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Paper Proposal: Run17 pp510 Collins Analysis

Updated on Tue, 2025-05-13 21:29. Originally created by yixinzhang on 2024-03-26 01:44.

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:

The STAR experiment reports high precision measurements of the Collins asymmetries for $\pi^{\pm}$ within jets from transversely polarized ${pp}$ collisions at $\sqrt{s}$ = 510 GeV. The energy-scaled distribution of jet $x_{\mathrm{T}} = 2p_{\mathrm{T,jet}}/\sqrt s$, shows a remarkable consistency for Collins asymmetries of $\pi^{\pm}$ in jets between 200 GeV and 510 GeV. This indicates that the Collins asymmetries are nearly energy independent with, at most, a very weak scale dependence in $pp$ collisions. These results extend to high momentum scales ($Q^2 \leq 3400$ GeV$^2$) and enable unique tests of evolution and universality in the transverse-momentum-dependent formalism, thus providing important constraints for the Collins fragmentation functions.

Paper draft:
    Paper with Supplementary Material
Paper draft (Previous version, Dec. 4):
    Energy Independence of the Collins Asymmetry in $pp$ Collisions

Analysis Note:
    2017_pp510_Collins_Analysis

Code path:
$CVSROOT/offline/paper/psn0851

The committee members are:
Chairperson: Renee Fatemi
Member(s) at large: Sehanseul Oh
Member for English/Grammar QA: Jim Drachenberg
Member for Code QA: Anuja Khanal
PWG representative: Xiaoxuan Chu
PA representative(s): Yixin Zhang

GPC Records:
    May 8
    Feb 11

Presentations:
At Spin PWG:

    Oct 25, 2023
    Sep 13, 2023
    Aug 30, 2023
    Aug 23, 2023
    May 31, 2023
At STAR Collaboration Meeting:
March 2024

At SPIN2023:

    SPIN 2023 Workshop Proceeding

Proposed Figures:

    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, $A_{\mathrm{UT}}^{\sin(\phi_S - \phi_H)}$, as a function of jet $x_{\mathrm{T}}$ ($\equiv \frac{2p_{\mathrm{T,jet}}}{\sqrt{s}}$) 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 $x_{\mathrm{T}}$ and $A_{\mathrm{UT}}$.

    Figure3:Collins asymmetries, $A_{\mathrm{UT}}^{\sin(\phi_S - \phi_H)}$ as a function of $\pi^{\pm}$ momentum fraction $z$ in $pp$ collisions at $\sqrt{s} = 510$ GeV and 200 GeV. Vertical bars show the statistical uncertainties; boxes show the systematic uncertainties

    Figure4:Collins asymmetries, $A_{\mathrm{UT}}^{\sin(\phi_S - \phi_H)}$, as a function of the $\pi^{\pm}$ momentum transverse to the jet axis, $j_{\mathrm{T}}$, 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 $\langle p_{\mathrm{T,jet}} \rangle = 32.3$ GeV/c, while the open points show the results from $\sqrt{s} = 200$ GeV $pp$ collisions with an average jet $\langle p_{\mathrm{T,jet}} \rangle = 13.3$ GeV/c~\cite{STAR:2022hqg}. Vertical bars show the statistical uncertainties and boxes show the systematic uncertainties in $j_{\mathrm{T}}$ and $A_{\mathrm{UT}}$

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.


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