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 = ×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.
elastic p0 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. contribution from r and w cross-section uncertainty
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 G f Slope is -0.011±0.036eV/ns
Fit parameters behavior VS tdif window G f
Slope is ±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. Bg from additional hits during ADC integration time= +
MC event
Clock-trig.
(same Run #)
Final product
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 Lead: 7.82±0.18eV
with accidentals correction 7.90±0.18eV
Lead: ±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 Target number of atoms 0.05 Photon beam flux 0.97
p Branching Ratio
0.03
Beam energy uncertainty
0.13
Beam position and slope uncertainty
0.1
Beam width uncertainty
0.3
Production angle resolution
0.25
Hycal response function
0.45*
Hycal z-position uncertainty
0.4*
Hycal efficiency simulations
0.3*
Target absorption
0.11
Trigger efficiency
<0.1

30. Error budget (continuation)
ADC status during the run
<0.1
Beam selection efficiency
0.2
Energy cut on single g
Timing cut (“tdif”)
0.13
gg invariant mass fit (signal / background separation)
0.9*
Theory parameters uncertainties
0.09
Background from accidentals
0.25
w and r background subtraction
0.24
Incoherent production shape
0.12
Total (quadratic) sum
1.6

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)