adding 04

_episodes/01-jets101.md

@@ -33,7 +33,7 @@ Full set of intro slides: Slides 1-24 (FIXME)
 
 > ## Open a notebook
 >
-> For the first part of this introduction open the notebook called `Basics.ipynb`.
+> For this part, open the notebook called `Jets_101.ipynb` and run Exercise 1.
 {: .checklist}
 
 This preliminary exercise will illustrate some of the basic properties of jets, like the four momentum quantiies: pt, eta, phi, mass.  We will use nanoAOD files, which are currently widely used with the CMS Collaborators. For more information about nanoAOD follow [this link](https://gitlab.cern.ch/cms-nanoAOD/nanoaod-doc/-/wikis/home). At the end of the notebook you will be able to see all the quantities stored in the `Jet` collection.
@@ -76,7 +76,7 @@ In CMS, CaloJets are used less often than PFJets. Examples of their use include
 
 > ## Open a notebook
 >
-> For this part open the notebook called `Jet_Types_and_Algorithms.ipynb` and run the Exercise 1.
+> For this part, open the notebook called `Jets_101.ipynb` (if it is not opened) and run Exercise 2.
 {: .checklist}
 
 > ## Question 1.1
@@ -106,7 +106,7 @@ Some excellent references about jet algorithms can be found here:
 
 > ## Open a notebook
 >
-> For this part open the notebook called `Jet_Types_and_Algorithms.ipynb` and run the Exercise 2.
+> For this part, open the notebook called `Jets_101.ipynb` (if it is not opened) and run Exercise 3.
 {: .checklist}
 
 > ## Discussion 1.3

_episodes/04-Jet_Substructure.md

@@ -10,11 +10,49 @@ keypoints:
 - "First key point. Brief Answer to questions. (FIXME)"
 ---
 
-Navigate to directory section4 and follow the instructions in the below notebooks.
+Full set of intro slides: Slides 58-76 (FIXME)
 
-Covered notebooks: Jets in CMS (Ex 4.1), Jet Substructure (Ex 4.2) and W and Top Tagging (Ex 4.3)
+> ## After following the instructions in the setup:
+>
+> ~~~
+> cd <YOUR WORKING DIRECTORY>/notebooks/
+> source /cvmfs/sft.cern.ch/lcg/views/LCG_103/x86_64-centos7-gcc11-opt/setup.sh
+> jupyter notebook --no-browser --port=8888 --ip 127.0.0.1
+> ~~~
+> {: .language-bash}
+>
+> This will open a jupyter notebook tree with various notebooks. 
+{: .callout}
 
-Full set of intro slides: Slides 58-76
+## Jet Substructure
+
+Because boosted jets represent the hadronic products of a heavy particle produced with high momentum, some tools have been developed to study the internal structure of these jets. This topic is usually called Jet Substructure.
+
+Jet substructure algorithms can be divided into three main tools:
+ * **grooming algorithms** attempt to reduce the impact of *soft* contributions to clustering sequence by adding some other criteria. Examples of these algorimths are softdrop, trimming, pruning.
+ * **subtructure variables** are observables that try to quantify how many cores or prongs can be identify within the structure of the boosted jet. Examples of these variables are n-subjetiness or energy correlation functions.
+ * **taggers** are more sofisticated algorithms that attempt to identify the origin of the boosted jet. Currently taggers are based on sofisticated machine-learning techniques which try to use as much information as possible in order to efficiency identify boosted W/Z/Higgs/top jets. Examples of these taggers in CMS are deepAK8/ParticleNet or deepDoubleB.
+
+For further reading, several measurements have been performed about jet substructure:
+ * [Studies of jet mass in dijet and W/Z+jet events](http://arxiv.org/abs/1303.4811) (CMS).
+ * [Jet mass and substructure of inclusive jets in sqrt(s) = 7 TeV pp collisions with the ATLAS experiment](http://arxiv.org/abs/1203.4606) (ATLAS).
+ * [Theory slides](http://www.hri.res.in/~sangam/sangam18/talks/Marzani-2.pdf)
+ * [More theory slides]( http://indico.hep.manchester.ac.uk/getFile.py/access?contribId=14&resId=0&materialId=slides&confId=4413)
+ * [Talk from Phil Harris](https://web.pa.msu.edu/seminars/hep_seminars/abstracts/2018/Harris-HEPSeminar-Slides-4172018.pdf) on searching for boosted $W$ bosons.
+
+ In this part of the tutorial, we will compare different subtructure algorithms as well as some usually subtructure variables.
+
+> ## Open a notebook
+>
+> For this part, open the notebook called `Jet_Substructure.ipynb` and run Exercise 1.
+{: .checklist}
+
+> ## Question 4.1
+> Look at the following histogram, which compares ungroomed, pruned, soft drop (SD), PUPPI, and
+> SD+PUPPI jets. 
+> <img src="../fig/ex5_rsg_jetmass.png" width=400px/>
+> Note that the histogram has two peaks. What do these correspond to? How do the algorithms affect the relative size of the two populations?
+{: .challenge}
 
 
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