Abstract
The AMADEUS experiment at the DAΦNE collider of LNF-INFN deals with the investigation of the at-rest, or low-momentum, K− interactions in light nuclear targets, with the aim to constrain the low energy QCD models in the strangeness sector. The 0 step of the experiment consisted in the reanalysis of the 2004/2005 KLOE data, exploiting K− absorptions in H, 4He, 9Be and 12C, leading to the first invariant mass spectroscopic study with very low momentum (about 100 MeV) in-flight K− captures. With AMADEUS step 1 a dedicated pure Carbon target was implemented in the central region of the KLOE detector, providing a high statistic sample of pure at-rest K− nuclear interaction. The first measurement of the non-resonant transition amplitude $\left| {{A_{{K^ - }n \to \Lambda {\pi ^ - }}}} \right|$ at $\sqrt s = 33\,MeV$ below the K̄N threshold is presented, in relation with the Λ(1405) properties studies. The analysis procedure adopted in the serarch for K− multi-nucleon absorption cross sections and Branching Ratios will be also described.
Highlights
IntroductionThe absorption of low momentum K− mesons (pK ∼ 127 MeV/c), produced by the DAΦNE [1] collider, on He and C nuclear targets is investigated, with the aim to get information on the resonant and non-resonant transition amplitudes few MeV below the K N threshold, these represent good tests for the theoretical predictions of the low energy QCD models in the strangeness sector
The absorption of low momentum K− mesons, produced by the DAΦNE [1] collider, on He and C nuclear targets is investigated, with the aim to get information on the resonant and non-resonant transition amplitudes few MeV below the K N threshold, these represent good tests for the theoretical predictions of the low energy QCD models in the strangeness sector.The detailed characterisation of the yield and spectral shape of the non-resonant antikaonnucleon absorption, resulting in a hyperon-pion final state below the KN threshold, is a fundamental reference to extract the Λ(1405) properties in KN absorption experiments from the competing non-resonant (Σπ)0 formation
For this reason the shape of the measured (Σπ)0 invariant mass distribution is expected to change depending on the decay channel, due to the isospin interference term and on the production channel
Summary
The absorption of low momentum K− mesons (pK ∼ 127 MeV/c), produced by the DAΦNE [1] collider, on He and C nuclear targets is investigated, with the aim to get information on the resonant and non-resonant transition amplitudes few MeV below the K N threshold, these represent good tests for the theoretical predictions of the low energy QCD models in the strangeness sector. According to the chiral unitary model [2,3,4] (see the review [5]) the Λ(1405) can be interpreted as a molecular mesonbaryon state, emerging from the interference of two poles, a lower mass pole (about 1390 MeV) which is mainly coupled to the Σπ channel and a high mass pole, coupled to the KN production channel, located around 1420 MeV (the next to leading order calculation of the poles masses and widths can be found in [6]) For this reason the shape of the measured (Σπ)0 invariant mass distribution is expected to change depending on the decay channel, due to the isospin interference term (which contributes with opposite sign to the Σ±π∓ cross sections, and vanishes for Σ0π0) and on the production channel. We will show how an insight on the Λ(1405) high mass pole characteristic can be obtained from the in-flight K− absorption reactions on He and C
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