1. PrimEx p0 radiative width extraction
Eric Clinton
Duke University
April 5, 2008

2. Outline Data Source and cuts Event selection
Hybrid Mass Signal enhancement
Yields
Yields over entire HyCal acceptance presented for information on Incoherent photo-pion production only
Systematic effects from yield extraction
Simulation
Results
Sytematic Error Analysis

3. Data Source and Cuts
mysql -h primexdb -u primex_user book_keeping -b --execute="select run from run_list where radiator='A' and target='carbon' and type='pi0' and production='good';" > run_list.example
mysql -h primexdb -u primex_user book_keeping -b --execute="select run from run_list where radiator='B' and target='carbon' and type='pi0' and production='good';" > run_list.example
1.) Two or more clusters/event.
2.) Minimum three (3) (PbWO4 or lead glass) detectors to define a “cluster”.
3.) 50 MeV or greater central (PbWO4 or lead glass) crystal detector energy in cluster.
4.) 10 MeV or greater minimum deposited energy in (PbWO4 or lead glass) detector.
5.) Max cluster energy 8 GeV.
6.) gg invariant mass greater than GeV in at least one of the cluster pairs.
7.) Elasticity (cluster pair energy sum/tagger energy) greater than 0.70.
8.) Cluster energy greater than 0.5 GeV.
9.) Cluster X or Y position must be greater than 4.1 cm.
10.) Cluster pair energy sum between 3.5 and 6.5 GeV -- additional software cut not imposed on the skim, but imposed later:
11.) Timing cut of -15 ns to +5ns.
“pi0gains” used as calibration

4. Event selection Eliminate Tagger and HyCal combinatorics
Likelihood
Event entries have invariant mass, elasticity, and timing
Which entry to choose in a mutli-entry event?
Which is "most likely"?
Fit invariant mass, elasticity, timing signal and background
Fitted signal lineshape as probability density function (PDF)
Evaluate the PDF for each parameter for each entry.
Three individual likelihoods. PDFInvariant mass, PDFElasticity, PDFTiming
Total likelihood = PDFInvariant mass × PDFElasticity ×PDFTiming
Entry with highest total likelihood "wins".

5. Misidentification Any Systematic effects. No
Misidentification Any Systematic effects? No. MisID is random, and event selection tends to pick smaller production angle pions.

6. Rotation of 2-D data onto 1-D Try to enhance signal to noise
Original 2-D data
Elasticity vs.Invariant Mass
New 1-D signal
AKA “Hybrid Mass”

7. Additional “Diagonal” Data Cut

8. Apply Diagonal Cut and Veto
Result
Greatly improved signal to noise
Removes 3rd order curvature from background
Requires well understood veto
Veto systematic error small in comparison to fit error and other systematic effect improvements

9. What does the “diffuse/diagonal” cut remove?

10. Plateau Elastic Pion Yields Additional minimization of signal to noise
Timing
Elastic p0 as a function of the timing cut
Integration Range (left, below)
Elastic p0 as a function of the integration range
Fitting Range (right, below)
Elastic p0 as a function of the fitting range

11. Timing cut vs. pion yield plateau
Original timing cut/data source
Timing cut vs. pion yield plateau
Timing cut set to ±3 ns

12. Radiative width vs. the Integration (Background Subtraction) range Incoherent = Sergey
Integration Range = HMU’s
Fitting Range = HMU’s

13. Selected Hybrid Mass Fits

14. p0 yields as a function of production angle.
These yields are extracted
from a data set where the
“diagonal” and veto cuts are
applied.
Final radiative width MUST
correct for veto
Photon Misidentification.

15. Yield extraction for various signal and background models

16. Simulation Work Thrown with E-Channel Photon flux weighting
Primakoff (with FSI), Coherent, Incoherent (Tulio’s latest and Sergey’s next to latest)
Energy correction added
Energy lost out back of HyCal, out of cluster mask
Added back about 10% of energy
Tracking threshold tuned
Proper shower development
Resolution and centroid tuned
Closely match simulation mass and elasticity to data
Vet the Simulation
Push 4 vectors from experiment thru sim
See how p0 candidate spectrum look, look for losses

17. Energy “loss” and correction in simulation
Reasons: Energy lost out back of HyCal,
Finite cluster size, airgap.
Energy leaking out of cluster mask but remain in HyCal. Simulation
Before any correction
Before and after
Energy leaking out of cluster mask but remaining in HyCal. Experimental data

18. Tuning experimental and simulation resolutions

19. Putting physics events thru the Simulation
Around 99.2% fidelity

20. Efficiencies as a function of the photo-pion process, HyCal Tungstate acceptance

21. Geometric efficiency and reconstruction (cut) efficiency HyCal tungstate acceptance
Turning off cluster energy
and invariant mass cuts

22. Fit to Data, and Extracted Width HyCal Tungstate Acceptance Extracted width – ± eV (± 1.57 %), fit to 2.5o** Extracted width – ± eV (± 1.64 %), fit to 2.0o** Both radiators A and B
Fit out to 2.5o
Fit out to 2.0o
**Plots reports slightly incorrect width

23. Fit to Data, and Extracted Width HyCal Tungstate Acceptance
Radiator B only
Extracted width – ± eV (± 1.89 %), fit to 2.5o Extracted width – ± eV (± 1.88 %), fit to 2.0o
Radiator A only
Extracted width – ± eV (± 2.89 %), fit to 2.5o Extracted width – ± eV (± 2.75 %), fit to 2.0o

24. Rad. Width vs. fit and point Incoherent = Sergey

25. Interference angle vs. fit end point Incoherent = Sergey

26. Acceptance Corrected Cross Sections

27. Systematic error sources?
Extracted yields over the entire pion angle range must be stable as these parameters are varied.

28. Systematic Effects from Yield Extraction HyCal Tungstate acceptance
Nominal NA
Cluster Position Finding Method
Method 0:
Method 1: * (+)
Method 2:
Method 4: * (-)
Lineshape (degrees of freedom)***
DG3Po: * (-)
TG2Po: * (+)
Incoherent theory model
Tulio % * (+)
***Nominal = Double gaussians with 2nd order polynominal
DG3Po = Double gaussians with 3rd order polynomial
TG2Po = Triple gaussians with 2rd order polynominal

29. Error Accounting HyCal Tungstate acceptance—Both radiators, fit to 2
Error Accounting HyCal Tungstate acceptance—Both radiators, fit to 2.5o
Source
% Error
Error from Fit
+1.57 %, %
Photon flux
+1.10 %, %
Cluster Position Reconstruction
+0.47 %, %
Signal Lineshape
+0.66 %, %
Background Model
+0.28 %, %
Dalitz Decay
+0.03 %, %
Target Thickness
+0.04 %, %
Veto Counter Inefficiency
+0.06 %, %
Incoherent theory model
+0.40 %, %
Total
%, %

30. Result HyCal Tungstate Acceptance
Gp0→gg = ± eV eV – eV
Gp0→gg = ± 1.57 % % +1.45% %

31. Extra slides

32. Scaled response functions
Fit parameters at 2.5o
Process Value Error
Primakoff e-05
Coherent
Interference e-05
Incoherent

33. The Veto—how it changes the angular spectrums