σ Production at BES
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Transcript of 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
/)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