Complex CKM matrix, spontaneous CP violation and generalized symmetry

The multi-Higgs models having spontaneous CP violation (SPCPV) and natural flavor conservation (NFC) lead to a real CKM matrix V contradicting current evidence in favour of a complex V. This contradiction can be removed by using a generalized μ–τ (called 23) symmetry in place of the discrete symmetry conventionally used to obtain NFC. If the 23 symmetry is exact then the Higgs induced flavour changing neutral currents (FCNC) vanish as in the case of NFC. 23 breaking introduces SPCPV, a phase in V and suppressed FCNC among quarks. The FCNC couplings between i and j generations show a hierarchy with the result that the FCNC can have observable consequences in B mixing without conflicting with the mixing. Detailed fits to the quark masses and the CKM matrix are used to obtain the (complex) couplings and . Combined constraints from flavour and CP violations in the K, B_d, B_s, D mesons are analyzed within the model. They allow (i) relatively light Higgs, 100–150 GeV (ii) measurable extra contributions to the magnitudes and phases of the mixing amplitudes and (iii) the mixing at the current sensitivity level.     

Measurement of at

We present a measurement of the cross section for Z boson production times the branching fraction to tau lepton pairs in collisions at . The measurement is performed in the channel in which one tau lepton decays into a muon and neutrinos, and the other tau lepton decays hadronically or into an electron and neutrinos. The data sample corresponds to an integrated luminosity of 1.0 fb⁻¹ collected with the DØ detector at the Fermilab Tevatron Collider. The sample contains 1511 candidate events with an estimated 20% background from jets or muons misidentified as tau leptons. We obtain , which is consistent with the standard model prediction.     

Baryonic D decay and its implication

The channel is the only kinematically allowed baryonic D decay. It proceeds solely through the W-annihilation topology. Hence, a recent observation of this mode by CLEO will shed light on the dynamics of W-annihilation. At the short-distance level, its branching ratio is very small, of order 10⁻⁶, owing to chiral suppression. It receives long-distance contributions through final-state scattering of the leading tree and color-suppressed amplitudes. Assuming that the long-distance enhancement of W-annihilation in the baryonic D decay is similar to that in the mesonic decay, where the latter can be obtained from the analysis of the diagrammatic approach, we find that becomes visible. The observation of this baryonic D decay implies the dynamical enhancement of the W-annihilation topology in the decay.     

Fractional quasiexcitons in incompressible electron liquids

A new kind of many-body excitonic state composed of fractionally charged constituents is introduced. The constituents are a trion (X^-) embedded in an incompressible electron liquid and Laughlin quasiholes (QH's). Laughlin electron–trion correlations lead to an effective trion charge of -e/3. This many-body excitation is called “quasiexciton” and denoted by to distinguish it from a normal trion. The can bind one or two (e/3)-charged QH's, giving a neutral or a positive . The energy spectra and photoluminescence from radiative quasiexciton decay are studied numerically and interpreted using a generalized composite Fermion model of the e–X^- fluid.     

Structure of light hypernuclei

The structure of light hypernuclei with strangeness S=−1 and −2 is investigated with the microscopic cluster model and the Gaussian expansion method (GEM). We emphasize that the cluster picture as well as the mean-field picture is invaluable to understand the structure of Λ hypernuclei, Σ hypernuclei and double Λ hypernuclei. A variety of aspects of Λ hypernuclei is demonstrated through a systematic study of p-shell hypernuclei (,, , , , , ) and sd-shell ones (, ): for example, the appearance of genuine hypernuclear states with new spatial symmetry which cannot be seen in ordinary nuclei, the glue-like role of the Λ particle which shrinks the size of nuclear core and thus reduces the B(E2) value, and the halo and skin structures in and etc. The typical light hypernucleus is thoroughly investigated, including its production, structure and decay. Precise three-body and four-body calculations of , and using GEM provide important information on the spin structure of the underlying ΛN interaction, by comparing with recent experimental data from γ-ray hypernuclear spectroscopy. The Λ–Σ coupling effect is studied in and . The binding mechanism of is discussed together with the possible existence of , emphasizing the fact that the study of is useful for extracting information on the ΣN interaction differing from that from . A systematic study of double-Λ hypernuclei, constrained by the NAGARA data () within a four-body cluster model indicates that the recently observed Demachi–Yanagi event can be interpreted as the 2⁺ state of . The effect of hyperon mixing in and is investigated using one-boson-exchange potentials and quark-cluster-model interactions for the S=−2 sector. A close relation between nuclear deep hole states and hypernuclei is discussed, emphasizing the selection rule for fragmentation of the s-hole in light nuclei, which is promising for understanding the production mechanism of double-Λ and twin-Λ hypernuclei via Ξ-atomic capture.     

Observation of γ-delayed 3α breakup of the 15.11 and 12.71 MeV states in C

The reactions at 4.9 MeV and at 8.5 MeV have been used to investigate the γ decay of states in ¹²C. By measuring the four-body final state in complete kinematics we are able to detect γ transitions indirectly. We find γ transitions from the 15.11 MeV state in ¹²C to the 12.71, 11.83, 10.3 and 7.65 MeV states followed by their breakup into three α particles. The relative γ-ray branching ratios obtained are (1.2±0.3), (0.32±0.12), (1.4±0.2) and (4.4±0.8)%, respectively, with the remaining (92.7±1.0)% of the γ decays going to the bound states. We obtain Γ_α/Γ=(2.8±1.2)% for the isospin-forbidden α decay of the 15.11 MeV state. From the 12.71 MeV state we find γ transitions to the 10.3 and 7.65 MeV states. The relative γ-ray branching ratios are and , respectively, with the remaining of the γ decays going to the bound states. Finally, we discuss the relation between the β decay of ¹²N and ¹²B to states in ¹²C and the γ decay of the 15.11 MeV analog in ¹²C to the same states.     

Theoretical structure and surface energy of the reconstructed {01.2} form of calcite (CaCO3) crystal

Two different reconstructions of the (01.2) face (Ca or CO₃ terminated) of calcite (CaCO₃) were studied: (i) R1 reconstruction: the outermost layer is based on the [0 1 0] × 1/3[2 1 1] rectangular mesh, which is symmetrical with respect to the c glide plane of the crystal, thus fulfilling the 2D symmetry of the face and (ii) R2 reconstruction: the outermost layer is based on a lozenge shaped mesh that does not respect the 2D symmetry of the face.The , , and slabs geometry optimizations of calcite (CaCO₃) were performed either at DFT level or by using empirical potentials; the results obtained with these two different calculation methodologies are in good agreement. With respect to their arrangement in the bulk, the CO₃ groups of the outermost layer are significantly rotated about the crystallographic a-axis and about the normal to the 01.2 plane; further, the thickness of the outermost layer is significantly lower than that of the underneath ones.The surfaces energies (γ) at 0 K, for relaxed and unrelaxed , , and faces, were determined either at DFT level or by using empirical potentials. Independently of the method of calculation employed, the stability order of the relaxed faces is < < < . Concerning the unrelaxed faces, whose energies were evaluated by using empirical potentials only, the stability order is instead < < < ; such different ordering shows the importance of geometry relaxation in the calculation of the surface energy. The values of the relaxed surface energies are , , and erg/cm².     

Low mass dilepton production at ultrarelativistic energies

Dilepton production in pp and Au+Au nucleus–nucleus collisions at as well as in In+In and Pb+Au at is studied within the microscopic HSD transport approach. A comparison to the data from the PHENIX Collaboration at RHIC shows that standard in-medium effects of the ρ,ω vector mesons—compatible with the NA60 data for In+In at and the CERES data for Pb+Au at —do not explain the large enhancement observed in the invariant mass regime from 0.2 to 0.5 GeV in Au+Au collisions at relative to pp collisions.     

Search for the rare decays , , and

Rare decay modes , J/ψ→D⁻π⁺+c.c., and are searched for using events collected with the BESII detector at the BEPC. No signal above background is observed. We present upper limits on the branching fractions of , B(J/ψ→D⁻π⁺)<7.5×10⁻⁵, and at the 90% confidence level.     

Absolute photoionization cross sections with ultra-high energy resolution for Ar, Kr, Xe and N2 in inner-shell ionization regions

The high-resolution absolute photoionization cross sections for Ar, Kr, Xe and N₂ in the inner-shell ionization region have been measured using a multi-electrode ion chamber and monochromatized synchrotron radiation. The energy ranges of the incident photons for the target gases were as follows: Ar: 242–252 eV (2p Rydberg excitation), Kr: 1650–1770 eV (near the 2p ionization thresholds), Xe: 665–720 eV (near the 3d ionization thresholds) and 880–1010 eV (near the 3p ionization thresholds), N₂: 400–425 eV (N 1s excitation and ionization). It is the first time to measure the absolute ionization cross sections of Ar, Kr, Xe and N₂ over the present energy ranges with the energy resolution of over 10,000. The natural lifetime widths of , , and resonances for Ar, resonance for Xe, and resonance for N₂ have been obtained based on the cross sections determined. The ionization energies into the Ar⁺ (), Ar⁺ () and Xe⁺ () ionic states are also determined using the Rydberg formula.     

Scaling and long-range dependence in option pricing I: Pricing European option with transaction costs under the fractional Black–Scholes model

This paper deals with the problem of discrete time option pricing by the fractional Black–Scholes model with transaction costs. By a mean self-financing delta-hedging argument in a discrete time setting, a European call option pricing formula is obtained. The minimal price of an option under transaction costs is obtained as timestep , which can be used as the actual price of an option. In fact, is an adjustment to the volatility in the Black–Scholes formula by using the modified volatility to replace the volatility σ, where is the Hurst exponent, and k is a proportional transaction cost parameter. In addition, we also show that timestep and long-range dependence have a significant impact on option pricing.     

Single transverse-spin asymmetry in very forward and very backward neutral particle production for polarized proton collisions at

In the 2001–2002 running period of the Relativistic Heavy Ion Collider (RHIC), transversely polarized protons were accelerated to 100 GeV for the first time, with collisions at . We present results from this run for single transverse-spin asymmetries for inclusive production of neutral pions, photons and neutrons of the energy region 20–100 GeV for forward and backward production for angles between 0.3 mrad and 2.2 mrad with respect to the polarized proton direction. An asymmetry of was observed for forward neutron production, where the errors are statistical and systematic, and the scale error is from the beam polarization uncertainty. The forward photon and π⁰, and backward neutron, photon, and π⁰ asymmetries were consistent with zero. The large neutron asymmetry indicates a strong interference between a spin–flip amplitude, such as one pion exchange which dominates lower energy neutron production, and remaining spin–non-flip amplitudes such as reggeon exchange.     

Discrete anomalies of binary groups

We derive the discrete anomaly conditions for the binary tetrahedral group as well as the binary dihedral groups . The ambiguities of embedding these finite groups into SU(2) and SU(3) lead to various possible definitions of the discrete indices which enter the anomaly equations. We scrutinize the different choices and show that it is sufficient to consider one particular assignment for the discrete indices. Thus it is straightforward to determine whether or not a given model of flavor is discrete anomaly free.     

Tree-level contributions to the rare decays , , and in the Standard Model

The tree-level contributions to the rare decays , , and are analyzed and compared to those occurring in , , and . It is shown that these purely long-distance contributions, arising from the exchange of a charged lepton, can be significant in B⁺ decays for an intermediate τ, potentially blurring the distinction between the modes used to extract B⁺→τ⁺ν_τ and those used to probe the genuine short-distance and FCNC transitions. Numerically, the tree-level contributions are found to account for 98%, 12% and 14% of the total , , and rates, respectively.     

The polarised valence quark distribution from semi-inclusive DIS

The semi-inclusive difference asymmetry A^h+−h− for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002–2004 using a 160 GeV polarised muon beam scattered off a large polarised ⁶LiD target in the kinematic range 0.006<x<0.7 and 1<Q²<100 (GeV/c)². In leading order QCD (LO) the deuteron asymmetry A^h+−h− measures the valence quark polarisation and provides an evaluation of the first moment of Δu_v+Δd_v which is found to be equal to 0.40±0.07(stat.)±0.06(syst.) over the measured range of x at Q²=10 (GeV/c)². When combined with the first moment of previously measured on the same data, this result favours a non-symmetric polarisation of light quarks at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario .     

Influence of spin on the activation energies at

The activation energy Δ of the fractional quantum Hall state at constant filling factor and also at and has been measured as a function of the perpendicular magnetic field B while modulating the electron density via a top gate. At small magnetic fields we observe a linear increase of Δ with the magnetic field. The slope of Δ vs. B allows us to directly extract the composite fermion g-factor.     

Three equations of state for solids considering thermal effect

 The Einstein model to consider thermal effect in universal equations of state (UEOS) is modified. It is proposed that the zero-point vibration term should be deleted in a thermal UEOS, and the parameters cannot be directly taken as experimental data at a reference temperature, V_R, B_R, and , but their values at absolute zero temperature, V₀, B₀, and . An approach is proposed to solve V₀, B₀, and from V_R, B_R, and . The approaches are applied to three typical universal EOSs, including the Baonza, mGLJ and Morse EOSs. The numerical results show that the solved values of parameters are almost identical for different EOSs. And the thermo-physical properties predicted through different EOSs are almost identical at zero- and low-pressure conditions, once the same approach and input experimental data are used to solve the parameters. It is concluded that the prediction of thermo-physical properties at zero- and low-pressure conditions cannot be taken as the criteria to judge the applicability of a universal EOS.     

Step formation on hydrogen-etched 6H-SiC{0 0 0 1} surfaces

The formation of step bunches and/or facets on hydrogen-etched 6H-SiC(0 0 0 1) and () surfaces has been studied, using both nominally on-axis and intentionally miscut (i.e. vicinal) substrates. It is found that small miscuts on the (0 0 0 1) surface produce full unit-cell high steps, while half unit-cell high steps are observed on the () surface. The observed step normal direction is found to be for both surfaces. Hence, for intentionally miscut material, a miscut oriented towards this direction produces much better order in the step array compared to a miscut oriented towards a direction. For (0 0 0 1) vicinal surfaces that are miscut towards the direction, the formation of surface ripples is observed for 3° miscut and the development of small facets (nanofacets) is found for higher miscut angles. Much less faceting is observed on miscut () surfaces. Additionally, the (0 0 01) surface is found to have a much larger spatial anisotropy in step energies than the () surface.     

Observation of the state of CH2 by optical–optical double resonance

We report the observation of levels in the state of CH₂ via optical–optical double resonance spectroscopy. Direct transitions between the lowest singlet state and the state are allowed by symmetry, but weak because they correspond to a two electron excitation in the single configuration approximation to the electronic wavefunction. The observed transitions involve sequential single photon absorptions at visible and near infrared wavelengths using state intermediate levels. Recent ab initio results (S.N. Yurchenko et al., J. Mol. Spectrosc. 208 (2001), 136) predicted the positions of some of the levels which are confirmed by the present results. The new spectra provide accurate energies for rotational levels in the , l = 0 level of the state.