01-introduction.md

title	teaching	exercises	questions	objectives	keypoints
Introduction	5	0	What are known as physics object in CMS? What will I need to do in this lesson?	Understand what physics objects are Understand the dynamics of this reading assignment	Basic information about physics objects in CMS can be found in the Cern Open Data portal site. A set of questions need to be answered in our [assignment form](https://forms.gle/sMyuLFiYJWRsUAew6).

Overview

The CMS is a giant detector that acts like a camera that "photographs" particle collisions, allowing us to interpret their nature.

Certainly we cannot directly observe all the particles created in the collisions because some of them decay very quickly or simply do not interact with our detector. However, we can infer their presence. If they decay to other stable particles and interact with the apparatus, they leave signals in the CMS subdetectors. These signals are used to reconstruct the decay products or infer their presence; we call these, physics objects. These objects could be electrons, muons, jets, missing energy, etc.; but also lower level objects like tracks. For the current releases of open data, we store them in ROOT files following the EDM data model in AOD format.

In the CERN Open Portal(CODP) site one can find a more detailed description of these physical objects and a list of them corresponding to 2010 and 2011/2012 releases of open data.

What is expected in this lesson?

In this lesson we will guide you through reading some documentation, which will give you a better idea about the physics objects in CMS. As you progress with the next episodes, you will find a set of simple questions that need to be answered in the corresponding questionary in our assignment form. The question numbers in the form match the numbers in this lesson. You can edit this form at any time.

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