Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Status of Beam Asymmetry Measurements for Non-Strange Meson Photoproduction from g8b ASU Meson Physics Group* (and friends) Work at ASU is supported by the National Science Foundation

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Meson Physics Group Patrick Collins Mike Dugger Brian Morrison Eugene Pasyuk Barry Ritchie Work at ASU is supported by the National Science Foundation

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 What is our ultimate goal? Understand nucleon structure in terms of its quark composition What do we need? – Identification of excited states – Coupling strengths for these states – Branching ratios for their various decay modes – Consistent overall theoretical picture

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Where to look? Need dense phase space coverage

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Meson photoproduction – a useful tool Strangeness zero mesons – Pion photoproduction –  and  ′ photoproduction Differential cross sections from ASU/CLAS Collaboration Hall B work –  + p →   + n : PRC (accepted) (2009). –  + p →   + p : PRC 76, (2007) –  + p →  + p : PRL 96, (2006). –  + p →  + p : PRL 89, (2002).

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Spin observables Differential cross sections are (relatively) simple Spin observables access interferences I. S. Barker, A. Donnachie, J. K. Storrow, Nucl. Phys. B 95, 347 (1975)

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 g8b running period (June 20- Sept 1, 2005) Incident electron E e = 4.55 GeV 50 -  diamond bremsstrahlung radiator Linearly polarized photon beam ( ┴, ║) Coherent edge set at 1.3, 1.5, … 2.1 GeV → E  = 1.1 to 2.1 GeV 40-cm-long LH 2 target Trigger: single charged particle + tagger Oriented / Un-oriented

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Photon beam polarization P Analytical QED coherent bremsstrahlung calculation fit to actual spectrum (Livingston/Glasgow) Unstable coherent edge location  Determined regions of reliable photon beam polarization P Estimated systematic uncertainty in P : ~3% Oriented/Un-oriented Polarization

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 “Para/Perp” approach for extracting  Use missing mass for reaction  + p → p + X Construct kinematical bins for parallel, perpendicular, and unpolarized data subsets Slice each kinematical bin into azimuthal angle φ slices (10, 20, 30 or so): “ φ slice method” Determine photoproduced meson yield in each slice Fit φ dependence to A (1 + B cos(2φ)), where B =  P. Preliminary results shown are from Patrick Collins and Mike Dugger

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Example:  p →   n

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Extracting  for  p →   n High yield and/or high asymmetry is easy High yield and/or high asymmetry is easy

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 A much harder job:  p →η´ p Low yield and/or low asymmetry is tough 

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Fourier moment method (CLAS Note ) Simultaneously uses full azimuthal φ acceptance of data set. Only a few (in principle, only 2) histograms per kinematic bin need to be fit. Re-binning data is comparatively easier than with the φ slice method.

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Flux-normalized yields Define a function f i,j for each kinematic bin i,j These are related to the yields normalized to integrated flux: Subscript denotes polarization: a ↔ unpolarized ┴ ↔ perpendicular || ↔ parallel

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Moments of flux-normalized yields Expand the f i, j in Fourier series. For example, Find the n th moment for the f i,j (called H n ): orthogonality

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Solving these for  Putting the pieces together, for the i,j kinematic bin, we find: The H n histograms are created by weighting each event by cos(nφ) for each i,j kinematic bin.

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Example: γ p → π 0 p numerator denominator

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary results for  from g8b Preliminary results:  0,  +, and  for 1.3 GeV coherent edge setting – Fourier moment method – Results from Mike Dugger’s work – “First and worst” coherent edge setting – Uncertainties in  less than 5% (more often ~1%) Two ways to view preliminary results – Fixed energy (~9-MeV-wide photon energy bins) – Fixed angle (0.1-wide bins in cos  ) – Both ways: compare with SAID predictions

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  0 Fixed energy – 4 slides Fixed angle – 3 slide

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  0

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  0

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  0

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  0

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  0

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  0

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  0

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  + Fixed energy – 4 slides Fixed angle – 3 slides

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  +

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  +

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  +

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  +

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  +

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  +

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  +

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for 

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Acceptance problem in g8b Clump of dead/bad TOF counters give “divot” in γ p →  p missing mass Simple background fit is problematic Monte Carlo backgrounds should work (next step)

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Choose a branch:  → p  +    0 (  ~22.7%) Look at  p → p X Look at M Y for p X → p  +   Y Cut on M Y =  0 mass Much less background under peak Lower acceptance (~ [0.5] 2  0.05) 

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Using branch for  in g8b Apply Fourier moment method for quick preliminary look. – Even with branch, lots of events in g8b – Ultimately will go back to proton yield in γ p →  p with good background MC

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  4 E-counters / bin

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  2 E-counters / bin

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Preliminary  results for  2 E-counters / bin

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Summary Good progress for the first/worst 200 MeV of photon energy range – Finish line is in sight for  for  +,  0, and  – Getting  for  ′ will be tough but doable The preliminary results for  +,  0, and  … – Look very good, even with fine binning – Incredibly stringent test for nucleon models – No indication of any narrow-width structures in any channel Goal: All four mesons ready for review by end of year

Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009 Meson Physics Group Patrick Collins Mike Dugger Brian Morrison Eugene Pasyuk Barry Ritchie Work at ASU is supported by the National Science Foundation