First measurement of massive virtual photon emission from N* baryon resonances

R. Abou Yassine; J. Adamczewski-Musch; O. Arnold; E. T. Atomssa; M. Becker; C. Behnke; J. C. Berger-Chen; A. Blanco; C. Blume; M. Böhmer; L. Chlad; I. Ciepał; S. Deb; C. Deveaux; D. Dittert; J. Dreyer; E. Epple; L. Fabbietti; J. Förtsch; P. Fonte; C. Franco; J. Friese; I. Fröhlich; T. Galatyuk; J. A. Garzón; R. Gernhäuser; R. Greifenhagen; M. Grunwald; M. Gumberidze; S. Harabasz; T. Heinz; T. Hennino; C. Höhne; F. Hojeij; R. Holzmann; M. Idzik; B. Kämpfer; K. H. Kampert; B. Kardan; V. Kedych; S. Kim; I. Koenig; W. Koenig; M. Kohls; J. Kolas; B. W. Kolb; G. Korcyl; G. Kornakov; R. Kotte; W. Krueger; A. Kugler; T. Kunz; R. Lalik; K. Lapidus; S. Linev; F. Linz; L. Lopes; M. Lorenz; T. Mahmoud; L. Maier; A. Malige; J. Markert; S. Maurus; V. Metag; J. Michel; D. M. Mihaylov; A. Molenda; C. Müntz; R. Münzer; M. Nabroth; L. Naumann; K. Nowakowski; A. Opíchal; J. Orliński; J. H. Otto; Y. Parpottas; M. Parschau; C. Pauly; V. Pechenov; O. Pechenova; K. Piasecki; J. Pietraszko; T. Povar; K. Prościński; A. Prozorov; W. Przygoda; K. Pysz; B. Ramstein; N. Rathod; P. Rodriguez-Ramos; A. Rost; A. Rustamov; P. Salabura; K. Scharmann; T. Scheib; N. Schild; K. Schmidt-Sommerfeld; H. Schuldes; E. Schwab; F. Scozzi; F. Seck; P. Sellheim; J. Siebenson; L. Silva; U. Singh; J. Smyrski; S. Spataro; S. Spies; A. Sreejith; H. Ströbele; J. Stroth; C. Sturm; K. Sumara; O. Svoboda; M. Szala; P. Tlusty; M. Traxler; S. Treliński; H. Tsertos; I. C. Udrea; O. Vazquez-Doce; V. Wagner; A. A. Weber; C. Wendisch; M. G. Wiebusch; J. Wirth; A. Władyszewska; H. P. Zbroszczyk; M. Zieliński; P. Zumbruch

doi:10.1016/j.physletb.2026.140338

First measurement of massive virtual photon emission from N* baryon resonances

R. Abou Yassine
, J. Adamczewski-Musch
, O. Arnold
, E. T. Atomssa
, M. Becker
, C. Behnke
, J. C. Berger-Chen
, A. Blanco
, C. Blume
, M. Böhmer
, L. Chlad
, I. Ciepał
, S. Deb
, C. Deveaux
, D. Dittert
, J. Dreyer
, E. Epple
, L. Fabbietti
, J. Förtsch
, P. Fonte

C. Franco, J. Friese, I. Fröhlich, T. Galatyuk, J. A. Garzón, R. Gernhäuser, R. Greifenhagen, M. Grunwald, M. Gumberidze, S. Harabasz, T. Heinz, T. Hennino, C. Höhne, F. Hojeij, R. Holzmann, M. Idzik, B. Kämpfer, K. H. Kampert, B. Kardan, V. Kedych, S. Kim, I. Koenig, W. Koenig, M. Kohls, J. Kolas, B. W. Kolb, G. Korcyl, G. Kornakov, R. Kotte, W. Krueger, A. Kugler, T. Kunz, R. Lalik, K. Lapidus, S. Linev, F. Linz, L. Lopes, M. Lorenz, T. Mahmoud, L. Maier, A. Malige, J. Markert, S. Maurus, V. Metag, J. Michel, D. M. Mihaylov, A. Molenda, C. Müntz, R. Münzer, M. Nabroth, L. Naumann, K. Nowakowski, A. Opíchal, J. Orliński, J. H. Otto, Y. Parpottas, M. Parschau, C. Pauly, V. Pechenov, O. Pechenova, K. Piasecki, J. Pietraszko, T. Povar, K. Prościński, A. Prozorov, W. Przygoda, K. Pysz, B. Ramstein, N. Rathod, P. Rodriguez-Ramos, A. Rost, A. Rustamov, P. Salabura, K. Scharmann, T. Scheib, N. Schild, K. Schmidt-Sommerfeld, H. Schuldes, E. Schwab, F. Scozzi, F. Seck, P. Sellheim, J. Siebenson, L. Silva, U. Singh, J. Smyrski, S. Spataro, S. Spies, A. Sreejith, H. Ströbele, J. Stroth, C. Sturm, K. Sumara, O. Svoboda, M. Szala, P. Tlusty, M. Traxler, S. Treliński, H. Tsertos, I. C. Udrea, O. Vazquez-Doce, V. Wagner, A. A. Weber, C. Wendisch, M. G. Wiebusch, J. Wirth, A. Władyszewska, H. P. Zbroszczyk, M. Zieliński, P. Zumbruch

Chair of Experimentalphysik - Dense and Strange Hadronic Matter

Technische Universität Darmstadt
University Paris-Sud
GSI Helmholtz Center
Excellence Cluster’Origin and Structure of the Universe’
Technical University of Munich
Justus-Liebig-Universität Gießen
Johann Wolfgang Goethe University
LIP-Laboratorio de Instrumentacao e Fisica Experimental de Particulas
Helmholtz Research Academy Hesse for FAIR (HFHF)
Nuclear Physics Institute of the Cas
Czech Technical University in Prague
Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences
HelmholtzZentrum Dresden-Rossendorf
Bergische Universität Wuppertal
Coimbra Polytechnic - ISEC
Helmholtz Research Academy Hesse for FAIR (HFHF)
Universidad de Santiago de Compostela
Technische Universität Dresden
Warsaw Institute of Technology
Univ of Mining and Metallurgy
Jagiellonian University
Palacky University
University of Warsaw
Frederick University
Charles University in Prague
INFN Sez. di Torino

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

1 Scopus citations

Abstract

First information on the timelike electromagnetic structure of baryons in the second resonance region has been obtained from measurements of the dielectron (e⁺e⁻) invariant mass and angular distributions with the High Acceptance Di-Electron Spectrometer (HADES) at GSI, using a secondary pion beam impinging on CH₂ and C targets. The quasi-free reaction π⁻+ p → n e⁺e⁻ at s_πp = 1.49 GeV is isolated in several analysis steps. The data set provides a crucial test for the description of baryon timelike transitions. Close to the kinematical limit the meassured e⁺e⁻ mass distribution shows deviations by up to a factor 8 from the Dalitz decay of a point-like baryon. Various theoretical approaches connecting information from hadronic and electromagnetic channels in the spacelike and timelike regime compare well with the measured e⁺e⁻ invariant mass distribution, including (i) a Vector Meson Dominance amplitude containing direct photon and vector meson (ρ) couplings to the baryon, (ii) electromagnetic timelike baryon transition form factors in a covariant spectator-quark model, where meson cloud effects dominate, and (iii) application of dispersion theory, which demonstrates the importance of the pion electromagnetic form factors. The dielectron angular distributions exhibit contributions of virtual photons (γ *) with longitudinal polarization, in contrast to real photons. The γ * angular dependence supports the dominance of J=3/2, I=1/2 contributions in both the γ ^⋆ n and the ππ N channels.

Original language	English
Article number	140338
Journal	Physics Letters B
Volume	875
DOIs	https://doi.org/10.1016/j.physletb.2026.140338
State	Published - Apr 2026

Keywords

Baryon Dalitz decay
Dilepton
Electromagnetic timelike transitions
Off-shell ρ meson
Pion-nucleon interaction

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10.1016/j.physletb.2026.140338

Cite this

Abou Yassine, R., Adamczewski-Musch, J., Arnold, O., Atomssa, E. T., Becker, M., Behnke, C., Berger-Chen, J. C., Blanco, A., Blume, C., Böhmer, M., Chlad, L., Ciepał, I., Deb, S., Deveaux, C., Dittert, D., Dreyer, J., Epple, E., Fabbietti, L., Förtsch, J., ... Zumbruch, P. (2026). First measurement of massive virtual photon emission from N* baryon resonances. Physics Letters B, 875, Article 140338. https://doi.org/10.1016/j.physletb.2026.140338

@article{d15dad70d907412dbaf356873ca66f53,

title = "First measurement of massive virtual photon emission from N* baryon resonances",

abstract = "First information on the timelike electromagnetic structure of baryons in the second resonance region has been obtained from measurements of the dielectron (e+e−) invariant mass and angular distributions with the High Acceptance Di-Electron Spectrometer (HADES) at GSI, using a secondary pion beam impinging on CH2 and C targets. The quasi-free reaction π−+ p → n e+e− at sπp = 1.49 GeV is isolated in several analysis steps. The data set provides a crucial test for the description of baryon timelike transitions. Close to the kinematical limit the meassured e+e− mass distribution shows deviations by up to a factor 8 from the Dalitz decay of a point-like baryon. Various theoretical approaches connecting information from hadronic and electromagnetic channels in the spacelike and timelike regime compare well with the measured e+e− invariant mass distribution, including (i) a Vector Meson Dominance amplitude containing direct photon and vector meson (ρ) couplings to the baryon, (ii) electromagnetic timelike baryon transition form factors in a covariant spectator-quark model, where meson cloud effects dominate, and (iii) application of dispersion theory, which demonstrates the importance of the pion electromagnetic form factors. The dielectron angular distributions exhibit contributions of virtual photons (γ *) with longitudinal polarization, in contrast to real photons. The γ * angular dependence supports the dominance of J=3/2, I=1/2 contributions in both the γ ⋆ n and the ππ N channels.",

keywords = "Baryon Dalitz decay, Dilepton, Electromagnetic timelike transitions, Off-shell ρ meson, Pion-nucleon interaction",

author = "\{Abou Yassine\}, R. and J. Adamczewski-Musch and O. Arnold and Atomssa, \{E. T.\} and M. Becker and C. Behnke and Berger-Chen, \{J. C.\} and A. Blanco and C. Blume and M. B{\"o}hmer and L. Chlad and I. Ciepa{\l} and S. Deb and C. Deveaux and D. Dittert and J. Dreyer and E. Epple and L. Fabbietti and J. F{\"o}rtsch and P. Fonte and C. Franco and J. Friese and I. Fr{\"o}hlich and T. Galatyuk and Garz{\'o}n, \{J. A.\} and R. Gernh{\"a}user and R. Greifenhagen and M. Grunwald and M. Gumberidze and S. Harabasz and T. Heinz and T. Hennino and C. H{\"o}hne and F. Hojeij and R. Holzmann and M. Idzik and B. K{\"a}mpfer and Kampert, \{K. H.\} and B. Kardan and V. Kedych and S. Kim and I. Koenig and W. Koenig and M. Kohls and J. Kolas and Kolb, \{B. W.\} and G. Korcyl and G. Kornakov and R. Kotte and W. Krueger and A. Kugler and T. Kunz and R. Lalik and K. Lapidus and S. Linev and F. Linz and L. Lopes and M. Lorenz and T. Mahmoud and L. Maier and A. Malige and J. Markert and S. Maurus and V. Metag and J. Michel and Mihaylov, \{D. M.\} and A. Molenda and C. M{\"u}ntz and R. M{\"u}nzer and M. Nabroth and L. Naumann and K. Nowakowski and A. Op{\'i}chal and J. Orli{\'n}ski and Otto, \{J. H.\} and Y. Parpottas and M. Parschau and C. Pauly and V. Pechenov and O. Pechenova and K. Piasecki and J. Pietraszko and T. Povar and K. Pro{\'s}ci{\'n}ski and A. Prozorov and W. Przygoda and K. Pysz and B. Ramstein and N. Rathod and P. Rodriguez-Ramos and A. Rost and A. Rustamov and P. Salabura and K. Scharmann and T. Scheib and N. Schild and K. Schmidt-Sommerfeld and H. Schuldes and E. Schwab and F. Scozzi and F. Seck and P. Sellheim and J. Siebenson and L. Silva and U. Singh and J. Smyrski and S. Spataro and S. Spies and A. Sreejith and H. Str{\"o}bele and J. Stroth and C. Sturm and K. Sumara and O. Svoboda and M. Szala and P. Tlusty and M. Traxler and S. Treli{\'n}ski and H. Tsertos and Udrea, \{I. C.\} and O. Vazquez-Doce and V. Wagner and Weber, \{A. A.\} and C. Wendisch and Wiebusch, \{M. G.\} and J. Wirth and A. W{\l}adyszewska and Zbroszczyk, \{H. P.\} and M. Zieli{\'n}ski and P. Zumbruch",

note = "Publisher Copyright: {\textcopyright} 2026 The Authors.",

year = "2026",

month = apr,

doi = "10.1016/j.physletb.2026.140338",

language = "English",

volume = "875",

journal = "Physics Letters B",

issn = "0370-2693",

publisher = "Elsevier B.V.",

}

Abou Yassine, R, Adamczewski-Musch, J, Arnold, O, Atomssa, ET, Becker, M, Behnke, C, Berger-Chen, JC, Blanco, A, Blume, C, Böhmer, M, Chlad, L, Ciepał, I, Deb, S, Deveaux, C, Dittert, D, Dreyer, J, Epple, E, Fabbietti, L, Förtsch, J, Fonte, P, Franco, C, Friese, J, Fröhlich, I, Galatyuk, T, Garzón, JA, Gernhäuser, R, Greifenhagen, R, Grunwald, M, Gumberidze, M, Harabasz, S, Heinz, T, Hennino, T, Höhne, C, Hojeij, F, Holzmann, R, Idzik, M, Kämpfer, B, Kampert, KH, Kardan, B, Kedych, V, Kim, S, Koenig, I, Koenig, W, Kohls, M, Kolas, J, Kolb, BW, Korcyl, G, Kornakov, G, Kotte, R, Krueger, W, Kugler, A, Kunz, T, Lalik, R, Lapidus, K, Linev, S, Linz, F, Lopes, L, Lorenz, M, Mahmoud, T, Maier, L, Malige, A, Markert, J, Maurus, S, Metag, V, Michel, J, Mihaylov, DM, Molenda, A, Müntz, C, Münzer, R, Nabroth, M, Naumann, L, Nowakowski, K, Opíchal, A, Orliński, J, Otto, JH, Parpottas, Y, Parschau, M, Pauly, C, Pechenov, V, Pechenova, O, Piasecki, K, Pietraszko, J, Povar, T, Prościński, K, Prozorov, A, Przygoda, W, Pysz, K, Ramstein, B, Rathod, N, Rodriguez-Ramos, P, Rost, A, Rustamov, A, Salabura, P, Scharmann, K, Scheib, T, Schild, N, Schmidt-Sommerfeld, K, Schuldes, H, Schwab, E, Scozzi, F, Seck, F, Sellheim, P, Siebenson, J, Silva, L, Singh, U, Smyrski, J, Spataro, S, Spies, S, Sreejith, A, Ströbele, H, Stroth, J, Sturm, C, Sumara, K, Svoboda, O, Szala, M, Tlusty, P, Traxler, M, Treliński, S, Tsertos, H, Udrea, IC, Vazquez-Doce, O, Wagner, V, Weber, AA, Wendisch, C, Wiebusch, MG, Wirth, J, Władyszewska, A, Zbroszczyk, HP, Zieliński, M & Zumbruch, P 2026, 'First measurement of massive virtual photon emission from N* baryon resonances', Physics Letters B, vol. 875, 140338. https://doi.org/10.1016/j.physletb.2026.140338

TY - JOUR

T1 - First measurement of massive virtual photon emission from N* baryon resonances

AU - Abou Yassine, R.

AU - Adamczewski-Musch, J.

AU - Arnold, O.

AU - Atomssa, E. T.

AU - Becker, M.

AU - Behnke, C.

AU - Berger-Chen, J. C.

AU - Blanco, A.

AU - Blume, C.

AU - Böhmer, M.

AU - Chlad, L.

AU - Ciepał, I.

AU - Deb, S.

AU - Deveaux, C.

AU - Dittert, D.

AU - Dreyer, J.

AU - Epple, E.

AU - Fabbietti, L.

AU - Förtsch, J.

AU - Fonte, P.

AU - Franco, C.

AU - Friese, J.

AU - Fröhlich, I.

AU - Galatyuk, T.

AU - Garzón, J. A.

AU - Gernhäuser, R.

AU - Greifenhagen, R.

AU - Grunwald, M.

AU - Gumberidze, M.

AU - Harabasz, S.

AU - Heinz, T.

AU - Hennino, T.

AU - Höhne, C.

AU - Hojeij, F.

AU - Holzmann, R.

AU - Idzik, M.

AU - Kämpfer, B.

AU - Kampert, K. H.

AU - Kardan, B.

AU - Kedych, V.

AU - Kim, S.

AU - Koenig, I.

AU - Koenig, W.

AU - Kohls, M.

AU - Kolas, J.

AU - Kolb, B. W.

AU - Korcyl, G.

AU - Kornakov, G.

AU - Kotte, R.

AU - Krueger, W.

AU - Kugler, A.

AU - Kunz, T.

AU - Lalik, R.

AU - Lapidus, K.

AU - Linev, S.

AU - Linz, F.

AU - Lopes, L.

AU - Lorenz, M.

AU - Mahmoud, T.

AU - Maier, L.

AU - Malige, A.

AU - Markert, J.

AU - Maurus, S.

AU - Metag, V.

AU - Michel, J.

AU - Mihaylov, D. M.

AU - Molenda, A.

AU - Müntz, C.

AU - Münzer, R.

AU - Nabroth, M.

AU - Naumann, L.

AU - Nowakowski, K.

AU - Opíchal, A.

AU - Orliński, J.

AU - Otto, J. H.

AU - Parpottas, Y.

AU - Parschau, M.

AU - Pauly, C.

AU - Pechenov, V.

AU - Pechenova, O.

AU - Piasecki, K.

AU - Pietraszko, J.

AU - Povar, T.

AU - Prościński, K.

AU - Prozorov, A.

AU - Przygoda, W.

AU - Pysz, K.

AU - Ramstein, B.

AU - Rathod, N.

AU - Rodriguez-Ramos, P.

AU - Rost, A.

AU - Rustamov, A.

AU - Salabura, P.

AU - Scharmann, K.

AU - Scheib, T.

AU - Schild, N.

AU - Schmidt-Sommerfeld, K.

AU - Schuldes, H.

AU - Schwab, E.

AU - Scozzi, F.

AU - Seck, F.

AU - Sellheim, P.

AU - Siebenson, J.

AU - Silva, L.

AU - Singh, U.

AU - Smyrski, J.

AU - Spataro, S.

AU - Spies, S.

AU - Sreejith, A.

AU - Ströbele, H.

AU - Stroth, J.

AU - Sturm, C.

AU - Sumara, K.

AU - Svoboda, O.

AU - Szala, M.

AU - Tlusty, P.

AU - Traxler, M.

AU - Treliński, S.

AU - Tsertos, H.

AU - Udrea, I. C.

AU - Vazquez-Doce, O.

AU - Wagner, V.

AU - Weber, A. A.

AU - Wendisch, C.

AU - Wiebusch, M. G.

AU - Wirth, J.

AU - Władyszewska, A.

AU - Zbroszczyk, H. P.

AU - Zieliński, M.

AU - Zumbruch, P.

PY - 2026/4

Y1 - 2026/4

N2 - First information on the timelike electromagnetic structure of baryons in the second resonance region has been obtained from measurements of the dielectron (e+e−) invariant mass and angular distributions with the High Acceptance Di-Electron Spectrometer (HADES) at GSI, using a secondary pion beam impinging on CH2 and C targets. The quasi-free reaction π−+ p → n e+e− at sπp = 1.49 GeV is isolated in several analysis steps. The data set provides a crucial test for the description of baryon timelike transitions. Close to the kinematical limit the meassured e+e− mass distribution shows deviations by up to a factor 8 from the Dalitz decay of a point-like baryon. Various theoretical approaches connecting information from hadronic and electromagnetic channels in the spacelike and timelike regime compare well with the measured e+e− invariant mass distribution, including (i) a Vector Meson Dominance amplitude containing direct photon and vector meson (ρ) couplings to the baryon, (ii) electromagnetic timelike baryon transition form factors in a covariant spectator-quark model, where meson cloud effects dominate, and (iii) application of dispersion theory, which demonstrates the importance of the pion electromagnetic form factors. The dielectron angular distributions exhibit contributions of virtual photons (γ *) with longitudinal polarization, in contrast to real photons. The γ * angular dependence supports the dominance of J=3/2, I=1/2 contributions in both the γ ⋆ n and the ππ N channels.

AB - First information on the timelike electromagnetic structure of baryons in the second resonance region has been obtained from measurements of the dielectron (e+e−) invariant mass and angular distributions with the High Acceptance Di-Electron Spectrometer (HADES) at GSI, using a secondary pion beam impinging on CH2 and C targets. The quasi-free reaction π−+ p → n e+e− at sπp = 1.49 GeV is isolated in several analysis steps. The data set provides a crucial test for the description of baryon timelike transitions. Close to the kinematical limit the meassured e+e− mass distribution shows deviations by up to a factor 8 from the Dalitz decay of a point-like baryon. Various theoretical approaches connecting information from hadronic and electromagnetic channels in the spacelike and timelike regime compare well with the measured e+e− invariant mass distribution, including (i) a Vector Meson Dominance amplitude containing direct photon and vector meson (ρ) couplings to the baryon, (ii) electromagnetic timelike baryon transition form factors in a covariant spectator-quark model, where meson cloud effects dominate, and (iii) application of dispersion theory, which demonstrates the importance of the pion electromagnetic form factors. The dielectron angular distributions exhibit contributions of virtual photons (γ *) with longitudinal polarization, in contrast to real photons. The γ * angular dependence supports the dominance of J=3/2, I=1/2 contributions in both the γ ⋆ n and the ππ N channels.

KW - Baryon Dalitz decay

KW - Dilepton

KW - Electromagnetic timelike transitions

KW - Off-shell ρ meson

KW - Pion-nucleon interaction

UR - https://www.scopus.com/pages/publications/105033247819

U2 - 10.1016/j.physletb.2026.140338

DO - 10.1016/j.physletb.2026.140338

M3 - Article

AN - SCOPUS:105033247819

SN - 0370-2693

VL - 875

JO - Physics Letters B

JF - Physics Letters B

M1 - 140338

ER -

First measurement of massive virtual photon emission from N* baryon resonances

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