γ*p →Δ(1232) →πN Results from CLAS Cole Smith University of Virginia Japan-US Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Δ(1232) Program at JLAB γv e e’ N 3/2 1/2 -1/2 -3/2 A1/2 S1/2 A3/2 Physics Goals Helicity amplitudes A3/2 A1/2 S1/2 vs. Q2 Deformation of N and Δ (E2/M1, C2/M1). Compare with quark models, lattice QCD. Reality Resonant and non-resonant contributions require models to separate. Theoretical tools: Effective Lagrangian (MAID,XPT), dynamical (Sato-Lee,DMT), Dispersion Relations (Aznauryan). Experiment: Identify observables sensitive to Born and rescattering terms in models. Experiments at JLAB Hall A – High luminosity, recoil polarization. Hall B – Large acceptance and kinematic coverage, polarized target and beam. Hall C – High Q2, search for onset of pQCD scaling (E2/M1→ 1). e e’ γv N △(1232) M1, E2, C2 3/2 1/2 -1/2 -3/2 A1/2 S1/2 A3/2 Δ3/2+(1232) N1/2+(938) λΔ λN Helicity conserving Spin flip Double spin flip Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

e / e / e e What do E2/M1 and C2/M1 ratios measure? E0+,S0+,M1-,S1- E1+,S1+,M1+,… M1, E2, C2 Short Range Physics? Gluon exchange → D-state admixtures Deformation of N / Δ Long Range Physics? χSB → Light pion mass Excite qq pairs from vacuum Shape of pion cloud Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

γ*p→Δ(1232) Magnetic Dipole – Quenched Lattice vs. Dynamical C. Alexandrou et al, PRL, 94, 021601 (2005) Pion Cloud Extrapolation of lattice GM* to Q2=0 is within 10% of experiment (where are the pions?). Predicted form factor falls with Q2 more slowly than data. Fits of dynamical pion models to π photoproduction data suggest 30-50% of M1 photocoupling strength near Q2=0 due to meson rescattering at EM vertex. Lattice shows a decreasing GM* coupling strength as quark mass decreases. Uncertainties: size of lattice volume (too small?), effects of unquenching (qq loops, Δ decay) Sato,Lee PRC 63, 055201 (2001) Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Quadrupole Transition – Lattice QCD vs. Pion Cloud Models γ*p→Δ(1232)→π0p C. Alexandrou et al, PRL, 94, 021601 (2005) E2/M1 (%) Quenched lattice consistent with E2/M1 data ! C2/M1 (%) Low Q2 behavior of C2/M1 strong test of calculations ! Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Reaction Models – Need to better constrain non-resonant backgrounds Non-resonant multipoles not well determined in models. Yang, Kamalov nucl-th/0303064 (DMT model) Sato, Lee nucl-th/0404025 Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

CLAS e1e Run (Nov-Dec 2002) Trigger Threshold Elastic Fiducial Cut Beam energy 1.046 GeV Q2=0.1-0.35 GeV2 W<1.4 GeV Beam polarization ~70% Current 10 nA LH2 target thickness 2.0 cm Q2 (GeV2) Trigger Threshold Elastic Elastic and inelastic data taken simultaneously. Normalization error ~ 3-4% Refined analysis since Aug 2004 More accurate target window background subtraction. Proton energy loss in target accounts for target geometry Elastic Bethe-Heitler background rejection uses finer W steps. W (GeV) Fiducial Cut Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

CEBAF Large Acceptance Spectrometer (CLAS) Six identical sectors 5 T toroidal B-field Δθ=15-140 degrees Δφ = 0-50 degrees Δp/p = 10-2-10-3 π0 electroproduction Proton detected Lorentz boost forms cone surrounding q vector. Cone angle Q2,W dependent Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Pion Electroproduction Structure Functions M1+ dominance. Re(M1+)=0 d2σ(MAID) vs θ* and φ* at Δ(1232) peak. Grid shows experimental (cosθ*,φ*) bins. Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

π0p Center-of-Mass Coverage - θLAB vs. φLAB of Detected Proton For Q2 < 1 GeV Torus coils block some angles, adjacent sectors provide additional coverage For Q2 > 1 GeV Full c.m. coverage is possible Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Acceptance Limitations at Low Q2 Magnet coils create acceptance asymmetry in φ*. Potential source of systematic error in σLT extraction. Mini-torus magnet coils Beam pipe hole exists in all low Q2 experiments. Removes yield near φ*=π which lowers sensitivity to σLT. Center-of-mass Acceptance (GEANT) Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Acceptance Monte Carlo Simulations Generated ~25M events using MAID03 physics model. W: 15 bins (1.10-1.40 GeV) Q2: 6 bins (0.16-0.36 GeV2) Cos θ*: 10 bins φ*: 24 bins GEANT simulation includes: Accurate magnet coil geometry Proton rescattering from coils. Drift chamber resolution. Bethe-Heitler radiation Hadronic interactions (FLUKA) Comparison of Geant and Data φ* cos θ* Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Bethe-Heitler Background (elastic tail) A potential source of φ* asymmetry which can bias extraction of σLT Largest background near φ*(proton)= 180o with tails extending beyond. Suppressed using overconstrained elastic kinematic cuts on proton angle. Residual BH tails subtracted using MC simulations. MM2 cut: 0.0056 < MM2 < 0.08 GeV2 After cut Missing Mass2 Missing Mass2 Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Typical pπ0 Cross Sections Near Pion Threshold Q2 = 0.2 GeV2 W=1.10-1.12 GeV Preliminary Preliminary Preliminary Preliminary φ* cos θ* Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Analysis: Obtain Legendre Coefficients φ* Fits Extract 3 structure functions for each cos θ* bin. Fit cos θ* to obtain Legendre coefficients. Works best with full angular distributions (no holes). Global Fits Fit φ*,cos θ* simultaneously More constrained fit Smooths over missing bins. Both methods used to check systematics of extracted Legendre coefficients. Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

CLAS Results for W=1.10-1.16 GeV at Q2 = 0.2 GeV2 Structure functions from φ* fits Legendre coefficients from global fits Preliminary Preliminary Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Model Dependence in Legendre Coefficients: 1.10 < W < 1.16 GeV Preliminary E1+ S1+ Largest differences between dynamical models occur for A1 and D0. Largest difference between MAID and dynamical models is for D1, which is largely sensitive to Re(S1+) Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Q2 Dependence of Legendre Coefficients – D1 Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Q2 Dependence of Legendre Coefficients – D0 Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Q2 Dependence of Legendre Coefficients – D0’ Model sensitivity in D0/ maximized at W=1.22 GeV in σLT/ whereas for σLT it vanishes. Joo, PRC 70, 042201 (2004) Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Q2 Dependence of Legendre Coefficients – A0 Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Q2 Dependence of Legendre Coefficients – A1 Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Q2 Dependence of Legendre Coefficients – A2 Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Q2 Dependence of Legendre Coefficients – C0 Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Typical Cross Sections vs cos θ* and φ* Q2 = 0.2 GeV2 W=1.22 GeV Preliminary Preliminary Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

W Dependence of Legendre Coefficients – A0,A1,A2,C0,D0,D1 Preliminary (M1+ dominance) Preliminary Resonant Multipoles Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Response Functions - Comparison to Bates at Q2=0.127 W=1.232 Mertz Kunz Sparveris MAID2003 CLAS Preliminary E=1.046 Q2=0.16 DMT Sato-Lee W=1.17 Model variation negligible between Q2=0.127 and 0.16. Good agreement between Bates and CLAS for T+L and TT measurements. Disagreement with Kunz point (■) for LT. Global fit (-----) favors Sato-Lee model at W=1.232. Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Is the Siegert Theorem Relevant? Many models use the long wavelength limit q*=0 to constrain S1+ as Q2→0: Long wavelength limit Data so far do not satisfy this condition. Models show large variation. Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Summary and Future Nearly complete angular distributions obtained for pizero electroproduction for Q2 = 0.14 - 0.38 GeV2 and W = 1.10 - 1.30 GeV. W and Q2 dependence of Legendre coefficients extracted from fits to φ* and cos θ* distributions. Both previous and current preliminary CLAS data show clear disagreement with MAID in D0 and D1 (σLT) below the Δ(1232) resonance. Preliminary E1+/M1+ in good agreement with MAID, while S1+/M1+ continues to show strong Q2 dependence. Analysis of π+ and polarization data at low Q2 underway. Systematics analysis underway. Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Backup Slides Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Structure Functions vs Invariant Mass W Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Structure Functions vs cosθ* Preliminary Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Δ(1232) – Global Fit to CLAS pπ0 + nπ+ data at Q2=0.4 and 0.65 GeV2 K. Joo et al., PRC 70, 042201 (2004) H. Egiyan et al., to be submitted to PRC Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan

Δ(1232) Multipoles – JANR Global Fit Results I.G. Aznauryan et al., PRC, 15201 (2005). Cole Smith Japan-U.S Workshop on Electromagnetic Meson Production and Chiral Dynamics Apr 2005 Osaka, Japan