Measurement of angular distributions and R = σL/σT in diffractive electroproduction of ρ0 mesons

K. Ackerstaff; A. Airapetian; N. Akopov; M. Amarian; E. C. Aschenauer; H. Avakian; R. Avakian; A. Avetissian; B. Bains; M. Beckmann; S. Belostotski; J. E. Belz; Th Benisch; S. Bernreuther; N. Bianchi; S. Blanchard; J. Blouw; H. Böttcher; A. Borissov; J. Brack; B. Braun; B. Bray; W. Brückner; A. Brüll; E. E.W. Bruins; H. J. Bulten; G. P. Capitani; P. Carter; E. Cisbani; G. R. Court; P. P.J. Delheij; E. De Sanctis; D. De Schepper; E. Devitsin; P. K.A. de Witt Huberts; M. Düren; A. Dvoredsky; G. Elbakian; J. Emerson; A. Fantoni; A. Fechtchenko; M. Ferstl; K. Fiedler; B. W. Filippone; H. Fischer; B. Fox; J. Franz; S. Frullani; M. A. Funk; Y. Gärber; N. D. Gagunashvili; P. Galumian; H. Gao; F. Garibaldi; G. Gavrilov; P. Geiger; V. Gharibyan; A. Golendukhin; G. Graw; O. Grebeniouk; P. W. Green; L. G. Greeniaus; C. Grosshauser; A. Gute; V. Gyurjyan; J. P. Haas; W. Haeberli; O. Häusser; J. O. Hansen; D. Hasch; R. Henderson; Th Henkes; R. Hertenberger; Y. Holler; R. J. Holt; H. Ihssen; M. Iodice; A. Izotov; H. E. Jackson; A. Jgoun; C. Jones; R. Kaiser; E. Kinney; M. Kirsch; A. Kisselev; P. Kitching; K. Königsmann; M. Kolstein; H. Kolster; W. Korsch; V. Kozlov; L. H. Kramer; B. Krause; V. G. Krivokhijine; M. Kückes; G. Kyle; W. Lachnit; W. Lorenzon; A. Lung; N. C.R. Makins; S. I. Manaenkov; F. K. Martens; J. W. Martin; A. Mateos; K. Mcllhany; R. D. McKeown; F. Meissner; F. Menden; D. Mercer; A. Metz; N. Meyners; O. Mikloukho; C. A. Miller; M. A. Miller; R. Milner; V. Mitsyn; A. Most; R. Mozzetti; V. Muccifora; A. Nagaitsev; Y. Naryshkin; A. M. Nathan; F. Neunreither; J. M. Niczyporuk; W. D. Nowak; M. Nupieri; P. Oelwein; H. Ogami; T. G. O'Neill; R. Openshaw; J. Ouyang; S. F. Pate; M. Pitt; H. R. Poolman; S. Potashov; D. H. Potterveld; G. Rakness; R. Redwine; A. R. Reolon; R. Ristinen; K. Rith; G. Röper; H. O. Roloff; P. Rossi; M. Ruh; D. Ryckbosch; Y. Sakemi; I. Savin; K. P. Schüler; A. Schwind; T. A. Shibata; T. Shin; A. Simon; K. Sinram; W. R. Smythe; J. Sowinski; M. Spengos; E. Steffens; J. Stenger; J. Stewart; F. Stock; U. Stösslein; M. Sutter; H. Tallini; S. Taroian; A. Terkulov; D. M. Thiessen; B. Tipton; A. Trudel; M. Tytgat; G. M. Urciuoli; J. F.J. van den Brand; G. van der Steenhoven; R. van de Vyver; M. C. Vetterli; M. G. Vincter; E. Volk; W. Wander; T. P. Welch; S. E. Williamson; T. Wise; K. Zapfe; H. Zohrabian

doi:10.1007/s100520000536

Measurement of angular distributions and R = σ_L/σ_T in diffractive electroproduction of ρ⁰ mesons

K. Ackerstaff, A. Airapetian, N. Akopov, M. Amarian, E. C. Aschenauer, H. Avakian, R. Avakian, A. Avetissian, B. Bains, M. Beckmann, S. Belostotski, J. E. Belz, Th Benisch, S. Bernreuther, N. Bianchi, S. Blanchard, J. Blouw, H. Böttcher, A. Borissov, J. BrackB. Braun, B. Bray, W. Brückner, A. Brüll, E. E.W. Bruins, H. J. Bulten, G. P. Capitani, P. Carter, E. Cisbani, G. R. Court, P. P.J. Delheij, E. De Sanctis, D. De Schepper, E. Devitsin, P. K.A. de Witt Huberts, M. Düren, A. Dvoredsky, G. Elbakian, J. Emerson, A. Fantoni, A. Fechtchenko, M. Ferstl, K. Fiedler, B. W. Filippone, H. Fischer, B. Fox, J. Franz, S. Frullani, M. A. Funk, Y. Gärber, N. D. Gagunashvili, P. Galumian, H. Gao, F. Garibaldi, G. Gavrilov, P. Geiger, V. Gharibyan, A. Golendukhin, G. Graw, O. Grebeniouk, P. W. Green, L. G. Greeniaus, C. Grosshauser, A. Gute, V. Gyurjyan, J. P. Haas, W. Haeberli, O. Häusser, J. O. Hansen, D. Hasch, R. Henderson, Th Henkes, R. Hertenberger, Y. Holler, R. J. Holt, H. Ihssen, M. Iodice, A. Izotov, H. E. Jackson, A. Jgoun, C. Jones, R. Kaiser, E. Kinney, M. Kirsch, A. Kisselev, P. Kitching, K. Königsmann, M. Kolstein, H. Kolster, W. Korsch, V. Kozlov, L. H. Kramer, B. Krause, V. G. Krivokhijine, M. Kückes, G. Kyle, W. Lachnit, W. Lorenzon, A. Lung, N. C.R. Makins, S. I. Manaenkov, F. K. Martens, J. W. Martin, A. Mateos, K. Mcllhany, R. D. McKeown, F. Meissner, F. Menden, D. Mercer, A. Metz, N. Meyners, O. Mikloukho, C. A. Miller, M. A. Miller, R. Milner, V. Mitsyn, A. Most, R. Mozzetti, V. Muccifora, A. Nagaitsev, Y. Naryshkin, A. M. Nathan, F. Neunreither, J. M. Niczyporuk, W. D. Nowak, M. Nupieri, P. Oelwein, H. Ogami, T. G. O'Neill, R. Openshaw, J. Ouyang, S. F. Pate, M. Pitt, H. R. Poolman, S. Potashov, D. H. Potterveld, G. Rakness, R. Redwine, A. R. Reolon, R. Ristinen, K. Rith, G. Röper, H. O. Roloff, P. Rossi, M. Ruh, D. Ryckbosch, Y. Sakemi, I. Savin, K. P. Schüler, A. Schwind, T. A. Shibata, T. Shin, A. Simon, K. Sinram, W. R. Smythe, J. Sowinski, M. Spengos, E. Steffens, J. Stenger, J. Stewart, F. Stock, U. Stösslein, M. Sutter, H. Tallini, S. Taroian, A. Terkulov, D. M. Thiessen, B. Tipton, A. Trudel, M. Tytgat, G. M. Urciuoli, J. F.J. van den Brand, G. van der Steenhoven, R. van de Vyver, M. C. Vetterli, M. G. Vincter, E. Volk, W. Wander, T. P. Welch, S. E. Williamson, T. Wise, K. Zapfe, H. Zohrabian

Faculty of Industrial Engineering, Mechanical Engineering and Computer Science

University of Iceland

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

Abstract

Production and decay angular distributions were extracted from measurements of exclusive electroproduction of the ρ⁰(770) meson over a range in the virtual photon negative four-momentum squared 0.5 < Q² < 4 GeV² and the photon-nucleon invariant mass range 3.8 < W < 6.5 GeV. The experiment was performed with the HERMES spectrometer, using a longitudinally polarized positron beam and a ³He gas target internal to the HERA e^± storage ring. The event sample combines ρ⁰ mesons produced incoherently off individual nucleons and coherently off the nucleus as a whole. The distributions in one production angle and two angles describing the ρ⁰ → π⁺π^- decay yielded measurements of eight elements of the spin-density matrix, including one that had not been measured before. The results are consistent with the dominance of helicity conserving amplitudes and natural parity exchange. The improved precision achieved at 4 < W < 7 GeV, in combination with other data at W > 7 GeV, reveals evidence for an energy dependence in the ratio R of the longitudinal to transverse cross sections at constant Q².

Original language	English
Pages (from-to)	303-316
Number of pages	14
Journal	European Physical Journal C
Volume	18
Issue number	2
DOIs	https://doi.org/10.1007/s100520000536
Publication status	Published - 2000

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10.1007/s100520000536

Cite this

Ackerstaff, K., Airapetian, A., Akopov, N., Amarian, M., Aschenauer, E. C., Avakian, H., Avakian, R., Avetissian, A., Bains, B., Beckmann, M., Belostotski, S., Belz, J. E., Benisch, T., Bernreuther, S., Bianchi, N., Blanchard, S., Blouw, J., Böttcher, H., Borissov, A., ... Zohrabian, H. (2000). Measurement of angular distributions and R = σ_L/σ_T in diffractive electroproduction of ρ⁰ mesons. European Physical Journal C, 18(2), 303-316. https://doi.org/10.1007/s100520000536

@article{1bebed9e7a684b3a8b592ff339d2d4a5,

title = "Measurement of angular distributions and R = σL/σT in diffractive electroproduction of ρ0 mesons",

abstract = "Production and decay angular distributions were extracted from measurements of exclusive electroproduction of the ρ0(770) meson over a range in the virtual photon negative four-momentum squared 0.5 < Q2 < 4 GeV2 and the photon-nucleon invariant mass range 3.8 < W < 6.5 GeV. The experiment was performed with the HERMES spectrometer, using a longitudinally polarized positron beam and a 3He gas target internal to the HERA e± storage ring. The event sample combines ρ0 mesons produced incoherently off individual nucleons and coherently off the nucleus as a whole. The distributions in one production angle and two angles describing the ρ0 → π+π- decay yielded measurements of eight elements of the spin-density matrix, including one that had not been measured before. The results are consistent with the dominance of helicity conserving amplitudes and natural parity exchange. The improved precision achieved at 4 < W < 7 GeV, in combination with other data at W > 7 GeV, reveals evidence for an energy dependence in the ratio R of the longitudinal to transverse cross sections at constant Q2.",

author = "K. Ackerstaff and A. Airapetian and N. Akopov and M. Amarian and Aschenauer, \{E. C.\} and H. Avakian and R. Avakian and A. Avetissian and B. Bains and M. Beckmann and S. Belostotski and Belz, \{J. E.\} and Th Benisch and S. Bernreuther and N. Bianchi and S. Blanchard and J. Blouw and H. B{\"o}ttcher and A. Borissov and J. Brack and B. Braun and B. Bray and W. Br{\"u}ckner and A. Br{\"u}ll and Bruins, \{E. E.W.\} and Bulten, \{H. J.\} and Capitani, \{G. P.\} and P. Carter and E. Cisbani and Court, \{G. R.\} and Delheij, \{P. P.J.\} and \{De Sanctis\}, E. and \{De Schepper\}, D. and E. Devitsin and \{de Witt Huberts\}, \{P. K.A.\} and M. D{\"u}ren and A. Dvoredsky and G. Elbakian and J. Emerson and A. Fantoni and A. Fechtchenko and M. Ferstl and K. Fiedler and Filippone, \{B. W.\} and H. Fischer and B. Fox and J. Franz and S. Frullani and Funk, \{M. A.\} and Y. G{\"a}rber and Gagunashvili, \{N. D.\} and P. Galumian and H. Gao and F. Garibaldi and G. Gavrilov and P. Geiger and V. Gharibyan and A. Golendukhin and G. Graw and O. Grebeniouk and Green, \{P. W.\} and Greeniaus, \{L. G.\} and C. Grosshauser and A. Gute and V. Gyurjyan and Haas, \{J. P.\} and W. Haeberli and O. H{\"a}usser and Hansen, \{J. O.\} and D. Hasch and R. Henderson and Th Henkes and R. Hertenberger and Y. Holler and Holt, \{R. J.\} and H. Ihssen and M. Iodice and A. Izotov and Jackson, \{H. E.\} and A. Jgoun and C. Jones and R. Kaiser and E. Kinney and M. Kirsch and A. Kisselev and P. Kitching and K. K{\"o}nigsmann and M. Kolstein and H. Kolster and W. Korsch and V. Kozlov and Kramer, \{L. H.\} and B. Krause and Krivokhijine, \{V. G.\} and M. K{\"u}ckes and G. Kyle and W. Lachnit and W. Lorenzon and A. Lung and Makins, \{N. C.R.\} and Manaenkov, \{S. I.\} and Martens, \{F. K.\} and Martin, \{J. W.\} and A. Mateos and K. Mcllhany and McKeown, \{R. D.\} and F. Meissner and F. Menden and D. Mercer and A. Metz and N. Meyners and O. Mikloukho and Miller, \{C. A.\} and Miller, \{M. A.\} and R. Milner and V. Mitsyn and A. Most and R. Mozzetti and V. Muccifora and A. Nagaitsev and Y. Naryshkin and Nathan, \{A. M.\} and F. Neunreither and Niczyporuk, \{J. M.\} and Nowak, \{W. D.\} and M. Nupieri and P. Oelwein and H. Ogami and O'Neill, \{T. G.\} and R. Openshaw and J. Ouyang and Pate, \{S. F.\} and M. Pitt and Poolman, \{H. R.\} and S. Potashov and Potterveld, \{D. H.\} and G. Rakness and R. Redwine and Reolon, \{A. R.\} and R. Ristinen and K. Rith and G. R{\"o}per and Roloff, \{H. O.\} and P. Rossi and M. Ruh and D. Ryckbosch and Y. Sakemi and I. Savin and Sch{\"u}ler, \{K. P.\} and A. Schwind and Shibata, \{T. A.\} and T. Shin and A. Simon and K. Sinram and Smythe, \{W. R.\} and J. Sowinski and M. Spengos and E. Steffens and J. Stenger and J. Stewart and F. Stock and U. St{\"o}sslein and M. Sutter and H. Tallini and S. Taroian and A. Terkulov and Thiessen, \{D. M.\} and B. Tipton and A. Trudel and M. Tytgat and Urciuoli, \{G. M.\} and \{van den Brand\}, \{J. F.J.\} and \{van der Steenhoven\}, G. and \{van de Vyver\}, R. and Vetterli, \{M. C.\} and Vincter, \{M. G.\} and E. Volk and W. Wander and Welch, \{T. P.\} and Williamson, \{S. E.\} and T. Wise and K. Zapfe and H. Zohrabian",

year = "2000",

doi = "10.1007/s100520000536",

language = "English",

volume = "18",

pages = "303--316",

journal = "European Physical Journal C",

issn = "1434-6044",

publisher = "Springer Nature",

number = "2",

}

Ackerstaff, K, Airapetian, A, Akopov, N, Amarian, M, Aschenauer, EC, Avakian, H, Avakian, R, Avetissian, A, Bains, B, Beckmann, M, Belostotski, S, Belz, JE, Benisch, T, Bernreuther, S, Bianchi, N, Blanchard, S, Blouw, J, Böttcher, H, Borissov, A, Brack, J, Braun, B, Bray, B, Brückner, W, Brüll, A, Bruins, EEW, Bulten, HJ, Capitani, GP, Carter, P, Cisbani, E, Court, GR, Delheij, PPJ, De Sanctis, E, De Schepper, D, Devitsin, E, de Witt Huberts, PKA, Düren, M, Dvoredsky, A, Elbakian, G, Emerson, J, Fantoni, A, Fechtchenko, A, Ferstl, M, Fiedler, K, Filippone, BW, Fischer, H, Fox, B, Franz, J, Frullani, S, Funk, MA, Gärber, Y, Gagunashvili, ND, Galumian, P, Gao, H, Garibaldi, F, Gavrilov, G, Geiger, P, Gharibyan, V, Golendukhin, A, Graw, G, Grebeniouk, O, Green, PW, Greeniaus, LG, Grosshauser, C, Gute, A, Gyurjyan, V, Haas, JP, Haeberli, W, Häusser, O, Hansen, JO, Hasch, D, Henderson, R, Henkes, T, Hertenberger, R, Holler, Y, Holt, RJ, Ihssen, H, Iodice, M, Izotov, A, Jackson, HE, Jgoun, A, Jones, C, Kaiser, R, Kinney, E, Kirsch, M, Kisselev, A, Kitching, P, Königsmann, K, Kolstein, M, Kolster, H, Korsch, W, Kozlov, V, Kramer, LH, Krause, B, Krivokhijine, VG, Kückes, M, Kyle, G, Lachnit, W, Lorenzon, W, Lung, A, Makins, NCR, Manaenkov, SI, Martens, FK, Martin, JW, Mateos, A, Mcllhany, K, McKeown, RD, Meissner, F, Menden, F, Mercer, D, Metz, A, Meyners, N, Mikloukho, O, Miller, CA, Miller, MA, Milner, R, Mitsyn, V, Most, A, Mozzetti, R, Muccifora, V, Nagaitsev, A, Naryshkin, Y, Nathan, AM, Neunreither, F, Niczyporuk, JM, Nowak, WD, Nupieri, M, Oelwein, P, Ogami, H, O'Neill, TG, Openshaw, R, Ouyang, J, Pate, SF, Pitt, M, Poolman, HR, Potashov, S, Potterveld, DH, Rakness, G, Redwine, R, Reolon, AR, Ristinen, R, Rith, K, Röper, G, Roloff, HO, Rossi, P, Ruh, M, Ryckbosch, D, Sakemi, Y, Savin, I, Schüler, KP, Schwind, A, Shibata, TA, Shin, T, Simon, A, Sinram, K, Smythe, WR, Sowinski, J, Spengos, M, Steffens, E, Stenger, J, Stewart, J, Stock, F, Stösslein, U, Sutter, M, Tallini, H, Taroian, S, Terkulov, A, Thiessen, DM, Tipton, B, Trudel, A, Tytgat, M, Urciuoli, GM, van den Brand, JFJ, van der Steenhoven, G, van de Vyver, R, Vetterli, MC, Vincter, MG, Volk, E, Wander, W, Welch, TP, Williamson, SE, Wise, T, Zapfe, K & Zohrabian, H 2000, 'Measurement of angular distributions and R = σ_L/σ_T in diffractive electroproduction of ρ⁰ mesons', European Physical Journal C, vol. 18, no. 2, pp. 303-316. https://doi.org/10.1007/s100520000536

TY - JOUR

T1 - Measurement of angular distributions and R = σL/σT in diffractive electroproduction of ρ0 mesons

AU - Ackerstaff, K.

AU - Airapetian, A.

AU - Akopov, N.

AU - Amarian, M.

AU - Aschenauer, E. C.

AU - Avakian, H.

AU - Avakian, R.

AU - Avetissian, A.

AU - Bains, B.

AU - Beckmann, M.

AU - Belostotski, S.

AU - Belz, J. E.

AU - Benisch, Th

AU - Bernreuther, S.

AU - Bianchi, N.

AU - Blanchard, S.

AU - Blouw, J.

AU - Böttcher, H.

AU - Borissov, A.

AU - Brack, J.

AU - Braun, B.

AU - Bray, B.

AU - Brückner, W.

AU - Brüll, A.

AU - Bruins, E. E.W.

AU - Bulten, H. J.

AU - Capitani, G. P.

AU - Carter, P.

AU - Cisbani, E.

AU - Court, G. R.

AU - Delheij, P. P.J.

AU - De Sanctis, E.

AU - De Schepper, D.

AU - Devitsin, E.

AU - de Witt Huberts, P. K.A.

AU - Düren, M.

AU - Dvoredsky, A.

AU - Elbakian, G.

AU - Emerson, J.

AU - Fantoni, A.

AU - Fechtchenko, A.

AU - Ferstl, M.

AU - Fiedler, K.

AU - Filippone, B. W.

AU - Fischer, H.

AU - Fox, B.

AU - Franz, J.

AU - Frullani, S.

AU - Funk, M. A.

AU - Gärber, Y.

AU - Gagunashvili, N. D.

AU - Galumian, P.

AU - Gao, H.

AU - Garibaldi, F.

AU - Gavrilov, G.

AU - Geiger, P.

AU - Gharibyan, V.

AU - Golendukhin, A.

AU - Graw, G.

AU - Grebeniouk, O.

AU - Green, P. W.

AU - Greeniaus, L. G.

AU - Grosshauser, C.

AU - Gute, A.

AU - Gyurjyan, V.

AU - Haas, J. P.

AU - Haeberli, W.

AU - Häusser, O.

AU - Hansen, J. O.

AU - Hasch, D.

AU - Henderson, R.

AU - Henkes, Th

AU - Hertenberger, R.

AU - Holler, Y.

AU - Holt, R. J.

AU - Ihssen, H.

AU - Iodice, M.

AU - Izotov, A.

AU - Jackson, H. E.

AU - Jgoun, A.

AU - Jones, C.

AU - Kaiser, R.

AU - Kinney, E.

AU - Kirsch, M.

AU - Kisselev, A.

AU - Kitching, P.

AU - Königsmann, K.

AU - Kolstein, M.

AU - Kolster, H.

AU - Korsch, W.

AU - Kozlov, V.

AU - Kramer, L. H.

AU - Krause, B.

AU - Krivokhijine, V. G.

AU - Kückes, M.

AU - Kyle, G.

AU - Lachnit, W.

AU - Lorenzon, W.

AU - Lung, A.

AU - Makins, N. C.R.

AU - Manaenkov, S. I.

AU - Martens, F. K.

AU - Martin, J. W.

AU - Mateos, A.

AU - Mcllhany, K.

AU - McKeown, R. D.

AU - Meissner, F.

AU - Menden, F.

AU - Mercer, D.

AU - Metz, A.

AU - Meyners, N.

AU - Mikloukho, O.

AU - Miller, C. A.

AU - Miller, M. A.

AU - Milner, R.

AU - Mitsyn, V.

AU - Most, A.

AU - Mozzetti, R.

AU - Muccifora, V.

AU - Nagaitsev, A.

AU - Naryshkin, Y.

AU - Nathan, A. M.

AU - Neunreither, F.

AU - Niczyporuk, J. M.

AU - Nowak, W. D.

AU - Nupieri, M.

AU - Oelwein, P.

AU - Ogami, H.

AU - O'Neill, T. G.

AU - Openshaw, R.

AU - Ouyang, J.

AU - Pate, S. F.

AU - Pitt, M.

AU - Poolman, H. R.

AU - Potashov, S.

AU - Potterveld, D. H.

AU - Rakness, G.

AU - Redwine, R.

AU - Reolon, A. R.

AU - Ristinen, R.

AU - Rith, K.

AU - Röper, G.

AU - Roloff, H. O.

AU - Rossi, P.

AU - Ruh, M.

AU - Ryckbosch, D.

AU - Sakemi, Y.

AU - Savin, I.

AU - Schüler, K. P.

AU - Schwind, A.

AU - Shibata, T. A.

AU - Shin, T.

AU - Simon, A.

AU - Sinram, K.

AU - Smythe, W. R.

AU - Sowinski, J.

AU - Spengos, M.

AU - Steffens, E.

AU - Stenger, J.

AU - Stewart, J.

AU - Stock, F.

AU - Stösslein, U.

AU - Sutter, M.

AU - Tallini, H.

AU - Taroian, S.

AU - Terkulov, A.

AU - Thiessen, D. M.

AU - Tipton, B.

AU - Trudel, A.

AU - Tytgat, M.

AU - Urciuoli, G. M.

AU - van den Brand, J. F.J.

AU - van der Steenhoven, G.

AU - van de Vyver, R.

AU - Vetterli, M. C.

AU - Vincter, M. G.

AU - Volk, E.

AU - Wander, W.

AU - Welch, T. P.

AU - Williamson, S. E.

AU - Wise, T.

AU - Zapfe, K.

AU - Zohrabian, H.

PY - 2000

Y1 - 2000

N2 - Production and decay angular distributions were extracted from measurements of exclusive electroproduction of the ρ0(770) meson over a range in the virtual photon negative four-momentum squared 0.5 < Q2 < 4 GeV2 and the photon-nucleon invariant mass range 3.8 < W < 6.5 GeV. The experiment was performed with the HERMES spectrometer, using a longitudinally polarized positron beam and a 3He gas target internal to the HERA e± storage ring. The event sample combines ρ0 mesons produced incoherently off individual nucleons and coherently off the nucleus as a whole. The distributions in one production angle and two angles describing the ρ0 → π+π- decay yielded measurements of eight elements of the spin-density matrix, including one that had not been measured before. The results are consistent with the dominance of helicity conserving amplitudes and natural parity exchange. The improved precision achieved at 4 < W < 7 GeV, in combination with other data at W > 7 GeV, reveals evidence for an energy dependence in the ratio R of the longitudinal to transverse cross sections at constant Q2.

AB - Production and decay angular distributions were extracted from measurements of exclusive electroproduction of the ρ0(770) meson over a range in the virtual photon negative four-momentum squared 0.5 < Q2 < 4 GeV2 and the photon-nucleon invariant mass range 3.8 < W < 6.5 GeV. The experiment was performed with the HERMES spectrometer, using a longitudinally polarized positron beam and a 3He gas target internal to the HERA e± storage ring. The event sample combines ρ0 mesons produced incoherently off individual nucleons and coherently off the nucleus as a whole. The distributions in one production angle and two angles describing the ρ0 → π+π- decay yielded measurements of eight elements of the spin-density matrix, including one that had not been measured before. The results are consistent with the dominance of helicity conserving amplitudes and natural parity exchange. The improved precision achieved at 4 < W < 7 GeV, in combination with other data at W > 7 GeV, reveals evidence for an energy dependence in the ratio R of the longitudinal to transverse cross sections at constant Q2.

UR - https://www.scopus.com/pages/publications/0000266248

U2 - 10.1007/s100520000536

DO - 10.1007/s100520000536

M3 - Article

SN - 1434-6044

VL - 18

SP - 303

EP - 316

JO - European Physical Journal C

JF - European Physical Journal C

IS - 2

ER -

Measurement of angular distributions and R = σL/σT in diffractive electroproduction of ρ0 mesons

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Measurement of angular distributions and R = σ_L/σ_T in diffractive electroproduction of ρ⁰ mesons