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Title: Separated response functions in exclusive, forward π ± electroproduction on deuterium

Abstract

Background: Measurements of forward exclusive meson production at different squared four-momenta of the exchanged virtual photon, Q(2), 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 pi(-) and pi(+) electroproduction are particularly informative. The 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. Purpose: We perform the first complete separation of the four unpolarized electromagnetic structure functions L/T/LT/TT in forward, exclusive pi(+/-) electroproduction on deuterium above the dominant resonances. Method: Data were acquired with 2.6-5.2-GeV electron beams and the HMS + SOS spectrometers in Jefferson Lab Hall C at central Q(2) values of 0.6, 1.0, and 1.6 GeV2 at W = 1.95 GeV, and Q(2) = 2.45 GeV2 at W = 2.22 GeV. There was significant coverage in phi and is an element of, which allowed separation of sigma(L), T, LT, TT. Results: sigma(L) shows a clear signature of the pion pole, withmore » a sharp rise at small -t. In contrast, sigma(T) is much flatter versus t. The longitudinal/transverse ratios evolve with Q(2) and t and at the highest Q(2) = 2.45 GeV2 show a slight enhancement for pi(-) production compared to pi(+). The pi(-)/pi(+) ratio for transverse photons exhibits only a small Q(2) 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 sigma(TT)/sigma(T) ratio also drops rapidly with Q(2), qualitatively consistent with s-channel helicity conservation. The pi(-)/pi(+) 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. Conclusions: The separated cross sections are compared to a variety of theoretical models, which generally describe sigma(L) but have varying success with sigma(T). Further theoretical input is required to provide a more profound insight into the relevant reaction mechanisms for longitudinal and transverse photons, such as whether the observed transverse ratio is indeed attributable to a transition from pion to quark knockout mechanisms and provide useful information regarding the twist-3 transversity generalized parton distribution, H-T« less

Authors:
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Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
National Science Foundation (NSF); Natural Sciences and Engineering Research Council of Canada (NSERC); National Research Foundation of Korea (NRF); USDOE Office of Science - Office of Nuclear Physics
Contributing Org.:
Jefferson Lab F_{π} Collaboration
OSTI Identifier:
1396041
DOE Contract Number:  
AC02-06CH11357
Resource Type:
Journal Article
Journal Name:
Physical Review. C, Nuclear Physics
Additional Journal Information:
Journal Volume: 91; Journal Issue: 1; Journal ID: ISSN 0556-2813
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

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., and Zihlmann, B. Separated response functions in exclusive, forward π± electroproduction on deuterium. United States: N. p., 2015. Web. doi:10.1103/PhysRevC.91.015202.
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. Separated response functions in exclusive, forward π± electroproduction on deuterium. United States. doi:10.1103/PhysRevC.91.015202.
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., and Zihlmann, B. Thu . "Separated response functions in exclusive, forward π± electroproduction on deuterium". United States. doi:10.1103/PhysRevC.91.015202.
@article{osti_1396041,
title = {Separated response functions in exclusive, forward π± electroproduction on deuterium},
author = {Huber, G. M. and Blok, H. P. and Butuceanu, C. and Gaskell, D. and Horn, T. and Mack, D. J. and Abbott, D. and Aniol, K. and Anklin, H. and Armstrong, C. and Arrington, J. and Assamagan, K. and Avery, S. and Baker, O. K. and Barrett, B. and Beise, E. J. and Bochna, C. and Boeglin, W. and Brash, E. J. and Breuer, H. and Chang, C. C. and Chant, N. and Christy, M. E. and Dunne, J. and Eden, T. and Ent, R. and Fenker, H. and Gibson, E. F. and Gilman, R. and Gustafsson, K. and Hinton, W. and Holt, R. J. and Jackson, H. and Jin, S. and Jones, M. K. and Keppel, C. E. and Kim, P. H. and Kim, W. and King, P. M. and Klein, A. and Koltenuk, D. and Kovaltchouk, V. and Liang, M. and Liu, J. and Lolos, G. J. and Lung, A. and Margaziotis, D. J. and Markowitz, P. and Matsumura, A. and McKee, D. and Meekins, D. and Mitchell, J. and Miyoshi, T. and Mkrtchyan, H. and Mueller, B. and Niculescu, G. and Niculescu, I. and Okayasu, Y. and Pentchev, L. and Perdrisat, C. and Pitz, D. and Potterveld, D. and Punjabi, V. and Qin, L. M. and Reimer, P. E. and Reinhold, J. and Roche, J. and Roos, P. G. and Sarty, A. and Shin, I. K. and Smith, G. R. and Stepanyan, S. and Tang, L. G. and Tadevosyan, V. and Tvaskis, V. and van der Meer, R. L. J. and Vansyoc, K. and Van Westrum, D. and Vidakovic, S. and Volmer, J. and Vulcan, W. and Warren, G. and Wood, S. A. and Xu, C. and Yan, C. and Zhao, W. -X. and Zheng, X. and Zihlmann, B.},
abstractNote = {Background: Measurements of forward exclusive meson production at different squared four-momenta of the exchanged virtual photon, Q(2), 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 pi(-) and pi(+) electroproduction are particularly informative. The 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. Purpose: We perform the first complete separation of the four unpolarized electromagnetic structure functions L/T/LT/TT in forward, exclusive pi(+/-) electroproduction on deuterium above the dominant resonances. Method: Data were acquired with 2.6-5.2-GeV electron beams and the HMS + SOS spectrometers in Jefferson Lab Hall C at central Q(2) values of 0.6, 1.0, and 1.6 GeV2 at W = 1.95 GeV, and Q(2) = 2.45 GeV2 at W = 2.22 GeV. There was significant coverage in phi and is an element of, which allowed separation of sigma(L), T, LT, TT. Results: sigma(L) shows a clear signature of the pion pole, with a sharp rise at small -t. In contrast, sigma(T) is much flatter versus t. The longitudinal/transverse ratios evolve with Q(2) and t and at the highest Q(2) = 2.45 GeV2 show a slight enhancement for pi(-) production compared to pi(+). The pi(-)/pi(+) ratio for transverse photons exhibits only a small Q(2) 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 sigma(TT)/sigma(T) ratio also drops rapidly with Q(2), qualitatively consistent with s-channel helicity conservation. The pi(-)/pi(+) 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. Conclusions: The separated cross sections are compared to a variety of theoretical models, which generally describe sigma(L) but have varying success with sigma(T). Further theoretical input is required to provide a more profound insight into the relevant reaction mechanisms for longitudinal and transverse photons, such as whether the observed transverse ratio is indeed attributable to a transition from pion to quark knockout mechanisms and provide useful information regarding the twist-3 transversity generalized parton distribution, H-T},
doi = {10.1103/PhysRevC.91.015202},
journal = {Physical Review. C, Nuclear Physics},
issn = {0556-2813},
number = 1,
volume = 91,
place = {United States},
year = {2015},
month = {1}
}

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