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
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.
© The Author(s), 2020