| Literature DB >> 28344505 |
Ilkka Helenius1,2, Hannu Paukkunen3,4,5, Kari J Eskola3,4.
Abstract
A well-established observation in nuclear physics is that in neutron-rich spherical nuclei the distribution of neutrons extends farther than the distribution of protons. In this work, we scrutinize the influence of this so called neutron-skin effect on the centrality dependence of high-[Formula: see text] direct-photon and charged-hadron production. We find that due to the estimated spatial dependence of the nuclear parton distribution functions, it will be demanding to unambiguously expose the neutron-skin effect with direct photons. However, when taking a ratio between the cross sections for negatively and positively charged high-[Formula: see text] hadrons, even centrality-dependent nuclear-PDF effects cancel, making this observable a better handle on the neutron skin. Up to 10% effects can be expected for the most peripheral collisions in the measurable region.Entities:
Year: 2017 PMID: 28344505 PMCID: PMC5347519 DOI: 10.1140/epjc/s10052-017-4709-9
Source DB: PubMed Journal: Eur Phys J C Part Fields ISSN: 1434-6044 Impact factor: 4.590
Fig. 1The nuclear modification factor for direct-photon production in peripheral Pb+Pb collisions with at mid-rapidity for two centralities 70–80% (left) and 90–100% (right). The results are compared to the isospin effect (dotted) and MB result (long-dashed) and the centrality-dependent results are shown with (solid) and without (short-dashed) the NS effect. The uncertainties from EPS09s nPDFs (light colour band) and 2pF parametrization (dark colour band around the solid lines) are calculated with the NS effect. The gray band shows the EPS09s uncertainty for the MB result in the right-hand panel
Fig. 2The central-to-peripheral ratio for direct-photon production in Pb+Pb collisions with at mid-rapidity for (0–10%)/(70–80%) (upper left) and (0–10%)/(90–100%) (upper right), and at forward rapidity for (0–10%)/(70–80%) (lower left) and (0–10%)/(90–100%) (lower right). The results with (solid) and without (dashed) NS effects are shown and the uncertainties are from the EPS09s nPDFs (light colour band) and from the 2pF parametrization (dark colour bands)
Fig. 3Upper left panel The ratio between positively and negatively charged hadrons in p+p (solid) and in n+n (dashed) collisions at and using DSS (green), Kretzer (blue), and AKK08 (red) FFs. Upper right panel The ratio between positively and negatively charged hadrons in Pb+Pb collisions at and using DSS (solid) and Kretzer (dashed) FFs for centrality classes 0–100% (red), 70–80% (green), and 90–100% (blue). The light colour bands show the uncertainty from the 2pF parametrization and the dark one the EPS09s uncertainty with DSS. For the 0–100% (90–100%) bin only the EPS09s (2pF) uncertainty is visible. Lower panels The ratio between positively and negatively charged hadrons in Pb+Pb collisions at and in 70–80% (green) and 90–100% (blue) centralities normalized with 0–100% using DSS (solid) and Kretzer (dashed) FFs. The colour bands show the nPDF uncertainties (dark) and uncertainty in the 2pF parametrization (light) with DSS FFs
Fig. 4The expected statistical precision for (light vertical bars) and for (darker vertical bars) nucleon–nucleon luminosity in 70–80% (green) and 90–100% (blue) centrality classes. The shaded boxes show the 2pF uncertainty as in the lower panels of Fig. 3. The Kretzer FFs have been used