https://doi.org/10.1140/epja/s10050-020-00225-6
Review
Particle correlations from the initial state
1
National Centre for Nuclear Research, 02-093, Warsaw, Poland
2
Instituto Galego de Física de Altas Enerxías IGFAE, Universidade de Santiago de Compostela, 15782, Santiago de Compostela, Galicia, Spain
* e-mail: tolga.altinoluk@ncbj.gov.pl
Received:
18
May
2020
Accepted:
12
August
2020
Published online:
26
August
2020
The observation in small size collision systems, pp and pA, of strong correlations with long range in rapidity and a characteristic structure in azimuth, the ridge phenomenon, is one of the most interesting results obtained at the large hadron collider. Earlier observations of these correlations in heavy ion collisions at the relativistic heavy ion collider are standardly attributed to collective flow due to strong final state interactions, described in the framework of viscous relativistic hydrodynamics. Even though data for small size systems are well described in this framework, the applicability of hydrodynamics is less well grounded and initial state based mechanisms have been suggested to explain the ridge. In this review, we discuss particle correlations from the initial state point of view, with focus on the most recent theoretical developments.
© The Author(s), 2020
