DAΦNE Exotic Atom Research Experiment Research Articles

The DEAR experiment—first results on kaonic hydrogen

The goal of the DEAR (DAΦNE exotic atom research) experiment is the precise determination of the isospin dependent antikaon–nucleon scattering lengths. The experiment accurately measures the Kα line shift and broadening, due to the strong interaction, in kaonic hydrogen and, for the first time, in kaonic deuterium. A precision measurement of kaonic hydrogen tests chiral symmetry breaking in systems with strangeness. An initial analysis of the DEAR experiment yields a shift ɛ 1 s = − 195 ± 45 eV and a width Γ 1 s = 250 ± 125 eV , which is more precise than the previous kaonic X-ray experiment KpX at KEK, and allows for the first time to disentangle the full pattern of the kaonic hydrogen K-series line Kα, Kβ and Kγ.

First results on kaonic hydrogen from the DEAR experiment

The objective of DEAR (DAφNE Exotic Atom Research) is the measurement of the K a line shift and width, due to the strong interaction, in kaonic hydrogen and a similar measurement — the first one — in kaonic deuterium. The aim is a precision determination of the antikaon-nucleon isospin dependent scattering lengths in order to obtain the kaon nucleon sigma terms. In a first phase, dedicated to the calibration and optimization of the setup, the experiment collected data on kaonic nitrogen: for the first time a complex of three transitions (7 → 6 at 4.6 keV, 6 → 5 at 7.6 keV and 5→ 4 at 14 keV) was measured, and the corresponding yields obtained. The kaonic hydrogen measurement was performed for a total integrated luminosity of about 60 pb-1 in the last months of the 2002 year. Data analyses are in progress, preliminary results being hereby presented, together with those on kaonic nitrogen.

The DEAR case

The scientific program and the experimental setup of the DEAR (DAΦNE Exotic Atom Research) experiment at the new φ-factory DAΦNE of Laboratori Nazionali di Frascati are described. The objective of DEAR is to perform a 1% measurement of the Kα line shift due to the strong interaction in kaonic hydrogen. A measurement will also be performed on kaonic deuterium for the first time. The aim is to investigate low-energy \(\overline K N\) physics and to understand SU(3) chiral symmetry breaking. The setup takes advantage of the unique features of the “kaon beam” from the φ decay in DAΦNE; of a low-temperature pressurized gaseous target; and of a detector for soft X-rays – the Charge-Coupled Device (CCD) – characterized by a very good energy (and spatial) resolution and by an unprecedented background rejection capability. The DEAR experiment represents a major effort in the study of low energy \(\overline K N\) interactions and has the potential to produce a breakthrough in the field.