https://doi.org/10.1140/epjc/s10052-020-08675-4
Regular Article – Experimental Physics
Two-particle correlations in azimuthal angle and pseudorapidity in central 
collisions at the CERN Super Proton Synchrotron
1
National Nuclear Research Center, Baku, Azerbaijan
2
Faculty of Physics, University of Sofia, Sofia, Bulgaria
3
Ruđer Bošković Institute, Zagreb, Croatia
4
LPNHE, University of Paris VI and VII, Paris, France
5
Karlsruhe Institute of Technology, Karlsruhe, Germany
6
University of Frankfurt, Frankfurt, Germany
7
Wigner Research Centre for Physics of the Hungarian Academy of Sciences, Budapest, Hungary
8
University of Bergen, Bergen, Norway
9
Jan Kochanowski University in Kielce, Kielce, Poland
10
Institute of Nuclear Physics, Polish Academy of Sciences, Kraków, Poland
11
National Centre for Nuclear Research, Warsaw, Poland
12
Jagiellonian University, Kraków, Poland
13
AGH-University of Science and Technology, Kraków, Poland
14
University of Silesia, Katowice, Poland
15
University of Warsaw, Warsaw, Poland
16
University of Wrocław, Wrocław, Poland
17
Warsaw University of Technology, Warsaw, Poland
18
Institute for Nuclear Research, Moscow, Russia
19
Joint Institute for Nuclear Research, Dubna, Russia
20
National Research Nuclear University (Moscow Engineering Physics Institute), Moscow, Russia
21
St. Petersburg State University, St. Petersburg, Russia
22
University of Belgrade, Belgrade, Serbia
23
University of Geneva, Geneva, Switzerland
24
Fermilab, Batavia, USA
25
University of Colorado, Boulder, USA
26
University of Pittsburgh, Pittsburgh, USA
bz
Bartosz.Maksiak@ncbj.gov.pl
Received:
5
June
2020
Accepted:
16
November
2020
Published online:
14
December
2020
A measurement of charged hadron pair correlations in two-dimensional 
space is presented. The analysis is based on total 30 million central Be + Be collisions observed in the NA61/SHINE detector at the CERN SPS for incident beam momenta of 19A, 30A, 40A, 75A, and 150A 
. Measurements were carried out for unlike-sign and like-sign charge hadron pairs independently. The 
correlation functions were compared with results from a similar analysis on p + p interactions at similar beam momenta per nucleon. General trends of the back-to-back correlations are similar in central Be + Be collisions and p + p interactions, but are suppressed in magnitude due to the increased combinatorial background. Predictions from the Epos and UrQMD models are compared to the measurements. Evolution of an enhancement around 
with incident energy is observed in central Be + Be collisions. It is not predicted by both models and almost non-existing in proton–proton collisions at the same momentum per nucleon.
© The Author(s) 2020
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