Session W07: Hadron Spectroscopy and Exotics II

Photoproduction of $\Xi(1820)^{-*}$ at Gluex

The flavor SU(3) symmetry allows as many $\Xi$ resonances as $N^{*}$ and $\Delta^{*}$ combined. Only a handful of these states have been identified experimentally and among these states, only six states have three and four-star status according to Review of Particle Physics.

The GlueX experiment, in Hall D located at Jefferson Lab, using a photon beam of energies up to 12 GeV allows us to study the Cascade baryon spectrum. Spectra of $N^{*}$ and $\Delta^{*}$ are broad and overlaping whereas Cascade states are expected to be narrow and less challenging to identify. Few measurements of Cascade photoproduction exist.

In this talk, we will present the preliminary cross section for $\Xi(1820)^{-*}$ in the t-channel production reaction $\gamma p \rightarrow K^{+}K^{+}\Xi^{-*}$ where $\Xi^{-*}$ decays to $K^{-} \Lambda$ for the Phase -I GlueX data. This is the first cross section result for $\Xi(1820)^{-*}$ in photoproduction.   

K-matrix Analysis of e+e- Annihilation in the Bottomonium Region

In recent years, a number of exotic hadron candidates have been observed in e⁺e^- annihilation in both the charmonium- and bottomonium-regions. Most commonly, the existence of these new, potentially exotic states is inferred from cross sections parameterized with sums of Breit-Wigner amplitudes. While this is a reasonable approximation in the case of narrow, well seperated resonances away from important thresholds, the complicated cross sections in the charmonium- and bottomonium regions cast doubt on the validity of these models. We therefore perform the first unitary analysis of bottomonium production data using both exclusive cross sections of open- and hidden-bottom meson production and the total cross section for bottom anti-bottom quark pair-production measured by the Belle and BABAR experiments. In the talk, our approach as well as first results including pole positions and partial widths of the vector-bottomonium(-like) states above 10.5 GeV will be presented and discussed.   

Charm-meson molecules production in a warm hadron gas

The $X(3872)$ has recently been observed in heavy-ion collisions by the CMS collaboration. Understanding the production rate of $X$ in heavy-ion collision could help resolve its nature. The number of $X$ produced by hadronization of the quark-gluon plasma is modified by hadronic interactions in the expanding hadron gas. We calculate the formation and break-up rates using XEFT for $X$ in a warm pion gas. These rates are used to evolve the number of $X$ from hadronization to past kinetic freeze-out.   

Analytic structure of Compton-like transitions to two-body states

We describe the on-shell representation of transitions from a single-hadron to a two-hadron state mediated by the insertion of two external electroweak currents. We demonstrate how structural information of resonances, which couple to the two-body state, can be extracted from the analytic continuation of these amplitudes. Similarly, reactions of this form are of interest within precision studies of the Standard Model like rare kaon decays or the hadronic contribution to the muon anomalous magnetic moment. To date, most of the theoretical descriptions of these amplitudes are data-driven or rely on low energy effective theories. However, the possibility of calculating them from first-principles has become attainable thanks to the development of techniques utilizing the non-perturbative correlation functions obtained from lattice QCD. Similar to S-matrix elements and hadronic transitions involving a single current, the on-shell representation is needed to constrain these amplitudes from lattice data. We will also outline how the on-shell representation is derived to all-orders in the strong coupling from the self-consistent integral equation describing the amplitude.   

The K* resonance in Kγ* → Kπ from QCD

We present the first calculation of the Kγ*→ Kπ transition with a resonant K* from lattice quantum chromodynamics. In this process, the kaon interacts with a photon and scatters strongly to a Kπ. The Kπ state is in a lowest relative S & P-wave, with the K* resonance appearing in the P-wave. To map the finite volume matrix elements from lattice QCD to the infinite volume transition amplitudes measured in experiments, we apply the Lellouch-Lüscher formalism [1] using information from the Kπ scattering in S & P-wave [2]. This is the first test for this formalism in the presence of multiple partial waves.

We determine the transition amplitude as a function of the Kπ energy and the photon virtuality and observe the expected enhancement due to the K* resonance. From the energy dependence, we extract the K* → Kπ transition form factor for the unstable K* by analytically continuing into the complex energy plane and from the residue at the K* pole.   

Exclusive $\pi^{-}$ Electroproduction off the Neutron in Deuterium in the Resonance Region

We report new results for the exclusive and quasi-free cross sections off neutrons bound in deuterium ${\gamma}^{\ast}n(p) \rightarrow p{\pi}^{-} (p)$, which are presented over a wide final hadron angle range with a kinematic coverage of the invariant mass ($W$) up to $1.825\;\text{GeV}$ and the virtual photon four-momentum squared ($Q^{2}$) from $0.4$ to $1.0 \; \text{GeV}^{2}$. The experimental data were collected with the CLAS detector in Hall B at Jefferson Laboratory. The exclusive structure functions have been extracted and their Legendre moments were obtained. The exclusive quasi-free process has been kinematically isolated as successfully demonstrated by the comparison of the spectator momentum distribution of the simulation with the missing momentum distribution of the data. Accordingly final-state-interaction contributions could be separated from the extracted quasi-free cross sections off bound neutrons solely based on the analysis of the experimental data. These new results will serve as long-awaited input for phenomenological analyses to extract the $Q^{2}$ evolution of previously unavailable n $\rightarrow \text N^{*}$ electroexcitation amplitudes and to improve state-of-the-art models of neutrino scattering off nuclei by augmenting the already available results from free protons.   

f1 Meson Production with the GlueX Experiment

We present preliminary cross-section measurements for photoproduction of the f₁(1285) meson at GlueX in the reaction yp ->K_sKπp at beam energies between 6.5 and 10.5 GeV. Measurements of the f₁(1285) meson have been performed recently using a 4 GeV electron beam at CLAS. The 12 GeV upgrade of CEBAF has allowed us to extend cross-section measurements of f₁(1285) to higher photon energies. Our measurement seeks to validate theoretical predictions of an interpolated Regge treatment for photoproduction of the f₁ meson to better understand the mechanism of production of this and other 1⁺⁺ resonances   

Photoproduction and lineshape of Λ(1405) ->Σ0π0at GlueX

The "line shape" of a resonance can be described as the mass or energy dependence of the resonance decay into a specific final state. For many resonances in hyperon spectroscopy the line shape can be modelled by a Breit-Wigner distribution. However, previous measurements of the line shape of Λ(1405) are significantly distorted from a Breit-Wigner form. Also the Λ(1405) is located around the $N\bar{K}$ threshold which adds more interest to study it. The Λ(1405) mainly decays to Σ⁺π^-, Σ^-π⁺ and Σ⁰π⁰ modes with each having ~33% branching fraction. Studying the  pure I=0 Σ⁰π⁰ decay mode provides the advantage that the Λ(1405) mass region is not contaminated by Σ⁰(1385) production, compared to the other two charged decay modes. This will provide important constraints for theoretical models of the Λ(1405). The GlueX experiment at Jefferson Lab provides an excellent opportunity to study the 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 a large acceptance electromagnetic calorimeter. In this talk, we focus on the preliminary results of dσ/dm from analyzing the reaction γ p -> K⁺Λ(1405) using the data collected during the first phase of the GlueX experiment. Preliminary fits to the line shape are also shown.