° status report analysis details: overview; “where we are”; plans: before finalizing result..

° status report

analysis details: overview; “where we are”;

plans: before finalizing result..

I.Larin 02/13/2009

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Data sample selection

• Carbon data have been rerun on new Linux OS (ifarms) with updated flux counting

(all flux corrections are incorporated)• Some of “end run files” look suspicious and

were excluded with negligible statistics losses• Total flux accounted for carbon target for this

analysis 1.396×1012

• Lead target rerun is in progress

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° yield VS flux ratio stability

“tail”

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Data sample for Carbon• List of runs used:

4979 4980 4981 4982 4984 4985 4987 4988 4989 4998 4999 5001 5002 5003 5004 5012 5013 5016 5018 5030 5032 5033 5034 5035 5037 5039 5041 5042 5043 50445047 5050 5051 5054 5055 5056 5057 5058 5059 5159 5160 5163 5165 5166 5168 5171 5172 5175 5180 5181 5183 5184 5185 5186 5187 5188 5189 5191 5192 5193 5195 5196 5199 5200 5201 5202 5203 5204 5205 5206 5207 5208 5209 5213 5214 5215 5216 5217 5218 5219 5223 5224 5226 5227 5228 5233 5236 5237 5238 5239 5240 5241 5242

some “end run files” were excluded

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Event selection

• M > 80 MeV• E > 0.5GeV• |tdif| < 4.5ns (after additional alignment)

• “best-in-time” beam candidate only• PWO-only region (except shielded central square)

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Event reconstruction• Variables to be analyzed after event selection:

– R – elasticity (all 0s in analysis supposed to be elastic with known beam energy (properly tagged). Deviation of parameter R from 1 comes from energy resolution or misidentified beam

– M – invariant mass of two clusters (any deviations from 134.976(6)MeV are from Hycal resolution

– – production angle. This variable allows to separate different 0

production mechanisms and extract Primakoff part of cross-section

RM

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° yield extraction• First split events on variable (production angle)• Then fit Mc (invariant mass) distributions for each bin• is a function of reconstructed gammas coordinates and

energies (x1,y1,x2,y2,e1,e2) :– e1, e2 – could be corrected using mass and elasticity constraint:

MC distributions before and after constraint

e1 e2

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Reconstruction efficiency convoluted with resolution

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θ-reconstructed distribution obtained from MC for each E-channel energy and for each 0.005 θ-actual bin.

This insures correct calculation with non-gaussian resolution shape.

actual measured transition matrix normalized to resolution

Correction to efficiency for background:first approximation

MC data

Bg simulated according to polynomial fit of the data for the given bin

Corrections to reconstructed number of °s for MC,(i.e. efficiency correction bin by bin)

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• More close agreement between MC distributions and the data could be useful:– Use of the same ° shape parameters in MC as in

the data fit– Use of more close to the data background shape

in MC:• Use of empty target data (increase stat. by picking up

adjacent theta bin – factor of 3 for Carbon)• Background simulation for empty target and non-

elastic °s

Further correction to efficiency for background

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Applying theory functionsTheory function use of transition matrix bin by bin function to fit data

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List of correction factorsapplied to MC efficiency

• Br ratio 0.988• Hycal resp. function 0.995

Carbon data:• Accidentals correction 0.994 (|tdif|<4.5ns )• Best-in-time beam selection 0.9916• Target impurity 1.0007

Lead data• Best-in-time beam selection 0.997• Target absorption (VS carbon) 0.9927

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Invariant mass fit: free shape of ° peak

Inv. mass distribution for “first” bin (0 – 0.02deg)

No constraint for Elasticity and mass constraint applied for

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dN/d yield extraction: effect of using different E energies for

0.02 binning -> 7.65eV 0.02 binning -> 7.86eV

Elasticity and mass constraint applied for

No constraint for

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Fit with the fixed shape of signalInv. mass distribution for ALL bins (0 – 2.50deg)

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Inv. mass distribution for “first” bin (0 – 0.02deg)

No constraint for Elasticity and mass constraint applied for

Invariant mass fit: fixed shape of ° peak

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Peak parameters fixed for each0.5deg. bins individually

dN/d yield extraction: effect of using different E energies for

0.02 binning -> 7.63eV 0.02 binning -> 7.68eV

Elasticity and mass constraint applied for

No constraint for

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Inv. mass distribution for “first” bin (0 – 0.02deg)

No constraint for Elasticity and mass constraint applied for

Invariant mass fit: fixed shape of ° peak

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Peak parameters the same for all

bins

dN/d yield extraction: effect of using different E energies for

0.02 binning -> 7.83eV 0.02 binning -> 7.86eV

Elasticity and mass constraint applied for

No constraint for

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dN/d yield extraction: effect of different binning

0.02 binning -> 7.86eV 0.05 binning -> 7.91eV

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Elasticity and mass constraint applied for

Elasticity and mass constraint applied for

Invariant mass fit: possible ways to cross check

• Check of ° inv. mass shape with increased statistics(include more stat. from less “reliable” runs)

• Out-of-target (“empty target”) background simulation (understanding the origin)

• Apply this background to MC (add adjacent bins for carbon to increase “empty” statistics)

• Add “empty” statistics to lead to double effect of background presence

• Unbinned M fit• Try “hybrid mass” cut• Check with unconstrained analysis

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dN/d fit: applying to Dustin’s cross section

Comparing extracted yield fit with yield renormalized toDustin’s cross section(no constraint on applied)

Renormalized fit: 0.9% higher

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Target properties 0.07

Photon beam flux 0.97

Branching Ratio 0.03

Beam parameters uncertainty 0.34

Trigger efficiency 0.1

Hycal response function 0.45

Production angle resolution 0.25

Setup acceptance 0.51

Event selection 0.33

Yield extraction 0.9 ? 1.5

Accidentals correction 0.25

and background subtraction 0.24

Theoretical uncertainties

Total

0.15

1.6 ? 2.0

Error budget [%]

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Conclusion

• With increasing of precision, number of details needed be taken into account grows geometrically

• Stat. VS Syst. error: available statistics applies certain limitation for precision with what we can know some of systematical error items

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Things to be done to finalize result(a short plan)

• More detailed study of M fit systematics• Background simulation• Fit systematics study with empty target data• Update Lead analysis• Use of Lead Glass part of Hycal• Look at unconstrained yield extraction• Finalize theory issues• Review HyCal reconstruction code

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