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Status of the  0  Experiment

Status of the  0  Experiment. A. Gasparian NC A&T State University, Greensboro, NC for the PrimEx Collaboration. Outline Physics Motivation PrimEx-I experiment and results Improvements over Primex-II experiment PrimEx-II Summary.

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Status of the  0  Experiment

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  1. Status of the 0 Experiment A. Gasparian NC A&T State University, Greensboro, NC for the PrimEx Collaboration Outline • Physics Motivation • PrimEx-I experiment and results • Improvements over Primex-II experiment • PrimEx-II • Summary

  2. Symmetries in QCD and Light Pseudoscalar Mesons • Classical QCD Lagrangian in Chiral limit is invariant under: • Chiral SUL(3)xSUR(3) spontaneously broken: • 8 Goldstone bosons (π,K,η) • UA(1) is explicitly broken: (Chiral anomalies) • Γ(0→), Γ(→), Γ(’→) • Mass of 0 • Massive quarks, SU(3) broken: • Goldstone bosons are massive • Mixing of π0ηη’ π0, η, η’ system provides a rich laboratory to study the symmetry structure of QCD. PrimEx experimental program: Γ(0→), Γ(→), Γ(’→) decay widths F(*→0), F(* →), F(* →) transition form factors • 0 mass is smallest  less mixing effects • Γ(0→) decay width is direct test of Chiral anomaly prediction in QCD at our energies Hall D Coll. meeting, Feb. 4, 2011

  3. 0 decay width (Theory) • 0→ decay proceeds primarily via the Chiral anomaly in QCD. • The chiral anomaly prediction is exact for massless quarks: • Corrections to the chiral anomaly prediction: (u-d quark masses and mass differences) Calculations in NLO ChPT: (J. Goity, at al. Phys. Rev. D66:076014, 2002) Γ(0) = 8.10eV ± 1.0% ~4% higher than LO, uncertainty: less than 1% • Recent calculations in QCD sum rule: (B.L. Ioffe, et al. Phys. Lett. B647, p. 389, 2007) • Γ() is only input parameter • 0- mixing included Γ(0) = 7.93eV ± 1.5% 0→ • Precision measurements of (0→) at the percent level will provide a stringent test of a fundamental prediction of QCD. Hall D Coll. meeting, Feb. 4, 2011

  4. Experimental Methods: Decay Length Measurement (Direct Method) • Measure 0decay length distribution • 1x10-16 sec  too small to measure solution: Create energetic 0 ‘s, L = vE/m But, for E= 1000 GeV, Lmean 100 μm very challenging experiments 1984 CERN experiment: P=450 GeV proton beam Two variable separation (5-250m) foils Result: (0) = 7.34eV3.1% (total) • Major limitations of method • unknown P0 spectrum • needs higher energies for improvement 0→ Hall D Coll. meeting, Feb. 4, 2011

  5. Primakoff Method ρ,ω 12C target Primakoff Nucl. Coherent Nucl. Incoh. Interference • Primakoff coherent cross section measurement required Challenge: Extract the Primakoff amplitude Hall D Coll. meeting, Feb. 4, 2011

  6. Previous Primakoff Experiments • DESY (1970) • bremsstrahlung  beam, E=1.5 and 2.5 GeV • Targets C, Zn, Al, Pb • Result: (0)=(11.71.2) eV 10.% • Cornell (1974) • bremsstrahlung  beam: E=4 and 6 GeV • targets: Be, Al, Cu, Ag, U • Result: (0)=(7.920.42) eV 5.3% • All previous experiments used: • Untagged bremsstrahlung  beam • Conventional Pb-glass calorimetry Hall D Coll. meeting, Feb. 4, 2011

  7. PrimEx Experiment • Requirements of Setup: • high angular resolution (~0.5 mrad) • high resolutions in calorimeter • small beam spot size (‹1mm) • Background: • tagging system needed • Particle ID for (-charged part.) • veto detectors needed • JLab Hall B high resolution, high intensity photon tagging facility • New pair spectrometer for photon flux control at high intensities • New high resolution hybrid multi-channel calorimeter (HYCAL) Hall D Coll. meeting, Feb. 4, 2011

  8. PrimEx-I Status • NewExperimental setup commissioned with beam: (10 days in Sept. 2004) • Beamline commissioned • All new detectors commissioned • Electronics and new readout system commissioned • New DAQ commissioned • HyCal gain equalizing and calibration scans done • Pair Spectrometer commissioned • Physics data runs started just after commissioning: (45 days, Oct. – Nov. 2004) • Good data set on 12C target • Good data set on 208Pb target • good statistics for Compton runs • good statistics on e+e- pair production • Final results have been submitted for publication Hall D Coll. meeting, Feb. 4, 2011

  9. Results from PrimEx-I Experiment • Nuclear targets: 12C and 208Pb; • 6 GeV Hall B tagged beam; • experiment performed in 2004 12C 208Pb Hall D Coll. meeting, Feb. 4, 2011

  10. PrimEx-I Result • PrimEx-I achieved 2.8% precision (total): (0) = 7.82 eV 1.8% (stat) 2.1% (syst.) PrimEx-II projected 1.4% PrimEx-I 7.82eV2.8% • Task for PrimEx-II: to achieve 1.4% precision: Projected errors: 0.5% (stat.) 1.3% (syst.) Hall D Coll. meeting, Feb. 4, 2011

  11. Estimated Systematic Errors Hall D Coll. meeting, Feb. 4, 2011

  12. Improvements for PrimEx-II: 1.4 % Total Error 0.5 % Stat. 1.3 % Syst. • New DAQ with 5 kHz rate, (factor of 5 gain) • Implement more stringent trigger (factor of 2 gain) (better HyCal gain equalizing) • However, the allocated time was barely enough for one target with 0.5% stat error only. • Better control of Background: • Add timing information in HyCal • Improve photon beam line • Improve PID in HyCal (add more veto counters, X and Y direction) • Measure HyCal detection efficiency (with TAC module) Hall D Coll. meeting, Feb. 4, 2011

  13. The PrimEx-I Beam line

  14. Improvements in PrimEx-II Photon Beam Line • Make the primary collimator “tapered”: (with 1 mm thick and 10 cm long insertion, diameter 12.7 mm). Monte Carlo Simulations • Upgrade the Permanent Magnet from 1 unit to 3 units. • Make the Pb-shielding wall’s hole diameter smaller (from 1.53” to 0.8”). • Extend distance from primary coll. to Pb-shielding wall by 32 cm (moving PS with production targets). Total relative gain: PrimEx-I config. 100 % suggested PrimEx-II config. 19 % Expect ~5 times less background events !!! Hall D Coll. meeting, Feb. 4, 2011

  15. Add Timing in HyCal Hall D Coll. meeting, Feb. 4, 2011

  16. PrimEx Current Result Hall D Coll. meeting, Feb. 4, 2011

  17. PrimEx-II Run Status • Experiment run period: Sep. 27 to Nov. 10. • Physics data collected: • First target, 28Si, completed at required level of statistics (~0.6%). • Second target, 12C, data taking completed in half only (~1.2%) • Good statistics for Compton is collected • Good statistics for e+e- pair production is collected Hall D Coll. meeting, Feb. 4, 2011

  18. PrimEx-II: Event Selection Hall D Coll. meeting, Feb. 4, 2011

  19. PrimEx-II: 0Event Distribution vs. Production Angle Very preliminary (90% of data) Very preliminary (30% of data) Hall D Coll. meeting, Feb. 4, 2011

  20. PrimEx-II: By-Products,  0+0+0 Detection of  produced in He-bag close to HyCal Z-vertex resolution Hall D Coll. meeting, Feb. 4, 2011

  21. PrimEx-II: By-Products,   0+ (crystal part only) Hall D Coll. meeting, Feb. 4, 2011

  22. PrimEx-II: By-Products, /  0+0+ Hall D Coll. meeting, Feb. 4, 2011

  23. PrimEx-II: By-Products, a0  + 0 Hall D Coll. meeting, Feb. 4, 2011

  24. Summary • The 0 lifetime is one of the few precision predictions of QCD. • Percent level measurement is a stringent test of QCD at these energies. • High resolution, high intensity tagging facility together with recent developments in calorimetry make the Primakoff method one of the best way to reach the required accuracy in 0 decay width. • Compton and pair-production cross section measurementsdemonstrate that the systematic errors are controlled at the 1.3% level. • The PrimEx setup is capable of percent level cross section measurements. • PrimEx-I achieved 2.8% total error for decay width. • Expected PrimEx-II result at 1.5% level Hall D Coll. meeting, Feb. 4, 2011

  25. The End Hall D Coll. meeting, Feb. 4, 2011

  26. 0 Event selection (cont.) Three groups analyzed the data independently Hall D Coll. meeting, Feb. 4, 2011

  27. Electromagnetic Calorimeter: HYCAL • Energy resolution • Position resolution • Good photon detection efficiency @ 0.1 – 5 GeV; • Large geometrical acceptance PbWO4 crystals resolution Pb-glass budget Kinematical constraint HYCAL only Hall D Coll. meeting, Feb. 4, 2011

  28. PrimEx Current Result Hall D Coll. meeting, Feb. 4, 2011

  29. Luminosity Control: Pair Spectrometer Measured in experiment: • absolute tagging ratios: • TAC measurements at low intensities • relative tagging ratios: • pair spectrometer at low and high intensities Scint. Det. • Uncertainty in photon flux at the level of 1% has been reached • Verified by known cross sections of EM processes • Compton scattering • e+e- pair production Hall D Coll. meeting, Feb. 4, 2011

  30. Beam Time Request • Will provide 0.44% Primakoff statistics on each target • Response to TAC comment on statistical error: 2% statistical error on current result Primakoff stat. (1.46%) + fit error • 0.44% error from proposal requires (1.46/0.44)2 = 11 times more events: • Increase DAQ rate from 1 kHz to 5 kHz • Implement more stringent trigger, (factor of 2-3) Hall D Coll. meeting, Feb. 4, 2011

  31. PrimEx-II Gain calibration Hall D Coll. meeting, Feb. 4, 2011

  32. Each dynode output goes to one of 36 Inputs of the UVA120A Sum module. Two linear output signals from UVA120A go to “electronics area” One of them used for further summation, The second one was not used in the PrimEx-1 configuration. Version #1 Use the second signal (cable) for the timing; Needs 61 Discriminator channels; 61 channels TDC. Use the PrimEx-I HyCal Trigger Configuration (Version #1)

  33. Verification of Overall Systematics: Compton Cross Section Δσ/ΔΩ (mb/6.9 msrad) Data with radiative corrections • Average stat. error: 0.6% • Average syst. error: 1.2% • Total: 1.3% Hall D Coll. meeting, Feb. 4, 2011

  34. PrimEx-II: HyCal Gain Re-Calibration (by 0 mass ) Hall D Coll. meeting, Feb. 4, 2011

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