G 0 Inelastics: Parity Violating Asymmetry in the N-  Transition Carissa Capuano College of William & Mary Hall C Meeting Jefferson Lab, Newport News VA January 14, 2011

G 0 :Overview G 0 : Overview Purpose: – Measure parity violating asymmetry in e-p and e-d scattering at backward angle Elastically scattered electrons: – Determine the strange quark contribution to the distributions of charge and magnetization in the proton Inelastically scattered electrons: – Determine the axial transition form factor for the N-  transition Data Collection: Complete – Finished taking data March Jefferson Lab’s Hall C – Four data sets: Hydrogen and deuterium targets each at two energies – Inelastic analysis only for higher energy measurements (2 data sets) Data Analysis: – Elastic: Complete! See Androic, et al. PRL 104 (2010) – Inelastic: Nearing completion - will provide an update in this talk… Hall C Meeting – January 14, 2011C. Capuano – College of W&M1

G 0 N-  : Overview Purpose: –Measurement of axial transition form factor, G A N  0.2 GeV/c 2 < Q 2 < 0.5 GeV/c 2. What does G A N  tell us? – G A (Q 2 )  Axial elastic form factor for N How is the spin distributed? – G A N  (Q 2 )  Axial transition form factor for N →Δ How is the spin redistributed during transition? What do we measure? –Parity violating asymmetry A inel Allows a direct measure of the axial (intrinsic spin) response during N →Δ Accessing G A N  : – Previous Measurements: Charged current process (W ± exchange) Both quark flavor change and spin flip – G 0 N- Measurement: Neutral current process (Z 0 exchange ) Quark spin flip only → First measurement in neutral current sector Hall C Meeting – January 14, 2011C. Capuano – College of W&M2

 (1) = 2(1  sin 2  W ) ≈ 1  (2) = non-resonant contribution  (3) = 2(1  4sin 2  W ) F(Q 2,s)  N-  resonance Accessing G A N  F contains kinematic information & all weak transition form factorsF contains kinematic information & all weak transition form factors →Extract G A N   from F G 0 N- : Theory Q 2 Range of G 0 Measurement Zhu et al. PRD 65 (2002) Hall C Meeting – January 14, 2011C. Capuano – College of W&M3

G 0 : Experimental Setup Cryotarget: –LH 2 or LD 2 Beam: –Longitudinally polarized beam with ~85% polarization throughout the run. Detector System: –Scintillators: Two sets allow for kinematic separation of elastic and inelastic regions –Cryostat Exit Detectors (CED) –Focal Plane Detectors (FPD) –Cerenkov Detectors (CER): Allow us to distinguish between pions and electrons –Measured events: Coincidences CED + FPD + CER fire  electron CED + FPD fire (CER doesn’t fire)  pion e - beam target CED + Cerenkov FPD Cutaway view of a single octant Eight detector arrays like the one above are arranged symmetrically around the target Hall C Meeting – January 14, 2011C. Capuano – College of W&M4

G 0 N-  :Data G 0 N-  : Data D 687 Electron Yield (Octant2) elastics inelastics CED FPD Hall C Meeting – January 14, 2011C. Capuano – College of W&M5 FPD CED Electron Yield (Octant2) elastics inelastics CED FPD CED H 687 Electron Yield (Octant 2) elastics inelastics

A inel Correct for Beam Polarization G 0 N-  : Analysis Strategy Raw Data A meas Correct for Backgrounds  Elastic Electrons  Target Windows (Al)  Electrons from  0 decay  Pion Contamination Correct for Backgrounds  Elastic Electrons  Target Windows (Al)  Electrons from  0 decay  Pion Contamination Correct for Beam & Instrumentation  Deadtime  Random Coincidences  Helicity Correlated Beam Properties Correct for Beam & Instrumentation  Deadtime  Random Coincidences  Helicity Correlated Beam Properties Correct for EM Radiative Effects Simulatio n Hall C Meeting – January 14, 2011C. Capuano – College of W&M6

G 0 N-  : Background Correction Contributing processes: – Electrons scattered from Al target windows – Contamination from  - (D target only) – Electrons from elastic e-p(d) scattering – Electrons from inelastic e-p(d) scattering – Electrons from  0 decay Fitting: Scale Yield vs. FPD for each CED – Before fitting, subtract  - contamination and target window yield – Scale the remaining contributions independently to fit the data Fit Requirements: – Fit across all octants - forces all to have the same scale factor – Require scale factors to vary smoothly across CEDs GEANT Simulation “Empty target” data ** Pion data analysis ** Gas target data scaled to remove the gas contribution and to account for the kinematic differences in the liquid and gas target Hall C Meeting – January 14, 2011C. Capuano – College of W&M7

Yield (Hz/A) FPD G 0 N-  : Background Correction H Target Fit Result: Single CED in a single octant CED 1 Inelastic RegionSuperelastic Region Hall C Meeting – January 14, 2011C. Capuano – College of W&M8

Yield (Hz/A) FPD G 0 N-  : Background Correction D Target Fit Result: Single CED in a single octant CED 2 Inelastic Region Superelastic Region Elastic Region Hall C Meeting – January 14, 2011C. Capuano – College of W&M9

G 0 N-  : Background Correction Results: Size of the different contributions averaged across all inelastic cells – H target: Elastic~ 26%  0 decay~ 11% Target windows (Al) ~ 16%  Inelastic ~ 47% – D Target: Elastic~ 31%  0 decay~ 14%  - contamination~ 11% Target windows (Al)~ 9%  Inelastic~35% Total f bg = 53% Total f bg = 65% Hall C Meeting – January 14, 2011C. Capuano – College of W&M10

G 0 N-  : Background Correction Correcting the Asymmetry: – Extract A inel from A meas by subtracting off backgrounds Background Asymmetries: – Elastic Electrons Use A el measured by G 0 Dominated by radiative tail  Use simulation to determine a scale factor – Target windows Dominated by inelastic events A inel al is unknown, but can use measured D asymmetry – Pion related: Misidentified  - and electrons from  0 decay A  measured by G 0 Hall C Meeting – January 14, 2011C. Capuano – College of W&M11

G 0 N-  : Other Corrections EM Radiation (Applies only to H) – Scale asymmetry to account for effects of radiation – Size of correction determined through simulation:  (1.17 ± 0.6)% – Uncertainty stems from inelastic cross section model Transverse Asymmetry – Determined an upper bound of <0.05ppm for both targets  Negligible effect, no correction applied Hall C Meeting – January 14, 2011C. Capuano – College of W&M12

D 687: Summary of corrections and uncertainties CorrectionA_inel  _stat  _sys dA_corr Raw Scalar Counting Prob Rate Corrections **-12.6 Linear Regression Beam Polarization Backgrounds A inel = ± 15.7 ppm (preliminary) ** Rate correction error TBD G 0 N-  : Preliminary A inel Hall C Meeting – January 14, 2011C. Capuano – College of W&M13 All values in ppm

G 0 N-  : Preliminary A inel H 687: Summary of corrections and uncertainties CorrectionA_inel  _stat  _sys dA_corr Raw Scalar Counting Prob Rate Corrections **-2.17 Linear Regression Beam Polarization Backgrounds EM Radiative Effects ** Rate correction error TBD A inel = ± 7.3 ppm (preliminary) Hall C Meeting – January 14, 2011C. Capuano – College of W&M14 All values in ppm

Measurement of G A N  – First time measurement w/neutral current Status: – Data collection: Complete March ’07 – Analysis: Nearly Done! : Summary G 0 N-  : Summary The G 0 Collaboration G 0 Spokesperson: Doug Beck (UIUC) N- Spokesperson: Steve Wells (LaTech), Neven Simicevic (LaTech) California Institute of Technology, Carnegie-Mellon University, College of William and Mary, Hendrix College, IPN Orsay, JLab, LPSC Grenoble, Louisiana Tech, New Mexico State University, Ohio University, TRIUMF, University of Illinois, University of Kentucky, University of Manitoba, University of Maryland, University of Winnipeg, Virginia Tech, Yerevan Physics Institute, University of Zagreb Analysis Coordinator: Fatiha Benmokhtar (CMU) Thesis Students: Carissa Capuano (W&M), Alexandre Coppens (Manitoba), Colleen Ellis (Maryland), Juliette Mammei (VaTech), Mathew Muether (Illinois), John Schaub (NMSU), Maud Versteegen (LPSC), Stephanie Bailey (Ph.D. W&M, Jan ’07) Hall C Meeting – January 14, 2011C. Capuano – College of W&M15

Backup Slides

Other Data: LD 2 Pion Matrix Yields LH 687MeV LD 687MeV

Other Data: GH 2 Hall C Meeting – January 23, 2010C. Capuano – College of W&MB2

G 0 N-  : Background Correction Yield Fraction: – Use fit result to determine final yield fraction, f i, for simulated processes: – For the target windows and pion contamination: Hall C Meeting – January 23, 2010C. Capuano – College of W&MB3