= Monte Carlo Event Generators at NLO and Jet Physics =

School of the Think Tank on Physics@LHC initiative.

5-9 December 2011 Sariska Palace, Rajasthan, India

https://indico.cern.ch/conferenceDisplay.py?confId=150478
 
 == Preparatory Material ==

The school is meant to introduce to young researchers in phenomenology and experimental LHC physics the MC tools necessary
to perform accurate simulations and analyses. Particular emphasis will be given to NLO calculations, their interface to the shower programs, and  applications to jet physics. While the basics will be reviewed during the lectures, the school assume basic knowledge of
perturbative QCD concepts and methods.

We invite the students to study the excellent introductory lectures:[[BR]]
	
Elements of QCD for hadron colliders.[[BR]]
Gavin P. Salam (CERN)[[BR]]
e-Print: arXiv:1011.5131 [hep-ph] [[BR]]

These lecture notes cover all the basic concepts assumed in our lectures. 

In order to develop an hand-on experience on QCD calculation, we propose the students to calculate the pp>H+X  cross section at NLO in the HEFT. The full computation is described [https://cp3.irmp.ucl.ac.be/projects/madgraph/attachment/wiki/SchoolIndia/Higgs.pdf here]. Mathematica Notebooks are provided below which contain all the details of the calculation and the implementation in a simple Notebook which can calculate cross section production at NLO at the LHC.

 * pp>H at LO (1-loop): details of the calculation (Mathematica Notebook) [https://cp3.irmp.ucl.ac.be/projects/madgraph/attachment/wiki/SchoolIndia/HiggsGG-LO-mtfinite.nb HiggsGG-LO-mtfinite.nb]
 * pp>H at NLO: details of the calculation (Mathematica Notebook) [https://cp3.irmp.ucl.ac.be/projects/madgraph/attachment/wiki/SchoolIndia/HiggsGG-NLO.nb higgsGG-NLO.nb]
 * pp>H at NLO: cross section evaluation for the LHC (Mathematica Notebook+PDF libraries to be compiled) [https://cp3.irmp.ucl.ac.be/projects/madgraph/attachment/wiki/SchoolIndia/phenHiggs.tar.gz phenHiggs.tar.gz ].



 = LHC Phenomenology with !MadGraph =


 == Lectures ==

Find the pdf of the 4 x 1 hour lectures and the tutorials:(available after lectures)

   * Lectures (mornings) : 
      * Basics of QCD
      * NLO
      * NLO+PS
      * Jets
 
== References ==

   * [http://www.hep.phy.cam.ac.uk/theory/webber/QCDbook.html QCD and Collider Physics] by Keith Ellis, James Stirling, Bryan Webber (Cambridge Monographs, 1996).
   * [https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FurtherReading Perspectives on LHC physics, Ed. by G. Kane and A. Pierce].
 
== !MadGraph and Pheno Exercises ==

A summary of advanced QCD and pheno exercises can be found [attachment:exercises-NBI.pdf here].

 === Tutorial 1: Familiarize with !MadGraph ===
   * Logon to the MadGraph web site and register: http://madgraph.hep.uiuc.edu.
   * Register with a valid e-mail address
   * Feynman diagrams. Generate a few processes (with different QED + QCD couplings) trying to guess which diagrams appear: 
      * u u~ > t t~
      * g g   > t t~
      * g g   > t t~ h
      * u u~ > t t~ b b~
   * Subprocess identification. List all subprocesses contributing to: 
      * p p > h > t t~ b b~
      * p p > t t~ b b~
      * p p > t t~ j j
   * Look at the new physics models and check the particle and interactions content.
   * Advanced: Download the MadGraph 5 package from launchpad and play with the standalone version.
   * [https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/SimpleKinematics Kinematics at the LHC]: refresh the kinematics of an hadron collider.
 
=== Tutorial 2: Calculate cross sections and generate events ===

Generate events for a few selected processes and look at the plots:

   * ttbar production with decays: p p > t t~, t > b mu+ vm , t~ > b~ e- ve~
   * VV production: pp>VV> leptons, with V=Z,W.
   * Single top + Higgs: p p > t H j (QCD=0, QED=3, j=gudsc,p=gudscb). Show that there is a large negative interference between the diagrams.
   * g g > H > W W
   * Weak boson fusion

Some phenomenological applications (at the parton level):

   * [https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/2Jets Jets] : Di-jet kinematics and rates in pp collisions.
   * [https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/3Jets 3 Jets] : Energy distributions in 3-jet events.
   * [https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/WAsymm Drell-Yan] : Study the rapidity asymmetry at the Tevatron.
   * [wiki:Tt top production] : $t \bar t$ production, Tevatron vs LHC.
   * [wiki:Tprime t' production] : $t'$ production at the LHC.
 
=== Tutorial 3: The full simulation chain and advanced features ===

Try out the Analysis Tools:
   * a Fortran-based package: MadAnalysis (just do install MadAnalysis)

Study what is known of a SM Higgs at the LHC:
   * Find the best prediction for Higgs production at the LHC [http://maltoni.web.cern.ch/maltoni/TeV4LHC/index.html here].
   * Find the Higgs branching ratios [attachment:h-br.pdf here].
Choose a channel and investigate signal and background:
   1. The 2 lepton + missing Et final state: $pp \to H\to W^+ W^- \to e^- \bar \nu_e \mu^+ \nu_\mu$ 
      * Signal 
         * Events: [attachment:hww-signal.lhe.gz Parton Level] [attachment:hww-signal.lhco.gz Detector Level]
         * Plots: [attachment:hww-signal-lhe.pdf Parton Level] [attachment:hww-signal-lhco.pdf Detector Level]
      * Background 
         * Events: [attachment:hww-background.lhe.gz Parton Level] [attachment:hww-background.lhco.gz][Detector Level]
         * Plots: [attachment:hww-background-lhe.pdf Parton Level] [attachment:hww-background-lhco.pdf Detector Level]
   2. Top associated production $pp \to t\bar tH$ with $H \to b \bar b$ 
      * Signal + Background samples: 
         * Events: [attachment:ttbb.lhe.gz Parton Level] [attachment:ttbb.lhco.gz Detector Level]
         * Plots: [attachment:ttbb-lhe.pdf Parton Level] [attachment:ttbb-lhco.pdf Detector Level]

 === Tutorial 4: The MadGraph BlackBox Challenge ===

Three "black boxes" are given, in the form of event files in the LHC Olympics format and a series of selected plots:

   * Box A : [attachment:A.lhco.gz Events] Plots: [attachment:A-lhe.pdf Parton level] [attachment:A.pdf Detector level]
   * Box B : [attachment:B.lhco.gz Events] Plots: [attachment:B-lhe.pdf Parton level] [attachment:B.pdf Detector level]
   * Box C : [attachment:C.lhco.gz Events] Plots: [attachment:C-lhe.pdf Parton level] [attachment:C.pdf Detector level]

Black boxes contain only signal events. The students are asked to pair up the boxes above with the following models and also answer to the questions:

   * Model 1 : Extra Z (zp) : What its mass? Does it have Standard Model couplings to fermions?
   * Model 2 : Heavy Scalar (h): What its mass? Is it a SM Higgs?
   * Model 3 : Extra W (wp+ or wp-) : What its mass? Does it have Standard Model couplings to fermions?

Useful extra information:
   * In the plots $H_T=\sum |p_T^{vis}| + E_T^{miss}$.
   * A SM-like Z' would decay (more or less democratically) into: jet jet (uu~,cc~,dd~,ss~,bb~), t tbar (tt~), lept+lept- (e+e-,mu+mu-,ta+ta-), neutrino anti-neutrino (ve ve~,vm vm~,vt vt~). It could also have couplings to SM W and Z, and in that case would decay in to ZZ and W+W-.
   * An Higgs couple to particles with a strength which is proportional to the particle masses. A SM-like heavy H would decay in to t tbar (tt~), W+W-, ZZ.
   * A SM-like W'+ would decay into: jet jet (ud~,cs~), t b (tb~), lept neutrino (e+ ve , mu+ vm, ta+ vt). It could also have couplings to SM W and Z, and in that case would decay in to ZW.

 === Monte Carlo's ===

For those interested in getting deeper into Monte Carlo techniques, here are some more exercises:

   * Write the simplest integration function based on the definition of average and error
   * Importance sampling via an analytic transformation
   * Von Neumann's rejection method : plain and improved
   * Phase space for 1 -> n particles
   * Vegas
   * Top decay : comparison among the various methods
   * qq -> tt production

All exercises are presented and solved this Mathematica Notebook: [attachment:/mc101.nb mc101.nb]. Reference: [http://www.slac.stanford.edu/spires/find/hep/www?eprint=hep-ph/0006269 Introduction to MC methods], by [http://wwwthep.physik.uni-mainz.de/~stefanw/ Stefan Weinzierl]
 === Animations ===
   * [http://madgraph.hep.uiuc.edu/Event/ Interactive Flash version] Note you may want to zoom in!
   * [http://madgraph.hep.uiuc.edu/Event/fast_collisionx6.avi Fast movie (.avi) of collision]
   * [http://madgraph.hep.uiuc.edu/Event/collision.mov Guided movie (.mov) of collision]
   * [http://www.thedailyshow.com/watch/thu-april-30-2009/large-hadron-collider John Ellis on Daily Show]