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

M. Svec

doi:10.1103/PhysRevD.55.5727

paper

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

arXiv:hep-ph/9607297 · doi:10.1103/PhysRevD.55.5727

Abstract

The measurements of reactions $I ¨ ^{-} p_{↑} \to I ¨ ^{-} I ¨ ^{+} n$ at 17.2 GeV/c and $I ¨ ^{+} n_{↑} \to I ¨ ^{+} I ¨ ^{-} p$ 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 $∣ S ∣^{2} I^£$ with recoil transversity ``up'' resonates near 750 MeV while the amplitude $∣ S ∣^{2} I^£$ with recoil transversity ``down'' is large and nonresonating. The amplitude $∣ S ∣^{2} I^£$ contributes as a strong background to S-wave intensity I_S = (|S|^2 + |\overline S |^2)Î£ $an dd i s t or t s t h e d e t er mina t i o n so f$ Ï $r eso nan ce p a r am e t er s f r o m$ I_S $. T o a v o i d t hi s p r o b l e m w e p er f or ma ser i eso f B r e i t - W i g n er f i t s d i r ec tl y t o t h e m e a s u r e dd i s t r ib u t i o n$ |\overline S |^2Î£ $. T h e in c l u s i o n o f v a r i o u s ba c k g r o u n d sc a u ses t h e w i d t h o f s i g ma (750) t o b eco m e v er y na r r o w . O u r b es t f i tw i t h$ t $- a v er a g e d co h er e n t ba c k g r o u n d y i e l d s$ m_Ï= 753 \pm 19 $M e V an d$ Î_Ï= 108 \pm 53 $M e V . T h ese v a l u es a r e in e x ce l l e n t a g r ee m e n tw i t h E l l i s - L anik t h eor e m f or t h e w i d t h o f sc a l a r g l u o ni u m . T h e g l u o ni u min t er p r e t a t i o n o f$ Ï(750) $i s a l sos u pp or t e d b y t h e ab se n ceo f$ Ï(750) $in r e a c t i o n s$ Î³Î³\to ÏÏ $. W e a l sos h o w h o w d a t a o n p o l a r i z e d t a r g e t in v a l i d a t eesse n t ia l a ss u m pt i o n so f p a s t d e t er mina t i o n so f$ ÏÏ$ phase shifts .

77 pages