Forward production in $d+\mathrm{Au}$ collisions by parton recombination

Hadron production at forward rapidities in $d+\mathrm{Au}$ collisions is studied in the framework of parton recombination in the final state. Multiple scattering and gluon saturation in the initial state are not explicitly considered. The recombination of soft and shower partons is found to be important. The soft parton densities are determined by extrapolation from the parametrization fixed at $\eta =0$ with no unconstrained adjustments. The suppression of $R_{\mathrm{CP}}$ observed at high η is understood as the simple consequence of the reduction of the soft parton density on the deuteron side compared to that on the gold side. The effect of momentum degradation responsible for baryon stopping is also considered. The asymmetry of backward-to-forward spectra can be reproduced within the same framework without any change in the basic physics.

Figure 1

Transverse momentum distributions of ${\pi }^{+}$ produced at midrapidity in $d+\mathrm{Au}$ collisions for three centrality cuts. Light solid lines are for the recombination from the $\mathcal{T}$$\mathcal{T}$ component, dashed lines for $\mathcal{T}$$\mathcal{S}$, and dashed-dotted lines for $\mathcal{S}$$\mathcal{S}$ components. Heavy solid lines are the sums of all three components.

Figure 2

Transverse momentum distributions of ${\pi }^{+}$ produced at different pseudorapidities for two centrality cuts.

Figure 3

Transverse momentum distributions of ${\pi }^{+}$ produced at $\eta =3.2$ for 0–20% centrality, showing the three components.

Figure 4

Distribution of gluons produced in central $d+\mathrm{Au}$ collisions at four pseudorapidities.

Figure 5

$R_{\mathrm{CP}}$ for $0\text{−}20\text{−}/60\text{−}80\%$ (filled circles and solid lines) and $30\text{−}50\%/60\text{−}80\%$ (open circles and dashed lines) for four pseudorapidities when $T$ is assumed to be constant. Data are from [9]. No momentum degradation is considered in the calculation.

Figure 6

Same as for Fig. 5 but with $T(\beta ,\eta )$ given by Eqs. (12) and (13).

Figure 7

Same as for Fig. 6 but with momentum degradation considered.

Figure 8

Ratio of $p_T$ distributions for backward to forward pseudorapidities at $\left|\eta \right|=0.75$. Data are for all charged hadrons from [36]. Solid line is the calculated ratio for ${\pi }^{+}+{\pi }^{-}+p+\overline{p}$.