FastJet is a C++ package that provides a broad range of jet finding and analysis tools. It includes efficient native implementations of all widely used 2→1 sequential recombination jet algorithms for pp and e
 +
 e
 − collisions, as well as access to 3rd party jet algorithms through a plugin mechanism, including all currently used cone algorithms. FastJet also provides means to facilitate the manipulation of jet substructure, including some common boosted heavy-object taggers, as well as tools for estimation of pileup and underlying-event noise levels, determination of jet areas and subtraction or suppression of noise in jets.

FastJet User Manual

We present phenomenological results for vector boson pair production at the LHC, obtained using the parton-level next-to-leading order program MCFM. We include the implementation of a new process in the code, pp → γγ, and important updates to existing processes. We incorporate fragmentation contributions in order to allow for the experimental isolation of photons in γγ, Wγ, and Zγ production and also account for gluon-gluon initial state contributions for all relevant processes. We present results for a variety of phenomenological scenarios, at the current operating energy of √ s = 7 TeV and for the ultimate machine goal, √ s = 14 TeV. We investigate the impact of our predictions on several important distributions that enter into searches for new physics at the LHC.

/pdf/vector-boson-pair-production-at-the-lhc-2qb9b07vr4.pdf

Vector boson pair production at the LHC

We introduce a new jet substructure technique called "soft drop declustering", which recursively removes soft wide-angle radiation from a jet The soft drop algorithm depends on two parameters--a soft threshold $z_\text{cut}$ and an angular exponent $\beta$--with the $\beta = 0$ limit corresponding roughly to the (modified) mass drop procedure To gain an analytic understanding of soft drop and highlight the $\beta$ dependence, we perform resummed calculations for three observables on soft-dropped jets: the energy correlation functions, the groomed jet radius, and the energy loss due to soft drop The $\beta = 0$ limit of the energy loss is particularly interesting, since it is not only "Sudakov safe" but also largely insensitive to the value of the strong coupling constant While our calculations are strictly accurate only to modified leading-logarithmic order, we also include a discussion of higher-order effects such as multiple emissions and (the absence of) non-global logarithms We compare our analytic results to parton shower simulations and find good agreement, and we also estimate the impact of non-perturbative effects such as hadronization and the underlying event Finally, we demonstrate how soft drop can be used for tagging boosted W bosons, and we speculate on the potential advantages of using soft drop for pileup mitigation

Soft Drop

We present first analytic, resummed calculations of the rates at which wide-spread jet substructure tools tag QCD jets. As well as considering trimming, pruning and the mass-drop tagger, we introduce modified tools with improved analytical and phenomenological behaviours. Most taggers have double logarithmic resummed structures. The modified mass-drop tagger is special in that it involves only single logarithms, and is free from a complex class of terms known as non-global logarithms. The modification of pruning brings an improved ability to discriminate between the different colour structures that characterise signal and background. As we outline in an extensive phenomenological discussion, these results provide valuable insight into the performance of existing tools and help lay robust foundations for future substructure studies.

https://link.springer.com/content/pdf/10.1007%2FJHEP09%282013%29029.pdf

Towards an understanding of jet substructure

N-subjettiness is a jet shape designed to identify boosted hadronic objects such as top quarks. Given N subjet axes within a jet, N-subjettiness sums the angular dis- tances of jet constituents to their nearest subjet axis. Here, we generalize and improve on N-subjettiness by minimizing over all possible subjet directions, using a new variant of the k-means clustering algorithm. On boosted top benchmark samples from the BOOST2010 workshop, we demonstrate that a simple cut on the 3-subjettiness to 2-subjettiness ratio yields 20% (50%) tagging efficiency for a 0.23% (4.1%) fake rate, making N-subjettiness a highly effective boosted top tagger. N-subjettiness can be modified by adjusting an angular weighting exponent, and we find that the jet broadening measure is preferred for boosted top searches. We also explore multivariate techniques, and show that additional improvements are possible using a modified Fisher discriminant. Finally, we briefly mention how our mini- mization procedure can be extended to the entire event, allowing the event shape N-jettiness to act as a fixed N cone jet algorithm.

/pdf/maximizing-boosted-top-identification-by-minimizing-n-4zjum07oxh.pdf

Maximizing Boosted Top Identification by Minimizing N-subjettiness

We present the report of the hadronic working group of the BOOST2010 workshop held at the University of Oxford in June 2010. The first part contains a review of the potential of hadronic decays of highly boosted particles as an aid for discovery at the LHC and a discussion of the status of tools developed to meet the challenge of reconstructing and isolating these topologies. In the second part, we present new results comparing the performance of jet grooming techniques and top tagging algorithms on a common set of benchmark channels. We also study the sensitivity of jet substructure observables to the uncertainties in Monte Carlo predictions.

/pdf/boosted-objects-a-probe-of-beyond-the-standard-model-physics-4h7kwrw6em.pdf

A. Katz

Papers

Boosted objects: a probe of beyond the standard model physics