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Dynamics of η → π 0 π 0 π 0. F. Ambrosino T. Capussela F. Perfetto. OUTLINE. KLOE Memo n. 359 α = − 0.027 ± 0.004 stat ± 0.006 syst ( blessed 19/07/2007; KLOE preliminary arXiv 0707.4137) Selection scheme & fit procedure & systematics evaluations
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Dynamics of η → π0π0π0 F. Ambrosino T. Capussela F. Perfetto
OUTLINE • KLOE Memo n. 359 • α = − 0.027 ± 0.004 stat ± 0.006 syst • (blessed 19/07/2007; KLOE preliminary arXiv 0707.4137) • Selection scheme & fit procedure & systematics evaluations • Introduction of a new selection scheme: NEW approach • NEW or OLD approach ? • KLOE Memo n. 359 + x • Update on the measurement using different samples • Final results
Dalitz plot expansion The decay η → 3π violates iso-spin invariance and itis induced dominantly by the strong interaction via the u−d quark mass difference. The Dalitz plot density corresponding to the intrinsic η→ π0 π0 π0 decay amplitude is approximately described by |A|2 ∝1 + 2αz With: Z ∈ [ 0 , 1 ] Ei = Energy of the i-th pion in the ηrest frame. ρ = Distance to the center of Dalitz plot. ρmax = Maximun value of ρ. η−>3π @ KLOE
Theory vs Experiment Calculations for α: J.Kambor et al. (1996): −0.007 or −0.0014 B.Borasoy et al. (2005): −0.031 ± 0.003 J.Bijnens et al. (2007): 0.013 ± 0.032 Experimental results for α: GAMS-2000 (1984): −0.022 ± 0.023 CBarrel at LEAR (1998): −0.052 ± 0.017 ± 0.010 CBall at AGS (2001): −0.031 ± 0.004 KLOE (prelim.2005): −0.013 ± 0.004 ± 0.005 CELSIUS-WASA (2007): −0.026 ± 0.010 ± 0.010 KLOE (prelim.2007): −0.027 ± 0.004 ± 0.005 CBall at MAMI-B (2009): −0.032 ± 0.002 ± 0.002 CBall at MAMI-C (2009): −0.032 ± 0.003 • Experiment: α = −0.031 ± 0.004 • KLOE, CBall and WASA consistent • ChPT LO: α = 0 • ChPT one and two loop: α > 0 • Quark masses from η → π0π0π0? • [ DeAndrea, Nehme, Talavera PRD78(2008)034032 ] η−>3π @ KLOE
Sample selection • The cuts used to select:η → π0 π0 π0are: • 7 and only 7 prompt neutral clusters with 21°<θγ<159° • and Eγ> 10 MeV • Opening angle between each couple of photons > 18° • Kinematic Fit with no mass constraint • P(χ2) > 0.01 • 320 MeV < Eγrec < 400 MeV (after kin fit) • The overall common selection efficiency (trigger, reconstruction, EVCL) is ε = (30.30 ± 0.01)% With these cuts the expected contribution from events other than the signal is < 0.1% Frascati 19 Luglio 2007
Matching γ to π0 s • In order to select the best π0 π0 π0 pairing, we introduce a pseudo−χ2 variable for each of the 15 possible pairs, • cutting on: • Minimum χ2 value • Δχ2 between “best” and “second” combination • one can obtain samples with different purity-efficiency Δχ2 Δχ2 min χ2 min χ2
Matching γ to π0 s • In order to select the best π0 π0 π0 pairing, we introduce a pseudo- χ2 variable for each of the 15 possible pairs, • cutting on: • Minimum χ2 value • Δχ2 between “best” and “second” combination • one can obtain samples with different purity-efficiency After pairing we perform kinematic fit with η andπ0 mass constraint η mass:MMC = 547.30 MeV /c2 MData = 547.822 MeV/c2 Δχ2 Δχ2
Fit procedure The fit is done using a binned likelihood approach We obtain an extimate by minimizing Where: • ni= recostructed events • νi= for each MC event (according pure phase space): • Evaluate its ztrue and its zrec (if any!) • Enter an histogram with the value of zrec • Weight the entry with 1 + 2αztrue • Weight the event with the fraction of combinatorial background, for the signal (bkg) if it has correct (wrong) pairing This procedure relies heavily on MC.
Test on fit procedure (I) • We have tested the fit procedure in different ways: • Looking at the result of our fit on MC (αMC = 0.)
Test on fit procedure (II) • We have tested the fit procedure in different ways: • Looking at the result of our fit on MC (αMC = 0.) • Using hit or miss and our reweighting we have generated • samples with different values of α and then we have • compared the two procedures.
Test on fit procedure (III) • We have tested the fit procedure in different ways: • Looking at the result of our fit on MC pure phase space(αMC = 0.) • Using hit or miss and the fit procedure we have generated samples with different values of α and then we have compared the two procedures. • Parameter scan:
Systematic checks Mean 134.2 RMS 11.83 Mean 134.2 RMS 11.99 Frascati 19 Luglio 2007
A further check can be done comparing the energies of the two photons in the pion rest frame as function of pion energy Systematic check vs
A further check can be done comparing the energies of the two photons in the pion rest frame as function of pion energy A data MC discrepancy at level of 1÷2 % is observed. Thus we fit filling a histo with: z’rec = zgen + η(zrec− zgen ). Systematic check
Systematic checks N2/N1 exp. = 0.7263 ± 0.0002 N3/N1 exp. = 0.4497 ± 0.0002 N4/N1 exp. = 0.3048 ± 0.0002 N5/N1 exp. = 0.1431 ± 0.0001 N2/N1 obs = 0.7258 ± 0.0004 N3/N1 obs. = 0.4556 ± 0.0004 N4/N1 obs. = 0.3140 ± 0.0004 N5/N1 obs. = 0.1498 ± 0.0003
Idea, try to fit the WPf on DATA. To check procedure, we fit the WPf on MC: WPf(MC) = 24.6 % WPf(MC fit) = (24.6 ± 0.2) % WPf(MC) = 15.5 % WPf(MC fit) = (15.5 ± 0.2) % WPf (MC) = 8.0 % WPf (MC fit) = (7.9 ± 0.3) % WPf (MC) = 5.2 % WPf (MC fit) = (5.2 ± 0.3) % WPf (MC) = 2.4 % WPf (MC fit) = (2.4 ± 0.4) % Systematic check
On DATA: WPf (MC) = 24.6 % WPf (DATA) = (26.45 ± 0.26) % WPf (MC) = 15.5 % WPf (DATA) = (16.6 ± 0.28) % WPf (MC) = 8.0 % WPf (DATA) = (8.90 ± 0.37) % WPf (MC) = 5.2 % WPf (DATA) = (6.0 ± 0.45) % WPf (MC) = 2.4 % WPf (DATA) = (3.25 ± 1.00) % Systematic check
Systematic check Frascati 19 Luglio 2007
α= − 0.027 ± 0.004stat ± 0.006 syst Results χ2/ndf = 13.72 / 17.
NEW approach: • 7 and only 7 pnc with • 21° < θγ< 159°and Eγ> 10 MeV • θγγ > 18° • Kin Fit with η mass constraint • (onDATAMη= 547.822 MeV/c2 ) • P(χ2) > 0.01 • 320 MeV < Eγrad < 400 MeV • AFTER PHOTON’S PAIRING • Kinematic Fit with π0mass • constraint Dalitz plot expansion • OLD approach: • 7 and only 7 pnc with • 21° < θγ< 159° and Eγ > 10 MeV • θγγ > 18° • Kin Fit with no mass constraint • P(χ2) > 0.01 • 320 MeV < Eγrad < 400 MeV • AFTER PHOTON’S PAIRING • Kinematic Fit with η and π0 mass constraints (on DATA Mη = 547.822 MeV/c2 )
NEW or OLD ? NEW APPROACH OLD APPROACH ……OLD APPROACH !!
Dalitz plot expansion • Now we have updated the measurement of a using: • Before the kinematic fit : qgg > 9° • In the kinematic fit on data : Mh = 547.874± 0.007 ±0.031MeV/c2 • MC sample generated according to a = -0.027 • New samples with different purity - efficiency • A correction of about 2% to the photon energies in the p0 rest frame.
qgg > 9° After kinematic fit After P(2) > 0.01 After E> 10 MeV After EVCL After 320 MeV < Erad < 400 MeV Afterg > 18°
qgg > 9° Low Med High
qgg > 9° Low Med High
New MC sample We have generated MC samples with different a values in input and we have fitted a on data: • We’ll use MC generated with: • = - 0.027. On this MC sample: • a = - 0.027 0.002 Status report on analysis Ponza 05 June 2008
3 new samples We have fix the cut on min c2< 5 obtaining: LOW Dc2 > 2.5 Pur 90.4% e 21% De / e 11% Res 0.1335 N = 948471 MEDIUM Dc2> 5 Pur 95% e 14% De / e 10% Res 0.1108 N = 614663 HIGH Dc2 > 9 Pur 97.3% e 7% De / e 10% Res 0.096 N = 333493
Resolution & efficiency Status report on analysis
Correction We have corrected the Data / MC discrepancy (at level of 1.5 %) with a smearing of the photon energies, obtaining:
Correction We have recovered the residual discrepancy (Low: h’ = 0.; Med: h’= 0.6%; High: h’ =0.9%),obtaining
Residuals in [0 – 0.7] = 0.0301 ± 0.0035stat
Systematic checks: Resolution The systematic uncertainty due to the resolution is obtained considering the fluctuation in the RMSdata / RMS MC
Systematic checks: Efficiency DATA NHigh / Nlow = 0.3516 ± 0.0007 NMedium / Nlow = 0.6481 ± 0.0011 MC NHigh / Nlow = 0.3511 ± 0.0003 NMedium / Nlow = 0.6461± 0.0005
Systematic checks: Efficiency Correction to the photon efficiency is applied weighting the Montecarlo events with a Fermi Dirac function obtained fitting the photon energy spectrum Data/MC discrepancy
Systematic checks: Efficiency Medium High Low
Systematic checks: WPF On DATA: Wrong pair fraction (MC) = 9.59 % Wrong pairfraction (DATA) = (10.01 ± 0.45) % Wrong pairfraction (MC) = 5 % Wrong pairfraction (DATA) = (5.51 ± 0.68) % Wrong pair fraction (MC) = 2.7 % Wrong pairfraction (DATA) = (3.31 ± 0.90) %
Systematic checks: WPF On DATA: Wrong pair fraction (MC) = 9.59 % Wrong pairfraction (DATA) = (10.01 ± 0.45) % Wrong pairfraction (MC) = 5 % Wrong pairfraction (DATA) = (5.51 ± 0.68) % Wrong pair fraction (MC) = 2.7 % Wrong pairfraction (DATA) = (3.31 ± 0.90) %
Final results 10-4 Status report on analysis
Conclusion 2005: we have published this preliminary result: = 0.013 ± 0.004stat ± 0.005 syst 2007: we have published this preliminary results: = 0.027 ± 0.004stat ± 0.006 syst 2009: we found this result: = 0.0301 ± 0.0035stat - 0.0036 syst + 0.0022 syst This result is compatible with the published Crystal Ball result: = 0.031 ± 0.004 And the calculations from the +- analysis using only the - rescattering in the final state. = 0.038 ± 0.003stat +0.012-0.008syst