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The $D\pi$ and $D^*\pi$ femtoscopy puzzle

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Pablo Encarnación, Miguel Albaladejo, Albert Feijoo, Juan Nieves

High Energy Physics - Phenomenology · Submitted 28 Sep 2026 · 64 references

Pith's verdict: A real technical advance in coupled-channel femtoscopy, and the case that ALICE's Dπ extraction is not robust holds up on reading — the main soft spot is that the empirical keystone rests on digitized thesis figures.

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arXiv ID2609.35133 (version 1)
Pith ID3A4RB577, Pith's permanent record of this paper and its review
CitationAlbert Feijoo, Juan Nieves, Miguel Albaladejo, Pablo Encarnaci\'on. "The $D\pi$ and $D^*\pi$ femtoscopy puzzle." arXiv:2609.35133 (2026). https://pith.science/paper/3A4RB577
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The paper

The paper claims

The paper claims the near-zero Dπ interaction found by ALICE is an artifact of assuming the correlation function reaches unity above 100 MeV, a region still driven by the lower D*_0(2300) pole, and demonstrates the extraction is…

The reading

The paper builds a fully relativistic, momentum-space framework for femtoscopic correlation functions with strong and Coulomb interactions in coupled channels, and applies it to the Dπ system. Its theoretical correlation functions agree with earlier calculations but disagree sharply with the ALICE extraction, which reports a Dπ strong interaction consistent with zero. The authors locate the discrepancy in a specific experimental assumption: that the genuine correlation function equals unity above a relative momentum of 100 MeV, even though the lower pole of the D*_0(2300) still acts there. Repeating the extraction over higher momentum windows shifts the extracted correlation systematically toward the theoretical prediction, so the paper concludes the published Dπ scattering parameters are not robust. Because heavy-quark spin symmetry maps Dπ onto D*π, the same concern applies to the D*π extraction, and the paper calls for a dedicated reanalysis of the experimental data.

What carries the argument

The central object is a coupled-channel extension of the Vincent–Phatak prescription to the three-dimensional Bethe–Salpeter equation: the long-range Coulomb potential is regularized with a Woods–Saxon regulator, the coupled-channel BSE is solved off-shell with a Gaussian UV cutoff, and the resulting wave-function matrix is matched at a finite radius to the exact Coulomb-plus-strong asymptotic solutions to fix the normalization and the Coulomb-modified scattering amplitudes. Two additions carry much of the argument: kinematic factors $\mathcal{K}_{ij}$ inserted into the inelastic wave functions so the relativistic treatment reproduces the correct non-relativistic limit, and factors $\xi_i(q;s)$ multiplying the Coulomb kernel so the BSE exactly reproduces the Klein–Gordon Coulomb solutions. The load-bearing test of the ALICE assumption is the window-dependence exercise: refitting the raw correlation over different $k$ intervals and observing that the extracted genuine correlation rises toward the theoretical curve as the lower edge of the fit window increases.

Extended reading notes

Core claim

On the paper's own terms, the central discovery is that the apparent absence of a sizable Dπ strong interaction in the ALICE femtoscopy measurement is most plausibly an artifact of the background modeling, not a property of the interaction. The ALICE analysis fixed the genuine correlation function to unity for relative momenta above 100 MeV, but the lower pole of the D*_0(2300) sits near $k \simeq 200$ MeV and still contributes strongly in that window. When the authors repeat the extraction with higher lower edges for the fitting window, the extracted genuine correlation rises away from the pure-Coulomb curve and toward the theoretical result, showing that the extracted scattering lengths ($a_{D^+\pi^-} = -0.017 \pm 0.021 \pm 0.007$ fm, $a_{D^+\pi^+} = -0.01 \pm 0.02 \pm 0.01$ fm) depend on which momentum range is assumed interaction-free. They acknowledge the re-extraction does not bring the curve into full agreement with theory, since it is a robustness test rather than a revised extraction, and the same issue propagates to the D*π system through heavy-quark spin symmetry.

Load-bearing premise

The robustness claim rests on digitized experimental input curves taken from a PhD thesis and from the ALICE paper; if those digitized curves carry systematic error, the window-dependence result and the shift toward theory are not quantitatively trustworthy, a limitation the authors acknowledge by noting the re-extraction does not bring the curve into full agreement with theory.

Editorial extensions

If this is right

  • If the paper is right, the ALICE Dπ scattering lengths near zero do not reflect the real interaction; a reanalysis that allows strong effects above 100 MeV should recover a sizable, attractive $D^+\pi^-$ interaction.
  • The D*π system should show a comparably sizable interaction through heavy-quark spin symmetry, contradicting the Coulomb-only modeling of the D* → D feed-down in the experimental analysis.
  • The framework supplies the machinery for a reliable future extraction of low-energy Dπ and D*π scattering parameters once the puzzle is resolved.
  • The unresolved Kπ femtoscopy tension strengthens the paper's case that the unity-above-a-cutoff assumption deserves scrutiny across pion-hadron systems, not just in the charm sector.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • A dedicated reanalysis of the ALICE raw data that lets the genuine correlation float above 100 MeV, or that raises the threshold into a genuinely interaction-free region, is the direct test: if the extracted $D^+\pi^-$ scattering length moves from about $-0.02$ fm toward the theoretical $-0.25$ fm, the puzzle resolves in favor of the theory.
  • The same window-sensitivity mechanism may contribute to the Kπ femtoscopy tension the authors cite, since a similar unity-above-a-momentum assumption could be masking low-energy rescattering there as well.
  • If confirmed, this would restore consistency between femtoscopy and the LHCb B-decay analyses and lattice QCD, strengthening the two-pole picture of the D*_0(2300) as a shared, testable consequence.
Original abstract

We present a relativistic momentum-space framework for femtoscopic correlation functions including strong and Coulomb interactions in coupled channels. The approach extends the Vincent--Phatak prescription to the three-dimensional Bethe--Salpeter equation, combining a fully relativistic treatment with the correct Coulomb asymptotics through wave-function matching. We apply it to the $D\pi$ system using a coupled-channel heavy-meson chiral interaction that reproduces the established two-pole structure of the $D_0^*(2300)$. Our correlation functions agree with previous theoretical calculations but differ significantly from those extracted by the ALICE Collaboration. We trace this tension to the assumption made in the experimental analysis that the genuine correlation function reaches unity above a relative momentum of $100$ MeV, whereas this region remains affected by the lower $D_0^*(2300)$ pole. Repeating the extraction over different fitting windows reveals a strong dependence of the extracted signal on the chosen range, demonstrating that the resulting $D\pi$ scattering parameters are not robust and motivating a dedicated reanalysis of the experimental data. We extend the analysis to the $D^*\pi$ system, where the same issue arises in close connection with heavy-quark spin symmetry. Together with the unresolved tension between theoretical calculations and the ALICE $K\pi$ femtoscopic measurements, this highlights the need to clarify the origin of this puzzle, with the aim of establishing femtoscopy as a reliable quantitative tool for precision studies of low-energy hadron interactions.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13.0 via TypeSafe API, question bank abstract-p1-20260923, 2026-09-29: 1 request, 6,483 input tokens.

What the abstract itself states, as probabilities: claims first 0.05 · states limitation 0.42 · human participants 0.02 · controlled comparison 0.13 · randomized assignment 0.01 · states quantitative result 0.59 · compares with prior results 0.98 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v1. Results and the main claim are underlined; .

We present a relativistic momentum-space framework for femtoscopic correlation functions including strong and Coulomb interactions in coupled channels. The approach extends the Vincent--Phatak prescription to the three-dimensional Bethe--Salpeter equation, combining a fully relativistic treatment with the correct Coulomb asymptotics through wave-function matching. We apply it to the $D\pi$ system using a coupled-channel heavy-meson chiral interaction that reproduces the established two-pole structure of the $D_0^*(2300)$. Our correlation functions agree with previous theoretical calculations but differ significantly from those extracted by the ALICE Collaboration. We trace this tension to the assumption made in the experimental analysis that the genuine correlation function reaches unity above a relative momentum of $100$ MeV, whereas this region remains affected by the lower $D_0^*(2300)$ pole. Repeating the extraction over different fitting windows reveals a strong dependence of the extracted signal on the chosen range, demonstrating that the resulting $D\pi$ scattering parameters are not robust and motivating a dedicated reanalysis of the experimental data. We extend the analysis to the $D^*\pi$ system, where the same issue arises in close connection with heavy-quark spin symmetry. Together with the unresolved tension between theoretical calculations and the ALICE $K\pi$ femtoscopic measurements, this highlights the need to clarify the origin of this puzzle, with the aim of establishing femtoscopy as a reliable quantitative tool for precision studies of low-energy hadron interactions.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 We present a relativistic momentum-space framework for femtoscopic correlation functions including strong and Coulomb interactions in coupled channels. contribution 0.72 0.89 0.05 asserted 0.99
s1 The approach extends the Vincent--Phatak prescription to the three-dimensional Bethe--Salpeter equation, combining a fully relativistic treatment with the correct Coulomb asymptotics through wave-function matching. method 0.92 0.70 0.04 asserted 1.00
s2 We apply it to the $D\pi$ system using a coupled-channel heavy-meson chiral interaction that reproduces the established two-pole structure of the $D_0^*(2300)$. method 0.57 0.86 0.05 asserted 1.00
s3 Our correlation functions agree with previous theoretical calculations but differ significantly from those extracted by the ALICE Collaboration. result 0.99 0.83 0.19 asserted 1.00
s4 We trace this tension to the assumption made in the experimental analysis that the genuine correlation function reaches unity above a relative momentum of $100$ MeV, whereas this region remains affected by the lower $D_0^*(2300)$ pole. interpretation 0.98 0.65 0.37 asserted 0.99
s5 Repeating the extraction over different fitting windows reveals a strong dependence of the extracted signal on the chosen range, demonstrating that the resulting $D\pi$ scattering parameters are not robust and motivating a dedicated reanalysis of the experimental data. result 0.56 0.92 0.40 asserted 1.00
s6 We extend the analysis to the $D^*\pi$ system, where the same issue arises in close connection with heavy-quark spin symmetry. contribution 0.94 0.89 0.06 asserted 1.00
s7 Together with the unresolved tension between theoretical calculations and the ALICE $K\pi$ femtoscopic measurements, this highlights the need to clarify the origin of this puzzle, with the aim of establishing femtoscopy as a reliable quantitative tool for precision studies of low-energy hadron interactions. future work 0.77 0.16 0.40 asserted 0.77

What kind of paper the classifier reports this is: method or tool 0.68 · evidence from simulation or computation 0.78.

What was examined, and what was not

sources read
  • arXiv listing abstract v1
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 2. FIG. 2. CFs for physical
Figure 3. FIG. 3. Our calculation of the
Figure 4. FIG. 4. Our calculation of the
Figure 5. FIG. 5. Fits to the raw data from Refs. [

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