International Workshop
"The Structure and Dynamics of Hadrons"
Hirschegg, Kleinwalsertal, Austria -
Information

Title:	Dr.
Family Name:	Rustamov
First Name:	Anar
Gender:	male
E-Mail:	a.rustamovgsi.de
Affiliation for Badge:	GSI, Darmstadt
Institute:	GSI
Address (Street):	Planckstr. 1
Postal Code, City:	64291
Country:	Germany
Phone:	+49 6159 71 1346
Fax:
Arrival Date:	January 16
Departure Date:	January 22
Accommodation:	Waldemar-Petersen-Haus
Room Type:	Single room ( ~260-275 ¿ depending on room size )
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Author(s):	Anar Rustamov for the HADES collaboration
Institute(s):	GSI Helmholtzzentrum f"{u}r Schwerionenforschung, Darmstadt, Germany.
Title of talk:	Probing the electromagnetic structure of hadrons with HADES
Abstract:	The High Acceptance Di-Electron Spectrometer (HADES) operates at the GSI Helmholtzzentrum f"{u}r Schwerionenforschung in Darmstadt, Germany. One of the main physics goals of HADES is to investigate spectral modifications of light vector mesons in strongly interacting matter. However, in order to search for any in- medium effects in heavy-ion collisions and/or elementary reactions on nuclei, the firm knowledge of reference N+N collisions is mandatory. Given this motivation, I present here the dielectron spectrum measured by HADES in p+p collisions at 1.25 and 3.5 GeV, as well as in quasi-free n+p collisions at 1.25 GeV. For the first time at 3.5 GeV beam energy, the inclusive production cross sections of $\pi^{0}$, $\eta$, $\omega$ and $\rho$ mesons have been measured. The data allow to improve the most recent value on the upper bound of direct $\eta \to e^{+} e^{-}$ decay by at least a factor of 3. Furthermore, the validity of the vector meson dominance model in describing the electromagnetic transition form-factors of nucleon resonances can be addressed. Indeed, already at 1.25 GeV the sensitivity of our data to the electromagnetic structure of $\Delta -N$ transition vertex had been observed. On the other hand, by exploiting the capability of HADES to measure charged hadrons, exclusive $pp \to ppe^{+}e^{-}$ channels were isolated in p+p collisions at 1.25 GeV. In this way the first direct measurements of the $\Delta$ Dalitz decay process was obtained. These results will also be discussed during this presentation.
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