1. Diphoton and dilepton production. Results and outlook Kh.U. Abraamyan, M.I. Baznat, A.V. Friesen, K.K. Gudima, M.A. Kozhin, S.A. Lebedev ʼ, A.I. Malakhov, G.L.Melkumov, M.A. Nazarenko, G.A. Ososkov, S.G. Reznikov, A.N. Sissakian, A.S. Sorin, and V.D. Toneev JINR, Dubna, Russia Institute of Applied Physics, Kishinev, Moldova Gesellschaft für Schwerionenforschung, Darmstadt, Germany MIREA, Moscow, Russia R o u n d T a b l e IV, 9 – 12 S e p t e m b e r, 2009

2. The plan of the report 4 The resolved tasks 4 New tasks. 4 NICA advantages. 18.02.20162Abraamyan Kh.U. et al. R o u n d T a b l e IV

3. FOTON setup on beams of the Synchrophasotron

4. Invariant γγ-mass distributions in the reactions (p,α,C)+(C,Cu)→πº + X at 4.5 A GeV/c

5. α + (С,Cu) С + (С,Cu) The target dependence of production ◊ - the reactions α + (С,Cu) ; ♦ - the reactions С + (С,Cu). Abraamyan et al. Phys.Lett. B323 (1994)1; Phys.Atom.Nucl. 60(1997)2014.

6. The target dependence of production n Calculations of n in frame of Quark Recombination Model (G.Berlad and A.Dar)

7. Transverse momenta of quarks in proton

8. The exponent m in A-dependence for projectile ◊ - the reactions (α,С) + С ; ♦ - the reactions (α,С) + Сu. □, ■ - data from LBL, Berkeley

9. 6-quark configuration formation probabilities

10. d + С → πº + X Double differential cross section of the reaction d + С → πº + X at 4.5 A GeV/c Abraamyan et al. Phys.Atom.Nucl. 68(2005)982.

11. d + С → πº + X x > 0.6 Check of the d + С → πº + X reaction mechanism in the region x > 0.6 In the CM of the cluster: In the Lab. System:

12. β(θ) ―――― T = 160 MeV ; - - - - - - T = 140 MeV

13. 18.02.2016Abraamyan Kh.U. et al.13 PHOTON-2 setup on internal beams of the NUCLOTRON R o u n d T a b l e IV

14. The experiments on the Nuclotron (p,d)+C  ,  The yield ratio of γγ- pairs from the interval of invariant masses 530÷570 MeV in the reactions d+C→γ+γ+x at 2.75 GeV/c per nucleon and p+C→γ+γ+x at 5.5 GeV/c. (p,α)+C  , 

15. The experiment on the Nuclotron (p,d)+C  ,  The yield ratio of γγ-pairs from the interval of invariant masses 530÷570 MeV in the reactions d+C→γ+γ+x at 2.75 GeV/c per nucleon and p+C→γ+γ+x at 5.5 GeV/c The experiment on Cynchrophasotron (d, ,C)+C , 

16. The experiments on the Nuclotron: p,d+C   +  +X, P=5.5 ГэВ/c.

17. 18.02.2016 Abraamyan Kh.U. et all.17 The selection criteria 1) the number of photons in an event, Nγ =2 or Nγ ≤ 3; 2) the energies of photons, Eγ ≥ 100 MeV; 3) the summed energy in real and random events ≤ 1.5 GeV. R o u n d T a b l e IV

18. 18.02.2016Abraamyan Kh.U. et all. 18 Invariant mass distributions of γγ pairs without (upper panel) and with (bottom panel) the background subtraction. R o u n d T a b l e IV

19. Invariant mass distributions of γγ pairs without (upper panel) and with (bottom panel) the background subtraction in d+C (left) and d+Cu (right) reactions. 18.02.2016Abraamyan Kh.U. et al.19 R o u n d T a b l e IV

20. 18.02.2016 Abraamyan Kh.U. et all. 20 Experimental (circles) and simulated (triangles) data under the same conditions. The solid lines – contribution of photons from the R decay R o u n d T a b l e IV

21. J.Banaigs, J.Berger et al. ABC and DEF effects// Nucl.Phys. B67, (1973),1.

22. ω(ρ) →ee and φ →ee detection

23. 18.02.2016Abraamyan Kh.U. et all.23 Concluding remarks To understand the nature of the observed effect were attempted some dynamic mechanisms:  production of the hypothetic R resonance in ππ interactions during the evolution of the nuclear collision;  formation of the R resonance with participation of photons from the Δ decay;  the πºπº interaction effect in the 3πº channel of the η decay;  a particular decoupled dibaryon mechanism;  the light sector of Higgs ???... R o u n d T a b l e IV

24. 18.02.2016Abraamyan Kh.U. et all.24 Concluding remarks, outlook 4 Due to the strangeness (sŝ) in η-mesons, comparison η and πº productions allows to clarify the mesons production mechanisms. 4 Investigations of πº mesons is interest in view of the NICA possibilities. The scan of the πº spectra in the nuclear- nuclear collisions allows to detect signals of the π- condensate state: the pion vacuum breaking at the strong QCD field in dense nuclear matter. R o u n d T a b l e IV

25. 18.02.2016Abraamyan Kh.U. et all.25 Concluding remarks, outlook 4 To clarify of the nature and further investigations of the resonance observed in the invariant mass spectrum of γγ pairs in dC-interactions at 2.75 GeV/c per nucleon and dCu- interactions at 3.83 GeV/c per nucleon: 1. pC→γγ+X at T p ~2 GeV 1. pC→γγ+X at T p ~2 GeV, 2. … 4 To search for some features in the invariant mass spectrum of -pairs in the interval of 270-750 MeV bounding up with the chiral symmetry restoration (A.N. Sysakian, A.S. Sorin, M.K. Suleymanov, V.D. Toneev and G.M. Zinovjev arXiv:nucl-ex/0601034). R o u n d T a b l e IV

27. 18.02.2016Abraamyan Kh.U. et all.27 The NICA advantages energymass polarization 4 The collider NICA allows to scan energy, mass and polarization dependencies of the resonance production in ion collisions at high luminosities. 4 To solve above tasks a calorimeter with large acceptance is needed (in consisting of MPD or SPD). The increasing of the calorimeter acceptance allows to investigate the invariant mass spectra of pairs in the wide range at different energies and transverse momenta of pairs (that means different production mechanisms). R o u n d T a b l e IV

28. 18.02.2016Abraamyan Kh.U. et all.28 R o u n d T a b l e IV

29. 18.02.2016Abraamyan Kh.U. et all.29 Dibaryon mechanism (I) Recently the idea of nontrivial dibaryon state becomes more attractive. The proposed mechanism NN→d*→NNγγ proceeds through a sequential emission of two photons: one is caused by production of the decoupled baryon resonance d*, second is its subsequent decay. A.S. Khrykin and S.B. Gerasimov, On a possible origin of a resonance-like structure in the two-photon invariant mass spectrum of the reaction pp→ppγγ, arXiv:0710.3331. A.S. Khrykin et al., PRC64 (2001) 034002, NPA721(2003)625 R o u n d T a b l e IV

30. 18.02.2016Abraamyan Kh.U. et all.30 Dibaryon mechanism (II) Very attractive candidate for its realization might be a model of the intermediate σ-dressed dibaryon. In this model the short-range NN-interaction is described with the s-channel σ exchange associated with the intermediate dibaryon production treated as a σ-dressed six-quark bag. As the result we have decrease of the assumed σ- mass, it is estimated Mσ ~ 350 ÷ 380 MeV. Therefore it should enhance the near-threshold pion and double-pion production. [ V.I.Kukulin et al. J.Phys.G30(2004)287, 30(2004),309] This mechanism is now under investigation. R o u n d T a b l e IV

31. 18.02.2016Abraamyan Kh.U. et all.31 Concluding remarks, outlook 1.The dibaryon mechanism is discussing as a possible explanation of observed enhancement. In this way it can be considered as σ-meson. 2.From the experimental side: new experiments are required to be carried out under conditions appropriate for registration of pairs of two photons within the invariant mass interval of 300-400 MeV. Some scanning in the beam energy will clarify the possible resonance structure of this effect. By varying the opening angle of the PHOTON-2 spectrometer it is possible to get information about momentum spectra of the resonance-like structure which could be a test of the R production mechanism. R o u n d T a b l e IV

32. 18.02.2016Abraamyan Kh.U. et all.32 Data simulation  To simulate pC-, dC- and dCu- reactions we used a two- phases transport code [ K.K. Gudima et al. LANL Report LA-UR-01- 6804, Los Alamos, 2001 ]  The following γ-decay channels are taken into account:  the direct decays of πº,η,ή hadrons into two γ’s;  ω → πºγ;  Δ → Nγ;  the Dalitz decays of η → ππγ, η → γee, πº → γee;  ή → ρºγ, Σ →Λγ,  the πN and NN-bremsstrahlung. R o u n d T a b l e IV

33. 18.02.2016Abraamyan Kh.U. et all.33 The calculated γγ invariant mass distributions in pC (left) and dC (right) collisions for selected events with Nγ = 2. R o u n d T a b l e IV

34. 18.02.2016Abraamyan Kh.U. et all.34 Invariant mass distributions of γγ pairs in two different runs of measurement under condition Eγ ≥ 50 MeV: with the empty target (dashed histogram) and with the internal carbon target (solid histogram) in the reaction dC = γ +γ +X at 2.75 GeV/c per nucleon. With the internal carbon target Without target R o u n d T a b l e IV

35. 18.02.2016Abraamyan Kh.U. et all.35 Charged particles contribution R o u n d T a b l e IV

36. 18.02.2016Abraamyan Kh.U. et all.36 Charged particles contribution after background subtraction R o u n d T a b l e IV

37. 18.02.2016Abraamyan Kh.U. et all.37 Invariant mass distributions of γγ pairs satisfying the criteria (1) − (2) after background subtraction in the reaction dC = γ +γ +X at 2.75 GeV/c per nucleon for two different beam intensities: 503 events/cycle (a) and 85 events/cycle. R o u n d T a b l e IV

38. 18.02.2016Abraamyan Kh.U. et all.38 The invariant mass distributions of two photons for the opening angles 0.55 < cos (Θγγ) < 0.65 (left) and 0.65 < cos (Θγγ) < 0.75 (right) under the selection criteria (1) − (2). R o u n d T a b l e IV

39. The invariant mass spectra of γγ pairs for the energy selection Eγ > 400 MeV under the selection criteria (1) - (2), Knorm = 0.973. 18.02.2016Abraamyan Kh.U. et all.39 R o u n d T a b l e IV

40. 18.02.2016Abraamyan Kh.U. et all.40 Nγ=3 0200400600800 -3000 -2000 -1000 0 1000 2000  R N  = 3, E  > 50 MeV dC, Exper. Counts M  [MeV] R o u n d T a b l e IV

41. 18.02.2016Abraamyan Kh.U. et all.41 Nγ=3: 1γ in the L.Arm, 2γ in the R.Arm + 2γ in the L.Arm, 1γ in the R.Arm R o u n d T a b l e IV

42. 18.02.2016Abraamyan Kh.U. et all.42 The invariant mass distribution of γγ pairs and the biparametric distribution of the GW of the 8-th order for dC (left) and pC (right) interactions. The distribution is obtained with an additional condition for photon energies Eγ1/Eγ2 > 0.8 and binning in 2MeV. R o u n d T a b l e IV

43. 18.02.2016Abraamyan Kh.U. et all.43 A.Taranenko et.all, Czech.J.Phys. 50S4 (2000) 139, nucl-ex/9910002. Results of the invariant-mass analysis of photon pairs (TAPS). The upper frame shows the invariant-mass spectrum which corresponds to the η trigger in the experiment 58Ni+58Ni at 1.9 AGeV. The combinatorial background (dotted line) was determined by event mixing. The lower frame shows the invariant-mass distribution after background subtraction and demonstrates the quality of the background determination. R o u n d T a b l e IV

44. R. Averbeck et al. (TAPS Collaboration), Z. Phys. A 359, 65 (1997). 18.02.2016Abraamyan Kh.U. et al.44 R o u n d T a b l e IV

45. 18.02.2016 Abraamyan Kh.U. et all. 45 Comparison with experiments on the “TAPS” 1. Z.Phys.A359, 65(1997): C+C reaction, 2.0A GeV 4 TAPS 4 Opening angles 65º-102º 4 η energies (GeV) > 0.70 4 Mean values 0.85 4 O.R. energies > 0.457 4 Mean values 0.552 4 Total cr. sect. (b) 2.021 4 Arm’s area (m²) 0.578 4 Arm’s solid angle (sr) 0.257 4 En.res. σ/E (m.v.,%) 3.0 4 Sig./B. in 300-420: ~ 0.0014 ª (<0.004) ª Sig. ~ √6 ∙ 10^5 4 PHOTON-2 42º-66º > 1.01 1.21 > 0.652 0.782 0.612 0.424 0.047 6.1 0.027 R o u n d T a b l e IV

46. 18.02.2016Abraamyan Kh.U. et all.46 Necessary statistics for same observation in the experiment on TAPS ( Z.Phys.A359, 65(1997): C+C reaction, 2.0A GeV) ~3∙10¹² ∙ ( ΔΩ PHOTON / ΔΩ TAPS )² ∙ (Δ M PHOTON / Δ M TAPS )² ∙ [(S/B) PHOTON / (S/B) TAPS ]² S/B=0.0014 ~ 3∙10¹² ∙ (0.047 / 0.257)² ∙ (3.0 / 6.1)² ∙ (0.027 / 0.0014)² = 9 ∙ 10¹² interactions, S/B<0.004 : > 1.1 ∙ 10¹² interactions. N cycle > ( 1.1 ∙ 10¹² ) / (5 ∙ 10^6 ∙ ω ) = = 4 500 000 accelerator cycles, ω = ρx∙(N A / A) ∙ σ(CC) = 0.049, ρx = 0.487 g/cm ² For indication (+3 st.err.) : > 550 000 acceler. cycles R o u n d T a b l e IV

47. WA80 Collaboration, Phys.Lett. B361 (1995) 14, hep-ex/9507009. Invariant mass distributions for the 200 AGeV/c (SPS) S+Au data in the  0 (a) and η (b) mass range after background subtraction. The signal to the background ratio is 5.7·10 -2 and 7·10 -4. 18.02.2016Abraamyan Kh.U. et al.47 R o u n d T a b l e IV

48. WASA-CELSIUS : (a) M spectrum after kinematic fit.The dotted histogram in shows background expected from misidentified π 0 π 0 events. (b) The same as (a), but for T p = 1.2 GeV. 18.02.2016Abraamyan Kh.U. et al.48 R o u n d T a b l e IV

49. Photon energy spectra from γγ pairs in the invariant mass interval Mγγ = 0.32 ч 0.4 GeV. Experimental (circles) and Monte-Carlo simulation (triangles) points calculated with inclusion of the R resonance formation are given separately for every spectrometer arm. Distributions are normalized to the same total number of events. 18.02.2016Abraamyan Kh.U. et al.49 R o u n d T a b l e IV

50. 18.02.2016Abraamyan Kh.U. et all.50 Invariant mass distributions of γγ pairs satisfying the criteria (1) − (2) after background subtraction in the reaction dC = γ +γ +X at 2.75 GeV/c per nucleon. Normalization of the background by the total number of pairs in the spectrum. R o u n d T a b l e IV

51. Invariant mass distributions of γγ pairs from the dC reaction. The top shaded histograms show the background contribution. The bottom histograms are invariant spectra after the background subtraction. 18.02.2016Abraamyan Kh.U. et all.51 R o u n d T a b l e IV

52. 18.02.2016Abraamyan Kh.U. et all.52 The invariant mass distributions of γγ pairs from the pC (left) and dC (right) reactions after background subtraction. R o u n d T a b l e IV

53. Eγ ≥ 100 MeV 18.02.2016Abraamyan Kh.U. et all.53 R o u n d T a b l e IV