Alpha-gamma decay studies of 255Rf, 251No and 247Fm

The decay of the isotopes ²⁵⁵Rf, ²⁵¹No and ²⁴⁷Fm produced in the reactions , and was investigated by means of α-γ spectroscopy. Previously observed γ transitions in coincidence with α decays of ²⁵⁵Rf were confirmed, their energies and line intensities were measured more precisely, and their multipolarities were determined as E1. In ²⁵¹No a new isomeric state at E ^* > 1700keV with a half-life of ≈ 2μs was identified. The decay of ²⁴⁷Fm was measured more precisely. A partial level scheme of the daughter nucleus ²⁴³Cf could be established.     

Study of spin and decay-plane correlations of W bosons in the e + e$^-\rightarrow$ W + W- process at LEP

Data collected at LEP at centre-of-mass energies GeV are used to study correlations of the spin of W bosons using events. Spin correlations are favoured by data, and found to agree with the Standard Model predictions. In addition, correlations between the W-boson decay planes are studied in and events. Decay-plane correlations are measured to be consistent with the Standard Model predictions.Received: 26 October 2004, Revised: 15 January 2005, Published online: 3 March 2005     

Alpha-gamma decay studies of 255No

The decay of ²⁵⁵No was investigated by means of α-γ spectroscopy. The isotope was produced in the reactions ²⁰⁸Pb(⁴⁸Ca, n)²⁵⁵No, , and $²³⁸U(²²Ne, 5n)²⁵⁵No$. Levels of the daughter nucleus ²⁵¹Fm were assigned by α-γ coincidence measurements and on the basis of systematics. Level energies were determined precisely using measured γ-rays. The results are compared with the known level schemes of the lighter isotones ²⁴⁷Cm and ²⁴⁹Cf as well as with data for ²⁵³No.     

Study of fusion cross-section in heavy-ion fusion-fission reactions at around fusion barrier energies using the Langevin dynamical approach

The neutron detector with ³He -filled counters placed in the focal plane of the VASSILISSA separator is used for measuring the average number and determining the multiplicity distribution of prompt neutrons from the spontaneous fission of heavy short-lived isotopes. The test reaction $\ensuremath \mathrm{{}^{48}Ca}+\mathrm{{}^{206}Pb}=2{\rm n}+\mathrm{{}^{252}No}$ is used for tuning the separator settings and calibrating the detector system with the spontaneous fission of the ²⁵²No . The average neutron number per ²⁵²No spontaneous fission event is as large as $\ensuremath \bar{\nu}=4.06 \pm 0.12$ . The short-lived heavy isotope ²⁴⁴Fm , produced in the complete fusion reaction ⁴⁰Ar + ²⁰⁶Pb , is investigated. The average number of neutrons per spontaneous fission of ²⁴⁴Fm from the experimental data ( $\ensuremath \bar{\nu}=3.3 \pm 0.3$ is determined for the first time.     

A measurement of semileptonic B decaysto narrow orbitally-excited charm mesons

The decay chain is identified in a sample of 3.9 million hadronic Z decays collected with the OPAL detector at LEP. The branching ratio BR is measured to be for the J ^P =1⁺ (D⁰ ₁) state. For decays into the J ^P =2⁺ (D₂ ^*0) state, an upper limit of 1.4 x 10^-3 is placed on the branching ratio at the 95% confidence level.Received: 20 December 2002, Revised: 15 April 2003, Published online: 12 September 2003     

Search for charged Higgs bosons at LEP in general two Higgs doublet models

A search for pair-produced charged Higgs bosons was performed in the data collected by the DELPHI detector at LEP II at centre-of-mass energies from 189 GeV to 209 GeV. Five different final states, , , , and were considered, accounting for the major expected decays in type I and type II Two Higgs Doublet Models. No significant excess of data compared to the expected Standard Model processes was observed. The existence of a charged Higgs boson with mass lower than 76.7 GeV/c² (type I) or 74.4 GeV/c² (type II) is excluded at the 95% confidence level, for a wide range of the model parameters. Model independent cross-section limits have also been calculated.Received: 30 September 2003, Revised: 12 February 2004, Published online: 8 April 2004     

Determination of the strong coupling αS from hadronic event shapes with \mathcal{O}(\ensuremath {\alpha _{\mathrm {S}}}^{3}) and resummed QCD predictions using JADE data

Event Shape Data from e⁺e^? annihilation into hadrons collected by the JADE experiment at centre-of-mass energies between 14 GeV and 44 GeV are used to determine the strong coupling α_S. QCD predictions complete to next-to-next-to-leading order (NNLO), alternatively combined with resummed next-to-leading-log-approximation (NNLO?+?NLLA) calculations, are used. The combined value from six different event shape observables at the six JADE centre-of-mass energies using the NNLO calculations is $$\begin{array}{rcl}\ensuremath {\ensuremath {\alpha _{\mathrm {S}}}(\ensuremath {m_{\ensuremath {\mathrm {Z^{0}}}}})}&=&0.1210\pm 0.0007\ensuremath {\mathrm {(stat.)}}\pm 0.0021\ensuremath {\mathrm {(exp.)}}\\[6pt]&&{}\pm 0.0044\ensuremath {\mathrm {(had.)}}\pm 0.0036\ensuremath {\mathrm {(theo.)}}\end{array}$$ and with the NNLO?+?NLLA calculations the combined value is $$\begin{array}{rcl}\ensuremath {\ensuremath {\alpha _{\mathrm {S}}}(\ensuremath {m_{\ensuremath {\mathrm {Z^{0}}}}})}&=&0.1172\pm 0.0006\ensuremath {\mathrm {(stat.)}}\pm 0.0020\ensuremath {\mathrm {(exp.)}}\\[6pt]&&{}\pm 0.0035\ensuremath {\mathrm {(had.)}}\pm 0.0030\ensuremath {\mathrm {(theo.)}}.\end{array}$$ The stability of the NNLO and NNLO?+?NLLA results with respect to missing higher order contributions, studied by variations of the renormalisation scale, is improved compared to previous results obtained with NLO?+?NLLA or with NLO predictions only. The observed energy dependence of α_S agrees with the QCD prediction of asymptotic freedom and excludes absence of running with 99% confidence level.     

Flavour-independent h<Superscript>0</Superscript>A<Superscript>0</Superscript> search and two Higgs doublet model interpretation of neutral Higgs boson searches at LEP

Upper limits on the cross-section of the pair-production process , assuming 100 branching fraction to hadrons, are derived from a new search for the hadrons final state, independently of the hadronic flavour of the decay products. This study, combined with previously published searches for the neutral Higgs bosons h⁰ and A⁰, is used to constrain the Type II Two Higgs Doublet Model (2HDM(II)) with no CP violation in the Higgs sector and no additional non-Standard Model particles besides the five Higgs bosons. The analysis combines LEP1 and LEP2 data collected with the OPAL detector up to the highest available centre-of-mass energies. The searches are sensitive to the and decay modes of the Higgs bosons. A benchmark scan of the 2HDM(II) parameter space is performed. Large regions of the 2HDM(II) parameter space explored are excluded at the 95% CL in the ( and planes, using both direct neutral Higgs boson searches and indirect limits derived from Standard Model high precision measurements. The region GeV and GeV is excluded at 95 % CL, independently of and for selected values of which are representative of a complete -scan.Received: 28 July 2004, Revised: 4 January 2005, Published online: 3 March 2005     

Ultrafast delocalization of hydrogen atoms in allene in intense laser fields

Ultrafast delocalization of hydrogen atoms in allene (CH₂=C=CH₂) induced by intense laser fields was investigated by the Coulomb explosion coincidence momentum imaging method. On the basis of the kinetic energy distributions of the fragment ions produced through the two three-body Coulomb explosion pathways, C₃H₄³⁺ ? H⁺ + CH⁺ + C₂H₂⁺\mathrm{C}_{3}\mathrm{H}_{4}^{3+} \rightarrow \mathrm{H}^{+} + \mathrm{CH}^{+} + \mathrm{C}_{2}\mathrm{H}_{2}^{+} and C₃H₄³⁺ ? H⁺ + C₂H⁺ +CH₂⁺\mathrm{C}_{3}\mathrm{H}_{4}^{3+} \rightarrow \mathrm{H}^{+} + \mathrm{C}_{2}\mathrm{H}^{+} +\mathrm{CH}_{2}^{+}, and the proton maps for both pathways, it was shown that the decomposition proceeds in a stepwise manner as well as in a concerted manner. The time scale of the hydrogen migration within an allene molecule was estimated to be ∼20 fs.     

Study of tau-pair production in photon-photon collisions at LEP and limits on the anomalous electromagnetic moments of the tau lepton

Tau-pair production in the process was studied using data collected by the DELPHI experiment at LEP2 during the years 1997 - 2000. The corresponding integrated luminosity is 650 pb^-1. The values of the cross-section obtained are found to be in agreement with QED predictions. Limits on the anomalous magnetic and electric dipole moments of the tau lepton are deduced.Received: 18 September 2003, Revised: 26 March 2004, Published online: 11 May 2004     

Critical Hardy–Lieb–Thirring Inequalities for Fourth-Order Operators in Low Dimensions

This paper considers Hardy–Lieb–Thirring inequalities for higher order differential operators. A result for general fourth-order operators on the half-line is developed, and the trace inequality

Time evolution of the Infrared Laser Induced Breakdown Spectroscopy of DNA bases Guanine and Adenine

Laser-Induced Breakdown Spectroscopy (LIBS) of DNA bases Guanine and Adenine was studied using a high-power CO₂ pulsed laser (λ=10.591 μm, τ _FWHM=64 ns and fluences ranging from 25 to 70 J/cm²). The strong emission of the adenine and guanine plasma, collected using a high-resolution spectrometer, at medium-vacuum conditions (4 Pa) and at 1 mm from the target, exhibits excited molecular bands of CN (B² Σ ⁺–X² Σ ⁺) and excited neutral H and ionized N⁺ and C⁺. The medium-weak emission is due to excited species C²⁺, C³⁺, N, O, O⁺, O²⁺ and molecular band systems of $\mathrm{C}_{2}(\mathrm{d}^{3}\varPi_{\mathrm{g}}\mbox{--}\mathrm{a}^{3}\varPi_{\mathrm{u}};\ \mathrm{D}^{1}\varSigma_{\mathrm{u}}^{+}\mbox{--}\mathrm{X}^{1}\varSigma_{\mathrm{g}}^{+})$ , OH(A² Σ ⁺–X² Π), NH(A³ Π–X³ Σ ^?), CH(A² Π–X² Π), $\mathrm{N}_{2}^{+}(\mathrm{B}^{2}\varSigma_{\mathrm{u}}^{+}\mbox{--} \mathrm{X}^{2}\varSigma_{\mathrm{g}}^{+})$ and N₂(C³ Π _u–B³ Π _g). We focus our attention on the temporal evolution of different atomic/ionic and molecular species. The velocity distributions for various (different) species were obtained from time-of-flight (TOF) measurements. Intensities of some lines from C⁺ were used for determining electron temperature and their Stark-broadened profiles were employed to estimate the temporal evolution of electron density.     

Loss of collectivity in 79Rb

High-spin states in ⁷⁹Rb were populated in the reaction at E(beam) = 60 MeV. The lifetimes of the excited states of the positive-parity yrast band and of the negative-parity band in ⁷⁹Rb were measured by the Doppler Shift Attenuation Method. The deduced transition quadrupole moments Q_t are found to have a decreasing trend with rotational frequency for both the bands, consistent with those found experimentally in neighbouring nuclei. An erratum to this article is available at .     

NLO contributions to <Emphasis Type="Italic">B</Emphasis>→<Emphasis Type="Italic">KK</Emphasis><Superscript>*</Superscript> decays in the pQCD approach

We calculate the important next-to-leading-order (NLO) contributions to the B→KK ^* decays from the vertex corrections, the quark loops, and the magnetic penguins in the perturbative QCD (pQCD) factorization approach. The pQCD predictions for the CP-averaged branching ratios are , , and Br(B ⁰→K ⁺ K ^*−+K ⁻ K ^*+)≈1.3×10⁻⁷, which agree well with both the experimental upper limits and the predictions based on the QCD factorization approach. Furthermore, the CP violating asymmetries of the considered decay modes are also evaluated. The NLO pQCD predictions for and decays are and .     

Polarized angular distributions in the decays of the 3D2 state of charmonium produced in unpolarized proton–antiproton annihilation

Using the helicity formalism, we calculate the combined angular distribution functions of the polarized gamma photons and electron in the triple cascade process $\bar{\mathrm{p}}\mathrm{p}\to{}^{3}\mathrm{D}_{\mathrm{2}}\to\chi_{\mathrm{\mathrm{{J}}}}+\gamma_{\mathrm{1}}\to(\psi +\gamma_{\mathrm{2}})+\gamma_{\mathrm{1}}\to(\mathrm{e}^{+}+\mathrm{e}^{-})+\gamma_{\mathrm{1}}+\gamma_{\mathrm{2}}\ (\mathrm{{J}}=0,1,2)$ , when $\bar{\mathrm{p}}$ and p are unpolarized. We also present the partially integrated angular distribution functions in different cases. Our results show that by measuring the two-particle angular distribution of γ ₁ and γ ₂ and that of γ ₂ and e^? with the polarization of either one of the two particles, one can determine the relative magnitudes as well as the relative phases of all the helicity amplitudes in the two radiative decay processes ³D₂→χ _J+γ ₁ and χ _J→ψ+γ ₂.     

Magnetocaloric properties of as-quenched Ni50.4Mn34.9In14.7 ferromagnetic shape memory alloy ribbons

The temperature dependences of magnetic entropy change and refrigerant capacity have been calculated for a maximum field change of Δ H=30 kOe in as-quenched ribbons of the ferromagnetic shape memory alloy Ni_50.4Mn_34.9In_14.7 around the structural reverse martensitic transformation and magnetic transition of austenite. The ribbons crystallize into a single-phase austenite with the L2₁-type crystal structure and Curie point of 284 K. At 262 K austenite starts its transformation into a 10-layered structurally modulated monoclinic martensite. The first- and second-order character of the structural and magnetic transitions was confirmed by the Arrott plot method. Despite the superior absolute value of the maximum magnetic entropy change obtained in the temperature interval where the reverse martensitic transformation occurs (|\varDelta S_M^max|=7.2 J kg^-1 K^-1)(|\varDelta S_{\mathrm{M}}^{\max}|=7.2\mbox{ J}\,\mbox{kg}^{-1}\,\mbox{K}^{-1}) with respect to that obtained around the ferromagnetic transition of austenite (|\varDelta S_M^max|=2.6 J kg^-1 K^-1)(|\varDelta S_{\mathrm{M}}^{\max}|=2.6\mbox{ J}\,\mbox{kg}^{-1}\,\mbox{K}^{-1}), the large average hysteretic losses due to the effect of the magnetic field on the phase transformation as well as the narrow thermal dependence of the magnetic entropy change make the temperature interval around the ferromagnetic transition of austenite of a higher effective refrigerant capacity (RC^magn_eff=95J kg^-1\mathrm{RC}^{\mathrm{magn}}_{\mathrm{eff}}=95\mbox{J}\,\mbox{kg}^{-1} versus RC^struct_eff=60J kg^-1)\mathrm{RC}^{\mathrm{struct}}_{\mathrm{eff}}=60\mbox{J}\,\mbox{kg}^{-1}).     

Isospin breaking in pion Compton scattering

Using chiral perturbation theory we calculate for pion Compton scattering the isospin-breaking effects induced by the difference between the charged and neutral pion mass. At one-loop order this correction is directly proportional to mp±2-mp02\ensuremath{m_{\pi^\pm}^2-m_{\pi^0}^2} and free of (electromagnetic) counterterm contributions. The differential cross-section for charged pion Compton scattering p-g? p-g\ensuremath{\pi^-\gamma \rightarrow \pi^-\gamma} gets affected (in backward directions) at the level of a few permille. At the same time the isospin-breaking correction leads to a small shift of the pion polarizabilities by d(ap- bp) @ 1.3 ·10-5\ensuremath{\delta(\alpha_\pi- \beta_\pi) \simeq 1.3 \cdot 10^{-5}} fm^3. In case of the low-energy gg? p0p0\ensuremath{\gamma\gamma \rightarrow \pi^0\pi^0} reaction isospin breaking manifests itself through a cusp effect at the p+p-\ensuremath{\pi^+\pi^-} threshold. We give an improved estimate for it based on the empirical p \pi p \pi -scattering length difference a0-a2\ensuremath{a_0-a_2} .     

Identification of \mathrm{\ensuremath J^{\pi} = 19/2^+} and \mathrm{\ensuremath 23/2^+} isomeric states in 127Sb

The nucleus $\ensuremath {\rm ^{127}Sb}$ , which is on the neutron-rich periphery of the $\ensuremath \beta$ -stability region, has been populated in complex nuclear reactions involving deep-inelastic and fusion-fission processes with $\ensuremath {\rm {}^{136}Xe}$ beams incident on thick targets. The previously known isomer at 2325 keV in $\ensuremath {\rm {}^{127}Sb}$ has been assigned spin and parity $\ensuremath 23/2^+$ , based on the measured $\ensuremath \gamma$ - $\ensuremath \gamma$ angular correlations and total internal conversion coefficients. The half-life has been determined to be 234(12) ns, somewhat longer than the value reported previously. The 2194 keV state has been assigned $\ensuremath J^{\pi} = 19/2^+$ and identified as an isomer with $\ensuremath T_{1/2} = 14(1) {\rm ns}$ , decaying by two $\ensuremath E2$ branches. The observed level energies and transition strengths are compared with the predictions of a shell model calculation. Two $\ensuremath 15/2^+$ states have been identified close in energy, and their properties are discussed in terms of mixing between vibrational and three-quasiparticle configurations.     

Radiative corrections to neutral pion-pair production

We calculate the one-photon loop radiative corrections to the neutral pion-pair photoproduction process p^-g ?p^-p⁰p⁰\pi^-\gamma \ensuremath \rightarrow\pi^-\pi^0\pi^0 . At leading order this reaction is governed by the chiral pion-pion interaction. Since the chiral p⁺ \pi^{+}_{} p^- \pi^{-}_{} ? \rightarrow p⁰ \pi^{0}_{} p⁰ \pi^{0}_{} contact vertex depends only on the final-state invariant mass it factors out of all photon loop diagrams. We give analytical expressions for the multiplicative correction factor R ~ a/2p\ensuremath R\sim \alpha/2\pi arising from eight classes of contributing one-photon loop diagrams. An electromagnetic counterterm has to be included in order to cancel the ultraviolet divergences generated by the photon loops. Infrared finiteness of the virtual radiative corrections is achieved (in the standard way) by including soft photon radiation below an energy cut-off l \lambda . The radiative corrections to the total cross-section vary between +2% and -2% for center-of-mass energies from threshold up to 7m_p\ensuremath 7m_{\pi} . We study also the radiative corrections to the p⁰p⁰\ensuremath \pi^0\pi^0 mass spectrum.