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Status Report on Final State Analysis of ηπ0γ (a0 → ηπ0) Decays

This report outlines the background evaluation, new analysis cuts, efficiency background assessment, and determination of weights for MC samples. The goal is to apply appropriate weights to the MC data to account for the inaccuracies in cross-sections and unknown efficiencies. The analysis is based on data from 2001-2002 captured with L = 217 pb-1.

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Status Report on Final State Analysis of ηπ0γ (a0 → ηπ0) Decays

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  1. Status report on 0 (a00)5  final state P.Gauzzi, R.Volpe

  2. Outline • Background evaluation: determination of the weights to apply to the MC samples for the relevant background processes, 3, 7, 00 (0 and f0) • New analysis cuts: to reduce the depencence of the efficiency on the π0 invariant mass. • Efficiency

  3. Background evaluation • Analysed sample: 2001– 2002 data  L = 217 pb-1 • The final sample has large irreducible background, that has to be subtracted • We cannot rely on the MC cross-sections: • For some process are wrong (e.g. π0) • In other cases are not well known (f0) • Other processes depend on merging/splitting (→3, 7), we don’t know how well they are reproduced by the MC • Our goal is to determine for each process a weight to apply to MC (‘rad04’ 2001-02 production): • Select a sample dominated by the specific background with a small signal (a0) content • Fit some distribution to determine the weight and check with other variables • w = Nfit / Nexpected(MC)

  4. data 7 KLKs 0 M (MeV)(a0)  (30) 2002 • Eprompt > 700 MeV • 2fit < 27 • E3 > 75 MeV • |M()-547.3| > 30 MeV • Erec(3) < 340 MeV • 2sel3 > 4 • 12<2f0sel< 20 N(a0)/Ntot  0.4% • KSKL contribution from MC “all_phys” • Free parameters: w(→7), w(KSKL) and w(π0), other pocesses fixed w(7)=1.190.02 w()=13.7  4.5 w(KLKS)=3.80.6

  5. M(f0 ) (MeV)  (30) 2002 Check with other distributions • data 7 KLKs 0 cos(ω)(0) Φ (rad) (0) cos(f0 ) cosψ(f0)

  6. 2fit  (30) 2002 • data 7 KLKs 0 cos(a0) M (MeV) (a0)

  7. M (MeV) (a0)  (30) 2001 • data 7 KLKs 0 w(7)=1.08  0.02 w()= 10.6  2.1 w(KLKS)=3.40.5 Different machine bckg conditions  8% correction in 2001 vs 19% in 2002

  8. M(f0 ) (MeV)  (30) 2001 • data 7 KLKs 0 cos(ω) (0) cos(f0) cosψ(f0) Φ (rad) (0)

  9. M (MeV) (a0)  (30) 2001 • data 7 KLKs 0 cos(a0) M (MeV) (a0) 2fit

  10. () () • data →3π0 7 f0 0 a0  () 2002 • Eprompt > 700 MeV • 2fit < 27 • 2a0sel < 27 • d2< M < d1 • |M()-547.3| < 30 MeV • E1+E2+E3 > 950 MeV N(a0)/Ntot  7% •  respectively in the hypoth.  and 0 w()=3.390.07 w()=3.920.52

  11.  () 2001 • data →3π0 7 f0 0 a0 () () w()=2.010.03 w()=3.130.03

  12.  () • Factor of 3 more 3 events in 2001 than in 2002 according to MC: N(2001) =19.4 evts/pb-1 ; N(2002)= 6.5 evts/pb-1 • Also in data N(2001) > N(2002) 2001 2002 E1+E2+E3 (MeV) E1+E2+E3 (MeV)

  13.  () 2002 • data →3π0 7 f0 0 a0 E1+E2+E3 (MeV) E() (MeV) M(MeV)(f0) cos (0) Ein t.w.(MeV)

  14. data →3π0 7 f0 0 a0  () 2001 E1+E2+E3 (MeV) E() (MeV) cos(f0) M(MeV) cos(0) Ein t.w.(MeV)

  15. d2 d1 Mπ (MeV) M(MeV) (f0) 0 Signal (a0 ) →7π0 3f0 0 • Eprompt >700 MeV • 2fit < 27 • 2a0sel < 27 • d1< M(0) <d2 N(a0)/Ntot  1.5 %

  16. 0 2002 • data →3π0 7 f0 0 M (MeV) w(ω)=0.7370.007 w(oth. bckg.)=1.830.25 Other bckg. is mainly f0, other processes fixed  (°) (0)

  17. 0 2001 • data →3π0 7 f0 0 M (MeV) w(ω)=0.6920.005 w(oth. bckg.)=1.08 0.03  (°) (0)

  18. M(a0) (MeV) cos(f0) 0 2002 M(a0)(MeV) cos(f0) 2001 M(a0) (MeV) M(a0)(MeV)

  19. f0  Signal (a0 ) →7π0 3f0 0 • Eprompt >700 MeV • 2fit < 27 • 2a0sel < 27 • |M()-547.3| > 30 MeV • M(0) <d1 N(a0)/Ntot  2 % Cut 4 rejects a0 and 3 d1 Mπ (MeV) M(MeV) (f0)

  20. f0  →7π0 3f0 0 • Fit with 7, 0 and all other processes fixed, but f0 and 0 2002 2001 cos(ω) cos(ω) w(f0) = 1.46 0.02 w() = 5.04  0.67 w(f0)=1.400.02 w()=1.70  0.30 w(0) is not relevant  in the final sample there is no 0

  21. f0  2002 →7π0 3f0 0 cos(f0)  (°) ()  (°) (f0)

  22. f0  2001 →7π0 3f0 0 cos(f0)  (°) ()  (°) (f0)

  23. Further check on weights • Final check, by using all the weights together on the same sample, with a small signal (a0) content • Eprompt >700 MeV • 2fit < 27 • 2a0sel < 27 • |M(3)-547.3| > 30 MeV • Erec(3) < 340 MeV

  24. Check on weights 2002 →7π0 3f0 0 2fit 2fit E (MeV) M (MeV) 12(°) cos(0) cos(f0)  (°) (0)

  25. Summary of weights • In order to evaluate systematics on weigths, we repeated the fit on some other variables and compare the results

  26. Old cuts • Eprompt > 700 MeV • Etot > 900 MeV • 2fit < 27 • 2a0sel < 27 • |M()-547.3| < 30 MeV • E() < 340 MeV • 2II fit < 33 • M(0) < d1 • Mππ(f0 hyp.) < 760 MeV • Residual 3 contamination around Mπ  1020 MeV • In order to reduce the (7) background, we would like to harden cut 7. • Cut 8 introduces a dependence of the efficiency on the 0 mass • 00mass for f0 in MC is simulated with the fit to 2000 data, then cut 9 is not reliable • Cuts 2 and 4 are not necessary anymore

  27. New cut to reject  • residual →3 events are concentrated around Mπ  1020 MeV • Cut on the energies of the three most energetic clusters E1+E2+E3 < 980 MeV →3 E1+E2+E3 (MeV) M(MeV)

  28. Old cut Cut on 2IIfit • Nseg/N back • cut * cutxNseg/Nback Signal (a0) →7π0 3f0 New cut Cut on 2IIfit cut 2IIfit Old cut: 2IIfit < 33 New cut: 2IIfit < 24 2IIfit < 18 2IIfit < 21 2IIfit < 24 2IIfit < 27 M (MeV)

  29. tot Mπ (MeV) π0 cut Old cut |M| (MeV) M(MeV) ~ 30% drop in efficiency

  30. new old 000      New π0 cut Exploit the angle between the ’s from the π0 of the  ω7 f03 a0  Old cut New cut d2 d1 |M| (MeV) |M|-d1 (MeV) New cut: M(0) < d1 .OR. M(0) > d2 .OR. (ω)<30° .OR. (ω)>60° M(MeV)

  31. New cut New f0 cut • * is the angle between the non associated  and the flight direction of , in the  rest frame Old cut cos(*) |cos(*)|<0.8 |cos(*)|<0.65 |cos(*)|<0.5 M (MeV) a0  f0

  32. New f0 cut • data ω7 f03 a0  is the angle between the 2  associated to the 0 in the 0 hypothesis Cut :  > 42° (0)

  33. Eprompt > 700 MeV 2fit < 27 |M()-547.3| < 30 MeV E1+ E2+ E3 < 980. MeV 2II fit(a0) < 24 M(0) < d1 .OR. M(0) > d2 .OR. (ω)<30° .OR. (ω)>60° |cos*(ω)| < 0.8 (0) > 42° New cuts to reduce 3 “ 7 “ 0 “ f0

  34. Efficiency Old analysis New analysis M (MeV) (Tr., Filfo, Evcl, preselection not included) Efficiencies still to be checked

  35. Efficiency Efficiencies averaged over the whole M spectrum 1. To be checked with data 2.+3. Check done with the min bias sample (Camilla’s sample): 1495 events selected, all 1495 pass both FILFO and EVCL, but better check needed, about 5% of our final sample is missing in the min bias one • In the old analysis i  64%, but we have moved the angular cut (21°) in the preselection • Old analysis: tot = 32%

  36. Efficiency matrix • To be used to fit the spectrum to the various models • Takes into account of the smearing due both to mass resolution and to photon pairing • According to MC  14% of wrong pairings Mrec (MeV) Mgen (MeV)

  37. Check of pairing on data • Data • Right p. • Wrong p. • 2sel is the difference between the first and the second photon combination for the a0 hypothesis • Two component (right and wrong pairing) fit to the 2sel distribution of the data (final sample) • Right and wrong pairing shapes from MC wrong pairings = (11.5 ± 0.70) % 2sel

  38. Final sample Other background (0, , KK,…) negligible

  39. Final sample • data ω7 f0 3 2002 2001 Mπ (MeV)

  40. Final sample • data ω7 f0 3 Bkcg subtracted 2001+2002 Mπ (MeV)

  41.  0  • data ω7 f0 3 Final sample cos cos

  42. Final sample M (MeV) M (MeV)

  43. Conclusions • New analysis scheme: efficiency vs π0 invariant mass became flatter than in the past • Background evaluation: weighting procedure seems to work  ~ 55% background to be subtracted from the final sample • Efficiency evaluation: still preliminary, other checks needed  smearing matrix • Systematics evaluation on analysis cuts is in progress • To do: evaluation of other systematic effects (MC energy scale correction, photon efficiency curves, accidentals, …) Fit(s) of the spectrum to get the a0 parameters and the Br(0)

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