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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. Kukulin Institute of Nuclear Physics Moscow State University
CONTENT Hard problems with 2π-exchange and scalar force. Dibaryon mechanism for scalar field generation in Roper resonance and in NN system. Experimental evidence: two-pion and two-gamma production in nuclear collisions. New three-body force based on dibaryon mechanism. Nonconventional picture for nuclei. New electro-magnetic currents and the deuteron structure at high momentum transfer. Conclusion.
“We show that the highly dominant configuration is |s4p2O FS due to its specific flavour-spin symmetry. Using the Born-Oppenheimer approximation we find a strong effective repulsion at zero separation between nucleonsin 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 0.830GeV 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 models Here we will focus mainly on the symmetry aspects rather than details of quark dynamics. So, the mixed symmetry 6q-configuration |s4p2x> is strongly dominating over the fully symmetric one |s6x> as: W():W()=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
Short- 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 < 1.2fm(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 shifts of NN scattering in dibaryon model
References • Dibaryon (dressed bag) model for NN interaction: • Nucl. Phys. A 689, 327c (2001). • Phys. At. Nucl. 64,1667 (2001). • J. Phys. G 27, 1851 (2001). • Int. J. Mod. Phys. E 11, 1 (2002). • AIP Conf. Proceeds. 892, 485 (2007). • Relativistic generalization of dibaryon model: • Phys. At. Nucl. 68, 1511 (2004). • 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
Summary about Roper-resonance characteristics • 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 → NNdominantlyN* → N • Scalar-isoscalar probes ( exchange) see „narrow“ monopole excitation at very low excitation energy : breathing mode @ 400 MeV !
Various mechanisms for the 2π- meson generation from the dressed intermediate dibaryon
III. Experimental evidence 3.1. 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.
Missing mass [ GeV/c2 ] .3 .4 .5 → | | | ABC effect (Abashian, Both, Crowe ) • Inclusive measurements: pd → 3He X Abashian et al. Berkeley Banaigs et al. Saclay low-mass enhancement ! = 0.3 deg pd = 3.14 GeV/c Tp = 893 MeV NP B67 (1973)1
First exclusive measurement: @ CELSIUS-WASA p d → d + pspectator M Md ()conventional Tp = 1.04 GeV ABC ()int Tp = 1.36 GeV Proc. MESON 06, Int. J. Mod. Phys. A22 (2007) 617
Energy Dependence of ABC M. Bashkanov et al., Phys. Rev. Lett. 102, 052301 (2009) (this work) (JINR, DESY) pn → d* → → d conventional pp → d (no ABC effect)
Angular Distribution of Isoscalar Low-Mass Enhancement ? Phys. Lett. B637, 223 (2006) Mp0p0 scalar – isoscalar !
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 Mγγ from π0 and η production gives practically no events in the intermediate area with Mγγ~300 – 400 MeV! Also from MC simulation of π+π- production we do not get any contributions in the Mγγ 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 Mγγ~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).
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).
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).
New s-channel meson-exchangecurrents.t-channel currents vss-channel current valid at long distances valid at intermediate and short distances s-channel (new) t-channel (conventional) ↔ ↔
Meson-exchange currents (continued) • References: • Bled Workshop in Physics, 7, 33 (2006). • Phys. Rev. C 74, 064005 (2006). • 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).
Conclusions • 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. • 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. • 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%. • 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: a1nn= -18.7 fm and a2nn= -16.3 fm. The first value has been extracted from the previous analysis of experiments d(π-γ)nn reaction and is used in all current NN potential models, while the second value a2nn= -16.3 fm has been derived from numerous three-body breakup experiments n+d nnpdone 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: appexp = - 8.72 fm (with Coulomb interaction).
In the conventional in the NN potential models (like CD Bonn, Nijmegen etc.) • appCC (CD Bonn) = - 17.3 fm • while in the DBM • appCC (DBM) = - 16.57 fm • This means that appCC is strongly model-dependent. • (ii) If to assume ann = - 16.3 fm extracted from ndnnp 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 ΔECtheor= 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.