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.

Baryon-Baryon Interactions

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.

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

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:

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

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

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!

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

Data from Uppsala and GEM p=1642.5 MeV/c

Triplet FSI absolute at and rt close to literature values

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!

More experiments Fäldt-Wikin relation

Full 3 body calculation Relativistic phase space Reid soft core potential

378+224 events in a 82 cm bubble chamber Lp elastic scattering 378+224 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

pp®LpK+ Simultaneous fit:

S+0 production

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

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

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

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

Flatté analysis

Elastic Lp scattering

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

All LL hypernuclei Event Nagara

LL interaction Clear FSI peak. Weakly attractive, No indication of S=-2 (H) dibaryon C.-J. Yoon et al., PRC 77(2007) 022201

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