ZZ production in e+ e- int eractions at $\sqrt{s} =$ 183-209 G eV

Measurements of on-shell ZZ production are described, using data from the DELPHI experiment at LEP in e ⁺ e ^- collisions at centre-of-mass energies between 183 and 209 GeV, corresponding to an integrated luminosity of about 665 pb^-1. Results obtained in each of the final states , , , , , l ⁺ l ^- l ⁺ l ^-, and (with ) are presented. The measured production cross-sections are consistent with the Standard Model expectations. These results update and supersede those already published at 183 and 189 GeV.Received: 3 March 2002, Revised: 28 May 2003, Published online: 19 September 2003     

The \pi h_{11/2}^{-1}\nu i_{13/2}^{-2} three-hole isomeric state and octupole core excitation in the 205 Tl nucleus

New high-spin states were identified in the ²⁰⁵Tl isotope produced in deep-inelastic heavy-ion reactions. The expected 29/2 ⁺ yrast state and 35/2^- isomeric state with 235 ns half-life were located above the 2.6 s isomer known from previous studies. Above this isomer a 7092 keV level was interpreted as a 41/2 ⁺ state arising from the coupling of the octupole vibration of the ²⁰⁸Pb core with the three-hole structure of the 35/2^- isomer.Received: 20 January 2003, Revised: 10 March 2003, Published online: 2 March 2004PACS: 21.60.Cs Shell model - 23.20.Lv Gamma transitions and level energies - 27.80. + w - 25.70.Lm Strongly damped collisions     

Optical manipulation of long-range interactions at the 3s + 3p asymptote of $\mathsf{Na_2}$

We investigate the influence of a laser field, which is near-resonant to the atomic sodium 3²P_1/2 3²D_3/2 transition, on the last bound levels of the A state in Na₂. In a molecular beam experiment level shifts up to 100 MHz and light induced line broadenings were observed using an optical double resonance excitation scheme. Moreover, the coupling laser can reduce the number of bound levels of the A state by one or more units, which effectively means that in the picture of a collision of a 3²S_1/2 and a 3²P_1/2-atom the scattering phase is altered by more than . The observed effects are interpreted as light induced couplings of the A state, which correlates to the 3s _1/2 + 3p _1/2 asymptote, to the and states at the 3s _1/2 + 3d _3/2 asymptote. We performed multi-channel calculations, applying the mapped Fourier grid method, which reproduce our experimentally observed level shifts well.Received: 7 October 2003, Published online: 21 November 2003PACS:   34.50.Rk Laser-modified scattering and reactions - 33.80.-b Photon interactions with molecules - 42.62.Fi Laser spectroscopy     

Configuration-dependent bands in 169Re

High-spin states in ¹⁶⁹Re were studied and resulted in the identification of a strongly coupled band based on the 9/2^-[514] Nilsson state and a decoupled band built on the h _9/2 1/2^-[541] intruder proton orbit. The cranked-shell-model calculations present configuration-dependent deformations that can explain the different band crossing frequencies. The 9/2^-[514] band in ¹⁶⁹Re shows the largest signature splitting at low spin among the known odd-mass Re isotopes. After the alignment of a pair of i _13/2 neutrons, the phase of the splitting is inverted with a significantly reduced amplitude. For the 9/2^-[514] bands in light odd-A Re isotopes, the signature splitting of the Routhians and its relation with the signature dependence of M1 transition matrix elements are investigated in connection with the deviation of nuclear shape from axial symmetry, suggesting an appreciable negative deformation for the very neutron-deficient odd-A Re isotopes. Additionally, a three-quasipariticle band was observed and assigned to be built likely on the configuration.Received: 9 May 2003, Published online: 18 December 2003PACS: 21.10.Re Collective levels - 23.20.-g Electromagnetic transitions - 23.20.Lv transitions and level energies - 27.70. + q      

The $\eta_{c}(2980)$ formation in two-photon collisions at LEP energies

production in interactions has been detected via its decays into ,K ⁺ K ^- K ⁺ K ^- and in the data taken with the DELPHI detector at LEP1 and LEP2 energies. The two-photon radiative width averaged over all observed decay channels is = 13.9 2.0 (stat.) 1.4(syst.) 2.7 (BR) keV. No direct decay channel has been observed. An upper limit < 5.5 keV at 95% confidence level has been evaluated for this decay mode.Received: 3 July 2003, Published online: 7 November 2003     

M easur em ent of th e $\mathit{H Z\gamma}$ coupling at th e futur e lin ear e+ e- collid er

We examine the prospects for measuring the coupling of a standard model-like Higgs boson with a mass between 120 and 160 GeV at the future TESLA linear e ⁺ e ^- collider, assuming an integrated luminosity of 1 ab^-1 and a center-of-mass energy of 500 GeV. We consider the Higgs boson produced in association with via the W W fusion reaction , followed by the rare decay into a Z boson and a photon, . Accounting for all main background contributions, a precision of 27% can be achieved in unpolarized e ⁺ e ^- collisions for M _H = 140 GeV. With appropriate initial state polarisations BF( )/BF( ), or the precisions on the partial width, can be improved to 17% and provide valuable information on the coupling. For M _H = 120 and 160 GeV, the small significance of the signals in unpolarized collisions sets upper limits of 79% respectively 72% at 90% confidence level on the branching fraction.Received: 5 March 2003, Revised: 14 July 2003, Published online: 5 September 2003     

The photoassociative spectroscopy, photoassociative molecule formation, and trapping of ultracold \mathsf{^{39}K^{85}Rb}

We have observed the photoassociative spectra of colliding ultracold ³⁹K and ⁸⁵Rb atoms to produce KRb* in all eight bound electronic states correlating with the ³⁹K (4s) + ⁸⁵Rb(5p _1/2 and 5p _3/2) asymptotes. These electronically excited KRb* ultracold molecules are detected after their radiative decay to the metastable triplet (a state and (in some cases) the singlet (X ground state. The triplet (a ultracold molecules are detected by two-photon ionization at 602.5 nm to form KRb ⁺ , followed by time-of-flight mass spectroscopy. We are able to assign a majority of the spectrum to three states (2(0 ⁺ ), 2(0^-), 2(1)) in a lower triad of states with similar C ₆ values correlating to the K(4s) + Rb (5p _1/2) asymptote; and to five states in an upper triad of three states (3(0 ⁺ ), 3(0^-), 3(1)) and a dyad of two states (4(1), 1(2)), with one set of similar C ₆ values within the upper triad and a different set of similar C ₆ values within the dyad. We are also able to make connection with the short-range spectra of Kasahara et al. [J. Chem. Phys. 111, 8857 (1999)], identifying three of our levels as v = 61, 62 and 63 of the 1 4(1) state they observed. We also argue that ultracold photoassociation to levels between the K(4s) + Rb (5p _3/2) and K(4s) + Rb (5p _1/2) asymptotes may be weakly or strongly predissociated and therefore difficult to observe by ionization of a (or X molecules; we do know from Kasahara et al. that levels of the 1 4(1) and 2 5(1) states in the intra-asymptote region are predissociated. A small fraction ( 1/3) of the triplet (a ultracold molecules formed are trapped in the weak magnetic field of our magneto-optical trap (MOT).Received: 22 September 2004, Published online: 23 November 2004PACS: 33.20.Fb Raman and Rayleigh spectra (including optical scattering) - 34.20.Cf Interatomic potentials and forces - 33.80.Ps Optical cooling of molecules; trapping     

NQR study of phase transitions in CH$\mathsf{_3}$HgX (X = Cl,Br, I)

The temperature dependence of halogen nuclear quadrupole resonance (NQR) in the series CH₃HgX (X = Cl, Br, I) is measured with special emphasis on the structural phase transitions at T _c = 162 K, 310 K, and 400 K, respectively. In the temperature dependences of NQR frequencies similarities are observed and discussed in relation with the structure and thermal vibrations on both sides of the phase transition. On the basis of known data a mechanism for the three analogous phase transitions is proposed. The chlorine spin-lattice relaxation behaviour in CH₃HgCl can be explained by a competition of fast thermal fluctuations of MMX molecules across the high temperature (h.t.) mirror plane and of infrequent transitions to the other equivalent fluctuation mode across the orthogonal h.t. mirror plane. Proton high temperature relaxation is probably dominated by the same slow motion, but at lower temperatures some other mechanism involving magnetic coupling prevails.Received: 23 June 2003, Published online: 15 October 2003PACS: 64.70.Kb Solid-solid transitions - 61.66.Fn Inorganic compounds - 76.60.Gv Quadrupole resonanceSupported in part by the Ministry of Education, Science and Sport, Republic of Slovenia     

New gauge bosons from the littlest Higgs modeland the process $e^{ + }e^{-}\rightarrow t\bar{t}$

In the context of the littlest Higgs (LH) model, we study the process . We find that the new gauge bosons Z _H and B _H can produce significant correction effects on this process, which can be further enhanced by suitably polarized beams. In most of the parameter space preferred by the electroweak precision data, the absolute value of the relative correction parameter is larger than 5 %. As long as and the absolute value of the relative correction parameter is larger than . With reasonable values of the parameters of the LH model, the possible signals of the new gauge bosons B _H and Z _H can be detected via the process in the future LC experiments with the CM energy . B _H exchange and Z _H exchange can generate significantly corrections to the forward-backward asymmetry only in a small part of the parameter space.Received: 29 October 2004, Revised: 29 November 2004, Published online: 15 February 2005     

Hard-to-reach nuclei studied with deep-inelastic heavy-ion reactions

Spectroscopic studies performed with deep-inelastic heavy-ion reactions are reviewed for two regions of neutron-rich nuclei. The identification of isomers in nearly complete series of Sn isotopes and the resulting systematic of B(E2) values for isomeric transitions is presented and followed by the discussion of shell model states studied in neutron-rich Te isotopes including the new four neutron-hole isomers identified in ¹³⁰Te. Yrast spectroscopy studies of nuclei from the doubly magic ²⁰⁸Pb region are described by outlining the highest spin states observed in the ²⁰⁸Pb core nucleus. The E3 transitions observed abundantly in yrast decays are discussed within the framework of particle-octupole vibration coupling and the validity of a simple rule connecting energy shifts of octupole states built on one-particle states with the ones observed for two-particle states is demonstrated.Received: 15 January 2003, Published online: 23 March 2004PACS: 21.60.Cs Shell model - 23.20.Lv transitions and level energies - 27.60. + j - 27.80. + w      

Spin-Peierls lattice fluctuations and disorders in CuGeO$_\mathsf{3}$ and its solid solutions

The inorganic quasi-one dimensional (1D) S = 1/2 antiferromagnetic (AF) system CuGeO₃ undergoes a 2nd order spin-Peierls (SP) phase transition at T _SP = 14.2 K. In this study we present an X-ray synchrotron radiation investigation which confirms that the SP instability is announced by an important regime of pretransitional structural fluctuations which have been detected until 36 K. Furthermore we show that these fluctuations are 1D above 24 K, a feature expected for a structural instability triggered by the Cu^{2 +} chains of spin 1/2. By extrapolating the thermal dependence of the correlation length in the chain direction, we show that formation of singlet dimers begins at about 50 K, a temperature that we identify as the mean field temperature of the SP chain. The critical nature of the pretransitional fluctuations does not change when low amounts (<1%) of non-magnetic dopants substitute either the Cu site (case of Zn and Mg) or the Ge site (case of Si and Al) of CuGeO₃. However, the spatial extension of the fluctuations is considerably reduced when the magnetic dopant Ni substitutes the Cu site. In the SP ground state of doped materials we have been able to detect, in addition to the superlattice SP reflections previously observed, a very weak anisotropic diffuse scattering. We give evidences that this scattering originates from dopant-induced quasi-1D domains in which the dimerisation is perturbed. If we assume that each domain is limited by a soliton-antisoliton pair, pinned either on the substituent of the Cu site or by the deformation field induced by the substituent of the Ge site, we deduce that the soliton and antisoliton are separated by a distance of about Å, and that the soliton half width amounts to about Å. With these numbers we are able to account for the rate of decrease of T _SP as a function of the dopant concentration, and to deduce the critical concentration above which the long-range SP order vanishes. The overall size of the perturbed domains thus obtained, Å, is comparable with the size of the magnetic inhomogeneities determined by muon spin spectroscopy in the AF phase of doped CuGeO₃.Received: 22 December 2003, Published online: 8 June 2004PACS: 71.27. + a Strongly correlated electron systems; heavy fermions - 61.72.Dd Experimental determination of defects by diffraction and scattering - 75.45. + j Macroscopic quantum phenomena in magnetic systems     

High resolution multiphoton ionization and dissociation of acetone via $\mathsf{3s\leftarrow n}$ Rydberg transitions

Measurements of multiphoton ionization and dissociation of acetone are reported in the wavelength range 582.60-585.80 nm at photon energy resolution of 0.3 cm^-1. To our knowledge there are not available results of (3 + 2) REMPI on acetone at 0.01 nm in this region. The experiments were performed using an Nd: YAG-OPO (optical parametric oscillator) laser system coupled to time-of-flight mass spectrometer. The ion yield and the single ion channel are presented. The high-resolution three-photon resonance multiphoton spectrum of the acetone Rydberg transition is also reported. The experimental results show three dissociation channels of the acetone ion, leading to the products: (CH₃CO ⁺ ), (CH₃ ⁺ ) and (COH ⁺ ); the channel CH₃COCH ₃CO ⁺ + CH₃ being the most favored. The acetone and acetyl ions are observed in all wavelength range investigated. In addition, we have measured the origin of the and transitions, and vibrational bands of the 3s state.Received: 21 March 2004, Published online: 11 May 2004PACS: 33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) - 33.15.Ta Mass spectra - 33.80.Gj Diffuse spectra; predissociation, photodissociation     

Study of Z pair production and anomalous couplingsin e + e- collisions at $\sqrt{s}$ between 190 GeV and 209 GeV

A study of Z-boson pair production in e ⁺ e^- annihilation at center-of-mass energies between 190 GeV and 209 GeV is reported. Final states containing only leptons, ( and ), quark and lepton pairs, ( , ) and only hadrons ( ) are considered. In all states with at least one Z boson decaying hadronically, lifetime, lepton and event-shape tags are used to separate pairs from final states. Limits on anomalous ZZ and ZZZ couplings are derived from the measured cross sections and from event kinematics using an optimal observable method. Limits on low scale gravity with large extra dimensions are derived from the cross sections and their dependence on polar angle.Received: 14 July 2003, Published online: 18 December 2003     

${K{\overline K}}$ photoproduction and S- P-wave interference

Results of a new analysis of the K ⁺ K^- photoproduction at two photon energies, and , with a particular emphasis on the S-wave production are presented. We show that the proper treatment of all the helicity components of the S- and P-waves enables one to eliminate the reported discrepancies in the extraction of the S-wave photoproduction cross section from the experimental data.Received: 28 August 2003, Revised: 3 February 2004, Published online: 23 March 2004     

Search for pair-produced leptoquarks in e + e- interactions at $\sqrt{s} \simeq 189\text{--}209$ GeV

A search for pair-produced leptoquarks is performed using collision events collected by the OPAL detector at LEP at centre-of-mass energies between 189 and 209 GeV. The data sample corresponds to a total integrated luminosity of 596 pb^-1. The leptoquarks are assumed to be produced via couplings to the photon and the Z⁰. For a given search channel only leptoquark decays involving a single lepton generation are considered. No evidence for leptoquark pair production is observed. Lower limits on masses for scalar and vector leptoquarks are calculated. The results improve most of the LEP limits derived from previous searches for the pair production process by 10-25 GeV, depending on the leptoquark quantum numbers.Received: 6 May 2003, Published online: 24 October 2003     

Stiffness exponents for lattice spin glasses in dimensions $\mathsf{d = 3,\ldots,6}$

The stiffness exponents in the glass phase for lattice spin glasses in dimensions are determined. To this end, we consider bond-diluted lattices near the T = 0 glass transition point p^*. This transition for discrete bond distributions occurs just above the bond percolation point p_c in each dimension. Numerics suggests that both points, p_c and p^*, seem to share the same 1/d-expansion, at least for several leading orders, each starting with 1/(2d). Hence, these lattice graphs have average connectivities of near p^* and exact graph-reduction methods become very effective in eliminating recursively all spins of connectivity , allowing the treatment of lattices of lengths up to L = 30 and with up to 10⁵-10⁶ spins. Using finite-size scaling, data for the defect energy width over a range of p > p^* in each dimension can be combined to reach scaling regimes of about one decade in the scaling variable . Accordingly, unprecedented accuracy is obtained for the stiffness exponents compared to undiluted lattices (p = 1), where scaling is far more limited. Surprisingly, scaling corrections typically are more benign for diluted lattices. We find in for the stiffness exponents y₃ = 0.24(1), y₄ = 0.61(2), y₅ = 0.88(5), and y₆ = 1.1(1).Received: 29 October 2003, Published online: 20 April 2004PACS: 05.50. + q Lattice theory and statistics (Ising, Potts, etc.) - 64.60.Cn Order-disorder transformations; statistical mechanics of model systems - 75.10.Nr Spin-glass and other random models - 02.60.Pn Numerical optimization     

Delayed crossing in the \pi h_{9/2} 1/2-[541] band of 173 Lu

High-spin states in the odd-proton nucleus ¹⁷³Lu have been populated in a ¹⁷⁰Er(⁷Li,4n) reaction and the emitted -radiation was detected with the GASP array. The favoured and unfavoured sequences of the band have been considerably extended. The favoured sequence does not show any indication of a band crossing up to a rotational frequency of 0.45 MeV. This is the largest crossing frequency ever observed for 1/2^- [541] bands of odd-proton nuclei with and . Previous Cranked Shell Model (CSM) calculations underestimate the crossing frequency by 100 keV.Received: 19 May 2003, Published online: 11 November 2003PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 21.10.Re Collective levels - 23.20.Lv transitions and level energies - 27.70. + q      

Optical evidence for the proximity to a spin-density-wave metallic state in $\mathsf{Na_{0.7}CoO_2}$

We present the optical properties of Na_0.7CoO₂ single crystals, measured over a broad spectral range as a function of temperature (T). The capability to cover the energy range from the far-infrared up to the ultraviolet allows us to perform reliable Kramers-Kronig transformation, in order to obtain the absorption spectrum (i.e., the complex optical conductivity). To the complex optical conductivity we apply the generalized Drude model, extracting the frequency dependence of the scattering rate ( ) and effective mass (m ^*) of the itinerant charge carriers. We find that at low temperatures and for . This suggests that Na_0.7CoO₂ is at the verge of a spin-density-wave metallic phase.Received: 6 August 2004, Published online: 9 September 2004PACS: 78.20.-e Optical properties of bulk materials and thin films - 74.70.Dd Ternary, quaternary and multinary compounds (including Chevrel phases, borocarbides, etc.) - 75.30.Fv Spin-density waves