High-precision measurement of the kaonic hydrogen 1s level shift and width with SIDDHARTA-2

Abstract

Kaonic atoms provide a unique experimental probe of strong interaction in the low-energy regime. In particular, the strong-interaction-induced shift (${\epsilon }_{1\text{s}}$) and width ($\hat{I}{“}_{1\text{s}}$) of kaonic hydrogen directly constrain the low-energy antikaon-nucleon ($\bar{K}N$) interaction at threshold and the theoretical description of the $\hat{I}›$(1405) resonance. We report a new high-precision measurement of kaonic hydrogen X-ray transitions performed by the SIDDHARTA-2 experiment at the DA$\hat{I}¦$NE collider (INFN-LNF), based on an integrated luminosity of 237 pb${}^{-1}$. The extracted values, ${\epsilon }_{1\text{s}}=-303.0\pm 17.0(stat.)\pm 2.5(syst.)$ eV and $\hat{I}{“}_{1\text{s}}=607\pm 62(stat.)\pm 6(syst.)$ eV, represent the most precise determination to date, improving the precision by approximately a factor-of-two with respect to the previous SIDDHARTA measurement. These results significantly tighten the experimental constraints on theoretical description of the low-energy $\bar{K}N$ interaction.

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