p 0 life time analysis: general method, updates and preliminary result

1. p0 life time analysis:general method, updates and preliminary result 02/22/2008 I.Larin

2. Data sample selection • Runs after shutdown, radiator B • Carbon: 94 runs (100nA, 130nA and 110nA), flux = 1.364×1012 • Lead: 42 runs (90nA, 115nA and 110nA), flux = 0.772 ×1012 Runs stable in terms of beam parameters and hardware conditions were selected

3. Event selection • Currently: PWO part of HyCal • Timing cut: |tdif| < 4ns • Eg > 0.5GeV Resolution for time difference between MOR and Hycal signals ~1.0…1.2 ns Selected events Time difference between MOR and Hycal, [ns]

4. Yield extraction: elastic 0 • All two cluster combinations were split in terms of production angle • Inv. Mass distribution with elasticity constraint has been used to extract p0 yield p0 mass with elasticity c. elasticp0 production angle

5. Angular spectrum for elastic 0 Carbon Lead

6. Possible Sources of background • Bg in non resonant 2g spectra • Vector mesons decays • Non resonant multiple pion production • Accidentals bg • Bg from beam hits substituted by accidental hits, which have “better” tdif • Out of target events • Bg from additional hits during ADC integration time

7. Bg in non resonant 2g spectra • bg with linear shape and line parameters obtained from the data (individually for each T-counter and each q-bin) was added to MC distributions and the same fitting procedure was performed as for the data MC data

8. w and r background subtraction: Carbon target: contribution from r and w was varied with its cross-section uncertainty (which is 20%) Estimated error budget contribution by this variation is 0.24%

9. Accidentals bg • No HyCal only trigger events – attempt to estimate effect indirectly by widening timing window in analysis Elastic p0 yield for different q shows different slope VS tdif window q = 0 – 0.25 deg q = 1.75 – 2 deg

10. Accidentals bg Fit parameters behavior VS tdif window G f Slope is -0.011±0.036eV/ns

11. Accidentals bg Fit parameters behavior VS tdif window CS CI

12. tdif cut: eff. & systematics ADC tdif mean VS ID • Individual counter tdif • from p0 runs: • 2 clusters • E > 3.5GeV • E2 <1.5GeV ADC tdif s VS ID

13. tdif cut: eff. & systematics tdif simulated for PWO (all ADCs uniformly populated) • PWO part: • 4ns cut: 0.09%±0.13% losses • 4.5ns cut: 0.003%±0.015% losses +/- std deviation in mean +/- std deviation in s

14. Bg from beam hits substituted by accidental hits, which have “better” tdif Best in time candidate, 4ns window Second after the best candidate, 2ns window to enhance the peak

15. Bg from beam hits substituted by accidental hits, which have “better” tdif • Both simulations and data show that such bg events will form the peak ~6 times wider than the signal peak • Number of lost beam candidates by substitution has been estimated from the second distribution (scaled) It is 0.85%±0.3% for Carbon, 0.52%±0.13% for Pb • Effect of wide structure appearance instead of substituted hits taken into account in the fit procedure. It compensates 40%±13% of lost by substitution hits

16. Out of target events Empty target run 4752, flux = 0.0121012 Elasticity of 2 clusters Inv. mass of 2 clusters

17. MC event Clock-trig. (same Run #) Final product + = Bg from additional hits during ADC integration time Sparsification (ADC threshold) is applied:

18. Fit to Extract 0 Decay Width p0 production terms: • Coulomb • Nuclear Coherent • Their interference • Incoherent • All together C Pb • Theoretical distributions of these processes were smeared with experimental resolution

19. Formfactor updates • Distorted formfactors have been calculated with oscillator model charge and nuclear density distributions • Finite nucleon radius is taken into account • Charge and nuclear densities are not exactly the same anymore • Shadowing parameter x=0.25 was introduced (full shadowing x=1.0)

20. Coulomb Formfactor

21. Strong Formfactor

22. Theory parameters: contribution to the systematics Variations in absorption parameter s 0.06%

23. Theory parameters: contribution to the systematics Variations in shadowing parameter x 0.06%

24. Theory parameters: contribution to the systematics Variations in power parameter in energy dependence of strong amplitude n  0.04%

25. Incoherent production • Two models were used for incoherent production: • Glauber – Sergey’s most up-to-date • Cascade Model – Tulio’s calculations • naive “Cornell” formula is not using for further analysis

26. Theory parameters: contribution to the systematics Variations in incoherent model  0.12% Wide incoherent shape variations give negligible variation in rad. width, unless the shape is close to other production terms (like “Cornell”, which is close to Coherent shape)

27. dN/dq fit 12C 208Pb

28. dN/dq fit • Carbon: 7.86±0.18eV • with accidentals correction 7.90±0.18eV • Lead: 7.82±0.18eV (accidentals correction to be implemented) • Not finalized yet: • will try new fitting procedure: simulated distribution from GEANT instead of double gaussian smearing • add lead glass part (could be properly done with the new procedure)

29. Error budget

30. Error budget (continuation)

31. Possible ways to minimize systematics • Increase total statistics to study syst. in more details • Hycal energy response function: setup simple leakage detector • Experimental acceptance: measure HyCal distance with precision of at least 3-5mm • Background from accidentals: either include pre scaled accidentals or change trigger to HyCal • Time equalization is also needed for ADCs (after dinode amplitude equalizing)