Open Access

Jörn Adamczewski-Musch, Oliver Werner Arnold, Claudia Behnke, Amel Belounnas, Alexei V. Belyaev, Jia-Chii Berger-Chen, Jacek Biernat, Alberto Blanco, Christoph Blume, Michael Böhmer, Paula Bordalo, Sergey P. Chernenko, Lukáš Chlad, Christina Anna Deveaux, Jörn Dreyer, Adrian Dybczak, Eliane Epple, Laura Fabbietti, Oleg Fateev, Peter Filip, Paulo Fonte, Celso Franco, Jürgen Friese, Ingo Fröhlich, Tetyana Galatyuk, Juan A. Garzón, Roman Gernhäuser, Marina Golubeva, Robert Greifenhagen, Fedor Guber, Malgorzata Gumberidze, Szymon Harabasz, Tobias Heinz, Thierry Hennino, Stanislav Hlaváč, Claudia Höhne, Romain Holzmann, Alexander P. Ierusalimov, Alexander Ivashkin, Burkhard Kämpfer, Tatiana L. Karavicheva, Behruz Kardan, Ilse Koenig, Wolfgang Koenig, Burkhard W. Kolb, Grzegorz Korcyl, Georgy Kornakov, Roland Kotte, Andrej Kugler, Tobias Kunz, Alexander Kurepin, Aleksey K. Kurilkin, Pavel Kurilkin, Vladimir P. Ladygin, Rafał Tomasz Lalik, Kirill Lapidus, Alexei Lebedev, Luis Alberto Vieira Lopes, Manuel Lorenz, Tariq Mahmoud, Ludwig W. Maier, Alessio Mangiarotti, Jochen Markert, Tomasz Matulewicz, Steffen Maurus, Volker Metag, Jan Michel, Dimitar Mihaylov, Sergey Morozov, Christian Müntz, Robert Helmut Münzer, Lothar Naumann, K. Nowakowski, Marek Palka, Yannis Parpottas, Vladimir Pechenov, Olga Pechenova, Oleg Petukhov, Krzysztof Piasecki, Jerzy Pietraszko, Witold Przygoda, Sérgio Ramos, Béatrice Ramstein, Andrey Reshetin, Pablo Rodriguez Ramos, Philippe Rosier, Adrian Rost, Alexander Sadovsky, Piotr Salabura, Timo Scheib, Heidi Schuldes, Erwin Schwab, Federico Scozzi, Florian Seck, Patrick Sellheim, Ilya Selyuzhenkov, Johannes Stephan Siebenson, Luis Silva, Yuri G. Sobolev, Stefano Spataro, Simon Spies, Herbert Ströbele, Joachim Stroth, Paweł Strzempek, Christian Thomas Sturm, Ondřej Svoboda, Melanie Szala, Pavel Tlustý, Michael Traxler, Haralabos Tsertos, Evgeny A. Usenko, Vladimir Wagner, Christian Wendisch, Michael Wiebusch, Joana Wirth, Daniel Krzysztof Wójcik, Yuri V. Zanevsky, Peter W. Zumbruch

• We investigate identical pion HBT intensity interferometry in central Au+Au collisions at 1.23A GeV. High-statistics π−π− and π+π+ data are measured with HADES at SIS18/GSI. The radius parameters, derived from the correlation function depending on relative momenta in the longitudinally comoving system and parametrized as three-dimensional Gaussian distribution, are studied as function of transverse momentum. A substantial charge-sign difference of the source radii is found, particularly pronounced at low transverse momentum. The extracted source parameters agree well with a smooth extrapolation of the center-of-mass energy dependence established at higher energies, extending the corresponding excitation functions down towards a very low energy.