Resonance-like Structure Research Articles

Role of the triangle singularity in the isospin breaking process J/ψ→ΛΛ¯π and the possible evidence of Σ*(12−) states

In this study, the impact of triangle singularity is investigated in the isospin breaking process J/ψ→ΛΛ¯π. The triangle singularity is found to play a significant role in the process, resulting in the creation of a resonancelike structure around 1.4 GeV in the Λπ(Λ¯π) invariant mass spectrum. To amplify the impact of this triangle singularity, the presence of two Σ*(12−) states around 1.4 GeV and 1.6 GeV is essential, yet these states have not been definitively identified in the current baryon spectrum. We recommend that experiments, particularly the Beijing Spectrometer and the future Super Tau-Charm Factory, investigate the process J/ψ→ΛΛ¯π to offer direct evidence for our predicted triangle singularity and additional evidence regarding the Σ(12−) states. Published by the American Physical Society 2024

Theoretical study of the B+→D−Ds+π+ reaction

Prompted by the recent discoveries of Tcs¯0(2900)++ in the Ds+π+ invariant mass distribution of B+→D−Ds+π+ process, we present a model that hopes to help us investigate the nature of Tcs¯0(2900)++ by reproducing the mass distribution of D−π+, Ds+π+, and D−Ds+ in B+→D−Ds+π+ decays. The structure of the triangular singularity peak generated from the χc1D*+K*+ loop near the D*+K*+ threshold is considered in our model may be the experimentally discovered resonancelike state structure Tcs¯0(2900)++. In addition, we employ a coupled-channel approach to describe the dominant contribution of the Dπ S-wave amplitude, and also consider other excitations. Our model provides a well fit to the invariant mass distributions of D−π+, Ds+π+, and D−Ds+ simultaneously. Published by the American Physical Society 2024

Search for Resonances in the Mass Spectrum of Two-Photon Events Produced in π+A-Interactions in the Hyperon-M Experiment at the U-70 Accelerator Complex

Studies at the Nuclotron in JINR indicate the presence of a previously unknown resonance-like structure in the two-photon mass spectrum in the region of 300–400 MeV/c2, observed in nucleus–nucleus interactions. The goal of this work is to search for such structures in the two-photon mass spectrum in meson–nuclear interactions at a momentum of 7 GeV/cat the Hyperon-M experiment of the U-70 accelerator complex. An upper limit has been established on the ratio of the cross section for the formation of unknown resonance structures to the cross section for the production ofη-mesonρ(R→2γ/η→2γ)3.2×10−3at the 95% confidence level.

Systematic study of the resonancelike structure in the collisional flavor instability of neutrinos

Systematic study of the resonancelike structure in the collisional flavor instability of neutrinos

Resonant contributions to polarized proton structure functions

Nucleon resonance contributions to the polarized proton ${g}_{1}$ and ${g}_{2}$ structure functions are computed from resonance electroexcitation amplitudes extracted from CLAS exclusive meson electroproduction data. Including resonances in the mass range up to 1.75 GeV, and taking into account the interference between excited states, we compare the resonant contributions with the polarized proton structure function and polarization asymmetry data from Jefferson Lab 6 GeV measurements. All resonance-like structure observed in the polarized structure functions and asymmetries can be attributed to the resonant contributions, confirming their essential role in the behavior of ${g}_{1}$ and ${g}_{2}$ in the resonant region over the entire range ${Q}^{2}<7.5\phantom{\rule{4pt}{0ex}}{\mathrm{GeV}}^{2}$ covered by the measurements. Comparing the resonance contributions with the ${g}_{1}$ and ${g}_{2}$ structure functions computed from parton distribution functions extrapolated from the deep-inelastic region, we also quantify the degree to which quark-hadron duality holds for ${g}_{1}$ and ${g}_{2}$ and their moments.

LUNA measurement found no evidence of a low-energy resonance in 6Li(p, γ)7Be reaction

The 6Li(p, γ)7Be reaction is mainly at work in three nucleosynthesis scenarios: Big Bang Nucleosynthesis, 6Li depletion in pre-main and in main sequence stars and cosmic ray interaction with interstellar matter. The 6Li(p, γ)7Be S-factor trend was poorly constrained at astrophysical energies because of conflicting experimental results reported in literature. A recent direct measurement, indeed, found a resonance-like structure at Ec.m. = 195 keV, corresponding to an excited state at Ex ∼ 5800 keV in 7Be which, however, has not been confirmed by either other direct measurements or predicted by theoretical calculations. In order to clarify the existence of this resonance, a new experiment was performed at the Laboratory for Underground Nuclear Astrophysics (LUNA), located deep underground in Gran Sasso Laboratory. Thanks to the extremely low background environment, the 6Li(p, γ)7Be cross section was measured in the center-of-mass energy range E = 60-350 keV with unprecedented sensitivity. No evidence for the alleged resonance was found. LUNA results was confirmed by latest published indirect determination of 6Li(p, γ)7Be S-factor and it is supported by a recent theoretical study.

Possibility of T_{cbar{s}}(2900) as the resonance-like structure induced by threshold effects

We investigate the process Brightarrow bar{D}D_s pi via several rescattering processes. It is shown that the triangle singularity (TS) peak around the D^*K^* threshold generated from the chi _{c1}K^* D^* loop is relatively narrow, which may simulate the resonance-like structure T_{cbar{s}}(2900) recently observed by LHCb in the D_spi spectrum. However, the TS peak around the D_s^*rho threshold generated from the D^{**} D_s^* rho loop is smoothed by the broad width of rho , which itself can hardly describe the T_{cbar{s}}(2900) structure. A non-resonance TS signal around the DK threshold generated from the chi _{c0}K D loop is also predicted.

Observation of a correlated free four-neutron system

A long-standing question in nuclear physics is whether chargeless nuclear systems can exist. To our knowledge, only neutron stars represent near-pure neutron systems, where neutrons are squeezed together by the gravitational force to very high densities. The experimental search for isolated multi-neutron systems has been an ongoing quest for several decades1, with a particular focus on the four-neutron system called the tetraneutron, resulting in only a few indications of its existence so far2–4, leaving the tetraneutron an elusive nuclear system for six decades. Here we report on the observation of a resonance-like structure near threshold in the four-neutron system that is consistent with a quasi-bound tetraneutron state existing for a very short time. The measured energy and width of this state provide a key benchmark for our understanding of the nuclear force. The use of an experimental approach based on a knockout reaction at large momentum transfer with a radioactive high-energy 8He beam was key.

Underground measurement at LUNA found no evidence for a low-energy resonance in the 6Li(p, γ)7Be reaction

The 6Li(p,γ)7Be reaction is involved in all three main nucleosynthesis scenarios: Big Bang Nucleosynthesis, the interaction of cosmic rays with interstellar matter, and stellar nucleosynthesis. Conflicting experimental results have been reported in literature for the 6Li(p,γ)7Be reaction cross section trend at astrophysical energies. A recent direct measurement found a resonance-like structure at Ec.m. = 195 keV, corresponding to an excited state at Ex ~ 5800 keV in 7Be which, however, has not been confirmed by either theoretical calculations or other direct measurements. In order to clarify the existence of this resonance, a new experiment was performed at the Laboratory for Underground Nuclear Astrophysics, located deep underground at Laboratori Nazionali del Gran Sasso (Italy). The 6Li(p,γ)7Be cross section was measured in the energy range Ec.m. = 60-350 keV with unprecedented sensitivity and no evidence for the alleged resonance was found.

Resonance-like structure near the ηd threshold in the γd→π0ηd reaction

To investigate the interaction between the nucleon $N$ and nucleon resonance $N(1535)1/2^-$, the $\eta d$ threshold structure connected to the isoscalar $S$-wave $N$-$N(1535)1/2^-$ system has been experimentally studied in the $\gamma{d}${$\to$}$\pi^0\eta{d}$ reaction at incident photon energies ranging from the reaction threshold to 1.15 GeV. A strong enhancement is observed near the $\eta d$ threshold over the three-body phase-space contribution in the $\eta d$ invariant-mass distribution. An analysis incorporating the known isovector resonance $\mathcal{D}_{12}$ with a spin-parity of $2^+$ in the $\pi^0d$ channel reveals the existence of a narrow isoscalar resonance-like structure with $1^-$ in the $\eta d$ system. Using a Flatt\'e parametrization, the mass is found to be $2.427_{-0.006}^{+0.013}$ GeV, close to the $\eta d$ threshold, and the width is $\left(0.029_{-0.029}^{+0.006}{\rm\ GeV}\right)+\left(0.00_{-0.00}^{+0.41}\right) p_\eta c$, where $p_\eta$ denotes the $\eta$ momentum in the rest frame of the $\eta d$ system. The observed structure would be attributed to a predicted isoscalar $1^-$ $\eta NN$ bound state from $\eta NN$ and $\pi NN$ coupled-channel calculation, or an $\eta d$ virtual state owing to strong $\eta d$ attraction.

Triangle Singularity as the Origin of the a_{1}(1420).

The COMPASS Collaboration experiment recently discovered a new isovector resonancelike signal with axial-vector quantum numbers, the a_{1}(1420), decaying to f_{0}(980)π. With a mass too close to and a width smaller than the axial-vector ground state a_{1}(1260), it was immediately interpreted as a new light exotic meson, similar to the X, Y, Z states in the hidden-charm sector. We show that a resonancelike signal fully matching the experimental data is produced by the decay of the a_{1}(1260) resonance into K^{*}(→Kπ)K[over ¯] and subsequent rescattering through a triangle singularity into the coupled f_{0}(980)π channel. The amplitude for this process is calculated using a new approach based on dispersion relations. The triangle-singularity model is fitted to the partial-wave data of the COMPASS experiment. Despite having fewer parameters, this fit shows a slightly better quality than the one using a resonance hypothesis and thus eliminates the need for an additional resonance in order to describe the data. We thereby demonstrate for the first time in the light-meson sector that a resonancelike structure in the experimental data can be described by rescattering through a triangle singularity, providing evidence for a genuine three-body effect.

Dirac–Fock internal conversion coefficients at low [formula omitted]-ray energy

Presented here are internal conversion coefficients (ICCs) for nuclear transitions of low γ-ray energies from 0.1keV to 1keV in elements with 10≤Z≤118. The low-energy nuclear transitions attract significant interest since the novel experimental technique and methods make it possible to study the transitions as well as to discover new low-lying isomers. Our ICC calculations are shown to be in excellent agreement with experimental data for the fairly low-energy nuclear transitions. The calculations are based on the Dirac–Fock method. The vacancy in the atomic shell from which an electron has been emitted is taken into account in the framework of the frozen core approximation. Experimental binding energies are used for elements Z≤95. Theoretical binding energies obtained in a good approximation are used for Z≥96. Peculiarities of the ICC behavior at low energies are considered. The resonance-like structure of ICC and the drastic decrease in magnitude as the energy increases are demonstrated to be responsible for a pronounced dependence of ICC on theoretical assumptions underlying the calculations. We discuss the influence on the low-energy ICCs of the exact taking account the exchange interaction between electrons, the inclusion of the vacancy after conversion, and a credible choice of the binding energy.

The Study of the 6Li(p,γ)7Be Reaction at LUNA

The 6Li(p,γ)7Be reaction is mainly involved in two astrophysical scenarios: the primordial nucleosynthesis and 6Li consumption in pre-main and main sequence stars. A recent measurement of 6Li(p,γ)7Be reaction S-factor reported a resonance-like structure at Ecm = 195 keV, which has not been confirmed neither by other direct measurements nor by theoretical calculations.A new experiment was performed at the Laboratory for Underground Nuclear Astrophysics (LUNA). The extremely low background environment allowed to measure the 6Li(p,γ)7Be cross section down to low energies with unprecedented sensitivity leading to clarify the existence of the claimed resonance. Details on the experimental setup and the preliminary results of the ongoing analysis are reported in this work.

Coherent photoproduction of \u03c10 vector mesons in ultra-peripheral Pb-Pb collisions at sqrt{{mathrm{s}}_{mathrm{NN}}} = 5.02 TeV

Cross sections for the coherent photoproduction of ρ0 vector mesons in ultra-peripheral Pb-Pb collisions at sqrt{{mathrm{s}}_{mathrm{NN}}} = 5.02 TeV are reported. The measurements, which rely on the π+π− decay channel, are presented in three regions of rapidity covering the range |y| < 0.8. For each rapidity interval, cross sections are shown for different nuclear-breakup classes defined according to the presence of neutrons measured in the zero-degree calorimeters. The results are compared with predictions based on different models of nuclear shadowing. Finally, the observation of a coherently produced resonance-like structure with a mass around 1.7 GeV/c2 and a width of about 140 MeV/c2 is reported and compared with similar observations from other experiments.

Towards the understanding of Zc(3900) from lattice QCD

Within the framework of three-channel Ross-Shaw effective range theory, we derive the constraints among different parameters of the theory in the case of a narrow resonance close to the threshold of the third channel, which is relevant for the resonance-like structure $Z_c(3900)$. The usage of these constraint relations, together with the multi-channel L\"uscher formula in lattice QCD calculations are also discussed and the strategies are outlined.

Examination of photon strength functions and nuclear level density in Pt196 from the γ -ray spectra measured at the DANCE facility

Background: The nuclear level density (NLD) and photon strength functions (PSFs) are necessary quantities for calculating the interaction of photons with nuclei, in particular the reaction cross sections. As such, they are important especially in nuclear astrophysics and in the development of advanced nuclear technologies.Purpose: The presence of a resonancelike structure in the $E1$ PSF at $\ensuremath{\gamma}$-ray energy of about 5.5 MeV was reported in $\ensuremath{\gamma}$-soft $A\ensuremath{\approx}200$ nuclei from several experimental techniques. However, as data from different experiments are not fully consistent, additional information on PSFs in this region is of great interest. In addition, present PSF models have difficulties to describe resonancelike structures for energies below the neutron separation energy ${S}_{n}$. There are also open questions about the energy and parity dependence of the NLD.Methods: The $\ensuremath{\gamma}$ rays following the radiative neutron capture on $^{195}\mathrm{Pt}\phantom{\rule{4pt}{0ex}}s$-wave resonances were measured with the highly segmented $\ensuremath{\gamma}$-ray calorimeter Detector for Advanced Neutron Capture Experiments at the Los Alamos Neutron Science Center. The $\ensuremath{\gamma}$-ray energy spectra for different multiplicities were gathered for several resonances of both possible spins.Results: The $\ensuremath{\gamma}$-ray energy spectra were analyzed within the statistical model and allowed us to get information about the NLD and PSFs in $^{196}\mathrm{Pt}$. Neither the PSFs from any previous experiment nor any available PSFs models are able to describe our spectra. We were able to find PSFs and NLD that reasonably describe experimental spectra and impose various restrictions on these quantities.Conclusions: The presence of a resonancelike structure in the $E1$ PSF at a $\ensuremath{\gamma}$-ray energy of about 5.6 MeV is confirmed. The constant temperature energy dependence is favored for a NLD with a significant parity dependence up to an excitation energy of at least 4 MeV. The preferred $M1$ PSF shape is close to a Lorentzian tail of the spin-flip resonance.

Paramagnetic rare-earth oxideNd2O3investigated by muon spin spectroscopy

In the context of a systematic study of oxide materials with the muon spin spectroscopy ($\ensuremath{\mu}\mathrm{SR}$) technique, we report here on an investigation of paramagnetic ${\mathrm{Nd}}_{2}{\mathrm{O}}_{3}$. The question was whether the magnetism of ${\mathrm{Nd}}^{3+}$ has an influence on the observed signals. In ${\mathrm{Nd}}_{2}{\mathrm{O}}_{3}$, as in the other oxides, a weakly paramagnetic component is observed besides the pure diamagnetic fraction. The paramagnetic part is assigned to a transient state formed between the initial atomic and the final bound muonium configuration. In addition, a fast relaxing signal ($\ensuremath{\lambda}\ensuremath{\sim}7\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}{\mathrm{s}}^{\ensuremath{-}1}$) with 10% to 20% fraction is seen in longitudinal field. Contrary to this general behavior of the oxide materials, in the present magnetic compound, a resonancelike structure is seen in the temperature range around 40 K. We assign it tentatively to a dynamical process related to the population of the first excited Kramers doublet of the ${\mathrm{Nd}}^{3+}$ ion at 2.6 meV.

Visible narrow cusp structure in Λc+→pK−π+ enhanced by triangle singularity

A resonance-like structure as narrow as 10 MeV is observed in the $K^-p$ invariant mass distributions in $\Lambda_c^+\to p K^- \pi^+$ at Belle. Based on the large data sample of about 1.5 million events and the small bin width of just 1 MeV for the $K^-p$ invariant mass spectrum, the narrow peak is found precisely lying at the $\Lambda\eta$ threshold. While lacking evidence for a quark model state with such a narrow width at this mass region, we find that this narrow structure can be naturally identified as a threshold cusp but enhanced by the nearby triangle singularity via the $\Lambda$-$a_0(980)^+$ or $\eta$-$\Sigma(1660)^+$ rescatterings.

A coupled-channel lattice study of the resonance-like structure Zc(3900) * * Supported in part by the Ministry of Science and Technology of China (MSTC) under 973 project "Systematic studies on light hadron spectroscopy" (2015CB856702). It is also supported in part by the DFG and the NSFC through funds provided to the Sino-Germen CRC 110 "Symmetries and the Emergence of Structure

In this exploratory study, near-threshold scattering of D and meson is investigated using lattice QCD with twisted mass fermion configurations. The calculation is performed in the coupled-channel Lüscher finite-size formalism. The study focuses on the channel with where the resonance-like structure was discovered. We first identify the two most relevant channels and the lattice study is performed in the two-channel scattering model. Combined with the two-channel Ross-Shaw theory, scattering parameters are extracted from the energy levels by solving the generalized eigenvalue problem. Our results for the scattering length parameters suggest that for the particular lattice parameters that we studied, the best fit parameters do not correspond to the peak in the elastic scattering cross-section near the threshold. Furthermore, in the zero-range Ross-Shaw theory, the scenario of a narrow resonance close to the threshold is disfavored beyond the 3 level.

Theoretical calculation of the [formula omitted] radiative capture reaction

We present a new calculation of the Li6(p,γ)7Be radiative capture astrophysical S-factor in a cluster model framework. We consider several intercluster potentials, adjusted to reproduce the Be7 bound state properties and the p−6Li elastic scattering phase shifts. Using these potentials, we calculate the astrophysical S-factor, obtaining a good agreement with available data, and the photon angular distribution. Finally, we discuss the consequences of a hypothetical resonance-like structure on the S-factor.