Momentum-space optical model for K+-nucleus scattering

The momentum-space optical model of K⁺-nucleus scattering is analyzed and comparison with other conventional models is shown. The model is based on the multiple scattering formalism in which the optimal factorization approximation is used. Off-energy-shell extension of the elementary K⁺-nucleon amplitude is neglected which reduces non localities in the optical potential. Predictions of the model are sensitive to the definition of the K⁺-nucleon energy (energy shifts) but they are independent (1–2%) of a particular form of the covariant K⁺-nucleus scattering equation (relativistic Lippmann-Schwinger, Gross, Erkelenz-Holinde). The Coulomb distortion in the total cross section is important for²⁸Si and⁴⁰Ca at low momenta (≈10%). Off-energy-shell effects in the optical potential are discussed too. Results for the total and reaction cross sections are systematically below the data. The reaction cross sections are in a larger disagreement with the data than the total cross sections. This work was supported by grants ASCR A1048703 (P. Bydžovsky) and GACR 202/96/1566 (M. Sotona).     

(K)-nucleus dynamics: from quasibound states to kaon condensation

Coupled-channel (K)N dynamics near threshold and its repercussions in few-body (K)-nuclear systems are briefly reviewed, highlighting studies of a K-pp quasibound state. In heavier nuclei, the extension of mean-field calculations to multi-(K) nuclear and hypernuclear quasibound states is discussed. It is concluded that strangeness in finite self-bound systems is realized through hyperons, with no room for kaon condensation.     

Overview of \boldsymbol{\bar{K} N} and \boldsymbol{\bar{K}}-nucleus dynamics

The main features of coupled-channel ${\bar K}N$ dynamics near threshold and its repercussions in few-body $\bar K$ -nuclear systems are briefly reviewed highlighting the I?=?1/2 ${\bar K}NN$ system. For heavier nuclei, the extension of mean-field calculations to multi- $\bar K$ nuclear quasibound states is discussed focusing on kaon condensation.     

Search for the Theta+ pentaquark in the reaction gammad --> pK-K+n

A search for the Theta+ in the reaction gammad --> pK-K+n was completed using the CLAS detector at Jefferson Lab. A study of the same reaction, published earlier, reported the observation of a narrow Theta+ resonance. The present experiment, with more than 30 times the integrated luminosity of our earlier measurement, does not show any evidence for a narrow pentaquark resonance. The angle-integrated upper limit on Theta+ production in the mass range of 1.52-1.56 GeV/c2 for the gammad --> pK-Theta+ reaction is 0.3 nb (95% C.L.). This upper limit depends on assumptions made for the mass and angular distribution of Theta+ production. Using Lambda(1520) production as an empirical measure of rescattering in the deuteron, the cross section upper limit for the elementary gamman --> K-Theta+ reaction is estimated to be a factor of 10 higher, i.e., approximately 3 nb (95% C.L.).     

The dilambda and the pentaquark in the constituent quark model

We use the non-relativistic constituent quark model and the bag model to study the stability of the dilambda H = (uuddss) and pentaquark states

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. While they are stable in the limit of exact SU(3)_F flavour symmetry between u, d, and s quarks, the H and the P become unbound when a realistic breaking of SU(3)_F is introduced.     

Isospin eigenstates of the color singlet-singlet-type pentaquark states

In this study, we constructed color singlet-singlet-type five-quark currents with isospins (I, I₃) = (■) and (■) unambiguously to explore the ■pentaquark states via the quantum chromodynamics sum rules for the first time, where ■,Σ_c, · · · represent the color singlet clusters with the same quantum numbers as the corresponding physical mesons or baryons. The numerical results support assigning P_c(4312), P_c(4380), P_c(4440), and P_c(4...     

Calculation of the pentaquark width using QCD sum rules

The pentaquark width Γ_? has been calculated using the QCD sum rules. The estimate shows that the width does not exceed 1 MeV. The main conclusion is that the sum rules indeed predict a narrow width of the pentaquark ?⁺, and the decay width is suppressed both parametrically and numerically.     

The ground state properties of the He4-nucleus

Conclusions Table VIII summarizes the computed binding energy of He⁴-nucleus which includes the zeroth order contribution and the correction up to the third order for three different potentials. The binding energy does not contain the C.M. energy, which has been calculated up to the second order. The r.m.s. radii corrected for the C.M. motion and for not-point-like nucleons are calculated up to the second order for potential RHEL 1 and up to the first order for Reid and RHEL 2 potentials. The binding energy and r.m.s. radii are computed for two different self-consistent conditions, the first of which is the usual classical condition (2.16), the second reads E ⁽¹⁾ = 0.In all cases the absolute value of the binding energy of the He⁴-nucleus is lower than the experimental value.It has been shown that the perturbation series built up on the Goldstone reaction matrix diverges, when a self-consistent technique is not used. This represents certain danger also for the self-consistent formulation, although it gives plausible results up to the third order. The result obtained seems to indicate that the discrepancy between the experimental and theoretical values for the binding energy may be caused by neglect of some fundamental facts (relativistic effects, many-body forces etc.) in the present many-body theory.The authors would like to thank the Rutherford High Energy Laboratory for the help in performing necessary computations and for the encouraging interest in this problem.     

Electromagnetic properties of the Pc(4312) pentaquark state

Using the light-cone QCD sum rules,we evaluate the magnetic moment of the P_c(4312) pentaquark state by considering both the \bar D\Sigma_c molecular and diquark-diquark-antiquark state,with quantum numbers J^P=2/1^-1.In the calculations,we use the diquark-diquark-antiquark and molecular form of the interpolating currents for the P_c4312 pentaquark and the distribution amplitudes of the photon.The numerical results for the magnetic moment obtained using the two different pictures are quite different from each other,which can be used to pin down the underlying structure of P_c4312 .Any experimental measurement of the magnetic moment in the near future will provide an understanding of the internal structure of this pentaquark state.     

Hydration structure of Na+ and K+ from ab initio molecular dynamics based on modern density functional theory

Molecular dynamics (Born–Oppenheimer) simulations based on density functional theory have been carried out to investigate the solvation structure of monovalent Na⁺ and K⁺ cations in water under ambient conditions. Four recently proposed van der Waals (vdW) density functionals (LMKLL, DRSLL, DRSLL-PBE, DRSLL-optB88), the semiempirical vdW method of Grimme (BLYP-D3) and conventional gradient-corrected (GGA-BLYP) density functionals are applied in order to evaluate their accuracy in describing the hydration structure of alkali metal ions. Theoretical results are compared to available experimental data. Our results indicate that addition of corrections accounting for dispersion forces significantly improves the agreement between predicted and measured coordination numbers for both Na⁺ and K⁺ cations. Analysis of radial distribution functions brings further support to the notion that the choice of the generalised gradient approximation density functional impacts crucially on the computed structural properties. DRSLL-optB88 and BLYP-D3 provide the best agreement with experiment.     

Wandering in color-space why is the life of pentaquark so long?

The problem of the long life time of the pentaquark Θ⁺ is investigated on the basis of the color molecular dynamics simulation. We find that it takes a long time (typically of 50–100 fm/c) for the initial pentaquark state to rearrange its color and spatial positions to decay into the nucleon+kaon final state. Structure of the potential surface in the color and position spaces also supports this picture. Pentaquark wanders on the potential surface to find a narrow channel to decay.     

A measurement of the K+ → e+v)(K+ → μ+v) branching ratio

The branching ratio $\text{R =}\text{Γ(}\text{K}{}^{\mathrm{+}}\text{→}\text{e}{}^{\mathrm{+}}\text{v)}\text{Γ(}\text{K}{}^{\mathrm{+}}\text{→ μ}{}^{\mathrm{+}}\text{v)}$ has been measured on the basis of 534 observed K⁺ → e⁺v decays. The K⁺ decay at rest; the momenta of the e⁺ and μ⁺ are measured in a magnetic spectrometer using multiwire driftchambers, and the electrons are identified in a gas Cerenkov counter. The result is R = (2.37 ± 0.17_× 10^?5. The value predicted for pure axial-vector interaction and μ-e-universality is R = 2.57 × 10^?5.