1. Ratios of Separated Response Functions Cornel Butuceanu in Forward Pion Electroproduction Hall C Users Meeting, JLab, January 19, 2008  Motivation  Data Analysis  Prelim. Results  Outlook

2. F π Collaboration D. GaskellD. Mack 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, G.M. HuberC. 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. Blok H. Blok, V. Tvaskis Vrije Universiteit, Amsterdam, Netherlands E. BeiseT. Horn 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 Hall C Users Meeting, JLab, January 19, 2008

3. Motivation  Pion electroproduction can proceed via isovector and isoscalar photons.  Testing the t-pole (isovector) dominance – key factor in the extraction of the pion ff ( ).  The experimental ratio evolution with -t gives a good indication of the presence of isoscalar processes.  Separated ratio tests the t-pole contribution to.  Good existent 2H data sets E93-021 : Q2=0.6, 1.0 & 1.6 GeV2. E01-004 : Q2=2.45 GeV2.  Both data sets needed to be brought to the same level of analysis. Hall C Users Meeting, JLab, January 19, 2008 t-pole q reactions

4. Previous Studies Hall C Users Meeting, JLab, January 19, 2008 Earlier studies at DESY suggested: At low –t we have purely isovector processes: Deviations of from 1 gives indication of the amount of isoscalar backgrounds in the. At large –t the ratio is dominated by isoscalar processes: Unseparated cross section ratios

5. Experimental Setup ExpQ2 (GeV/c) 2 W (GeV) |t min | (Gev/c) 2 E e (GeV) Fπ-1 1.6 0.6-1.61.95 0.150 0.03-0.1502.445-4.045 Fπ-2 1.6 1.6,2.52.22 0.093 0.093,0.1893.779-5.246 Hall C Users Meeting, JLab, January 19, 2008 Hall C spectrometers:  Coincidence measurement.  SOS detects e -.  HMS detects π + and π -. Targets:  Liquid 4-cm H/D cells.  Al (dummy) target for background measurement.  12 C solid targets for optics calibration.

6. Event selection Hall C Users Meeting, JLab, January 19, 2008  Coincidence measurement between charged pions in HMS and electrons in SOS. -Coincidence time resolution -Coincidence time resolution ~200-230 ps. ~200-230 ps. -Cut value ±1 ns. -Cut value ±1 ns.  Missing mass cut 0.875<MM<1.05 assures exclusivity of the event.  π+ and π- are detected in HMS Cerenkov and coincidence using Cerenkov and coincidence time for PID. time for PID. -random coincidences subtracted  Electrons in SOS – identified by Cerenkov /Lead Glass Calorimeter. Cerenkov /Lead Glass Calorimeter.

7. Corrections to Fpi1 data set  By using the new tracking algorithm (2003 CVS engine) on 1998 data (E93021) we extended multitrack event capabilities and implicit a more accurate event reconstruction.  We corrected the HMS Delta/xpfp correlations with a linear dependent function of form. New wire chambers tracking efficiencies as a function of event rate were extracted.  HMS Cerenkov blocking correction as a function of event rate was used to recover pions lost due to a severe threshold cut in the Fpi1 initial trigger.  New target boiling corrections were extracted for H and D using elastic data with updated tracking efficiencies. Hall C Users Meeting, JLab, January 19, 2008

8. SOS Optics Calibration For low momentum (<1.6 GeV/c) we used the Fpi1 (1999) optics matrix & delta/xpfp correction. For high momentum (>1.6 GeV/c) we used the Fpi2 (2003) new optics matrix & delta/xpfp correction. Hall C Users Meeting, JLab, January 19, 2008

9. HMS Cerenkov Blocking  Used data taken with open trigger (el. & pions) to fit the effective time window.  The TDC time window in Fpi1 is 23% larger than in Fpi2.  Used the Fpi2 data to fit the effective TDC gate (for the same CC cut).  For a CC cut of npe<1.5 the effective TDC gate for Fpi1 set is ~184 ns.  Implies a larger correction for Fpi1 data (18-20 % at 1MHz).  Significant impact in pi- (high rate) data. Hall C Users Meeting, JLab, January 19, 2008 HMS CC TDC spectrum for e as identified by the HMS CC ADC  Uncertainties associated with this correction are of the order of 1.6% at 1MHz.

10. Tracking efficiency Two issues: 1.The Fpi1 version of the Trk. Eff. algorithm used a ‘’cleaner’’ data sample by removing the multiple hits events resulting in overevaluated trk. eff. 2. The Fpi2 version used a ‘’dirty’’ data sample by including the multiple hits events resulting in subevaluated trk. eff.  The high rate data (pi-) is the most sensitive to the tracking efficiency correction (~10% at 1.4 MHz).  A linear correction dependent of event rate was applied to the tracking efficiencies of pi- data. Hall C Users Meeting, JLab, January 19, 2008

11. Corrections due to the Target Boiling Hydrogen has a boiling effect of 8 1% at 100 microA. Deuterium has a boiling effect of 12 2% at 100 microA. Hall C Users Meeting, Jlab, January 19, 2008 To account for target boiling effects the pion yields were normalized with a linear function of the beam current.

12. Kinematic Coverage Kinematic Coverage Need full coverage in φ toNeed full coverage in φ to measure σ TT and σ LT. Take data at three angles: θ πq =0 o, +4 o, -4 o. (W,Q 2 ) phase space covered at low and high ε is different.(W,Q 2 ) phase space covered at low and high ε is different. Diamond cuts define common (W,Q 2 ) coverage at both ε. Hall C Users Meeting, JLab, January 19, 2008  = [1+2(1+  )tan 2 (  /2)] -1

13. Simulations vs Experimental data Simulated Missing Mass spectrum was improved by implementing pions that were penetrating the collimator. Hall C Users Meeting, JLab January 19, 2008 Pion Punchthrough Implementation resulted in an overall improved simulated kinematic variables (W,Q2,-t).

14. Extraction of separated cross sections Hall C Users Meeting, JLab, January 19, 2008  MC is based on the quasielastic pion electroproduction data.  Radiative effects, pion decay, energy loss, multiple scattering.  COSY model for spectrometer optics.  were extracted by a simultaneous fit a simultaneous fit using measured azimuthal angle and calculated photon polarization ε.  = [1+2(1+  )tan 2 (  /2)] -1  The unseparated pi- & pi+ cross sections were obtained from the model cs weighted by the ratio of experimental to simulated yields.

15. Preliminary Results vs VGL Model Pi- : Λ π 2 =0.450 GeV 2, Λ ρ 2 =1.5 GeV 2.  Pion electroproduction in terms of exchange of π and ρ Regge trajectories. [VGL, PRC 57(1998)1454]  Model parameters fixed from pion photoproduction. Λ 2 Λ 2  Free parameters: Λ π 2 and Λ ρ 2.  ρ exchange does not significantly influence σ L at small –t. Hall C Users Meeting, JLab, January 19, 2008 Pi+ : Λ π 2 =0.500 GeV 2, Λ ρ 2 =1.5 GeV 2.

16. Separated Response Functions Ratio Hall C Users Meeting, JLab, January 19, 2008 Pi- : Λ π 2 =0.450 GeV 2, Λ ρ 2 =1.5 GeV 2. Pi+ : Λ π 2 =0.500 GeV 2, Λ ρ 2 =1.5 GeV 2.

17. Separated Response Functions Ratio Hall C Users Meeting, JLab, January 19, 2008 Pi- : Λ π 2 =0.450 GeV 2, Λ ρ 2 =1.5 GeV 2. Pi+ : Λ π 2 =0.500 GeV 2, Λ ρ 2 =1.5 GeV 2.

18. OUTLOOK Completed all the corrections to Fpi1 (E93-021) data set (CC blocking, Rate Dependent, Tracking Efficiencies and Target Boiling) and optical calibrations. Preliminary separated cross sections were extracted using L/T separation Rosenbluth technique. Preliminary ratios were extracted as a function of -t. To do list: - include the Fpi2 Q2=2.45 in these results. - estimate the correlated and uncorrelated sys. err. - fine tuning of MC deuterium model. - prepare a draft paper by the end of the summer. Hall C Users Meeting, JLab, January 19, 2008

19. Kinematic Variables DNP Meeting, NN, Virginia, 13 October 2007

20. HMS Q3 corrections The W vs X’ distribution was the fitted with 1 degree polynomial for each. Hall C Users Meeting, JLab, January 19, 2008 Using central HMS kinematics and detected proton momentum we reconstruct the invariant mass W (electron mass).

21. Corrected Tracking Efficiencies Hall C Collaboration Meeting, JLab, January 19, 2008 A ~8% correction to the tracking efficiencies at 1.4MHz was applied to the high rate data (pi-).

22. Simulations vs Experimental data (optics) HMS & SOS exp vs sim comparison of the optics for pi+ data. Hall C Users Meeting, JLab, January 19, 2008 SIM/EXP comparison for other kinematic variables.