Diphoton and dilepton production. Results and outlook

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

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

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. The target dependence of production ◊ - the reactionsα + (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 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. Double differential cross section of thereaction d + С → πº + X at 4.5 A GeV/cAbraamyan et al. Phys.Atom.Nucl. 68(2005)982.

11. 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)―――― Tₒ = 160 MeV;- - - - - - Tₒ = 140 MeV

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

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

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

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

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

20. R o u n d T a b l e IV Experimental(circles) andsimulated (triangles)data underthesameconditions. The solid lines – contributionofphotonsfromthe R decay Abraamyan Kh.U. et all.

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

22. ω(ρ)→ee andφ →ee detection

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

24. R o u n d T a b l e IV Concluding remarks, outlook • Due to the strangeness (sŝ) in η-mesons, comparison ηand πºproductions allows toclarify the mesons production mechanisms. • Investigations of πºmesons is interest in view of the NICA possibilities. The scanof the πºspectra in the nuclear-nuclear collisions allows to detect signals of theπ-condensate state: the pion vacuum breaking at the strong QCD field in densenuclear matter. Abraamyan Kh.U. et all.

25. R o u n d T a b l e IV Concluding remarks, outlook • To clarify of the nature and further investigations of the resonance observed in theinvariant mass spectrum of γγ pairs in dC-interactions at 2.75 GeV/c per nucleonand dCu-interactions at 3.83 GeV/c per nucleon: 1. pC→γγ+X at Tp~2 GeV, 2. … • To search for some features in the invariant mass spectrum of -pairs in the intervalof 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. ZinovjevarXiv:nucl-ex/0601034). Abraamyan Kh.U. et all.

27. R o u n d T a b l e IV The NICA advantages • The collider NICA allows to scan energy , mass and polarization dependencies of the resonance production in ion collisions at high luminosities. • 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). Abraamyan Kh.U. et all.

28. R o u n d T a b l e IV Thank you for attention! Abraamyan Kh.U. et all.

29. R o u n d T a b l e IV Dibaryon mechanism (I) Recently the idea of nontrivial dibaryon state becomes more attractive. The proposed mechanism NN→d*→NNγγproceeds 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 Abraamyan Kh.U. et all.

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

31. R o u n d T a b l e IV Concluding remarks, outlook • The dibaryon mechanism is discussing as a possible explanation of observed enhancement. In this way it can be considered as σ-meson. • 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. Abraamyan Kh.U. et all.

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

33. R o u n d T a b l e IV ThecalculatedγγinvariantmassdistributionsinpC(left) anddC(right) collisionsforselectedeventswithNγ = 2. Abraamyan Kh.U. et all.

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

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

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

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

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

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

40. R o u n d T a b l e IV h dC, Exper. R N = 3 , E > 50 MeV 2000 g g 1000 0 Counts -1000 -2000 -3000 0 200 400 600 800 M [MeV] gg Nγ=3 Abraamyan Kh.U. et all.

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

42. R o u n d T a b l e IV Theinvariantmassdistributionofγγpairsandthebiparametric distributionofthe GW ofthe 8-th orderfordC (left) and pC (right)interactions. Thedistributionisobtainedwithanadditionalconditionforphotonenergies Eγ1/Eγ2 > 0.8 andbinningin 2MeV. Abraamyan Kh.U. et all.

43. R o u n d T a b l e IV 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 frameshows the invariant-mass spectrum which corresponds to the η trigger in the experiment58Ni+58Ni at 1.9 AGeV. The combinatorial background (dotted line) was determined byevent mixing. The lower frame shows the invariant-mass distribution after backgroundsubtraction and demonstrates the quality of the background determination. Abraamyan Kh.U. et all.

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

45. TAPS Opening angles 65º-102º η energies (GeV) > 0.70 Mean values 0.85 O.R. energies > 0.457 Mean values 0.552 Total cr. sect. (b) 2.021 Arm’s area (m²) 0.578 Arm’s solid angle (sr) 0.257 En.res. σ/E (m.v.,%) 3.0 Sig./B. in 300-420: ~ 0.0014 ª (<0.004) ª Sig. ~ √6 ∙ 10^5 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 Comparison with experiments on the“TAPS” 1. Z.Phys.A359, 65(1997): C+C reaction, 2.0A GeV Abraamyan Kh.U. et all.

46. R o u n d T a b l e IV Necessary statistics for same observation in the experiment on TAPS ( Z.Phys.A359, 65(1997): C+C reaction, 2.0A GeV) ~3∙10¹² ∙ (ΔΩPHOTON / ΔΩ TAPS)² ∙ (ΔMPHOTON / ΔMTAPS)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. Ncycle > (1.1 ∙ 10¹² ) / (5 ∙ 10^6 ∙ ω ) = = 4 500 000 accelerator cycles, ω = ρx∙(NA / A)∙ σ(CC) = 0.049, ρx = 0.487g/cm ² For indication (+3 st.err.) : > 550 000 acceler. cycles Abraamyan Kh.U. et all.

47. R o u n d T a b l e IV 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. Abraamyan Kh.U. et al.

48. R o u n d T a b l e IV WASA-CELSIUS :(a) M spectrum after kinematic fit.The dotted histogram in shows background expected from misidentified π0π0 events. (b) The same as (a), but for Tp = 1.2 GeV. Abraamyan Kh.U. et al.

49. R o u n d T a b l e IV 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 forevery spectrometer arm. Distributions are normalized to the same total number of events. Abraamyan Kh.U. et al.

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