First measurement of low momentum dielectrons radiated off cold nuclear matter

G. Agakishiev , A. Balanda , D. Belver , A. Belyaev , J. C. Berger-Chen , A. Blanco , M. B\"ohmer , J. L. Boyard

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P. Cabanelas S. Chernenko A. Dybczak E. Epple L. Fabbietti O. Fateev P. Finocchiaro P. Fonte J. Friese I. Fr\"ohlich T. Galatyuk J. A. Garz\'on R. Gernh\"auser K. G\"obel M. Golubeva D. Gonz\'alez-D\'iaz F. Guber M. Gumberidze T. Heinz T. Hennino R. Holzmann A. Ierusalimov I. Iori A. Ivashkin M. Jurkovic B. K\"ampfer T. Karavicheva I. Koenig W. Koenig B. W. Kolb G. Kornakov R. Kotte A. Kr\'asa F. Krizek R. Kr\"ucken H. Kuc W. K\"uhn A. Kugler A. Kurepin V. Ladygin R. Lalik S. Lang K. Lapidus A. Lebedev T. Liu L. Lopes M. Lorenz L. Maier A. Mangiarotti J. Markert V. Metag B. Michalska J. Michel D. Mishra C. M\"untz L. Naumann Y. C. Pachmayer M. Palka Y. Parpottas V. Pechenov O. Pechenova J. Pietraszko W. Przygoda B. Ramstein A. Reshetin A. Rustamov A. Sadovsky P. Salabura A. Schmah E. Schwab J. Siebenson Yu. G. Sobolev S. Spataro B. Spruck H. Str\"obele J. Stroth C. Sturm A. Tarantola K. Teilab P. Tlusty M. Traxler R. Trebacz H. Tsertos T. Vasiliev V. Wagner M. Weber C. Wendisch J. W\"ustenfeld S. Yurevich Y. Zanevsky

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classification ⚛️ nucl-ex hep-ex

keywords datafirstmeasurementstrongcolddielectronmassmatter

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We present data on dielectron emission in proton induced reactions on a Nb target at 3.5 GeV kinetic beam energy measured with HADES installed at GSI. The data represent the first high statistics measurement of proton-induced dielectron radiation from cold nuclear matter in a kinematic regime, where strong medium effects are expected. Combined with the good mass resolution of 2%, it is the first measurement sensitive to changes of the spectral functions of vector mesons, as predicted by models for hadrons at rest or small relative momenta. Comparing the e+e invariant mass spectra to elementary p+p data, we observe for e+e momenta Pee < 0.8 GeV/c a strong modification of the shape of the spectrum, which we attribute to an additional rho-like contribution and a decrease of omega yield. These opposite trends are tentatively interpreted as a strong coupling of the rho meson to baryonic resonances and an absorption of the omega meson, which are two aspects of in-medium modification of vector mesons.

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First measurement of low momentum dielectrons radiated off cold nuclear matter

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