REVIEW
Leptoproduction of Heavy Quarks I-- General Formalism and Kinematics of Charged Current and Neutral Current Production Processes
High Energy Physics - Phenomenology · Submitted 21 Dec 1993 · 29 references
Pith's verdict: The framework paper behind general-mass heavy-quark DIS: the helicity factorization and the target-mass correction to the slow-rescaling variable are the real content, and both hold up; the phenomenology figure is thin and the factorization ansatz is acknowledged rather than closed.
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Referee report
The paper
The paper claims
Heavy-quark leptoproduction should be described by one factorization formula that keeps the quark mass and the target mass exactly, rather than by a slow-rescaling patch applied to a massless parton formula.
The reading
What carries the argument
The load-bearing device is the helicity decomposition of the hadronic tensor into three structure functions $F_+, F_0, F_-$ (right-handed, longitudinal, left-handed vector boson), combined with the observation that the polarization vectors built from the target momentum $P$ and from the struck parton momentum $k_1$ coincide because the two are collinear in the parton model. That coincidence is what makes factorization transparent in the helicity basis and opaque in the invariant basis, where $k_1^μ = ζ_P P^μ + ζ_q q^μ$ with mass-dependent coefficients $ζ_P, ζ_q$ that mix $W_1, W_2, W_3$ with $W_4, W_5, W_6$. The second device is the exact on-shell condition for the final heavy quark, $k_2^2 - m_2^2 = 0$, which localizes the convolution at $ξ = χ ≡ [η(Q^2 - m_1^2 + m_2^2) + Δ(-Q^2, m_1^2, m_2^2)]/(2Q^2)$, with $η$ the target-mass-corrected Bjorken variable. In the small-mass limit this reduces to $χ ≃ x(1 + m_2^2/Q^2)(1 - x^2 M^2/Q^2)$, which is the usual slow-rescaling variable multiplied by a target-mass correction the authors say has been overlooked.
Extended reading notes
Core claim
The paper's central claim is that charged-current and neutral-current heavy-quark leptoproduction admit a single description, $W = f_N(ξ,μ) ⊗ ω(ξ,Q,m_1,m_2,M)$, in which the partonic hard amplitude $ω$ is computed with the full quark-mass dependence and the convolution variable $ξ$ is fixed by exact kinematics including the target mass. The authors show that in the helicity basis this statement takes an especially clean form, $F^{N}_{λ}(q,P) = Σ_a f_{aN} ⊗ ω^{a}_{λ}$, because the hadron and parton helicity amplitudes are related without any transformation, whereas the invariant structure functions require the mass-dependent mixing coefficients tabulated in the paper. They then evaluate the leading-order diagram with all masses retained and find $ω_+ = 0$, $ω_- = g_{La}^2 (Q^2 + m_1^2 + m_2^2 - Δ)/Δ · δ(ξ/χ - 1)$, and a longitudinal piece $ω_0$ proportional to $(m_2^2 - m_1^2)^2/Q^2 + m_2^2 + m_1^2$ that does not vanish as the quark masses go to zero only in the massless limit — so the Callan-Gross relation fails at finite quark mass already at leading order. The resulting neutrino cross section, their Eq. (31), is claimed to be the correct leading-order answer with full target-mass dependence, and the conventional slow-rescaling prescription is recovered only as a particular truncation of it.
Load-bearing premise
The paper assumes that the factorization theorem holds in its simple convolution form across the whole intermediate region where the quark mass is neither much smaller than nor comparable to the hard scale, even though the authors state plainly that the theorem is proven only in the two asymptotic limits and that they are treating it as an ansatz.
Editorial extensions
If this is right
- The Callan-Gross relation fails at leading order once the produced quark has mass: the longitudinal helicity structure function $F_0$ is non-zero and of order $m_2^2/Q^2$ even for massless initial partons.
- The conventional slow-rescaling substitution $x → x(1 + m_2^2/Q^2)$ is an inconsistent truncation, because the correct kinematic variable also carries the target-mass factor $(1 - x^2 M^2/Q^2)$.
- For fixed-target neutrino charm production, the complete leading-order cross section deviates from the slow-rescaling prescription by more than 25 percent at small $y$ and at large $x$, for neutrino energies between 50 and 300 GeV.
- Because the target mass $M$ is comparable to the charm mass $m_c$ in existing neutrino experiments, retaining one mass effect while dropping the other is not a controlled approximation.
- The same framework is claimed to apply unchanged to neutral-current production and to bottom quarks, providing the starting point for the next-to-leading-order analysis promised in the companion paper.
Reading between the lines
- If the target-mass correction to $χ$ is physically real, reanalyses of dimuon data would shift the extracted strange-quark distribution and any $|V_{cs}|$ determination that depends on it, so the correction is testable against existing fits rather than only against new data.
- The gap between the ansatz and a proof could be closed numerically: comparing the complete leading-order formula to a full massive next-to-leading-order calculation in the intermediate region $m^2 \sim Q^2$ would show whether the interpolation the authors assume actually holds there.
- The helicity bookkeeping relies only on the collinearity of the polarization reference momenta, which suggests the same no-mixing factorization should carry over to hadroproduction of heavy quarks, where the same collinear structure appears.
- A sharper experimental discriminator than the total rate would be the small-$y$ shape of $dσ/dy$ at $E_ν \approx 50$–$80$ GeV, where the threshold region makes the two prescriptions diverge most and where the target-mass and quark-mass corrections add rather than cancel.
Original abstract
Existing calculations of heavy quark production in charged-current and neutral current lepton-hadron scattering are formulated differently because of the artificial distinction of ``light'' and ``heavy'' quarks made in the traditional approach. A proper QCD formalism valid for a wide kinematic range from near threshold to energies much higher then the quark mass should treat these processes in a uniform way. We formulate a unified approach to both types of leptoproduction processes based on the conventional factorization theorem. In this paper, we present the general framework with complete kinematics appropriate for arbitrary masses, emphasizing the simplifications provided by the helicity formalism. We illustrate this approach with an explicit calculation of the leading order contribution to the quark structure functions with general masses. This provides the basis for a complete QCD analysis of charged current and neutral current leptoproduction of charm and bottom quarks to be presented in subsequent papers.
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.
The abstract, sentence by sentence
Existing calculations of heavy quark production in charged-current and neutral current lepton-hadron scattering are formulated differently because of the artificial distinction of ``light'' and ``heavy'' quarks made in the traditional approach. A proper QCD formalism valid for a wide kinematic range from near threshold to energies much higher then the quark mass should treat these processes in a uniform way. We formulate a unified approach to both types of leptoproduction processes based on the conventional factorization theorem. In this paper, we present the general framework with complete kinematics appropriate for arbitrary masses, emphasizing the simplifications provided by the helicity formalism. We illustrate this approach with an explicit calculation of the leading order contribution to the quark structure functions with general masses. This provides the basis for a complete QCD analysis of charged current and neutral current leptoproduction of charm and bottom quarks to be presented in subsequent papers.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Existing calculations of heavy quark production in charged-current and neutral current lepton-hadron scattering are formulated differently because of the artificial distinction of ``light'' and ``heavy'' quarks made in the traditional approach. | background 0.87 | 0.06 | 0.06 | asserted 1.00 |
| s1 | A proper QCD formalism valid for a wide kinematic range from near threshold to energies much higher then the quark mass should treat these processes in a uniform way. | gap 0.78 | 0.08 | 0.16 | asserted 0.94 |
| s2 | We formulate a unified approach to both types of leptoproduction processes based on the conventional factorization theorem. | contribution 0.74 | 0.93 | 0.24 | asserted 1.00 |
| s3 | In this paper, we present the general framework with complete kinematics appropriate for arbitrary masses, emphasizing the simplifications provided by the helicity formalism. | contribution 0.89 | 0.92 | 0.14 | asserted 0.99 |
| s4 | We illustrate this approach with an explicit calculation of the leading order contribution to the quark structure functions with general masses. | contribution 0.81 | 0.94 | 0.11 | asserted 1.00 |
| s5 | This provides the basis for a complete QCD analysis of charged current and neutral current leptoproduction of charm and bottom quarks to be presented in subsequent papers. | future work 1.00 | 0.26 | 0.15 | asserted 0.98 |
What was examined, and what was not
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Figures
Figures reproduced from arXiv:hep-ph/9312318 by the authors.
References
How later papers used it
60 later papers cite it
1 paper by the same authors is listed below: 1 used its method or tool.
Uses its method or tool 1 of 13 papers with this label · 1 by the same authors
By the same authors
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Included only the dominant target mass effects in the structure function expressions in the ACOT scheme of this paper.
nCTEQ15 - Global analysis of nuclear parton distributions with uncertainties in the CTEQ framework (2015) (same authors) · 0.97 · paraphrased: the licence does not allow quoting
How the literature uses it
49 arXiv papers cite this in 81 sentences
Papers citing it · 42 sentences without a confident label
Builds on it 1 paper
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The S-ACOT-MPS scheme is based on an amended version of the S-ACOT scheme developed for DIS [ref] , and is applied to proton-proton collisions.
Probing heavy-flavor parton distribution functions at hadron colliders · Introduction and Motivations · 0.89
Uses its method or tool 9 papers
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The neutron structure functions $F_i^neutron, A$ are computed correspondingly by assuming the isospin symmetry, i.e. [equation] The effects of the heavy quarks are taken into account by the SACOT-prescription [ref] .
Compatibility of neutrino DIS data and global analyses of parton distribution functions · Computation Framework · 0.99
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Since each diagram contains different physics, we can use parity invariant projectors [ref] to extract their individual gauge invariant structure functions; for example,
Testing collinear factorization in a spectator model with mass corrections · DIS in a spectator model · 0.97
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We work in the ACOT formalism [ref] to compute the structure functions in the helicity basis.
Target mass corrections in lepton--nucleus DIS: theory and applications to nuclear PDFs · The parton model with quark and hadron masses · 1.00
Compares with it 2 papers
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We find in this way that for a specified renormalization and factorization scheme (namely $MS$), the FONLL [ref] and ACOT [ref] constructions give formally identical results, to all orders in perturbation theory.
Charm in Deep-Inelastic Scattering · Introduction · 0.81
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We draw further comparison to heavy quark PDFs, where quark masses $(m_𝒬)$ violate scaling (“slow rescaling”) at $𝒪(m_𝒬^2/Q^2)$ but vanish in the DIS limit [ref] .
Weak bosons as partons below 10 TeV partonic center-of-momentum · Introduction · 0.96
Cites it as background 22 papers
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[ref], the exact form of the mass-dependent part of these coefficient functions is not uniquely fixed in the case of perturbatively generated charm: this has led to the construction of several different (though equally valid) formulations in the literature, such as ACOT [ref] , S-ACOT [ref] , TR and TR$^'$ [ref] , FONLL [ref] , and the recent formulation of Ref. [ref] .
Charm in Deep-Inelastic Scattering · The 4 flavour scheme · 0.99
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There are a number of such schemes available, namely the ACOT scheme [ref] (and its simplified variants S-ACOT [ref] , S-ACOT-$χ$ [ref] , and the more recent m-ACOT [ref] for hadron-hadron collisions), the TR scheme [ref] , and the FONLL scheme [ref] .
Resummation and Matching of $b$-quark Mass Effects in $b\bar{b}H$ Production · Introduction · 0.89
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A number of such variable flavor number (VFN) schemes have been proposed for DIS structure functions, including ACOT [ref] S-ACOT [ref] , ACOT-$χ$ [ref] , TR and TR' [ref] , and FONLL [ref] , etc.
Mass corrections to the DGLAP equations · Introduction · 0.97
Discussion
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