Energy-independent Partial-wave Analysis Research Articles

Energy-independent PWA of the reaction γp → K+Λ

Using all recent data on the differential cross sections and spin observables for the reaction γp → K + Λ, an energy-independent partial-wave analysis is performed for center-of-mass energies from 1.462 to 1.662 GeV. The analysis requires multipoles up to L = 2; there is no evidence that the fit requires multipoles with L = 3. At present the available data allow us to extract the dominant multipoles only. These are compatible with the multipoles obtained in the energy-dependent fit. This result supports the reliability of the Bonn-Gatchina energy-dependent results.

A study of K−π+ scattering in the reaction K−p→K−π+n at 11 GeV/c

Results from a high statistics study of the reaction K−p→K−π+n are presented. These results are based on data obtained with an 11 GeV/c beam using the LASS spectrometer at SLAC. The mass dependence of the spherical harmonic moments provides clear evidence for the production of the complete leading orbitally excited K∗ series up through JP = 5−. These moments are used to perform an energy independent partial wave analysis of the K−π+ system from threshold to 2.6 GeV/c2 using a t-dependent parametrization of the production amplitudes. The amplitudes corroborate the leading K∗(892), K2∗(1430), K3∗(1780), K4∗(2060), and K5∗(2380) resonances observed directly in the moments, and also provide new evidence for underlying states. The 0+ amplitude contains the K0∗(1350) and a second 0+K∗(1950) at higher mass. The 1−K∗(1790) seen earlier two and three-body analyses is confirmed, and evidence is provided for suppressed K−π+ decay mode of a second 1− state, the K∗(1410), which has been seen in earlier three-body analyses.

Observation of new resonant structures in the natural spin-parity strange meson system

High statistics data for the reaction K −p→K − π +n have been obatined using the LASS spectrometer at SLAC. An energy independent partial wave analysis of these data yields unique K − π + elastic scatering partila wave amplitudes in the K π invariant mass region from 0.7 GeV to 1.8 GeV, and two distinguishable sets of amplitudes between 1.8 GeV and 2.3 GeV. Besides the three “old” K ∗ resonances [J P = 1 − K ∗(892), 2 + K ∗(1430), 3 − K ∗(1780)] these partial waves display evidence for a K ∗ resonance with J P =4 + near 2.07 GeV. The energy dependence of the S wave amplitude confirms the existence of a resonant 0 + state in the 1.4 GeV region [the k(1500)], and provides evidence for a new high-mass S wave resonance [′'(1850)] near 1.85 GeV. Resonant behavior is also observed in the P wave amplitude around 1.7 GeV.

An isobar model partial-wave analysis of three-body final states in π+p interactions from threshold to 1700 MeV c.m. energy

We present the results of an energy-independent partial-wave analysis of the reaction π +p→ ππN at nine c.m. energies between 1400 and 1700 MeV. New bubble chamber data from the Cambridge-Imperial College-Westfield College Collaboration were fitted, together with earlier data from Oxford, using the isobar model in a maximum likehood fitting program. The isobars used were Δ(1236), N ∗(1470) and ϱ(770) and allowance was made for an incoherent contribution from an I=2 s-wave phase shift produced by one-pion exchange in the t-channel. The results of this analysis are compared with the predictions of symmetry schemes. The ϱ 1N amplitudes of the S 31 and D 33 members of the {70, 1 −} multiplet are clearly observed and their signs unambiguously determined for the first time. Structure in the P 31 wave is discussed in relation to recent claims of a low mass resonance. Possible explanations of the complicated behaviour of the P 33 wave are discussed; its N ∗(1470)π decay is observed for the first time.

Low-energy πN partial wave analysis

An energy-independent partial-wave analysis has been performed on pion-nucleon elastic and charge-exchange differential cross sections and elastic polarizations, for lab. momenta below 500 MeV/ c. The amplitudes were constrained by a simultaneous fixed momentum transfer analysis, which leads to a unique and smooth solution. The masses and widths of Δ ++ and Δ 0 have been redetermined from total cross sections as m Δ ++ = 1230.9 ± 0.3 MeV, m Δ 0 = 1233.6 ± 0.5 MeV, Γ Δ ++ = 111 ± 1 MeV and Γ Δ 0 = 113 ± 1.5 MeV. For the pion-nucleon coupling constant the value | 2 = 0.079 ± 0.001 was obtained.

Energy-independent partial-wave analysis of the reactions π±p → N ππ in the c.m. energy range 1.36–1.76 GeV

The amplitudes describing one-pion production in pion-nucleon interactions have been obtained from the data in the c.m. energy range 1.36–1.76 GeV. A partial-wave expansion of the amplitudes in the framework of the generalized isobar model was used to fit simultaneously data from the reactions π −p → p π − π 0, π −p → n π + π − and π +p → p π + π 0. The production of Δ, ϱ and σ( ππ, i = l = 0) is assumed, and a new parametrization of the σ and of the centrifugal barrier is adopted. The mass and angular distributions of the above three reactions are well reproduced by our solution; in addition, a good prediction is obtained for the values of the cross sections of the reactions π −p → n π 0 π 0 and π +p → n π + π + which were not used in the fit. At our highest energy, there is evidence for N ∗ production and for the presence of an ( i = 2, l = 0) ππ interaction, contributing about 5% to the cross sections of the reactions π −p → p π − π 0 and π +p → p π + π 0. Finally, assuming that the phases of the predominant inelastic waves vary with energy like the phases of the corresponding elastic waves, we obtain Argand plots, and in particular the signs of the dominant inelastic couplings of ten resonances in our energy region.

Energy-independent partial-wave analysis of [formula omitted] between 1540 and 2150 MeV

An exhaustive partial-wave analysis of the reaction KN → Λπ has been carried out on a compilation of all available data using two separate semi-energy-independent methods. Particular attention has been given to finding all ambiguous solutions. Two possible solutions are found consistent with the physical assumptions imposed. The parameters of the resonances appearing in the two solutions are given.

Energy independent partial wave analysis of single pion photoproduction in the first resonance region

We present results of an energy independent multipole analysis of π +, π 0 and π − photoproduction on nucleons for photon energies between 240 MeV and 500 MeV. New data which are included in the present analysis are the asymmetry by polarized photons for γn → π −p and the π −/ π + ratio recently measured at Tokyo. Each isospin part of the l ⩽ 1 amplitudes has been parametrized; the 2 ⩽ l ⩽ 3 amplitudes have been fixed to the values given by Berends, Donnachie and Weaver, and the l ≧ 4 amplitudes have been approximated by the Born terms. Imaginary parts of l ≦ 3 amplitudes have been calculated from the real parts by Watson's theorem. Without any isotensor current or anomalous energy dependence of non-resonant multipoles, we obtained a good fit to the π +, π 0 and π − photoproduction. The results are compared with dispersion theoretical calculations and phenomenological multipole analyses. M 1− (1 2) is small and consistent with the dispersion theory of Schwela but contradicts the previous results of Pfeil and Schwela. The strong energy dependence of E 0+ (0) given by Noelle and Pfeil is not justified. Discrepancies between our analysis and dispersion theories occur in the magnitude of M 1− (3 2) and in the energy dependences of E 0+ (0), E 0+ (1 2) and E 1+ (1 2) . Above 400 MeV two types of solution have been obtained. It is pointed out that the measurement of polarized target asymmetry for γp → π 0p will distinguish the two solutions.

Analysis ofK−p→Λπ+π−in the Region of theΛ(1520)

The rate for the decay $\ensuremath{\Lambda}(1520)\ensuremath{-}\ensuremath{\Sigma}(1385)\ensuremath{\pi}$ has been measured in a study of the reaction sequence ${K}^{\ensuremath{-}}p\ensuremath{\rightarrow}\ensuremath{\Lambda}(1520)\ensuremath{\rightarrow}\ensuremath{\Sigma}(1385)\ensuremath{\pi}\ensuremath{\rightarrow}\ensuremath{\Lambda}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$. A sample of 9200 events of the type ${K}^{\ensuremath{-}}p\ensuremath{\rightarrow}\ensuremath{\Lambda}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ has been obtained in the Berkeley 25-in. hydrogen bubble chamber. The incident momenta range from 300 to 470 MeV/c. An energy-independent partial-wave analysis was performed using an isobar model. The model included a coherent mixture of six partial waves to describe all mass distributions, angular distributions, and the polarization of the $\ensuremath{\Lambda}$. The $\ensuremath{\Sigma}(1385)\ensuremath{\pi}$ decay mode was found to dominate the $\ensuremath{\Lambda}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ decay of the $\ensuremath{\Lambda}(1520)$, in disagreement with the results of a production reaction study of the same decay. The width for the decay was measured to be 1.40 \ifmmode\pm\else\textpm\fi{} 0.26 MeV. Mixing between the $\ensuremath{\Lambda}(1520)$ and the $\ensuremath{\Lambda}(1690)$ has been used in the past to describe the ${J}^{P}={\frac{3}{2}}^{\ensuremath{-}}$ baryons as SU(3) singlet and octet. Combining our rate for $\ensuremath{\Lambda}(1520)$ with a recently measured rate for $\ensuremath{\Lambda}(1690)\ensuremath{\rightarrow}\ensuremath{\Sigma}(1385)\ensuremath{\pi}$, we calculate the mixing angle $|\ensuremath{\theta}|=63\ifmmode^\circ\else\textdegree\fi{} \mathrm{to} 83\ifmmode^\circ\else\textdegree\fi{}$. This is in strong disagreement with the mixing angle derived from the two-body $D$-wave decays of the singlet and octet of -25 \ifmmode\pm\else\textpm\fi{} 6\ifmmode^\circ\else\textdegree\fi{}. Thus, some modification of the usual SU(3) description of these states needs to be made.

Energy-independent partial-wave analysis of [formula omitted] between 600 and 1200 MeV/c

The reactions K −p → Λπ O and K −n → Λπ − in the centre-of-mass energy range from ≈1.6 to ≈1.9 GeV have been interpreted in terms of an energy-independent partial-wave analysis. Solutions are presented and the possible existence of new resonant states is discussed.