Open Access

Jörn Adamczewski-Musch, Oliver Arnold, Claudia Behnke, Amel Belounnas, Alexander Belyaev, Jia-Chii Berger-Chen, Alberto Blanco, Christoph Blume, Michael Böhmer, Paula Bordalo, Sergey Chernenko, Lukáš Chlad, Izabela Ciepał, Christina Anna Deveaux, Jens Dreyer, 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, Torsten Heinz, Thierry Hennino, Stanislav Hlaváč, Claudia Höhne, Romain Holzmann, Alexander P. Ierusalimov, Ivashkin Ivashkin, Burkhard Kämpfer, Tatiana Karavicheva, Behruz Kardan, Ilse Koenig, Wolfgang Koenig, Marvin Kohls, Burkhard W. Kolb, Grzegorz Korcyl, Georgy Kornakov, Frédéric Julian Kornas, Roland Kotte, Andrej Kugler, Tobias Kunz, Alexei Kurepin, A. Kurilkin, Pavel Kurilkin, Vladimir P. Ladygin, Rafał Tomasz Lalik, Kirill Lapidus, Alexander Lebedev, Luis Lopes, M. Lorenz, Tariq Mahmoud, Ludwig Maier, A. Malige, Alessio Mangiarotti, Jochen Markert, T. Matulewicz, Steffen Maurus, Volker Metag, Jan Michel, Dimitar M. Mihaylov, S. Morozov, Christian Müntz, Robert Helmut Münzer, L. Naumann, K. Nowakowski, Y. Parpottas, Vladimir Pechenov, Olga Pechenova, Oleg Petukhov, Krzysztof Piasecki, Jerzy Pietraszko, Witold Przygoda, Krzysztof Pysz, S. Ramos, Béatrice Ramstein, N. Rathod, Andrey Reshetin, Pablo Rodríguez 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, U. Singh, Jerzy Smyrski, Yuri G. Sobolev, Stefano Spataro, Simon Spies, Herbert Ströbele, Joachim Stroth, Christian Sturm, Ondřej Svoboda, M. Szala, Pavel Tlustý, Michael Traxler, Haralabos Tsertos, Evgeny A. Usenko, Vladimir Wagner, Christian Wendisch, Michael Wiebusch, Joana Wirth, D. Wójcik, Yuri Zanevsky, Peter W. Zumbruch

• In this letter we report the first multi-differential measurement of correlated pion-proton pairs from 2 billion Au+Au collisions at sNN=2.42 GeV collected with HADES. In this energy regime the population of Δ(1232) resonances plays an important role in the way energy is distributed between intrinsic excitation energy and kinetic energy of the hadrons in the fireball. The triple differential d3N/dMπ±pdpTdy distributions of correlated π±p pairs have been determined by subtracting the πp combinatorial background using an iterative method. The invariant-mass distributions in the Δ(1232) mass region show strong deviations from a Breit-Wigner function with vacuum width and mass. The yield of correlated pion-proton pairs exhibits a complex isospin, rapidity and transverse-momentum dependence. In the invariant mass range 1.1<Minv(GeV/c2)<1.4, the yield is found to be similar for π+p and π−p pairs, and to follow a power law 〈Apart〉α, where 〈Apart〉 is the mean number of participating nucleons. The exponent α depends strongly on the pair transverse momentum (pT) while its pT-integrated and charge-averaged value is α=1.5±0.08st±0.2sy.