Mass and width of sigma(750) scalar meson from measurements of piN->pi(-)pi(+)N on polarized targets

Abstract

The measurements of reactions ${\pi }^{-}{p}_{\uparrow }\to {\pi }^{-}{\pi }^{+}n$ at 17.2 GeV/c and ${\pi }^{+}{n}_{\uparrow }\to {\pi }^{+}{\pi }^{-}p$ at 5.98 and 11.85 GeV/c made at CERN with polarized targets provide a model-independent and solution-independent evidence for a narrow scalar state sigma(750). The original chi^2 minimization method and the recent Monte Carlo method for amplitude analysis of data at 17.2 GeV/c are in excellent agreement. Both methods find that the mass distribution of the measured amplitude $|\overline{S}{|}^2\Sigma$ with recoil transversity ``up'' resonates near 750 MeV while the amplitude $|S{|}^2\Sigma$ with recoil transversity ``down'' is large and nonresonating. The amplitude $|S{|}^2\Sigma$ contributes as a strong background to S-wave intensity I_S = (|S|^2 + |\overline S |^2)Σ$anddistortsthedeterminationsof$σ$resonanceparametersfrom$I_S$.ToavoidthisproblemweperformaseriesofBreit-Wignerfitsdirectlytothemeasureddistribution$|\overline S |^2Σ$.Theinclusionofvariousbackgroundscausesthewidthofsigma(750)tobecomeverynarrow.Ourbestfitwith$t$-averagedcoherentbackgroundyields$m_σ= 753 \pm 19$MeVand$Γ_σ= 108 \pm 53$MeV.ThesevaluesareinexcellentagreementwithEllis-Laniktheoremforthewidthofscalargluonium.Thegluoniuminterpretationof$σ(750)$isalsosupportedbytheabsenceof$σ(750)$inreactions$γγ\to ππ$.Wealsoshowhowdataonpolarizedtargetinvalidateessentialassumptionsofpastdeterminationsof$ππ$ phase shifts .

arXiv comment77 pages

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• Pion propagation in the linear sigma model at finite temperature
• Unitarity and Interfering Resonances in pipi Scattering and in Pion Production piN->pipiN
• Pion dispersion relation at finite temperature in the linear sigma model from chiral Ward identities
• Relevance of nucleon spin in amplitude analysis of reactions pi(-)p->pi(0)pi(0)n and pi(-)p->eta eta n
• Charge asymmetry in ${\pi }^{+}{\pi }^{-}$ electroproduction on proton at high energies as a test of $\sigma ,\rho$ mesons degeneration
• Amplitude analysis of reactions pi(-)p->etapi(-)p and pi(-)p->etapi(0)n on polarized target and the exotic 1-+ meson
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