REVIEW 2 major objections 6 minor 29 references
Exploring the scattering of vector bosons at LHCb
T0 review · 2 major / 6 minor · reviewed 2026-08-14 · deepseek-v4-flash
Pith's one-line read The paper argues that LHCb can measure vector-boson scattering in its forward region by tagging a single jet together with two same-sign muons, making a combined electroweak-plus-QCD measurement, and possibly the electroweak component…
desk verdict A genuinely new one-jet VBS tag for LHCb with clean LO numerics, but the claim that the EW component alone is in reach overstates the paper's own yields (~1.5 sigma at 300/fb). read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is the inclusive signature $pp \to \mu^+\mu^+ j + X$, selected with a forward single-jet tag: one anti-$k_T$ jet with $p_T > 20$ GeV and $2.2 < \eta < 4.2$, two same-sign muons with $p_T > 20$ GeV and $2.0 < y < 4.5$ separated from the jet by $\Delta R > 0.5$, and a veto on any extra lepton with $2.0 < \eta < 4.5$. This signature replaces the conventional two-tag-jet VBS topology and exploits LHCb's forward muon coverage. Cross sections are computed at leading order with the Recola matrix-element generator and the MoCaNLO integrator, using the complex-mass scheme for resonant gauge bosons and the NNPDF31 parton distribution set; the anti-$k_T$ algorithm with $R=0.4$ defines the jet.
What would settle it
Run-3 LHCb data or a detector-level simulation could settle it: if the trigger and reconstruction efficiency for the $\mu^+\mu^+ j$ selection is far below the level needed to retain a usable fraction of the predicted ~0.35 fb (muon-only) or ~1.4 fb (all flavour/charge) yield, the measurement would not be in reach. Concretely, at 300 fb$^{-1}$ the electroweak component predicts only about 8 $\mu^+\mu^+ j$ events before detector effects; an efficiency below ~20% would leave fewer than two EW events and make a standalone EW measurement impossible.
Extended reading notes
Core claim
The central claim is that VBS can be observed at LHCb in the forward region using an event selection that deliberately does not reconstruct the full VBS topology. Instead of requiring two high-rapidity tagging jets and central bosons, one tags a single forward jet ($p_T > 20$ GeV, $2.2 < \eta_j < 4.2$) together with two same-sign anti-muons ($p_T > 20$ GeV, $2.0 < y < 4.5$, $\Delta R > 0.5$ from the jet), vetoing additional leptons in the forward region. In this selection, the same-sign WW process dominates the electroweak signal, while WZ and ZZ contribute at the percent level and are suppressed by the lepton veto. The summed electroweak cross section is $0.0258~\mathrm{fb}$ against $0.3217~\mathrm{fb}$ of irreducible QCD background for $\mu^+\mu^+ j$, and the electroweak fraction grows with jet transverse momentum and at low muon rapidity. The author therefore argues that a combined QCD+EW measurement, and even the EW component alone, is in reach for the high-luminosity LHCb runs.
Load-bearing premise
The feasibility conclusion rests on the untested assumption that LHCb can trigger on and reconstruct the forward same-sign-dimuon-plus-jet signature with sufficient efficiency and can keep fake and non-prompt lepton backgrounds under control; the paper explicitly leaves this experimental verification to a future study.
Editorial extensions
If this is right
- A combined measurement of the QCD and electroweak contributions to $pp \to \mu^+\mu^+ j + X$ is in reach at LHCb's high-luminosity runs, with a total selected cross section of about $0.35~\mathrm{fb}$ for the muon-only channel.
- The electroweak component alone is separable: it is about 8% of the inclusive sample and rises to roughly 20% at high jet $p_T$, so phase-space cuts can improve the signal-to-background ratio.
- Including all lepton flavour and charge combinations yields about $1.4~\mathrm{fb}$ total, of which about $0.1~\mathrm{fb}$ is electroweak, multiplying the available statistics.
- Because LHCb covers forward rapidities, such a measurement would probe VBS kinematics not accessible to the central LHC experiments and would provide an independent test of the electroweak sector.
Reading between the lines
- If the detector-efficiency and fake-background assumptions are confirmed by a dedicated LHCb study, the yield projections imply that the first forward-region VBS observation could be made with early high-luminosity data rather than only in the far future.
- The single-tag, same-sign-dilepton strategy could be adapted to search for new physics in the forward region, since the electroweak fraction is largest at high jet $p_T$ and low muon rapidity where anomalous couplings would show up first.
- The same selection could be applied to the $e^+e^+$ and $e^+\mu^+$ channels with essentially identical cross sections in the massless-lepton limit, which would allow a forward-region lepton-universality check in VBS.
- An EW-only differential measurement would supply a high-rapidity anchor for global electroweak fits, a region where next-to-leading-order corrections are known to be large.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes measuring vector-boson scattering (VBS) at the LHCb experiment using a signature with one forward jet and two same-sign muons, exploiting LHCb's forward coverage. It defines an event selection, computes leading-order cross sections and differential distributions for the electroweak (O(α^6)) and QCD (O(α^4 α_s^2) / O(α^4 α_s)) contributions to pp→μ+μ+j+X using Recola and MoCaNLO, and argues that both the combined QCD+EW process and the EW component alone could be measured in high-luminosity LHCb runs.
Significance. The proposal is original and, if realizable, would provide a forward-region VBS measurement that is independent of ATLAS and CMS. The LO computation is standard and transparent: it is a direct phase-space integration with no fitted parameters, and the paper quotes Monte Carlo integration errors and scale uncertainties. These are genuine strengths. The weakness is that the central feasibility claim rests on two unquantified pillars: the statistical significance implied by the paper's own cross sections, and the detector/trigger/fake-lepton performance, which the author explicitly defers to a future experimental study. As a result, the paper identifies a promising signature but does not yet demonstrate that the EW component is measurable.
major comments (2)
- [Table I, Eq. (15), Discussion] The quoted cross sections do not support the Discussion's claim that the EW contribution on its own can be in reach. From Table I and Eq. (15), the inclusive e/μ same-sign sample at 300 fb^-1 has about 420 events, of which roughly 30 are EW and 390 are QCD. A counting test against a QCD-only hypothesis gives 30/sqrt(390) ≈ 1.5 sigma, and at 50 fb^-1 it is below 1 sigma. Please provide a quantitative significance statement, including binned projections such as the high-pT,j region of Fig. 3 where the EW fraction reaches about 20%, or revise the conclusion to match the statistical reach of the presented numbers.
- [Measurement strategy, paragraph after Eq. (4)] The feasibility claim depends on the unverified assumption that LHCb can trigger on and reconstruct the mu+ mu+ j signature with sufficient efficiency and that fake or non-prompt lepton backgrounds can be controlled. The paper states that such optimizations "require experimental knowledge on efficiencies, event yields, fake backgrounds and therefore go beyond this exploratory theoretical work," but no efficiency or fake-rate assumptions are supplied. Without any detector-level modeling or explicit efficiency assumptions, the step from a 0.35 fb inclusive cross section to the statement that a measurement is "in reach" is not established. Please include explicit assumptions or restrict the claim to a theoretical identification of a promising signature.
minor comments (6)
- [Measurement strategy] The phrase "two anti-muons" should be clarified as "two positively charged muons" to avoid confusion with antimuons in the experimental sense.
- [Eq. (15)] The relations sigma(WW→e+mu+) ≈ 2 sigma(WW→mu+mu+) and sigma(ZZ→e+mu+) ≈ 2 sigma(ZZ→mu+mu+) rely on identical-particle symmetry and the massless-lepton limit; this should be stated explicitly at that point.
- [Figs. 3 and 4] The lower panels are labeled "Sumδ [%]" but they show the EW fraction of the sum; the label should be changed to something unambiguous such as "EW fraction of total".
- [Numerical results, third paragraph] The sentence calling the summed cross section "the physical cross section" should note that the interference of order O(α^5 α_s) is neglected, so the sum is approximate even though the interference is expected to be small.
- [References] Reference [13] is listed as "to be published (2020)"; this should be updated with the current status of the dedicated experimental study, or removed if no longer available.
- [Footnote [27]] The statement that electrons and muons are identical in the computation should be accompanied by a note that experimental reconstruction and trigger efficiencies differ, which is relevant for the flavor-combination argument in Eq. (15).
Circularity Check
No circularity: the cross sections are direct LO phase-space integrations with fixed SM inputs, and self-citations are used only for context.
full rationale
The paper contains no circular derivation. The central numerical results in Table I are obtained by integrating tree-level matrix elements for pp -> mu+ mu+ j + X using Recola and MoCaNLO, with Standard Model parameters fixed from measured on-shell masses, G_mu, and the NNPDF31 set. No parameter is fitted to any subset of data, and no predicted quantity is defined in terms of the quantity it is supposed to predict. The selection cuts in Eqs. (1)-(4) are imposed on the final state, not learned from the computed yields. The author explicitly labels the study as exploratory and states that cut optimisation 'require experimental knowledge on efficiencies, event yields, fake backgrounds and therefore go beyond this exploratory theoretical work,' which is an honest limitation rather than a circular move. Self-citations, including Ref. [11] and Ref. [12], are invoked only to justify the smallness of the omitted O(alpha^5 alpha_s) interference and the choice of the positive-sign muon channel; these prior results do not enter as inputs that determine the quoted cross sections. The claim that the EW component may be in reach for high-luminosity LHCb runs is an inference from the computed yields and not a quantity forced by construction. Whether that inference is numerically optimistic is a correctness or statistical-reach question, not a circularity one.
Assumptions & free parameters
assumptions (4)
- domain assumption The Standard Model and its electroweak gauge structure are the correct underlying theory for the simulated processes.
- domain assumption Leading-order collinear factorization with PDF set NNPDF31_lo_as_0118 gives predictions reliable enough for a feasibility study.
- domain assumption The EW-QCD interference of order O(alpha^5 alpha_s) is negligible and can be omitted.
- ad hoc to paper Detector efficiencies, trigger performance, and fake-lepton backgrounds will not invalidate the measurement.
Cite this review
Pith. "Pith review of Exploring the scattering of vector bosons at LHCb." pith.science (2026). https://pith.science/paper/H6UDLNK7
@misc{pith2026190806805,
author = {Pith},
title = {Pith review of: Exploring the scattering of vector bosons at LHCb},
year = {2026},
howpublished = {\url{https://pith.science/paper/H6UDLNK7}},
note = {Machine review of arXiv:1908.06805}
}
read the original abstract
In this letter, I propose a strategy to measure vector-boson scattering (VBS) at the LHCb experiment. The typical VBS topology at hadron colliders features two energetic back-to-back jets with large rapidities and two gauge bosons produced centrally. In this article, I show that such a topology can actually be probed by the LHCb detector. In particular, tagging only one of the two jets in combination with two same-sign leptons allows for a measurement with upcoming luminosities. I present an illustrative event selection where cross sections and differential distributions are computed for VBS and its irreducible background.
Figures
Reference graph
Works this paper leans on
-
[1]
R. Contino, C. Grojean, M. Moretti, F. Piccinini, and R. Rattazzi, JHEP 05, 089 (2010), 1002.1011
arXiv 2010
-
[2]
Implications of Vector Boson Scattering Unitarity in Composite Higgs Models
D. Buarque Franzosi and P. Ferrarese, Phys. Rev. D96, 055037 (2017), 1705.02787
work page Pith review arXiv 2017
-
[3]
B. Henning, D. Lombardo, M. Riembau, and F. Riva, Phys. Rev. Lett. 123, 181801 (2019), 1812.09299
arXiv 2019
- [4]
-
[5]
A. M. Sirunyan et al. (CMS), Phys. Rev. Lett. 120, 081801 (2018), 1709.05822
arXiv 2018
- [6]
-
[7]
A. M. Sirunyan et al. (CMS) (2019), 1905.07445
arXiv 2019
-
[8]
A. M. Sirunyan et al. (CMS), Phys. Lett. B774, 682 (2017), 1708.02812
arXiv 2017
Show all 29 references
- [9]
- [10]
- [11]
- [12]
-
[13]
Kenzie and M
M. Kenzie and M. Pellen, to be published (2020)
2020
-
[14]
Denner, S
A. Denner, S. Dittmaier, P. Maierh¨ ofer, M. Pellen, and C. Schwan, JHEP 06, 067 (2019), 1904.00882
2019 arXiv
- [15]
-
[16]
Gehrmann-De Ridder, T
A. Gehrmann-De Ridder, T. Gehrmann, E. W. N. Glover, A. Huss, and D. M. Walker, Eur. Phys. J. C79, 526 (2019), 1901.11041
2019 arXiv
-
[17]
Denner et al., Nucl
A. Denner et al., Nucl. Phys. B560, 33 (1999), hep- ph/9904472
1999
-
[18]
Denner et al., Nucl
A. Denner et al., Nucl. Phys. B724, 247 (2005), hep- ph/0505042
2005
-
[19]
Actis et al., JHEP 04, 037 (2013), 1211.6316
S. Actis et al., JHEP 04, 037 (2013), 1211.6316
2013 arXiv
- [20]
-
[21]
Biedermann, A
B. Biedermann, A. Denner, and M. Pellen, Phys. Rev. Lett. 118, 261801 (2017), 1611.02951
2017 arXiv
- [22]
-
[23]
R. D. Ball et al. (NNPDF), Eur. Phys. J. C77, 663 (2017), 1706.00428
2017 arXiv
- [24]
-
[25]
Bellan et al., in 2nd VBSCan Annual Meeting Thes- saloniki, Greece, June 19-21, 2018 (2019), 1906.11332
R. Bellan et al., in 2nd VBSCan Annual Meeting Thes- saloniki, Greece, June 19-21, 2018 (2019), 1906.11332
2019 arXiv
-
[26]
Schwan, PoS RADCOR2017, 081 (2018)
C. Schwan, PoS RADCOR2017, 081 (2018)
2018
-
[27]
Therefore, a computation with electrons would be strictly identical
In the calculation presented below, leptons are chosen to be massless. Therefore, a computation with electrons would be strictly identical
-
[28]
In principle, different sign could also be considered but it has the huge disadvantage of also encompassing the pro- duction of top-antitop pairs whose cross section is several orders of magnitude larger
-
[29]
[25, 26]
PDF uncertainties for VBS have been shown to be well under control in Refs. [25, 26]
Reviewed August 14, 2026 · model on record in the stance chip above.
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