad range of parameters: 1>_ce/>0·1, 0·3<n/n _UH <25, 10^–5<v/< <10^–3. The heating of electrons near the second electron cyclotron harmonic was investigated in greater detail.We are grateful to the members of the Staff of the Institute of Plasma Physics Drs. P.unka, R.Klí'ma, V.Kopecký, J.Musil for discussion of the results. We also thank Drs. J.Musil, F.áek for the help and advice in the early stages of experimental work during construction of different diagnostic devices. Our thanks are due to the director of the Institute Dr. J.Váa for encouraging support of this experimental program.     

The existence of (n, γf) process on235U nucleus and uranium X-ray yields

The measurement of X-rays emitted before the fission of²³⁵U induced by resonance neutrons is described. Preliminary results show the dependence of the X-ray yield on fission width _f. It is explained on the bases of the existence of the two-step (n,f) process. The estimate of the width of the (n,f) process is of the order of 4 MeV and the-transitions taking place before fission of²³⁶U compound nucleus are mostly of the M1 type.In conclusion the authors would like to express their gratitude to L. B.Pikelner for many useful discussions, to I. M.Salamattn and A.Mateeva for the programme supply of the experiment, V. G.Tisin, A. A.Bogdzel, Yu. I.Kolgin and N.Chikov for taking part in the different steps of the work. The authors are also grateful toYu. P.Popov and I.Wilhelm for taking interest in the work.     

Luminescent properties of A1N activated by europium

The concentration and temperature dependence of emission and excitation spectra was measured on powder A1NEu phosphors. It was shown that A1N: Eu has two luminescent modifications which depend on the activator concentration. At low activator concentration the wide emission band is found in the blue-green region, while at high concentration it is in green region. The excitation spectra of A1NEu consist of wide bands extended from 40×10³ cm^–1 to 22 × × 10³ cm^–1. The emission and excitation spectra are interpreted as transitions between energy levels of Eu²⁺ ions (4f⁷4f⁶ 5d transitions). The structure of the Eu²⁺ luminescent centres and the temperature dependence of luminescence are discussed.The authors thank Dr. M.Polcarová for the RTG measurements and Mrs. I.Míková for the spectral analysis of the A1N: Eu samples. The authors are also grateful to Prof. M.Trlifaj, Dr. J.Pastrák and Dr. J.Kubátová for valuable discussions.