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

/)2( JS /J

Motivation

One Boson Exchange Potential (OBEP) introduce σ particle.OBEP is successful to describe nuclear forces.

Linear model (LM ) also introduced .LM 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 of π –π scattering.

New analysis strongly suggest the existence of σ .

But properties of σ still need to be clarified.

Current states of (PDG2004)Different exp. results not consistent .

Mass and width of σ have large uncertainty .

σ production in

Two PWA method used : Covariant Helicity Amplitude and Covariant Tensor

Several B-W parameterizations describe σ .

/J

B-W parameterizations

Sample of /J

Fit to J/→+ (Method I)

0++ contribution 2++ contribution

preliminary

b1(1235)Channels fitted to the data:

J/f2(1270) f0(980) b1(1235) ’(1450) f2(1565) f2(2240)

++0 2++

Fit to J/→+ (Method II)

Channels fitted to the data:

J/f2(1270) f0(980) b1(1235) phase space

2++

0++

Fit results:

Averaged pole position:

(541 39) (252 42)i MeV

Method I

Method II

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.

/)2( JS

Some distribution of /)2( JS

Dipion invariant mass spectrum Dipion recoiling mass spectrum

cosθ of pion in lab. System cosθ of muon in lab. System

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

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

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

dipion invariant mass Cosθ of π+

Cosθ of σ

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 .

Fit Method

Max. Likelihood method is used;M.C integration is used to do efficiency correction .

Strong cancellation