Title: Energy Independence of the Collins Asymmetry in $pp$ Collisions

PAs: Carl Gagliardi, Ting Lin, Qinghua Xu, Yike Xu and Yixin Zhang

Target Journal: Phys. Rev. Lett. 

Abstract:

Paper draft (Dec. 4):
    Energy Independence of the Collins Asymmetry in $pp$ Collisions

Analysis Note:
    2017_pp510_Collins_Analysis

Code path:
/star/u/yixinzhang/pp500_2017/code4run17Collins

Presentations:
At Spin PWG:

At SPIN2023:

    Figure 1:The representation of the reaction plane along with the definitions of the azimuthal angles $\phi_S$ and $\phi_H$
             

    Figure 2: Collins asymmetries, $A_{UT}^{\sin(\phi_S - \phi_H)}$, as a function of jet $x_T$ ($\equiv \frac{2p_T}{\sqrt{s}}$) for $\pi^+/\pi^-$ in $pp$ collisions at $\sqrt{s} = 510$ GeV (solid points), compared with previous results at $\sqrt{s} = 200$ GeV (open points). Vertical bars show the statistical uncertainties; boxes show the systematic uncertainties in $x_T$ and $A_{UT}$

    Figure3:Difference of Collins asymmetries at 510 GeV and 200 GeV, as a function of jet $x_T$ ($\equiv \frac{2p_T}{\sqrt{s}}$) for $\pi^+/\pi^-$ in $pp$ collisions. The error bars encompass the uncertainties from both the 510 GeV and 200 GeV results, as well as the uncertainties introduced by fitting the 200 GeV data


    Figure4: Collins asymmetries, $A_{UT}^{\sin(\phi_S - \phi_H)}$, as a function of the $\pi^{\pm}$ momentum transverse to the jet axis, $j_T$, in four longitudinal momentum fraction $z$ bins. The solid points show the results from this analysis of $\sqrt{s} = 510$ GeV $pp$ collisions with an average jet $\langle p_T \rangle = 32.3$ GeV/c, while the open points show the results from $\sqrt{s} = 200$ GeV $pp$ collisions with an average jet $\langle p_T \rangle = 13.3$ GeV/c. Vertical bars show the statistical uncertainties and boxes show the systematic uncertainties in $j_T$ and $A_{UT}$

conclusion:

• New precision results Collins asymmetries for π^±  within jets in pp collisions at √s   = 510 GeV, ~13 times more statistics to previous measurement. 
  
• The Collins results, in good consistency with 200 GeV data vs. xT, no energy dependence observed, which provide important constraints on the scale evaluation, and testing of universality for Collins asymmetries.
• The theoretical curves exhibit a comparable trend to the experimental measurements, but undershoot the observed asymmetries.