Separated Response Function Ratios in Exclusive, Forward ${\pi }^{\pm }$ Electroproduction

Journal Article · Mon May 05 00:00:00 EDT 2014 · Physical Review Letters

DOI:https://doi.org/10.1103/PhysRevLett.112.182501· OSTI ID:1356650

Huber, G. M. ; Blok, H. P.; Butuceanu, C.; Gaskell, D.; Horn, T.; Mack, D. J.; Abbott, D.; Aniol, K.; Anklin, H.; Armstrong, C.; Arrington, J.; Assamagan, K.; Avery, S.; Baker, O. K.; Barrett, B.; Beise, E. J.; Bochna, C.; Boeglin, W.; Brash, E. J.; Breuer, H. ; Chang, C. C.; Chant, N.; Christy, M. E.; Dunne, J.; Eden, T.; Ent, R.; Fenker, H.; Gibson, E. F.; Gilman, R.; Gustafsson, K.; Hinton, W.; Holt, R. J.; Jackson, H.; Jin, S.; Jones, M. K.; Keppel, C. E.; Kim, P. H.; Kim, W.; King, P. M.; Klein, A.; Koltenuk, D.; Kovaltchouk, V.; Liang, M.; Liu, J.; Lolos, G. J.; Lung, A.; Margaziotis, D. J.; Markowitz, P.; Matsumura, A.; McKee, D.; Meekins, D.; Mitchell, J.; Miyoshi, T.; Mkrtchyan, H.; Mueller, B.; Niculescu, G.; Niculescu, I.; Okayasu, Y.; Pentchev, L.; Perdrisat, C.; Pitz, D.; Potterveld, D.; Punjabi, V.; Qin, L. M.; Reimer, P. E.; Reinhold, J.; Roche, J.; Roos, P. G.; Sarty, A.; Shin, I. K.; Smith, G. R.; Stepanyan, S.; Tang, L. G.; Tadevosyan, V.; Tvaskis, V.; van der Meer, R. L. J.; Vansyoc, K.; Van Westrum, D.; Vidakovic, S.; Volmer, J.; Vulcan, W.; Warren, G.; Wood, S. A.; Xu, C.; Yan, C.; Zhao, W. -X.; Zheng, X.; Zihlmann, B.

The study of exclusive π{sup ±} electroproduction on the nucleon, including separation of the various structure functions, is of interest for a number of reasons. The ratio R{sub L}=σ{sup π{sup -}}{sub L}/σ{sup π{sup +}}{sub L} is sensitive to isoscalar contamination to the dominant isovector pion exchange amplitude, which is the basis for the determination of the charged pion form factor from electroproduction data. A change in the value of R{sub T}=σ{sup π{sup -}}{sub T}/σ{sup π{sup +}}{sub T} from unity at small -t, to 1/4 at large -t, would suggest a transition from coupling to a (virtual) pion to coupling to individual quarks. Furthermore, the mentioned ratios may show an earlier approach to pQCD than the individual cross sections. We have performed the first complete separation of the four unpolarized electromagnetic structure functions above the dominant resonances in forward, exclusive π± electroproduction on the deuteron at central Q{sup 2} values of 0.6, 1.0, 1.6 GeV{sup 2} at W=1.95 GeV, and Q{sup 2}=2.45 GeV{sup 2} at W=2.22 GeV. Here, we present the L and T cross sections, with emphasis on R{sub L} and R{sub T}, and compare them with theoretical calculations. Results for the separated ratio RL indicate dominance of the pion-pole diagram at low -t, while results for R{sub T} are consistent with a transition between pion knockout and quark knockout mechanisms.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States); Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP); National Science Foundation (NSF)
• Contributing Organization: Jefferson Lab F_{π} Collaboration
• Grant/Contract Number: AC02-06CH11357; AC05-84ER40150; AC05-06OR23177
• OSTI ID: 1356650
• Alternate ID(s): OSTI ID: 1130751
• Report Number(s): JLAB-PHY-14-1868; DOE/OR/-23177-3057; arXiv:1404.3985; 101260
• Journal Information: Physical Review Letters, Vol. 112, Issue 18; ISSN 0031-9007
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS