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σ Production at BES

σ Production at BES. Gang LI For BES Collaboration IHEP, Beijing,100039,China MENU04, Beijing, Aug. 29th — Sep.4th. Outline. Motivation Production in Production in Summary. Motivation. One Boson Exchange Potential ( OBEP ) introduce σ particle .

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σ Production at BES

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  1. σ Production at BES Gang LI For BES Collaboration IHEP, Beijing,100039,China MENU04, Beijing, Aug. 29th—Sep.4th

  2. Outline • Motivation • Production in • Production in • Summary

  3. Motivation • One Boson Exchange Potential (OBEP) introduce σ particle. • OBEP is successful to describe nuclear forces. • Linear  model (LM ) also introduced . • LM naturally realized the spontaneous breaking of chiral symmetry and PCAC, also the SU(2)×SU(2) current algebra. • σ has disappeared for a long time from PDG due to negative phase shift results ofπ –π scattering. • New analysis strongly suggest the existence of σ . • But properties of σ still need to be clarified.

  4. Current states of  (PDG2004) • Different exp. results not consistent . • Mass and width of σ have large uncertainty .

  5. σ production in • Two PWA method used : Covariant Helicity Amplitude and Covariant Tensor • Several B-W parameterizations describe σ .

  6. B-W parameterizations

  7. Sample of

  8. Fit to J/→+ (Method I) b1(1235) Channels fitted to the data: J/f2(1270)  f0(980) b1(1235) ’(1450) f2(1565) f2(2240) preliminary 2++ ++0  0++ contribution 2++ contribution

  9. Fit to J/→+(Method II) 2++ 0++ Channels fitted to the data: J/f2(1270)  f0(980) b1(1235) phase space

  10. Fit results: Method I Method II Averaged pole position: MeV

  11. σ production in • pion-pion rescattering corrections and Ψ-πInteractions both small. (Brown&Cahn, PRL,35:1(1975)) • Dipion S-wave dominant (small D-wave). (J.Z. Bai et.al, PRD62:032002(2000)) • Very pure sample obtained with J/Ψ tagged by muon pair; • Contaminations from other decay channels very small (<0.2%). • Good place to study σ.

  12. Some distribution of Dipion invariant mass spectrum Dipion recoiling mass spectrum cosθ of pion in lab. System cosθ of muon in lab. System

  13. cosθand φdistribution of  and πin lab. and  rest frame system respectively

  14. Analysis Method • Covariant helicity amplitude method used; • Three components are put into fit :  (0+), 2+, IPS • A non-interference bkgd to estimate the pions decay effect. Interference phase space M. Ishida,hep-ph/0212383

  15. Fit results • B-W + IPS + interference fit data well. • Strong destructive interference required by chiral constraint. • Pole position consistent with that of J/Ψ ωππ. Preliminary

  16. Cosθ of σ dipion invariant mass Cosθ of π+

  17. Summary • Isospin scalar  particle studied at BES with different decay channels of J/Ψ and Ψ(2S) • Different analysis methods were used; • All results are consistent .

  18. Fit Method • Max. Likelihood method is used; • M.C integration is used to do efficiency correction .

  19. Strong cancellation

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