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arxiv: 2605.02890 · v2 · submitted 2026-05-04 · ✦ hep-ph

Recognition: 2 theorem links

· Lean Theorem

Collins asymmetries for pion-in-jet production in polarized ell p collisions at the EIC

Umberto D'Alesio , Carlo Flore , Marco Zaccheddu
Authors on Pith no claims yet

Pith reviewed 2026-05-08 18:06 UTC · model grok-4.3

classification ✦ hep-ph
keywords Collins asymmetrypion-in-jet productiontransversity distributionTMD factorizationEICazimuthal asymmetryWeizsacker-Williamssea quarks
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The pith

Collins asymmetries for pion-in-jet production offer clearer access to transversity at the EIC

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper investigates Collins azimuthal asymmetries in pion-in-jet production within polarized lepton-proton collisions at the Electron-Ion Collider. It extends prior work on polarized proton-proton scattering by using a simplified TMD approach with collinear initial states and known transversity and Collins functions. Calculations cover leading-order processes and include quasireal photon contributions via the Weizsäcker-Williams approximation for EIC kinematics. This reveals that such asymmetries enable more direct probing of the transversity distribution, particularly its sea-quark components, with quark channels dominating. Future EIC measurements could further validate the universality of the Collins function and TMD factorization assumptions.

Core claim

Collins asymmetries in lepton-proton processes allow for a much clearer access to the transversity distribution, including its sea-quark component. Although the Weizsäcker-Williams quasireal photon exchange contributes across the kinematical range, it does not spoil the dominance of quark-initiated channels, leaving gluon counterparts with only a marginal role.

What carries the argument

The Collins azimuthal asymmetry for pion-in-jet production in a simplified TMD framework with transversity distributions and Collins fragmentation functions.

Load-bearing premise

Transversity and Collins fragmentation functions extracted from SIDIS and e+e- annihilation can be directly applied to lepton-proton collisions assuming TMD factorization and Collins universality.

What would settle it

Observation of Collins asymmetries in EIC data that significantly differ from those predicted using SIDIS and e+e- inputs would challenge the assumption of direct applicability and universality.

Figures

Figures reproduced from arXiv: 2605.02890 by Carlo Flore, Marco Zaccheddu, Umberto D'Alesio.

Figure 1
Figure 1. Figure 1: Unpolarized cross sections for ℓp → jet π ± X as a function of ηj at three different values of √ s, with the corresponding pjT ranges, see legend. Upper panels: LO and (LO+WW) results; middle panels: ratio of full (LO+WW) contribution to the LO piece; lower panels: relative contribution of quark- and gluon￾induced channels to the total cross section. precisely, we consider three different center-of-mass en… view at source ↗
Figure 2
Figure 2. Figure 2: Collins asymmetries for ℓp ↑ → jet π ± X as a function of ηj ; LO (dashed lines and gray bands) and LO+WW (solid lines and colored bands). Left to right: √ s = 45, 105, 141 GeV, with the corresponding pjT ranges, see legend. Uncertainty bands at 2σ CL. π + production the asymmetries are relatively small, around 1%, the corresponding ones for π − tend to grow at forward rapid￾ity, ranging from 2 to 4-8%, de… view at source ↗
Figure 3
Figure 3. Figure 3: Collins asymmetries for ℓp ↑ → jet π ± X as a function of xT : LO (dashed lines and gray bands) and LO+WW (solid lines and colored bands). Left to right: √ s = 45, 105, 141 GeV. Upper panels: forward rapidities; lower panels: backward rapidities. Uncertainty bands at 2σ CL. (see view at source ↗
Figure 4
Figure 4. Figure 4: Collins asymmetries for for ℓp ↑ → jet π ± X as a function of z: LO (dashed lines and gray bands) and LO+WW (solid lines and colored bands). Left to right: 45, 105, 141 GeV, with the corresponding pjT ranges, see legend. Upper panels: forward rapidities; lower panels: backward rapidities. Uncertainty bands at 2σ CL. computed new predictions for the EIC kinematics, still employ￾ing the transversity and Coll… view at source ↗
Figure 5
Figure 5. Figure 5: Collins asymmetries for ℓp ↑ → jet π ± X as a function of jT for different z bins, only central values. Left to right: √ s = 45, 105, 141 GeV, with the corresponding pjT ranges, see legend. Upper panels: forward rapidities; lower panels: backward rapidities. References [1] A. Kotzinian, New quark distributions and semiinclusive electroproduction on the polarized nucleons, Nucl. Phys. B 441 (1995) 234–248. … view at source ↗
read the original abstract

We study Collins azimuthal asymmetries for pion-in-jet production in polarized lepton-proton collisions, extending previous analyses of polarized $pp$ scattering to a complementary and theoretically simpler process. We keep adopting a simplified transverse momentum dependent (TMD) approach, with a collinear configuration for the initial state, and employ the transversity and Collins fragmentation functions as extracted from semi-inclusive deep inelastic scattering and $e^+ e^-$ annihilation processes. We then compute azimuthal asymmetries for the Electron-Ion Collider (EIC) kinematics, both within a leading order (LO) approach and by including quasireal photon exchange in the Weizs\"acker-Williams approximation. Although this contribution is relevant in the whole kinematical range explored, it does not spoil the dominance of quark-initiated channels, leaving only a marginal role to their gluon counterparts. In this respect, Collins asymmetries in lepton-proton processes allow for a much clearer access to the transversity distribution, including its sea-quark component. As we will argue, a comparison with future EIC data could represent a further step in testing the hypothesis of the universality of the Collins function as well as of the TMD factorization for this class of processes.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 1 minor

Summary. The paper computes Collins azimuthal asymmetries for pion-in-jet production in polarized lepton-proton collisions at the EIC using a simplified TMD framework with collinear initial state. It inserts transversity and Collins functions previously extracted from SIDIS and e+e- annihilation, evaluates the asymmetries at leading order and with Weizsäcker-Williams quasireal photon exchange for EIC kinematics, and reports that quark-initiated channels dominate while gluon contributions remain marginal. This leads to the claim of clearer access to transversity, including its sea-quark component, with future EIC data comparison positioned as a test of TMD factorization and Collins universality.

Significance. If the reported dominance holds under the stated inputs, the work supplies concrete, falsifiable predictions for a process that is theoretically simpler than polarized pp scattering and could provide complementary constraints on transversity with reduced gluon contamination. The explicit numerical demonstration that the WW term, while relevant across the kinematics, does not alter the quark dominance is a clear strength of the analysis.

minor comments (1)
  1. Abstract: the phrase 'as we will argue' for clearer access to the sea-quark component of transversity should be accompanied by an explicit pointer to the section or figure containing the supporting numerical comparison of quark versus gluon channels.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and the positive overall assessment. We appreciate the recognition that our work supplies concrete predictions for a theoretically simpler process than polarized pp scattering and that the explicit demonstration of quark dominance (even with the Weizsäcker-Williams contribution) is a strength. We address the report below.

Circularity Check

0 steps flagged

No significant circularity; derivation uses independent prior extractions

full rationale

The paper inserts transversity and Collins functions previously extracted from SIDIS and e+e- data into a standard TMD framework (collinear initial state, LO hard scattering plus WW photons) to compute EIC asymmetries. The reported dominance of quark channels and clearer access to transversity (including sea) is a numerical outcome of that insertion, not a definitional equivalence or self-fit. No equations reduce the target prediction to the input parametrizations by construction, no uniqueness theorem is invoked from self-citation, and no ansatz is smuggled. The calculation is self-contained against external benchmarks from other processes; any future data comparison is presented as a test rather than an internal verification.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claim rests on the applicability of previously extracted transversity and Collins functions to this new process and on the validity of the simplified TMD approach with collinear initial states.

axioms (2)
  • domain assumption Universality of the Collins fragmentation function across processes
    Invoked when employing functions extracted from SIDIS and e+e- for lp collisions; the paper states this is to be tested.
  • domain assumption Validity of TMD factorization for this class of processes
    Underlying the entire calculation; the abstract positions EIC data as a test of this hypothesis.

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Reference graph

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