Study of the electromagnetic transition form-factors in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:mi>η</mml:mi><mml:mo>→</mml:mo><mml:msup><mml:mi>μ</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:msup><mml:mi>μ</mml:mi><mml:mo>−</mml:mo></mml:msup><mml:mi>γ</mml:mi></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"><mml:mi>ω</mml:mi><mml:mo>→</mml:mo><mml:msup><mml:mi>μ</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:msup><mml:mi>μ</mml:mi><mml:mo>−</mml:mo></mml:msup><mml:msup><mml:mi>π</mml:mi><mml:mn>0</mml:mn></mml:msup></mml:math> decays with NA60

R. Arnaldi(Istituto Nazionale di Fisica Nucleare, Sezione di Torino), K. Banicz(Heidelberg University), J. Castor(Centre National de la Recherche Scientifique), B. Chaurand(Centre National de la Recherche Scientifique), C. Cicalò(University of Cagliari), A. Colla(Istituto Nazionale di Fisica Nucleare, Sezione di Torino), P. Cortese(Istituto Nazionale di Fisica Nucleare, Sezione di Torino), S. Damjanović(Heidelberg University), A. David(University of Lisbon), A. de Falco(University of Cagliari), A. Devaux(Centre National de la Recherche Scientifique), L. Ducroux(Université Claude Bernard Lyon 1), H. En’yo(RIKEN), J. Fargeix(Centre National de la Recherche Scientifique), A. Ferretti(Istituto Nazionale di Fisica Nucleare, Sezione di Torino), M. Floris(University of Cagliari), A. Förster(European Organization for Nuclear Research), P. Force(Centre National de la Recherche Scientifique), N. Guettet(Centre National de la Recherche Scientifique), A. Guichard(Université Claude Bernard Lyon 1), H. Gulkanian(A. Alikhanyan National Laboratory), X. He(RIKEN), M. Keil(University of Lisbon), C. Lourenço(European Organization for Nuclear Research), J. Lozano, F. Manso(Centre National de la Recherche Scientifique), P. Martins(University of Lisbon), A. Masoni(University of Cagliari), A. Neves(European Organization for Nuclear Research), H. Ohnìshì(RIKEN), C. Oppedisano(Istituto Nazionale di Fisica Nucleare, Sezione di Torino), P. G. Ferreira Parracho(University of Lisbon), P. Pillot(Université Claude Bernard Lyon 1), T. Poghosyan(A. Alikhanyan National Laboratory), G. Puddu(University of Cagliari), E. Radermacher(European Organization for Nuclear Research), P. Ramalhete(University of Lisbon), P. Rosinský(European Organization for Nuclear Research), E. Scomparin(Istituto Nazionale di Fisica Nucleare, Sezione di Torino), J. Seixas, S. Serci(University of Cagliari), R. Shahoyan(University of Lisbon), P. Sonderegger, Karsten Specht(Heidelberg University), R. Tieulent(Université Claude Bernard Lyon 1), G. L. Usaı́(University of Cagliari), R. Veenhof(European Organization for Nuclear Research), H. K. Wöhri(University of Cagliari)
Physics Letters B
May 21, 2009
10.1016/j.physletb.2009.05.029
Cited by 147Open Access
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Abstract

The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158AGeV In–In collisions. The mass and pT spectra associated with peripheral collisions can quantitatively be described by the known neutral meson decays. The high data quality has allowed to remeasure the electromagnetic transition form factors of the Dalitz decays η→μ+μ−γ and ω→μ+μ−π0. Using the usual pole approximation F=(1−M2/Λ2)−1 for the form factors, we find Λ−2 (in GeV−2) to be 1.95±0.17(stat.)±0.05(syst.) for the η and 2.24±0.06(stat.)±0.02(syst.) for the ω. While the values agree with previous results from the Lepton-G experiment, the errors are greatly improved, confirming now on the level of 10σ the strong enhancement of the ω form factor beyond the expectation from vector meson dominance. An improved value of the branching ratio BR(ω→μ+μ−π0)=[1.73±0.25(stat.)±0.14(syst.)]×10−4 has been obtained as a byproduct.

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