Eta production Resonances, meson couplings

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Eta productionResonances, meson couplings
exotic hadronic matter?
Humberto Garcilazo, IPN Mexico Dan-Olof
Riska, Helsinki
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1) Motivation. Generalities. 2) The ?N system
and the (non)existence of an eta-NN quasi-bound
state. The ?d scattering problem. The riddle
of the enhancement of the pn ? eta d at
threshold. 3) The pp ?pp ? reaction at
threshold. Probing ?NN ?NN couplings.
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?The eta is I0. It is isospin selective and a
clean probe for N(I1/2) 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.
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(?, ? ) Reactions
M.Robig-Landau,Phys.Rev. Lett.B 176, 257 (1986)
Quasi-free 1 nucleon production Scaling with A
2/3
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? 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. )
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The ?d scattering problem
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Reliable way of dealing with re-scattering
Faddeev summation
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Dynamics
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Ap2
?N Dynamics
t calculated dynamically from coupled LS
equations and potentials
Separable t directly fixed to scattering length
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?N Scattering length extracted from ?N ? ? N
?N ??N
?N??N
Different data analysis
1992
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Batinic et al. model
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Example of description quality obtained for the
?d ? ? NN reaction with model from Batinic et
al.
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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 0.87i0.27
0.89
1999 B
1.23 1999 C
2.66 1999 D
1.54 1997 0.75i0.27
0.83
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Non-dynamical ?N model as input
Eta N Scattering length eta-d MST
eta-d Faddeev
0.25i0.16 0.66i0.71
0.64i0.71 0.30i0.30
0.39i1.28 0.38i.125 0.579i0.
399 -0.13i2.64
-0.08i2.31 0.876i0.274
-0.76i4.24 -1.54i2.55 0.98i0.37
-2.75i2.77
-1.16i2.05
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Deuteron-eta Real(a0) changes sign as etaN a0
increases
Energy
This is not the whole story there is NN
short-range repulsion
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Dynamical ?N models as input
Realistic NN short-range correlations wipe out
the sign change
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A genuine three-particle scattering effect
No resonant effect from a quasi-bound state.
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Ratio between A and driving term
Minimum 2.5 Maximum 5.1
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Conclusions on np? ?d
? The enhancement for the reaction np? ?d is
explained within our calculations as a genuine
three-body re-scattering effect .
? No evidence of a quasi-bound state for the
etaNN system. Dynamical ?N models and realistic
short-range interactions prevent it.
? We predict a an enhancement factor from 2.5 to
5.1 depending on the off-shell properties of the
etaN model.
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The pp ? ?pp reaction
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impulse
? and ? exchange
? and ? exchange
? exchange
1S0
3P0
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g?NN coupling not sufficiently constrained by NN
models
In this calculation g?NN2/4? 0.4 from ?
photoproduction (L. Tiator, C. Bennhold)
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Impulse re-scattering
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Impulse re-scattering ? ?
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
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Short-range contributions associated to the
short-range NN force

• The NN interaction contains an isospin
  independent scalar exchange component Vs
  vs (1-p2/M 2) ...
• The p2/M 2 term can be combined with the kinetic
  term M M(1 vs /M) two body
  correction from scalar and vector exchanges.

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Impulse re-scattering short-range? ?
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Theoretical uncertainty The mechanism involves
high momentum transfer Different NN interactions
may have different effects
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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.
? Dependence on the off-shell ?N scattering
amplitude enables discrimination between extant
models.
? 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.
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A scientific theory cannot be verified only
falsified.
Karl Popper
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Off-shell structure given by the Dirac structure.
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Ap2
?N Dynamics
t calculated dynamically from coupled LS
equations and potentials
Separable t directly fixed to scattering length