Jet Trimming

Initial state radiation, multiple interactions, and event pileup can contaminate jets and degrade event reconstruction. Here we introduce a procedure, jet trimming, designed to mitigate these sources of contamination in jets initiated by light partons. This procedure is complimentary to existing methods developed for boosted heavy particles. We find that jet trimming can achieve significant improvements in event reconstruction, especially at high energy/luminosity hadron colliders like the LHC.Comment: 20 pages, 11 figures, 3 tables - Minor changes to text/figure

Generating the future proportion of directed sardine catch taken west of Cape Agulhas in the absence of explicit spatial management

The relationship governing the proportion of directed sardine catch simulated to be taken west of Cape Agulhas during projections underlying the development of OMP-18 is updated. The relationship now differs for each draw from the posterior distribution

Search for the Elusive Higgs Boson Using Jet Structure at LHC

We consider the production of a light non-standard model Higgs boson of order 100~\GEV with an associated $W$ boson at CERN Large Hadron Collider. We focus on an interesting scenario that, the Higgs boson decays predominately into two light scalars $\chi$ with mass of few GeV which sequently decay into four gluons, i.e. $h\to 2\chi \to 4g$. Since $\chi$ is much lighter than the Higgs boson, it will be highly boosted and its decay products, the two gluons, will move close to each other, resulting in a single jet for $\chi$ decay in the detector. By using electromagnetic calorimeter-based and jet substructure analyses, we show in two cases of different $\chi$ masses that it is quite promising to extract the signal of Higgs boson out of large QCD background.Comment: 20 pages, 7 figure

Updated sardine assessment

The previous full assessment of the SA sardine resource, used to develop OMP-08, was tuned to data up to and including November 2006 (Cunningham and Butterworth 2007, with further undocumented updates). Since then 2 further years of below average recruitment have been observed in the May recruitment surveys, together with a low November 2007 survey biomass estimate. This document presents an update of the sardine assessment (posterior modes only), now taking data up to October 2008 into account. This is to obtain a better understanding of the current status of the population and assist in 2009 directed sardine fishery planning

Assessment of the South African sardine resource using data from 1984-2011: further results for a two stock hypothesis

As part of the process of updating the assessment of the South African sardine resource, a model of the sardine two mixing-stock hypothesis is being developed. This hypothesis postulates a “west” stock distributed west of Cape Agulhas and a “south” stock distributed south-east of Cape Agulhas with movement from the “west” to the “south” stock in November as recruits age to 1 year olds. de Moor and Butterworth (2012a) presented some initial results for a two mixing-stock model, but cautioned that those results may not yet have fully converged and that the lack of a Hessian prevented MCMC simulation to estimate posterior distributions for key model parameters. Work has continued on this model to try to ascertain in which areas the model may be overparameterised and which “unimportant” parameters can be fixed at their estimated values without influencing results. In this document further results for the model of a two sardine mixing-stock hypothesis are presented. The current fit is improved from that of de Moor and Butterworth (2012a) and a Hessian is estimated by ADMB. The main changes to the model are detailed below. Some ideas for further work are also listed

The 2004 re-assessment of the South African sardine and anchovy populations to take account of revisions to earlier data and recent record abundances

Hydroacoustic surveys off the coast of South Africa over the early years of the 21st century indicated that both the sardine Sardinops sagax and anchovy Engraulis encrasicolus populations had simultaneously reached record abundances. The South African pelagic fishery is regulated using an Operational Management Procedure (OMP). The OMP in use at that time had been developed using data from the two populations prior to this rapid and substantial increase in abundances. This paper documents the revised assessments that were urgently required to provide a basis to update the OMP. These assessments resulted in a changed perception of the status and productivity of these populations. In particular, estimates of the stock-recruitment relationships and the extent of variation about them, which play a key role in evaluating risk when developing OMPs, altered substantially from estimates derived from earlier assessments

Re-considering the appropriate risk level for anchovy in OMP-13 development

The acceptable level of risk changes from one MP to the next given changes in the perceived level of productivity of a resource resulting from the inclusion of revised and new data in the underlying operating models. This is because the more or less the abundance of an unexploited resource fluctuates naturally (see, for example, the biomass distributions in the absence of catches that are implied by different operating models which are shown in Figure A.1), the more or less resilient it is likely to be to reduction to a specified level through exploitation, and hence the greater or lesser the acceptable probability that fishing reduce the resource to below that level. de Moor and Butterworth (2010) developed an objective method for determining an acceptable level of risk for a new MP that maintained comparability with that adopted in selecting the previous MP. This method was applied to obtain a revised level of risk for sardine in developing Interim OMP-13 (de Moor and Butterworth 2012b). However, the application of this method to obtain a revised level of risk for anchovy for Interim OMP-13 was not straightforward given changes (supported by analyses of updated time series of data) in the selected natural mortality values and stock-recruitment relationships from the operating model used to develop OMP-08 (de Moor and Butterworth 2012a)

When would a survey estimate be considered "appreciably outside the bounds predicted in the OMP testing"

Anon. (2009), outlining the procedures for deviating from or initiating an early review of the pelagic OMP, was discussed at the Scientific Working Group (Pelagic) on 26th February 2009. The document lists examples as to what might constitute Exceptional Circumstances in the case of sardine and anchovy. One such example was: “Survey estimates of abundance that are appreciably outside the bounds predicted in the OMP testing.” A request was made to develop a rule to determine what determines when a survey estimate is “appreciably outside the bounds predicted in the OMP testing.

Assessment of the South African sardine resource using data from 1984-2015: Results at the joint posterior mode for the single stock hypothesis

The assessment of the South African sardine resource has been revised and updated using data available up to November 2015. Two primary hypotheses regarding the sardine stock structure have been agreed for investigation. The first considers sardine distributed off the west and south coasts of South Africa to form a single homogeneous “stock” (or “population”). The second considers the sardine to consist of a western stock and southern stock with some mixing between the two. While there is growing evidence supporting the existence of sub-population structure amongst sardine distributed off the west and south coasts of South Africa (e.g. Coetzee et al. 2008, van der Lingen et al. 2009, 2015, van der Lingen 2011, Weston et al. 2015), the single stock hypothesis continues to be modelled as it allows for easy comparison to past assessments and, in particular, to past risk statistics and previous Operational Management Procedures. It also reflects a limiting case of the mixing model as the extent of mixing becomes very large. This document presents results at the joint posterior mode for the single stock hypothesis only