can the s(980) mesons be described as kk? introduction: the f 0 /a 0 (980) resonances structure:...
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Can the S(980) mesons be described as KK?
• introduction: the f0/a0(980) resonances
• structure: leading hypotheses
• test: radiative decays of phi(1020)
• experiments and recent results
• evaluation: what have we learned?
• conclusions
Richard JonesUniversity of Connecticut
EMI2001, Osaka, Dec. 4-7 2001
Electromagnetic Interactions in Nuclei and Hadrons Symposium
Introduction: f0(980)
EMI2001, Osaka, Dec. 4-7 2001
primary decay s-wave
PDG: m0 = 980 10 MeV = 40 – 100 MeV
often seen through interferencewith background ()
also seen as large thresholdenhancement in K+ K
- s-wave
strong coupling to strange quarksobserved in J/ radiative decays
2
Introduction: a0(980)
EMI2001, Osaka, Dec. 4-7 2001
primary decay s-wave
PDG: m0 = 983 1 MeV = 50 – 100 MeV
seen through interference with
background in final state
observed as a peak in inclusivephotoproduction data
neutral a0 has strong coupling tostrange quarks (unexpected)
)( 0m )( 00m
Crystal Barrel
CERN Omega
)( 0m
3
EMI2001, Osaka, Dec. 4-7 2001
Structure: leading hypotheses4
1. Exotic (nsns) state explains near-degeneracy of two states narrow widths explained by OZI suppression explains strong couplings to strange quarks? where are the other members of the nonet?? few constraints
2. KK molecule (or non-exotic nsns state) inspired by nearness of states to 2K threshold narrow widths explained by large physical size of hadron explains strong couplings to strange quarks no missing states are required to exist
? few constraints
3. Dynamics of 2-pseudoscalar scattering coupled-channel fits to 2P scattering data exhibit dynamical poles in the
s-wave near 2K threshold that arise from kaon loops no resonances have to be included (in contrast to p-wave)? simple no physical picture (like a molecule) is correct
EMI2001, Osaka, Dec. 4-7 2001
5Test: radiative decays of Phi
Close, Isgur, Kumano (1993):
look at the decays
can discriminate between 3 models using
members of ordinary nonet
molecular kaon/antikaon state
members of exotic qqqq nonet
BR of order expected in the molecular model
a real prediction (no data on these channels existed in 1993)
)980(Sγ
019
5105
EMI2001, Osaka, Dec. 4-7 2001
6Experiment: results from VEPP-2M
e+e- collider (Novirsibirsk)
2 experiments:
SND CMD-2
2001:total of 90 M analyzed
)γfBR( 0
4105.0
3.13.05.3
EMI2001, Osaka, Dec. 4-7 2001
8Experiment: results from DA NE
e+e- collider (Frascatti)
KLOE detector
2001:total of 90 M recorded
50 M analyzed
700MeV)ππ(m
)γfBR( 0
4102.06.04.2
EMI2001, Osaka, Dec. 4-7 2001
10Radphi at JLab: analysis in progress
0π
ω
η
Fixed-target (Jlab):
Radphi detector E GeV
status:40 M collected Y
expected:
ppγ
γa60~γf200~
0
0
Parameters of model canaccommodate a largerange in absolute B.R.s
Ratio r = 1 is a predictionof the molecule only forthe I=1/I=0 states; moregenerally r = tan2 mixing
Neutral a0/f0 mixing anglerecently measured incentral production gives
EMI2001, Osaka, Dec. 4-7 2001
11Evaluation: does the molecule survive?
Close, Kirk: cautious yes Achasov: molecule excluded
05.03.0tan2
B.R. of 10-4 is too largefor a molecular KK state.
EMI2001, Osaka, Dec. 4-7 2001
12Evaluation: a simple model
V r
V0
a
Simple non-relativistic model
V0 ~ 250 MeV
a = 1 fm
Eb = -8 MeV
(Born approximation)Apm
e'V
EMI2001, Osaka, Dec. 4-7 2001
13Can you stretch a molecule far enough?
Restore unitarity usingBreit Wigner propagator
constant m0, (n.r.a.)
transition strength thatappears above 2Kthreshold assumed100% absorbed to KKfinal state
EMI2001, Osaka, Dec. 4-7 2001
13Can you stretch a molecule far enough?
Try moving shifting andbroadening resonance
Restore unitarity usingBreit Wigner propagator
constant m0, (n.r.a.)
transition strength thatappears above 2Kthreshold assumed100% absorbed to KKfinal state
EMI2001, Osaka, Dec. 4-7 2001
13Can you stretch a molecule far enough?
Try forcing a dipolemoment very large
no
Restore unitarity usingBreit Wigner propagator
constant m0, (n.r.a.)
transition strength thatappears above 2Kthreshold assumed100% absorbed to KKfinal state
Try moving shifting andbroadening resonance
EMI2001, Osaka, Dec. 4-7 2001
14Evaluation: threshold dynamics
Oset et.al. (2000): Effective field theory
Uses only leading-order XPT interactions
Unitarization leads to expansion of T-1 instead of T
Coefficients set from fits to 2-pseudoscalar elastic scattering data
Dominant contributions come from imaginary part of K+K- loops
Some phases remain ambiguous
1. Surprising early results from SND/CMD-2 now supported bymore data, and independent confirmation from KLOE:
2. In the molecular picture, B.R. ratio of 0.3 measures neutrala0/f0 isospin mixing angle, in quantitative agreement withanalyses of data in central production.
BUTThe magnitude of these radiative decay widths is unnaturallylarge for the molecular picture – a major problem
3. A unitarized XPT analysis of 2-pseudoscalar scatteringobtains qualitative agreement; updated comparison is needed
4. New results from Radphi at Jefferson Lab are expected soon.
Conclusions
EMI2001, Osaka, Dec. 4-7 2001
15
40 101.08.0)γaBR(
40 103.05.2)γfBR(