Eur. Phys. J. A (2020) 56: 140
https://doi.org/10.1140/epja/s10050-020-00116-w

Regular Article – Experimental Physics

Identical pion intensity interferometry at

HADES collaboration

¹ Institute of Physics, Slovak Academy of Sciences, 84228, Bratislava, Slovakia
² LIP-Laboratório de Instrumentação e Física Experimental de Partículas, 3004-516, Coimbra, Portugal
³ Smoluchowski Institute of Physics, Jagiellonian University of Cracow, 30-059, Kraków, Poland
⁴ GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291, Darmstadt, Germany
⁵ Technische Universität Darmstadt, 64289, Darmstadt, Germany
⁶ Institut für Strahlenphysik, Helmholtz-Zentrum Dresden-Rossendorf, 01314, Dresden, Germany
⁷ Joint Institute of Nuclear Research, 141980, Dubna, Russia
⁸ Institut für Kernphysik, Goethe-Universität, 60438, Frankfurt, Germany
⁹ Excellence Cluster ‘Origin and Structure of the Universe’, 85748, Garching, Germany
¹⁰ Physik Department E62, Technische Universität München, 85748, Garching, Germany
¹¹ II. Physikalisches Institut, Justus Liebig Universität Giessen, 35392, Giessen, Germany
¹² Institute for Nuclear Research, Russian Academy of Science, 117312, Moscow, Russia
¹³ Institute of Theoretical and Experimental Physics, 117218, Moscow, Russia
¹⁴ National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 115409, Moscow, Russia
¹⁵ Department of Physics, University of Cyprus, 1678, Nicosia, Cyprus
¹⁶ Institut de Physique Nucléaire, CNRS-IN2P3, Univ. Paris-Sud, Université Paris-Saclay, 91406, Orsay Cedex, France
¹⁷ Nuclear Physics Institute, The Czech Academy of Sciences, 25068, Rez, Czech Republic
¹⁸ LabCAF. F. Física, Univ. de Santiago de Compostela, 15706, Santiago de Compostela, Spain
¹⁹ Uniwersytet Warszawski-Instytut Fizyki Doświadczalnej, 02-093, Warsaw, Poland
²⁰ Torino, Italy

^* e-mail: hades-info@gsi.de

Received: 19 October 2019
Accepted: 1 March 2020
Published online: 19 May 2020

Abstract

High-statistics and femtoscopy data are presented for Au + Au collisions at , measured with HADES at SIS18/GSI. The experimental correlation functions allow the determination of the space-time extent of the corresponding emission sources via a comparison to models. The emission source, parametrized as three-dimensional Gaussian distribution, is studied in dependence on pair transverse momentum, azimuthal emission angle with respect to the reaction plane, collision centrality and beam energy. For all centralities and transverse momenta, a geometrical distribution of ellipsoidal shape is found in the plane perpendicular to the beam direction with the larger extension perpendicular to the reaction plane. For large transverse momenta, the corresponding eccentricity approaches the initial eccentricity. The eccentricity is smallest for most central collisions, where the shape is almost circular. The magnitude of the tilt angle of the emission ellipsoid in the reaction plane decreases with increasing centrality and increasing transverse momentum. All source radii increase with centrality, largely exhibiting a linear rise with the cube root of the number of participants. A substantial charge-sign difference of the source radii is found, appearing most pronounced at low transverse momentum. The extracted source parameters are consistent with the extrapolation of their energy dependence down from higher energies.