Low-energy Hadron Research Articles

Entanglement between valence and sea quarks in hadrons of 1+1 dimensional QCD

The conceptual interpretation of valence- and sea-quark separation, which is a key aspect of the parton model and of an intuitive picture of hadron structure, becomes obscured by quantum effects in QCD. This suggests that there may be measures of entanglement between quark degrees of freedom that are present in QCD, but absent in the intuitive picture with a clear valence-sea (VS) separation. In this paper, we define the first rigorous measure of VS entanglement in QCD in an attempt to bring conceptual clarity to this issue, and, potentially, to find a measure of the applicability of the parton model to QCD bound states. This VS entanglement vanishes in the large-Nc limit, and it remains low when finite-Nc states resemble their large-Nc counterparts. We perform a numerical study of VS entanglement in 1 + 1 dimensional discrete light-cone quantized QCD, and in the process develop a method for building the color-singlet basis of 1 + 1d QCD that is manifestly complete and orthogonal by construction. We calculate this VS entanglement entropy for the first time and find that it is relatively low for the first few excited states of both mesons and baryons compared to all other states in the spectrum, with the VS entropy of ground state hadrons providing a minimum. We also see that for ground state mesons the entropy is well described in the 1/Nc approximation. These results suggest that low energy hadrons may be the only QCD bound states for which the large-Nc expansion, and perhaps the parton model, provide an accurate description. This work also provides the first evidence that the VS entanglement entropy of QCD in 3 + 1d, which would likely serve as an order parameter for the transition between quark and hadron degrees of freedom, may be perturbatively accessible through a large-Nc expansion.

Unitarized one-loop graviton-graviton scattering

In this work we interpret the Einstein-Hilbert (EH) Lagrangian of gravitation as the first term of a low-energy effective theory similar to those considered in the chiral Lagrangian approach to low-energy hadron physics or the electroweak chiral Lagragians describing the symmetry breaking sector of the Standard Model (SM). Starting from the one-loop computation of the elastic gravitongraviton scattering amplitude by Dunbar and Norridge, we unitarize the IR regularized partial waves by using the Inverse Amplitude Method (IAM). This method enlarges the regime of applicability of the perturbative results to higher energies of the order of the Plank scale MP and allows for the possibility of poles in the second Riemann which have the natural interpretation of dynamical resonances. In this work we look for these possible resonances for the ++++ and −−−− helicity channels and the J = 0, 2 and 4 partial waves.

Quantum phase transitions within a nuclear cluster model and an effective model of QCD

The catastrophe theory is applied to a nuclear cluster model and an effective model for QCD at low energy. The study of quantum phase transitions in the cluster model was considered in an earlier publication, but restricted to spherical clusters and on a semi-classical level. In the present contribution, we include the case of deformed clusters and determine the spectrum numerically as a function of an interaction parameter, where signatures of a quantum phase transition can be seen. It is shown that in this more complicated case, with deformation of the clusters, the catastrophe theory can be applied with some interesting consequences. A further example of a many-body problem is considered, namely an effective model of QCD, which is able to describe the low energy hadron spectrum and, when temperature is introduced, even ratios of particle-antiparticle productions. The catastrophe theory is able to provide useful information on the phase transition from a perturbative to a non-perturbative vacuum. These contributions show the universal usefulness of catastrophe theory, while more examples of applications to different fields are mentioned in the Introduction.

Constraints on the two-pion contribution to hadronic vacuum polarization

At low energies hadronic vacuum polarization (HVP) is strongly dominated by two-pion intermediate states, which are responsible for about 70% of the HVP contribution to the anomalous magnetic moment of the muon, aμHVP. Lattice-QCD evaluations of the latter indicate that it might be larger than calculated dispersively on the basis of e+e−→ hadrons data, at a level which would contest the long-standing discrepancy with the aμ measurement. In this Letter we study to which extent this 2π contribution can be modified without, at the same time, producing a conflict elsewhere in low-energy hadron phenomenology. To this end we consider a dispersive representation of the e+e−→2π process and study the correlations which thereby emerge between aμHVP, the hadronic running of the fine-structure constant, the P-wave ππ phase shift, and the charge radius of the pion. Inelastic effects play an important role, despite being constrained by the Eidelman–Łukaszuk bound. We identify scenarios in which aμHVP can be altered substantially, driven by changes in the phase shift and/or the inelastic contribution, and illustrate the ensuing changes in the e+e−→2π cross section. In the combined scenario, which minimizes the effect in the cross section, a uniform shift around 4% is required. At the same time both the analytic continuation into the space-like region and the pion charge radius are affected at a level that could be probed in future lattice-QCD calculations.

Particle production, transport, and identification in the regime of 1−7 GeV/c

The recently constructed H4-VLE beam line, a tertiary extension branch of the existing H4 beam line in the CERN North Area, was commissioned in October 2018. The beam line was designed with the purpose of providing very low energy (VLE) hadrons and positrons to the NP-04 experiment, in the momentum range of $1--7\text{ }\mathrm{GeV}/c$. The production of these low-energy particles is achieved with a mixed hadron (pions, kaons, protons), $80\text{ }\text{ }\mathrm{GeV}/c$ secondary beam impinging on a thick target. The H4-VLE beam line has been instrumented with prototype scintillating fiber detectors providing the beam profile, intensity, and time-of-flight measurement of the beam particles, that, together with Cherenkov threshold counters, permit an event-by-event particle identification over the entire momentum spectrum. In this paper, we present detailed results of the beam line performance and the measured beam composition, as well as the comparison of these measurements with simulations performed during the design phase using fluka and geant-4-based Monte-Carlo codes.

Radiative corrections in Dalitz decays of π0, η and η′ mesons

We briefly summarize current experimental and theoretical results on the two important processes of the low-energy hadron physics involving neutral pions: the Dalitz decay of π0 and the rare decay π0 → e+e−. As novel results we present the complete set of radiative corrections to the Dalitz decays η(′) → l+l−γ beyond the soft-photon approximation, i.e. over the whole range of the Dalitz plot and with no restrictions on the energy of a radiative photon. The corrections inevitably depend on the η(′) → γ*γ(*) transition form factors.

From QCD symmetries to nuclei and neutron stars

Global symmetries and symmetry breaking patterns of QCD with light quarks, in particular chiral symmetry, provide basic guidance not only for low-energy hadron physics but also for nuclear forces and the nuclear many-body problem. Recent developments of Chiral Effective Field Theory (ChEFT) applications to nuclear and neutron matter are summarized, with special emphasis on a (nonperturbative) extension using functional renormalization group methods. Topics include: nuclear thermodynamics, extrapolations to dense baryonic matter and constraints from neutron star observables.

Electron-deuteron deep-inelastic scattering with spectator nucleon tagging and final-state interactions at intermediate x

We consider electron-deuteron deep-inelastic scattering (DIS) with detection of a proton in the nuclear fragmentation region ("spectator tagging") as a method for extracting the free neutron structure functions and studying their nuclear modifications. Such measurements could be performed at a future Electron-Ion Collider (EIC) with suitable forward detectors. The measured proton recoil momentum (~< 100 MeV in the deuteron rest frame) specifies the deuteron configuration during the high-energy process and permits a controlled theoretical treatment of nuclear effects. Nuclear and nucleonic structure are separated using methods of light-front quantum mechanics. The impulse approximation (IA) to the tagged DIS cross section contains the free neutron pole, which can be reached by on-shell extrapolation in the recoil momentum. Final-state interactions (FSI) distort the recoil momentum distribution away from the pole. In the intermediate-x region 0.1 < x < 0.5 FSI arise predominantly from interactions of the spectator proton with slow hadrons produced in the DIS process on the neutron (rest frame momenta ~< 1 GeV, target fragmentation region). We construct a schematic model describing this effect, using final-state hadron distributions measured in nucleon DIS experiments and low-energy hadron scattering amplitudes. We investigate the magnitude of FSI, their dependence on the recoil momentum (angular dependence, forward/backward regions), their analytic properties, and their effect on the on-shell extrapolation. We comment on the prospects for neutron structure extraction in tagged DIS with EIC. We discuss possible extensions of the FSI model to other kinematic regions (large/small x). In tagged DIS at x << 0.1 FSI resulting from diffractive scattering on the nucleons become important and require separate treatment.

Witten Effect and Fractional Charges on the Domain Wall and the D-Brane-Like Dot

We have discussed the anomalous excitations such as dyons, Majorana fermions, and quark-like fermions on the domain wall in topological materials and the D-brane-like dot, and the relation to low-energy hadrons in QCD, from the viewpoint of a field-theoretical formula.

Experimental and theoretical premises of new stable hadron existence

The hypothesis of the new stable heavy hadrons existence is proposed which follows from Cosmic rays physics indirect data. It is shown that the hypothesis does not contradict Cosmochemical data, Cosmological test and the restrictions on New Physics effects. The conclusion is based on the most important property of the new hadrons — repulsion strong interaction with nucleons at large distance asymptote. This effect is substantiated theoretically in the framework of the low-energy hadron interaction model. Some extensions of Standard Model is considered where new stable and metastable quarks appear.

Generalized fermion symmetry, its currents algebra, and Ward-Takahashi identities

We introduce a new local symmetry into the fermion sector of a gauge invariant Lagrangian which may or may not contain a scalar or spontaneous symmetry breaking. The Standard Model in the unitary gauge and QCD are particular cases where this symmetry may apply. We determine the associated vector and axial vector currents and their conservation laws. We show that a single current conservation law may lead to multiple Ward-Takahashi identities. Our results can potentially have important consequences for effective models of low-energy QCD and hadron structure. As an specific example, we discuss the construction of tetraquark states within a generalized linear sigma model and show that this new symmetry probes the tetraquarks in a manner that is consistent with the large $N_c$ limit of QCD.

Induced Topological-charges on a Domain Wall of the Semiconductor Dot and the D-brane-like Dot

Anomalous excitations in the electron state of the semiconductor-dot have been analyzed from viewpoint of field-theoretical formula. We have introduced the toy-model of the quantum-dot, which is composed of three degenerated D4-branes-like solitons. The relation to low energy hadron in QCD has been suggested.

A generalized description of the signal size in extensive air shower detectors and its applications

The number as well as the energy and angular distributions of particles in extensive air showers (EAS) depend on the stage of the shower development and the distance to the shower axis. In this work we derive an analytic parameterization of the particle distributions at ground from air shower simulations convolved with the response of a surface detector array. Shower particles are classified into four components according to the shower component they belong to: the muonic component, the electromagnetic component stemming from muon interactions and muon decay, the purely electromagnetic component, and the newly introduced electromagnetic component from low-energy hadrons. Using this scheme, we will show that the total signal at ground level for different surface detectors can be described with minimal fluctuations with parameterizations depending on the primary energy, position of the shower maximum, and the overall number of muons in the shower. The simulation results for different combinations of primaries and hadronic interaction models are reproduced with an accuracy better than 5–10% in the range from 100 m to 2000 m from the shower core. This parameterization is then used as a Lateral Distribution ansatz to reconstruct showers in current EAS experiments. Since this ansatz depends on physical parameters, it opens the possibility to infer them from data.

New complex EAS installation of the Tien Shan mountain cosmic ray station

In this paper we present a description of the new complex installation for the study of extensive air showers which was created at the Tien Shan mountain cosmic ray station, as well as the results of the test measurements made there in 2014–2016. At present, the system for registration of electromagnetic shower component consists of ∼100 detector points built on the basis of plastic scintillator plates with the sensitive area of 0.25m2 and 1m2, spread equidistantly over ∼104m2 space. The dynamic range of scintillation amplitude measurements is currently about (3–7)·104, and there is a prospect of it being extended up to ∼106. The direction of shower arrival is defined by signal delays from a number of the scintillators placed cross-wise at the periphery of the detector system. For the investigation of nuclear active shower components a multi-tier 55m2 ionization-neutron calorimeter with a sum absorber thickness of ∼1000g/cm2, typical spatial resolution of the order of 10cm, and dynamic range of ionization measurement channel about ∼105 was created. Also, the use of saturation-free neutron detectors is anticipated for registration of the high- and low-energy hadron components in the region of shower core. A complex of underground detectors is designed for the study of muonic and penetrative nuclear-active components of the shower.The full stack of data acquisition, detector calibration, and shower parameters restoration procedures are now completed, and the newly obtained shower size spectrum and lateral distribution of shower particles occur in agreement with conventional data. Future studies in the field of 1014–1017eV cosmic ray physics to be held at the new shower installation are discussed.

The constituent-quark model — Nowadays

The present performance of the constituent-quark model as an effective tool to describe low-energy hadrons on the basis of quantum chromodynamics is exemplified along the relativistic constituent-quark model with quark dynamics relying on a realistic confinement and a Goldstone-boson-exchange hyperfine interaction. In particular, the spectroscopy of all known baryons is covered within a universal model in good agreement with phenomenology. The structure of the nucleons as probed under electromagnetic, weak, and gravitational interactions is produced in a correct manner. Likewise, the electroweak form factors of the baryons with u, d, and s flavor contents, calculated so far, result reasonably. Shortcomings still remain with regard to hadronic resonance decays.

Low Energy Hadron Physics with {\sf carlomat\_3.0}

Low Energy Hadron Physics with {\sf carlomat\_3.0}

Automatic track recognition for large-angle minimum ionizing particles in nuclear emulsions

We previously developed an automatic track scanning system which enables the detection of large-angle nuclear fragments in the nuclear emulsion films of the OPERA experiment. As a next step, we have investigated this system's track recognition capability for large-angle minimum ionizing particles (1.0 ⩽ |tan θ| ⩽ 3.5). This paper shows that, for such tracks, the system has a detection efficiency of 95% or higher and reports the achieved angular accuracy of the automatically recognized tracks. This technology is of general purpose and will likely contribute not only to various analyses in the OPERA experiment, but also to future experiments, e.g. on low-energy neutrino and hadron interactions, or to future research on cosmic rays using nuclear emulsions carried by balloons.

Time evolution of the sQGP with hydrodynamic models

The strongly interacting Quark-Gluon-Plasma (sQGP) created in relativis- tic nucleus-nucleus collisions, can be described by hydrodynamic models. Low energy hadrons are created after the so called freeze-out of this medium, thus their distributions reveal information about the final state of the sQGP. Photons are created throughout the evolution, so their distributions carry information on the whole expansion and cool down. We show results from an analytic, 1+3 dimensional perfect relativistic hydrodynamic so- lution, and compare hadron and photon observables to RHIC data. We extract an average equation of state of the expanding quark matter from this comparison. In the second part of this paper, we generalize the before mentioned analytic solution of relativistic perfect fluid hydrodynamics to arbitrary temperature-dependent Equation of State. We inves- tigate special cases of this class of solutions, in particular, we present hydrodynamical solutions with an Equation of State determined from lattice QCD calculations.

Low energy hadron phenomenology

This talk discusses some of latest theoretical, phenomenological and experimental results is hadron spectroscopy.

Facets of chiral perturbation theory

Chiral perturbation theory is the effective field theory of the Standard Model at low energies. After a short introduction and overview, I discuss three topics where the chiral approach leads to a deeper understanding of low-energy hadron physics: radiative kaon decays, carbogenesis in stellar nucleosynthesis and the interplay of chiral perturbation theory and lattice QCD.