Study of the process ee→ππγ in c.m. energy range 600–970 MeV at CMD-2

The cross section of the process e⁺e⁻→π⁰π⁰γ has been measured in the c.m. energy range 600–970 MeV with the CMD-2 detector. The following branching ratios have been determined:

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and

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. Evidence for the ρ⁰→f₀(600)γ decay has been obtained:

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. From a search for the process e⁺e⁻→ηπ⁰γ the following upper limit has been obtained: at 90% CL.     

Semileptonic decays B → (π, )eν in relativistic quark model

Quark model results for the B → π, decays are analysed, making use of the dispersion formulation of the model: The form factors at q² > 0 are expressed as relativistic invariant double spectral representation over invariant masses of the initial and final mesons through their light-cone wave functions. The dependence of the results on the quark model parameters is studied. For various versions of the quark model the ranges

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,

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, and Γ_L/Γ_T = 0.7 ± 0.08 are found. The effects of the constituent quark transition form factor are briefly discussed.     

Coupled Hamiltonians and three-dimensional short-range wetting transitions

We address three problems faced by effective interfacial Hamiltonian models of wetting based on a single collective coordinate

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(y) representing the position of the unbinding fluid interface. Problems (P1) and (P2) refer to the predictions of non-universality at the upper critical dimension d = 3 at critical and complete wetting, respectively, which are not borne out by Ising model simulation studies. (P3) relates to mean-field correlation function structure in the underlying continuum Landau model. Building on earlier work by Parry and Boulter we investigate the hypothesis that these concerns arise due to the coupling of order parameter fluctuations near the unbinding interface and wall. For quite general choices of collective coordinates X_i(y) we show that arbitrary two-field models H[X₁,X₂] can recover the required anomalous structure of mean-field correlation functions (P3). To go beyond mean-field theory we introduce a set

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of Hamiltonians based on proper collective coordinates s(y) near the wall which have both interfacial and spin-like components. We argue that an optimum model H[s,

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]

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, in which the degree of coupling is controlled by an angle like variable δ^*, best describes the non-universality of the Ising model and investigate its critical behaviour. For critical wetting the appropriate Ginzburg criterion shows that the true asymptotic critical regime for the local susceptibility χ₁ is dramatically reduced consistent with observations of mean-field behaviour in simulations (P1). For complete wetting the model yields a precise expression for the temperature dependence of the renormalised critical amplitude θ in good agreement with simulations (P2). We highlight the importance of a new wetting parameter which describes the physics that emerges due to the coupling effects.     

Decay of Bc (3S) → B D

The decay constant for the vector state of 3S-level in the heavy (

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c)-quarkonium is evaluated in the framework of sum rules for the mesonic currents. A scaling relation for the constants of vector quarkonia with different quark contents is derived. The numerical estime gives Γ (B^*+_c(3S) → B⁺ D⁰) = 90 ± 35 MeV.     

The ν1 and 2ν1 bands of DNSO

The infrared spectrum of DNSO has been recorded in the region of the N-D stretching fundamental vibration and of the first overtone. The results of the analysis are the following (in cm⁻¹):

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Synthesis and characterization of HgBa2Can−1CunO2n+2+δ (n = 1, 2, and 3)

We have successfully prepared the first three members of the mercury-based superconducting compounds Hg--- Ba₂Ca_n−1Cu_nO_2n+2+δ, namely Hg---1201, Hg---1212 and Hg---1223 with high purity and very good quality. T he influence of the synthesis parameters is studied in detail. Using the sealed quartz tube method, very simple procedures are found to ensure a 100% reproducibility of nearly 100% pure Hg---1201 and 85–90% Hg---1212 and Hg---1223. Oxygen annealing of the sample Hg---1201 at 300°C for 18 h results in an enhancement of its critical temperature up to 97 K. The symmetry of the first and second members is tetragonal with lattice parameters

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, respectively. X-ray diffraction lines of Hg---1223 can be indexed in a tetragonal cell with

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as well as in an orthorhombic cell with lattice parameters

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.     

The ν1 progression of HNSO in the ground state

The infrared spectrum of HNSO has been observed in the region of the N---H stretching fundamental and in those of the first and second overtones. The main results (in cm⁻¹) for the excited states are:

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Transition rates between negative-parity states in odd-mass gold nuclei

The half-lives of low-lying negative-parity states in ¹⁸⁵Au and ¹⁸⁷Au have been measured using mass-separated sources from the ISOCELE separator. The results,

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,

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,

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,

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,

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and

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, are discussed within the generalized particle-plus-asymmetric-rotor model, giving information on the structure of the states and on the nuclear-shape parameters.     

Four-dimensional high-branes as intersecting D-branes

We show that a class of external four-dimensional supersymmetric “high-branes”, i.e. string and domain wall solutions, can be interpreted as intersections of four ten-dimensional Dirichlet branes. These d = 4 solutions are related, via T-duality in ten dimensions, to the four-dimensional extermal Maxwell/scalar black holes that are characterized by a scalar coupling parameter a with a = 0,1

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, 1,

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.     

Electromagnetic transition probabilities in odd-mass erbium isotopes

Nanosecond lifetimes of ^{163, 165}Er excited states have been measured by means of delayed γ-γ coincidences in the (α, 2n) reaction on enriched Dy targets and delayed γ-ce coincidences in the ^163,165Tm decay. The following half-lives unknown so far were obtained:

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,

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for ¹⁶³Er levels as well as

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for ¹⁶⁵Er levels. From the investigation of γ-ray spectra populating the isomer, the rotational levels at

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in ¹⁶³Er could be confirmed as well as the level at 1078.1 keV with in ¹⁶⁵Er could be established. In order to obtain the wave functions of K-mixed nuclear levels, Coriolis coupling calculations taking into account the δN = 2 mixing in ¹⁶⁵Er are performed for^{161, 163, 165}Er including in the fit all the experimentally known band-head and rotational energies of positive-parity and negative-parity states, respectively. Partial γ-ray half-lives of E1, M1 and E2 transitions in ^{161,163,165,167,169}Er are deduced from the present results and earlier data. Electromagnetic transition probabilities are calculated within a non-adiabatic approach and compared with the experimental values. The influence of pairing correlations and configuration admixtures on the transition probabilities is demonstrated using hindrance factors and numerical values of transition matrix elements.     

Quantitative tests of color evaporation: charmonium production

The color evaporation model simply states that charmonium production is described by the same dynamics as D

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production, i.e., by the formation of a colored c

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pair. Its color happens to be bleached by soft final-state interactions. We show that the model gives a complete picture of charmonium production including low-energy production by proton, photon and antiproton beams, and high-energy production at the Tevatron and HERA.     

The O(g) coefficient in the thermodynamic potential of hot SU(N) gauge theories and MQCD

The non-perturbative input necessary for the determination of the

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(g⁶) part of the weak coupling expansion of the free energy density for SU(2) and SU(3) gauge theories is estimated. Although the perturbative information completing the contribution to this order is missing, we give arguments that the magnetic fluctuations are dominated by screened elementary magnetic gluons.     

A temperature programmed desorption study of the reaction of methylacetylene on Pt(111) and Sn/Pt(111) surface alloys

The adsorption and reaction of methylacetylene (H₃CC≡CH) on Pt(111) and the p(2×2) and

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surface alloys were investigated with temperature programmed desorption, Auger electron spectroscopy and low energy electron diffraction. Hydrogenation of methylacetylene to form propylene is the most favored reaction pathway on all three surfaces accounting for ca 20% of the adsorbed monolayer. Addition of Sn to the Pt(111) surface to form these two ordered surface alloys suppresses the decomposition of methylacetylene to surface carbon. The alloy surfaces also greatly increase the amount of reversibly adsorbed methylacetylene, from none on Pt(111) to 60% of the adsorbed layer on the

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surface alloy. Methylacetylene reaction also leads to a small amount of desorption of benzene, along with butane, butene, isobutylene and ethylene. There is some difference in the yield of these other reaction products depending the Sn concentration, with the (2×2)-Sn/Pt(111) surface alloy having the highest selectivity for these. Despite previous experiments showing cyclotrimerization of acetylene to form benzene on the Pt–Sn surface alloys, the analogous reaction of methylacetylene on the alloy surfaces was not observed, that is, cyclotrimerization of methylacetylene to form trimethylbenzene. It is proposed that this and the high yield of propylene is due to facile dehydrogenation of methylacetylene because of the relatively weak H–CH₂CCH bond compared to acetylene. The desorption of several C₄ hydrocarbon products at low (<170 K) temperature indicates that some minor pathway involving C–C bond breaking is possible on these surfaces.     

Bd,s– mass-differences from QCD spectral sum rules

We present the first QCD spectral sum rules analysis of the SU(3) breaking parameter ξ and an improved estimate of the renormalization group invariant (RGI) bag constant both entering into the B⁰_d,s– mass-differences. The averages of the results from the Laplace and moment sum rules to order α_s are and

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, in units where f_π=130.7 MeV. Combined with the experimental data on the mass-differences ΔM_d,s, one obtains the constraint on the CKM weak mixing angle |V_ts/V_td|²20.0(1.1). Alternatively, using the weak mixing angle from the analysis of the unitarity triangle and the data on ΔM_d, one predicts ΔM_s=18.6(2.2) ps⁻¹ in agreement with the present experimental lower bound and within the reach of Tevatron 2.     

The rate difference between the weak decays of t and in supersymmetry

We find that the CP-violating asymmetry

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at the one-loop order within the minimal supersymmetric extension of the standard model is of the order of few percent for maximal CP violation. It could be measured by considering the rate difference in the one-lepton events.     

Multi-instanton check of the relation between the prepotential F and the modulus u in N = 2 SUSY Yang-Mills theory

By examining multi-instantons in N = 2 supersymmetric SU(2) gauge theory, we derive, on very general grounds, and to all orders in the instanton number, a relationship between the prepotential

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(Φ), and the coordinate on the quantum moduli space u = TrΦ². This relation was previously obtained by Matone in the context of the explicit Seiberg-Witten low-energy solution of the model. Our findings can be viewed as a multi-instanton check of the proposed exact results in supersymmetric gauge theory.     

Measurement of Vcb from the decay process

A new precise measurement of |V_cb| and of the branching ratio BR ) has been performed using a sample of about 5000 semileptonic decays , selected by the DELPHI detector at LEP I by tagging the soft pion from D^*+→D⁰π⁺. The results are: V_cb=(39.0±1.5 (stat.)^+2.5_−2.6 (syst. exp.)±1.3 (syst. th.))×10⁻³,

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. The analytic dependencies of the differential cross-section and of the Isgur–Wise form factor as functions of the variable w=v_B⁰·v_D^* have also been obtained by unfolding the experimental resolution.     

Behaviour of gluons at high temperature

The screening of colour electric and magnetic fields and plasma oscillations in a high-temperature gluon plasma are investigated using linear response theory and self-consistent nonperturbative solutions to the Schwinger-Dyson equation. Static electric fields are screened, with

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. This result is proven to be gauge invariant in two ways: by computing π₀₀ in temporal axial, Coulomb and covariant gauges, and by computing the physical free energy of a heavy quark pair in the plasma in temporal axial gauge. To order g³ static magnetic fields are not screened.     

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.     

A precise study of the rotational spectrum of formaldehyde H2CO, H2CO, H2CO, H2CO

The rotational spectra of formaldehyde, H₂¹²C¹⁶O and its isotopic species H₂¹³C¹⁶O, H₂¹²C¹⁸O, and H₂¹³C¹⁸O have been investigated in the ground vibrational state in the frequency region between 8 and 460 GHz. For most cases in which measurements of the a-type R- and Q-branch transitions already existed the accuracy of the line position has been improved to about 10 kHz. For H₂¹²C¹⁶O and H₂¹³C¹⁶O a large number of ΔK_a = ±2 transitions were measured with similar accuracy. These new data when combined with all other available data and appropriate weightings lead to a set of ground state parameters which for the first time are compatible with infrared and ultraviolet data. The rotational constants (and 3σ standard deviations) obtained using Watson's A-reduced Hamiltonian are:

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