Polyarush A. Yu. INR RAC Поляруш Александр Юрьевич polyarush@inr.ru

1. The inсlusiveproduсtionof the meson resonanсesρ0(770),K*(892), f0(980), f2(1270) in neutrino-nuсleon interaсtions Polyarush A. Yu. INR RAC Поляруш Александр Юрьевич polyarush@inr.ru

2. Overview The inclusive production of the meson resonances ρ0(770), K*(892)±, f0(980), f2(1270) in neutrino-nucleonchargedcurrent (CC)interactions has been studied with the NOMAD detector exposed to the wide band neutrino beam generated by 450-GeV protons at CERN-SPS. For the first time the f0(980) meson is observed in neutrino interactions. The significance of its observation is 5 standard deviations. The presence of f2(1270) in the neutrino interactions is reliably established. Theaverage multiplicity of all these resonances is measured as a function of several kinematic variables. The experimental results are compared to the multiplicities obtained from a simulation based on the Lund model. Matrix element of spin density matrix for K∗ (892) meson have been measured.

3. IHEPPSU-70

4. Neutrino flux • Neutrino sources : • π+-› μ++ νμ • K+-› μ++ νμ • K+-› μ++ νμ + π~ 1% • <EνCC> = 7.8GeV

5. Bubble chamber SKAT • Пузырьковая камера СКАТ проектировалась и строилась с 1964г. по 1975г. • Облучалась в нейтринном канале ИФВЭ с 1975г. по 1989г.

6. Event selection • A neutrino event was selected for processing if • there was an identified muon at the primary vertex; • ˆthere were at least 3 tracks (including muon) at the primary vertex; • EνCC > 3GeV; • the invariant mass of the hadronic system W was higher than 2 GeV. • After cuts we obtain 5792 νμCC

7. Meson resonance ρ0(770) • Since the ρ0is a resonance decaying into π+π-, its analysis is based on the quantitative determination of the corresponding resonance signal in the invariant mass distribution of π+π-combinations.

8. Reflections • One can see the contribution from several resonances different from ρ0(770) (reflections). The largest contribution is from the ω resonance which decays mainly to 3 pions. Since reflections are situated asymmetrically with respect to the ρ0(770) position, experiments where a treatment of reflections was absent or was notcorrect enough may obtain shifted value of the ρ0(770) mass.

9. Experimental resolution • In order to take into account the increase of the widths of the resonances due to the experimental resolution we estimated the invariant mass resolution function corresponding to the propagation of the errors on the track parameters in data as given by the reconstruction program. • ∆Г = 47 МэВ

10. В массовом распределении пар одинакового знака резонансов быть не должно.

12. NOMAD detector

13. NOMAD detector • 47 drift chambers, 2.7 tons

14. Typical νCC event • The main goal of theNOMADexperimentwas the searchνμ→ντoscillation. • ντCC interactions identified by using kinematical criteria. This required a very good quality of event reconstruction.

15. Neutrino beam WANF CERN • Neutrino sources: • π+ -› μ+ + νμ • K+ -› μ+ + νμ • K+ -› μ+ + νμ + π at1% level • νμin beam ~93% • <EνCC> = 43.8GeV

16. NOMAD experiment • The present analysis is based on the full sample of data of NOMAD. • A neutrino event was selected for processing if • the primary vertex is inside the following fiducial volume: |X, Y | < 120cm, 10cm < Z < 390cm; • there was an identified muon at the primary vertex with momentum pμ>3GeV/c • ˆthe invariant mass of the hadronic system W was higher than 2 GeV; • ˆthere were at least 3 tracks (including muon) at the primary vertex; • ˆthe event should be measured with reasonable accuracy (ΔEvis/Evis< 30%); • _ • After cuts we obtain 667252 νμCC15927νμCC • In this analysis the Monte Carlo (MC) simulation software is based on the LEPTO6.1 - JETSET7.4 -Geant321.

17. Raw distribution of the invariant π+π-mass in νμCCsample.

18. Signal extractoin

19. Raw distribution of the invariant mass of (π+π+), (π-π-) pairs in νμCC sample.

20. Reflectoins • Reflections are contributions to the π+π-− invariant mass distribution from resonances decaying to π+π-+ some other particles or contributions from events where not all the particles of a resonance decay are correctly identified and thus a wrong mass is assigned to them. • ω→π+π-π0

21. After reflection subtraction

22. After the combinatorialbackground subtraction f0 f2

24. Masses and widths NOMAD: PDG:

25. Compared to other mesons within its mass region the f0(980) has a small total width and a low partial width to γγ. • A number of nonstandard interpretations of the f0(980) state were suggested: • one approach regards the f0(980) as four quark bound state [1]. • Jaffe had combined f0(980), a0(980), f0(470), K*(700) to form a nonettetraquark states.

26. K+K- molecule states. • V.N.Gribovhas proposed a theory of confinement in QCD, in which the f0(980) plays a special role of a novel vacuum scalar state. F.E. Close et al. noticed that signature of Gribov's vacuum scalar states would be a large yield in low multiplicity events. • D. Robson proposed an interpretation of the f0(980) as scalar glueball.

27. M2(π+π−)− distribution from D+ → π+π+π− decays. Data of E791 collaborationare shown with error bars, the histogram representa fit without (a) and with a Breit-Wigner resonance (the σ(485)) Eberhard Klemptand Alexander Zaitsev arXiv:0708.4016v1 (Rhys Rep)

28. Previous neutrino experiments Big European Bubble Chamber (BEBC)

29. Previous experiments • ВЕВС WA21 • 15752 νp CC events • ̵ • 10452 νp CC events • Nρ0= 2838 ± 245 ± 340 • < ρ0 > = 0.180±0.016±0.022 • Nf2 = 615±226 • <f2> = 0.047± 0.017

30. Previous experiments

31. Previous neutrino experiments • All the previous experiments observed an overestimation of the average multiplicities of ρ0(770)by the Lund model by 50-70%, while the shapes of the Lund distributions were in agreement with the experimental distributions. • 1986. BEBC WA21 1991.

32. W2distribution • W2 = m2 +2mν –Q2 − the hadronic invariant mass squared. • ν = Eν - Eμ • The solid line represents the result of the Lund simulation. • The dashed line represent a fitted function a+b×lnW2

33. Eνdistribution

34. Q2distribution

35. XF distribution • xF = 2p L*/W • Forward production of ρ0(770) and f2(1270) is stronger than the backward production.

36. Z distribution Z =Eρ/E hadr

37. PT2 distribution • The solid line represents the result of the Lund simulation. • The dashed straight line represents the result of the fit by the exponent function. • A fit performed in the range • p2T< 0.5(GeV/c)2gives the following result: • b = (5.33 ± 0.19)(GeV/c)−2. • p2T> 0.5(GeV/c)2 we obtain values: • b = (4.12 ± 0.12)(GeV/c)−2.

38. Gribovtheory verification • V.N.Gribov has proposed a new theory of confinement in QCD, in which the f0(980) plays a special role of a novel vacuum scalar state. F.E.Close et al. noticed that signature of Gribov's vacuum scalar states would be a large yield in low multiplicity events.

39. L. Maiania, et al. arXiv:hep-ph/0606217 • R AA - nuclear modification factor

40. K*(892)+ NK*+ = 26676 ± 1784 ± 1863 <K*+> = 0.026 ±0.002±0.002

41. K*(892)+ • For K∗+ (892) we present the dependencies of production yields for the same kinematic variables. • Matrix element of spin density matrix for K∗+ (892) meson have been measured • ρ00= 0.40 ± 0.06(stat) ± 0.03(syst.) • Result are in agreement within errors with the ρ00= 1/3, which corresponds to no spin alignment for this meson.

42. K*(892)+

43. K*(892)+

44. Conclusion • The inclusive production of the meson resonance ρ0(770) in neutrino – nucleon charged current interactions has been studied with much better statistical accuracy than previous experiments. • We also looked for other resonances decaying into +π−pairs. For the first time the f0(980) meson in the neutrino interactions is observed (significance about 5 standard deviations). • We see a clear signal of f2(1270). Its presence in the neutrino interactions is reliably established (5σ). • A global fit to the π+π− pair mass distribution allows us to obtain the masses and the widths of the ρ0(770), f0(980) and f2(1270). • The average multiplicities of ρ0(770), f0(980), K∗+ (892) and f2(1270) are measured as a function of W2,Q2 and other kinematic variables. • These results are compared with a simulation based on LEPTO6.1 - JETSET7.4. A good agreement for most of the distributions is found.

45. We checked the dependence on the hadron jet multiplicity in our W range for f0(980) against the predictions of the model of Gribov.We see no evidence of the enhanced f0(980) production in low multiplicity events. • For K∗(892) we present the dependencies of production yields for the same kinematic variables. • Matrix element of spin density matrix for K∗+ (892) meson have been measured ρ00= 0.40 ± 0.06(stat) ± 0.03(syst.) • Result are in agreement within errors with the ρ00= 1/3, which corresponds to no spin alignment for this meson.