π0 Lifetime Final ResultsDustin McNulty

MIT/UMassmcnulty@jlab.org

July 1, 2010

PrimEx Collaboration Jefferson Lab Hall B'

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What’s been done recently:

• Fit uses Tulios latest/final nuclear incoherent cross section calculation

• Fit uses same nuclear coherent cross section parameterization as Ilya:

(2.28E0)2 * ((2E0mp+m2p)0.641)2

• Fit uses Sergey’s latest Coulomb and Strong form factor calculations

(same as Ilya)

• Fit uses high statistics MC generated cross section shapes (smeared

by exp resolutions)

• Performed check of the fitting algorithm stability for12C and208Pb

• Performed careful comparison of12C cross section with Ilya’s

Dustin McNulty, /pio/ analysis Meeting, July 1, 2010 1

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12C: 4 parameter Independent Fit

(degrees)θ Production Angle, 0π0 0.5 1 1.5 2 2.5

o Y

ield

/0.0

20 π

0

100

200

300

400

500

600

700

800C, crystal only)12 Photoproduction yield (0π

/ndf : 128.81 / 1212χ

Dustin McNulty, /pio/ analysis Meeting, July 1, 2010 2

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208Pb: 4 parameter Independent Fit

(degrees)θ Production Angle, 0π0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

o Y

ield

/0.0

20 π

0

100

200

300

400

500

Pb, crystal only)208 Photoproduction yield (0π

/ndf : 79.98 / 832χ

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7 parameter Combined Fits

(degrees)θ Production Angle, 0π0 0.5 1 1.5 2 2.5

o Y

ield

/0.0

20 π

0

100

200

300

400

500

600

700

800C, crystal only)12 Photoproduction yield (0π

/ndf : 128.83 / 1232χ

(degrees)θ Production Angle, 0π0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

o Y

ield

/0.0

20 π

0

100

200

300

400

500

Pb, crystal only)208 Photoproduction yield (0π

/ndf : 83.35 / 852χ

.

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Yield Fit Parameter Summary: 12Cand 208PbΓγγ± fit err in eV (fit χ2)

Target 4 Parm Indep. Fits 7 Parm Comb. Fits

12C 7.938±0.153 (1.06) 7.959±0.115 (1.05)208Pb 7.985±0.174 (0.96) 7.959±0.115 (0.98)

bNC± fit err

12C 1.651±0.033 1.653±0.032208Pb 1.184±0.111 1.190±0.103

φ± fit err in radians

12C 1.07±0.044 1.07±0.040208Pb 1.13±0.080 1.12±0.073

bINC± fit err

12C 0.89±0.069 0.89±0.068208Pb 0.19±0.178 0.44±0.171

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12C: Fitter Stability

bnc_histEntries 200

Mean 1.652

RMS 0.01833

1.5 1.55 1.6 1.65 1.7 1.75 1.80

2

4

6

8

10

12

14

16

18

20

22bnc_histEntries 200

Mean 1.652

RMS 0.01833

bp_histEntries 200

Mean 7.937e-06

RMS 9.096e-08

7.5 7.6 7.7 7.8 7.9 8 8.1 8.2 8.3

-610×0

2

4

6

8

10

12

14

16 bp_histEntries 200

Mean 7.937e-06

RMS 9.096e-08

phi_histEntries 200

Mean 1.068

RMS 0.02573

0.9 0.95 1 1.05 1.1 1.15 1.20

2

4

6

8

10

12

14

16

18

20 phi_histEntries 200

Mean 1.068

RMS 0.02573

binc_hist

Entries 200

Mean 0.8864

RMS 0.03837

0.6 0.7 0.8 0.9 1 1.1 1.20

2

4

6

8

10

12

14binc_hist

Entries 200

Mean 0.8864

RMS 0.03837

Dustin McNulty, /pio/ analysis Meeting, July 1, 2010 6

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208Pb: Fitter Stability

bnc_histEntries 100

Mean 1.177

RMS 0.06428

0.6 0.8 1 1.2 1.4 1.6 1.8 20

1

2

3

4

5

6

7

8

9 bnc_histEntries 100

Mean 1.177

RMS 0.06428

bp_histEntries 100

Mean 7.985e-06

RMS 1.1e-07

7.5 7.6 7.7 7.8 7.9 8 8.1 8.2 8.3 8.4 8.5

-610×0

1

2

3

4

5

6

7

8

9 bp_histEntries 100

Mean 7.985e-06

RMS 1.1e-07

phi_histEntries 100

Mean 1.129

RMS 0.04955

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.50

2

4

6

8

10phi_histEntries 100

Mean 1.129

RMS 0.04955

binc_histEntries 100

Mean 0.199

RMS 0.09227

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

1

2

3

4

5

6

7 binc_histEntries 100

Mean 0.199

RMS 0.09227

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12C Differential Cross Section Comparison

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12C Total Cross Section Comparison

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12C dsig Cross Section Ratio Comparison

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12C Total Cross Section Ratio Comparison

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Systematic Error Table, part 1

Item Error (%)

Photon Flux ±0.97

Target Thickness ±0.1

Branching Ratio (π0→ γγ) ±0.03

Yield Extraction ±1.77

Timing Accidental Bkgd Corr. ±0.22

ω Bkgd Subtraction (±20%) ±0.26

Tagged Photon Energy ±0.1

Fiducial Acceptance ±0.30

Trigger Efficiency ±0.1

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Systematic Error Table, part 2

Item Error (%)

Timing Cut ±0.30

Elasticity Cut ±0.25

Veto Cut ±0.17

Theory Parameters ±0.42

Incoherent Shape ±0.28

Error Due to Group inconsistancy ±1.1

Total Quadrature Sum (parts 1 & 2)±2.44

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Summary

• Results have been stable within a standard deviation for years and the

method has been stable

• Since last year and recent work,Γγγ results from12C have increased

by ∼ 0.06eV, and from208Pb have decreased by∼ 0.075eV

• I’ve done what has been asked and there have been no major

problems found

• I’ve worked hard mainly on the12C XS’s because I’m short on time

• XS comparisons with Ilya indicate small differences in shape in

certain angular regions but none are bigger than 2 sigma and so are

not serious

• However, these differences indicate that we should be careful to not

underquote the errors

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Final Results

4 Parameter Independent Fits

target Γγγ fit (stat) err syst err total err

12C: 7.938 0.153(1.93%) 0.194(2.44%) 0.247(3.11%)208Pb: 7.985 0.174(2.18%) 0.195(2.44%) 0.261(3.27%)

Average 7.962 0.164(2.05%) 0.195(2.44%) 0.255(3.20%)

7 Parameter Combined-Γγγ Fits

target Γγγ fit (stat) err syst err total err

12C: 7.959 0.115(1.45%) 0.194(2.44%) 0.226(2.84%)208Pb: 7.959 0.115(1.45%) 0.194(2.44%) 0.226(2.84%)

Average 7.959 0.115(1.45%) 0.194(2.44%) 0.226(2.84%)

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