Module 9: Event Hypothesis


This page documents the lecture given on Event Hypotheses and Group-Dependent Analysis Layers in the framework of the e-learning in CMS activity Using Physics Analysis Toolkit (PAT) in your analysis.

The whole e-learning activity is based on the PAT as integrated in CMSSW_2_2_3.

Event Hypotheses

An "Event Hypothesis" is the hypothesis of a given composite physics hypothesis given a group of detector objects. This module will discuss some tools developed to make this process easier.

Naturally, this situation lends itself to specific PAG's and search groups to develop their own event hypothesis classes. In the 2.2.3 CMSSW version, there are several tools available from PAGs as well as from the Physics Tools Candidate Model itself, so we'll go through a few of them (although not in much detail, merely to give you a flavor).

Generic Event Hypothesis

The generic event hypothesis is handled by the Candidate framework. The CompositeCandidate class naturally accommodates event hypotheses. We discuss these in detail now.

First, we need a few definitions. The "name" of the hypothesis would correspond to the physics signature you're trying to represent (for instance, "Z"). The "roles" are the names of the daughters that play a specific role. In the case of a Z decay, it could be "muon1" and "muon2". While this doesn't serve a meaningful difference in the Z case, there are cases where the role will carry additional information (such as a mass hypothesis). This frequently arises in B physics (such as in the case of B_s to j/psi + phi).

The intrinsic nature of an event hypothesis is that it is most often hierarchical. The hierarchical structure of the Candidate class naturally handles this situation.

Very simple examples of this can be seen in the Analysis Starter Kit.

Please read this section, since it will form the basis for some of our homework assignments. You can find the prescription for using this workbook here.

-- SalvatoreRoccoRappoccio - 06 Feb 2009

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Topic revision: r1 - 2009-02-06 - unknown
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