1. Investigation Few-Nucleon System Dynamics in Medium Energy Domain
Hartmut Machner
Fakultät für Physik
Universität Duisburg-Essen
The strong interaction is mediated in priciple by gluons. However, between hadrons it shows up as a residual interaction. Changing the quark content inside the hadrons gives –hopefully- insights into the bare interaction.

2. Baryon-Baryon Interactions

3. Baryon-baryon interaction
Standard method: elastic Scattering:
Often it is impossible to have either beam or target. Way out FSI in (at least) three body reaction. If the potential is strong enough one has resonances or even bound states.
Fäldt & Wilkin derived a formula ( for small k)
From this follows, that from a the cross section of a known pole (bound or quasi bound) the continuum cross section is given [N({1+2})®N(1+2)t®xN(1+2)s].
The fsi is large for excitation energies Q of only a few MeV.

4. Example: neutron-neutron scattering
Bonn
TUNL
neutron-neutron coincidences
same side of the beam
neutron and proton coincidences
different sides of the beam

5. neutron-neutron scattering
Bonn equipment at TUNL yielded:
Obviously ist the geometry which makes the difference. Three body effects?
Better method: a meson in the final state:

6. Why meson assisted? Problem factorisation: with leads to
baryon-baryon interaction strong
meson-baryon interaction weak
factorisation:
with
leads to

7. resonances
Strategy: choose beam momentum so that no resonance is close to the fsi region.
Note: different sign conventions in a. a<0 unbound

8. The pp®p0pp case
Elastic pp scattering, Coulomb force seems to be well under controle: app=-7.83 fm
However: an IUCF group
Claimed „…the data require app=-1.5 fm.“ They questioned the validity of the factorization.
Experiment at GEM, differential and total cross sections.
FIT Ss, Pp (Ps from polarisation experiments)
no D resonance
with D resonance, usual fsi
with D but fsi with half the usual pp scattering length
No need to change the standard value!

9. Saclay pp®p+(pn) 1000 MeV pp®p+(pn) dp®p(pn) triplet (from fit to all)
singlet (from deuteron)

10. Data from Uppsala and GEM
p= MeV/c

11. Triplet FSI absolute
at and rt close to literature values

12. Singlet FSI absolute No singlet state! singlet fraction Ref. 0.40±0.05
Boudard et al.
< 0.10
Betsch et al.
<0.10
Uzikov & Wilkin
Abaev et al.
< 0.003
GEM
No singlet state!

13. More experiments
Fäldt-Wikin relation

14. Full 3 body calculation Relativistic phase space
Reid soft core potential

15. 378+224 events in a 82 cm bubble chamber
Lp elastic scattering
events in a 82 cm bubble chamber
fit as rs at rt A
-2.0
5.0
-2.2
3.5 B
-2.3
3.0 F
-8.0
1.5
-0.6

16. pp®LpK+
Simultaneous fit:

17. S+0 production

18. Resonances without/with resolution folding Upper limits (99%)
solid G=1 MeV
dashed 0.5 MeV
dotted 0.1 MeV
Aerts and Dover

19. L deuteron?
FW-theorem:» 2000 nb
Exp.: 75±3 nb
c2/dof = 1.3

20. peak Peak below threshold: S-deuteron Peak at threshold: cusp
Peak above threshold:
Resonance (dibaryon?)
Shaded: HIRES only Lp; dots TOF (submitted)

21. Peak analysis lower mass peak at S+n threshold
higher mass peak or shoulder =???

22. Flatté analysis

23. Elastic Lp scattering

24. Potential models - bound state (deuteron like SN):
3D1 phase passes through 90°:
Nijmegen NSC97f, Nijmegen NF, Jül89
S1 phase passes through 90°:
Nijmegen ESC04, Toker&Gal&Eisenberg
inelastic virtual state = peak direct at threshold = genuine cusp, none of the relevant phases passes through 90°:
Nijmegen NSC89, ND, ESC08, Jülich05, EFT

25. All LL hypernuclei
Event Nagara

26. LL interaction Clear FSI peak. Weakly attractive,
No indication of S=-2 (H) dibaryon
C.-J. Yoon et al., PRC 77(2007)

27. Summary
Meson accompanied baryon-baryon interaction is a powerful tool to study bb-potential.
Low energy interaction can be studied via fsi and resonances as well as bound states.
pp®p0pp: indicates the factorization is valid. No different parameters than in pp®pp elastic scattering.
pp®p+pn: only triplet scattering. Why?
pp®K+Lp: mostly singlet scattering. Why? The potential is to weak to form a bound state. No dibaryon resonance! Strong enough to form a resonance?
pp®K+SN: potential strong enough to bind? But no fsi visible.
LL®LL shows FSI. Weakly attractive.
No S=-2 dibaryon
Thank you to my collaborators esp. Johann Haidenbauer, Frank Hinterberger, Jouni Niskanen, Andrzej Magiera, Jim Ritman, Regina Siudak