REVIEW
Large Jets at Hadron Colliders at Order $\alpha_s^3$: A Look Inside
High Energy Physics - Phenomenology · Submitted 26 Aug 1992 · 10 references
Pith's verdict: The first order-αs³ look inside the jet, and the paper is candid that its shape agreement comes from a tuned merging cutoff rather than a prediction.
T0 · AI review
Why Pith says this
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Referee report
The paper
The paper claims
A third-order QCD calculation claims to describe not just how often jets are produced at a hadron collider, but how their energy is distributed inside the jet cone, and it agrees with CDF measurements at 100 GeV once a hand-set merging rule
The reading
What carries the argument
The load-bearing object is the fractional transverse-energy profile $F(r,R,E_T)$: for a sample of jets of transverse energy $E_T$ defined by a cone of radius $R$, it is the average fraction of the jet's energy falling inside a concentric inner cone of radius $r<R$. The authors compute the complement $1-F$ rather than $F$ itself, because the energy in the annulus between $r$ and $R$ is free of the collinear singularity at $r=0$; the numerator is a purely order $alpha_s^3$ integral of the three-parton cross section over the annulus, normalized to $E_T$ times the Born cross section. The second piece of machinery is the merging rule. The default algorithm merges any two partons that can be covered by one cone, up to a separation of $2R$, which counts two partons sitting $2R$ apart with a valley between them as a single jet centered on the valley. The authors add a cutoff $R_{sep} leq 2R$ so that partons separated by more than $R_{sep}$ are not merged, and they set $R_{sep}=1.3R$ as a simple stand-in for what an experimental jet algorithm would do.
Extended reading notes
Core claim
The central claim is that an order $alpha_s^3$ perturbative calculation of single-jet production, equipped with a jet definition that includes a merging cutoff, reproduces the CDF measurements of both the jet rate versus cone radius and the distribution of transverse energy inside the jet, at $sqrt{s}=1800$ GeV and $E_T=100$ GeV. The authors show that the order $alpha_s^3$ cross section is far less sensitive to the renormalization/factorization scale $mu$ than the Born result, with residual scale dependence estimated at about 10%, and that its dependence on the cone radius $R$ is qualitatively right: stable near $R approx 0.7$, dominated by real emission at large $R$, and dominated by the virtual correction at small $R$. Fitting both data and theory to $sigma = A + B ln R + C R^2$, they find the $R$-independent piece $A$ agrees well, the piece $C$ associated with radiation far from the jet axis agrees at $mu = E_T/2$, but the piece $B$ associated with radiation near the jet direction comes out too small. Lowering the scale to $E_T/4$ raises $B$ toward the data while overshooting $C$; adding the merging cutoff $R_{sep}=1.3R$ at $mu = E_T/4$ then restores $C$ and leaves both parameters in reasonable agreement with the measured values.
Load-bearing premise
The agreement on jet shapes depends on a merging cutoff $R_{sep}=1.3R$ that is chosen by hand to imitate the experimental jet algorithm, with its detailed justification deferred to a paper still in preparation.
Editorial extensions
If this is right
- Fixed-order QCD at order $alpha_s^3$ becomes a usable tool for jet physics at hadron colliders, since the residual scale dependence drops to roughly 10% and the predicted radius dependence of the cross section has the right shape.
- The cone radius $R approx 0.7$ is singled out as the size at which the order $alpha_s^3$ result is most stable, which is the size actually used in the CDF inclusive jet analysis.
- The comparison of the fitted parameters $B$ and $C$ against data gives a diagnostic for how much radiation is emitted near the jet axis versus far from it, and hence a handle on the effective strong coupling.
- Because the merging rule changes the predicted energy profile at the cone edge by a sizeable amount while changing the total cross section by at most about 10%, details of jet definition matter more for jet substructure than for jet rates.
- Differences in internal jet structure are suggested as a possible way to separate quark-initiated from gluon-initiated jets.
Reading between the lines
- If the merging cutoff is really standing in for finite angular resolution and fragmentation spread, then its value should scale with $E_T$ and with the detector's angular resolution rather than stay fixed at $1.3R$; a measurement of the profile at several $E_T$ would test that.
- The pattern of a correct $A$, a too-small $B$ and a correct $C$ at $mu = E_T/2$ reads like a mismatch in the angular distribution of radiation rather than an overall normalization error, which points at higher-order corrections that populate the collinear region rather than at the parton distributions.
- Since the profile is computed at lowest nontrivial order, its scale dependence is monotonic, so the fact that data prefer a lower scale than the cross section does is itself a signal that the two observables need different effective scales at this order.
- A natural extension is to use the same profile machinery on photon-tagged or $Z$-tagged jet samples, where the parton flavour of the jet is fixed at leading order, to see whether the merging prescription is flavour-independent.
Original abstract
Results from the study of hadronic jets in hadron-hadron collisions at order $\alpha_s^3$ in perturbation theory are presented. The focus is on various features of the internal structure of jets. The numerical results of the calculation are compared with data where possible and exhibit reasonable agreement.
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
Results from the study of hadronic jets in hadron-hadron collisions at order $\alpha_s^3$ in perturbation theory are presented. The focus is on various features of the internal structure of jets. The numerical results of the calculation are compared with data where possible and exhibit reasonable agreement.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Results from the study of hadronic jets in hadron-hadron collisions at order $\alpha_s^3$ in perturbation theory are presented. | contribution 0.99 | 0.89 | 0.12 | asserted 0.98 |
| s1 | The focus is on various features of the internal structure of jets. | contribution 0.98 | 0.57 | 0.07 | asserted 0.93 |
| s2 | The numerical results of the calculation are compared with data where possible and exhibit reasonable agreement. | result 0.94 | 0.89 | 0.36 | asserted 0.84 |
What was examined, and what was not
- arXiv listing abstract v1
- full text
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- references and citing sentences
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- P abstract
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Figures
Figures reproduced from arXiv:hep-ph/9208249 by the authors.
References
How the literature uses it
32 arXiv papers cite this in 37 sentences
Papers citing it · 22 sentences without a confident label
Builds on it 1 paper
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This corresponds to the jet shape [ref] but defined with respect to the WTA axis instead of the standard jet axis.
Phenomenology with a recoil-free jet axis: TMD fragmentation and the jet shape · Introduction · 0.83
Compares with it 1 paper
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This is in contrast to, e.g., the integrated jet shape $Ψ(R)$ [ref] , which requires a detailed calculation even for its leading order behavior [ref] .
Angular Scaling in Jets · Calculating the average · 0.98
Cites it as background 13 papers
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The jet shape [ref] is one of the classic jet substructure observables and it probes the transverse energy profile inside a jet.
Towards the understanding of jet shapes and cross sections in heavy ion collisions using soft-collinear effective theory · Introduction · 0.99
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Jet shapes [ref] are defined as the normalised transverse momentum flow as a function of the distance to the jet axis.
Determination of the $b$-quark mass $m_b$ from the angular screening effects in the ATLAS $b$-jet shape data · Introduction · 0.97
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With such additional handles, we might have a chance to distinguish boosted $$ signal from the QCD background even at a smaller integrated luminosities.[ There are other approaches dealing with a similar situation in a different perspective in recent literature [ref] .] We discuss jet substructure later in the text.
Top Jets at the LHC · Introduction · 0.88
Discussion
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