Low-energy Strong Interaction Research Articles

Cold isospin asymmetric baryonic rich matter in nonlocal NJL-like models

We study the features of low energy strong interactions for a system at zero temperature and finite baryon and isospin chemical potentials, in the framework of a Nambu–Jona-Lasinio-like model that includes nonlocal four-point interactions. We analyze the phase transitions corresponding to chiral symmetry restoration and pion condensation, comparing our results with those obtained from local NJL-like models and lattice QCD calculations. Published by the American Physical Society 2024

Cross-Channel Constraints on Resonant Antikaon-Nucleon Scattering.

Chiral perturbation theory and its unitarized versions have played an important role in our understanding of the low-energy strong interaction. Yet, so far, such studies typically deal exclusively with perturbative or nonperturbative channels. In this Letter, we report on the first global study of meson-baryon scattering up to one-loop order. It is shown that covariant baryon chiral perturbation theory, including its unitarization for the negative strangeness sector, can describe meson-baryon scattering data remarkably well. This provides a highly nontrivial check on the validity of this important low-energy effective field theory of QCD. We show that the K[over ¯]N related quantities can be better described in comparison with those of lower-order studies, and with reduced uncertainties due to the stringent constraints from the πN and KN phase shifts. In particular, we find that the two-pole structure of Λ(1405) persists up to one-loop order reinforcing the existence of two-pole structures in dynamically generated states.

SIDDHARTA-2 veto system design and performance for kaonic atoms studies at DAΦNE

Light kaonic atoms spectroscopy provides a unique approach to study the low-energy strong interaction in the strangeness sector. Precise measurements of X-ray emission from light kaonic atoms provide valuable information on kaon-nucleus interaction at threshold without the need for extrapolation as required in scattering experiments. The SIDDHARTA-2 experiment at the DAΦNE collider of INFN-LNF is now poised to perform the challenging measurements of the K−- d 2p → 1s transition to extract the isospin-dependent antikaonnucleon scattering lengths. To achieve this goal, the background reduction is a crucial factor. This paper provides an overview of the SIDDHARTA-2 Veto-1 system, which uses scintillators outside the vacuum chamber to detect charged particles produced by K− absorption by the nucleus. The arrival time of these particles is correlated with the position where the kaonic atom has been created inside the setup, allowing for the rejection of kaons stopped outside the target cell, which is a critical component for reducing the background and improve the accuracy of the measurement.

Radiative corrections of order O(αEe/mN) to Sirlin’s radiative corrections of order O(α/π) , induced by the hadronic structure of the neutron

We investigate the contributions of the hadronic structure of the neutron to radiative $O(\alpha E_e/m_N)$ corrections (or the inner $O(\alpha E_e/m_N)$ RC) to the neutron beta decay, where $\alpha$, $E_e$ and $m_N$ are the fine-structure constant, the electron energy and the nucleon mass, respectively. We perform the calculation within the effective quantum field theory of strong low-energy pion-nucleon interactions described by the linear $\sigma$-model with chiral $SU(2) \times SU(2)$ symmetry and electroweak hadron-hadron, hadron-lepton and lepton-lepton interactions for the electron-lepton family with $SU(2)_L \times U(1)_Y$ symmetry of the Standard Electroweak Theory (Ivanov et al., Phys. Rev. D99, 093006 (2019)). We show that after renormalization, carried out in accordance with Sirlin's prescription (Sirlin, Phys. Rev. 164, 1767 (1967)), the inner $O(\alpha E_e/m_N)$ RC are of the order of a few parts of $10^{-5} - 10^{-4}$. This agrees well with the results obtained in (Ivanov et al., Phys. Rev. D99, 093006 (2019)).

On the $$\hbox {K}^{-}$$ Absorptions in Light Nuclei by AMADEUS

The aim of the AMADEUS collaboration is to provide experimental information on the low-energy strong interaction of antikaons with nucleons, exploiting the absorptions of low momentum \(\hbox {K}^{-}\) mesons (\(p_\mathrm {K} \sim \) 127 MeV/c) produced at the \(\hbox {DA}\mathrm {\Phi }\hbox {NE}\) collider, in the materials composing the KLOE detector setup, used as an active target. The \(\hbox {K}^{-}\) single and multi-nucleon absorptions in light nuclei (\(^4\hbox {He}\) and \(^{12}\hbox {C}\)) are investigated by reconstructing hyperon–pion, hyperon–nucleon/nucleus pairs, emitted in the final state of the reactions. In this paper the results obtained from the study of \(\mathrm {\Lambda }\pi ^{-}\), \(\mathrm {\Lambda }\hbox {p}\) and \(\mathrm {\Lambda }\hbox {t}\) correlated production are presented.

Studies of K−-nuclei interactions at low-energies by AMADEUS

The AMADEUS collaboration is providing unique experimental information on the low-energy strong interaction between K− and nucleons exploiting the low momentum K− (pK ∼ 127 MeV/c) produced at the DAΦNE collider and using the KLOE detector as active target. The absorption of the K− in light nuclei (H, 4He, 9Be and 12C) are investigated and hyperon-pion/hyperon-nucleons, emitted in the final state, are reconstructed. In the present work the results obtained from the study of Λπ−, Ap and At correlated production will be presented.

Precision analysis of pseudoscalar interactions in neutron beta decays

We analyze the contributions of the one–pion–pole (OPP) exchange, caused by strong low–energy interactions, and the pseudoscalar interaction beyond the Standard Model (BSM) to the correlation coefficients of the neutron β−–decays for polarized neutrons, polarized electrons and unpolarized protons. The strength of contributions of pseudoscalar interactions is defined by the effective coupling constant Cps=Cps(OPP)+Cps(BSM). We show that the contribution of the OPP exchange is of order Cps(OPP)∼−10−5. The effective coupling constant Cps(BSM) of the pseudoscalar interaction BSM can be in principle complex. Using the results, obtained by González-Alonso et al. (2019) [34] we find that the values of the real and imaginary parts of the effective coupling constant Cps(BSM) are constrained by −3.5×10−5<ReCps(BSM)<0 and ImCps(BSM)<−2.3×10−5, respectively. The obtained results can be used as a theoretical background for experimental searches of contributions of interactions BSM in asymmetries of the neutron β−–decays with a polarized neutron, a polarized electron and an unpolarized proton at the level of accuracy of a few parts of 10−5 or even better Abele (2016) [40].

Large N_c scaling of meson masses and decay constants

We perform an ab initio calculation of the N_c scaling of the low-energy couplings of the chiral Lagrangian of low-energy strong interactions, extracted from the mass dependence of meson masses and decay constants. We compute these observables on the lattice with four degenerate fermions, N_f=4, and varying number of colours, N_c=3–6, at a lattice spacing of asimeq 0.075 fm. We find good agreement with the expected N_c scaling and measure the coefficients of the leading and subleading terms in the large N_c expansion. From the subleading N_c corrections, we can also infer the N_f dependence, that we use to extract the value of the low-energy couplings for different values of N_f. We find agreement with previous determinations at N_c=3 and N_f=2, 3 and also, our results support a strong paramagnetic suppression of the chiral condensate in moving from N_f=2 to N_f=3.

The modern era of light kaonic atom experiments

This review covers the modern era of experimental kaonic atom studies, encompassing 20 years of activity, defined by breakthroughs in technological developments which allowed performing a series of long-awaited precision measurements. Kaonic atoms are atomic systems where an electron is replaced by a negatively charged kaon, containing the strange quark, which interacts in the lowest orbits with the nucleus also by the strong interaction. As a result, their study offers the unique opportunity to perform experiments equivalent to scattering at vanishing relative energy. This allows one to study the strong interaction between the antikaon and the nucleon or the nucleus “at threshold,” namely, at zero relative energy, without the need of ad hoc extrapolation to zero energy, as in scattering experiments. The fast progress achieved in performing precision light kaonic atom experiments, which also solved long-pending inconsistencies with theoretical calculations generated by old measurements, relies on the development of novel cryogenic targets, x-ray detectors, and the availability of pure and intense charged kaon beams, which propelled an unprecedented progress in the field. Future experiments, based on new undergoing technological developments, will further boost the kaonic atom studies, thus fostering a deeper understanding of the low-energy strong interaction extended to the second family of quarks.

Gauge and infrared properties of hadronic structure of nucleon in neutron beta decay to order O(α/π) in standard V − A effective theory with QED and linear sigma model of strong low-energy interactions

Within the standard [Formula: see text] theory of weak interactions, Quantum Electrodynamics (QED) and the linear [Formula: see text]-model [Formula: see text] of strong low-energy hadronic interactions we analyze gauge and infrared properties of hadronic structure of the neutron and proton in the neutron [Formula: see text]-decay to leading order in the large nucleon mass expansion. We show that the complete set of Feynman diagrams describing radiative corrections of order [Formula: see text], induced by hadronic structure of the nucleon, to the rate of the neutron [Formula: see text]-decay is gauge noninvariant and unrenormalizable. We show that a gauge noninvariant contribution does not depend on the electron energy in agreement with Sirlin’s analysis of contributions of strong low-energy interactions (Phys. Rev. 164, 1767 (1967)). We show that infrared divergent and dependent on the electron energy contributions from the neutron radiative [Formula: see text]-decay and neutron [Formula: see text]-decay, caused by hadronic structure of the nucleon, are canceled in the neutron lifetime. Nevertheless, we find that divergent contributions of virtual photon exchanges to the neutron lifetime, induced by hadronic structure of the nucleon, are unrenormalizable even formally. Such an unrenormalizability can be explained by the fact that the effective [Formula: see text] vertex of hadron–lepton current–current interactions is not a vertex of the combined quantum field theory including QED and [Formula: see text], which are renormalizable theories. We assert that for a consistent gauge invariant and renormalizable analysis of contributions of hadronic structure of the nucleon to the radiative corrections of any order to the neutron decays one has to use a gauge invariant and fully renormalizable quantum field theory including the Standard Electroweak Model (SEM) and the [Formula: see text], where the effective [Formula: see text] vertex of hadron–lepton current–current interactions is caused by the [Formula: see text]-electroweak-boson exchange.

Spectroscopy of kaonic atoms at DAFNE and J-PARC

The interaction of antikaons (K−) with nucleons and nuclei in the low-energy regime represents a very active research field in hadron physics. A unique and rather direct experimental access to the antikaon-nucleon scattering lengths is provided by precision X-ray spectroscopy of transitions in low-lying states in the lightest kaonic atoms (i.e. kaonic hydrogen and deuterium). In the SIDDHARTA experiment at the electron-positron collider DAFNE of LNFINFN we measured the most precise values of the strong interaction observables in conic hydrogen. The strong interaction on the 1s ground state of the electromagnetically bound K-p atom causes an energy shift and broadening of the 1s state. SIDDHARTA will extend the spectroscopy to kaonic deuterium to get access to the antikaon-neutron interaction and thus the isospin dependent scattering lengths. At J-PARC a kaon beam is used in a complementary experiment with a different setup for spectroscopy of kaonic deuterium atoms. The talk will give an overview of the of the upcoming experiments SIDDHARTA and the complementary experiment at J-PARC.Furthermore, the implications of the experiments for the theory of low-energy strong interaction with strangeness will be discussed.

Gauge properties of hadronic structure of nucleon in neutron radiative beta decay to order O(α/π) in standard V − A effective theory with QED and linear sigma model of strong low-energy interactions

Within the standard [Formula: see text] theory of weak interactions, Quantum electrodynamics (QED) and the linear [Formula: see text]-model (L[Formula: see text]M) of strong low-energy hadronic interactions, we analyze gauge properties of hadronic structure of the neutron and proton in the neutron radiative [Formula: see text]-decay. We show that the Feynman diagrams, describing contributions of hadronic structure to the amplitude of the neutron radiative [Formula: see text]-decay in the tree-approximation for strong low-energy interactions in the L[Formula: see text]M, are gauge invariant. In turn, the complete set of Feynman diagrams, describing the contributions of hadron–photon interactions in the one-hadron-loop approximation, is not gauge invariant. In the infinite limit of the scalar [Formula: see text]-meson, reproducing the current algebra results (S. Weinberg, Phys. Rev. Lett. 18, 188 (1967)), and to leading order in the large nucleon mass expansion the Feynman diagrams, violating gauge invariance, do not contribute to the amplitude of the neutron radiative [Formula: see text]-decay in agreement with Sirlin’s analysis of strong low-energy interactions in neutron [Formula: see text] decays. We assert that the problem of appearance of gauge noninvariant Feynman diagrams of hadronic structure of the neutron and proton is related to the following. The vertex of the effective [Formula: see text] weak interactions does not belong to the combined quantum field theory including the L[Formula: see text]M and QED. We argue that gauge invariant set of Feynman diagrams of hadrons, coupled to real and virtual photons in neutron [Formula: see text] decays, can be obtained within the combined quantum field theory including the Standard Electroweak Model (SEM) and the L[Formula: see text]M, where the effective [Formula: see text] vertex of weak interactions is a result of the [Formula: see text]-electroweak boson exchange.

Lorentz structure of the vector part of matrix elements of n↔p transitions, caused by strong low-energy interactions and hypothesis of conservation of charged vector current

We analyse the Lorentz structure of the matrix elements of the ‘neutron proton’ transitions, induced by the charged hadronic vector current. We show that the term providing conservation of the charged hadronic vector current in the sense of the vanishing matrix element of the divergence of the charged hadronic vector current of the ‘neutron proton’ transitions even for different neutron and proton masses (see T Leitner et al 2006 Phys. Rev. C 73 065502 and A M Ankowski 2016 arXiv:1601.06169 [hep-ph]) has a dynamical origin, related to the G-even first class current contribution. We show that because of the invariance of strong low-energy interactions under G-parity transformations, the G-odd contribution with Lorentz structure , where is a transferred momentum, does not appear in the matrix elements of the ‘neutron proton’ transitions.

The kaonic atoms research program at DAΦNE: from SIDDHARTA to SIDDHARTA-2

The interaction of antikaons with nucleons and nuclei in the low-energy regime represents an active research field in hadron physics with still many important open questions. The investigation of light kaonic atoms, in which one electron is replaced by a negatively charged kaon, is a unique tool to provide precise information on this interaction; the energy shift and the broadening of the low-lying states of such atoms, induced by the kaon-nucleus hadronic interaction, can be determined with high precision from the atomic X-ray spectroscopy, and this experimental method provides unique information to understand the low energy kaon-nucleus interaction at the production threshold. The lightest atomic systems, like the kaonic hydrogen and the kaonic deuterium deliver, in a model-independent way, the isospin-dependent kaon-nucleon scattering lengths. The most precise kaonic hydrogen measurement to-date, together with an exploratory measurement of kaonic deuterium, were carried out in 2009 by the SIDDHARTA collaboration at the DAΦNE electron-positron collider of LNF-INFN, combining the excellent quality kaon beam delivered by the collider with new experimental techniques, as fast and very precise X-ray detectors, like the Silicon Drift Detectors. The SIDDHARTA results triggered new theoretical work, which achieved major progress in the understanding of the low-energy strong interaction with strangeness reflected by the antikaon-nucleon scattering lengths calculated with the antikaon-proton amplitudes constrained by the SIDDHARTA data. The most important open question is the experimental determination of the hadronic energy shift and width of kaonic deuterium; presently, a major upgrade of the setup, SIDDHARTA-2, is being realized to reach this goal. In this paper, the results obtained in 2009 and the proposed SIDDHARTA-2 upgrades are presented.

AMADEUS Experiment: Studies on Antikaon Interactions with Nucleons and Nuclei

The understanding of the low-energy strong interaction involving strangeness is a challenging topic due to resonances and predicted kaonic nuclear bound states. The K- nucleon interaction is strongly attractive at low energies verified in kaonic hydrogen studied in the SIDDHARTA experiment at the DA[Formula: see text]NE electron-positron collider of LNF-INFN (Frascati/Italy). Hyperon resonances like the elusive [Formula: see text] in the s-wave impose questions about its nature. According to theoretical studies it can be described as a dynamically generated resonance with two poles or a quasi-bound [Formula: see text]N state, which could lead to kaonic nuclear bound states (e.g. K-pp). An insight in many open facets of the antikaon interactions can be provided by the AMADEUS experiment at DA[Formula: see text]NE based on the analysis of the data collected in 2004/2005 by the KLOE collaboration, and of the dedicated data set collected in 2012 by AMADEUS in collaboration with KLOE. As a first step data from antikaon-induced reactions in the drift chamber of KLOE were analyzed and yielded new results on antikaon absorption on nuclei. Recent results of the experimental studies and an outlook to the future possibilities within AMADEUS are presented.

Recent development in theoretical studies of hyperon-nucleon interaction

Hypernuclear physics is the study of hypernuclei, their decays and productions, and the role they play in other related fields. It has always been at the frontier of experimental and theoretical nuclear physics since the quantum number strangeness was introduced and the first Λ hypernuclus was discovered in 1953. In recent years, open questions such as the large change symmetry breaking in A =4 Λ hypernuclei, the overbinding problem of A =5 Λ hypernucleus, the existence of the H-dibaryon and the hyperon puzzle in neutron stars have attracted a lot of attention. Today facilities like J-PARC, KEK, JLab, MAMI and COSY allow one to study the properties of hypernuclei with a precision and scope hitherto impossible. The experiments focus not only on the spectroscopy and weak decays of hypernuclei with strangeness S= − 1 and S = − 2, but also on the fundamental ΣN cross sections. In the meantime, theoretical techniques of few- and many-body calculations for hypernuclei have made steady progress, such as the Gaussian expansion method, the lattice QCD simulations and the Dirac-Brueckner-Hartree-Fock approach. Hyperon-nucleon interaction is the key input of the hypernuclear few- and many-body calculations. It plays a fundamental role in the microscopic understanding of hypernuclear physics. Meanwhile, it can also help improve our understanding of the role of strangeness in particle and nuclear physics, as well as the SU(3) symmetry and its breaking. In this paper, we first review the origin of hypernuclear physics and enmumerrate the aforementioned open questions of current interest. These outstanding issues reflect that the hyerpon-nucleon interaction is not fully understood so far. Then we discuss at length the history and current status of theoratical studies of hyperon-nucleon interaction, which are mainly performed in phenomenological models, lattice quantumchromo dynamics (lattice QCD) simulations and chiral effective field theory. The construction of phenomenological models, such as meson exchange models and quark models, has a rather long history. However, they predict very different results even for some of the low-energy phase shifts and scattering lengths, owing to the rather loose constraint from the small number of hyperon-nucleon scattering data. Lattice QCD simulations have made impressive progress since the 21st century, which provide an ab-initio numerical solution to QCD from first principles. With the ever-growing computing power and evolving numerical algorithms, lattice QCD simulations are getting close to the physical point (but still with large error bars). As the effective theory of low-energy QCD, chiral effective field theory has proven to be a useful tool in studies of low-energy strong interaction phenomena. The main feature of this approach is that by using a proper power counting scheme, one can improve calculations systematically by going to higher orders in powers of external momenta and light quark masses, and meantime the uncertainties of any given order. Furthermore, three- and four-body forces can be derived in a consistent manner. Studies of hadron-hadron interaction in chiral effective field theory have made remarkable progress in the past two decades and in the last part of this article we discuss the recent construction of hyperon-nucleon interaction in chiral effective field theory in detail.

Precision theoretical analysis of neutron radiative beta decay to order O(α2/π2)

In the Standard Model (SM) we calculate the decay rate of the neutron radiative beta decay to order "O(\alpha^2/\pi^2 ~ 10^{-5})", where "\alpha$"is the fine--structure constant, and radiative corrections to order "O(\alpha/\pi ~ 10^{-3})". The obtained results together with the recent analysis of the neutron radiative beta decay to next-to-leading order in the large proton-mass expansion, performed by Ivanov et al. Phys. Rev. D95, 033007 (2017), describe recent experimental data by the RDK II Collaboration (Bales et al., Phys. Rev. Lett. 116, 242501 (2016)) within 1.5 standard deviations. We argue a substantial influence of strong low-energy interactions of hadrons coupled to photons on the properties of the amplitude of the neutron radiative beta decay under gauge transformations of real and virtual photons.

On the Frequency Distribution of Neutral Particles from Low-Energy Strong Interactions

The rejection of the contamination, or background, from low-energy strong interactions at hadron collider experiments is a topic that has received significant attention in the field of particle physics. This article builds on a particle-level view of collision events, in line with recently proposed subtraction methods. While conventional techniques in the field usually concentrate on probability distributions, our study is, to our knowledge, the first attempt at estimating the frequency distribution of background particles across the kinematic space inside individual collision events. In fact, while the probability distribution can generally be estimated given a model of low-energy strong interactions, the corresponding frequency distribution inside a single event typically deviates from the average and cannot be predicted a priori. We present preliminary results in this direction and establish a connection between our technique and the particle weighting methods that have been the subject of recent investigation at the Large Hadron Collider.

Kaon decay studies at CERN SPS in the last decades

This review summarizes the kaon experimental results obtained in the last 15 years on the basis of data collected on the SPS in CERN with a participance of JINR physicists. These results contribute essentially into the Standard Model checks and search for its extension, fundamental symmetry violations and low energy strong interactions theory development. A progress in the experimental technique and prospects for the future results are also discussed.

Scale-invariant hidden local symmetry, topology change, and dense baryonic matter

When scale symmetry is implemented into hidden local symmetry in low-energy strong interactions to arrive at a scale-invariant hidden local symmetric (HLS) theory, the scalar $f_0(500)$ may be interpreted as pseudo-Nambu-Goldstone (pNG) boson, i.e., dilaton, of spontaneously broken scale invariance, joining the pseudo-scalar pNG bosons $\pi$ and the matter fields $V=(\rho,\omega)$ as relevant degrees of freedom. Implementing the skyrmion-half-skyrmion transition predicted at large $N_c$ in QCD at a density roughly twice the nuclear matter density found in the crystal simulation of dense skyrmion matter, we determine the intrinsically density-dependent (IDD) "bare parameters" of the scale-invariant HLS Lagrangian matched to QCD at a matching scale $\Lambda_M$. The resulting effective Lagrangian, with the parameters scaling with the density of the system, is applied to nuclear matter and dense baryonic matter relevant to massive compact stars by means of the double-decimation renormalization-group $V_{lowk}$ formalism. We satisfactorily post-dict the properties of normal nuclear matter and more significantly {\it predict} the EoS of dense compact-star matter that quantitatively accounts for the presently available data coming from both the terrestrial and space laboratories. We interpret the resulting structure of compact-star matter as revealing how the combination of hidden-scale symmetry and hidden local symmetry manifests itself in compressed baryonic matter.