October 31, 2023 to November 4, 2023
Europe/Athens timezone

Measurement of Transverse Spin Dependent $\mathbf{\pi^+\pi^-}$ Asymmetry and Unpolarized $\mathbf{\pi^+\pi^-}$ Cross Section in polarized $\mathbf{pp}$ Collisions at RHIC

Nov 1, 2023, 5:30 PM
Talk in workshop 1 "QCD at the EIC: Experimental Opportunities and Detector Challenges" Parallel workshop 1


Bernd Surrow (Temple University)


The transversity distribution function of quarks, $h_1^{q}(x)$, encapsulates the transverse spin structure of the proton at leading twist, where $x$ represents the longitudinal momentum fraction carried by the quark $q$. Extracting $h_1^{q}(x)$ poses a formidable challenge due to its chiral-odd nature. Measurements of final-state hadron pairs in transversely polarized proton-proton ($p^\uparrow p$) collisions directly probe collinear quark transversity through its coupling with a chiral-odd interference fragmentation function (IFF), $H_1^{\sphericalangle, q}$. This coupling leads to an experimentally measurable azimuthal correlation asymmetry, $A_{UT}$.
To extract $h_1^{q}(x)$ from $A_{UT}$ asymmetry measurements, precise knowledge of IFF and unpolarized di-hadron fragmentation functions is needed.
The former is provided from $e^{+}e^{-}$ experiments, owing to the factorization and universality of the physics mechanism in the collinear framework.
On the other hand, the latter is largely unknown but can be extracted from unpolarized di-hadron cross-section measurements in pp collisions.
In this presentation, we will present preliminary results of $A_{UT}$ using $p^\uparrow p$ data collected in 2015 at $\sqrt{s}=200\,$GeV and in 2017 at $\sqrt{s}=510\,$GeV, and the unpolarized cross section using $pp$ data collected in 2012 for $\pi^+\pi^-$ pairs at $\sqrt{s} = 200$ GeV by the STAR experiment. The presentation will also discuss prospects for additional data at both $\sqrt{s}=200\,$GeV and $\sqrt{s}=510\,$GeV.

Primary author

Bernd Surrow (Temple University)

Presentation materials