{
  "id": "1905.06697",
  "version": "v1",
  "published": "2019-05-16T12:40:59.000Z",
  "updated": "2019-05-16T12:40:59.000Z",
  "title": "Consistent treatment of charm production in higher-orders at tree-level within $k_T$-factorization approach",
  "authors": [
    "Rafal Maciula",
    "Antoni Szczurek"
  ],
  "comment": "33 pages, 21 figures",
  "categories": [
    "hep-ph",
    "hep-ex"
  ],
  "abstract": "We discuss production of $c \\bar c$-pairs within $k_T$-factorization approach (off-shell initial partons) with unintegrated parton distribution functions (uPDFs). We present a consistent prescription which merges the standard leading-order (LO) $k_T$-factorization calculations for this process with tree-level next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) matrix elements. For the first time we include in this framework 2 $\\to$ 3 and 2 $\\to$ 4 processes with extra partonic emissions for single particle distributions as well as for correlation observables. The use of the KMR uPDF leads to a good description of the existing charm ($D$-meson) data already at the leading-order. On the other hand, a new Parton-Branching (PB) uPDF strongly underestimates the same experimental data. A direct inclusion of the higher-orders at tree-level leads to an overestimation of the data, especially for the KMR uPDF. This suggests a significant double-counting. We propose a simple method how to avoid the double-counting. Our procedure leads to a much better description of the experimental data when including the higher-order contributions. Then with the KMR uPDF we get similar results (both for single particle and correlation observables) as for the standard calculations of the 2 $\\to$ 2 processes. For the PB uPDF inclusion of the higher-orders considerably improves description of the experimental data. We conclude that the LO calculation with the KMR uPDF effectively includes the higher-orders which is not the case for the PB uPDF.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2019-05-16T12:40:59.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "factorization approach",
      "consistent treatment",
      "charm production",
      "higher-order",
      "kmr updf"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 33,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}