Single Transverse Spin Asymmetries of Identified Charged Hadrons in Polarized p+p Collisions at $\sqrt{s}$ = 62.4 GeV

TL;DR

The first measurements of xF-dependent single-spin asymmetries of identified charged hadrons, pi+/-, K-, and protons, from transversely polarized proton-proton collisions at RHIC are presented.

Abstract

The first measurements of $x_F$-dependent single spin asymmetries of identified charged hadrons, $π^{\pm}$, $K^{\pm}$, and protons, from transversely polarized proton-proton collisions at 62.4 GeV at RHIC are presented. The measurements extend to high-$x_F$ ($|x_F|\sim 0.6$) in both the forward and backward directions.Large asymmetries are seen in the pion and kaon channels. The asymmetries in inclusive $π^{+}$ production, $A_N(π^+)$, increase with $x_F$ from 0 to $\sim$0.25 %at $x_F = 0.6$ and $A_N(π^{-})$ decrease from 0 to $\sim$$-$0.4. Even though $K^-$ contains no valence quarks, observed asymmetries for $K^-$ unexpectedly show positive values similar to those for $K^+$, increasing with $x_F$, whereas proton asymmetries are consistent with zero over the measured kinematic range. Comparisons of the data with predictions of QCD-based models are presented. The flavor dependent single spin asymmetry measurements of identified hadrons allow for stringent tests of theoretical models of partonic dynamics in the RHIC energy regime.

Figures (5)

• Figure 1: $p_T$ vs. $x_{F}$ for the data used in the SSA analysis. The dotted boxes are for the measurements from FS at 6$^\circ$, the filled boxes are from FS at 2.3$^\circ$ and the empty boxes with solid line are from 3$^\circ$. Data from FS at 2.3$^\circ$ and 3$^\circ$ are used in combination for kaons and protons. The size of the boxes represents the relative intensity of the data in logarithmic scale. The 5 bands marked as (a)-(e) are the $p_T$ ranges used in the Fig. \ref{['fig:pt_dep']}.
• Figure 2: $A_N$ vs. $x_F$ for $\pi^+$ and $\pi^-$. Circle symbols are for $\pi^+$ and box symbols are for $\pi^-$ measured in FS at 2.3$^\circ$ (solid symbols) and 3$^\circ$ (open symbols). The curves are from theoretical calculations. Solid lines are to be compared with the data at 2.3$^\circ$ and dotted lines are for 3$^\circ$. Thick (solid and dotted) lines are from the initial-state Twist-3 calculations fengfeng_c, medium lines are from the final-state Twist-3 calculations koikeyuji_c. Predictions from the Sivers function calculations are shown as thin lines dalesioumberto_c. Only statistical errors are shown where larger than symbols.
• Figure 3: $A_N$ vs. $x_F$ for $\pi^+$ and $\pi^-$ for positive $x_F$ at fixed $p_T$ values: (a)$0.4<p_T<0.5$, (b)$0.5<p_T<0.6$, (c)$0.6<p_T<0.8$, (d)$0.8<p_T<1.0$, and (e)$1.0<p_T<1.2$ GeV/$c$ as shown in Fig. \ref{['fig:acc']}, respectively.
• Figure 4: $A_N(K^+)$ and $A_N(K^-)$ vs. $x_F$. Circle symbols are for $K^+$ and box symbols are for $K^-$. The solid ($K^+$) and dotted ($K^-$) lines are from the initial-state twist-3 calculations with (thick lines) and without (medium lines) sea- and anti-quark contribution. Calculations for the Sivers function are shown as thin lines. Errors are statistical only.
• Figure 5: $A_N$ vs. $x_F$ of the proton.