Optimization of C<Superscript>5+</Superscript> Balmer-α line intensity at 182 Å from laser-produced carbon plasma

Parametric dependence of the intensity of 182 Å Balmer-α line (C⁵⁺; n = 3 → 2), relevant to xuv soft X-ray lasing schemes, from laser-produced carbon plasma is studied in circular spot focusing geometry using a flat field grating spectrograph. The maximum spectral intensity for this line in space integrated mode occurred at a laser intensity of 1.2 × 10¹³ W cm^?2. At this laser intensity, the space resolved measurements show that the spectral intensity of this line peaks at ～1.5 mm from the target surface indicating the maximum population of C⁵⁺ ions (n = 3), at this distance. From a comparison of spatial intensity variation of this line with that of C⁵⁺ Ly-α (n = 2 → 1) line, it is inferred that n = 3 state of C⁵⁺ ions is predominantly populated through three-body recombination pumping of C⁶⁺ ions of the expanding plasma consistent with quantitative estimates on recombination rates of different processes.     

Excitation of Tm<Superscript>+3</Superscript> at a wavelength of 1064 nm

We report on the experimental study of the excitation mechanism of fluorescence in a 10000-ppm wt. Tm⁺³-doped ZBLAN fiber. Visible (at 453 nm and 480 nm) and near-infrared (∼800 nm) radiations were studied under excitation at 1.064 μm. The up-conversion mechanisms responsible are investigated, based on experimental data. The results show that the³ H ₄ and the ¹ D ₂ levels are predominantly excited by ion-ion cross-relaxation processes. Received: 19 August 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +41/31-631-3765, E-mail: Reda.El-Agmy@iap.unibe.ch     

Spin physics at e<Superscript>+</Superscript>e<Superscript>−</Superscript> colliders

A large number of measurement related to spin was performed during the last decade at the e ⁺ e ^? colliders LEP and SLC providing important information on the dynamics of high energy interactions. In this paper three main topics will be covered: the measurements of the electroweak couplings, the study of fragmentation dynamics and the search for physics beyond the Standard Model.     

Absolute cross section of p(<Superscript>7</Superscript>Be,γ)<Superscript>8</Superscript>B using a novel approach

The absolute cross section σ (E) of the radiative capture reaction p(⁷Be,γ)⁸B at the center-of-mass energy E = 992 keV has been measured using a radioactive ⁷Be ion beam and a windowless gas target system filled with H₂ gas. The ⁸B residual nuclides were detected with a recoil separator consisting of momentum and velocity filters and a ΔE-E detector telescope. The ⁸B yield was observed concurrently with the ⁷Be + p elastic scattering yield, relating σ(E) to the Rutherford scattering cross section. The resulting value, σ(E) = 0.41 ± 0.11 μb, leads to an S(E) factor at zero energy of S(0) = 16 ± 4 eV b, in fair agreement with recommended values. Received: 8 February 2000     

Absolute frequency measurement of the iodine-stabilized Ar<Superscript>+</Superscript> laser at 514.6 nm using a femtosecond optical frequency comb

The frequency of ¹²⁷I₂ hyperfine component a₃ of the P(13) 43-0 transition at 514.6 nm has been measured with an optical clockwork based on a femtosecond laser frequency comb generator. The measured frequency at an iodine pressure of 0.12 Pa is 67.3(0.75) kHz higher than the value of 582490603.38(15) MHz, adopted by the CIPM in 2003 [9] but is in a good agreement with the value measured by [29]. In our experiment we used H-maser reference frequency located at BNM-SYRTE Observatoire de Paris and transported to our laboratory by a 43 km optical fibre link. PACS 06.20.-f; 06.20.Fn; 06.30.Bp; 06.30.Ft     

Potential energy of <Superscript>∞</Superscript>H<Stack><Subscript>2</Subscript><Superscript>-</Superscript></Stack>(<Superscript>2</Superscript>∑<Stack><Subscript>u</Subscript><Superscript>+</Superscript></Stack> in the bound-state region

An accurate calculation of the lowest negative electronic state of H ₂ ^- (fixed nuclei) is reported using the CCSD(T) method and doubly augmented cc-pv5z basis set. Comparison has been made with the reference data by Senekowitsch et al. [Chem. Phys. Lett. 111 (1984) 211]. Owing to larger size of the basisset and inclusion of triple excitations, no vertical shift in this work is necessary to reproduce the asymptotics of H + H ^-. In addition, the effect of basis-set truncation is estimated, based on the complete-basis-set extrapolation method. The contribution of correlated electron-proton motion to the electron-energy curve for H₂ ^– dynamics is pointed out.Dedicated to Prof. Jií Horáek on the occasion of his 60th birthday.     

Bose-Einstein Correlations in W<Superscript>+</Superscript> W<Superscript>–</Superscript> events at LEP2

Bose-Einstein correlations (BEC) between final state particles in the reaction have been studied. Data corresponding to a total integrated luminosity of 550 pb^-1, recorded by the DELPHI detector at centre-of-mass energies ranging from 189 to 209 GeV, were analysed. An indication for inter-W BEC between like-sign particles has been found at the level of 2.4 standard deviations of the combined statistical and systematic uncertainties. Received: 11 January 2005, Revised: 13 July 2005, Published online: 13 September 2005 This paper is dedicated to the late Frans Verbeure. Frans was a very active member of the DELPHI collaboration and its QCD and WW working groups. The loss of Frans touched us all deeply.     

Narrow α + <Superscript>28</Superscript>Si elastic-scattering states at high excitation in <Superscript>32</Superscript>S

The excitation function and angular distributions of elastic α-particle scattering on ²⁸Si have been measured in the laboratory energy range 6-28 MeV using a backscattering technique on a thick target, yielding a continuous energy distribution. More than 200 narrow states are observed, with widths in the range ∼ 30-100 keV at excitation energies E ^* = 13-32 MeV. Angular distributions at backward angles were measured, and angular momentum values of more than 83 states have been deduced. The analysis gives spin-parities J ^π, α-partial widths Γ_α and reduced widths of the narrow high-lying resonant states in ³²S. The experimentally observed states display both the negative- and the positive-parity rotational-like sequences with seemingly no parity splitting, a finding which is at variance with most potential-model predictions. The deduced effective moment of inertia indicates a more extended structure than the ground-state configuration. The observed strength of each ℓ-value is analyzed in terms of an underlying split doorway state of Lorentzian form, which yields an interpretation as fragmented rotational α + ²⁸Si states. Received: 26 June 2000 / Accepted: 16 September 2002 / Published online: 4 February 2003 RID="a" ID="a"e-mail: kkallman@abo.fi RID="b" ID="b"Present address: Swedish Polytechnic, FIN-65200 Vasa, Finland. Communicated by D. Guerreau     

Two photons into π<Superscript>0</Superscript>π<Superscript>0</Superscript>

We perform a theoretical study based on dispersion relations of the reaction γγ → π ⁰ π ⁰ emphasizing the low-energy region. We discuss how the ƒ ⁰(980) signal emerges in γγ → ππ within the dispersive approach and how this fixes to a large extent the phase of the isoscalar S-wave γγ → ππ amplitude above the threshold. This allows us to make sharper predictions for the cross-section at lower energies and our results could then be used to distinguish between different ππ isoscalar S-wave parameterizations with the advent of new precise data on ππ → π ⁰ π ⁰. We compare our dispersive approach with an updated calculation employing the unitary chiral perturbation theory (U _gC PT). We also pay special attention to the role played by the σ-resonance in γγ → ππ and calculate its coupling and width to γγ, for which we obtain Γ(σ → γγ) = (1.68 ± 0.15) keV.     

<Superscript>16</Superscript>O/<Superscript>18</Superscript>O oxygen isotope exchange kinetics in MnO<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> as probed by <Superscript>55</Superscript>Mn NMR

The effect of the ¹⁶O ? ¹⁸O substitution in the coordination sphere of permanganate anion MnO ₄ ^? on the chemical shift of ⁵⁵Mn nuclei have been studied by ¹⁷O and ⁵⁵Mn NMR. Time constants τ _n,k of oxygen exchange in the water–permanganate anion system have been estimated. In nearly neutral solutions (pH ≈ 6.8–7.2), the oxygen exchange time is on the order of tens of hours. Bubbling gaseous HCl through this solution for a few seconds leads to the equilibrium distribution of oxygen isotopes in the manganese coordination sphere. The observed temperature dependences of isotope-induced ⁵⁵Mn NMR shifts in Mn¹⁶ O _44-n ¹⁸ O _n ^– (n = 0–4) have been treated as a result of rovibrational averaging of Mn–O bond lengths. The change in the Mn—O bond length in caused by the ¹⁶O → ¹⁸O isotope substitution is on the order of 10^–4 Å.     

The evaluation of the branching ratios of the decays φ(1020)→2π<Superscript>+</Superscript>2π<Superscript>−</Superscript>π<Superscript>0</Superscript>, π<Superscript>+</Superscript>π<Superscript>−</Superscript>3π<Superscript>0</Superscript>

Combining the Okubo-Zweig-Iizuka rule in the decay φ→ρπ→π⁺π^?π⁰ with the ρ→4π decay amplitudes, we calculate the φ→2π⁺2π^?π⁰ and φ→π⁺π^?3π⁰ ones. The partial widths of the above φ decays are evaluated, and the excitation curves in e⁺e^? annihilation are obtained, assuming reasonable particular relations among the parameters characterizing the anomalous terms of the HLS Lagrangian. The evaluated branching ratios B_φ→π⁺_π^?_3π⁰ ≈ 2 × 10^?7 and B_φ→2π⁺_2π^?_π⁰ ≈ 7 × 10^?7 are such that, with the luminosity L=500 pb^?1 attained at DAΦNE φ factory, one may already possess about 1685 events of the decays φ→5π.     

Hyperfine nuclear interaction at copper lattice sites of high-temperature superconductors studied by <Superscript>61</Superscript>Cu(<Superscript>61</Superscript>Ni) Mössbauer emission spectroscopy

Mössbauer emission spectroscopy on the ⁶¹Cu(⁶¹Ni) isotope has been used to determine the quadrupole coupling constant C(Ni) and magnetic induction B(Ni) for the ⁶¹Ni²⁺ probe at copper sites in Cu₂O, CuO, La_{2 ?x}Ba_xCuO₄, Nd_2?xCe_xCuO₄, RBa₂Cu₃O₆, and RBa₂Cu₃O₇ (R=Y, Nd, Gd, Yb). The compounds containing divalent copper were found to exhibit linear C(Ni) vs. C(Cu) and B(Ni) vs. B(Cu) relations [C(Cu) and B(Cu) are the quadrupole coupling constant and magnetic induction for the ⁶³Cu probe, respectively, found by NMR], which is interpreted as an argument for the copper being in divalent state. The deviation of the data points corresponding to the Cu(1) sites in RBa₂Cu₃O₆ and RBa₂Cu₃O₇ from the C(Ni) vs. C(Cu) straight line may be due either to the copper valence being other than 2+ (in the RBa₂Cu₃O₆ compounds) or to the principal axes of the total and valence electric field gradient being differently oriented (in the RBa₂Cu₃O₇ compounds).     

Exclusive ωπ<Superscript>0</Superscript> production with muons<Superscript>⋆</Superscript>

Using 160GeV muon scattering data collected with the COMPASS experiment at CERN, the exclusive production of ωπ⁰ via virtual photons was studied. Selective population of a peak around 1250MeV is observed. Possible contributions from spin-parity 1^- are searched for, inspecting decay angular correlations. In particular, the orientation of the ω decay plane may allow a distinction from the 1⁺ b ₁(1235) state. Our observation is compared with indications of a (1250) in annihilation and in γp . Original article based on material presented at HADRON 2007.     

<Superscript>57</Superscript>Fe emission Mössbauer spectroscopy following dilute implantation of <Superscript>57</Superscript>Mn into In <Subscript>2</Subscript>O<Subscript>3</Subscript>

Emission Mössbauer spectroscopy has been utilised to characterize dilute ⁵⁷Fe impurities in In ₂O₃ following implantation of ⁵⁷Mn (T _1/2 = 1.5 min.) at the ISOLDE facility at CERN. From stoichiometry considerations, one would expect Fe to adopt the valence state 3 + , substituting In ³⁺, however the spectra are dominated by spectral lines due to paramagnetic Fe²⁺. Using first principle calculations in the framework of density functional theory (DFT), the density of states of dilute Fe and the hyperfine parameters have been determined. The hybridization between the 3d-band of Fe and the 2p band of oxygen induces a spin-polarized hole on the O site close to the Fe site, which is found to be the cause of the Fe²⁺ state in In ₂O₃. Comparison of experimental data to calculated hyperfine parameters suggests that Fe predominantly enters the 8b site rather than the 24d site of the cation site in the Bixbyite structure of In ₂O₃. A gradual transition from an amorphous to a crystalline state is observed with increasing implantation/annealing temperature.     

Inversion of the <Emphasis Type="Italic">K</Emphasis><Superscript>π</Superscript>=1<Superscript>−</Superscript> states in <Superscript>156</Superscript>Gd and <Superscript>170</Superscript>Yb

For the ¹⁵⁶Gd and ¹⁷⁰Yb nuclei, where the inversion of levels in the K^π=1^? bands is observed, the energies of rotational levels are calculated on the basis of the Coriolis interaction model for the states of two bands whose quantum numbers are K^π=1^?. New 0^? levels are introduced in ¹⁷⁰Yb, and the structure of ¹⁷⁰Er is refined. The interaction parameters calculated for six nuclei are considered within the structure predicted by the quasiparticle-phonon model.     

Processes e<Superscript>+</Superscript>e<Superscript>−</Superscript> → π<Superscript>0</Superscript>(π<Superscript>0</Superscript>′) γ in extended NJL model

The processes of electron-positron annihilation into π⁰γ and into π′(1300)γ are considered within an extended NJL model. The intermediate vector mesons ρ ⁰, ω ρ′(1450), and ω(1420) are taken into account. The latter two mesons are treated as the first radial excited states. They are incorporated into the NJL model by means of a polynomial form factor. Numerical predictions for the cross-sections of these processes are received for the center-of-mass energies below 2 GeV. Our results for the π⁰γ production are in agreement with experimental data obtained in the energy region 600–1020 MeV.     

Decays of baryon resonances into ΛK<Superscript>+</Superscript>, ΣK<Superscript>+</Superscript> and Σ<Superscript>+</Superscript>K<Superscript>0</Superscript>

Cross-sections, beam asymmetries, and recoil polarisations for the reactions γp → K ⁺Λ;γp → K ⁺Σ⁰, and γp → K ⁰Σ⁺ have been measured by the SAPHIR, CLAS, and LEPS Collaborations with high statistics and good angular coverage for centre-of-mass energies between 1.6 and 2.3 GeV. The combined analysis of these data with data from π and η photoproduction reveals evidence for new baryon resonances in this energy region. A new P₁₁ state with mass 1840 MeV and width 140 MeV was observed contributing to most of the fitted reactions. The data demand the presence of two D₁₃ states at 1875 and, optimistically, at 2170 MeV.     

Diagnostics of an O<Subscript>2</Subscript>(<Superscript>1</Superscript>Δ) generator using multichannel recording of oxygen emission spectra

The concentrations of water vapor and O₂(¹Δ), as well as the temperature in the gas flow at the exit of a singlet oxygen generator, are determined using multichannel recording of the singlet oxygen emission spectrum in the bands at 634, 703, 762, and 1268 nm. The water vapor concentration is found from the intensity ratio of the 762-nm band, which corresponds to the ¹Σ → ³Σ transition of the oxygen molecule, and the dimole emission band at 634 nm. From the ratio of the integrated intensities of the bands at 634 and 1268 nm, the O₂(¹Δ) concentration is determined and it is shown that the yield of O₂(¹Δ) at the exit from the gas generator is about 52%. The temperature of the gas flow, determined by the rotational structure of the oxygen emission spectrum in the band at 762 nm, is about 300 K under the nominal conditions of the gas generator operation. The ratio of the photon fluxes in the 703 and 634nm bands of the O₂(¹Δ) dimole emission is 1.06. The temperature dependence of the dimole emission bandwidths is determined, which can be used for estimating the gas temperature at the exit of the O₂(¹Δ) generator.