Study of Nuclear Effects on Charm Production in Light-Ion Collisions

The onset of nuclear effects in light-ion collisions is studied by measuring the ratio of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:msup> <a:mrow> <a:mi>D</a:mi> </a:mrow> <a:mrow> <a:mn>0</a:mn> </a:mrow> </a:msup> </a:mrow> </a:math> meson production between NeNe and OO collisions at a center-of-mass energy per nucleon pair of 5.36 TeV recorded by the LHCb detector. The <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:msup> <c:mi>D</c:mi> <c:mn>0</c:mn> </c:msup> </c:math> meson yields are measured differentially in transverse momentum ( <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:msub> <e:mi>p</e:mi> <e:mi mathvariant="normal">T</e:mi> </e:msub> </e:math> ) for <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"> <h:mrow> <h:mn>0.5</h:mn> <h:mo><</h:mo> <h:msub> <h:mrow> <h:mi>p</h:mi> </h:mrow> <h:mrow> <h:mi mathvariant="normal">T</h:mi> </h:mrow> </h:msub> <h:mo><</h:mo> <h:mn>20</h:mn> <h:mtext> </h:mtext> <h:mtext> </h:mtext> <h:mi>GeV</h:mi> </h:mrow> </h:math> in the rapidity ( <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:mi>y</k:mi> </k:math> ) region <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:mn>2.0</m:mn> <m:mo><</m:mo> <m:mi>y</m:mi> <m:mo><</m:mo> <m:mn>4.5</m:mn> </m:math> , and are normalized to the total number of recorded inelastic nucleus-nucleus collisions in each data sample. The resulting production ratio shows evidence of variation as a function of <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"> <o:msub> <o:mi>p</o:mi> <o:mi mathvariant="normal">T</o:mi> </o:msub> </o:math> , which is inconsistent with predictions based on nuclear modification of nucleon structure alone. This measurement is consistent with the onset of quark-gluon plasma production with increasing nucleus size in high-energy nuclear collisions.