REVIEW
On the role of NLL corrections and Energy Conservation in the High Energy Evolution of QCD
High Energy Physics - Phenomenology · Submitted 20 Feb 2006 · 19 references
Pith's reading: A new direct Monte Carlo solution of the BFKL equation shows that energy-momentum conservation cuts are separate from the NLL corrections to the evolution kernel.
The paper
The paper claims
A new direct Monte Carlo solution of the BFKL equation shows that energy-momentum conservation cuts are separate from the NLL corrections to the evolution kernel.
The reading
This paper rewrites the BFKL solution so that the total rapidity span of the event emerges automatically. Instead of fixing the span and summing over everything, the new Monte Carlo algorithm first picks a set of gluon emissions and their momenta, then draws rapidity separations between consecutive emissions from a simple exponential distribution, and finally reads off the rapidity span as the sum of those separations. The same physics is computed, but the bookkeeping is cleaner and faster.
The authors then use this formulation to settle a conceptual dispute. Some earlier work had suggested that the large corrections due to energy and momentum conservation were part of the next-to-leading-logarithmic, or NLL, corrections to the BFKL kernel. The paper argues this is wrong: the kernel is local, while energy conservation is a statement about the whole final state. Cutting away emissions that violate energy conservation is, they claim, an independent restriction on the phase space that can be imposed whether the kernel is leading or next-to-leading order. The effect of these cuts is large, so getting the interpretation right matters for predictions of multi-jet rates at the LHC.
Extended reading notes
Core claim
Section 4 states that phase space restrictions in terms of energy and momentum conservation are completely independent of the logarithmic accuracy to which the BFKL evolution is performed, and specifically that the NLL corrections to the evolution kernel do not implement energy and momentum conservation. If true, energy-momentum-conservation cuts can be imposed as a separate, additive restriction on top of either an LL or an NLL kernel, and the large corrections seen in observables such as jet azimuthal decorrelation are not evidence for NLL kernel effects.
Load-bearing premise
Section 3, footnote 1: the probabilistic interpretation of the iterative solution, on which the new algorithm and the phase-space rejection step both rely, holds only for omega(q_i) < 0, which the paper asserts can always be fulfilled in the regularization procedure of Refs [1-3] at LL and [7,8] at NLL. The NLL fidelity of that regularization scheme was validated only by comparison to the conformal N=4 SYM case (Ref [11]), not by a direct derivation in QCD. If this premise fails for some momentum configurations, both the Monte Carlo weights and the claimed separation between phase-space cuts and kernel accuracy would need revisiting.
Original abstract
We present a new method for solving the BFKL evolution applicable at both leading and next-to-leading logarithmic accuracy, and tailored to the study of QCD multi-jet events at colliders. We utilise this to discuss corrections to the standard analysis. There are known, large corrections from energy and momentum conservation. We show that, despite claims to the contrary in the literature, these are unrelated to the next-to-leading logarithmic corrections to the evolution kernel.
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
We present a new method for solving the BFKL evolution applicable at both leading and next-to-leading logarithmic accuracy, and tailored to the study of QCD multi-jet events at colliders. We utilise this to discuss corrections to the standard analysis. There are known, large corrections from energy and momentum conservation. We show that, despite claims to the contrary in the literature, these are unrelated to the next-to-leading logarithmic corrections to the evolution kernel.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We present a new method for solving the BFKL evolution applicable at both leading and next-to-leading logarithmic accuracy, and tailored to the study of QCD multi-jet events at colliders. | contribution 0.85 | 0.94 | 0.08 | asserted 1.00 |
| s1 | We utilise this to discuss corrections to the standard analysis. | contribution 0.73 | 0.84 | 0.04 | asserted 0.59 |
| s2 | There are known, large corrections from energy and momentum conservation. | background 1.00 | 0.06 | 0.05 | asserted 1.00 |
| s3 | We show that, despite claims to the contrary in the literature, these are unrelated to the next-to-leading logarithmic corrections to the evolution kernel. | result 0.94 | 0.87 | 0.75 | asserted 1.00 |
What was examined, and what was not
- arXiv listing abstract v2
- full text
- figures and tables
- references and citing sentences
- relations to other papers
- P abstract
- S sections
- T body sentences
- C citations
- R cross-paper relations
Figures
Figures reproduced from arXiv:hep-ph/0602182 by the authors.
Human review
References
How the literature uses it
1 arXiv paper cite this in 1 sentence
Papers whose main result relates to this one's
States a conflicting result 1 paper
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This explicitly violates energy and momentum conservation in the evolution and could be a source of the reported large NLL corrections.
The Quark-Antiquark Contribution to the Fully Exclusive BFKL Evolution at NLL Accuracy · 0.82
Discussion
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