Charged-pion production in $$\mathbf {Au+Au}$$ collisions at $$\sqrt{\mathbf {s}_{\mathbf {NN}}} = 2.4~{\mathbf {GeV}}$$
J. Adamczewski-Musch, O. Arnold, C. Behnke, A. Belounnas, A. Belyaev, J. C. Berger-Chen, A. Blanco, C. Blume, M. Böhmer, P. Bordalo, S. Chernenko, L. Chlad, I. Ciepał, C. Deveaux, J. Dreyer, E. Epple, L. Fabbietti, O. Fateev, P. Filip, P. Fonte, C. Franco, J. Friese, I. Fröhlich, T. Galatyuk, J. A. Garzón, R. Gernhäuser, S. Gläßel, M. Golubeva, R. Greifenhagen, F. Guber, M. Gumberidze, S. Harabasz, T. Heinz, T. Hennino, S. Hlavac, C. Höhne, R. Holzmann, A. Ierusalimov, A. Ivashkin, B. Kämpfer, T. Karavicheva, B. Kardan, I. Koenig, W. Koenig, M. Kohls, B. W. Kolb, G. Korcyl, G. Kornakov, F. Kornas, R. Kotte, A. Kugler, T. Kunz, A. Kurepin, A. Kurilkin, P. Kurilkin, V. Ladygin, R. Lalik, K. Lapidus, A. Lebedev, L. Lopes, M. Lorenz, T. Mahmoud, L. Maier, A. Malige, A. Mangiarotti, J. Markert, T. Matulewicz, S. Maurus, V. Metag, J. Michel, D. M. Mihaylov, S. Morozov, C. Müntz, R. Münzer, L. Naumann, K. Nowakowski, Y. Parpottas, V. Pechenov, O. Pechenova, O. Petukhov, K. Piasecki, J. Pietraszko, W. Przygoda, K. Pysz, S. Ramos, B. Ramstein, N. Rathod, A. Reshetin, P. Rodriguez-Ramos, P. Rosier, A. Rost, A. Rustamov, A. Sadovsky, P. Salabura, T. Scheib, H. Schuldes, E. Schwab, F. Scozzi, F. Seck, P. Sellheim
Abstract
Abstract We present high-statistic data on charged-pion emission from Au + Au collisions at $$\sqrt{s_{\mathrm{NN}}} = 2.4~\hbox {GeV}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msqrt> <mml:msub> <mml:mi>s</mml:mi> <mml:mi>NN</mml:mi> </mml:msub> </mml:msqrt> <mml:mo>=</mml:mo> <mml:mn>2.4</mml:mn> <mml:mspace/> <mml:mtext>GeV</mml:mtext> </mml:mrow> </mml:math> (corresponding to $$E_{beam} = 1.23~\hbox {A GeV}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>E</mml:mi> <mml:mrow> <mml:mi>beam</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>1.23</mml:mn> <mml:mspace/> <mml:mtext>A GeV</mml:mtext> </mml:mrow> </mml:math> ) in four centrality classes in the range 0–40% of the most central collisions. The data are analyzed as a function of transverse momentum, transverse mass, rapidity, and polar angle. Pion multiplicity per participating nucleon decreases moderately with increasing centrality. The polar angular distributions are found to be non-isotropic even for the most central event class. Our results on pion multiplicity fit well into the general trend of the available world data, but undershoot by $$2.5~\sigma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>2.5</mml:mn> <mml:mspace/> <mml:mi>σ</mml:mi> </mml:mrow> </mml:math> data from the FOPI experiment measured at slightly lower beam energy. We compare our data to state-of-the-art transport model calculations (PHSD, IQMD, PHQMD, GiBUU and SMASH) and find substantial differences between the measurement and the results of these calculations.