Ratios of Separated Response Functions

1. Ratios of Separated Response Functions from Pion Electroproduction at and • Motivation • Analysis • Results • Summary Cornel Butuceanu 1 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

2. Jefferson Lab FπCollaboration 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 University of Regina, Regina, SK, Canada H. Blok, V. Tvaskis VrijeUniversiteit, 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 2 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

3. Motivation reactions q • Testing the t-pole dominance – key factor in • the extraction of the pion form factor . • Pion electroproduction can proceed • via isovector and isoscalar photons. • The experimental ratio evolution with • -t gives a good indication of the presence of isoscalar processes. • Separated ratios and tests the t-pole contribution to . t-pole 3 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

4. Previous Studies • At low -t • At high -t [A. Nachmann, Nucl. Phys. B 115 (1976) 61] Unseparated cross section ratios 4 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

5. KinematicsCoverage & L/T Separation Technique Take data at three angles: θπq=0o, +4o, -4o. Diamond cuts define common (W,Q2) coverage at both ε. Extract σL by simultaneous fit of L,T,LT,TT using measured azimuthal angle (φπ) and knowledge of photon polarization (ε). 5 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

6. Event selection Electron-pion coincidences Pions detected in HMS – Cerenkov & Coincidence time for PID Electrons detected in SOS –Cerenkov & Lead Glass Calorimeter Random coincidences Exclusivity assured via 0.875<MM<1.05 GeV cut 6 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

7. Collimator Pion Punch Through in SIMC Simulated Missing Mass spectrum was improved by implementing pions that were penetrating the HMS collimator. Pion Punchthrough Implementation resulted in an overall improved simulated kinematic variables (W,Q2,-t). 7 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

8. Data Analysis Magnetic Spectrometer Calibrations - Over-constrained p(e,e’p) and elastic e + 12C reactions were used to calibrate spectrometer acceptances, momenta and angular offsets. - SOS & HMS Delta/xpfp correlations were corrected with a linear dependent function of form . • Corrections to the high rate data set data were taken at high rates while data were taken at low rates. Understanding the rate dependent corrections was very important with respect to the final ratios. -New high rate tracking algorithm. -Improved high rate tracking efficiencies (2-9%). - HMS Cerenkov blocking correction (2-18%). -High current ( data set) target boiling correction (2-13%). 8 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

9. Tracking Efficiency For High Rate Data • Tracking Efficiency as defined for Fpi2 data fails for Fpi1 high • rate data (pi-). 9 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

10. Tracking Efficiencies For High Rate Data • A ~8% correction to the tracking efficiencies at 1.4MHz was • applied to the Fpi1 high rate data (pi-). 10 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

11. Target Boiling Corrections Hydrogen Deuterium • Hydrogen had a boiling effect of ~ 11% at 100 microA. • Deuterium had a boiling effect of ~ 13.5% at 100 microA. 11 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

12. Fpi2 Pion Absorption and Beta efficiency Beta > .925 Pi- data Pi+ data • The thick HMS exit window and the addition of the aerogel Cherenkov resulted in an improved overall pion transmission. 12 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

13. Fpi1 Beta Cut Random coincidences Real coincidences b > .95 beta cut protons p- data p+ data • A tight beta cut was applied to remove protons from the p+ data sample. • No Aerogel used in Fpi1 experiment. 13 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

14. Error Analysis • Spectrometers well-understood after careful comparison with MC simulations. • Beam energy and spectrometer • momenta determined to <0.1%. • Spectrometer angles to ~0.5 mr. • Agreement with published p+e • elastics cross sections <2%. • Per data t-bin: • Typical statistical error per bin: 1-2%. • Uncorrelated syst. unc. in UNS • common to all t-bins: 1.8(1.9)%. • Additional uncorrelated unc. also • uncorrelated in t: 1.1(0.9)%. • Total correlated uncertainty: 3.5%. • Uncorrelated uncertainties in UNS are amplified by 1/Δεin L-T separation. • Scale uncertainty propagates directly into separated cross section. 14 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

15. VGL Regge Model • Pionelectroproduction in terms of exchange of π and ρReggetrajectories. • - exchanged of a series of particles • compared to a single particle. • Model parameters fixed from pionphotoproduction. • Free parameters: Λπ2and Λρ2 (trajectory cutoffs). • ρ exchange does not significantly influence σL at small –t. [Vanderhaeghen, Guidal, Laget, PRC 57(1998)1454] 15 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

16. Separated Response Functions 16 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

17. Separated Response Functions Ratios 17 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

18. Summary • Separated cross sections were extracted using Rosenbluth L/T separation technique. • Ratios were extracted as a function of -t. • Preliminary results show that is consistent with 1 over the whole range in –t indicating a dominance of isovector processes at low –t in the longitudinal response function . • These findings confirm the expectation that is indeed dominated by the t-pole term. • In the kinematic region studied here both ratios and present a very slight dependence of . • The evolution of with –t shows a rapid fall off which is consistent with earlier theoretical predictions, expected to approach ¼, the square of the ratio of the quark charges involved. 18 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

19. HMS Cerenkov Blocking Using data taken with open trigger (el. & pions). The TDC time window in Fpi1 is 23% larger than in Fpi2. Use the Fpi2 data to fit the effective gate (same CC cut). For npe<2.0 gate width – 190 ns. Implies a larger correction in Fpi1 (18-20 % at 1MHz). Significant impact in pi- (high rate) data. HMS CC TDC spectrum for e as identified by the HMS CC ADC Backup slide 1 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

20. Beta Cut Corrections Real Coincidences Random coincidences Slow pions Included in the pion absorption correction Backup Slide 2 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

21. SOS Q3 Corrections Low momentum (<1.6 GeV/c) – old settings & corrections works fine. High momentum (>1.6 GeV/c) – use of new SOS optic matrix & new delta/xpfp correction. Backup Slide 3 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

22. 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 used in Fpi1). • 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. 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. Backup Slide 4 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

23. HMS Q3 corrections • Using central HMS kinematics and detected proton momentum we reconstruct the invariant mass W (electron mass). • The W vs X’ distribution was fitted with 1 degree polynomial for each. Backup Slide 5 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

24. Deuterium Corrections & Uncertainties Backup Slide 6 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org

25. Uncertainties Associated with Applied Corrections Backup Slide 6 Hall C Collaboration Meeting, JLab, January 31, 2009 ccbutu@jlab.org