Pseudorapidity asymmetry and centrality dependence of charged hadron spectra in $d+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$

The pseudorapidity asymmetry and centrality dependence of charged hadron spectra in $d+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$ are presented. The charged particle density at midrapidity, its pseudorapidity asymmetry, and centrality dependence are reasonably reproduced by a multiphase transport model, by HIJING, and by the latest calculations in a saturation model. Ratios of transverse momentum spectra between backward and forward pseudorapidity are above unity for $p_T$ below $5\mathrm{GeV}∕c$. The ratio of central to peripheral spectra in $d+\mathrm{Au}$ collisions shows enhancement at $2<p_T<6\mathrm{GeV}∕c$, with a larger effect at backward rapidity than forward rapidity. Our measurements are in qualitative agreement with gluon saturation and in contrast to calculations based on incoherent multiple partonic scatterings.

Figure 1

The $p_T$ spectra of charged hadrons. From the top, the open circles correspond to the 0–20 %, 20–40 %, minimum bias, and 40–100 % centralities in $-1.0<\eta <-0.5$. Similarly, the solid triangles, open squares, and solid squares correspond to $p_T$ spectra in $0.0<\eta <0.5$, $-0.5<\eta <0.0$, and $0.5<\eta <1.0$, respectively. Spectra have been scaled by the factors indicated in the figure.

Figure 2

(Color online) The pseudorapidity dependence of charged particle densities for various centrality classes. Particle tracking efficiency and background corrections were carried out for each pseudorapidity bin $(\Delta \eta =0.1)$. The point-to-point systematic uncertainties shown for each distribution (indicated by bands) are the quadratic sum of the efficiency and background correction uncertainties; statistical uncertainties are negligible. The results of AMPT (with default parameters) and parton saturation are indicated by the dashed and solid lines, respectively.

Figure 3

(Color online) The ratio of charged hadron spectra in the backward rapidity to forward rapidity region for minimum bias and ZDC-$d$ neutron-tagged events. Calculations based on pQCD [3] $(y=-1∕y=1)$ for minimum bias events are also shown for cases with no shadowing (solid curve), HIJING shadowing (dashed curve), and EKS shadowing (dot-dashed curve). Calculations in a gluon saturation model [13] for minimum bias events are shown for $0.5<\mid \eta \mid <1.0$ (filled circles with solid line) and for $0.0<\mid \eta \mid <0.5$ (open squares with solid line).

Figure 4

(Color online) (a) The centrality dependence of the ratio of charged hadron spectra in backward rapidity to forward rapidity $(0.5<\mid \eta \mid <1.0)$. The gluon saturation model calculations are also shown for the 0–20 % (solid curve), 20–40 % (dashed curve), and 40–100 % (dot-dashed curve) centrality classes. (b) The centrality dependence of the ratio of charged hadron spectra in backward rapidity to forward rapidity $(0.0<\mid \eta \mid <0.5)$. The gluon saturation model calculations are also shown for the 0–20 % (solid curve), 20–40 % (dashed curve), and 40–100 % (dot-dashed curve) centrality classes.

Figure 5

(Color online) The ratio of central (0–20 %) to peripheral (40–100 %) spectra in $d+\mathrm{Au}$ collisions for various pseudorapidity regions and in $\mathrm{Au}+\mathrm{Au}$ collisions at midrapidity.