Toshimitsu Yamazaki

Formation of the

Analyzing DISTO data of pp → pΛK+ at Tp = 2.50 and 2.85GeV to populate a previously reported X(2265) -resonance with Mx = 2267 MeV/c2 and Γx = 118 MeV at 2.85GeV, we found that the yield of X(2265) at 2.50GeV is much less than that at 2.85GeV (less than 10%), though it is expected from a kinematical consideration to be produced as much as 33% of that at 2.85GeV. The small population of X(2265) at 2.50GeV is consistent with the very weak production of Γ(1405) at the same incident energy toward its production threshold, thus indicating that Γ(1405) plays an important role as a doorway state for the formation of X(2265).

S=-1

Abstract The Σπ invariant-mass spectra in the resonant capture of K − at rest in 4He, 3He and d are calculated by a coupled-channel procedure for a K − p quasi-bound state of an arbitrary chosen mass (M) and width (Γ). A χ 2 analysis of old 4He bubble chamber data shows a dominance of the s-orbit absorption, and yielded M = 1405.5 − 1 + 1.4 MeV / c 2 and Γ = 24 − 3 + 4 MeV , where a possible population of Σ 0 ( 1385 ) and also a small p-orbit capture contribution are taken into account. This result confirms the Λ ( 1405 ) ansatz, whereas recent chiral-SU(3) predictions ( M ∼ 1420 MeV / c 2 ) are excluded. A more stringent test by using a 3He target is proposed.

resonance X(2265) in the reaction

The data from the DISTO Collaboration on the exclusive pp ! pK + production acquired at T p = 2:85 GeV have been re-analysed in order to search for a deeply bound K pp( X) state, to be formed in the binary process pp! K + X. The preliminary spectra of the MK+ missingmass and of the Mp invariant-mass show, for large transverse-momenta of protons and kaons, a distinct broad peak with a mass MX = 2265 2 MeV=c 2 and a width X = 118 8 MeV=c 2 .

pp -> X + K^+

We have studied the structure of K−pp by solving this system in a variational treatment, starting from Ansatz that Λ(1405) is a K−p quasi-bound state, Λ∗ with mass 1405 MeV/c2. The structure of K−pp reveals a molecular feature, namely, the K− in an “atomic center”, Λ∗, plays a key role in producing strong covalent bonding with the other proton. Deeply bound K¯ nuclear systems are formed by this “super-strong” nuclear force due to migrating real bosons, K¯, a la Heitler-London-Heisenberg, which overcompensates the stiff nuclear incompressibility. Theoretical background of the Λ(1405) Ansatz is discussed in connection with the double-pole picture of Λ(1405) based on chiral SU(3) dynamics. Detailed analysis reveals single-pole nature of the observable Λ(1405). There are two kinds of Σπ invariant masses experimentally observable, the usual T22 invariant mass and the conversion T21 invariant mass. It is of virtual importance to determine whether the Λ∗ mass is 1405 MeV or 1420 MeV. The T21 invariant mass from K− absorption at rest in deuteron can provide decisive information about this Λ∗ mass problem.

at 2.50 and 2.85 GeV

We have studied the structure of K−pp by solving this system in a variational treatment, starting from Ansatz that Λ(1405) is a K−p quasi-bound state, Λ∗ with mass 1405 MeV/c2. The structure of K−pp reveals a molecular feature, namely, the K− in an “atomic center”, Λ∗, plays a key role in producing strong covalent bonding with the other proton. Deeply bound K¯ nuclear systems are formed by this “super-strong” nuclear force due to migrating real bosons, K¯, a la Heitler-London-Heisenberg, which overcompensates the stiff nuclear incompressibility. Theoretical background of the Λ(1405) Ansatz is discussed in connection with the double-pole picture of Λ(1405) based on chiral SU(3) dynamics. Detailed analysis reveals single-pole nature of the observable Λ(1405). There are two kinds of Σπ invariant masses experimentally observable, the usual T22 invariant mass and the conversion T21 invariant mass. It is of virtual importance to determine whether the Λ∗ mass is 1405 MeV or 1420 MeV. The T21 invariant mass from K− absorption at rest in deuteron can provide decisive information about this Λ∗ mass problem.

Experimental confirmation of the Λ(1405) Ansatz from resonant formation of a K−p quasi-bound state in K− absorption by 3He and 4He

A new spectrometer system was designed and constructed at the secondary beam line K1.8BR in the hadron hall of J-PARC to investigate

DISTO data on K pp

bar K N

Single-pole nature of Λ(1405) and structure of K−pp

interactions and

Single-pole nature of Lambda (1405) and structure of K-pp

bar K

The K1.8BR spectrometer system at J-PARC

-nuclear bound systems. The spectrometer consists of a high precision beam line spectrometer, a liquid