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arxiv: 2604.15543 · v2 · submitted 2026-04-16 · ✦ hep-ex

Recognition: unknown

Energy Correlators Within Jets in Transversely Polarized Proton-Proton Collisions at sqrt{s} = 200 GeV

The STAR Collaboration
Authors on Pith no claims yet

Pith reviewed 2026-05-10 09:08 UTC · model grok-4.3

classification ✦ hep-ex
keywords energy correlatorstransversitypolarized pp collisionsjet fragmentationspin asymmetriesMellin momentsnucleon structureSTAR experiment
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The pith

Energy correlators within jets show spin asymmetries sensitive to nucleon transversity in polarized collisions.

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

The paper measures one- and two-point energy correlators inside jets from transversely polarized proton-proton collisions at 200 GeV for the first time. It finds sizable spin-dependent asymmetries in the distributions of charged pions and pion pairs. These asymmetries point to the start of nonperturbative effects at particular angular scales inside the jets. By using Mellin moments to project the data, the measurements gain sensitivity to the transversity of the nucleon while lowering the impact of uncertainties in how hadrons form. This sets up energy correlators as a new tool for studying nucleon structure and points toward detailed three-dimensional imaging at future colliders.

Core claim

The authors report the observation of sizable spin-dependent asymmetries in one- and two-point energy correlators for π⁺, π⁻, and π⁺π⁻ pairs within jets. Projecting the fragmentation dynamics onto Mellin moments provides sensitivity to the nucleon's transversity distribution while minimizing uncertainties from nonperturbative fragmentation functions. These results establish energy correlators as a novel probe of nucleon structure.

What carries the argument

One- and two-point energy correlators that quantify energy-weighted angular distributions of hadrons and hadron pairs within jets, with projection onto Mellin moments to extract transversity information.

Load-bearing premise

The projection onto Mellin moments isolates the transversity contribution while suppressing fragmentation uncertainties, which depends on the validity of the factorization theorem at the measured scales.

What would settle it

A measurement showing no spin asymmetries or asymmetries inconsistent with transversity predictions at the identified angular scales would challenge the interpretation.

Figures

Figures reproduced from arXiv: 2604.15543 by The STAR Collaboration.

Figure 1
Figure 1. Figure 1: FIG. 1. Representation of the jet scattering plane and the angular distance [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Azimuthal single spin asymmetries as functions of [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Transverse single spin asymmetries for charged pions [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. The transverse single spin asymmetry as a function of angular separation [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
read the original abstract

We report the first measurement of one- and two-point energy correlators within jets in transversely polarized proton-proton collisions at $\sqrt{s}=200$ GeV, using the STAR detector at RHIC. These observables quantify the energy-weighted angular distribution of single hadrons and hadron pairs within jets, respectively. Sizable spin-dependent asymmetries are observed for $\pi^+$, $\pi^-$, and $\pi^+\pi^-$ pairs, revealing the onset of nonperturbative dynamics at specific angular scales. By projecting the fragmentation dynamics onto Mellin moments, these measurements provide sensitivity to the nucleon's transversity while minimizing uncertainties from nonperturbative fragmentation functions. These results establish energy correlators as a novel and precise probe of nucleon structure and open a promising avenue for three-dimensional nucleon tomography at the future Electron-Ion Collider.

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

1 major / 1 minor

Summary. The manuscript reports the first measurement of one- and two-point energy correlators within jets in transversely polarized proton-proton collisions at √s = 200 GeV using the STAR detector at RHIC. It observes sizable spin-dependent asymmetries for π⁺, π⁻, and π⁺π⁻ pairs that indicate the onset of nonperturbative dynamics at specific angular scales. By projecting the observables onto Mellin moments, the authors claim sensitivity to the nucleon's transversity distribution while minimizing uncertainties associated with nonperturbative fragmentation functions, and they position the results as a new probe for nucleon structure relevant to future EIC studies.

Significance. If the measurement holds and the Mellin-moment interpretation is substantiated, the work introduces energy correlators as a novel experimental handle on transversity in polarized collisions. The direct observation of asymmetries at the transition to nonperturbative regimes could provide a useful test of factorization assumptions and support more precise three-dimensional nucleon tomography, complementing existing SIDIS and Drell-Yan approaches.

major comments (1)
  1. Abstract: The central interpretive claim that 'projecting the fragmentation dynamics onto Mellin moments... minimizes uncertainties from nonperturbative fragmentation functions' is load-bearing for the transversity sensitivity result. However, the same abstract states that sizable asymmetries appear precisely at angular scales revealing the onset of nonperturbative dynamics; this raises a consistency issue with the assumed applicability of the underlying factorization theorem (energy correlators in polarized jets) at those scales, and the manuscript must provide explicit validation or references demonstrating that higher Mellin moments systematically suppress Collins-like FF dependence without circular reliance on the data itself.
minor comments (1)
  1. The abstract would be clearer if it quantified the specific angular scales (e.g., in radians or as a function of jet p_T) at which the nonperturbative onset is claimed, allowing readers to assess the regime directly.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading and insightful comments on our manuscript. We have addressed the concern regarding the consistency of the abstract's interpretive claims with the observed nonperturbative dynamics by clarifying the role of Mellin-moment projections and adding supporting references.

read point-by-point responses

  1. Referee: Abstract: The central interpretive claim that 'projecting the fragmentation dynamics onto Mellin moments... minimizes uncertainties from nonperturbative fragmentation functions' is load-bearing for the transversity sensitivity result. However, the same abstract states that sizable asymmetries appear precisely at angular scales revealing the onset of nonperturbative dynamics; this raises a consistency issue with the assumed applicability of the underlying factorization theorem (energy correlators in polarized jets) at those scales, and the manuscript must provide explicit validation or references demonstrating that higher Mellin moments systematically suppress Collins-like FF dependence without circular reliance on the data itself.

    Authors: We appreciate the referee drawing attention to this potential tension. The factorization framework for energy correlators in jets (as established in the theoretical literature) is applied in the regime where the angular scales allow perturbative treatment, while the data reveal the transition to nonperturbative effects. The projection onto higher Mellin moments is a theoretical operation that weights the energy correlator to suppress sensitivity to nonperturbative fragmentation functions, including Collins-like contributions; this suppression arises from the moment structure itself and is independent of the specific experimental data, as demonstrated in prior works on Mellin moments of energy-energy correlators. We will revise the abstract for greater precision on this point and insert explicit references to the relevant theoretical papers establishing the moment-based suppression. This avoids any circularity, as the suppression property is a general feature of the formalism rather than derived from our measurements. revision: partial

Circularity Check

0 steps flagged

Direct experimental measurement; no circular derivation chain

full rationale

The paper reports first measurements of one- and two-point energy correlators in jets from transversely polarized pp collisions at 200 GeV using STAR detector data. Observed spin-dependent asymmetries for pions and pairs, plus the Mellin-moment projection for transversity sensitivity, are extracted directly from recorded events. No equations or steps reduce by construction to fitted parameters, self-citations, or ansatze internal to the paper; the interpretive link to nucleon structure follows from standard factorization applied to the measured observables rather than re-deriving those observables from themselves. The result is self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

This is an experimental measurement paper. The abstract introduces no new free parameters, axioms, or invented entities; the claim rests on standard high-energy physics analysis techniques and existing concepts of energy correlators and Mellin moments applied to new data.

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discussion (0)

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Forward citations

Cited by 2 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Simplified approach to extracting nucleon transversity in collinear factorization using near-side energy-energy correlators

    hep-ph 2026-04 unverdicted novelty 7.0

    A new method extracts the nucleon transversity PDF via near-side energy-energy correlators in dihadron fragmentation under collinear factorization, with leading-order results for SIDIS and e+e- annihilation that resem...

  2. Simplified approach to extracting nucleon transversity in collinear factorization using near-side energy-energy correlators

    hep-ph 2026-04 unverdicted novelty 7.0

    A new approach using near-side energy-energy correlators in dihadron fragmentation enables extraction of nucleon transversity PDF in collinear factorization without modeling intrinsic transverse momentum or dihadron r...

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