Presentation on theme: "1 Eta production Resonances, meson couplings Humberto Garcilazo, IPN Mexico Dan-Olof Riska, Helsinki … exotic hadronic matter?"— Presentation transcript:
1 Eta production Resonances, meson couplings Humberto Garcilazo, IPN Mexico Dan-Olof Riska, Helsinki … exotic hadronic matter?
2 1) Motivation. Generalities.Generalities. 2) The N system and the (non)existence of an eta-NN quasi-bound state. The d scattering problem.problem. The riddle of the enhancement of the pn eta d at threshold.at threshold. 3) The pp pp reaction at threshold.at threshold Probing NN NN* couplings.
3 The eta is I=0. It is isospin selective and a clean probe for N*(I=1/2) resonances, contrarily to the pion. Threshold is dominated by s wave production (centrifugal barrier). S11(1353) resonance has a large eta branching ratio. Eta production data is a learning ground for studying the S11. etaN scattering length is very strong (min 0.3fm). May imply an exotic of hadronic matter: eta-mesic nuclei and eta-mesic hypernuclei.
4 ( , ) Reactions Quasi-free 1 nucleon production Scaling with A 2/3 M.Robig-Landau,Phys.Rev. Lett.B 176, 257 (1986)
5 Large cross-sections for eta absorption give eta mesons a small chance of escaping from nuclei. Mean free path at normal density is 2 fm. Study of eta-nuclei may provide clues on possible chiral symmetry restoration in a nuclear medium at normal densities (0.17 fm -3 ) In the SU(6) model, eta differs from 0 in an additional ss quark-antiquark structure. Information on the dynamical role of this pair in I) meson-baryon interactions for calculations of nuclear matter with strangeness. (Bruckner-Hartree-Fock) II) isospin symmetry breaking in few-body reactions (relate to the mixing angle). (Brookhaven, Nefkens et al. )Nefkens et al.
10 N Dynamics Separable t directly fixed to scattering length t calculated dynamically from coupled LS equations and potentials A+p 2
11 Different data analysis N Scattering length extracted from N N N N N N 1992 1985 1995 Krusche 0.579+ i0.394 Arima and Yazaki 0.980+ i0.37 Batinic et al. 0.876+ i0.274 Bhalerau and Liu 0.27+i0.22 Wilkin 0.30+ i0.30 Bennhold and Tanabe 0.25+i0.16
13 Example of description quality obtained for the d NN reaction with model from Batinic et al.
14 1999 Phys. Rev. C 60, 035208 A. M. Green and S. Wycech A, B, C, D models confirm larger value for Re a N 2 /dof 1999 A 0.87+i0.27 0.89 1999 B 1.23 1999 C 2.66 1999 D 1.54 1997 0.75+i0.27 0.83
15 Eta N Scattering length eta-d MST eta-d Faddeev 0.25+i0.16 0.66+i0.71 0.64+i0.71 0.30+i0.30 0.39+i1.28 0.38+i.125 0.579+i0.399 -0.13+i2.64 -0.08+i2.31 0.876+i0.274 -0.76+i4.24 -1.54+i2.55 0.98+i0.37 -2.75+i2.77 -1.16+i2.05 Non-dynamical N model as input
16 Deuteron-eta Real(a 0 ) changes sign as etaN a 0 increases This is not the whole story … there is NN short-range repulsion Energy
17 Largest 2 Dynamical N models as input Larger than the value for which non-dynamical models give sign change Realistic NN short-range correlations wipe out the sign change
18 A genuine three-particle scattering effect No resonant effect from a quasi-bound state.
20 Ratio between A and driving term Minimum: 2.5 Maximum: 5.1
21 Conclusions on np d : The enhancement for the reaction np d is explained within our calculations as a genuine three- body re-scattering effect. We predict a an enhancement factor from 2.5 to 5.1 depending on the off-shell properties of the etaN model. No evidence of a quasi-bound state for the etaNN system. Dynamical N models and realistic short-range interactions prevent it.
27 Another unknown coupling: NN* coupling cannot be determined from the decay width of N* N : N* lies below the threshold for that decay. A 3 quark-model was used for the baryons Impulse + re-scattering+ +
28 Short-range contributions associated to the short-range NN force The NN interaction contains an isospin independent scalar exchange component Vs = v s (1-p 2 /M 2 )... The p 2 /M 2 term can be combined with the kinetic term: M*= M(1+ v s /M) two body correction from scalar and vector exchanges.
30 Theoretical uncertainty The mechanism involves high momentum transfer Different NN interactions may have different effects
31 Conclusions relative to the pp pp reaction: Large effect of the cross-section on the off-shell N scattering amplitude. Agreement with Batinic, Svarc and H. Lee. Large effect from non-resonant amplitudes from isoscalar scalar and vector exchanges. Only with a NN coupling constant smaller than the one used in earlier NN OBE models, namely the one extracted from the analysis of eta photoproduction data, allows a description of the data. ISI and FSI NN interactions are important. Dependence on the off-shell N scattering amplitude enables discrimination between extant models.
32 A scientific theory cannot be verified ; only falsified. Karl Popper
33 Off-shell structure given by the Dirac structure.
34 N Dynamics Separable t directly fixed to scattering length t calculated dynamically from coupled LS equations and potentials A+p 2
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