Study of the Lambda(1405) resonance via kaon-induced reactions
ORAL · Invited
Abstract
The Λ(1405) hyperon resonance has been attracting us for a long time if it is an "exotic" meson-baryon molecular state. Recent experimental results on extracted anti-kaon-nucleon (KbarN) scattering amplitude in isospin I = 0 and the pole mass of Λ(1405) at J-PARC will be presented.
We measured πΣ invariant mass spectra below and above the KbarN mass threshold in the K-d -> NπΣ in order to study the KbarN interaction and the Λ(1405) resonance [1]. For this purpose, a negatively-charged kaon (K-) beam of 1 GeV/c was irradiated on a deuterium target at the K1.8BR beam line in the J-PARC Hadron Experimental Facility. In the experiment, a nucleon (N: neutron or proton) knocked out from a deuteron (d) by an incident K- was detected at a very forward angle, and four different final states of π+Σ-, π-Σ+, π0Σ0, and π-Σ0 were identefied by measuring the charged particles emitted around the target.
This reaction can be described by the following two-step process: (i) K-"N1"->KbarN and (ii) Kbar"N2"->πΣ, where "N1" and "N2" are nucleons bound in the deuteron.
Since the nucleon emitted at the forward angle carries away most of the collision energy in (i), the center-of-mass energy in (ii) can be lower, even below the KbarN mass threshold. Since the recoiled kaon is slow down below 250 MeV/c, one expects that the S-wave Kbar"N2"->πΣ scattering is dominant around the KbarN mass region. In order to separate the I=0 and 1 amplitudes in (ii), we demonstrate that an isospin relation of the cross sections between the four final πΣ states is satisfied as π0Σ0 = [π+Σ- + π-Σ+ - π-Σ0]/2.
The scattering amplitudes of step (i) has been well analyzed by Gopal et al. [2]. Employing their amplitudes in step (i), we could deduce the S-wave scattering amplitudes of step (ii): KbarN->KbarN as well as KbarN->πΣ in I = 0 in the framework of the KbarN-πΣ coupled channel by reproducing the πΣ spectrum of the I=0 channel. We find a resonance pole at 1417.7+6.0-7.4(fitting error)+1.1-1.0(systematic error) -i[26.9+6.0-7.9(fitting error)+1.7-2.0(systematic error)] MeV in the deduced KbarN->KbarN amplitude [3].
We measured πΣ invariant mass spectra below and above the KbarN mass threshold in the K-d -> NπΣ in order to study the KbarN interaction and the Λ(1405) resonance [1]. For this purpose, a negatively-charged kaon (K-) beam of 1 GeV/c was irradiated on a deuterium target at the K1.8BR beam line in the J-PARC Hadron Experimental Facility. In the experiment, a nucleon (N: neutron or proton) knocked out from a deuteron (d) by an incident K- was detected at a very forward angle, and four different final states of π+Σ-, π-Σ+, π0Σ0, and π-Σ0 were identefied by measuring the charged particles emitted around the target.
This reaction can be described by the following two-step process: (i) K-"N1"->KbarN and (ii) Kbar"N2"->πΣ, where "N1" and "N2" are nucleons bound in the deuteron.
Since the nucleon emitted at the forward angle carries away most of the collision energy in (i), the center-of-mass energy in (ii) can be lower, even below the KbarN mass threshold. Since the recoiled kaon is slow down below 250 MeV/c, one expects that the S-wave Kbar"N2"->πΣ scattering is dominant around the KbarN mass region. In order to separate the I=0 and 1 amplitudes in (ii), we demonstrate that an isospin relation of the cross sections between the four final πΣ states is satisfied as π0Σ0 = [π+Σ- + π-Σ+ - π-Σ0]/2.
The scattering amplitudes of step (i) has been well analyzed by Gopal et al. [2]. Employing their amplitudes in step (i), we could deduce the S-wave scattering amplitudes of step (ii): KbarN->KbarN as well as KbarN->πΣ in I = 0 in the framework of the KbarN-πΣ coupled channel by reproducing the πΣ spectrum of the I=0 channel. We find a resonance pole at 1417.7+6.0-7.4(fitting error)+1.1-1.0(systematic error) -i[26.9+6.0-7.9(fitting error)+1.7-2.0(systematic error)] MeV in the deduced KbarN->KbarN amplitude [3].
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Publication: [1] Experimental Proposal for J-PARC (E31), Spectroscopic study of hyperon resonances below KbarN threshold via the (K-, n) reaction on deuteron, KEK/J-PARC-PAC 2009-5.<br>[2] G. P. Gopal et al., Partial-wave analyses of KN two-body reactions between 1480 and 2170 MeV, Nucl. Phys. B119(1977)362.<br>[3] S. Aikawa et al., Pole position of Λ(1405) measured in d(K-,n)πΣ reactions, Phys. Lett. B837(2023)137637; https://doi.org/10.1016/j.physletb.2022.137637.
Presenters
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Hiroyuki Noumi
Research Center for Nuclear Physics,Osaka University
Authors
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Hiroyuki Noumi
Research Center for Nuclear Physics,Osaka University