1. Separated π - /π + Ratios from the Pion Form Factor Experiments → Separated π - /π + Ratios from the Pion Form Factor Experiments → Phys.Rev.Lett. 112, 182501 (2014) JLab Users Group Meeting, June 4, 2014. Garth Huber

2. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 2 Jefferson Lab F π Collaboration R. Ent, D. Gaskell, M.K. Jones, D. Mack, D. Meekins, J. Roche, G. Smith, W. Vulcan, G. Warren, S.A. Wood Jefferson Lab, Newport News, VA, USA C. Butuceanu, E.J. Brash, G.M. Huber, V. Kovaltchouk, G.J. Lolos, S. Vidakovic, C. Xu C. Butuceanu, E.J. Brash, G.M. Huber, V. Kovaltchouk, G.J. Lolos, S. Vidakovic, C. Xu University of Regina, Regina, SK, Canada H.P. Blok, V. Tvaskis V.U. University, Amsterdam, Netherlands E. Beise, H. Breuer, C.C. Chang, T. Horn, P. King, J. Liu, P.G. Roos University of Maryland, College Park, MD, USA W. Boeglin, P. Markowitz, J. Reinhold Florida International University, FL, USA J. Arrington, R. Holt, D. Potterveld, P. Reimer, X. Zheng Argonne National Laboratory, Argonne, IL, USA H. Mkrtchyan, V. Tadevosyan Yerevan Physics Institute, Yerevan, Armenia S. Jin, W. Kim Kyungook National University, Taegu, Korea M.E. Christy, C. Keppel, L.G. Tang Hampton University, Hampton, VA, USA J. Volmer DESY, Hamburg, Germany A. Matsumura, T. Miyoshi, Y. Okayasu Tohuku University, Sendai, Japan B. Barrett, A. Sarty St. Mary’s University, Halifax, NS, Canada K. Aniol, D. Margaziotis California State University, Los Angeles, CA, USA L. Pentchev, C. Perdrisat College of William and Mary, Williamsburg, VA, USA

3. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 3 GPDs in Deep Exclusive Meson Production Four GPDs at leading twist: → Unpolarized: H(x,ξ,t), E(x,ξ,t) → Polarized: H(x,ξ,t), E(x,ξ,t) ~ ~ Second set of four GPDs at twist-3: H T, H T, E T, E T In the forward limit, H T reduces to the transversity distribution h 1 (x). → Dominant twist-3 contribution from H T contributes to M 0-,++ amplitude → Manifested in the transverse cross section or interference terms: σ T, σ TT, σ LT, and various single spin asymmetries. ~ ~ ρ,π,ηρ,π,η p+Δ γ*γ* Factorization

4. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 4 Deep Exclusive π ± Production Single π + produced from proton, or π - from neutron at high momentum transfer. Single π + produced from proton, or π - from neutron at high momentum transfer. Can form ratios of separated cross- sections for which non-perturbative corrections may partially cancel, yielding insight into soft-hard factorization at modest Q 2. Can form ratios of separated cross- sections for which non-perturbative corrections may partially cancel, yielding insight into soft-hard factorization at modest Q 2. q A. Nachtmann, Nucl. Phys. B 115 (1976) 61. Pseudoscalar meson production has been identified as especially sensitive to chiral-odd transverse GPDs. Pseudoscalar meson production has been identified as especially sensitive to chiral-odd transverse GPDs. → R T is not complicated by the π –pole term.

5. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 5  ± t-channel diagram is purely isovector (G-parity conservation).  ± t-channel diagram is purely isovector (G-parity conservation). A significant deviation of R L from unity would indicate the presence of isoscalar backgrounds (such as b 1 (1235) contributions to t-channel). A significant deviation of R L from unity would indicate the presence of isoscalar backgrounds (such as b 1 (1235) contributions to t-channel). **   N N’ At low –t, Meson-Nucleon Degrees of Freedom Relevant for extraction of pion form factor from p(e,e’π + )n data, which uses model including some isoscalar background.

6. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 6 Only Prior 2 H(e,e’ π ± ) NN Data Only prior exclusive 2 H(e,e’ π ± )NN data was obtained at DESY in the 1970’s. Only prior exclusive 2 H(e,e’ π ± )NN data was obtained at DESY in the 1970’s. Unseparated cross sections only, due to incomplete azimuthal coverage. Unseparated cross sections only, due to incomplete azimuthal coverage. Q 2 =0.70, 1.35 GeV 2. Q 2 =0.70, 1.35 GeV 2. π - /π + ratio intriguingly approaches Nachtmann’s quark counting ratio →1/4 at high –t. π - /π + ratio intriguingly approaches Nachtmann’s quark counting ratio →1/4 at high –t. Ratio approaches π pole dominance →1 at low –t. Ratio approaches π pole dominance →1 at low –t. Need separated 2 H(e,e’ π ± )NN data over a wide kinematic range to better interpret ratios! Need separated 2 H(e,e’ π ± )NN data over a wide kinematic range to better interpret ratios!

7. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 7 1. At small – t,  L has maximum contribution from the  pole. 2. Need to investigate t dependence at relatively fixed Q 2, W, but only three of Q 2, W, t, θ  are independent. Vary θ  to measure t dependence. Vary θ  to measure t dependence. Since non-parallel data needed, LT and TT must also be determined. Since non-parallel data needed, LT and TT must also be determined.

8. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 8 Jefferson Lab Hall C Experimental Setup Exp Q 2 (GeV/c) 2 W (GeV) |t min | (Gev/c) 2 (Gev/c) 2 E e (GeV) Fπ-1 0.6-1.61.950.03-0.1502.445-4.045 Fπ-2 2.452.220.1894.210-5.246 Hall C spectrometers:  Coincidence measurement.  SOS detects e -.  HMS detects π + and π -. Targets:  Liquid 4-cm H/D cells.  Al target for empty cell measurement.  12 C solid targets for optics calibration. SOS: SOS: 1.7 GeV/c 1.7 GeV/c HMS: 7 GeV/c

9. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 9 2 H(e,e’ π ± )NN Event selection 2 H(e,e’ π ± )NN Event selection Electron-pioncoincidences Random coincidences Exclusivity assured via 0.875<MM<1.03 GeV cut Pions detected in HMS – Cerenkov & Coincidence time for PID Electrons detected in SOS –Cerenkov & Lead Glass Calorimeter Coincidence time resolution ~200-230 ps. Cut value ±1 ns. After PID & MM cuts, almost no random coincidences remain. Diamond cuts define common (W,Q 2) coverage at both ε.

10. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 10 Corrections to π -, π + Data Negative polarity of HMS field for 2 H(e,e’π - )pp means these runs have high electron rates not shared by 2 H(e,e’π + )nn runs. Negative polarity of HMS field for 2 H(e,e’π - )pp means these runs have high electron rates not shared by 2 H(e,e’π + )nn runs. Understanding rate dependent corrections very important with respect to separated π - /π + ratios. Improved high rate HMS tracking algorithm. Improved high rate HMS tracking algorithm. More accurate high rate tracking efficiencies (91-98%). More accurate high rate tracking efficiencies (91-98%). HMS π - misidentification correction due to e - pileup in Čerenkov (13%/MHz e - ). HMS π - misidentification correction due to e - pileup in Čerenkov (13%/MHz e - ). High current 2 H target boiling correction (4.7%/100μA) for old `beer can’ target cell and square beam raster. High current 2 H target boiling correction (4.7%/100μA) for old `beer can’ target cell and square beam raster. Q 2 =0.60, 0.75, 1.0, 1.6 GeV 2

11. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 11 F π -1 ran in 1997. F π -2 ran in 2003. Many changes in between. HMS Tracking Efficiencies for High Rate Data 1998 Engine overestimates tracking efficiencies, since 2-track events have lower efficiency than 1-track events. For the F π -2 p(e,e’ π + )n analysis (low rates), it was found that better results were found if the cut to exclude multiple good PMT ADC signals within the fiducial region of the hodoscope plane was removed. → This removal fails at high rates. 2003 Engine tracking efficiencies are lower, but still overestimated. 2003 Engine tracking efficiencies with correction factor applied. To bring F π -1 data to same level of reconstruction quality as F π -2 data, a lot of effort went into modifying the Hall C Analysis Engine to accept the older format data. To bring F π -1 data to same level of reconstruction quality as F π -2 data, a lot of effort went into modifying the Hall C Analysis Engine to accept the older format data. Makes use of redesigned tracking algorithm that does a significantly better job in selecting the best track for multi-track events. Makes use of redesigned tracking algorithm that does a significantly better job in selecting the best track for multi-track events.

12. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 12 Carbon Luminosity Scans To better understand HMS tracking efficiencies, the normalized yields from carbon target were studied vs. rate and vs. current. To better understand HMS tracking efficiencies, the normalized yields from carbon target were studied vs. rate and vs. current. Carbon target should not “boil”, so normalized yields should be flat vs. current if all efficiencies are calculated correctly. Carbon target should not “boil”, so normalized yields should be flat vs. current if all efficiencies are calculated correctly. Unfortunately, no 12 C luminosity scans were taken at different beam currents in the F π -1 experiment. Unfortunately, no 12 C luminosity scans were taken at different beam currents in the F π -1 experiment. → Conclusions from the F π -2 study will have to be applied. → Conclusions from the F π -2 study will have to be applied.

13. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 13 2 H Cryotarget Boiling Corrections After the tracking efficiencies are finalized, the cryotarget boiling corrections can be determined. After the tracking efficiencies are finalized, the cryotarget boiling corrections can be determined. F π -2: “tuna can” target cell and uniform circular rastering. Consistent with no 1 H cell correction in T. Horn F π -2 analysis. F π -1: “beer can” target cell and non-uniform square rastering. Consistent with 6±1% 1 H cell correction in J. Volmer F π -1 analysis.

14. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 14 HMS Čerenkov Blocking Correction ( π - ) In both F π -1,2, the HMS gas Čerenkov was used as a veto in the trigger for 2 H(e,e’ π - ) runs In both F π -1,2, the HMS gas Čerenkov was used as a veto in the trigger for 2 H(e,e’ π - ) runs → needed to avoid high DAQ deadtime due to large e - rates in HMS. Čerenkov Blocking: Čerenkov Blocking: π - are lost when e - pass through the gas Čerenkov within ~100ns after π - has traversed the detector. → results in mis-identification of π - as e - Actual veto thresholds vary according to PMT gain variations at high rates. Actual veto thresholds vary according to PMT gain variations at high rates. slightly more restrictive software thresholds are applied in the analysis: slightly more restrictive software thresholds are applied in the analysis: F π -1: accept < 1.5 hcer_npe F π -1: accept < 1.5 hcer_npe F π -2: accept < 2 hcer_npe F π -2: accept < 2 hcer_npe

15. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 15 HMS Čerenkov Blocking Correction ( π - ) Čerenkov Blocking Correction is obtained from Trigger TDC information, since that is independent of tracking efficiency and cryotarget corrections. Čerenkov Blocking Correction is obtained from Trigger TDC information, since that is independent of tracking efficiency and cryotarget corrections. Result is consistent with τ from other studies (not shown here) within statistical errors. Result is consistent with τ from other studies (not shown here) within statistical errors. F π -2: 116±6 ns F π -1: 138±6 ns Region due to early e- passing through detector before e- associated with trigger.Region due to early e- passing through detector before e- associated with trigger. Already addressed in coincidence time blocking correction.Already addressed in coincidence time blocking correction. F π -2: τ = 115±6 ns F π -1: τ = 138±6 ns

16. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 16 Extract Response Functions through Iterative Procedure Improve φ coverage by taking data at multiple π (HMS) angles, -4 o < θ πq <4 o. θ πq =0θ πq =+4 -t=0.1 -t=0.3 Extract via simultaneous fit of L,T,LT,TT d 2 σ/dtdφ (μb/GeV 2 ) Q 2 =1.60 π + φ πq (deg) For each π HMS setting, form ratio: Combine ratios for π settings together, propagating errors accordingly.

17. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 17 Over-constrained p(e,e’p) reaction and elastic e+ 12 C reactions used to calibrate spectrometer acceptances, momenta, offsets, etc. Over-constrained p(e,e’p) reaction and elastic e+ 12 C reactions used to calibrate spectrometer acceptances, momenta, offsets, etc. Spectrometers well-understood after careful comparison with MC simulations. Spectrometers well-understood after careful comparison with MC simulations. Beam energy and spectrometer Beam energy and spectrometer momenta determined to <0.1%. Spectrometer angles to <1 mrad. Spectrometer angles to <1 mrad. Agreement with published p+e Agreement with published p+e elastics cross sections <2%. Systematic Uncertainties (F π -1) SourcePt-Pt ε uncorr. t corr, Scale Beam and Spectrometer Kinematic Offsets 0.2%0.8-1.1% HMS β-cut corrections 0.4% Particle ID 0.2% Pion Absorption Correction 1.0% Pion Decay Correction 0.03%1.0% HMS Tracking 0.4% (π+) 1.3% (π-) 1.0% (π+) 1.0% (π-) SOS Tracking 0.2%0.5% Integrated Beam Charge 0.3%0.5% Target Thickness 0.3%1.0% CPU and Trigger Dead time 0.3% HMS Cerenkov Veto Correction (π-) 0.7%2.0% Missing Mass Cut 0.8%1.3% Spectrometer Acceptance 1.0%0.6%1.0% MC Model Dependence (L,T) 0.4%0.7-3.5%0.3-2.0% Radiative Corrections 0.4%2.0% TOTAL (π+) 1.4%1.4-3.6%3.1-3.5% TOTAL (π-) 1.6%2.3-4.4%3.7-4.2% Typical Statistical Uncertainty (per t-bin) 5-10%

18. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 18 2 H data Kinematic coverage 2 H(e,e’π + )nn 2 H(e,e’π - )pp Q 2 =0.6 GeV 2, W=1.95 GeV (F π -1) ε=0.37, E e =2.445 GeV 3 HMS settings: θ πq =+0.5,+2.0,+4.0 o. 2 HMS settings: Missing +2.0 o. ε=0.74, E e =3.548 GeV 4 HMS settings: θ πq =-2.7, +0.0,+2.0,+4.0 o. 1 HMS setting: Only +0.0 o. Q 2 =0.75 GeV 2, W=1.95 GeV (F π -1) ε=0.43, E e =2.673 GeV 2 HMS settings: θ πq =+0.0,+4.0 o. ε=0.70, E e =3.548 GeV 3 HMS settings: θ πq =-4.0, +0.0,+4.0 o. NO HMS settings. Q 2 =1.0 GeV 2, W=1.95 GeV (F π -1) ε=0.33, E e =2.673 GeV 2 HMS settings: θ πq =+0.0,+4.0 o. ε=0.65, E e =3.548 GeV 3 HMS settings: θ πq =-4.0, +0.0,+4.0 o. 1 HMS setting: Only +0.0 o. Q 2 =1.6 GeV 2, W=1.95 GeV (F π -1) ε=0.27, E e =3.005 GeV 2 HMS settings: θ πq =+0.0,+4.0 o. ε=0.63, E e =4.045 GeV 3 HMS settings: θ πq =-4.0, +0.0,+4.0 o. Q 2 =2.45 GeV 2, W=2.20 GeV (F π -2) ε=0.27, E e =4.210 GeV 2 HMS settings: θ πq =+1.35,+3.0 o. ε=0.55, E e =5.248 GeV 3 HMS settings: θ πq =-3.0, +0.0,+3.0 o.

19. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 19 2 H(e,e’ π ± ) NN Separated dσ/dt Longitudinal cross- section shows steep rise due to π pole at small –t. Longitudinal cross- section shows steep rise due to π pole at small –t. Transverse cross-section much flatter. Transverse cross-section much flatter. Both follow nearly universal curves vs –t, with weak Q 2 -dependence. Both follow nearly universal curves vs –t, with weak Q 2 -dependence. Data points have slightly different All data scaled to W =2.0 GeV assuming 1/(W 2 -M 2 ) dependence, M =free nucleon mass. No scaling applied in Q 2. L T L T Q 2 =0.6 Q 2 =1.0 Q 2 =1.6 Q 2 =2.45 Error bars indicate statistical and pt-pt systematic uncertainties in quadrature. Bands indicate L,LT,TT MC model dependence systematic uncertainty.

20. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 20 Error bars indicate statistical and pt-pt systematic uncertainties in quadrature. Bands indicate L,LT,TT MC model dependence systematic uncertainty. VGL Regge Model: Free parameters: Λ π 2, Λ ρ 2 (from 1 H data).Free parameters: Λ π 2, Λ ρ 2 (from 1 H data). [PRC 57(1998)1454] KM Regge+DIS Model: σ L from 1 H data, DIS process dominates σ T.σ L from 1 H data, DIS process dominates σ T. [PRC 81(2010)045202] VR Regge+DIS Model: Similar to KM but with improved DIS parametersSimilar to KM but with improved DIS parameters [PRC 89(2014)025203] Model dσ x /dt

21. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 21 π - /π + Separated Response Function Ratios Transverse Ratios tend to ¼ as –t increases: Transverse Ratios tend to ¼ as –t increases: → Is this an indication of Nachtmann’s quark charge scaling? -t=0.3 GeV 2 seems too low for this to apply. Might indicate the partial cancellation of soft QCD corrections in the formation of the ratio. -t=0.3 GeV 2 seems too low for this to apply. Might indicate the partial cancellation of soft QCD corrections in the formation of the ratio. R L ≈0.8 near –t min at each Q 2. Predicted in large N c limit calculation. Frankfurt, et al. PRL 84(2000)2589. Error bars indicate statistical and pt-pt systematic uncertainties in quadrature. Bands indicate MC model dependence systematic uncertainty.

22. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 22 Relevance to Pion Form Factor Extraction Vrancx-Ryckebusch Model: VGL Regge Model underpredicts σ T by large factor.VGL Regge Model underpredicts σ T by large factor. VR extend VGL with hard DIS process of virtual photons off nucleons.VR extend VGL with hard DIS process of virtual photons off nucleons. [PRC 89(2014)025203] Qualitatively in agreement with our F π-1 analysis: Qualitatively in agreement with our F π-1 analysis: We found evidence for small additional contribution to σ L at W=1.95 GeV not taken into account by the VGL model. We found evidence for small additional contribution to σ L at W=1.95 GeV not taken into account by the VGL model. We found little evidence for this contribution in F π-2 analysis at W=2.2 GeV. We found little evidence for this contribution in F π-2 analysis at W=2.2 GeV. R L =0.8 consistent with |A S /A V |<6%.

23. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 23 Comparison with Goloskokov-Kroll GPD model Model parameters optimized for small skewness ( ξ 4 GeV. Model parameters optimized for small skewness ( ξ 4 GeV. Application to our kinematics requires substantial extrapolation in W, ξ. Application to our kinematics requires substantial extrapolation in W, ξ. → Please be cautious in the comparison. Although model does reasonable job at predicting ratios, agreement of model with our σ T is not good. Although model does reasonable job at predicting ratios, agreement of model with our σ T is not good. Model optimized for JLab kinematics should be sensitive to transverse GPD, H T Model optimized for JLab kinematics should be sensitive to transverse GPD, H T π ± electroproduction in a handbag framework.π ± electroproduction in a handbag framework. Modified perturbative approach with full F π (Q 2 ).Modified perturbative approach with full F π (Q 2 ). Substantial contributions from transverse photons as twist-3 effect (H T )Substantial contributions from transverse photons as twist-3 effect (H T ) [Eur.Phys.J.A47(2011)112] [Eur.Phys.J.A47(2011)112]

24. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 24 σ L /σ T and σ TT /σ T Ratios for π +, π - L/T ratio becomes more favorable for π - production as Q 2 increases. L/T ratio becomes more favorable for π - production as Q 2 increases. Another prediction of quark-parton mechanism is the suppression of σ TT /σ T due to s -channel helicity conservation. Another prediction of quark-parton mechanism is the suppression of σ TT /σ T due to s -channel helicity conservation. Data qualitatively consistent with this, since σ TT decreases more rapidly than σ T with increasing Q 2. Data qualitatively consistent with this, since σ TT decreases more rapidly than σ T with increasing Q 2. Error bars indicate statistical and pt-pt systematic uncertainties in quadrature. Bands indicate MC model dependence systematic uncertainty.

25. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 25 Projected Data from F π -12 Experiment E12-06-101 approved for 52 days of beam with SHMS+HMS, A rating, selected by PAC41 as “High Impact”. E12-06-101 approved for 52 days of beam with SHMS+HMS, A rating, selected by PAC41 as “High Impact”. 2 H data to determine R L π - /π + ratio to constrain modeling of non- pole backgrounds in σ L, relevant for extraction of pion form factor 2 H data to determine R L π - /π + ratio to constrain modeling of non- pole backgrounds in σ L, relevant for extraction of pion form factor 44 hrs ( π + ), 174 hrs ( π - ). 44 hrs ( π + ), 174 hrs ( π - ). If R T is ~1/4 at higher Q 2 and similar x B, the hypothesis of a quark knockout mechanism will be strengthened. If R T is ~1/4 at higher Q 2 and similar x B, the hypothesis of a quark knockout mechanism will be strengthened. Projected Data Predictions of Vrancx-Ryckebusch Regge+DIS Model [PRC 89(2014)025203]

26. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 26Summary Separated σ L, σ T, σ LT, σ TT cross sections for the 2 H(e,e’ π ± )NN reactions were extracted using the Rosenbluth L/T separation technique. F π-1: W=1.95 GeV: Q 2 =0.6, 1.0, 1.6 GeV 2. F π-1: W=1.95 GeV: Q 2 =0.6, 1.0, 1.6 GeV 2. F π-2: W=2.2 GeV: Q 2 =2.45 GeV 2. F π-2: W=2.2 GeV: Q 2 =2.45 GeV 2. π - /π + ratios for σ L, σ T extracted as a function of -t. R L ≈0.8, trending towards unity at low –t. R L ≈0.8, trending towards unity at low –t. Indicates the dominance of isovector processes at low –t in the longitudinal response function. Indicates the dominance of isovector processes at low –t in the longitudinal response function. The evolution of R T with –t shows rapid fall off consistent with earlier theoretical predictions, expected to approach ¼, the square of the ratio of the quark charges involved. The evolution of R T with –t shows rapid fall off consistent with earlier theoretical predictions, expected to approach ¼, the square of the ratio of the quark charges involved. Further theoretical work needed re. alternate explanations. Further theoretical work needed re. alternate explanations.

27. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 27

28. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 28 Cerenkov trigger about 90% efficient at vetoing electrons. F π -2 HMS Čerenkov Trigger TDC study Multi-hit TDC of the Čerenkov signal into the HMS trigger was investigated for HMS singles rate up to ~600 kHz. Multi-hit TDC of the Čerenkov signal into the HMS trigger was investigated for HMS singles rate up to ~600 kHz. Compare runs without and with HMS Čerenkov veto. Compare runs without and with HMS Čerenkov veto. Main peak: Signal (primarily e - ) that starts TDC. 2 nd peak: Second e - arriving within timing window, but after 1st 40ns long discriminator pulse. Pedestal: Earlier or later e -. Tail to 410ns: Noise crossing discriminator threshold. Chan 4096: Very late TDC stops. Chan 0: Mostly π -, not giving TDC stop. Ratio of 0 to 1 st peak much greater with veto trigger. Without Veto With Veto Normalized Difference

29. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 29 F π -2 HMS Singles Yield Study Plot normalized HMS singles yields for each kinematic setting vs. rate. Plot normalized HMS singles yields for each kinematic setting vs. rate. For each setting, fit with Ae -bτ and divide by A. For each setting, fit with Ae -bτ and divide by A. τ values sensitive to applied tracking eff. and cryotarget boiling corrections. τ values sensitive to applied tracking eff. and cryotarget boiling corrections. These τ values determined with singles events, and need to be adjusted for effective gate width for coincidence evts. These τ values determined with singles events, and need to be adjusted for effective gate width for coincidence evts. 2 H( e,e’ π - ) runs were taken without HMS Cerenkov trigger veto at different currents for several kinematic settings. 2 H( e,e’ π - ) runs were taken without HMS Cerenkov trigger veto at different currents for several kinematic settings. Apply “veto” via hcer_npe<2.0 cut. Apply “veto” via hcer_npe<2.0 cut. Expect a loss of yield at higher rate due to Cerenkov blocking. Expect a loss of yield at higher rate due to Cerenkov blocking. τ value found in 2009 analysis significantly larger, 160ns. τ value found in 2009 analysis significantly larger, 160ns.

30. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 30 Final HMS Tracking Efficiency Correction Correction is applied to both F π -1 and F π -2 tracking efficiencies.Correction is applied to both F π -1 and F π -2 tracking efficiencies. Particularly important for F π -1 2 H(e,e’ π - ) data, with HMS rate up to 1.4 MHz.Particularly important for F π -1 2 H(e,e’ π - ) data, with HMS rate up to 1.4 MHz. After application of correction, carbon normalized yields show NO residual current dependence.

31. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 31 2 H(e,e’ π ± )NN MC Model and Reconstruction L/T/LT/TT separation needs a model to take into account kinematic correlations between Q 2, W, t and θ π in a given (t,φ) bin. L/T/LT/TT separation needs a model to take into account kinematic correlations between Q 2, W, t and θ π in a given (t,φ) bin. Various choices can be made for treating off-shell effects, and these could affect the interpretation of our results. Various choices can be made for treating off-shell effects, and these could affect the interpretation of our results. In SIMC Monte Carlo simulation: Generate vertex quantities, taking Fermi motion into account with spectator on- shell and the struck nucleon carrying all off-shellness. Generate vertex quantities, taking Fermi motion into account with spectator on- shell and the struck nucleon carrying all off-shellness. E_struck depends on the assumed Fermi momentum (taken from Bonn 2 H wave function) E_struck depends on the assumed Fermi momentum (taken from Bonn 2 H wave function) Follow outgoing particles (including radiation) through target, spectrometer, detectors and determine 'experimental' values of k e' and k π. Follow outgoing particles (including radiation) through target, spectrometer, detectors and determine 'experimental' values of k e' and k π. Data reconstruction (both exp data and simulation): Since the Fermi momentum of the struck nucleon is not known, the values of Q 2, W, t, M X, φ, θ are computed in the quasi-free Since the Fermi momentum of the struck nucleon is not known, the values of Q 2, W, t, M X, φ, θ are computed in the quasi-free approximation where the struck nucleon is at rest. CM frame is γ* and stationary N, φ CM =φ LAB, as in 1 H analysis. CM frame is γ* and stationary N, φ CM =φ LAB, as in 1 H analysis. t=(p target -p recoil ) 2 used. Not necessarily equivalent to t=(p γ -p π ) 2 due to Fermi momentum and radiation. t=(p target -p recoil ) 2 used. Not necessarily equivalent to t=(p γ -p π ) 2 due to Fermi momentum and radiation. Reconstructed Q 2, W, t are also used to compute the weighting for simulated events according to the model cross section. Reconstructed Q 2, W, t are also used to compute the weighting for simulated events according to the model cross section.

32. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 32 Good Agreement for Optics and Kinematic Variables DataSIMC

33. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 33 Comparison of π + from 1 H and 2 H Intriguing differences between π + production from hydrogen and deuterium. Intriguing differences between π + production from hydrogen and deuterium. Keep in mind that 2 H cross sections are effective ones, not trivially comparable to 1 H. Keep in mind that 2 H cross sections are effective ones, not trivially comparable to 1 H. Role of off-shell effects in 2 H? Role of off-shell effects in 2 H? Role of Fermi momentum in 2 H? Role of Fermi momentum in 2 H? L T 1 H(e,e’π + )n 2 H(e,e’π + )nn Error bars indicate statistical and pt-pt systematic uncertainties in quadrature. Bands indicate MC model dependence systematic uncertainty.

34. Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada. 34 Error bars indicate statistical and pt-pt systematic uncertainties in quadrature. Bands indicate L,LT,TT MC model dependence systematic uncertainty. MAID07 Isobar Model: Parameters optimized for W<2 GeV. Q 2 =2.45 GeV 2 results are an extrapolation. [EPJA 34(1999)145] GK GPD-Based Model: σ L based on full F π (Q 2 ) from 1 H data, σ T substantial contribs from twist-3 H T.σ L based on full F π (Q 2 ) from 1 H data, σ T substantial contribs from twist-3 H T. Params optimized for small skewness (ξ 4 GeV.Params optimized for small skewness (ξ 4 GeV. [EPJA 47(2011)112] Model dσ x /dt