Forward $D$ predictions for $p\rm Pb$ collisions, and sensitivity to cold nuclear matter effects

TL;DR

The study addresses how cold nuclear matter modifies forward $D^0$ production in $p$Pb collisions at LHC energies. It employs an NLO+LL framework with EPS09 nPDFs (paired to a fixed-flavour scheme and parton showering via POWHEG-BOX+Pythia8) to predict double-differential cross sections and the forward-backward ratio $R_{fb}$ within the LHCb acceptance. The results indicate CNM effects can change cross-section ratios by roughly 10–30% with $R_{fb}$ dominated by nPDF uncertainties and a near-flat dependence on $p_T$ due to compensation between shadowing and anti-shadowing; forward rapidity shows stronger suppression due to low-$x$ gluon shadowing. The work highlights the need for improved low-$x$ gluon nPDF constraints and suggests complementary measurements (e.g., low-mass Drell-Yan) to sharpen CNM interpretations in heavy-ion data.

Abstract

Predictions are provided for double differential cross sections and forward-backward ratios of $D^{0}$ production in $p\rm Pb$ (forward) and $\rm{Pb}$$p$ (backward) collisions at 5.02~TeV. The effect of nuclear corrections on the ratio of differential cross sections ratios is estimated to be $\simeq$ (10-30)\% in the kinematically accessible region of LHCb, and interestingly this ratio is approximately flat with respect to $p_T(D^0)$ due to a compensation of shadowing and anti-shadowing effects arising from the input nuclear PDFs. In comparison to $J/ψ(\rightarrowμ^-μ^+)$ measurements which have already been performed with the available data, the cross section for $D^{0}(\rightarrow K^-π^+)$ production is expected to be two-orders of magnitude higher.

Figures (4)

• Figure 1: Upper region: NLO EPS09 gluon nuclear modification factor $R^{\rm{nuc}}_{g/Pb} (x_g,Q)$ for $Q = 3, 5$ GeV. Lower region: Normalised differential $D^0$ cross section with respect to $\rm{Log}$$(x_i)$. The $D^0$ is required to be within the COM overlap region of forward and backward collisions accessible to LHCb, and the effect of placing $p_T$ cuts on the $D^0$ is indicated.
• Figure 2: Differential $D^0$ cross section in forward $p\rm Pb$ collisions at 5 TeV. Both the central value and total uncertainty for each rapidity bin is shown, and a multiplication factor of $10^{-m}$ has been applied to different rapidity bins as indicated on the plot.
• Figure 3: Predictions of $R_{fb}$ in $p\rm Pb$ collisions with respect to rapidity for $D^0$ production at 5 TeV. Both the total uncertainty, and uncertainty excluding the dominant nPDF uncertainties are shown. The experimentally accessible region to LHCb is also highlighted.
• Figure 4: The same as Figure \ref{['fig:Rfbdy']}, but differentially in $p_T$. This prediction is also for $p\rm Pb$ collisions at 5 TeV.