Separated response functions in exclusive, forward ${\pi }^{\pm }$ electroproduction on deuterium

Journal Article · Wed Jan 07 00:00:00 EST 2015 · Physical Review C, Nuclear Physics

DOI:https://doi.org/10.1103/PhysRevC.91.015202· OSTI ID:1167105

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.

Background: Measurements of forward exclusive meson production at different squared four-momenta of the exchanged virtual photon, Q², and at different four-momentum transfer, t, can be used to probe QCD's transition from meson-nucleon degrees of freedom at long distances to quark-gluon degrees of freedom at short scales. Ratios of separated response functions in π⁻ and π⁺ electroproduction are particularly informative. Ratio for transverse photons may allow this transition to be more easily observed, while the ratio for longitudinal photons provides a crucial verification of the assumed pole dominance, needed for reliable extraction of the pion form factor from electroproduction data. Method: Data were acquired with 2.6-5.2 GeV electron beams and the HMS+SOS spectrometers in Jefferson Lab Hall C, at central Q² values of 0.6, 1.0, 1.6 GeV² at W=1.95 GeV, and Q²=2.45 GeV² at W=2.22 GeV. There was significant coverage in Φ And ϵ, which allowed separation of σ_L,T,LT,TT. Results: σL shows a clear signature of the pion pole, with a sharp rise at small -t. In contrast, σ_T is much flatter versus t. The longitudinal/transverse ratios evolve with Q² and t, and at the highest Q²=2.45 GeV² show a slight enhancement for π⁻ Production compared to π⁺. The π⁻/π⁺+ ratio for transverse photons exhibits only a small Q²-dependence, following a nearly universal curve with t, with a steep transition to a value of about 0.25, consistent with s-channel quark knockout. The σ_TT/σ_T ratio also drops rapidly with Q², qualitatively consistent with s-channel helicity conservation. The π⁻/π⁺ ratio for longitudinal photons indicates a small isoscalar contamination at W=1.95 GeV, consistent with what was observed in our earlier determination of the pion form factor at these kinematics.

• Research Organization: Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
• Sponsoring Organization: USDOE; USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
• Contributing Organization: Jefferson Lab F _π Collaboration
• Grant/Contract Number: AC05-84ER40150
• OSTI ID: 1167105
• Alternate ID(s): OSTI ID: 1181345; OSTI ID: 1396041
• Report Number(s): DOE/OR/23177--3258; JLAB-PHY--14-1996; arXiv:1412.5140; ArticleNumber: 015202
• Journal Information: Physical Review C, Nuclear Physics, Journal Name: Physical Review C, Nuclear Physics Journal Issue: 1 Vol. 91; ISSN 0556-2813; ISSN PRVCAN
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

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73 NUCLEAR PHYSICS AND RADIATION PHYSICS