Chromodynamics Research Articles

Observation of a rare beta decay of the charmed baryon with a Graph Neural Network

The beta decay of the lightest charmed baryon Λc+ provides unique insights into the fundamental mechanism of strong and electro-weak interactions, serving as a testbed for investigating non-perturbative quantum chromodynamics and constraining the Cabibbo-Kobayashi-Maskawa (CKM) matrix parameters. This article presents the first observation of the Cabibbo-suppressed decay Λc+→ne+νe, utilizing 4.5 fb−1 of electron-positron annihilation data collected with the BESIII detector. A novel Graph Neural Network based technique effectively separates signals from dominant backgrounds, notably Λc+→Λe+νe, achieving a statistical significance exceeding 10σ. The absolute branching fraction is measured to be (3.57 ± 0.34stat. ± 0.14syst.) × 10−3. For the first time, the CKM matrix element Vcd is extracted via a charmed baryon decay as 0.208±0.011exp.±0.007LQCD±0.001τΛc+. This work highlights a new approach to further understand fundamental interactions in the charmed baryon sector, and showcases the power of modern machine learning techniques in experimental high-energy physics.

Probing the soft rescattering parameters in B decays involving a scalar meson with QCD factorization

In this work, the soft rescattering parameters in the B±→π±π+π− and B±→K±π+π− decays with the light scalar meson f0(500) as the intermediate resonance are studied within the quantum chromodynamics (QCD) factorization. Considering the interference effect between ρ(770)0 and f0(500), we utilize the experimentally more direct event yields for fitting and get the soft rescattering parameters |ρkSP|=3.29±1.01 and |ρkPS|=2.33±0.73 in B→PS and B→SP decays (P and S denote pseudoscalar and scalar mesons, respectively), respectively. We also study the branching ratios and CP asymmetries in the decay modes involving other scalar mesons, including f0(980), a0(980), a0(1450) and K0*(1430), to test the rationality of the values of |ρkSP| and |ρkPS|. Meanwhile, the wealth of experimental data facilitate the examination of the forward-backward asymmetry induced CP asymmetries (FB-CPAs), and the localized CP asymmetries (LACPs). We investigate these asymmetries resulting from the interference between ρ(770)0 and f0(500) for B±→π±π+π− and B±→K±π+π− decays when the invariant mass of π+π− locates in the low-energy region 0.445 GeV<mππ<0.795 GeV. Our theoretical results of FB-CPAs and LACPs align with the experimental findings. We propose that the interference between ρ(770)0 and f0(500) can be extended to other beauty and charmed mesons decays. Published by the American Physical Society 2025

Semileptonic decay of the triply heavy Ωccb to the observed Ξcc++ state

We investigate the weak semileptonic decay of the Ωccb+→Ξcc++ℓν¯ℓ, where a triply heavy baryon with spin 1/2 decays into the observed doubly heavy baryon with spin 1/2, using quantum chromodynamics (QCD) sum rule method in all lepton channels. We compute the six relevant vector and axial vector form factors entering the low energy matrix elements in full theory. The invariant form factors are building blocks, using the fit faction of which in terms of q2 in whole physical region, we calculate the exclusive widths in three lepton channels. Our predictions may help the present and future experiments in the course of their search for doubly and triply heavy baryons. Published by the American Physical Society 2025

Quantitative analysis of the gravitational wave spectrum sourced from a first-order chiral phase transition of QCD

We investigate the cosmological first-order chiral phase transition of quantum chromodynamics (QCD), and for the first time calculate its parameters which can determine the gravitational wave spectrum. With the state-of-the-art calculation from the functional QCD method, we found that the large chemical potential of QCD phase transition results in very weak and fast first-order phase transitions at the temperature lower than O(102) MeV. These results further suggest that the gravitational wave (GW) signals of NANOGrav are very unlikely sourced from the chiral phase transition of QCD. Published by the American Physical Society 2025

Self-consistent M1 radiative transitions of excited Bc and heavy quarkonia with different polarizations in the light-front quark model

In this study, we investigate the properties of pseudoscalar and vector charmonia, bottomonia, and Bc mesons using the light-front quark model, focusing on the M1 radiative transition. For that purpose, we conduct a variational analysis with a quantum chromodynamics (QCD)-motivated effective Hamiltonian, employing a trial wave function expanded in the harmonic oscillator basis functions up to the 3S state. We fit the model parameters to mass spectra and decay constants, obtaining reasonable agreement with experimental data and correctly reflecting the hierarchy of mass spectra and decay constants. In analyzing the M1 radiative transition, we consider both good (μ=+) and transverse (μ=⊥) current components with both longitudinal (h=0) and transverse (h=±1) polarizations, demonstrating that the results from both components of currents and polarizations are identical. Self-consistency is achieved by substituting M with M0 when computing the operators for decay constants and radiative transitions. We also find that the difference between longitudinal and transverse polarizations of the observables may quantify the anisotropy of the model wave function. Our results on radiative transitions align reasonably well with experimental data, lattice QCD, and theoretical predictions. Furthermore, we also provide predictions for Bc mesons that can be tested in experiments. Published by the American Physical Society 2025

Chiral transition and meson melting within improved holographic soft wall models

We describe the chiral transition for the quark condensate and the melting of scalar and vector mesons in two-flavor holographic quantum chromodynamics (holographic QCD). This is done by extending the improved holographic soft wall models proposed in Ballon-Bayona [] to finite temperature, by means of introducing an asymptotically anti–de Sitter black brane. We find that the chiral transition is second order in the chiral limit and a crossover for physical quark masses, as expected in two-flavor QCD. We investigate the melting of vector and scalar mesons in the deconfined plasma through the calculation of hadronic spectral functions. Fixing the model parameters by the meson spectrum at zero temperature, we find that the mesons melt at temperatures between 90 and 110 MeV and the chiral transition occurs around 129 MeV. We also provide a prediction for the hydrodynamic diffusion constant associated with a flavor current in the deconfined plasma. Published by the American Physical Society 2025

Neutral pion to two-photons transition form factor revisited

Based upon a combined formalism of Schwinger-Dyson and Bethe-Salpeter equations in quantum chromodynamics (QCD), we propose a QCD-kindred algebraic model for the dressed quark propagator, for the Bethe-Salpeter amplitude of the pion and the electromagnetic quark-photon interaction vertex. We then compute the γ*π0γ transition form factor Gγ*π0γ(Q2) for a wide range of photon momentum transfer squared Q2. The quark propagator is expanded out in its perturbative functional form but with dynamically generated dressed quark mass. It has complex conjugate pole singularities in the complex-momentum plane, which is motivated by the solution of the quark gap equation with rainbow-ladder truncation of the infinite set of Schwinger-Dyson equations. This complex pole singularity structure of the quark propagator can be associated with a signal of confinement, which prevents quarks from becoming stable asymptotic states. The Bethe-Salpeter amplitude is expressed without a spectral density function, which encapsulates its low- and large-momentum behavior. The QCD evolution of the distribution amplitude is also incorporated into our model through the direct implementation of Efremov-Radyushkin-Brodsky-Lepage evolution equations. We include the effects of the quark anomalous magnetic moment in the description of the quark-photon vertex, whose infrared enhancement is known to dictate hadronic properties. Once the QCD-kindred model is constructed, we calculate the form factor Gγ*π0γ(Q2) and find it consistent with direct QCD-based studies, as well as most available experimental data. It slightly exceeds the conformal limit for large Q2, which might be attributed to the scaling violations in QCD. The associated interaction radius and neutral pion decay width turn out to be compatible with experimental data. Published by the American Physical Society 2024

Electric field induction in quark-gluon plasma due to thermoelectric effects

Relativistic heavy-ion collisions produce quark-gluon plasma (QGP), which is locally thermalized. Due to electrically charged particles (quarks), QGP exhibits interesting thermoelectric phenomena during its evolution, resulting in an electromagnetic (EM) field in the medium. In this study, for the first time, we estimate the induced electric field in QGP due to the thermoelectric effect. This phenomenon can induce an EM field even in QGP produced by the head-on heavy-ion collision. In peripheral heavy-ion collisions, the presence of a spectator current generates a transient magnetic field at the early stage, which disrupts the isotropy of the induced electric field. For the numerical estimation, we use a quasiparticle-based model that incorporates the lattice quantum chromodynamics equation of state for QGP. The induced electric field is estimated with cooling rates derived from Gubser hydrodynamic flow. Thermoelectric coefficients such as Seebeck, magneto-Seebeck, and Nernst coefficients play a crucial role in determining the induced field. Additionally, we account for the temperature evolution of QGP using different hydrodynamic cooling rates to calculate the transport coefficients. We also estimate the transport coefficients and the induced electric field in the presence of an external time-varying magnetic field, including the quantum effect of Landau quantization, and explore the effects of the intensity and decay parameter of the magnetic field on the induced electric field. Our findings reveal that the space-time profile of the induced electric field is zero at the center and increases as we go away from the center. During the early stages of evolution, the electric field can reach a maximum value of eE≈1mπ2, decreasing in strength over time. Published by the American Physical Society 2024

Search for baryon junctions in e+A collisions at the electron ion collider

Constituent quarks in a nucleon are the essential elements in the standard “quark model” associated with the electric charge, spin, mass, and baryon number of a nucleon. Quantum chromodynamics (QCD) describes nucleon as a composite object containing current quarks (valence quarks and sea (anti-)quarks) and gluons. These subatomic elements and their interactions are known to contribute in complex ways to the overall nucleon spin and mass. In the early development of QCD theory in the 1970s, an alternative hypothesis postulated that the baryon number might manifest itself through a non-perturbative configuration of gluon fields forming a Y-shaped topology known as the gluon junction. In this work, we propose to test such hypothesis by measuring (i) the Regge intercept of the net-baryon distributions for e+(p)Au collisions, (ii) baryon and charge transport in the isobaric ratio between e+Ru and e+Zr collisions, and (iii) target flavor dependence of proton and antiproton yields at large rapidity, transported from the hydrogen and deuterium targets in e+p(d) collisions. Our study indicates that these measurements at the EIC can help determine what carries the baryon number.

Investigation of the internal structure of the deuteron against the background of two-photon exchange effects in elastic electron-deuteron scattering

This work aims to investigate the simultaneous influence of two-photon effects in quantum electrodynamics and logarithmic corrections in quantum chromodynamics on certain observable experimental quantities (structure functions A(Q2) and B(Q2) in elastic electron-deuteron scattering). Analyzing these effects broadens our understanding of electron scattering physics, particularly the manifestations of quark-gluon degrees of freedom in the deuteron.

Multijet event shape variables for Mueller-Navelet jet topologies

This paper presents a new set of multijet event shape variables introduced to further understand the Mueller-Navelet jet topology. This topology consists of having at least one pair of jets with a very large rapidity separation between them, treating additional jet activity inclusively. This multijet topology is expected to shed light on the radiation pattern that is expected in the high-energy limit of the strong interaction. The paper relies on a Monte Carlo event generator analysis. One set of predictions uses the ex event generator, which is based on Balitsky-Fadin-Kuraev-Lipatov (BFKL) perturbative quantum chromodynamics (pQCD) evolution with a resummation of large logarithms of energy at leading-logarithmic accuracy. The ex predictions are compared with a fixed-order next-to-leading order pQCD calculation using matched to the parton shower of ythia8 (NLO+PS), which is the standard for NLO generator predictions at the LHC. We find that both approaches lead to compatible results at current LHC energies, assuming the current experimental constraints for the reconstruction of low transverse momentum jets in ATLAS and CMS. This shows the reliability of the BFKL approach at describing the behavior of the strong interaction in the preasymptotic limit of high center-of-mass energies. Differences between the NLO+PS and the BFKL-based approaches are found when the jet multiplicity is increased or when the minimum transverse momentum of the jets is decreased. Published by the American Physical Society 2024

QCD axion: Some like it hot

We compare the quantum chromodynamics (QCD) axion phase-space distribution from unitarized next-to-leading order chiral perturbation theory with the one extracted from pion-scattering data. We derive a robust bound by confronting momentum-dependent Boltzmann equations against up-to-date observations of the cosmic microwave background, of the baryonic acoustic oscillations and of primordial abundances. These datasets imply ma≤0.16 eV for the 95% credible interval, i.e., ∼30% stronger bound than what previously found. We present forecasts using dedicated likelihoods for future cosmological surveys and the sphaleron rate from unquenched lattice QCD. Published by the American Physical Society 2024

Nuclear correlation functions using first-principle calculations of lattice quantum chromodynamics

Exploring nuclear physics through the fundamental constituents of the strong force—quarks and gluons—is a formidable challenge. While numerical calculations using lattice quantum chromodynamics offer the most promising approach for this pursuit, practical implementation is arduous, especially due to the uncontrollable growth of quark-combinatorics, the so-called Wick-contraction problem of nuclei. We present here two novel methods providing a state-of-the art solution to this problem. In the first, we exploit randomized algorithms inspired from computational number theory to detect and eliminate redundancies that arise in Wick contraction computations. Our second method explores facilities for automation of tensor computations—in terms of efficient utilization of specialized hardware, algorithmic optimizations, as well as ease of programming and the potential for automatic code generation—that are offered by new programming models inspired by applications in machine learning (e.g., ensorlow). We demonstrate the efficacy of our methods by computing two-point correlation functions for Deuteron, Helium-3, Helium-4, and Lithium-7, achieving at least an order of magnitude improvement over existing algorithms with efficient implementation on GPU-accelerators. Additionally, we discover an intriguing characteristic shared by all the nuclei we study: specific spin-color combinations dominate the correlation functions, hinting at a potential connection to an as-yet-unidentified symmetry in nuclei. Moreover finding them beforehand can reduce the computing time further and substantially. Our results, with the efficiency that we achieved, suggest the possibility of extending the applicability of our methods for calculating properties of light nuclei, potentially up to A∼12 and beyond. Published by the American Physical Society 2024

PHENOMENOLOGY OF HIGH MULTIPLICITY IN LEPTON INTERACTIONS

Interest to processes of multiparticle production in lepton and hadron interactions is not decreased. Development of strong interaction theory, quantum chromodynamics, allowes describing of these interactions at the quark-gluon level. Transit from partons to observable hadrons at the hadronization stage is extremely difficult. This paper presents the gluon dominance model that describes multiparticle production of secondary particles including the hadronization stage. This model is applied to the description of 𝑒+𝑒−- annihilation. It confirms the active role of the gluon component at the secondary particle formation, evidences about fragmentation mechanism of hadronization, which is realized in vacuum, describes multiplicity distribution data.

PRODUCTION OF POLARIZED 𝐽/ MESONS WITHIN NRQCD AND GENERALIZED PARTON MODEL

In the present paper, we study the production of polarized 𝐽/ mesons at the NICA collider energy (√𝑠 = 27 GeV) within the generalized parton model (GPM) in the leading order (LO) of perturbative quantum chromodynamics (QCD). The hadronization of 𝑐𝑐¯-quarks into a 𝐽/ -meson is described within the nonrelativistic QCD (NRQCD) model. Nonperturbative parameters of the models were fixed from a comparison with existing experimental data for production prompt 𝐽/ -mesons at the energies √𝑠 = = 19.4 GeV (NA3) and √𝑠 = 200 GeV (PHENIX).

Generalized susceptibilities of the net-baryon number based on the three-dimensional Ising universality class* *Supported by Research Start-up Fund Project of Chengdu University (X2110) and I acknowledge fruitful discussions with Xiaofeng Luo and Lizhu Chen

Assuming the equilibrium of the Quantum Chromodynamics (QCD) system, we investigate the critical behavior of the sixth-, eighth-, and tenth-order susceptibilities of the net-baryon number through mapping the results in the three-dimensional Ising model to that of QCD. Both the leading and sub-leading critical contributions from the Ising model are discussed. When considering only the leading critical contribution, the density plots of susceptibilities of the same order demonstrate a consistent general pattern independent of the values of the mapping parameters. As the critical point is approached from the crossover side, a negative dip followed by a positive peak is observed in the dependence of the three different orders of susceptibilities. When sub-leading critical contribution is considered, modifications become apparent in the density plots of the susceptibilities. The emergence of negative dips in the dependence of the susceptibilities is not an absolute phenomenon, whereas the positive peak structure is a more robust feature of the critical point.

Electroweak corrections and EFT operators in W+W− production at the LHC

We investigate the impact of electroweak corrections and effective field theory operators on W+W− production at the Large Hadron Collider (LHC). Utilizing the Standard Model effective-field theory (SMEFT) framework, we extend the Standard Model by incorporating higher-dimensional operators to encapsulate potential new physics effects. These operators allow for a model-independent approach to data interpretation, essential for probing beyond the Standard Model physics. We generate pseudodata at the next-to-leading order in quantum chromodynamics and include approximate electroweak corrections. Our analysis focuses on the interplay between these corrections and SMEFT operators at leading order. The inclusion of electroweak corrections is crucial as they can counteract the effects predicted by SMEFT operators, necessitating precise theoretical and experimental handling. By examining pp→W+W− production, a process sensitive to the electroweak symmetry-breaking mechanism, we demonstrate the importance of these corrections in isolating and interpreting new physics signatures. Our results highlight the significant role of electroweak corrections in enhancing the interpretative power of LHC data and in obtaining reliable constraints on new physics interactions. Published by the American Physical Society 2024

Collective description of low energy mesonic states

The phenomenology of hadronic states at high energy is well described in the framework of quantum chromodynamics. By the other hand, that is the description of the low-energy regime, e.g., mesoniclike states, requires the introduction of effective degrees of freedom, a condition resulting from confinement. As an alternative to lattice gauge calculations, and own to the similarities with other quantum many-body systems, we have adopted a nonperturbative scheme where quarks are treated as quasiparticles. These quasiquarks interact between them, allowing mesonlike states to be described as collective superposition of quasiquark pairs. The results of the calculations, performed in the context of the random phase approximation method, show that this scheme is a suitable one to describe meson states up to energies of the order of couple of GeV. Published by the American Physical Society 2024

Quasifragmentation functions in the massive Schwinger model

We introduce the concept of the quark quasifragmentation function (qFF) using an equal-time and spatially boosted form of the Collins-Soper fragmentation function where the out-meson fragment is replaced by the current asymptotic condition. We derive the qFF for a fermion in two-dimensional quantum electrodynamics (QED2) using the Kogut-Susskind Hamiltonian after a mapping onto spin qubits in a spatial lattice with open boundary conditions. This form is suitable for quantum computations. We compute the qFF by exact diagonalization of the spin Hamiltonian. The results are compared to the qFF following from the Drell-Levy-Yan result for QED2, both at strong and weak coupling, and to two-dimensional quantum chromodynamics in the lowest Fock approximation. Published by the American Physical Society 2024

Hidden strangeness in meson weak decays to baryon pair

Our study focuses on the weak decay of Ds+→pn¯, which is the only possible two-body baryonic decay in the D meson system. An analysis using perturbative quantum chromodynamics (pQCD) is challenging in this decay due to the small amount of energy released. In particular, naive factorization, suppressed by the light quark masses, results in a minor contribution to this channel. In the framework of final state interactions, the hidden strangeness in the intermediate state naturally avoids this chiral suppression from light quark masses. The branching fraction is predicted to be B(Ds+→pn¯)=(1.43±0.10)×10−3, in agreement with the experimental value of (1.22±0.11)×10−3. We also analyze the decays of B mesons into two charmed baryons involving annihilation-type topological diagrams. In these decays, we conduct a joint analysis of naive factorization and final state interactions. Using the experimental upper bound of B(Bs0→Λc+Λ¯c−)<8×10−5, we set a constraint on the coupling constant gD+Λc+n<7.5. Final state interactions lead to a prediction of the decay parameter γ(Bs0→Λc+Λ¯c−)>0.8, whereas pQCD predicts it to be negative. We propose future measurements of B0→Ξc+Ξ¯c−, predicting a significant SU(3)F breaking effect with B(B0→Ξc+Ξ¯c−)B(Bs0→Λc+Λ¯c−)=1.4%, contrary to the naive estimate of 5.3%. We strongly recommend future measurements. Published by the American Physical Society 2024