Pith. sign in

REVIEW 3 major objections 6 minor 36 references

Photoinduced inclusive cross sections in hadronic collisions at the LHC

T0 review · 3 major / 6 minor · reviewed 2026-08-06 · deepseek-v4-flash

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗

Pith's one-line read The paper derives inclusive electromagnetic dissociation in pp and pA collisions at the LHC from deep inelastic structure functions, with simultaneous Delta(1232) excitation dominating the pp rate.

desk verdict A competent and honest application of a 1974 formula to LHC kinematics, with useful new numbers for Coulomb dissociation, though the TeV gamma-p extraction idea depends on an unvalidated extrapolation. read the letter →

arxiv 2507.00682 v1 pith:27XXXIDT submitted 2025-07-01 hep-ph

Robert Gȩbarowski , Agnieszka {L}uszczak , Marta {L}uszczak , Wolfgang Schäfer This is my paper
classification hep-ph
keywords electromagneticdissociationone-photonexchangevirtualphotoabsorptioncrosssectiondeepinelasticstructurefunctionsproton-protoncollisionsproton-nucleusDelta(1232)LHC
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

Electromagnetic dissociation in hadron collisions, where one or both incoming hadrons break up by exchanging a single photon, is not an irreducible background but a calculable quantity once deep inelastic structure functions are known. The paper derives the one-photon-exchange cross section as the contraction of two hadronic tensors, so that the entire process is fixed by virtual photoabsorption cross sections. It then evaluates the result for $pp\to XY$ at $\sqrt{s}=13\,\mathrm{TeV}$, finding dominance of simultaneous $\Delta(1232)$ excitation, and for $pA\to XA$ at $\sqrt{s_{NN}}=8.79\,\mathrm{TeV}$, where the predicted rates reach photon-proton energies of order 1 TeV. That last channel is presented as a possible route to measuring the total photoabsorption cross section of the proton at energies where no direct data exist.

What carries the argument

The load-bearing object is the master formula Eq. (2.10), a compact expression for $d\sigma/dQ^2\,dM_X^2\,dM_Y^2$ as a sum of products of transverse and longitudinal virtual photoabsorption cross sections of the two hadrons, weighted by kinematic coefficients $C_{TT}$, $C_{LT}$, $C_{LL}$. This factorisation into two single-hadron tensors is what turns measured deep inelastic structure functions into predictions for hadron-hadron dissociation. The paper feeds into it a merged parametrization of the proton: the resonance-region fit of Ref. [14], the ALLM description beyond the resonance region, and a LUX-like fit at large $Q^2$, while $\sigma_L$ is included but numerically negligible.

What would settle it

Measure the proton-nucleus dissociation cross section $pA\to XA$ with a detector that captures the full hadronic final state of the dissociated proton and determines the invariant mass $M_X$ calorimetrically; if the observed $M_X$ distribution at photon-proton energies above roughly 200 GeV deviates from the resonance-plus-ALLM and LUX-like predictions by more than their mutual spread, the extrapolation that carries the paper's claims is wrong.

Watch

Extended reading notes

Core claim

On its own terms, the paper establishes that the inclusive reactions $AB\to XY$ mediated by one-photon exchange are fully determined by the virtual photoabsorption cross sections $\sigma_T(\gamma^* A; M_X^2, Q^2)$ and $\sigma_L(\gamma^* A; M_X^2, Q^2)$ of the two colliding hadrons. The threefold differential cross section of Eq. (2.10) assembles these from the hadronic tensors, with the coefficient functions $C_{TT}, C_{LT}, C_{LL}$ carrying all kinematic dependence on $s$, $Q^2$, $M_X^2$, and $M_Y^2$. Using a resonance-region fit joined to the ALLM parametrization, plus a LUX-like structure-function fit, the paper predicts for $pp\to XY$ at $\sqrt{s}=13\,\mathrm{TeV}$ a cross section dominated by the simultaneous excitation of $\Delta(1232)$ resonances, dropping steeply with invariant mass. For $p\,^{208}\mathrm{Pb}\to X\,^{208}\mathrm{Pb}$ at $\sqrt{s_{NN}}=8.79\,\mathrm{TeV}$, it predicts substantial rates up to photon-proton centre-of-mass energies in the TeV range, and it argues that measuring the full dissociative final state there could determine the total photoabsorption cross section of the proton.

Load-bearing premise

The calculation rests on assuming the parametrized curves for how a proton absorbs a virtual photon remain correct when the photon is nearly real and when the photon-proton energy reaches the TeV region, ranges in which the fits are not directly tested by data.

Editorial extensions

If this is right

  • The $pp\to XY$ cross section at $\sqrt{s}=13\,\mathrm{TeV}$ is dominated by simultaneous $\Delta(1232)$ excitation, with a steep falloff in $M_X$, $M_Y$ and a strong correlation between large mass on one side and small mass on the other.
  • For $pA\to XA$ at $\sqrt{s_{NN}}=8.79\,\mathrm{TeV}$, sizeable cross sections extend to photon-proton energies in the TeV region, so the channel can in principle measure the total photoabsorption cross section of the proton at energies beyond any direct measurement.
  • The longitudinal contribution $\sigma_L$ is numerically negligible, so the predictions are effectively controlled by the transverse structure function $F_2$ at low $Q^2$.
  • The same final-state topology as single and double diffractive dissociation is distinguished by a strong dominance of very small $Q^2$, near the kinematic limit, which can serve as an experimental tag.

Reading between the lines

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

  • (Editorial inference) The same master formula could be applied to ion-ion collisions, where measured electromagnetic-dissociation cross sections would provide a direct cross-check of the $Q^2$ flux and structure-function inputs at lower photon energies.
  • (Editorial inference) The predicted double-$\Delta(1232)$ peak in $pp\to XY$ is a distinctive two-resonance signal that could be searched for in existing large-rapidity-gap LHC data, separating the photon-exchange contribution from diffractive dissociation by its tiny $Q^2$.
  • (Editorial inference) A dedicated calorimetric measurement of the dissociated proton in $pA\to XA$ would not only test the paper's curves but also discriminate between the ALLM and LUX-like extrapolations of $\sigma_{\gamma p}(W)$ at high $W$, a discrimination the paper does not itself quantify.
Share X Bluesky LinkedIn Reddit HN

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 6 minor

Summary. The manuscript derives and applies a one-photon-exchange formula for inclusive electromagnetic dissociation in pp and pA collisions. Starting from the hadronic tensor and virtual photoabsorption cross sections, it presents the Carimalo et al. master formula, Eq. (2.10), for dsigma/dQ^2 dM_X^2 dM_Y^2, including TT, LT, and LL terms, and applies it to pp -> XY at sqrt(s)=13 TeV and pA -> XA at sqrt(s_NN)=8.79 TeV. The inputs are merged parametrizations of the resonance region (Bosted-Christy), ALLM, and a LUX-like F2+FL parametrization. The results show a dominance of simultaneous Delta(1232) excitation, a rapid fall-off with invariant mass, and sizable cross sections extending to photon-proton energies of order TeV. The authors propose pA -> XA as a possible way to measure the total photoabsorption cross section of the proton at very high energies, while explicitly stating that further studies are necessary to assess that potential.

Significance. If the numerical predictions hold, the paper provides useful estimates for a class of LHC processes that share a final-state topology with single and double diffractive dissociation, and the pA proposal offers an interesting route toward extending measurements of the total photoabsorption cross section beyond HERA energies. The formalism itself is not new, following the 1974 Carimalo et al. convolution, but applying it with modern structure-function inputs and highlighting Coulomb dissociation of protons on nuclei is a useful contribution. The paper is commendably explicit that no quantity is fitted to new data and that the high-energy extraction idea requires further assessment. The main value depends on the reliability of the input sigma_T and sigma_L in unmeasured kinematics, which is currently not quantified.

major comments (3)
  1. [Sec. III.A, Figs. 4 and 6] The central numerical predictions depend on sigma_{T,L}(gamma* p; M_X^2, Q^2) extrapolated to low Q^2 and to photon-proton center-of-mass energies W up to the TeV region, where the input is unconstrained by data and where the ALLM and color-dipole curves in Fig. 5 visibly differ in energy dependence. The authors themselves describe the dipole-model agreement as "somewhat fortuituous," but no uncertainty band or alternative-input calculation is provided. Since the high-M_X tails in Figs. 4 and 6, and the proposed pA measurement, are controlled by exactly this region, the quantitative predictions are not yet robust. Please repeat the calculation with at least one alternative high-energy input, such as the dipole model shown in Fig. 5, and state which features of the distributions are stable under that change.
  2. [Sec. III.A and Eqs. (2.6)-(2.7)] The exact merging of the resonance-region fit [14], ALLM [15,16], and the LUX-like parametrization [11] is not specified: there is no transition point in W or Q^2, no interpolation procedure, and no statement of which flux-factor convention phi_A from Eq. (2.6) is used when converting F_2 and F_L into sigma_{T,L} via Eq. (2.7). The master formula Eq. (2.10) and the coefficient functions C_{ij} depend on that convention, so as written the numerical results are not reproducible. The authors should specify the matching conditions and the convention explicitly, or provide the code or interface used for the numerical evaluation.
  3. [Sec. III.B, Fig. 6] The suggestion that pA -> XA could measure the total photoabsorption cross section assumes both that the full dissociative proton final state can be measured calorimetrically and that the photon-exchange contribution can be isolated from the same final-state topology generated by strong single-diffractive dissociation. The paper does not quantify these backgrounds or compare the photon-exchange rate with the QCD-induced single-diffraction rate in the same phase space. If the extraction idea is to remain a central motivation, an estimate of this background ratio should be included; otherwise, the abstract-level claim should be softened further.
minor comments (6)
  1. [Eq. (2.8)] The definition of Bjorken x uses m_p in the denominator for a generic hadron A; it should use m_A (or be restricted to the proton case) for consistency with the other formulas in Section II.
  2. [Figs. 2 and 3 captions] The captions of Figs. 2 and 3 are identical, although the text describes them as showing different content; one caption should describe the two-dimensional maps in M_X and log Q^2.
  3. [Fig. 5 and Sec. III.B] The text says the solid red curve is the LUX-like fit of Ref. [11], while the caption says the red curve merges the fit of Ref. [14] with ALLM; the relationship between ALLM and the LUX-like fit should be clarified, and the caption should match the text.
  4. [Sec. III.A and Sec. III.B] There are several typographical errors: "in tems of QCD partons," "decribes," and "texbook-like" should be corrected.
  5. [Eq. (2.12)] The expression for cosh eta is typeset in a way that is hard to parse, with a large brace containing several terms; it should be checked against Ref. [13] and reformatted for clarity.
  6. [Fig. 6 caption] The caption says the right panels show the high-mass contribution, but the relevant distinction is between the upper and lower panels; the caption should say "lower panels."

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: Eq. (2.10) is a standard 1974 convolution of external DIS-based inputs; nothing is fitted to the predicted cross sections.

full rationale

The derivation chain is not circular. The master formula Eq. (2.10) is attributed to Carimalo et al. [13], an independent 1974 derivation, and is simply the contraction of two hadronic tensors; no quantity in this paper is fitted to the predicted pp->XY or pA->XA cross sections. The numerical inputs are prior parametrizations of sigma_{T,L}(gamma* p): the resonance-region fit of Bosted and Christy [14], the ALLM parametrization [15,16], and the LUX-like fit of Ref. [11]. Refs. [11] and [35] are self-citations by overlapping authors, but they are anchored to HERA and fixed-target DIS measurements and are not defined in terms of the cross sections calculated here. The color-dipole model [35] is used only to illustrate the energy dependence of the input, with the authors explicitly noting that its agreement with HERA data 'may be somewhat fortuituous'. The real-photon curves shown in Fig. 5 are displays of the adopted input parametrizations, not independent predictions derived in this paper. The proposed pA->XA measurement of the total photoabsorption cross section is explicitly qualified: 'Further studies are necessary to assess the potential...'. The genuine scientific risk is that the input sigma_{gamma p} is extrapolated to Q^2 near zero and W up to the TeV region, where ALLM and the dipole model disagree; this is a model-uncertainty and correctness concern, not a circularity of the derivation.

Assumptions & free parameters 5 free parameters · 5 assumptions · 0 invented entities

The calculation adds no new fitted parameters or entities; it consumes existing structure-function and dipole parametrizations. The main model dependence is the unvalidated extrapolation of these parametrizations to very high gamma-proton energies and low Q^2.

free parameters (5)
  • Quark masses in color-dipole model = m_u=m_d=m_s=140 MeV, m_c=1.5 GeV
    Taken from Ref. [35]; used in Eq. (3.2) to compute the gamma-p total cross section for illustration. Not fitted in this paper.
  • Dipole cross-section fit parameters = fit to DIS data with Q^2 > 3.5 GeV^2 (Ref. [35])
    Underlies the color-dipole curve in Fig. 5; the authors note the agreement with HERA data 'may be somewhat fortuituous'.
  • ALLM parametrization parameters = from Refs. [15,16]
    Input for sigma_{T,L} beyond the resonance region; determines the high-M_X part of the predictions.
  • LUX-like structure function parameters = from Ref. [11]
    Input for the large-Q^2 part of the calculation; Ref. [11] is by two of the present authors but is fit to HERA DIS data.
  • Resonance-region fit parameters = from Bosted and Christy (Ref. [14])
    Input for the low-M_X, low-Q^2 region that dominates the cross section.
assumptions (5)
  • domain assumption Master formula Eq. (2.10) from Carimalo et al. (1974) is correct for inclusive dissociation via one-photon exchange
    The paper relies on this formula without re-deriving it; stated as 'the compact form [13]'.
  • domain assumption Factorization of the cross section into two independent photoabsorption vertices
    Used in the hadronic-tensor treatment (Eqs. 2.1-2.10); valid at small Q^2 where photon exchange is perturbative.
  • domain assumption The virtual photoabsorption cross sections sigma_{T,L} for the proton can be continued from the fitted DIS region to the low-Q^2, large-W region relevant at the LHC
    Required for the high-M_X predictions; no data constrain these kinematics (Fig. 5).
  • standard math Elastic vertex is described by Sachs form factors (Eq. 2.15)
    Standard electromagnetic form factor representation for the intact hadron.
  • domain assumption Color-dipole representation (Eqs. 3.1-3.4) with a gluon-driven dipole cross section describes the energy dependence of sigma_{gamma-p}
    Used only for the blue curve in Fig. 5; not essential to the main calculation.

how reviews work

0 comments
Cite this review

Pith. "Pith review of Photoinduced inclusive cross sections in hadronic collisions at the LHC." pith.science (2026). https://pith.science/paper/27XXXIDT

@misc{pith2026250700682,
  author       = {Pith},
  title        = {Pith review of: Photoinduced inclusive cross sections in hadronic collisions at the LHC},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/27XXXIDT}},
  note         = {Machine review of arXiv:2507.00682}
}
abstract

We discuss inclusive electromagnetic dissociation processes in proton--proton ($pp$) and proton--nucleus ($pA$) scattering at the LHC where one or both of the protons dissociate. These processes which involve the exchange of a virtual photon in the $t$--channel are calculable in terms of deep inelastic structure functions (virtual photoabsorption cross sections). For the $pA \to XA$ reaction there emerges the possibility of measuring the total photoabsorption cross section on the proton at very high energies.

Figures

Figures reproduced from arXiv: 2507.00682 by the authors.

Figure 1
Figure 1. FIG. 1: Diagrams for the cross sections with dissociation of both hadrons, [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. FIG. 2: Distributions in invariant masses [PITH_FULL_IMAGE:figures/full_fig_p005_2.png] view at source ↗
Figure 3
Figure 3. FIG. 3: Distributions in invariant masses [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figures from the paper (3 more)
Figure 4
Figure 4. Figure 4: FIG. 4: Distributions of invariant mass (left panels) and photon virtuality (right panels) in the [PITH_FULL_IMAGE:figures/full_fig_p006_4.png]
Figure 5
Figure 5. Figure 5: FIG. 5: Total [PITH_FULL_IMAGE:figures/full_fig_p007_5.png]
Figure 6
Figure 6. Figure 6: FIG. 6: Distributions of invariant mass (left panels) and photon virtuality (right panels) in the [PITH_FULL_IMAGE:figures/full_fig_p009_6.png]

Discussion (0). Sign in to comment.

Reference graph

Works this paper leans on

36 extracted references · 26 canonical work pages

  1. [13]

    F. E. Low and S. B. Treiman, Phys. Rev. D5, 756 (1972)

    work page 1972

  2. [14]

    Carimalo, G

    C. Carimalo, G. Cochard, P. Kessler, J. Parisi, and B. Roehner, Phys. Rev. D10, 1561 (1974)

    work page 1974

  3. [11]

    Lux–like

    inspired by the procedure proposed in [10]. In Fig.2 we show the two–dimensional distributions inMX, MY both for the low–mass res- onance region as well as a larger mass range. We see that the cross section is dominated by the simultaneous excitation of ∆+(1232)–resonances. The cross section quickly drops with invariant masses of the excited system. We se...

    work page 2025

  4. [1]

    G. Baur, K. Hencken, D. Trautmann, S. Sadovsky, and Y. Kharlov, Phys. Rept.364, 359 (2002), hep-ph/0112211

    arXiv 2002

  5. [2]

    C. A. Bertulani, S. R. Klein, and J. Nystrand, Ann. Rev. Nucl. Part. Sci.55, 271 (2005), nucl-ex/0502005

    arXiv 2005

  6. [3]

    Klein and P

    S. Klein and P. Steinberg, Ann. Rev. Nucl. Part. Sci.70, 323 (2020), 2005.01872

    arXiv 2020

  7. [4]

    Schäfer, Eur

    W. Schäfer, Eur. Phys. J. A56, 231 (2020)

    work page 2020

  8. [5]

    C. A. Bertulani, J. Phys. Conf. Ser.2619, 012003 (2023), 2304.12475

    work page Pith review arXiv 2023

Show all 36 references
  1. [6]

    Grund (ALICE), Phys

    D. Grund (ALICE), Phys. Proc. UPC1, 4 (2024), 2502.18621

    2024 arXiv

  2. [7]

    Maj (ATLAS), Phys

    K. Maj (ATLAS), Phys. Proc. UPC1, 25 (2024)

    2024

  3. [8]

    Glück, C

    M. Glück, C. Pisano, and E. Reya, Phys. Lett. B540, 75 (2002), hep-ph/0206126

    2002 arXiv

  4. [9]

    Łuszczak, W

    M. Łuszczak, W. Schäfer, and A. Szczurek, Phys. Rev. D93, 074018 (2016), 1510.00294

    2016 arXiv

  5. [10]

    Manohar, P

    A. Manohar, P. Nason, G. P. Salam, and G. Zanderighi, Phys. Rev. Lett.117, 242002 (2016), 1607.04266

    2016 arXiv

  6. [12]

    Łuszczak, W

    M. Łuszczak, W. Schäfer, and A. Szczurek, JHEP05, 064 (2018), 1802.03244

    2018 arXiv

  7. [15]

    P. E. Bosted and M. E. Christy, Phys. Rev. C77, 065206 (2008), 0711.0159

    2008 arXiv

  8. [16]

    Abramowicz, E

    H. Abramowicz, E. M. Levin, A. Levy, and U. Maor, Phys. Lett. B269, 465 (1991)

    1991

  9. [17]

    Abramowicz and A

    H. Abramowicz and A. Levy (1997), hep-ph/9712415

    1997 arXiv

  10. [18]

    T. A. Armstrong et al., Phys. Rev. D5, 1640 (1972)

    1972

  11. [19]

    Symposium on Electron and Photon Interactions at High Energies (1969)

    E.D.Bloometal., in 4th Int. Symposium on Electron and Photon Interactions at High Energies (1969)

    1969

  12. [20]

    Michalowski, D

    S. Michalowski, D. Andrews, J. Eickmeyer, T. Gentile, N. B. Mistry, R. Talman, and K. Ueno, Phys. Rev. Lett.39, 737 (1977)

    1977

  13. [21]

    Meyer, B

    H. Meyer, B. Naroska, J. H. Weber, M. Wong, V. Heynen, E. Mandelkow, and D. Notz, Phys. Lett. B33, 189 (1970)

    1970

  14. [22]

    H. G. Hilpert et al., Phys. Lett. B27, 474 (1968)

    1968

  15. [23]

    M. L. Perl, T. Braunstein, J. Cox, F. Martin, W. T. Toner, B. Dieterle, T. F. Zipf, W. L. Lakin, and H. C. Bryant, Phys. Rev. Lett.23, 1191 (1969)

    1969

  16. [24]

    Ballam et al., Phys

    J. Ballam et al., Phys. Rev. D5, 545 (1972)

    1972

  17. [25]

    D. O. Caldwell et al., Phys. Rev. Lett.40, 1222 (1978)

    1978

  18. [26]

    G. M. Vereshkov, O. D. Lalakulich, Y. F. Novoseltsev, and R. V. Novoseltseva, Phys. Atom. Nucl. 66, 565 (2003)

    2003

  19. [27]

    Aid et al

    S. Aid et al. (H1), Z. Phys. C69, 27 (1995), hep-ex/9509001

    1995 arXiv

  20. [28]

    Chekanov et al

    S. Chekanov et al. (ZEUS), Nucl. Phys. B627, 3 (2002), hep-ex/0202034

    2002 arXiv

  21. [29]

    Thiel, F

    A. Thiel, F. Afzal, and Y. Wunderlich, Prog. Part. Nucl. Phys.125, 103949 (2022), 2202.05055

    2022 arXiv

  22. [30]

    N. N. Nikolaev, J. Speth, and V. R. Zoller, Phys. Lett. B473, 157 (2000), hep-ph/9911433

    2000 arXiv

  23. [31]

    Watanabe and K

    A. Watanabe and K. Suzuki, Phys. Rev. D86, 035011 (2012), 1206.0910

    2012 arXiv

  24. [32]

    M. M. Block, L. Durand, and P. Ha, Phys. Rev. D89, 094027 (2014), 1404.4530

    2014 arXiv

  25. [33]

    Britzger, C

    D. Britzger, C. Ewerz, S. Glazov, O. Nachtmann, and S. Schmitt, Phys. Rev. D100, 114007 (2019), 1901.08524

    2019 arXiv

  26. [34]

    Chwastowski and J

    J. Chwastowski and J. Figiel, Phys. Part. Nucl.35, 619 (2004), hep-ex/0311044. 10

    2004 arXiv

  27. [35]

    N. N. Nikolaev and B. G. Zakharov, Z. Phys. C49, 607 (1991)

    1991

  28. [36]

    Łuszczak and H

    A. Łuszczak and H. Kowalski, Phys. Rev. D95, 014030 (2017), 1611.10100. 11

    2017 arXiv

Pith tools

Reviewed August 6, 2026 · model on record in the stance chip above.