We have measured the shift and width of the kaonic hydrogen 1s state due to the KN strong interaction. We have observed, for the first time, distinct K-series kaonic hydrogen x rays with good signal-to-noise ratio in the energy spectrum. The measured energy shift and width were determined to be DE͑1s͒ 2323 6 63͑stat͒ 6 11͑syst͒ eV (repulsive) and G͑1s͒ 407 6 208͑stat͒ 6 100͑syst͒ eV, respectively. [S0031-9007(97)02992-X] PACS numbers: 13.75. Jz, 25.80.Nv, 29.30.Kv, 36.10.Gv The determination of the strong-interaction energy level shift and width of the kaonic hydrogen x rays is one of the most important subjects for the understanding of the KN interaction. It is strongly affected by the presence of the L͑1405͒ subthreshold resonance. The study of the KN interaction is also relevant to the important question of K 2 condensation in dense matter [1,2].The observation of the shift and width of the kaonic hydrogen K a ͑2p ! 1s͒ x rays gives direct information about the KN s-wave interaction at the K 2 p threshold energy in a fairly model independent way [3]. The status of the study was quite puzzling due to the contradiction between the signs of the scattering lengths obtained by the previous x-ray measurements [4-6] and those extracted from the analyses of the low energy KN data, e.g., , as shown in Fig. 1. This contradiction is known to be almost impossible to reconcile within the conventional theoretical framework. Moreover, the x-ray signals of the previous experiments are very difficult to identify in their spectra. Therefore, a definitive experiment has been long awaited.We accumulated data for 760 hours at KEK-PS K3. A detailed description of our experimental setup is given in a separate paper [10]. Here we present a short summary.Optimization of the target density is quite important for this experiment. As a compromise between kaon stopping yield and kaon loss during the atomic cascade due to the Stark effect, we chose to operate the hydrogen FIG. 1. The energy shift and width of 1s state. One-standarddeviation region of shift and width of the previous experiments are plotted together with theoretical calculations. The present result is shown in bold.

We have searched for a deeply bound kaonic state by using the FINUDA spectrometer installed at the e(+)e(-) collider DAPhiNE. Almost monochromatic K(-)'s produced through the decay of phi(1020) mesons are used to observe K(-) absorption reactions stopped on very thin nuclear targets. Taking this unique advantage, we have succeeded to detect a kaon-bound state K(-)pp through its two-body decay into a Lambda hyperon and a proton. The binding energy and the decay width are determined from the invariant-mass distribution as 115(+6)(-5)(stat)(+3)(-4)(syst) MeV and 67(+14)(-11)(stat)(+2)(-3)(syst) MeV, respectively.

In Fig. 3 and its inset the vertical scales should be reduced by a factor of 4. This plotting error affects only the figure. All relevant quantities in the text and in the table are correct as published. We regret the oversight.The corrected version of Fig. 3 is reproduced here. This correction does not affect any results or conclusions of the published paper.FIG. 3. Inclusive ÿ ; K spectrum on Si at K 6 2 . The curves are the calculated spectra for the repulsive (solid) and shallow (dashed) -nucleus potentials, fitted to the measured spectrum. A value of the scaling factor and 2 per degree of freedom are shown for each fitting.

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The ⌳ 13 C hypernucleus was studied by measuring ␥ rays in coincidence with the 13 C(K Ϫ , Ϫ ) reaction. ␥ rays from the 1/2 Ϫ and 3/2 Ϫ states, which are the partners of the spin-orbit doublet states with a predominant configuration of ͓ 12 C g.s. (0 ϩ ) p ⌳ ͔, to the ground state were measured. The splitting of the states was found to be ⌬E(1/2 Ϫ Ϫ3/2 Ϫ )ϭϩ152Ϯ54(stat)Ϯ36(syst) keV. This value is 20-30 times smaller than that of single particle states in nuclei around this mass region. The j ⌳ ϭl ⌳ Ϫ1/2͓(p 1/2 ) ⌳ ͔ state appeared higher in energy, as in normal nuclei. The value gives new insight into the Y N interaction. The excitation energies of the 1/2 Ϫ and 3/2 Ϫ states were obtained as 10.982Ϯ0.031(stat)Ϯ0.056(syst) and 10.830Ϯ0.031(stat)Ϯ0.056(syst) MeV, respectively. We also observed ␥ rays from the 3/2 ϩ state, which has a ͓ 12 C(2 ϩ ) s ⌳ ͔ configuration, to the ground state in ⌳ 13 C. The excitation energy of the 3/2 ϩ state was obtained as 4.880Ϯ0.010(stat) Ϯ0.017(syst) MeV. Nuclear ␥ rays with energies of 4.438 and 15.100 MeV had similar yields, which suggests that a quasifree knockout of a ⌳ particle is dominant in highly excited regions.