First Model-Independent Measurement of the Spin Triplet $p\Lambda$ Scattering Length from Final State Interaction in the $\vec{p}p \rightarrow pK^{+}\Lambda$ Reaction

TL;DR

This study measures the spin triplet $p ext{-} ext{Lambda}$ scattering length directly from the final state interaction in polarized proton-proton collisions, providing a model-independent value consistent with theoretical expectations.

Contribution

It presents the first model-independent measurement of the $p ext{-} ext{Lambda}$ spin triplet scattering length using polarized proton-proton reactions.

Findings

Measured the scattering length as $a_t = (-2.55^{+0.72}_{-1.39})$ fm.

First model-independent extraction of the $p ext{-} ext{Lambda}$ scattering length.

Results agree with theoretical predictions.

Abstract

The $\vec{p}p \rightarrow pK^{+}\Lambda$ reaction has been measured with the COSY-TOF detector at a beam momentum of $2.7\,\mathrm{GeV}/c$. The polarized proton beam enables the measurement of the beam analyzing power by the asymmetry of the produced kaon ($A_N^{K}$). This observable allows the $p\Lambda$ spin triplet scattering length to be extracted for the first time model independently from the final-state interaction in the reaction. The obtained value is $a_{t} = (-2.55 ^{+0.72}_{-1.39} {}_{\textrm{stat.}} \pm 0.6_{\textrm{syst.}} \pm 0.3_{\textrm{theo.}})\mathrm{fm}$. This value is compatible with theoretical predictions and results from model-dependent analyses.