{
  "id": "nucl-th/0501049",
  "version": "v2",
  "published": "2005-01-20T19:58:55.000Z",
  "updated": "2005-12-08T14:44:32.000Z",
  "title": "Using chiral perturbation theory to extract the neutron-neutron scattering length from pi- d -> n n gamma",
  "authors": [
    "A. Gardestig",
    "D. R. Phillips"
  ],
  "comment": "35 pages, 14 eps figures, references and figure added, discussions of errors extended and clarified, improved conclusions, typos corrected, to be published in PRC",
  "journal": "Phys.Rev.C73:014002,2006",
  "doi": "10.1103/PhysRevC.73.014002",
  "categories": [
    "nucl-th",
    "nucl-ex"
  ],
  "abstract": "The reaction pi- d -> n n gamma is calculated in chiral perturbation theory so as to facilitate an extraction of the neutron-neutron scattering length (a_nn). We include all diagrams up to O(Q^3). This includes loop effects in the elementary pi- p -> gamma n amplitude and two-body diagrams, both of which were ignored in previous calculations. We find that the chiral expansion for the ratio of the quasi-free (QF) to final-state-interaction (FSI) peaks in the final-state neutron spectrum converges well. Our third-order calculation of the full spectrum is already accurate to better than 5%. Extracting a_nn from the shape of the entire pi- d -> n n gamma spectrum using our calculation in its present stage would thus be possible at the +-0.8 fm level. A fit to the FSI peak only would allow an extraction of a_nn with a theoretical uncertainty of +-0.2 fm. The effects that contribute to these error bars are investigated. The uncertainty in the $nn$ rescattering wave function dominates. This suggests that the quoted theoretical error of +-0.3 fm for the most recent pi- d -> n n gamma measurement may be optimistic. The possibility of constraining the nn rescattering wave function used in our calculation more tightly--and thus reducing the error--is briefly discussed.",
  "revisions": [
    {
      "version": "v2",
      "updated": "2005-12-08T14:44:32.000Z"
    }
  ],
  "analyses": {
    "subjects": [
      "25.80.Hp",
      "12.39.Fe",
      "21.45.+v",
      "13.75.Cs"
    ],
    "keywords": [
      "chiral perturbation theory",
      "neutron-neutron scattering length",
      "calculation",
      "final-state neutron spectrum converges",
      "rescattering wave function dominates"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "publisher": "APS",
      "journal": "Phys. Rev. C"
    },
    "note": {
      "typesetting": "TeX",
      "pages": 35,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 675313
    }
  }
}