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Paper Proposal: Run17 pp510 Collins Analysis

Updated on Thu, 2024-04-18 03:10. 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 statistics measurements of the Collins asymmetries for $\pi^{\pm}$ within jets from transversely polarized ${pp}$ collisions at $\sqrt{s}$ = 510 GeV. With energy-scaled jet $x_T$= $2p_T/\sqrt s$, a remarkable consistency is observed for Collins asymmetries of $\pi^{\pm}$ 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 ($Q^2$ up to 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.


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:


Proposed Figures:
    Figure 1:The representation of the reaction plane along with the definitions of the azimuthal angles ϕ_S and ϕ_H
             

    Figure 2: Collins  asymmetries, A_UT^(sin⁡(ϕ_S-ϕ_H)), as a function of jet x_T  (≡2p_T/√s) for π^+/π^- in pp collisions at √s = 510 GeV (solid points), compared with previous results at √s = 200 GeV (open points). Vertical bars show the statistical uncertainties; boxes show the systematic uncertainties in xT and AUT

    Figure3:Collins  asymmetries, A_UT^(sin⁡(ϕ_S-ϕ_H)), as a function of the π^± 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 √s = 510 GeV pp collisions with an average jet <pT> = 33.4 GeV/c, while the open points show the results from √s = 200 GeV pp collisionswith an average jet < p_T > = 13.3 GeV/c. Vertical bars show the statistical uncertainties; boxes show the systematic uncertainties in jT and AUT

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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