Hadronic Transitions Research Articles

Neutron Beta Decay and Exact Conservation of Charged Weak Hadronic Vector Current in the Standard Model

We investigate the reliability of the hypothesis of exact conservation of the charged weak hadronic vector current in neutron β−-decay with a polarized neutron and an unpolarized proton and electron. We calculate the contributions of the phenomenological term responsible for Exact Conservation of the charged weak hadronic Vector Current (or the ECVC effect) in neutron β−-decay, even for different masses of the neutron and proton, to the correlation coefficients, together with a complete set of contributions of scalar and tensor interactions beyond the Standard Model (SM). We argue that if the total contributions of scalar and tensor interactions beyond the SM fail to reconcile the experimental data on the correlation coefficients with the contributions of the ECVC effect, one may conclude that the charged weak hadronic vector current is not conserved in the hadronic transitions of weak processes with different masses of incoming and outgoing hadrons.

Measurements of the branching fractions of semileptonic Ds+ decays via e+e−→Ds*+Ds*−

We measure the absolute branching fractions of semileptonic Ds+ decays via the e+e−→Ds*+Ds*− process using e+e− collision data corresponding to an integrated luminosity of 10.64 fb−1 collected by the BESIII detector at center-of-mass energies between 4.237 and 4.699 GeV. The branching fractions are B(Ds+→ηe+νe)=(2.35±0.11stat±0.10syst)%, B(Ds+→η′e+νe)=(0.82±0.09stat±0.04syst)%, B(Ds+→ϕe+νe)=(2.21±0.16stat±0.11syst)%, B(Ds+→f0(980)e+νe,f0(980)→π+π−)=(0.15±0.02stat±0.01syst)%, B(Ds+→K0e+νe)=(0.24±0.04stat±0.01syst)%, and B(Ds+→K*0e+νe)=(0.19±0.03stat±0.01syst)%. These results are consistent with those measured via the e+e−→Ds*±Ds∓ process by BESIII and CLEO. Using two-parameter series expansion, the hadronic transition form factors of Ds+→ηe+νe, Ds+→η′e+νe, and Ds+→K0e+νe are determined to be f+η(0)=0.442±0.022stat±0.017syst, f+η′(0)=0.557±0.062stat±0.024syst, and f+K0(0)=0.677±0.098stat±0.023syst. Published by the American Physical Society 2024

The Λc → Λ ℓ+νℓ weak decay including new physics

We investigate the Λc → Λℓ+νℓ decay with a focus on potential new physics (NP) effects in the ℓ = μ channel. We employ an effective Hamiltonian within the framework of the Standard Model Effective Field Theory (SMEFT) to consider generalized dimension-6 semileptonic c → s operators of scalar, pseudoscalar, vector, axial-vector and tensor types. We rely on Lattice QCD (LQCD) for the hadronic transition form factors, using heavy quark spin symmetry (HQSS) to determine those that have not yet been obtained on the lattice. Uncertainties due to the truncation of the NP Hamiltonian and different implementations of HQSS are taken into account. As a result, we unravel the NP discovery potential of the Λc → Λ semileptonic decay in different observables. Our findings indicate high sensitivity to NP in lepton flavour universality ratios, probing multi-TeV scales in some cases. On the theoretical side, we identify LQCD uncertainties in axial and vector form factors as critical for improving NP sensitivity, alongside better SMEFT uncertainty estimations.

Hadronization of heavy quarks

Heavy-flavor hadrons produced in ultrarelativistic heavy-ion collisions are a sensitive probe for studying hadronization mechanisms of the quark-gluon-plasma. In this paper, we survey how different transport models for the simulation of heavy-quark diffusion through a quark-gluon plasma in heavy-ion collisions implement hadronization and how this affects final state observables. Utilizing the same input charm-quark distribution in all models at the hadronization transition, we find that the transverse-momentum dependence of the nuclear modification factor of various charm hadron species has significant sensitivity to the hadronization scheme. In addition, the charm-hadron elliptic flow exhibits a nontrivial dependence on the elliptic flow of the hadronizing partonic medium. Published by the American Physical Society 2024

Searching for QCD critical point with light nuclei

Density fluctuations and correlations due to a first-order quark-gluon plasma to hadronic matter phase transition and its critical end point, if they remain present after the hadronic evolution in a heavy ion collisions, can lead to an enhanced production of light nuclei in these collisions. This would then result in a non-monotonic collision energy dependence of the yield ratio $$N_\text {t} N_\text {p} / N_\text {d}^2$$ of proton number $$N_\text {p}$$ , deuteron number $$N_\text {d}$$ , and triton number $$N_\text {t}$$ . Measurements of this yield ratio as a function of collision energy thus provides the possibility to probe the equation of state of strong-interaction matter and its phase diagram.

Confirming the existence of a new higher charmonium ψ(4500) by the newly released data of e+e−→K+K−J/ψ

Recently, the BESIII Collaboration published the Born cross section of $e^+e^- \to K^+K^- J/\psi$, in which a new vector enhancement structure $Y(4500)$ was observed for the first time. The mass of the $Y(4500)$ resonance structure is in good agreement with our previous prediction for a $5S$-$4D$ mixing charmonium candidate $\psi(4500)$, while the measured width is $2\sigma$ larger than the theoretical estimate. In this work, we reanalyzed the cross section of $e^+e^- \to K^+K^- J/\psi$ by introducing two theoretically predicted charmonium states $\psi(4220)$ and $\psi(4500)$ as intermediate resonances, and found that this width deviation problem can be resolved. Meanwhile, we found that the inclusion of two established charmonium states $\psi(4160)$ and $\psi(4415)$ can further improve the fit quality, with four sets of widely different solutions to $\Gamma_{e^+e^-} \mathcal{B}(\psi \to K^+K^- J/\psi)$. In order to better identify the properties of the $Y(4500)$, we calculated the charmonium hadronic transition to final states $K^+K^- J/\psi$ within the charmed meson loop mechanism, where the fitted branching ratio of $\psi(4500) \to K^+K^- J/\psi$ can be well explained by the theoretical calculation, further supporting the new enhancement structure around 4.5 GeV as a higher charmonium $\psi(4500)$ that we predicted. Finally, we also discussed the possible signal of another predicted charmonium candidate $\psi(4380)$ in $e^+e^- \to K^+K^- J/\psi$. These research results should be an important step in constructing the charmonium family and thoroughly solving the charmoniumlike $Y$ problem.

Cancellation of the Sigma Mode in the Thermal Pion Gas by Quark Pauli Blocking

In this study, we calculate the pressure of the interacting pion gas using the Beth–Uhlenbeck approach to the relativistic virial expansion with Breit–Wigner phase shifts for the σ- and ϱ-meson resonances. The repulsive phase shift δ02 is taken from the quark interchange model of Barnes and Swanson, which is in very good agreement with the experimental data. In this work we show that the cancellation of the attractive (I = 0) and repulsive (I = 2) isospin channel contributions to the scalar ππ interaction in the low-energy region that is known for the vacuum phase shifts also takes place at a finite temperature. This happens despite the strong medium dependence of these phase shifts that enters our model by the temperature dependence of the σ-meson and constituent quark masses, because for these masses the relation Mσ(T)≈2mq(T) holds and the scattering length approximation is valid as long as the strong decay channel σ→ππ is open. Exploiting the Nambu–Jona-Lasinio model for describing the dynamical breaking of chiral symmetry in the vacuum and its restoration at a finite temperature, we justify with our approach that the σ-meson should be absent from the hadron resonance gas description at low temperatures because the above cancellation holds. However, since this cancellation breaks down in the vicinity of the hadronization transition, where due to chiral symmetry restoration the decay channel σ→ππ closes and the σ-meson becomes a good resonance, the latter should be included into the statistical model description of chemical freeze-out in heavy-ion collisions.

A CRITICAL ANALYSIS OF CHAOS BASED BEHAVIOR INSPIRED COHERENT SMATTERING WITH ITS POTENTIAL SIGNIFICANCE

In this paper, we investigated the influence of temperature and momentum-dependent coherence-chaos radiations on particle excretion from a fluid with quantum supremacy. The dynamics interpretation of a system can become exceedingly complex and femtoscopy is an efficient quantum tool that captures and explores the complicated dynamical properties. This research presents a comprehensive and brief analysis of fluid in the context of quantum interference for partially chaotic systems, as well as novel findings for chaos synchronization of identical bosons in the extending source are evaluated. The eminence of coherence on chaotic production has been demonstrated using correlation plots in the existence of the quantum influence. The temperature profile is described with the mitigation of graphs created for various flow peculiarities, and the density equations are derived through feasible interferences transformation approaches. Results exhibit the quantitative data of chaotic and droplets exhibiting coherence features and illustrate a premise that depicts motivated conversions between cold and hot bosonic particles crossover during the expanding of emitted sources. The emergent phase can contain a partially thermalized distribution of particles which is elucidated by the swiftness of the hadronic transition and this phase reveals marvelous entirely quantum correlations according to our findings. In particular, we formulate the normalized interception for the hybrid system using particular methods to probe the source configurations.

Strangeness thermodynamic instabilities in hot and dense nuclear matter

We explore the presence of thermodynamic instabilities and, consequently, the realization of a pure hadronic phase transition in the hot and finite baryon density nuclear matter. The analysis is performed by means of an effective relativistic mean-field model with the inclusion of hyperons, varDelta -isobars, and the lightest pseudoscalar and vector meson degrees of freedom. The Gibbs conditions on the global conservation of baryon number and zero net strangeness in symmetric nuclear matter are required. Similarly to the liquid–gas phase transition, we show that a phase transition, characterized by mechanical instabilities (due to fluctuations on the baryon number) and chemical-diffusive instabilities (due to fluctuations on the strangeness number), can take place for a finite range of varDelta -meson coupling constants, compatible with different experimental constraints. The hadronic phase transition, which presents similar features to the quark-hadron phase transition, is characterized by different strangeness content during the mixed phase and, consequently, by a sensible variation of the strange anti-particle to particle ratios.

Binary neutron star mergers as a probe of quark-hadron crossover equations of state

It is anticipated that the gravitational radiation detected in future gravitational wave (GW) detectors from binary neutron star (NS) mergers can probe the high-density equation of state (EOS). We perform the first simulations of binary NS mergers which adopt various parametrizations of the quark-hadron crossover (QHC) EOS. These are constructed from combinations of a hadronic EOS ($n_{b} ~5~n_0$), where $n_{b}$ and $n_0$ are the baryon number density and the nuclear saturation density, respectively. At the crossover densities ($2~ n_0 < n_{b} < 5~ n_0$) the QHC EOSs continuously soften, while remaining stiffer than hadronic and first-order phase transition EOSs, achieving the stiffness of strongly correlated quark matter. This enhanced stiffness leads to significantly longer lifetimes of the postmerger NS than that for a pure hadronic EOS. We find a dual nature of these EOSs such that their maximum chirp GW frequencies $f_{max}$ fall into the category of a soft EOS while the dominant peak frequencies ($f_{peak}$) of the postmerger stage fall in between that of a soft and stiff hadronic EOS. An observation of this kind of dual nature in the characteristic GW frequencies will provide crucial evidence for the existence of strongly interacting quark matter at the crossover densities for QCD.

Toward the discovery of novel Bc states: Radiative and hadronic transitions

The properties of the $B_c$-meson family ($c\bar b$) are still not well determined experimentally because the specific mechanisms of formation and decay remain poorly understood. Unlike heavy quarkonia, i.e. the hidden heavy quark-antiquark sectors of charmonium ($c\bar c$) and bottomonium ($b\bar b$), the $B_c$-mesons cannot annihilate into gluons and they are, consequently, more stable. The excited $B_c$ states, lying below the lowest strong-decay $BD$-threshold, can only undergo through radiative decays and hadronic transitions to the $B_c$ ground state, which then decays weakly. As a result of this, a rich spectrum of narrow excited states below the $BD$-threshold appear, whose total widths are two orders of magnitude smaller than those of the excited levels of charmonium and bottomonium. In a different article, we determined bottom-charmed meson masses using a non-relativistic constituent quark model which has been applied to a wide range of hadron physical observables, and thus the model parameters are completely constrained. Herein, continuing to our study of the $B_c$ sector, we calculate the relevant radiative decay widths and hadronic transition rates between $c\bar b$ states which are below $BD$-threshold. This shall provide the most promising signals for discovering excited $B_c$ states that are below the lowest strong-decay $BD$-threshold. Finally, our results are compared with other models to measure the reliability of the predictions and point out differences.

Simulation of multiple hadron production and transition to quark-gluon plasmas based on nonlinear dynamics

A dynamics of quark-gluon plasmas has been defined by the evolution parameter, which at high energies depends on collision energy of atomic nuclei for appropriate multiplicities of secondary hadrons. The paper is based on the solution of evolution equation for patrons momentum distribution. A transition from regular propagation to irregular chaotic is an indicator of the quark-gluon plasma emerging. Nonlinear renormalization group equation has been solved by the method of Poincaré mappings. The equation is a model of the evolution of the momentum distribution of partons due to competing processes of their creation and fusion. As the energy increases, sequential bifurcation (doubling) of phase trajectories occurs, and scale-invariant fractal structures are to create. At sufficiently high energies of quarks and gluons, a dynamically determined quark-gluon system, corresponding to QGP, arises in space. There are also hadron-like structures. Quantum coherence effects follow by dynamic chaos. As a result, quarks and gluons merge into stable attractor structures with their subsequent decay into hadrons. The nonlinear equation introduced for quark-gluon cascade, which comprises dynamical chaos, has include effects of parton recombination. The chaotic dynamics has been connected specifically to the transverse momenta of partons. Clearly, the formation of dynamically determined stable structures should be unknown before, attractor mechanism of quark hadronization.

Study of χbJ(nP ) → ωΥ(1S) at Belle

We report preliminary results from a study of hadronic transitions of the χbJ (nP) states of bottomonium at Belle. The P-wave states are reconstructed in transitions to the Υ(1S) with the emission of an ω meson. The transitions of the n = 2 triplet states provide a unique laboratory in which to study nonrelativistic quantum chromodynamics, as the kinematic threshold for production of an ω and Υ(1S) lies between the J = 0 and J = 1 states. A search for the χbJ (3P) states is also reported.

Form factor counting and HQET matching for new physics in Λb→Λc*lν

We calculate the $\Lambda_b \to \Lambda_c^*(2595) l \nu$ and $\Lambda_b \to \Lambda_c^*(2625) l \nu$ form factors and decay rates for all possible $b \to c l \bar\nu$ four-Fermi interactions in and beyond the Standard Model (SM), including nonzero charged lepton masses and terms up to order $\mathcal{O}(\alpha_s, 1/m_{c,b})$ in the heavy quark effective theory (HQET). We point out a subtlety involving the overcompleteness of the representation of the spin-parity $1/2^+ \to 3/2^-$ antisymmetric tensor form factors, relevant also to other higher excited-state transitions, and present a general method for the counting of the physical form factors for any hadronic transition matrix element and their matching onto HQET. We perform a preliminary fit of a simple HQET-based parametrization of the $\Lambda_b \to \Lambda_c^*$ form factors at $\mathcal{O}(\alpha_s, 1/m_{c,b})$ to an existing quark model, providing preliminary predictions for the lepton universality ratios $R(\Lambda_c^*)$ beyond the SM. Finally, we examine the possible incompatibility of recent lattice QCD results with expectations from the heavy-quark expansion and available experimental data.

Decay of baryon inhomogeneities in an expanding universe

Baryon inhomogeneities are generated early in the universe. These inhomogeneities affect the phase transition dynamics of subsequent phase transitions, they also affect the nucleosynthesis calculations. We study the decay of the inhomogeneities in the early universe using the diffusion equation in the Friedmann–Lemaître–Robertson–Walker metric. We calculate the interaction cross section of the quarks with the neutrinos, the electrons and the muons and obtain the diffusion coefficients. The diffusion coefficients are temperature dependent. We find that the expansion of the universe causes the inhomogeneities to decay at a faster rate. We find that the baryon inhomogeneities generated at the electroweak epoch have low amplitudes at the time of the quark hadron transition and hence will not affect the phase transition dynamics unless they are generated with a amplitude greater than 10^{5} times the background density. After the quark hadron transition, we include the interaction of the muons with the hadrons till 100 MeV. We find that large density inhomogeneities generated during the quark hadron transition with sizes of the order of 1 km must have amplitudes greater than 10^{5} times the background density to survive upto the nucleosynthesis epoch. This puts constraints on any models that generate these inhomogeneities

Holographic nuclear physics with massive quarks

We discuss nuclear physics in the Witten-Sakai-Sugimoto model, in the limit of large number $N_c$ of colors and large 't Hooft coupling, with the addition of a finite mass for the quarks. Individual baryons are described by classical solitons whose size is much smaller than the typical distance in nuclear bound states, thus we can use the linear approximation to compute the interaction potential and provide a natural description for lightly bound states. We find the classical geometry of nuclear bound states for baryon numbers up to B=8. The effect of the finite pion mass - induced by the quark mass via the GMOR relation - is to decrease the binding energy of the nuclei with respect to the massless case. We discuss the finite density case with a particular choice of a cubic lattice, for which we find the critical chemical potential, at which the hadronic phase transition occurs.

CP violation in non-leptonic B_c decays to excited final states

We study the CP violation in two-body nonleptonic decays of B_c meson. We concentrate on the decay channels which contain at least one excited heavy meson in the final states. Specifically, the following channels are considered: B_crightarrow c{bar{c}}(2S, 2P)+{bar{c}}q(1S, 1P), B_crightarrow c{bar{c}}(1S)+{bar{c}}q(2S, 2P), B_crightarrow c{bar{c}}(1P)+{bar{c}}q(2S), B_crightarrow c{bar{c}}(1D)+{bar{c}}q(1S, 1P), and B_crightarrow c{bar{c}}(3S)+{bar{c}}q(1S). The improved Bethe-Salpeter method is applied to calculate the hadronic transition matrix element. Our results show that some decay modes have large branching ratios, which is of the order of 10^{-3}. The CP violation effect in B_c rightarrow eta _c(1S)+D(2S), B_c rightarrow eta _c(1S)+D_0^{*}(2P), and B_c rightarrow J/psi +D^{*}(2S) are most likely to be found. If the detection precision of the CP asymmetry in such channels can reach the 3sigma level, at least 10^7B_c events are needed.

Natural interpretation on the data of Λc→Σπ

Even though the Standard Model (SM) has achieved great success, its application to the field of low energies still lacks solid foundation due to our limited knowledge on non-perturbative QCD. Practically, all theoretical calculations of the hadronic transition matrix elements are based various phenomenological models. There indeed exist some anomalies in the field which are waiting for interpretations. The goal of this work is trying to solve one of the anomalies: the discrepancy between the theoretical prediction on the sign of the up-down asymmetry parameter of $\Lambda_c\to\Sigma\pi$ and the experimental measurement. In the literatures several authors calculated the rate and determined the asymmetry parameter within various schemes, but there exist obvious loopholes in those adopted scenarios. To solve the discrepancy between theory and data, we suggest that not only the direct transition process contributes to the observed $\Lambda_c\to\Sigma\pi$, but also other portals such as $\Lambda_c\to \Lambda\rho$ also play a substantial role via an isospin-conserving re-scattering $\Lambda\rho\to\Sigma\pi$. Taking into account of the effects induced by the final state interaction, we re-evaluate the relevant quantities. Our numerical results indicate that the new theoretical prediction based on this scenario involving an interference between the direct transition of $\Lambda_c\to\Sigma\pi$ and the portal $\Lambda_c\to\Lambda\rho\to\Sigma\pi$ can make both the decay rate and sign of the asymmetry parameter to be consistent with data.

Strangeonium-like hybrids on the lattice * *Supported by the National Key Research and Development Program of China (2017YFB0203202) and the Strategic Priority Research Program of Chinese Academy of Sciences (No.XDC01040100, XDB34030302). The numerical calculations are carried out on Tianhe-1A at the National Supercomputer Center (NSCC) in Tianjin and the GPU cluster at IHEP. We also acknowledge the support of the

The strangeonium-like hybrids are investigated from lattice QCD in the quenched approximation. In the Coulomb gauge, spatially extended operators are constructed for and states with the color octet component being separated from the chromomagnetic field strength by the spatial distance , whose matrix elements between the vacuum and the corresponding states are interpreted as Bethe-Salpeter (BS) wave functions. In each of the channels, the masses and the BS wave functions are reliably derived. The ground state mass is approximately 2.1-2.2 GeV, and that of is approximately 2.3-2.4 GeV, whereas the mass of the first excited state is approximately 1.4 GeV higher. This mass splitting is much larger compared to that expected based on the phenomenological flux-tube model or constituent gluon model for hybrids, which is usually a few hundred MeV. The BS wave functions with respect to exhibit clear radial nodal structures of a non-relativistic two-body system, which imply that is a meaningful dynamical variable for these hybrids and motivate a color halo picture of hybrids, in which the color octet is surrounded by gluonic degrees of freedom. In the channel, the properties of the lowest two states are consistent with those of and . We did not obtain convincing information with respect to . However, we argue that regardless of whether is a conventional meson or a hybrid in the color halo scenario, the ratio of partial decay widths and observed by BESIII can be understood based on the mechanism of hadronic transition of a strangeonium-like meson in addition to mixing.

Effects of vector leptoquarks on decay

Experimental data on , , and , provided by different collaborations, show sizable deviations from the standard model predictions. To describe these anomalies, many new physics scenarios have been proposed. One of them is the leptoquark model, which introduces the simultaneous coupling of vector and scalar leptoquarks to quarks and leptons. To look for similar possible anomalies in the baryonic sector, we investigate the effects of a vector leptoquark on various physical quantities related to the tree-level decays ( ), which proceed via transitions at the quark level. We calculate the differential branching ratio, forward-backward asymmetry, and longitudinal polarizations of leptons and baryons at the and lepton channels in the leptoquark model and compare their behavior to the predictions of the SM in terms of . In the calculations, we use the form factors calculated in full QCD as the main input and account for all errors coming from the form factors and model parameters. We observe that at the channel, the fit solution to data related to the leptoquark model sweeps some regions out of the SM band; nevertheless, the fit has a considerable intersection with the SM predictions. The type solution gives roughly the same results as the SM on . At the channel, the leptoquark model gives results that are consistent with the SM predictions and existing experimental data on the behavior of with respect to . Concerning the behavior of the , the two types of fits for and the predictions at the channel in the leptoquark model give exactly the same results as the SM. We also investigate the behavior of the parameter with respect to and the value of in both the vector leptoquark and SM models. Both fit solutions lead to results that deviate considerably from the SM predictions for and . Future experimental data on and , made available by measurements of the channel, will be particularly helpful. Any experimental deviations from the SM predictions in this channel would emphasize the importance of tree-level hadronic weak transitions as good probes of new physics effects beyond the SM.