Journal of High Energy Physics

, 2017:74 | Cite as

Collectivity from interference

  • Boris Blok
  • Christian D. Jäkel
  • Mark Strikman
  • Urs Achim WiedemannEmail author
Open Access
Regular Article - Theoretical Physics


In hadronic collisions, interference between different production channels affects momentum distributions of multi-particle final states. As this QCD interference does not depend on the strong coupling constant α s , it is part of the no-interaction baseline that needs to be controlled prior to searching for other manifestations of collective dynamics, e.g., in the analysis of azimuthal anisostropy coefficients v n at the LHC. Here, we introduce a model that is based on the QCD theory of multi-parton interactions and that allows one to study interference effects in the production of m particles in hadronic collisions with N parton-parton interactions (“sources”). In an expansion in powers of 1/(N c 2  − 1) and to leading order in the number of sources N , we calculate interference effects in the m-particle spectra and we determine from them the second and fourth order cumulant momentum anisotropies v n {2} and v n {4}. Without invoking any azimuthal asymmetry and any density dependent non-linear dynamics in the incoming state, and without invoking any interaction in the final state, we find that QCD interference alone can give rise to values for v n {2} and v n {4}, n even, that persist unattenuated for increasing number of sources, that may increase with increasing multiplicity and that agree with measurements in proton-proton (pp) collisions in terms of the order of magnitude of the signal and the approximate shape of the transverse momentum dependence. We further find that the non-abelian features of QCD interference can give rise to odd harmonic anisotropies. These findings indicate that the no-interaction baseline including QCD interference effects can make a sizeable if not dominant contribution to the measured v n coefficients in pp collisions. Prospects for analyzing QCD interference contributions further and their possible relevance for proton-nucleus and nucleus-nucleus collisions are discussed shortly.


Heavy Ion Phenomenology 


Open Access

This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.


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Authors and Affiliations

  • Boris Blok
    • 1
  • Christian D. Jäkel
    • 2
  • Mark Strikman
    • 3
  • Urs Achim Wiedemann
    • 4
    Email author
  1. 1.Department of PhysicsTechnion — Israel Institute of TechnologyHaifaIsrael
  2. 2.Department of Applied MathematicsUniversity of São Paulo (USP)São PauloBrazil
  3. 3.Department of PhysicsPenn State UniversityUniversity ParkU.S.A.
  4. 4.Theoretical Physics DepartmentCERNGenève 23Switzerland

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