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KLOE results on scalar mesons from   decays

KLOE results on scalar mesons from   decays. Federico Nguyen Università Roma TRE July 29 th 2006. open points:. KK,  “couplings” of f 0 (980) and to   |ss> ? 2) is the  (500) needed to describe the mass spectra?. K +. g  KK g SKK g SPP. P. S. P. K -.

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KLOE results on scalar mesons from   decays

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  1. KLOEresults on scalar mesons fromdecays Federico Nguyen Università Roma TRE July 29th 2006 open points: KK, “couplings” of f0(980) and to  |ss>? 2) is the (500) needed to describe the mass spectra?

  2. K+ gKK gSKK gSPP P S P K- Models for thespectra 1) Kaon Loop [KL] [N.N.Achasov, V.N.Ivanchenko, NPB315 (1989) 465] [N.N.Achasov, V.V.Gubin, PRD 56 (1997) 4084] 2) “No Structure” [NS] [G.Isidori, L.Maiani, M.Nicolaci, S.Pacetti, JHEP 0605 (2006) 049] e+ S gVS gSpp V P e-  crucial quantities

  3. ISR The analysis → +- published in PLB 634 (2006) 148 event selection: 2 tracks with >45o; missing momentum >45o; e+e- events rejection on calorimetric PID basis; +- and +-0 suppressed by means of kinematics; 6.7 × 105 events / 350 pb-1 Events/1.2 MeV f0(980) region M (MeV) the fitting function:

  4. Results for → +- NS: 2min /dof = 533/479 P(2 > 2min) = 4.4% after bckg subtraction both fits are satisfactory in describing the f0(980) structure KL: 2min/dof = 538/483 P(2 > 2min) = 4.2% further check:  Data  ISR+FSR predictions □ ISR+FSR+f0(980) KL predictions [G.Pancheri, O.Shekhovtsova, G.Venanzoni, hep-ph/0506332]

  5. Summary for→ +- • peak at M~ 980 MeV due to →f0(980), with negative interf. with FSR • in both models the f0(980) is strongly coupled to kaons and to the  • introduction of the (500) does not improve the fit • qualitative agreement in the forward backward asymmetry: • Clear signal in the f0(980) mass region • Discrepancy at low M disappears including f0(980)

  6. The analysis →  a)5 photons from the interaction point b) 1st kinematic fit with 4-mom. conservation c) 2nd kinematic fit also with constraints on  masses and cut 2/dof < 5 4 × 105 events / 450 pb-1 M vs. M Dalitz Plot Fit, bin widths: 10 MeV (M) 12.5 MeV (M) →f0(980) →00 e+e-→0→00 √s = 1019.6 MeV

  7. Results for the analysis →  unrolled Dalitz slices:  Data ─Fit ■ Free parameters: Mf0 , gf0+- , gf0K+K- , VMD couplings ■ /KK scattering phases and (500) introduced and fixed (m  [400,710] MeV,  [400,710] MeV) from a combined fit to published KLOE  decays and to existing  scattering data, by [N.N.Achasov, A.V.Kiselev, PRD73 (2006) 054029] KL: 2min/dof = 2754/2676 P(2 > 2min) = 14.5% both models are able to describe well the data NS: 2min /dof = 2799/479 P(2 > 2min) = 4.4%

  8. Summary table and comparison ranges are given by exp. systematics, except for KL in the 00 channel, due to model variants KL fit results: 00:(500) [but with fixed values] needed to describe data, +-:(500) is not needed both channels: f0(980) strongly coupled to KK NS fit results: both channels: only f0(980) sufficient to describe data 00wrt +-: larger gf0 but weaker KK coupling

  9. 0  0 More scalars with KLOE chance to benefit of off-peak data e+ e- → e+ e-  → e+ e- 0 0 e+ e- →  → 0 0

  10. Conclusions and outlook • Extensive study of f0(980) properties with 2001-2002 KLOE data: • First clear evidence of the  f0 process both in invariant mass and in the forward-backward asymmetry • The data sample allows for an accurate Dalitz plot analysis in the  final state for the first time • Perspectives with our new data sets: • Combined fit using both final states • Search for f0(980)/a0(980) →KK • Search for (500) with off-peak data using the reaction   •  a0(980) in progress with both   and    final states

  11. Spare Slides

  12. The analysis →  results soon! • 2001-2002 data: 395 pb-1 at  peak • 1) →  (39.43%) 2.2  104 events • 2) →π+π-π0 (22.6%) 4180 events • Fit the two spectra simultaneously • Negligible irreducible VMD background Kaon Loop → No Structure Mπ (MeV) →+-0

  13. pions, muons electrons Background rejection /eseparation is performed with a particle ID function based on time and quantity/shape of the energy released in the calorimeter pions deposit ~ 40 MeV in each plane PID+ electrons deposit mostly in the first plane and negligible amount in the rest PID-

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