1 / 36

Precision Measurements with GlueX at 12 GeV

This outline discusses the Primakoff Experiments with GlueX at 12 GeV, focusing on the precision measurements of various decay widths and transition form factors to test chiral symmetry and anomalies.

mfredricks
Download Presentation

Precision Measurements with GlueX at 12 GeV

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Primakoff Experiments at 12 GeV with GlueX Outline • The project and physics motivation: • The first experiment @ 6 GeV: 0 lifetime • Development of precision technique • Results for 0 lifetime • Experiments @ 12 GeV with GlueX • Summary A. Gasparian NC A&T State University, Greensboro, NC For the PrimEx Collaboration Hall D, March 7, 2008 1

  2. Experimental program Precision measurements of: Two-Photon Decay Widths: Γ(0→), Γ(→), Γ(’→) Transition Form Factors at low Q2 (0.001-0.5 GeV2/c2): F(*→0), F(* →), F(* →) The PrimEx Project at JLab Test of Chiral Symmetry and Anomalies via the Primakoff Effect Hall D, March 7, 2008 2

  3. Physics Motivation Fundamental input to Physics: • precision test of chiral anomaly predictions • determination of quark mass ratio • -’ mixing angle • 0, and ’ interaction electromagnetic radius • is the ’ an approximate Goldstone boson? Hall D, March 7, 2008 3

  4. First experiment: 0 decay width • 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 levelwill provide a stringent test of a fundamental prediction of QCD.

  5. Decay Length Measurements (Direct Method) Measure 0decay length 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 experiment 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→

  6. e+e- Collider Experiment DORIS II @ DESY e+e-e+e-**e+e-0e+e- e+,e- scattered at small angles (not detected) only  detected Results: Γ(0) = 7.7 ± 0.5 ± 0.5 eV ( ± 10.0%) 0→ • Not included in PDG average • Major limitations of method • knowledge of luminosity • unknown q2 for **

  7. ρ,ω Primakoff Method 12C target Primakoff Nucl. Coherent Nucl. Incoh. Interference Challenge: Extract the Primakoff amplitude Hall D, March 7, 2008 7

  8. 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

  9. PrimEx Experiment at Hall B • 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)

  10. Electromagnetic Calorimeter: HYCAL • Energy resolution • Position resolution • Good photon detection efficiency @ 0.1 – 5 GeV; • Large geometrical acceptance PbWO4 crystals resolution Pb-glass budget HYCAL only Kinematical constraint

  11. Fit to Extract 0 Decay Width: Γ(0)  7.93 eV  2.1%(stat.)  2.0% (syst)

  12. PrimEx Current Result () = 7.93eV2.1%2.0% 0 Decay width (eV) ±1.%

  13. Estimated Systematic Errors

  14. PrimEx @ 12 GeVPrecision Measurement of → decay width • All  decay widths are calculated from  decay width and experimental Branching Ratios (B.R.): Γ(η→ decay) = Γ(→) × B.R. • Any improvement in Γ(→) will change the whole - sector in PDB Hall D, March 7, 2008 14

  15. Physics Outcome from  Experiment • light quark mass ratio •  - ’ mixing angle Γ(η→3)=Γ(→)×B.R. Hall D, March 7, 2008 15

  16. ρ,ω Primakoff Method 12C target Primakoff Nucl. Coherent Interference Nucl. Incoh. Challenge: Extract the Primakoff amplitude Hall D, March 7, 2008 16

  17. Why do we need 12 GeV? • Increase Primakoff cross section: • Better separation of Primakoff reaction from nuclear processes: • Momentum transfer to the nuclei becomes less reduce the incoherent background

  18.  Experiment with GlueX Advantages: • High energy tagged photon beam Eγ=10 – 11.5 GeV • High acceptance electromagnetic calorimeter (FCAL) • Solenoid detector to veto charged particles, and reduce background on FCAL • Targets (~1-5% R.L.): • LH2, • LHe4, • solid 12C Challenges: • Photon flux stability and control: possible solutions: • e+e- pair spectrometer; • Compton scattering; • High resolution FCAL needed for precision experiments: possible solution: • Pb-glass + PbWO4 crystals Hall D, March 7, 2008 18

  19. FCAL Geometrical Coverage • Forward Calorimeter FCAL (~2800 Pb-glass blocks • Radius = 120 cm: • Central beam hole3x3 blocks removed (12x12 cm2) • FCAL has a good coverage for the forward →production Hall D, March 7, 2008 19

  20. Geometrical Acceptances • Forward Calorimeter FCAL (~2800 Pb-glass blocks • Radius = 120 cm: • Central beam hole: 3x3 blocks removed (12x12 cm2) • A good geometrical acceptance can be reached for L = 6-9 m for η forward production angles needed for the experiment A. Gasparian Hall D, March 7, 2008 20

  21. Experimental Resolutions (prod. angle) • Precision cross section measurement requires high resolutions in: • luminosity (flux + target) • production angle (for fit); • invariant mass (background) • … FCAL with all Pb-glass FCAL with Pb-glass and PbWO4 crystal insertion (75x75 blocks (150x150 cm2) Hall D, March 7, 2008 21

  22. Experimental Resolutions (inv. mass) FCAL with all Pb-glass FCAL with Pb-glass and PbWO4 crystal insertion (75x75 blocks (150x150 cm2) Hall D, March 7, 2008 22

  23. Experimental Resolutions (production angle vs. beam spot size) Photon beam size up to 5 mm, as it is designed, seams reasonable Hall D, March 7, 2008 23

  24. Experimental Resolutions(production angle vs. target length) • Reaction vertex can not be reconstructed in this experiment (recoil energies are too small T< 1 MeV) • Large size of the FCAL calorimeter provides longer target to FCAL distance • That makes less sensitivity from the target length up to designed 30 cm liquid targets Hall D, March 7, 2008 24

  25. 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

  26. Luminosity Control: Pair Production Cross Section Theoretical Inputs to Calculation: • Bethe-Heitler (modified by nuclear form factor) • Virtual Compton scattering • Radiative effects • Atomic screening • Electron field pair production Experiment/Theory = 1.0004

  27. 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%

  28. Beam Time and Statistics • Target: L=20 cm, LHe4 NHe = 4x1023 atoms/cm2 Nγ = 1x107 photon/sec (10-11.5 GeV part) <Δσ(prim.)> = 1.6x10-5 mb N() = NHexNγx<Δσ>xεx(BR) = 4x1023x 1x107x 1.6x10-32x0.7x0.4 = 64 events/hour = 1500 events/day = 45,000 events/30 days • Will provide sub-percent systematic error 15 Days

  29. Estimated Error Budget

  30. Summary • PrimEx collaboration has developed an experimental program to perform precision test of chiral symmetry and anomaly effects in the light pseudoscalar meson sector. • A state-of-the-art high resolution experimental setup has been designed, developed and constructed for the 6 GeV run. • The first experiment, the 0 lifetime measurement has been successfully performed in Hall B in 2004. Preliminary result: Γ(0)  7.93 eV  2.10%(stat.)  2.0%(syst.) • New proposal for the 1.4% accuracy in Γ(0) has been approved for the second 6 GeV run. • Reachexperimental program for η, η’ widths measurements has been developed and approved by high energy PACs. These precision experiments can be performed with the upgraded GlueX experimental setup at 12 GeV. Hall D, March 7, 2008 30

  31. The End Hall D, March 7, 2008 31

  32. ρ, ω The Primakoff Effect Challenge: Extract the Primakoff amplitude Hall D, March 7, 2008 32

  33. PbWO4 Energy Resolution 6 x 6 crystals E/E = 1.3 % 3 x 3 1 x 1 Hall D, March 7, 2008 33

  34. PbWO4 Position Resolution x = 1.3 mm Hall D, March 7, 2008 34

  35. Experimental Setup Development: Pair Spectrometer • Precision cross section measurements need control of photon flux at 1% level Scint. Det. • Pair spectrometer was designed for relative photon flux monitoring at high beam intensities: Dipole e+ HYCAL e- • Combination of: • 16 KGxm dipole magnet • 2 telescopes of 2x8 scintillating detectors Photon beam Hall D, March 7, 2008 35

  36. (0→)World Data • 0 is lightest quark-antiquark hadron • The lifetime:  = B.R.( 0 →γγ)/(0 →γγ) 0.8 x 10-16 second ±1% • Branching ratio: B.R. ( 0→γγ)= (98.8±0.032)% 0→ Hall D, March 7, 2008 36

More Related