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How robust is a thermal photon interpretation of the ALICE low-p T data?

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Abstract

We present a systematic theoretical analysis of the ALICE measurement of low-p T direct-photon production in central lead-lead collisions at the LHC with a centre-of-mass-energy of \( \sqrt{{{s_{NN }}}}=2.76 \) TeV. Using NLO QCD, we compute the relative contributions to prompt-photon production from different initial and final states and the theoretical uncertainties coming from independent variations of the renormalisation and factorisation scales, the nuclear parton densities and the fragmentation functions. Based on different fits to the unsubtracted and prompt-photon subtracted ALICE data, we consistently find T = 304 ± 58MeV and 309 ± 64MeV for the effective temperature of the quark-gluon plasma (or hot medium) at p T ∈ [0.8; 2.2] GeV and p T ∈ [1.5; 3.5] GeV as well as a power-law (\( p_T^{-4 } \)) behavior for p T > 4 GeV as predicted by QCD hard scattering.

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Authors and Affiliations

  1. Institut für Theoretische Physik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 9, D-48149, Münster, Germany

    M. Klasen & F. König

  2. Institut für Kernphysik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 9, D-48149, Münster, Germany

    C. Klein-Bösing & J.P. Wessels

  3. ExtreMe Matter Institute, GSI, Planckstraße 1, D-64291, Darmstadt, Germany

    C. Klein-Bösing

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  1. M. Klasen
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Correspondence to M. Klasen.

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ArXiv ePrint: 1307.7034

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Klasen, M., Klein-Bösing, C., König, F. et al. How robust is a thermal photon interpretation of the ALICE low-p T data?. J. High Energ. Phys. 2013, 119 (2013). https://doi.org/10.1007/JHEP10(2013)119

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