2015 CERN Summer student workshop

Exercises : discover the Higgs boson at the LHC

• Find predictions for Higgs boson production at the LHC ​here.
• Find the Higgs boson branching ratio table here​.
• Choose a channel and investigate both the signal and background:
  1. The 4 lepton final state: $pp \to H\to Z Z \to e^+e- \mu^{+ \mu}-$
     • Signal Plots: Parton Level​ Detector Level​
     • Background Plots: Parton Level​ Detector Level​
  2. Top associated production $pp \to t\bar tH$ with $H \to b \bar b$
     • Signal + Background Plots: Parton Level​ Detector Level​

The Challenge

Three "black boxes" are given, in the form of event files in the LHC Olympics (LHCO) format and a series of selected figures.

• Box A : Events​, parton level figures​, detector level figures​
• Box B : Events​, parton level figures​, detector level figures​
• Box C : Events​, parton level figures​, detector level figures​

These Black boxes are associated with signal events only. It is asked to pair up the boxes above with the three following new physics models and answer the related questions:

• Model 1 - Extra neutral gauge boson (Z'): what is its mass and does it have Standard Model couplings to fermions?
• Model 2 - Heavy scalar (heavy Higgs boson): what is its mass and is it a Standard Model Higgs boson?
• Model 3 - Extra charged gauge boson (W'): what its mass and does it have Standard Model couplings to fermions?

To solve these exercises, useful extra information can be found below:

In the figures, $H_T=\sum

p_T{vis}

+ E_T{miss}$.

• A Z' boson with Standard Model couplings would decay (more or less democratically) into: jet jet (uu~,cc~,dd~,ss~,bb~), t tbar (tt~), l+l- (e+e-,mu+mu-,ta+ta-), neutrino anti-neutrino (ve ve~,vm vm~,vt vt~). It could also have couplings to the Standard Model W and Z bosons, and in that case would decay in to ZZ and W+W-.
• A Higgs boson couples to particles with a strength which is proportional to the particle masses. A Standard Model-like heavy Higgs boson would decay in to t tbar (tt~), W+W- and ZZ.
• A W' boson with Standard Model-like couplings would decay into: jet jet (ud~,cs~), t b (tb~), lepton-neutrino (e+ ve , mu+ vm, ta+ vt). It could also have couplings to the Standard Model W and Z bosons, and in that case would decay in to ZW.

Animations

• ​Interactive Flash version Note you may want to zoom in!
• ​Fast movie (.avi) of collision
• ​Guided movie (.mov) of collision
• ​LHC_Rap

Slides

• Download here