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Sep 5 – 9, 2022
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Decay of the $\Lambda(1405)$ to $\Sigma^{0}\pi^{0}$ measured at GlueX

Sep 7, 2022, 3:50 PM
25m
online

online

FSU, Tallahassee, FL, USA

Speaker

Nilanga Wickramaarachchi (The Catholic University of America)

Description

Among the light baryons, the $J^\pi = \frac{1}{2}^-$ $\Lambda(1405)$ baryon is an important special case by sitting just below the $\bar{K}N$ threshold and decaying almost exclusively to $\Sigma\pi$. It has long been hypothesized to be either a molecular bound state or a continuum resonance, or that it is a simple quark-model resonance, the $P$-wave companion of the $\Lambda(1520)$. In recent years chiral unitary models have suggested$^a$ that there are two isospin zero poles present in this mass region, and that the ``line shape" of the $\Lambda(1405)$ depends to what extent each of the two poles are stimulated in a given reaction. Evidence for this interpretation was reported by the CLAS collaboration$^b$ in elementary photoproduction, albeit with limited statistics. Below the $N\bar{K}$ threshold, the $\Lambda(1405)$ decays to the three $\Sigma\pi$ charge combinations, but the $\Sigma^{0}\pi^{0}$ mode is purely $I=0$, uncontaminated by complications arising from $I=1$ scattering processes contributing to the reaction mechanism in the $\Sigma^{+}\pi^{-}$ and $\Sigma^{-}\pi^{+}$ decays, nor from production and decay of the nearby $\Sigma^{0}(1385)$ hyperon.

The GlueX experiment at Jefferson Lab has been used to study the $\Lambda(1405) \to \Sigma^{0}\pi^{0}$ 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 $d\sigma/dM_{\Sigma^{0}\pi^{0}}$ in the $-(t-t_{min})$ range 0 - 1.5 GeV$^2$ from analyzing the reaction $\gamma p \to K^{+}\Lambda^*$ using the data collected during the first phase of the GlueX experiment.

Two hypotheses were compared for fitting the line shape of $\Lambda(1405)$ - a single $\Lambda(1405)$ state and two coherent states parameterized with Flatt\'{e} amplitudes. Our preliminary results favor the use of two coherent states to fit the line shape and indicate the $\Lambda(1405)$ is a composite baryon state.

$^a$cf. recent review: M. Mai, U-G, Meissner, Eur. Phys. J. A 51, 30 (2015)

$^b$K. Moriya et al.(CLAS Collaboration), Phys. Rev. C 87, 035206 (2013)

speaker affiliation The Catholic University of America

Primary authors

Nilanga Wickramaarachchi (The Catholic University of America) Reinhard A. Schumacher (Carnegie Mellon University) Grzegorz Kalicy (The Catholic University of America)

Presentation materials