Les Houches

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====== Shower Uncertainties ======


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==== Overview ====

The basic ida is to first do a study on the purely pQCD level. Different shower algorithms should be compared at LO+PS level first, along with their recommended variations.

Having cross-validated these uncertainties between different algorithms, matching/merging approaches should be included and an assessment on accuracy improvements should be made, again cross-validating different algorithms.

A comparison to analytic resummation (where possible) and at different levels of perturbative accuracy is desirable. The range of observables should be kept small and concise, ranging from quantities which exhibit resummation, transition and fixed order regions, but also including these observables, where shower uncertainties are expected to indicate large hadronization corrections, as well.

A preliminary list includes:

  * e+ e- event shapes, notably thrust, major, Minor, hemisphere masses, jet broadening -- mainly for comparing to analytics
  * e+ e- (differential) jet rates to quantify the interplay between shower uncertainties and regions of large hadronization corrections
  * the Higgs and Z pt spectra, including heavy Z and H variants to enlargen phase space as prime examples for a resummation region which is limited in comparison to the available physical phase space
  * more complex observables with interesting fixed-order structures such as the lego plot separation between the Z and first jet in Z plus jet events have also been discussed.

==== Work Plan ====

  * The full list f observables and their binning, algon with relevant process/collider settings needs to be agreed on.
  * Generators/analytics groups interested should sign up on this page, providing a list of input they can/will provide.

== Proposal ==

  * Use the Rivet ALEPH_2004_S5765862 analysis for e+e- as it contains all observables discussed and start with that. Once a preliminary comparison is available we can move to pp->h/Z etc.
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