Revisiting the Kπ puzzle in the pQCD factorization approach

In this paper,we calculated the branching ratios and direct CP violation of the four B→Kπ decays with the inclusion of all currently known next-to-leading order(NLO) contributions by employing the perturbative QCD(pQCD) factorization approach.We found that(a) Besides the 10%enhancement from the NLO vertex corrections,the quark-loops and magnetic penguins,the NLO contributions to the form factors can provide an additional~15%enhancement to the branching ratios,and lead to a very good agreement with the data;(b) The NLO pQCD predictions are A_(CP)~(dir)(B~0→K~+π~0)=(-6.5±3.1)%and A_(CP)~(dir)(B~+→K~+π~0)=(2.2±2.0)%,become well consistent with the data due to the inclusion of the NLO contributions.     

A theoretical study of N–H ··· π H-bond interaction of pyrrole: from clusters to the liquid

The N–H?···?π H-bond interactions of clusters and liquid formed by pyrrole molecules were investigated by Quantum Mechanics (QM) and classical Molecular Dynamics (MD), respectively. Based on the optimized geometry at the B97-D/aug-cc-pVTZ level of theory including dispersion correction, the nature and the origin of N–H?···?π H-bond interactions were unveiled by atoms in molecules (AIM), natural bond orbital (NBO), and energy decomposition analysis (EDA). Among them, the AIM analysis gives evidence to the presence of N–H?···?π H-bond interactions, the NBO examination reveals that π?→?σ* donor-acceptor orbital interaction is of great importance. EDA study indicates that N–H?···?π interactions are governed by the electrostatic and dispersion term. Meanwhile, MD simulation with OPLS-AA (optimized potentials for liquid simulations all-atom) was applied to study the pure liquid pyrrole at different temperature. The results confirm the existence of the N–H?···?π H-bond in the pure liquid pyrrole, and further characterized the structures of this H-bond which is somewhat different to the clusters.     

Chalcogen bonds tuned by an N–H···π or C–H···π interaction: investigation of substituent,cooperativity and solvent effects

In the present work, ab-initio calculations are performed to investigate cooperativity effects between chalcogen bond and H···π interactions in XHY···NCH···C₆H₆ and XHY···CNH···C₆H₆ complexes, where X = F, Cl, Br, CN, NC, and Y = S, Se. The nature of these interactions and the mechanism of cooperativity are studied by means of quantum theory of atoms in molecules, noncovalent interaction index, many-body analysis of interaction energy and electron density shift analysis. For each ternary complex, the shortening of the Y···N(C) distance is more pronounced than that of the H···π. The cooperative energies of these complexes are all negative which demonstrate a positive cooperativity between the Y···N(C) and H···π interactions. The many-body analysis of interaction energy reveals that the two-body energy term has the largest contribution to the total interaction energies of ternary complexes. A good linear correlation is established between the three-body energy and cooperative energy values in the ternary systems. The cooperative energies of XHY···CNH···C₆H₆ complexes indicate a larger sensitivity on the polarity of solvent than XHY···NCH···C₆H₆ ones.     

Measuring dynamical K/π and p/π fluctuations in AuAu collisions from the STAR experiment

Results from new measurements of dynamical K/?? and p/?? ratio fluctuations are presented. Dynamical fluctuations in global conserved quantities such as baryon number, strangeness, or charge may be observed near a QCD critical point. The STAR experiment has previously acquired data in AuAu collisions at the energies $\sqrt {s_{NN} }$ = 200, 130, 62.4, and 19.6 GeV and CuCu collisions at $\sqrt {s_{NN} }$ = 200, 62.4, and 22.4 GeV. The commencing of a QCD critical point search at RHIC has extended the reach of possible measurements of dynamical K/?? and p/?? ratio fluctuations from AuAu collisions to lower energies. New results are compared to previous measurements and to theoretical predictions from the UrQMD model.     

What do we learn from the ρ-π puzzle

The experimental observation indicates that the branching ratio of ψ＇→ρπ is very small while the ρ-π channel is a main one in J/ψ decays. To understand the puzzle, various interpretations have been proposed. Meanwhile according to the hadronic helicity selection rule, this decay mode should be suppressed. Numerical calculations are needed to determine how it is suppressed. We calculate the branching ratios of J/ψ→ρπ and ππ in the framework of QCD. The results show that the branching ratios are proportional to （mu＋md/MJ/ψ）^2 for the ρπ mode and （mu-md/MJ/ψ）^2 for the ππ mode which is isospin violated. The theoretical prediction of the ratio of J/ ψ→ρπ is smaller than data, but not too small to invoke a completely new mechanism. Thus the puzzle is still standing even though we learn much knowledge towards the puzzle and this will help to finally interpret the puzzle and then gain a deeper insight to the heavy quarkonia.     

What do we learn from the ρ-π puzzle

The experimental observation indicates that the branching ratio of ψ→ρπ is very small while the ρ-π channel is a main one in J/ψ decays.To understand the puzzle,various interpretations have been proposed.Meanwhile according to the hadronic helicity selection rule,this decay mode should be suppressed.Numerical calculations are needed to determine how it is suppressed.We calculate the branching ratios of J/ψ→ρπ and ππ in the framework of QCD.The results show that the branching ratios are proportional to [(Mu+md)/(mJ/ψ)]2 for the ρπ mode and [(Mu-md)/(mJ/ψ)]2 for the ππ mode which is isospin violated.The theoretical prediction of the ratio of J/ψ→ρπ is smaller than data,but not too small to invoke a completely new mechanism.Thus the puzzle is still standing even though we learn much knowledge towards the puzzle and this will help to finally interpret the puzzle and then gain a deeper insight to the heavy quarkonia.     

Study of the B_c→B_sπ decay with the perturbative QCD approach

The Bc→Bsπ decay is studied with the perturbative QCD approach. Three types of wave functions for Bsmeson are considered.The transition form factor FBc→Bs0(0) and the branching ratio Br(Bc→Bsπ)aresensitivetothemodelofthe Bsmeson wave functions.With appropriate inputs, our estimate on Br(Bc→Bsπ) is comparable with the recent LHCb measurement. A clear signal of Bc→Bsπ decay should be easily observed at the Large Hadron Collider.     

Depopulation of the Jπ = 9- isomer in 180Ta to the Jπ = 1+ ground state by Coulomb excitation

In-beam Coulomb excitation of the exotic odd-odd nucleus ¹⁸⁰Ta has been studied by using a ¹³⁶Xe beam and a setup consisting of five EUROBALL CLUSTER detectors and the Darmstadt-Heidelberg Crystal Ball array. Spectroscopic information on the extremely rare ¹⁸⁰Ta is obtained from the comparison between an enriched (3.6±0.3% ¹⁸⁰Ta) and a natural tantalum target. Possible evidence for a depopulation from the long-lived high-spin J ^π = 9^- isomer to the short-lived J ^π = 1⁺ ground state is searched for by different methods. The decay of low-K bandheads, which are nanosecond isomers, towards the ground-state band can be demonstrated in delayed spectroscopy. A γγ coincidence analysis provides indications of K = 5 in-band transitions. Finally, when the Crystal Ball is used as an energy and γ multiplicity filter, signals of decay into the K = 0 band are observed. Received: 23 January 2001 / Accepted: 8 February 2001     

Implications of unitarity and analyticity for the Dπ form factors

We consider the vector and scalar form factors of the charm-changing current responsible for the semileptonic decay D → πlν. Using as input dispersion relations and unitarity for the moments of suitable heavy-light correlators evaluated with Operator Product Expansions, including O(α _s ²) terms in perturbative QCD, we constrain the shape parameters of the form factors and find exclusion regions for zeros on the real axis and in the complex plane. For the scalar form factor, a low-energy theorem and phase information on the unitarity cut are also implemented to further constrain the shape parameters. We finally propose new analytic expressions for the Dπ form factors, derive constraints on the relevant coefficients from unitarity and analyticity, and briefly discuss the usefulness of the new parametrizations for describing semileptonic data.     

The 8π spectrometer

The 8π spectrometer installed at the TRIUMF-ISAC radioactive beam facility provides a powerful and versatile detection system for radioactive decay, allowing measurements of γ rays and conversion electrons with high resolution, tagging on β particles, and fast-timing measurements. The facility supports a wide program of research in the fields of nuclear structure, nuclear astrophysics and fundamental symmetries with low-energy radioactive beams.     

Monte Carlo study on the low momentum μ-π identification of the BESⅢ EM calorimeter

The BESⅢ detector has a high-resolution electromagnetic calorimeter which can be used for low momentum μ-π identification.Based on Monte Carlo simulations, μ-π separation was studied.A multilayer perceptron neural network making use of the defined variables was used to do the identification and a good μ-π separation result was obtained.     

Monte Carlo study on the low momentum μ-π identification of the BESⅢ EM calorimeter

The BESⅢ detector has a high-resolution electromagnetic calorimeter which can be used for low momentum μ-π identification. Based on Monte Carlo simulations, μ-π separation was studied. A multilayer perceptron neural network making use of the defined variables was used to do the identification and a good μ-π separation result was obtained.     

Molecular two-centre integrals between 2 pπ and 3 pπ atomic orbitals

The evaluation of two-centre Coulomb-penetration and exchange-penetration integrals is discussed. All possible penetration integrals between 2pπ and 3pπ atomic orbitals exponent α are reduced analytically and tabulated for α = 1·00 (0·25) 10·00.     

Measurement of the matrix element for the decay η′ → ηπ 0 π 0 with the GAMS-4π spectrometer

The parameters of the Dalitz diagram for the decay η′ → ηπ ⁰ π ⁰ in a generalized and a linear representation were determined by using a statistical sample of 15 × 10³ events. A charge-exchange reaction at a momentum of 32 GeV/c was a source of monoenergetic η′ mesons. The experiment was performed with the aid of the GAMS-4π spectrometer.     

Effect of rescattering on polarization observables of the reaction γd → ppπ in the delta-resonance region

The effect of pion-nucleon and nucleon-nucleon rescatterings on polarization observables of the reaction γd → ppπ^? are calculated in the delta-isobar region. Pion-nucleon and nucleon-nucleon rescatterings are considered on the basis of a diagrammatic approach. Lorentz invariant expressions are used for the operators of photoproduction and of pion scattering on a free nucleon. A unitarization procedure in the K-matrix approximation is used for resonance partial-wave amplitudes. It is shown that, in the delta-resonance region, rescattering has a sizable effect on polarization observables of the reaction γd → ppπ^? at high momenta of final protons.     

The first π*←π transition of the benzene single crystal in polarized light

The first π*←π transition in the benzene single crystal is investigated at 82 K. Intensities and polarization ratios for both true and false origins in crystal planes (100) and (010) have been measured and rationalized in terms of crystal field perturbation. At liquid nitrogen temperature the origin of the transition is located at 37865 cm^-1 (b), 37817 cm^-1 (c) and 37807 cm^-1(a).     

0-π transition induced by the barrier strength in spin superconductor Josephson junctions

The Andreev-like levels and the free energy of the spin superconductor/insulator/spin superconductor junction are obtained by using the Bogoliubov-de Gennes equation. The phase dependence of the spin supercurrents exhibits a 0-π transition by changing the barrier strength. The dependences of the critical current on the barrier strength and the temperature are also presented.