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Investigations of Anisotropic Flow Using Multiparticle Azimuthal Correlations in pp, p-Pb, Xe-Xe, and Pb-Pb
S Acharya1, D Adamová2, S P Adhya1
1Variable Energy Cyclotron Centre, Homi Bhabha National Institute.
Physical Review Letters
|November 9, 2019
Summary
Anisotropic flow coefficients (v_n) were measured in various high-energy particle collisions. Results show similarities to larger systems and reveal new insights into collective effects in small systems.
Area of Science:
- High-energy nuclear and particle physics.
- Quantum chromodynamics and the quark-gluon plasma.
- Collective phenomena in small collision systems.
Background:
- Anisotropic flow coefficients (v_n) characterize the azimuthal anisotropy of particle production in high-energy collisions.
- Previous studies focused on large systems (nucleus-nucleus collisions), with limited understanding of collective effects in smaller systems (proton-proton and proton-nucleus).
- Understanding the origin and behavior of v_n in small systems is crucial for a comprehensive picture of particle interactions.
Purpose of the Study:
- To measure anisotropic flow coefficients (v_n) and their correlations in proton-proton (pp), proton-nucleus (p-Pb), Xenon-Xenon (Xe-Xe), and lead-lead (Pb-Pb) collisions.
- To investigate the multiplicity dependence of v_n across a wide range of particle production.
- To explore collective effects and azimuthal correlations in small collision systems and compare them with theoretical models.
Main Methods:
- Utilized the ALICE detector at the Large Hadron Collider.
- Employed two- and multiparticle cumulant methods, including a novel subevent method for v_2 measurements.
- Analyzed data from pp at 13 TeV, p-Pb at 5.02 TeV, Xe-Xe at 5.44 TeV, and Pb-Pb at 5.02 TeV.
Main Results:
- Observed the ordering v_2 > v_3 > v_4 in pp and p-Pb collisions, similar to larger systems.
- Found a weaker multiplicity dependence of v_2 in pp and p-Pb compared to nucleus-nucleus collisions.
- Symmetric cumulant (SC(m,n)) results indicate positive correlations for (v_2, v_4) and negative for (v_2, v_3) that change sign below 100 multiplicity, suggesting different fluctuation patterns.
Conclusions:
- High-multiplicity pp and p-Pb collisions exhibit long-range multiparticle azimuthal correlations.
- Current theoretical models (e.g., Pythia 8, IP-Glasma, MUSIC, URQMD) fail to describe these observed correlations.
- The findings provide new insights into the emergence of collective effects in small collision systems, challenging existing theoretical frameworks.
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