1. PrimEx p0 radiative width extraction
Eric Clinton
University of Massachusetts Amherst
July 19, 2007

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 systematics. No
Misidentification – any systematics? 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 Warning—departure from analysis note

8. Apply Additional Cut and Veto Warning—departure from analysis note
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. 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

10. Timing cut vs. pion yield plateau
Original timing cut/data source
Timing cut vs. pion yield plateau
Timing cut set to ±5 ns

11. Integration range plateau

12. Fitting range plateau

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 (Cornell with FSI), Incoherent (Glauber)
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
Get invariant mass right to proper mock physics
Vet the Simulation
Push 4 vectors from experiment thru sim
See how p0 candidate spectrum look, look for losses
Turn off detectors, see how acceptance behaves

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

18. Turning off glass detectors HyCal Tungstate Acceptance Only

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

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

21. Fit to Data, and Extracted Width HyCal Tungstate Acceptance Extracted width – eV ± eV (1.63%)

22. Acceptance Corrected Cross Sections
PRELIMINARY
HyCal Tungstate Acceptance

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

24. 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: * (+)
Integration range (nom. = ±0.013 HMU’s)
± %
± %
± %
± NA
± %
± %
± %
No systemtatic effect will be claimed. Fit errors go up faster than any shifts above, and yield plateau for smaller pion angles is present.
Fit Range (nominal = ±0.029 HMU’s)
± %
± % * (-)
± %
± NA
± % * (+)
± %
± %
± %
± %
Total Error will be “asymmetric” since many of “systematic effects” tend to go in only one direction.
All positive contribution will be added in quadrature for the total “positive systematic error”
Vice versa for the negative contributions
***Nominal = Double gaussians with 2nd order polynominal
DG3Po = Double gaussians with 3rd order polynomial
TG2Po = Triple gaussians with 2rd order polynominal

25. Error Accounting HyCal Tungstate acceptance
Source
% Error
Error from Fit
+1.63 %, %
Photon flux
+1.10 %, %
Cluster Position Reconstruction
+0.43 %, %
Fitting Range
+0.31 %, %
Signal Lineshape
+0.26 %, %
Background Model
+0.08 %, %
Dalitz Decay
+0.03 %, %
Target Thickness
+0.04 %, %
Veto Counter Inefficiency (if used)
+0.06 %, %
Total (w/ Veto, w/out Error from Fit)
+1.25 %, %
Total (with Veto)
%, %

26. Result HyCal Tungstate Acceptance
Gp0→gg = eV ± eV eV – eV
Gp0→gg = eV ± 1.63 % +1.25% %

27. Future work Work another nuclear incoherent generator
Latest from Tulio in hand
Evolve cross sections to the weighted mean photon energy
“Conjoined” analysis
Lead Target Data?

28. Extra slides

29. The Veto—how it changes the angular spectrums

30. Extracting a Photon Misidentification Efficiency PME = 0. 80 ± 0
Extracting a Photon Misidentification Efficiency PME = 0.80 ± 0.057% (HYCALCLUSTER veto flag == 4) PME = 2.20 ± 0.16% (HYCALCLUSTER veto flag == 3) PME = 2.80 ± 0.21% (HYCALCLUSTER veto flag == 2) PME = 3.20 ± 0.23% (HYCALCLUSTER veto flag == 1) ** ongoing work

31. Photon flux

32. Poor Elasticity

33. Energy Correction Across entire HyCal acceptance

34. Tracking Threshold, resolution, and centroid tuning

35. Turning off glass detectors Entire HyCal Acceptance

36. Turning off tungstate detectors Entire HyCal Acceptance

37. Efficiencies as a function of the photo-pion process, entire HyCal acceptance

38. Geometric efficiency and reconstruction (cut) efficiency
Geometric efficiency and reconstruction (cut) efficiency. Entire HyCal Acceptance