We present a new and improved model-independent amplitude analysis of the reactions ϩ n ↑ → ϩ Ϫ p at 5.98 and 11.85 GeV/c and Ϫ p ↑ → Ϫ ϩ n at 17.2 GeV/c measured with transversely polarized targets at the CERN Proton Synchrotron. For dipion masses below 1000 MeV the pion production process is described by two S-wave and six P-wave production amplitudes. Previous analyses suffered from the presence of unphysical solutions for moduli of amplitudes or cosines of their relative phases, causing uncertainties regarding the signal for the scalar state Iϭ0 0 ϩϩ (750). To remove the unphysical solutions we use a Monte Carlo approach to amplitude analysis. In each (m,t) bin we randomly varied the input spin-density-matrix elements 30 000 times within their experimental errors and performed an amplitude analysis for each selection. Unphysical solutions were rejected and the physical solutions produced a continuous range of values for moduli, cosines of relative phases, and for partial wave intensities. A clear signal for (750) resonance emerges in all four solutions for an S-wave intensity I S at 5.98 and 11.85 GeV/c and in both solutions for an S-wave amplitude ͉S ͉ 2 ⌺ at 17.2 GeV/c. Its ϩ Ϫ decay width is estimated to be in the range 200-300 MeV. We find a significant suppression of 0 production in the amplitudes ͉U͉ 2 ⌺, ͉N ͉ 2 ⌺ and at 17.2 GeV/c in ͉L͉ 2 ⌺. The mass dependence of the amplitudes ͉L ͉ 2 ⌺ and ͉L͉ 2 ⌺ shows unexpected structures within the 0 mass region which correlate the mass spectra corresponding to opposite nucleon spins. These features of the P-wave moduli reveal the essential role of nucleon spin in the pion production process and contradict the factorization hypothesis. Our results emphasize the need for a systematic study of pion production on the level of amplitudes in a new generation of dedicated experiments with spin at the recently proposed high-intensity hadron facilities.
We present a model independent amplitude analysis of reaction p i n f -+ a +~-~ at 5.98 and 11.85 GeV/c using Saclay data obtained with a transversely polarized deuteron target at the CERN Proton Synchrotron. The analysis makes use of the data in two sets of binnings to examine the dependence of amplitudes on momentum transfer t [t 5 1.0 (GeV/c )' I in the mass region and their dependence on dipion mass below 1000 MeV for momentum transfers -t=0.2-0.4 (GeV/c )'. The analysis is performed in both t-channel and s-channel helicity frames of the dimeson state and it is verified by comparison with linear bounds on the moduli. The data yield two solutions for 8 moduli and 6 cosines of relative phases of nucleon transversity amplitudes with dimeson spin J = O (S wave) and J = 1 (P wave). The two solutions differ mainly in the S-wave contributions. Both solutions require nonzero nucleon helicity-nonflip amplitudes ( A , exchange) with phases different from phases of nucleon helicity-flip amplitudes (a exchange). Natural exchange amplitudes (A, exchange) with opposite nucleon transversities show a crossover in their t dependence att,=0.4-0.5 (GeV/c 1' which has not been observed in the earlier amplitude analysis of a -p i -+ a P a + n at 17.2 GeV/c. We suggest this difference may signal the influence of composite structure of hadrons and nonperturbative QCD effects in pion production. Although the mass dependence of partial-wave cross sections averaged over nucleon spins is smooth, we observe large and systematic structures in moduli squared of nucleon transversity amplitudes which reveal the essential role of nucleon spin in the pion production process. This behavior of moduli does not support the hypothesis of factorization of mass and t dependence of production amplitudes previously used in studies of meson-meson scattering. The mass dependence of S-wave amplitudes suggests the existence of a scalar state I = 0 0++(750) with a width of 100-150 MeV. Our results emphasize the need for a systematic study of pion production on the level of amplitudes in a new generation of dedicated experiments with spin at the recently proposed high-intensity hadron facilities. PACS numbeds): 13.75.Gx, 13.85.Hd, 13.88. + e AMPLITUDE ANALYSIS OF REACTION a f n t --t~+ a -~ AT . . .
Model independent amplitude analyses of π − p ↑ → π − π + n on polarized target at 17.2 GeV/c reveal resonant structure of S-wave transversity amplitudes |S| 2 Σ and |S| 2 Σ near 750 MeV. Simultaneous fit to |S| 2 Σ and |S| 2 Σ with a single σ pole yields m σ = 775 ± 17 MeV and Γ σ = 147 ± 33 MeV. Simultaneous fit with two common σ poles yields a lower χ 2 /dpt. Their resonance parameters are m σ = 786 ± 24 MeV, Γ σ = 130 ± 47 MeV and m σ ′ = 670 ± 30 MeV, Γ σ ′ = 59 ± 58 MeV.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.