Longitudinal double-spin asymmetries for dijet production at intermediate pseudorapidity in polarized $pp$ collisions at $\sqrt{s}=200\mathrm{GeV}$

We present the first measurements of the longitudinal double-spin asymmetry $A_{LL}$ for dijets with at least one jet reconstructed within the pseudorapidity range $0.8<\eta <1.8$. The dijets were measured in polarized $pp$ collisions at a center-of-mass energy $\sqrt{s}=200\mathrm{GeV}$. Values for $A_{LL}$ are determined for several distinct event topologies, defined by the jet pseudorapidities, and span a range of parton momentum fraction $x$ down to $x\sim 0.01$. The measured asymmetries are found to be consistent with the predictions of global analyses that incorporate the results of previous RHIC measurements. They will provide new constraints on $\mathrm{\Delta }g(x)$ in this poorly constrained region when included in future global analyses.

Figure 1

Data/simulation comparisons of the relative jet yields as functions of $\mathrm{Barrel}+\mathrm{end}$cap jet pseudorapidity (upper left) and jet azimuthal angle (upper right), or as functions of detector jet transverse momentum for the barrel (lower left) and endcap (lower right). The solid circle points represent the data, and the histograms are the simulation.

Figure 2

Data/simulation comparisons of the jet yields vs jet neutral energy fraction (NEF), shown separately for jets in different pseudorapidity ranges. The points represent the data (solid circle for barrel, open square and open cross for endcap jets at two different pseudorapidity ranges), and the histogram is the simulation.

Figure 3

Data/simulation comparisons of dijet yields as a function of invariant mass (left) for all the accepted events. Similar comparisons for barrel-endcap dijets only as a function of the pseudorapidity gap (upper right) and azimuthal opening angle (lower right) between the jets. The points are the data and the histogram is the simulation.

Figure 4

Data/simulation comparisons of the underlying event $\delta M$ (difference before and after the underlying event subtraction) vs underlying event corrected dijet invariant mass. The points represent the data and the histogram is the simulation.

Figure 5

Jet particle-level $p_T$ divided by detector-level $p_T$ as a function of detector $\eta$ before (upper plot) and after (lower plot) a $p_T$ shift correction was made. The correction is determined using machine-learning techniques. The black lines are the average values and the vertical uncertainties are the standard deviations.

Figure 6

The dijet $p_T$ imbalance distribution before (red) and after (blue) $p_T$ corrections were made. The points represent the data (solid circle for before and open square for after the correction), and the histogram is the simulation.

Figure 7

The jet mass distribution after corrections were made. The points represent the data (solid circle for barrel and open square for endcap), and the histogram is the simulation.

Figure 8

The distributions of the parton $x_1$ and $x_2$, which has been weighted by the partonic ${\widehat{a}}_{LL}$, from Pythia detector level simulations at $\sqrt{s}=200\mathrm{GeV}$ for different jet pseudorapidity ranges.

Figure 9

$A_{LL}$ as a function of parton-level invariant mass for dijets with the East barrel-endcap (top), West barrel-endcap (middle) and endcap-endcap (bottom) event topologies. The curves and uncertainty symbols are explained in the text.