Session C05: Resonances

Search for Resonances in the ωη System at GlueX

The GlueX experiment has produced the world's largest data sample for peripheral photoproduction of mesons with a goal to expand our understanding of the strong interaction and search for hybrid mesons. The data set was obtained at the Thomas Jefferson National Accelerator Facility utilizing the GlueX detector and a tagged linearly polarized photon beam that peaks between 8 - 9 GeV incident on a liquid hydrogen target. We will present the current status of the search for possible intermediate resonances which decay to ωη. Little is known about the established ω(1650), and the states with exotic quantum numbers J^PC= 0^--, 2^+- have not yet been observed. The ω, in this reaction, is identified via the π⁺ π^- π⁰ decay mode and the η and π⁰ are identified via the decay to 2γ. We present a description of the data following an angular moment analysis approach and outline our strategy for future studies.    

Partial Wave Analysis for Pion-Induced Resonance Studies in the HADES Experiment

The High Acceptance Di-lepton Spectrometer (HADES) collaboration at GSI employs a pion beam to examine the characteristics of baryonic resonances and their decay channels. This pion-beam facility enables the generation of baryonic resonances at a fixed center of mass energy ($sqrt{s}$), i.e. in the S-channel. Consequently, these beams possess a significant advantage over proton-induced reactions and are complementary to photo-induced studies conducted elsewhere. Partial Wave Analysis (PWA) techniques are used to study the coupling of the resonances to different final states. HADES has a particular interest in studying the role and medium modification of vector mesons in heavy-ion collisions in baryon-dense matter. Elementary pion-induced studies on the proton combined with a PWA will provide insights into the couplings of baryonic resonances to $ ho N$ and $omega N$ final states in greater detail will provide insights into the impact of the melting of the $ ho$ meson in heavy ion collisions and the involvement of intermediary vector mesons in dilepton emissions.\

In anticipation of conducting a more comprehensive exploration of the resonance regions in pion-proton collisions, a new implementation of the K-Matrix & N/D frameworks is currently under development. This updated implementation aims to offer a refined mapping of these regions. Example fits will be presented showing current status and the potential of the new framework.   

Amplitude Analysis of a2→ηπ at GlueX

The primary goal of the GlueX experiment at Jefferson Lab is to search for and map the spectrum of light hybrid mesons. Many experiments have studied and reported evidence of exotic mesons decaying into ηπ  final states. GlueX, which has a linearly polarized photon beam and a large acceptance for both charged and neutral particles, has access to both the neutral, γp→ηπ ⁰p, and charged, γp→ηπ^-Δ⁺⁺, processes. This presentation will discuss the amplitude analysis of a₂→ηπ channels at GlueX. It will focus on and compare the extraction of differential cross sections for the photoproduction of a₂→ηπ as a function of t for the neutral and charged ηπ systems. This work is the first step towards studying the production of the hybrid π₁(1600) in η(')π channels at GlueX.   

Thermal Self-Energy of a Charm-Meson Molecule in a Pion Gas

The thermal corrections to the propagator of a loosely bound charm-meson molecule in a pion gas are calculated to next-to-leading order in the heavy-meson expansion using a zero-range effective field theory. Ultraviolet divergences in the charm-meson-pair self energy are canceled by corrections to the charm-meson-pair contact vertex. Terms that are singular at the charm-meson-pair threshold can be absorbed into thermal corrections to the rest energies and kinetic masses of the charm-meson constituents. The remaining terms reduce to a thermal correction to the binding momentum that is proportional to the pion number density and suppressed by the pion/charm-meson mass ratio. The correction gives a tiny decrease in the binding energy of the charm-meson molecule relative to the charm-meson-pair threshold in the pion gas and a change in its thermal width that is small compared to the thermal widths of the charm-meson constituents. These results are encouraging for the prospects of observing $X(3872)$ and $T_{cc}^+(3875)$ in the expanding hadron gas produced by

heavy-ion collisions.   

Low-energy K+N scattering revisited and in-medium strange quark condensate

It is important to investigate the in-medium quark condensates to understand the mechanism of the spontaneous breaking of chiral symmetry. The up and down quark condensates in nuclear medium are studied by pionic atoms and low energy pion nucleus scattering. It is found that the magnitude of the ud quark condensates may be reduced by 30% at the nuclear saturation density. This is known as partial restoration of chiral symmetry in nuclear medium. For a systematic study of partial restoration of chiral symmetry, it is interesting to see how the strange quark condensate behaves in nuclear matter. The chiral ward identity connects the in-medium quark condensate to the soft limit value of a correlation function of the pseudoscalar fields evaluated in nuclear medium. For the strange quark condensate, one considers the correlation function of the pseudoscalar fields with strangeness. The correlation function describes in-medium propagation of kaon and it is obtained phenomenologically by kaon-nucleon scattering in the low density approximation. In this talk we describe the kaon-nucleon scattering amplitude in chiral perturbation theory and its low energy constants are determined by existent K⁺N scattering data. Performing analytic continuation of the scattering amplitude obtained by chiral perturbation theory, we can take soft limit of the scattering amplitude. With this amplitude, we evaluate the in-medium strange quark condensate based on hadron phenomenology. We also discuss a possible broad resonance with S=+1 appearing in the KN scattering with I=0 around W=1650 MeV.   

Low-lying baryon resonances from lattice QCD

Recent results studying the masses and widths of low-lying baryon resonances in lattice QCD are presented. The s-wave scattering lengths with both total isospins I=1/2 and I=3/2 are inferred from the finite-volume spectrum below the inelastic threshold together with the I=3/2 p-wave containing the Δ(1232) resonance. A lattice QCD computation employing a combined basis of three-quark and meson-baryon interpolating operators with definite momentum to determine the coupled channel Σπ−NK scattering amplitude in the Λ(1405) region is also presented. Our results support the picture of a two-pole structure suggested by theoretical approaches based on SU(3) chiral symmetry and unitarity.   

Is the LHCb $P_c(4312)^+$ plausible in the GlueX $gamma p o J/psi p$ total cross sections ?

New high-statistics total cross section data for $gamma p o J/psi p$ from the GLUonic EXcitation (GlueX) experiment are fitted in a search for the exotic $P_c(4312)^+$ state observed by the Large Hadron Collider beauty (LHCb) collaboration. The integrated luminosity of this GlueX experiment was about $320~mathrm{pb^{-1}}$. The fits show that destructive interference involving an $S$-wave resonance and associated non-resonance background produces a sharp dip structure about $75~mathrm{MeV}$ below the LHCb mass, in the same location as a similar structure is seen in the data. Limitations of the employed model and the need for improved statistics are discussed.   

f1(1285) Meson Production With GlueX

The GlueX experiment at Jefferson Lab, in its search for exotic and hybrid mesons, has accumulated the world's largest meson photoproduction dataset. We present preliminary cross-section measurements for  photoproduction of the f₁(1285) meson at GlueX in the reactions γp → K_sK⁺π^- and γp → K_sK^-π⁺  at beam energies between 6 and 11 GeV. The 12 GeV upgrade of CEBAF has allowed us to extend cross-section measurements of f₁(1285) to higher photon energies than previously measured. Our measurement seeks to validate different theoretical predictions for the photoproduction cross-section of the f₁(1285) meson to better understand the mechanism of production of this and other 1⁺⁺ resonances. Furthermore, many of the potential exotic mesons of interest to GlueX are expected to decay  in channels which include the f1(1285), like π₁ → f₁π, so studying this meson sets the foundation for those more complicated studies.    

Decay of the Λ(1405) to Σ0π0 measured at GlueX

The Λ(1405) hyperon with J^π = ½^- is located just below the $ar{K}N$ threshold. In recent years chiral unitary models have suggested that there are two poles with isospin I=0 present in this mass region and that the line shape of the Λ(1405) depends to what extent each of the two poles are stimulated in a given reaction.

The GlueX experiment at Jefferson Lab has been used to study the purely I=0, Λ(1405) → Σ⁰π⁰ decay mode with a photon beam in the energy range 6.5 - 11.6 GeV incident on a liquid hydrogen target and using a large acceptance charged particle tracking and electromagnetic calorimeter system. We focus on the preliminary results of dσ/dM_Σ⁰π⁰ in the -(t-t_min) range 0 - 1.5 GeV² from analyzing the reaction γ p → K⁺Λ^* using the data collected during the first phase of the GlueX experiment. The event statistics are the highest ever obtained for this state. The line shape has been investigated within a unitary framework with multiple poles and multiple decay modes, and preliminary results will be shown.   

K- d → πΛN reaction with in-flight kaons for studying the ΛN interaction

We calculate the different cross sections of K^- d → π^-Λp and K^- d → π⁰Λn reactions in order to study the difference between low energy Λp and Λn interactions. The reactions contain scattering of Λp and Λn in the final-state interactions. We can detect low-energy behavior of the ΛN interaction when we focus on the different cross sections near the ΛN mass thresholds. The calculations have been performed for in-flight kaons with a momentum of 1000 Mev/c. We suppress the background processes using the angular restriction to forward imposed on the outgoing pions. This restriction also serves as the spin selection rule, where the spin triplet state of ΛN interaction becomes dominant. The amplitudes are constructed using the meson-baryon and baryon-baryon scattering amplitudes and deuteron wave function. We employ the chiral unitary amplitude obtained from partial wave analysis up to p-wave as the meson-baryon amplitude, and the effective-range expansion, taking into account the spin-flip term, as the baryon-baryon amplitude. To investigate the impact of the inequality in the low-energy behavior of Λp and Λn, we set two parameters: the ratio of the scattering length between Λn and Λp and the ratio of the effective range. We obtain the differential cross section ratio of π⁰Λn to π^-Λp as a function of the ΛN invariant mass when varying these parameters.