We investigate the two-body reactions KN → KN , KN → πΛ, and KN → πΣ via single-energy partial-wave analyses in the center-of-mass (c.m.) energy range 1480 to 2100 MeV. The partialwave amplitudes for these reactions thus extracted were constrained by a multichannel energydependent model satisfying unitarity of the partial-wave S-matrix. We obtain excellent predictions of differential cross sections, polarizations, polarized cross sections, and cross sections for these reactions from a global energy-dependent solution.

We present results of a new multichannel partial-wave analysis for KN scattering in the center-of-mass (c.m.) energy range from 1480 to 2100 MeV. Resonance parameters were extracted by fitting partial-wave amplitudes from all considered channels using a multichannel parametrization that is consistent with S-matrix unitarity. The resonance parameters are generally in good agreement with predictions of the Koniuk-Isgur quark model.

We consider the effect of an exotic S=+1 Θ + resonance on the scattering of neutral kaons off protons. Explicit results are presented for the K 0 L p total cross sections.PACS numbers: 13.75. Jz, 11.80.Et, 14.20.Jn Results from a wide range of recent experiments are now consistent with the existence of an exotic S=+1 resonance, the Θ + (1540), having a narrow width and a mass near . In fact, these older measurements seem to require a width much smaller than 10 MeV [4,5,6,7]. Most investigations of the older data have focused on K + d experiments from which the K + n interaction has been extracted. The effect of Fermi motion in the deuteron is particularly important for a narrow structure, making the observation of a 'bump' in any cross section unlikely. This point has been extensively demonstrated by Nussinov [4], and by Cahn and Trilling [7].The problems of Fermi motion can be avoided if instead one considers the K where Z 0,1 are the strangeness S = 1, I = 0 and 1 amplitudes, and Y 1 is the S = −1, I = 1 amplitude. The Y 1 contribution dominates at low energies, the S = 1 component growing in relative importance with increasing energy. Our result for the K 0 L p total cross section, calculated from the imaginary part of the forward scattering amplitude, is given in Fig. 1. Note that this is not a fit but rather a prediction based on analyses of other reactions.Starting from this description of the data, we have added a narrow Breit-Wigner resonance in order to demonstrate the magnitude of its effect. In doing so, we have taken into account the fact that the incident K 0 L beam has a momentum spread, which also tends to smear out a narrow structure. In Fig. 2, we have added an S = +1 resonance, having a 5 MeV width, to the P 01 partial wave. Here we compare the result for beam momentum distributions (assumed Gaussian) having widths of 10 and 20 MeV/c at 440 MeV/c, the latter being an estimate of the momentum spread associated with the beam used in Ref. [10]. A resonance in the D 03 partial wave is also included for comparison.The measurement of Ref.[10] was reported with total cross sections calculated over 20 MeV/c bins. We have accordingly averaged over this interval, finding a further minimal reduction in the peak. Results for resonances with a range of widths are compared in Fig. 3. From Fig. 1, the most pronounced deviations from our predicted smooth behavior occur near 280 and 460 MeV/c (corresponding to C.M. energies of 1480 and 1550 MeV). The apparent 'bump' at 1480 MeV could be more than a statistical fluctuation. The PDG [12] reports a 1-star Σ(1480) based on an analysis of K − p → K 0 pπ − , with a 3.5 standard deviation signal being seen in K 0 p. (The data of Ref.[11] does not show this structure.) Given the large experimental uncertainties, a fluctuation near 1550 MeV is only interesting in that it occurs near the expected Θ + (1540) signal. (The overall momentum scale has a quoted uncertainty of 2%.) Here too the PDG reports a weak evidence for a nearby bump, the Σ(1560).

We consider the effect of an exotic S=+1 Θ + resonance on the scattering of neutral kaons off protons. Explicit results are presented for the K 0 L p total cross sections. Results from a wide range of recent experiments are now consistent with the existence of an exotic S=+1 resonance, the Θ + (1540), having a narrow width and a mass near 1540 MeV [1]. Width determinations have been hindered by limitations on experimental resolutions, resulting in upper bounds of order 10 MeV. The quantum numbers of this state remain unknown, though a prediction of J P = 1/2 + was obtained in the work [2] that provided a motivation for the original search. An examination of older K + d and K + p data has provided no confirmation for the Θ + or an associated Θ ++ state [3]. In fact, these older measurements seem to require a width much smaller than 10 MeV [4, 5, 6, 7]. Most investigations of the older data have focused on K + d experiments from which the K + n interaction has been extracted. The effect of Fermi motion in the deuteron is particularly important for a narrow structure, making the observation of a 'bump' in any cross section unlikely. This point has been extensively demonstrated by Nussinov [4], and by Cahn and Trilling [7]. The problems of Fermi motion can be avoided if instead one considers the K 0 L p interaction. However, as the K 0 L is a mixture of K 0 and K 0 , this approach requires an accounting of the KN interaction. This we have done, combining results from analyses of KN [8] and KN [9] data. The amplitude for K 0 L p scattering is given by M K 0 L p = 1 4 (Z 1 + Z 0 + 2Y 1) (1) where Z 0,1 are the strangeness S = 1, I = 0 and 1 amplitudes, and Y 1 is the S = −1, I = 1 amplitude. The Y 1 contribution dominates at low energies, the S = 1 component growing in relative importance with increasing energy. Our result for the K 0 L p total cross section, calculated from the imaginary part of the forward scattering amplitude, is given in Fig. 1. Note that this is not a fit but rather a prediction based on analyses of other reactions. Starting from this description of the data, we have added a narrow Breit-Wigner resonance in order to demonstrate the magnitude of its effect. In doing so, we have taken into account the fact that the incident K 0 L beam has a momentum spread, which also tends to smear out a narrow structure. In Fig. 2, we have added an S = +1 resonance, having a 5 MeV width, to the P 01 partial wave. Here we compare the result for beam momentum distributions (assumed Gaussian) having widths of 10 and 20 MeV/c at 440 MeV/c, the latter being an estimate of the momentum spread associated with the beam used in Ref. [10]. A resonance in the D 03 partial wave is also included for comparison. The measurement of Ref. [10] was reported with total cross sections calculated over 20 MeV/c bins. We have accordingly averaged over this interval, finding a further minimal reduction in the peak. Results for resonances with a range of widths are compared in Fig. 3. From Fig. 1, the most pronounced deviations from our ...

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