Jun 22 – 27, 2023
Auditorium Maximum
Europe/Warsaw timezone

Measurement of KbarN scattering below the KbarN mass threshold

Jun 23, 2023, 4:45 PM
25m
Conference room (Auditorium Maximum)

Conference room

Auditorium Maximum

Invited parallel Parallel session C4

Speaker

Hiroyuki Noumi (Osaka University)

Description

We measured \pi\Sigma invariant mass spectra below and above the KbarN mass threshold in the K-d -> N\pi\Sigma in order to study the KbarN interaction and the Lambda(1405) resonance. 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 \pi^+\Sigma^-, \pi^-\Sigma^+, \pi^0\Sigma^0, and \pi^-\Sigma^0 were identefied by measuring the charged particles emitted around the target.

This reaction can be described by the two step process: (i) K-"N_1"->KbarN and (ii) Kbar"N_2"->\pi\Sigma, where "N_1" and "N_2" 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. Around the KbarN mass region, one expects that the S-wave Kbar"N_2"->\pi\Sigma scattering is dominant. 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 \pi\Sigma states is satisfied as \pi^0\Sigma^0 = [\pi^+\Sigma^- + \pi^-\Sigma+ - \pi^-\Sigma^0]/2.
By reproducing the \pi\Sigma spectra of the I=0 channel, we deduced the S-wave scattering amplitude of KbarN->KbarN as well as KbarN->\pi\Sigma in I=0 in the framework of the KbarN-\pi\Sigma coupled 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.

Collaboration J-PARC E31

Primary author

Hiroyuki Noumi (Osaka University)

Presentation materials

Peer reviewing

Paper