Ππ Transition Research Articles

M1 radiative and spin-nonflip ππ transitions of Bc states in the Cornell potential model

In this paper, we mainly predict the rates of M1 radiative and spin-nonflip ππ transitions of the Bc-meson under the nonrelativistic Cornell potential model with a screening potential effect. We employ the numerical wave function to determine the M1 radiative transition widths of Bc excited states and utilize the Kuang-Yan proposed method for the spin-nonflip ππ transitions among Bc states. Our theoretical results are valuable for studying the M1 radiative and spin-nonflip ππ transition processes of Bc states in experiments. Published by the American Physical Society 2024

CP asymmetry from hadronic charm rescattering in B± → π−π+π± decays at the high mass region

A model for the B±→π−π+π± decay amplitude is proposed to study the large CP violation observed at the high mass region of the Dalitz plane. A short distance b→u amplitude with the weak phase γ is considered together with the contribution of a hadronic charm loop and a s-wave DD¯→ππ rescattering. In the model, the χc0 appears as a narrow resonant state of the DD¯ system below threshold. It is introduced in an unitary two channel S-matrix model of the coupled DD¯ and ππ channels, where the χc0 complex pole in DD¯ channel shows its signature in the off-diagonal matrix element and in the associated DD¯→ππ transition amplitude. The strong phase of the resulting decay amplitude has a sharp sign change at the DD¯ threshold, changing the sign of the CP asymmetry, as it is observed in the data. We conclude that the hadronic charm loop and rescattering mechanism are relevant to the broadening of the CP asymmetry around the χc0 resonance in the ππ channel. This novel mechanism provides a possible interpretation for the CP asymmetry challenging experimental result presented by the LHCb collaboration for the B±→π−π+π± decay in the high mass region.

Classification of novel thiazole compounds for sensitizing Ru–polypyridine complexes for artificial light harvesting

A systematic study of the Förster resonance energy transfer (FRET) efficiency between thiazole dyes and a ruthenium–polypyridine complex is presented. While ruthenium–polypyridines are conventionally used in artificial light harvesting systems as primary electron donors, their application suffers from rather low extinction coefficients in the visible spectral range and an absorption gap between the ππ ⁎ transitions of the ligands and the MLCT transitions. In this paper it is shown how thiazoles might help to circumvent theses issues. The absorption and emission spectra of the thiazole can be synthetically adjusted to fall into the absorption gap of the Ru dye and to efficiently overlap with the 1MLCT absorption of the complex, respectively. Thereby, the thiazoles might serve as antenna structures to funnel energy to the Ru-polypyridine unit, which finally can act as a photoactivated primary electron donor. Systematic investigations of the Förster radii of representative thiazole Ru-polypyridine dye pairs corroborate this potential quantitatively.

Confinement singularities in two-pion decays of mesons

We consider as an example the two-pion decay of the ρ meson, the 3S1q\( \bar q \) state of the constituent quarks—the decay being determined by the transition q\( \bar q \) → ππ contains information about confinement interactions. One can specify in this decay two types of transitions: (i) the bremsstrahlung radiation of a pion q → q + π (or \( \bar q \) → \( \bar q \) + π) with a subsequent fusion q\( \bar q \) → π, and (ii) the direct transition q\( \bar q \) → ππ. We demonstrate how in the amplitudes of the corresponding transitions the quark singularities have to disappear, i.e., what is the way the quark confinement at relatively short distances can be realized. We calculate and estimate the contributions of processes with bremsstrahlung radiation of the pion and of the direct transition q\( \bar q \) → ππ. The estimates demonstrate that the processes involving the direct transition q\( \bar q \) → ππ are necessary, but they cannot be determined unambiguously by the decay ρ(775) → ππ. We conclude that for the determination of the q\( \bar q \) → ππ transition more complete data on the resonance decays into the ππ channels are needed than those available at the moment.

Strong isospin-breaking effects in K→2 π at next-to-leading order in the chiral expansion

Strong isospin-breaking (IB) contributions to both the octet and 27-plet weak K→ ππ transitions are evaluated at next-to-leading order (NLO) in the chiral expansion. NLO contributions are shown to significantly reduce the leading order result for the potentially large contribution to the ΔI=3/2 amplitude resulting from strong isospin-breaking modifications to the weak ΔI=1/2 amplitude. The ratio of strong IB 27-plet to strong IB octet contributions is found to be small for all decay amplitudes. Combined with recent results on the corresponding electromagnetic contributions, we find that the ratio of the intrinsic strengths of octet and 27-plet effective weak operators can be taken to be that obtained from experimental data, analyzed ignoring isospin breaking, to an accuracy better than of order ∼10%.

Weak Transition Matrix Elements¶from Finite-Volume Correlation Functions

The two-body decay rate of a weakly decaying particle (such as the kaon) is shown to be proportional to the square of a well-defined transition matrix element in finite volume. Contrary to the physical amplitude, the latter can be extracted from finite-volume correlation functions in euclidean space without analytic continuation. The K -> pi pi transitions and other non-leptonic decays thus become accessible to established numerical techniques in lattice QCD.

Non-perturbative renormalisation and kaon physics

A general review is presented on the problem of non perturbative computation of the K → ππ transition amplitude.

EXTENDED ANALYSIS OF THE “PENGUIN” PART OF THE K→ππ AMPLITUDE

We make an attempt to clarify the role of the annihilation or “penguin” mode in the description of the K→ππ decay within the Standard Model. Attention is centered on new operators in the effective ΔS=1 Hamiltonian and the violation of factorization for mesonic matrix elements of the local four-quark operators. We propose a regular method to evaluate the mesonic matrix elements of K→ππ transitions based on the study of three-point correlators via QCD sum rules using the chiral effective theory as an underlying low energy model for strong interaction. Matrix elements of the QCD penguin operator are calculated within this approach. The total “penguin” contribution is found to be relatively large, which improves the theoretical description of the ΔI=1/2 rule in nonleptonic kaon decays.

COMPLEXITY OF HADRONIC AMPLITUDES VIA QUARK LOOPS

The structure of hadronic transition amplitudes h→h′+h″ via quark triangle loops is investigated in terms of hadron quark vertex functions [Formula: see text], using for illustration the case of the ρ→ππ transition. A Bethe-Salpeter model based on the Covariant-Instantaneity-Ansatz (CIA) for its kernel which provides an exact interconnection between the 3D and 4D forms the BS wave function, determines the structure [Formula: see text]. The nonlocality feature inherent in the vertex function causes the imaginary part of gρππ calculated from the loop integral to be generally different from its dispersion relation value which would be obtained from analyticity of gρππ in the ρ-mass. Pending a proper understanding of this nonlocality (associated with confining interactions) only the real part of gρππ is found unambiguous while the imaginary part is model-dependent.

Ultraviolet preresonance Raman scattering of benzene derivatives. II. Interference effects in the excitation profiles of the vibronically active fundamentals

Raman resonance and antiresonance behavior is observed in the ultraviolet preresonance excitation region for the scattering of those vibrations known to be vibronically active in the 1La and 1Lb electronic transitions of toluene, m-xylene, and fluorobenzene. These effects are found to be due to the constructive and destructive interferences between scattering contributions derived from the vibronic coupling of the low lying ππ transitions and transitions in the far-UV region. This behavior is seen to reflect the varying sign of the allowed 1Lb and 1La transition moment among these derivatives. Calculations are performed which show how the allowed transition moment in m-xylene is of opposite sign to that of these two monosubstituted benzenes.

Unitarity constraints on resonance mixing and the Okubo-Zweig-Iizuka rule

We discuss unitarity constraints on the (complex) mixing angle (δ) between resonances. In particular, when the mixing is small, as when it is forbidden by the Okubo-Zweig-Iizuka (OZI) rule, or some other mechanism, one can derive useful bounds on δ or determine Arg (δ) from the data of allowed decays of the resonances. In the case of f′−f mixing the unitarity bound |δ|≳0.05±0.015 is barely compatible with the experimental f′←ππ rate (if one assumes that it is dominated by f′←f←ππ transition). Furthermore, experimentally Im δ≈0 which together with unitarity gives Re δ=−0.08±0.03, in clear discrepancy with the observed f′←ππ rate. This suggests that the mixing of f′ with higher f-like recurrences, which would at least partly cancel the f′←f←ππ transition, cannot be neglected. For the φ-ω mixing the unitarity bound is well satisfied and our prediction of Arg δ≈−5° is in agreement with the experimental estimate.