Hadron Spectroscopy Research Articles

Refining radiative decay studies in singly heavy baryons

In this work, we systematically study the radiative decays of singly heavy baryons, a crucial aspect of their spectroscopic behavior. To enhance the accuracy of our calculations, we utilize numerical spatial wave functions for the singly heavy baryons obtained through the Gaussian expansion method, which also yields their mass spectrum. As hadron spectroscopy enters an era of high precision, we believe our study of the radiative decays of singly heavy baryons will provide valuable insights for further exploration of these particles. Published by the American Physical Society 2024

Meson spectroscopy from spectral densities in lattice gauge theories

Spectral densities encode nonperturbative information that enters the calculation of a plethora of physical observables in strongly coupled field theories. Phenomenological applications encompass aspects of standard-model hadronic physics, observable at current colliders, as well as correlation functions characterizing new physics proposals, testable in future experiments. By making use of numerical data produced in a Sp(4) lattice gauge theory with matter transforming in an admixture of fundamental and 2-index antisymmetric representations of the gauge group, we perform a systematic study to demonstrate the effectiveness of recent technological progress in the reconstruction of spectral densities.To this purpose, we write and test new software packages that use energy-smeared spectral densities to analyze the mass spectrum of mesons. We assess the effectiveness of different smearing kernels and optimize the smearing parameters to the characteristics of available lattice ensembles. For concreteness, we analyze the Sp(4) lattice gauge theory with matter transforming in an admixture of fundamental and 2-index antisymmetric representations of the gauge group. We generate new ensembles for the theory in consideration, with lattices that have a longer extent in the time direction with respect to the spatial ones. We run our tests on these ensembles, obtaining new results about the spectrum of light mesons and their excitations. We make available our algorithm and software for the extraction of spectral densities, that can be applied to theories with other gauge groups, including the theory of strong interactions (QCD) governing hadronic physics in the standard model. Published by the American Physical Society 2024

Second resonance of the Higgs field: motivations, experimental signals, unitarity constraints

Perturbative calculations predict that the effective potential of the Standard Model should have a new minimum, well beyond the Planck scale, which is much deeper than the electroweak vacuum. So far, most authors have accepted the metastability scenario in a cosmological perspective which is needed to explain why the theory remains trapped in our electroweak vacuum but requires to control the properties of matter in the extreme conditions of the early universe. As an alternative, one can consider the completely different idea of a non-perturbative effective potential that, as at the beginning of the Standard Model, is restricted to the pure Φ4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Phi ^4$$\\end{document} sector but is consistent with the indications of the now existing analytical and numerical studies, namely “triviality” and a description of SSB as weak first-order phase transition. In this approach, the electroweak vacuum is now the lowest energy state because, besides the state with mass mh=125\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$m_h=125$$\\end{document} GeV, defined by the quadratic shape of the potential at its minimum, there is a second much larger mass scale (MH)Theor∼690(30)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(M_H)^\ extrm{Theor} \\sim 690(30)$$\\end{document} GeV associated with the zero-point energy determining the potential depth. Despite its large mass, the heavier state would couple to longitudinal Ws with the same typical strength as the low-mass state at 125 GeV and thus represent a relatively narrow resonance mainly produced at LHC by gluon-gluon fusion. Therefore, it is interesting that, in the LHC data, one can find combined indications of a new resonance of mass (MH)comb∼685(10)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(M_H)^\ extrm{comb} \\sim 685 (10)$$\\end{document} GeV, with a statistical significance which is far from negligible. Since this non-negligible evidence could become an important new discovery with forthcoming data, we outline further refinements of the theoretical predictions, that could be obtained by implementing unitarity constraints, in the presence of fermion and gauge fields, with the type of coupled-channel calculations nowadays used in meson spectroscopy.

Exotic Hadrons at LHCb

It has been 5 years since the data sample from the LHCb detector, the first experiment optimized for heavy-flavor physics studies at a hadronic collider, was completed. These data led to many major discoveries in exotic hadron spectroscopy, which we review in this article. We supplement the experimental results with a selection of phenomenological interpretations. As the upgraded LHCb detector is expected to collect a larger data sample starting in 2024, we also discuss the potential of the LHCb program in exotic hadron physics for the near future and beyond.

Purely leptonic decays of heavy-flavored charged mesons

We study the purely leptonic decays of heavy-flavored charged pseudoscalar (P) and vector (V) mesons (D(s)(*)+, B(c)(*)+) in the relativistic independent quark (RIQ) model based on an average flavor-independent confining potential in an equally mixed scalar-vector harmonic form. We first compute the mass spectra of the ground-state-mesons and fix the model parameters necessary for the present analysis. Using the meson wave functions derivable in the RIQ model, and model parameters so fixed from hadron spectroscopy, we predict the decay constants: fP(V), ratios of decay constants: fV/fP, fP1/fP2, fV1/fV2, and the branching fractions (BFs): B(P(V)→l+νl), l=e, μ, τ, which agree with the available experimental data and other Standard Model (SM) predictions. For the unmeasured decay constants, especially in the purely leptonic decays of the charged vector mesons, our predictions could be tested in the upcoming Belle-II, SCTF, CEPC, FCC-ee, and LHCb experiments in the near future. Published by the American Physical Society 2024

Four-charm-quark matter from the CMS collaboration as a witness of the development of high-precision Hadron spectroscopy

Four-charm-quark matter from the CMS collaboration as a witness of the development of high-precision Hadron spectroscopy

The effect of cutoff dependence on heavy quark spin symmetry partners

Hadron spectroscopy is revealed by observing heavy resonances. Among various explanations of the internal structure of these hadronic states, hadronic molecules play a unique role. For hadronic molecules, which are associated with meson–meson or meson–baryon interactions, the [Formula: see text] cutoff is a significant factor in determining the composite states’ binding energies and overall properties. The cutoff becomes important when it comes to the location of hadronic molecules’ masses because it influences the predictions. From this perspective, in the light of cutoff dependency, heavy quark spin partners of near-threshold the [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] resonances, which are considered as hadronic molecules, are examined.

Light meson decays at BESIII

The world's largest sample of J/ψ events(1010) collected at BESIII detector offers a unique opportunity to investigate η and η′ physics via the J/ψ radiative or hadronic decays with unprecedented precision. In recent years the BESIII experiment has made significant progresses in η/η′ decays. A selection of recent highlights in light meson spectroscopy at BESIII is reviewed in this report.

Hadron Spectroscopy with lattice QCD: Challenges and opportunities

Ongoing challenges in computing the spectrum of hadronic resonances and shallow bound-states from lattice QCD are reviewed. Since such states are identified as poles in the scattering matrix, nearby non-analyticities must be treated to analytically continue to complex center-of-mass energies. Significant lattice spacing effects have also been observed in some channels, necessitating a continuum limit. Recent achievements are also highlighted, including lattice investigations of states in the charm region, baryon-baryon scattering, and the first coupled channel meson-baryon amplitude in the Λ(1405) channel.

Spectroscopy of heavy exotic mesons using lattice QCD static potentials and the Born-Oppenheimer approximation

I discuss the investigation of heavy exotic mesons using lattice QCD static potentials and the Born-Oppenheimer approximation. I summarize selected recent results for b¯b¯qq tetraquarks, for I = 0 bottomonium and for I = 1 bottomonium.

Exploring Light Meson Resonances in Two-Pion Photoproduction: A Regge Formalism Analysis

In the domain of hadron spectroscopy, the investigation of meson resonances plays a pivotal role. This study focuses on the significance of twopion photoproduction as a prominent avenue for studying meson resonances in the ππ system. By employing the Regge formalism, our model incorporates the background contribution from the well-known “Deck Mechanism” and emphasizes the significant ρ(770) resonance, representing the P-wave contribution arising from pomeron and f2 exchanges. The model is extended by accounting for scalar mesons, namely σ, f0(980) and f0(1370), contributing to the S-wave behavior, as well as the tensor meson f2(1270) corresponding to the D-wave contributions, while also considering non-resonant P- and S-wave components. The model contains a number of free parameters, which are constrained from a global fit of the available experimental data for angular moments up to L = 2 for M = 0, …, 2. The fitted angular moments are compared with experimental data obtained from CLAS. The key physical insights gained from the model are summarized. Furthermore, we extract the t-dependence of the Regge amplitude residue function for the subdominant exchanges, shedding light on their contribution to the overall dynamics.

Recent results on charmed baryons from Belle

Charmed baryon spectroscopy can provide unique insights into QCD at low energies. The large data sample accumulated by the Belle experiment at the KEKB asymmetric-energy e+e− collider enables new opportunities to study charmed baryons. We present recent measurements of charmed baryons at Belle, including studies of Λc+ → Σ+η ('), Λc+ → pKS0KS0 / pKS0η, Ωc0 → Ξ−π+ / Ξ−K+ / Ω−K+, and recent results on the properties of the excited state Λc(2625)+.

Overview of hadron photoproduction experiments in SPring-8 LEPS2 project

An experimental project to study hadron properties through photoproduction reactions is carried out in SPring-8 LEPS2 beamline. As an overview of this project, recent physics achievements and prospects on light baryon spectroscopy, exotic hadrons / bound states, and the origin of hadron mass are discussed with the description of experimental setups.

Heavy–Light meson spectroscopy with strong coupling at N2LO level in V-scheme

The quark–antiquark potential is one of the basic ingredients of QCD-inspired potential models. This work will report the results of the masses and decay constants of heavy-flavor pseudo-scalar mesons within a QCD-based potential model having both inverse distance Coulomb and the linear confinement pieces. To that end, we use the inverse piece incorporating two-loop effects as suggested in V-scheme. Quantum mechanical perturbative methods: Dalgarno’s method of perturbation theory and variationally improved perturbation theory are used for the investigation. We use the Coulombic piece as the parent which is allowed by both Dalgarno’s perturbation theory and variationally improved perturbation theory. The results are compared with the latest updated theoretical predictions and PDG data. The sensitivity of the input parameters of the model has been discussed.

Spectroscopy of Mesons Produced by Linearly Polarized Photons

A formalism for the experimental analysis of mesons produced by a beam of linearly polarized photons is presented. This formalism introduces a more general use of the reflectivity operator. The goal is to recognize resonances in cross-sections, their associated quantum numbers, and production mechanisms by performing partial wave analysis of multiple-meson final states.

The large-area hybrid-optics CLAS12 RICH: First years of data-taking

The CLAS12 deep-inelastic scattering experiment at the upgraded 12 GeV continuous electron beam accelerator facility of Jefferson Lab conjugates luminosity and wide acceptance to study the 3D nucleon structure in the yet poorly explored valence region, and to perform precision measurements in hadron spectroscopy. A large area ring-imaging Cherenkov detector has been designed to achieve the required hadron identification in the momentum range from 3 GeV/c to 8 GeV/c, with the kaon rate about one order of magnitude lower than the rate of pions and protons. The adopted solution comprises aerogel radiator and composite mirrors in a novel hybrid optics design, where either direct or reflected light could be imaged in a high-packed and high-segmented photon detector. The first RICH module was assembled during the second half of 2017 and installed at the beginning of January 2018, in time for the start of the experiment. The second RICH module, planned with the goal to be ready for the beginning of the operation with polarized targets, has been timely built despite the complications caused by the pandemic crisis and successfully installed in June 2022. The detector performance is here discussed with emphasis on the operation and stability during the data-taking, calibration and alignment procedures, reconstruction and pattern recognition algorithms, and particle identification.

Light Baryon Spectroscopy

The precise understanding of the interaction inside the nucleons is still an open question in hadron spectroscopy. To tackle this issue, nucleons are excited by photons and their excitation spectra are determined. This effort is addressed by several different experiments worldwide, where different polarization observables are extracted for various reactions. This proceeding will give a short overview about the current status in Light Baryon Spectroscopy.

The ANDA experiment at FAIR

The Facility for Antiproton and Ion Research, FAIR, is presently under construction near Darmstadt, Germany. Among other large-scale installations, the ANDA (Antiproton annihilations in Darmstadt) experiment is designed to address pertinent questions of the strong interaction in the non-perturbative region. At ANDA, an antiproton beam, with momenta between 1.5 GeV/c and 15 GeV/c, circulating in the high-energy storage ring HESR will interact with internal targets. High interaction rates and unprecedented momentum resolusion will allow for a high discovery potential and precision experiments. The detector system of ANDA is optimised to meet the challenges of high-resolution hadron spectroscopy in formation and production with very good background suppression. At the same time, it meets the requirements of other parts of the physics program such as hyperon and hadron structure physics. The detector is reviewed and physics goals are presented.

Delta Baryon Spectroscopy in Lattice QCD

A variational analysis is performed within the framework of lattice QCD to extract the masses of the spin-3/2 positive parity Delta ^+ baryons, including radial excitations. 2 + 1 flavour dynamical gauge-field configurations provided by the PACS-CS collaboration via the ILDG are considered. To improve our interpolator basis, we perform an iterative process of source and sink smearing and solve a generalised eigenvalue problem using the resulting fermion operators. We obtain a clear signal for the ground and first excited states at a light quark mass corresponding to m_pi = 413 MeV. Furthermore, we show that one can use the eigenvectors obtained in this method to investigate the nature of these states, allowing us to classify our results as 1s and 2s states for the ground and first excited states respectively. Finally, we briefly highlight the method of Hamiltonian effective field theory which can be used to make comparison with quark model expectations.

Baryon Spectroscopy at GlueX

Baryon Spectroscopy at GlueX