Abstract
Following on our earlier work on leading-logarithmic (LLR) resummations for the properties of jets with a small radius, R, we here examine the phenomenological considerations for the inclusive jet spectrum. We discuss how to match the NLO predictions with small-R resummation. As part of the study we propose a new, physically-inspired prescription for fixed-order predictions and their uncertainties. We investigate the R-dependent part of the next-to-next-to-leading order (NNLO) corrections, which is found to be substantial, and comment on the implications for scale choices in inclusive jet calculations. We also examine hadronisation corrections, identifying potential limitations of earlier analytical work with regards to their $p_t$-dependence. Finally we assemble these different elements in order to compare matched (N)NLO+LLR predictions to data from ALICE and ATLAS, finding improved consistency for the R-dependence of the results relative to NLO predictions.
Highlights
Here we examine the R dependence in the next-to-next-to-leading order (NNLO) part of the inclusive jet cross section to evaluate the size of these terms
For yet smaller values of R, the NNLOR+LLR result starts to be substantially above the NNLOR and NNLOR-mult. ones. This is because the NNLOR and NNLOR-mult. results have unresummed logarithms that, for very small-R, cause the cross section to go negative, whereas the resummation ensures that the cross section remains positive
Our main observation is that LLR and NNLO terms both have a significant impact on the R dependence of the inclusive jet spectrum, with the inclusion of both appearing to be necessary in order to obtain reliable predictions for R 0.4
Summary
As for the inclusive hadron spectrum [29], the small-R inclusive “microjet” spectrum can be obtained [7] from the convolution of the leading-order inclusive spectrum of partons of flavour k and transverse momentum pt, dσ(k) dpt. For R = R0, or equivalently t = 0, the fragmentation function has the initial condition fjientc/lk(z, 0) = δ(1 − z) It can be determined for other t values by solving a DGLAP-like evolution equation in t [7]. From the point of view of phenomenological applications, the question that perhaps matters more is the impact of corrections beyond NLO (or forthcoming NNLO), since fixed order results are what are most commonly used in comparisons to data. This will be most quantifiable when we discuss matched results in sections 3 and 4. A brief discussion of the different features of t and αs expansions is given in appendix A
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