Lowest- Q2 measurement of the γp → Δ reaction: Probing the pionic contribution

S. Stave; M. O. Distler; I. Nakagawa; N. Sparveris; P. Achenbach; C. Ayerbe Gayoso; D. Baumann; J. Bernauer; A. M. Bernstein; R. Böhm; D. Bosnar; T. Botto; A. Christopoulou; D. Dale; M. Ding; L. Doria; J. Friedrich; A. Karabarbounis; M. Makek; H. Merkel; U. Müller; R. Neuhausen; L. Nungesser; C. N. Papanicolas; A. Piegsa; J. Pochodzalla; M. Potokar; M. Seimetz; S. Širca; S. Stiliaris; Th Walcher; M. Weis

doi:10.1140/epja/i2006-10162-1

Lowest- Q² measurement of the γp → Δ reaction: Probing the pionic contribution

S. Stave
, M. O. Distler
, I. Nakagawa
, N. Sparveris
, P. Achenbach
, C. Ayerbe Gayoso
, D. Baumann
, J. Bernauer
, A. M. Bernstein
, R. Böhm
, D. Bosnar
, T. Botto
, A. Christopoulou
, D. Dale
, M. Ding
, L. Doria
, J. Friedrich
, A. Karabarbounis
, M. Makek
, H. Merkel

U. Müller, R. Neuhausen, L. Nungesser, C. N. Papanicolas, A. Piegsa, J. Pochodzalla, M. Potokar, M. Seimetz, S. Širca, S. Stiliaris, Th Walcher, M. Weis

Physics and Astronomy

Massachusetts Institute of Technology
Duke University
Johannes Gutenberg University Mainz
University of Kentucky
RIKEN
National and Kapodistrian University of Athens
University of Zagreb
University of Ljubljana
University of Bonn

Research output: Contribution to journal › Article › peer-review

58 Scopus citations

Abstract

To determine nonspherical angular-momentum amplitudes in hadrons at long ranges (low Q²), data were taken for the p(̄e, e'p)π⁰ reaction in the Δ region at Q ² = 0.060 (GeV/c)² utilizing the magnetic spectrometers of the A1 Collaboration at MAMI. The results for the dominant transition magnetic dipole amplitude and the quadrupole to dipole ratios at W = 1232 MeV are M₁₊ ^3/2=(40.33 ± 0.63_stat+syst ± 0.61 _model)(10^-3/m_π+), Re(E₁₊ ^3/2/M₁₊^3/2)=(-2.28 ± 0.29 _stat+syst ± 0.20_model)%, and Re(S₁₊ ^3/2/M₁₊^3/2) =(-4.81 ± 0.27 _stat+syst ± 0.26_model)%. These disagree with predictions of constituent quark models but are in reasonable agreement with lattice calculations with nonlinear (chiral) pion mass extrapolations, with chiral effective field theory, and with dynamical models with pion cloud effects. These results confirm the dominance, and general Q² variation, of the pionic contribution at large distances.

Original language	English
Pages (from-to)	471-476
Number of pages	6
Journal	European Physical Journal A
Volume	30
Issue number	3
DOIs	https://doi.org/10.1140/epja/i2006-10162-1
State	Published - Dec 2006

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Stave, S., Distler, M. O., Nakagawa, I., Sparveris, N., Achenbach, P., Ayerbe Gayoso, C., Baumann, D., Bernauer, J., Bernstein, A. M., Böhm, R., Bosnar, D., Botto, T., Christopoulou, A., Dale, D., Ding, M., Doria, L., Friedrich, J., Karabarbounis, A., Makek, M., ... Weis, M. (2006). Lowest- Q² measurement of the γp → Δ reaction: Probing the pionic contribution. European Physical Journal A, 30(3), 471-476. https://doi.org/10.1140/epja/i2006-10162-1

@article{740b02f124ee43acab9c4688f9cd0014,

title = "Lowest- Q2 measurement of the γp → Δ reaction: Probing the pionic contribution",

abstract = "To determine nonspherical angular-momentum amplitudes in hadrons at long ranges (low Q2), data were taken for the p{\=(}e, e'p)π0 reaction in the Δ region at Q 2 = 0.060 (GeV/c)2 utilizing the magnetic spectrometers of the A1 Collaboration at MAMI. The results for the dominant transition magnetic dipole amplitude and the quadrupole to dipole ratios at W = 1232 MeV are M1+ 3/2=(40.33 ± 0.63stat+syst ± 0.61 model)(10-3/mπ+), Re(E1+ 3/2/M1+3/2)=(-2.28 ± 0.29 stat+syst ± 0.20model)\%, and Re(S1+ 3/2/M1+3/2) =(-4.81 ± 0.27 stat+syst ± 0.26model)\%. These disagree with predictions of constituent quark models but are in reasonable agreement with lattice calculations with nonlinear (chiral) pion mass extrapolations, with chiral effective field theory, and with dynamical models with pion cloud effects. These results confirm the dominance, and general Q2 variation, of the pionic contribution at large distances.",

author = "S. Stave and Distler, \{M. O.\} and I. Nakagawa and N. Sparveris and P. Achenbach and \{Ayerbe Gayoso\}, C. and D. Baumann and J. Bernauer and Bernstein, \{A. M.\} and R. B{\"o}hm and D. Bosnar and T. Botto and A. Christopoulou and D. Dale and M. Ding and L. Doria and J. Friedrich and A. Karabarbounis and M. Makek and H. Merkel and U. M{\"u}ller and R. Neuhausen and L. Nungesser and Papanicolas, \{C. N.\} and A. Piegsa and J. Pochodzalla and M. Potokar and M. Seimetz and S. {\v S}irca and S. Stiliaris and Th Walcher and M. Weis",

year = "2006",

month = dec,

doi = "10.1140/epja/i2006-10162-1",

language = "English",

volume = "30",

pages = "471--476",

journal = "European Physical Journal A",

issn = "1434-6001",

number = "3",

}

Stave, S, Distler, MO, Nakagawa, I, Sparveris, N, Achenbach, P, Ayerbe Gayoso, C, Baumann, D, Bernauer, J, Bernstein, AM, Böhm, R, Bosnar, D, Botto, T, Christopoulou, A, Dale, D, Ding, M, Doria, L, Friedrich, J, Karabarbounis, A, Makek, M, Merkel, H, Müller, U, Neuhausen, R, Nungesser, L, Papanicolas, CN, Piegsa, A, Pochodzalla, J, Potokar, M, Seimetz, M, Širca, S, Stiliaris, S, Walcher, T & Weis, M 2006, 'Lowest- Q² measurement of the γp → Δ reaction: Probing the pionic contribution', European Physical Journal A, vol. 30, no. 3, pp. 471-476. https://doi.org/10.1140/epja/i2006-10162-1

TY - JOUR

T1 - Lowest- Q2 measurement of the γp → Δ reaction

T2 - Probing the pionic contribution

AU - Stave, S.

AU - Distler, M. O.

AU - Nakagawa, I.

AU - Sparveris, N.

AU - Achenbach, P.

AU - Ayerbe Gayoso, C.

AU - Baumann, D.

AU - Bernauer, J.

AU - Bernstein, A. M.

AU - Böhm, R.

AU - Bosnar, D.

AU - Botto, T.

AU - Christopoulou, A.

AU - Dale, D.

AU - Ding, M.

AU - Doria, L.

AU - Friedrich, J.

AU - Karabarbounis, A.

AU - Makek, M.

AU - Merkel, H.

AU - Müller, U.

AU - Neuhausen, R.

AU - Nungesser, L.

AU - Papanicolas, C. N.

AU - Piegsa, A.

AU - Pochodzalla, J.

AU - Potokar, M.

AU - Seimetz, M.

AU - Širca, S.

AU - Stiliaris, S.

AU - Walcher, Th

AU - Weis, M.

PY - 2006/12

Y1 - 2006/12

N2 - To determine nonspherical angular-momentum amplitudes in hadrons at long ranges (low Q2), data were taken for the p(̄e, e'p)π0 reaction in the Δ region at Q 2 = 0.060 (GeV/c)2 utilizing the magnetic spectrometers of the A1 Collaboration at MAMI. The results for the dominant transition magnetic dipole amplitude and the quadrupole to dipole ratios at W = 1232 MeV are M1+ 3/2=(40.33 ± 0.63stat+syst ± 0.61 model)(10-3/mπ+), Re(E1+ 3/2/M1+3/2)=(-2.28 ± 0.29 stat+syst ± 0.20model)%, and Re(S1+ 3/2/M1+3/2) =(-4.81 ± 0.27 stat+syst ± 0.26model)%. These disagree with predictions of constituent quark models but are in reasonable agreement with lattice calculations with nonlinear (chiral) pion mass extrapolations, with chiral effective field theory, and with dynamical models with pion cloud effects. These results confirm the dominance, and general Q2 variation, of the pionic contribution at large distances.

AB - To determine nonspherical angular-momentum amplitudes in hadrons at long ranges (low Q2), data were taken for the p(̄e, e'p)π0 reaction in the Δ region at Q 2 = 0.060 (GeV/c)2 utilizing the magnetic spectrometers of the A1 Collaboration at MAMI. The results for the dominant transition magnetic dipole amplitude and the quadrupole to dipole ratios at W = 1232 MeV are M1+ 3/2=(40.33 ± 0.63stat+syst ± 0.61 model)(10-3/mπ+), Re(E1+ 3/2/M1+3/2)=(-2.28 ± 0.29 stat+syst ± 0.20model)%, and Re(S1+ 3/2/M1+3/2) =(-4.81 ± 0.27 stat+syst ± 0.26model)%. These disagree with predictions of constituent quark models but are in reasonable agreement with lattice calculations with nonlinear (chiral) pion mass extrapolations, with chiral effective field theory, and with dynamical models with pion cloud effects. These results confirm the dominance, and general Q2 variation, of the pionic contribution at large distances.

UR - https://www.scopus.com/pages/publications/33845950857

U2 - 10.1140/epja/i2006-10162-1

DO - 10.1140/epja/i2006-10162-1

M3 - Article

AN - SCOPUS:33845950857

SN - 1434-6001

VL - 30

SP - 471

EP - 476

JO - European Physical Journal A

JF - European Physical Journal A

IS - 3

ER -

Lowest- Q² measurement of the γp → Δ reaction: Probing the pionic contribution

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