The mass distribution of jets produced in hard processes at the LHC plays an important role in several jet substructure related studies involving both Standard Model and BSM physics, especially in the context of boosted heavy particle searches. We compute analytically the jet-mass distribution for both Z+jet and dijet processes, for QCD jets defined in the anti-k t algorithm with an arbitrary radius R, to next-to-leading logarithmic accuracy and match our resummed calculation to full leading-order results. We note the important role played by initial state radiation (ISR) and non-global logarithms explicitly computed here for the first time for hadron collider observables, as well as the jet radius dependence of these effects. We also compare our results to standard Monte Carlo event generators and discuss directions for further studies and phenomenology.

We consider jet-shape observables of the type proposed recently [1,2] where the shapes of one or more high-p T jets, produced in a multi-jet event with definite jet multiplicity, may be measured leaving other jets in the event unmeasured. We point out the structure of the full next-to-leading logarithmic resummation specifically including resummation of non-global logarithms in the leading-N c limit and emphasising their properties. We also point out differences between jet algorithms in the context of soft gluon resummation for such observables.

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Abstract:We analytically compute non-global logarithms at finite N c fully up to 4 loops and partially at 5 loops, for the hemisphere mass distribution in e + e − → di-jets to leading logarithmic accuracy. Our method of calculation relies solely on integrating the eikonal squared-amplitudes for the emission of soft energy-ordered real-virtual gluons over the appropriate phase space. We show that the series of non-global logarithms in the said distribution exhibits a pattern of exponentiation thus confirming -by means of brute force -previous findings. In the large-N c limit, our results coincide with those recently reported in literature. A comparison of our proposed exponential form with allorders numerical solutions is performed and the phenomenological impact of the finite-N c corrections is discussed.

Clustering logs have been the subject of much study in recent literature. They are a class of large logs which arise for non-global jet-shape observables where final-state particles are clustered by a non-cone-like jet algorithm. Their resummation to all orders is highly non-trivial due to the non-trivial role of clustering amongst soft gluons which results in the phase-space being non-factorisable. This may therefore significantly impact the accuracy of analytical estimations of many of such observables. Nonetheless, in this paper we address this very issue for jet shapes defined using the k t and C/A algorithms, taking the jet mass as our explicit example. We calculate the coefficients of the Abelian α 2 s L 2 , α 3 s L 3 and α 4 s L 4 NLL terms in the exponent of the resummed distribution and show that the impact of these logs is small which gives confidence on the perturbative estimate without the neglected higher-order terms. Furthermore we numerically resum the nonglobal logs of the jet mass distribution in the k t algorithm in the large-N c limit.