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Collectivity from interference

Journal of High Energy Physics volume 2017, Article number: 74 (2017) Cite this article

A preprint version of the article is available at arXiv.

Abstract

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 2 c  − 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.

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Authors and Affiliations

  1. Department of Physics, Technion — Israel Institute of Technology, Haifa, 3200003, Israel

    Boris Blok

  2. Department of Applied Mathematics, University of São Paulo (USP), CEP 05508-090, São Paulo, Brazil

    Christian D. Jäkel

  3. Department of Physics, Penn State University, 104 Davey Lab, University Park, PA, 16802-6300, U.S.A.

    Mark Strikman

  4. Theoretical Physics Department, CERN, CH-1211, Genève 23, Switzerland

    Urs Achim Wiedemann

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  1. Boris Blok
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  2. Christian D. Jäkel
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Correspondence to Urs Achim Wiedemann.

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ArXiv ePrint: 1708.08241

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Blok, B., Jäkel, C.D., Strikman, M. et al. Collectivity from interference. J. High Energ. Phys. 2017, 74 (2017). https://doi.org/10.1007/JHEP12(2017)074

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Keywords

  • Heavy Ion Phenomenology