19th International IUPAP Conference on Few-Body Problems in Physics

31.08 - 05.09.2009 - University of Bonn / Germany

Experimental and theoretical backgrounds for generation of

dibaryons in NN and 3N interactions

V.I. KukulinV.I. KukulinInstitute of Nuclear Physics Institute of Nuclear Physics

Moscow State UniversityMoscow State University

CONTENT

1. Hard problems with 2π-exchange and scalar force.

2. Dibaryon mechanism for scalar field generation in Roper resonance and in NN system.

3. Experimental evidence: two-pion and two-gamma production in nuclear collisions.

4. New three-body force based on dibaryon mechanism. Nonconventional picture for nuclei.

5. New electro-magnetic currents and the deuteron structure at high momentum transfer.

6. Conclusion.

Problems with scalar NN force at intermediate distances

“We show that the highly dominant configuration is |s4p2[42]O [51]FS due to its specific flavour-spin symmetry. Using the Born-Oppenheimer approximation we find a strong effective repulsion at zero separation between nucleons in both 3S1 and 1S0 channels. The symmetry structure of the highly dominant configuration implies the existence of a node in the S-wave relative motion wave function at short distances. The amplitude of the oscillation of the wave function at short range will be however strongly suppressed.”

“The main outcome is that VNN(R=0) is highly repulsive in both 3S1 and 1S0 channels, the height being 0.830 GeV in the former case and 1.356 GeV in the latter one.” “Thus it is the GBE interaction which brings about 1 GeV repulsion, consistent with the previous discussion.”

Short- and intermediate-range nuclear force in quark Short- and intermediate-range nuclear force in quark modelsmodels

Here we will focus mainly on the symmetry aspects rather than details of quark dynamics.

So, the mixed symmetry 6q-configuration |s4p2[42]x> is strongly dominating

over the fully symmetric one |s6[6]x> as:

W([42]):W([6])=8:1 (for two non-interacting nucleons)

• It was proved (Y.Yamauchi, A.Buchmann, A.Faessler; I.T.Obukhovsky, O.Kusainov; M.Oka, K.Yazaki and many others) that this dominating mixed-symmetry configuration is preserved also for any reasonable qq interaction model.

The nucleon-nucleon phase shifts found with GBE-and OGE-models for q-q force

OGE qq force

GBE qq force

NN potential extracted from Lattice QCD

Short- and intermediate-range nuclear forceShort- and intermediate-range nuclear force• At rNN>1.2-1.4 fm the NN interaction is mediated by π and 2π -exchange (i.e.

Yukawa picture). However when rNN < 1.2 fm (i.e. at intermediate and short ranges) two nucleons overlapped and the whole picture of interaction is dictated by quark dynamics.

The dibaryon mechanism for scalar field generation in Roper resonance and NN system

Expansion of the total dibaryon propagator into Δ+Δ,N+R etc. loops in Dyson equation.

The phase shiftsof NN scattering in dibaryon model

The phase shifts of NN scattering in low partial waves

References

Dibaryon (dressed bag) model for NN interaction:1.Nucl. Phys. A 689, 327c (2001).2.Phys. At. Nucl. 64,1667 (2001).3.J. Phys. G 27, 1851 (2001).4.Int. J. Mod. Phys. E 11, 1 (2002). 5.AIP Conf. Proceeds. 892, 485 (2007).

Relativistic generalization of dibaryon model:1.Phys. At. Nucl. 68, 1511 (2004).2.Ann. Phys. 320, 71 (2005).

Interpretation in terms of the 2ω-excited string.

See A. Faessler, V.I. Kukulin and M.A.Shikhalev, Ann. Phys. 320 (2005) 71.

The dibaryon model prediction for the two-pion production via σ-meson in the Roper resonance decay

and at p+n or p+p collisions

• Roper resonance now: M (MeV)– SAID N partial wave analysis: 1357 160– Bonn (Sarantsev et al) N + N 1371(2) 184(20)– Explicitly seen in:– p → X 1390 190 (?)– J/ → n p 1358 160– p p → p n 1355 140

• Roper decay N* → N • pp → NN dominantly N* → N • Scalar-isoscalar probes ( exchange) see „narrow“

monopole excitation at very low excitation energy : breathing mode @ 400 MeV !

Summary about Roper-resonance characteristics

Various mechanisms for the 2π- meson generation from the dressed intermediate

dibaryon

III. Experimental evidence3.1. Early evidences for dibaryon production in pp

collisions.3.2. New observation for the σ-channel in Roper

decay (T. Scorodko et al., Progr. Part. Nucl. Phys. 61,168 (2008)).

3.3. ABC-puzzle (historically).3.4. Exclusive (WASA- PROMICE) measurements for

the ABC-puzzle: p+d → 3He +2π, p+d → d(π π) +p, p+n → d +(π π) 0 etc. (M.Bashkanov et al., Progr. Part. Nucl. Phys. 61,168 (2008)).

3.5. γγ-correlations in p+p, p+C and d+C intermediate-energy collisions in GeV region.

ABC effect

• Inclusive measurements: pd → 3He X Abashian et al. Berkeley Banaigs et al. Saclay

low-mass enhancement !

Missing mass [ GeV/cMissing mass [ GeV/c22 ] ] .3 .4 .5 → .3 .4 .5 → | | |

= 0.3 deg

pd = 3.14 GeV/c

Tp = 893 MeV

((AAbashian, bashian, BBoth, oth, CCrowe )rowe )

NP B67 (1973)1

First exclusive measurement: @ CELSIUS-WASAFirst exclusive measurement: @ CELSIUS-WASA

p d p d →→ d d + p + pspectatorspectator

M Md

Tp = 1.04 GeV

ABC

()int

()conventional

Proc. MESON 06, Int. J. Mod. Phys. A22 (2007) 617

Tp = 1.36 GeV

Energy Dependence of ABC

pn → d* → → d

(this work)

(JINR, DESY)

conventional

pp → d (no ABC effect)

M. Bashkanov et al., Phys. Rev. Lett. 102, 052301 (2009)

Angular Distribution of Isoscalar Low-Mass Enhancement ?

00

0cos

M

scalar – isoscalar !

Phys. Lett. B637, 223 (2006)

Direct experimental evidence for the s-channel dibaryon induced σ-meson production

The spike around 2π-threshold turns out to be very stable against cuts. E.g., increase of the threshold Eγ= 50 MeV to Eγ = 100 MeV has no significant effect on this intermediate spike. Moreover, the model which incorporates very well the γγ events and M γγ from π0 and η production gives practically no events in the intermediate area with M γγ ~300 – 400 MeV! Also from MC simulation of π+π- production we do not get any contributions in the M γγ spectrum.

Then the experimentalists (CELSIUS-WASA) conlude:

“Since none of these simulated processes is able to account for the structure observed near the ππ threshold and also detailed and comprehensive tests of detector performance and event structures have not given any hint for an artifact, we are led to consider seriously the possibility that the observed structure (at M

γγ ~300 – 400 MeV) is real and might be due to the process pp ppσ ppγγ, in particular also since pp ppπ+π- and pp ppπ0π0 reactions are dominated by σ production.“

The new γγ-data with large statistics

In these nice experiments done at the Dubna Nuclotron machine the authors analyzed the γγ-spectra from pC and dC collisions at 5.5 GeV/c (for protons) and 1.7-3.8 GeV/c per nucleon (for deuterons).

To be published in Phys. Rev. C (2009).

γγ-yield from dC collisions at E=2.75 GeV/cA

γγ-yield from pC collisions at E=5.5 GeV/c

Production of two γ-quanta according to dibaryon model

New three-body forces in DBM and the properties of 3N system

The dibaryon model leads inevitably to appearance of new scalar and spin-orbit three-body forces which may modify the whole nuclear dynamics.

J. Phys. G 30, 287,309, (2004);Phys. At. Nucl. 68, 1511 (2005).

New dibaryon induced 3N force

Two-proton density in 3He (solid line) and two-neutron density in 3H for dibaryon model vs two-proton density in 3He for Bonn NN potential (triangles).

s-channel (new)t-channel (conventional)

↔

↔

New s-channel meson-exchange currents.t-channel currents vs s-channel current

valid at long distances valid at intermediate and short distances

Meson-exchange currents (continued)

↔

References:1.Bled Workshop in Physics, 7, 33 (2006).2.Phys. Rev. C 74, 064005 (2006).3.Phys. Rev. C 77, 041001 (2008).

There are also some new terms in s-channel:

All these new currents will be manifested at sufficiently high q2

The structure function B(Q2) for elastic e-d scattering.See V.I. Kukulin, I.T. Obukhovsky, P. Grabmayr, and A. Faessler, Phys. Rev. C74, 064005 (2006).

Conclusions1. The deficiency of scalar fields in OBE- and constituent quark

models gives a very strong evidence in favour of existence of σ-dressed intermediate dibaryons in which the scalar field is generated in the string deexcitation process.

2. New experimental data of Tübingen and Dubna groups on 2π and 2γ production in nuclear collisions confirm very nicely the dibaryon mechanism for NN interaction.

3. The dibaryon model for nuclear force leads to numerous implications for nuclear physics – main of them is an appearance of a new non-nucleonic (i.e. the dressed dibaryon) components in nuclear wave functions with probability ≥10%.

4. In turn, these new components leads to new e.-m. currents, new powerful 3N force, existence of new Coulomb effects, revision of CSB effects, appearance of cumulative processes in hadronic scattering off nuclei, etc.

Charge symmetry breaking effects in DBM

Two alternative values of the nn scattering length are assumed:a1

nn= -18.7 fm and a2nn= -16.3 fm.

The first value has been extracted from the previous analysis ofexperiments d(π-γ)nn reaction and is used in all currentNN potential models, while the second value a2

nn= -16.3 fm has been derived from numerous three-body breakup experiments n+d nnp done for the last three decades.CSB effect means the difference between ann and “pure nuclear” app values, i.e. app value corrected for the Coulomb pp interaction: app

exp = - 8.72 fm (with Coulomb interaction).

In the conventional in the NN potential models (like CD Bonn, Nijmegen etc.) app

CC (CD Bonn) = - 17.3 fm

while in the DBMapp

CC (DBM) = - 16.57 fm

(i)This means that appCC is strongly model-dependent.

(ii) If to assume ann = - 16.3 fm extracted from nd nnp breakup experiments the CSB effects in dibaryon model are rather small !! In conventional potential models the CSB effects are much stronger !!

Solution for ΔEC-problem: ΔEC = EB(3He)-EB(3H)

ΔECexp = 760 keV while the modern ΔEC

theor = 640 keV . The difference in ΔEC 120 keV is explained now mainly by CSB effects.

New three-body Coulomb force in DBM approach.

Vcoul(ρ) is the Coulomb force between the charged dibaryon (ZD = +1 in 3He) and the external proton. This force has been ignored in all previous few-nucleon models.

The explanation of the ΔEC puzzle is reached within the conventional NN potential model (AV18 + UIX) only with ann = - 18.7 fm. However, this value is in contradiction with ann = - 16.3 fm extracted from nd breakup.

The circular polarization Pγ of γ-quantum

in the n+p → d+ γ reaction.

The γ-induced polarization P’y of the neutron measured in the d(γ, n)p reaction at polar angles =45, 90 and 135o.