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Fit to the Dalitz plot of the p 0 p 0 g final state with 2001/2002 data

Fit to the Dalitz plot of the p 0 p 0 g final state with 2001/2002 data. S. Giovannella, S.Miscetti. Related documentation: KLOE Memo 319 (November 2005) S.Giovannella, S.Miscetti, “Study of the e + e - → p 0 p 0 g process using 2001/2002 data” KLOE Memo 326 (March 2006)

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Fit to the Dalitz plot of the p 0 p 0 g final state with 2001/2002 data

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  1. Fit to theDalitz plot of the p0p0g final statewith 2001/2002 data S. Giovannella, S.Miscetti • Related documentation: • KLOE Memo 319(November 2005) S.Giovannella, S.Miscetti, “Study of the e+e-→p0p0g process using 2001/2002 data” • KLOE Memo 326(March 2006) S.Giovannella, S.Miscetti, “Fit to the p0p0g Dalitz plot” Blessing Meeting – 27 Apr 2006

  2. Composition of the p0p0g final state Two main contributions to p0p0g final state @ Mf: 1.e+e-wp0 p0p0g svis(Mf) ~ 0.5 nb 2.f Sg p0p0g svis(Mf) ~ 0.3 nb Backgrounds: S= wp + Sg

  3. p2(1) e+ V g f/w/r p1(2) e─ Data and Montecarlo samples DATA 2001+2002 data : Lint = 450 pb─1 Data have some spread aroud the f peak + two dedicated off-peak runs @ 1017 and 1022 MeV : All data set divided in 100 keV bins of  s RAD04 MC production: 5  Lint GG04 MC production: 1  Lint Improved e+e wp0p0p0ggenerator Three body phase space according to VDM from NPB 569 (2000), 158 MC

  4. e+e-→wp0→p0p0g events: data-MC comparison Old exclusive analysis applied on the 2001/2002 data Old ee  0 MC

  5. Data quality • Runs with the following characteristics removed: • Missing beam parameters • Not standard EMC trigger thresholds • Unexpected event counting for f→hg→p0p0g events Total: 1.3 pb-1 • f→hg→p0p0p0g • Biggest rate in DRN • Background free • Very simple selection criteria • ♦ 7 neutral clusters with 23<qg<157° • ♦ At least 1 photon with E>280 MeV • Number of events normalized using VLAB • luminosity and f→hg visible x-sec • Central value in good agreement with • the expected value: • eana×BR(h→p0p0p0) = 0.41×0.325 = 0.13

  6. Sample preselection and kinematic fit 1. Acceptancecut: 5 neutral clusters in TW with E > 7 MeV and |cosq|<0.92 [ TW: |Tcl-Rcl/c| < MIN( 5sT, 2 ns ) ] 2. Kinematic fit requiring 4-momentum conservation and the “promptness” of g’s ( TclRcl/c = 0 ) 3. Pairing: best g’s comb. for the p0p0g hypothesis 4. Kinematic fit for both g’s pairing, requiring also constraints on p masses of the assigned gg pairs

  7. - - - EMC resolution — FIT1 resolution Efit (MeV) Photon pairing p0 mass resolution parametrized as a function of the photon energy resolution after kinematic fit: Fit function for energy resolution: The photon combination that minimizes the following c2 is chosen:

  8. Photon pairing: data-MC comparison Distributions after all analysis cuts Pairing c2 First kinematic fit

  9. Analysis cuts 1.e+e- → gg rejection using the two most energetic clusters of the event: E1+E2 > 900 MeV 2. ggg+accidentals background rejection: Eg(Fit2) > 7 MeV 3. Cut on 2nd kinematic fit: c2Fit2/ndf < 5 4. Cut on p masses of the assigned gg pairs: |Mgg-Mp| < 5 sM • S= wp + Sg • eana(Sg) obtained using the 2000 data Mpp shape

  10. Cut 1: e+e- gg(g) rejection e+e- gg rejection using the two most energetic clusters of the event: E1+E2 > 900 MeV Data MC p0p0g events

  11. Cut 3: c2Fit2 after sample selection Analysis @ √s = 1019.75 MeV (Lint = 145 pb-1)

  12. Analysis efficiency and c2Fit2 cut Sg: efficiency almost flat, with a small constant drop when hardening the cut wp:efficiency not flat, with an increasing drop in the region Mpg~750 MeV Sg wp This is related to the fact that our kinematic fit constrains the total energy of the event to the beam energy with an error of 300 keV A c2/Ndof<5 cut reduces this effect while keeping the background to an acceptable level

  13. ISR: f→Sgvse+e-→wp0 • Very different ISR behaviour: • The resonant Sg process has large (25%) radiative corrections with a ISR energy spectrum constrained by Gf to be lower than 10 MeV • The not-resonant wp0 behaviour makes instead small the overall radiative correction while the ISR energy spectrum shows large tails Sg wp Sg ─ GEANFI ─ DAPHNE Handbook wp

  14. Pairing efficiency • Pairing efficiency evaluted for events where all p0’s are correctly • matched • Overall efficiency: epair~ 85% • The non-flat behaviour is due to a similar energy distribution of the two pions in some particular Mpp-Mpg region • The difference between Sg and wp processes is mainly due to their different ISR tails

  15. Pairing efficiency: standard ISR vs EISR<10 MeV All ISR tails EISR < 10 MeV

  16. Data-MC comparison after all analysis cuts Analysis @ √s = 1019.75 MeV (Lint = 145 pb-1)

  17. Data-MC comparison after all analysis cuts Analysis @ √s = 1019.75 MeV (Lint = 145 pb-1) Discrepancies on Mpp: not precise description of the MC scalar mass spectrum or possible interference between the two p0p0g final states Good agreement on Mpg: reliable VMD description in our simulation

  18. Effect of Trigger, FILFO and ECL 1. Trigger and Cosmic Veto efficiency Calorimeter trigger fully efficient on the signal. Cosmic Veto losses evaluated with prescaled events: CV = (99.54 ± 0.08)% 2. MC evaluation of FILFO and ECL losses FLF = (99.95 ± 0.01)% ECL = (96.5 ± 0.1)% 3. DATA evaluation of FILFO and ECL losses The minimum bias sample streamed by C.DiDonato was used to evaluate with data FLF and ECL Only data with √s =1019.6 used. FLF = (99.90 ± 0.05)% ECL = (99.2 ± 0.1)% !!! The large difference on ECL mainly due to the a wrong parametrization of time resolution in neurad code! Total overall correction factor applied to (MC): Rpresel = 1.022 ± 0.004

  19. Systematics on background evaluation (I) In order to study the systematics connected to the background subtraction we found for each category a distribution “background dominated” to be fitted with two MC components: Hdata = a1 Hbckg + a2 Hothers • fhg p0p0p0g (most relevant bckg contribution) • Background enriched sample : 4 < c2/ndf < 20 a1(hg7) = 1.064 ±0.002

  20. Systematics on background evaluation (II) For f  hg  ggg , f  p0g, f  a0g we calculate a c2 in the mass hypothesis For e+e- gg, we fit the Df distribution for c2/ndf < 5 (and no gg rejection cut ) a1(hg3) =0.86 ± 0.02 a1(pg) =2.35 ± 0.02 a1(gg) =1.85 ± 0.03 a1(hpg) =0.86 ± 0.02

  21. Systematics on background evaluation (III) Fit results are used to evaluate the systematic error on the background counting, defined asdB = ( 1 -a1 )/2 Summary of relative systematic uncertainties on background estimate compared with the errors on the applied BRs (PDG+KLOE) and the S/B ratio after c2 cut:

  22. Systematics on cluster counting: signal The counting of 5 photons in TW with Ecut and tcut can be affected by: 1. MC energy scale  1.4% miscalibration in RAD04 2. MC cluster efficiency (old curves applied to RAD04 production) a. change of the opening cone when evaluating the MC correction b. new curves without residual Bhabha contamination 3. Angular acceptance  NEGLIGIBLE 1. For each bin of the Dalitz plot the variation of the efficiency (enew-eold)/eold (red) is compared with the statistical error (black) 2.a 2.b

  23. Systematics on cluster counting: background The change in the MC cluster efficiency also affects the quantity of residual background, especially for f→hg→p0p0p0g The relative syst.error (red), defined as the difference of the background estimated with the two efficiency curves , is compared with the error in the Dalitz plot after background subtraction (blue)

  24. Systematics on photon pairing: rate To assign a systematics to the pairing procedure we studied the difference between c2SEL for the best and second best choise of photons: Dc2SEL = c2SEL (Best)-c2SEL (SecondBest) We then fit the Dc2SEL distribution in data with a linear combination of MC spectra for the right and wrong choise of paired photons (by MC truth) Rpair = 1.08 ± 0.02

  25. Systematics on photon pairing: off-diagonal check All events • In the old exclusive analysis the region • with Mpp>700 MeV is dominated by • wp events with wrong photon pairing • Good data-MC agreement • The 1.08 scale factor applied to • wp events show a better data-MC • agreement!!!! Mpp>700 MeV Mpp>700 MeV

  26. Dalitz plot @ √s=1019.75 MeV • VMD description reliable only at the f peak • Only the √s bin with higher statistics around Mf considered • Fit to the Dalitz plot with the VDM and scalar term, including also • interference • Two model considered: Kaon Loop (KL) and “No Structure” (NS) • Binning choice driven by the Mpp, Mpg • mass resolutions after the second • kinematic fit: • 10.0 MeV in Mpp • 12.5 MeV in Mpg

  27. Fit method Dalitz plot density after background subtraction fitted using the expected number of events in the ith bin, Ni, built as the sum of contributions from all theoretical bins: V = VMD S = scalar I = interference fj : integration of the differential cross section in the jth bin ; correction for the radiator function applied A(i,j) : smearing matrix ej : analysis efficiency

  28. g(fKK) from G(f K+K–) g(f0KK) g(a0KK) g(f0pp) g(a0hp) p2(1) p2(1) } f0/a0 e+ e+ w r f fit output g g r/r/r f/w/w/w Charged kaon loop final state p1(2) p1(2) e─ e─ Fit function: the Achasov parametrization (I) • Scalar produced through a kaon loop [N.N.Achasov and V.N.Ivanchenko, Nucl. Phys. B 315 (1989) 465]  one scalar [N.N.Achasov and V.V.Gubin, Phys. Rev. D 56 (1997) 4084]  two scalars • VDM contribution from the following diagrams : • All interferences considered

  29. Fit function: the Achasov parametrization (II) Sg Model dependent term wp/rp f0g/VP interf [N.N.Achasov, A.V.Kiselev, private communication]

  30. Improved Kaon Loop parametrization [N.N.Achasov, A.V.Kiselev, PRD73 (2006) 054029] • Insertion of a KK phase: • Beyond to its contribution in the interference term, • IT CHANGES THE SCALAR TERM AMPLITUDE • IN THE Mpp<2MK+ REGION • New parametrization of the pp phase:

  31. Improved KL parametrization on OLD KLOE data Combined fit to KLOE 2000 + pp scattering data d00 dBR/dMpp (KLOE 2000 data) Mpp(GeV) dBR/dMpp× 108 (MeV-1) h00 Mpp(MeV) Mpp(GeV)

  32. Theory advantages of the improved KL parametrization • Able to reproduce mass spectrum, 00 and inelasticity • Sum of overlapping resonances with the correct propagator matrix • A lot of theory restrictions applied: - The  scattering length a00 fixed to the recent calculation of Colangelo - In the scattering amplitude the Adler zero in T() is granted in the region below the threshold (0 < m2 < 4M2) • Besides f0(980), a (600) meson is needed to obtain a good fit

  33. Improved KL parametrization: the 10 “variants” We cannot leave all f0(980) and s(600) parameters free: elastic background and the s(600) parameters are closely related We have used as free parameters some VMD parameters and the f0(980) mass and couplings The s(600) and the parameters of pp and KK scattering are taken from Achasov’s paper, where ten sets of different parameters are reported, defined as K1…K10

  34. KL fit results: the scalar term • We consider acceptable just the six variants with P(c2)>1% • We use the best fit results, adding the maximal variation with all the other accepted variants as the error associated to the theory • When leaving the s(600) mass free, the pp scattering phase does not reproduce data

  35. KL fit results: the VMD term • Pretty stable results on the VMD side • arp≈ 0.6 • Crp and frp unstable but determined with large errors • Mw = ( 782.5  0.3fit- 0.4mod ) MeV

  36. Kaon Loop fit, variant K1: Dalitz plot slices  Data ─Fit result

  37. Kaon Loop fit, variant K1: residuals

  38. Kaon Loop fit, variant K1: VMD/Sg compositions Scalar term f0g sg

  39. gVS gSpp e+ S V P e- g Fit function: the No Structure model [G.Isidori, L.Maiani, M.Nicolaci, S.Pacetti, hep-ph/0603241] • Point-like Sg coupling • Scalar propagator described by a simple BW shape corrected by the Flatte’ condition on the pp and KK thresholds • Not resonant continuum background added as a expansion in Mpp

  40. No Structure fit results Scalar term VMD term

  41. No Structure fit: Dalitz plot slices  Data ─Fit result

  42. No Structure fit: residuals

  43. No Structure fit: VMD/Sg compositions and phase Unexpected shape observed in fS @ Mpp≈ 600 MeV

  44. No Structure vs Kaon Loop: VMD/Sg comparison ─ Kaon Loop ─ No Structure ─ 2000 data

  45. Fit systematics • Fit repeated by varying quantities related to the syst. described before: • Absolute normalization scale: Lint and Gee varied by 1s • Beam energy scale: -150 keV shift applied on √s • 3. Cluster efficiency curve: new parametrization used to evaluate • analysis efficiency, smearing matrix and background contribution • c2Fit2 cut: tighter cut applied c2/Ndof <3 • 5. Smearing matrix: fraction of off-diagonal elements increased by 8% • 6. Folding of interference term: Sg radiative correction, analysis • efficiency and smearing matrix used for the interference term • 7. Background scale factors applied to the background

  46. Fit systematics: summary for Kaon Loop model

  47. Fit systematics: summary for No Structure model

  48. Final results BR obtained by taking into account both KL and NS results: Mf0 = ( 976.8  0.3fit +0.9/-0.6syst + 10.1mod ) MeV gf0K+K-= ( 3.76  0.04fit +0.15/-0.08syst+1.16/-0.48mod ) GeV gf0p+p- = ( -1.43  0.01fit +0.01/-0.06syst +0.03/-0.60mod) GeV Rf0 = 6.9  0.1fit +0.2/-0.1syst +0.3/-3.9mod gff0g = ( 2.78 +0.02/-0.05fit +0.13/-0.05syst +1.31mod ) GeV-1 KL Mf0 = ( 984.7  0.4fit +2.4/-3.7syst ) MeV gf0K+K-= ( 0.40  0.04fit +0.62/-0.29syst ) GeV gf0p+p- = ( 1.31  0.01fit +0.09/-0.03syst) GeV Rf0 = 0.09  0.02fit +0.44/-0.08syst gff0g = ( 2.61  0.02fit +0.31/-0.08syst ) GeV-1 Fit results Derived NS

  49. Conclusions • A lot of checks done on the experimental side • KL fit results: • Comprehensive description of f→Sg and pp scattering data • f0(980) and s(600) needed to describe data • f0(980) strongly coupled to K+K- • NS fit results: • Only f0(980) [+continuum background!] needed to describe data • f0(980) weakly coupled to K+K- • pp scattering phase not well reproduced • Next step will be writing the paper • Comparison with p+p-g results: • Reasonable agreement for KL • Contradictory results for NS for gf0pp and gf0KK Combined fit to p+p-g and p0p0g mass spectra needed for a final answer

  50. Spare slides

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