Page tree

Let's start with some questions, small tasks and exercises to familiarize yourself with a few things. If you like, you can copy these questions to your Logbook and write down your answer there!

Warm-up quiz

For fun: You can also try this quiz.

  • What is the heaviest particle in the Standard Model (SM)? How does it decay and what is its decay lifetime?
  • What quarks are contained in the proton? What is the difference between valence quarks and sea quarks? What else is in the proton?
  • The Higgs mechanism is responsible for the masses of the electroweak (EW) gauge bosons (W,Z) and the fermions. What are their masses, expressed in terms of their interaction strength with the Higgs boson?
  • What is meant by integrated luminosity \mathcal{L}_\text{int} = \int dt \mathcal{L} at the LHC? How do we calculate the number of events N for a process with production cross section \sigma and branching fraction \mathrm{BR} ?
  • What is the dominant production mode for the Higgs boson at the LHC? For a mass of 125 GeV, what is the cross section (in pb) for 7, 8 and 13 TeV? (Tipp: see here)
  • Which other Higgs production modes are relevant at the LHC? Find out the dominant five and look up their 13 TeV cross section.
  • What are the dominant Higgs decay modes and their branching ratios? Can you explain why they appear in this order?
  • Which Higgs decay modes were the most relevant for the LHC discovery in 2012, and why?
  • Calculate the expected number of events for LHC at 13 TeV for \mathcal{L}_\text{int} = 100~\text{fb}^{-1} for Higgs production in gluon fusion, decaying to (a) two photons, (b) 4 leptons (i.e. electrons or muons) via ZZ, and (c) bb (use the numbers from previous questions!).

SUSY questions

(more advanced)

  • What is the hierarchy problem?
  • What are the phenomenological consequences of R-parity conservation?
  • Why do we need two Higgs doublet fields for Supersymmetry?
  • Assuming that all SUSY particles are not too heavy (i.e. around the TeV scale), which SUSY particles are expected to be produced predominantly at the LHC? Why?
  • What are typical production rates of squarks and gluinos with mass of 1 TeV at the LHC with 13 TeV center-of-mass energy? How does it compare to the production rate of one of the main backgrounds, t t-bar production?
  • What are neutralinos and charginos?
  • How does a ``typical'' SUSY collider event look like at the LHC (assuming R-parity conservation)? What particles / objects are expected to be seen in the detector?
  • Which particles cannot be detected at the LHC? How can they still be ``seen'' indirectly?
  • What is the upper value of the light Higgs boson mass MSSM prediction at tree-level? How can it be lifted to the observed value (125 GeV)?
  • What are the tree-level expressions for the Higgs (h,H,A) couplings to fermions and vector bosons (W, Z), with respect to the SM value? (Tipp: A good source is Section 1.2.3 of this review)
  • What are the couplings of the MSSM Higgs bosons (h,H,A) to neutralinos and charginos? What happens if the neutralinos are pure ``Higgsinos''? What if they do not contain a ``Higgsino'' component? (Tipp: same source, Section 1.2.4)
  • What are the couplings of the MSSM Higgs bosons (h,H,A) to staus? (Tipp: same source, Section 1.2.4)

Some exercises

Download the example model file found in your project page. This is an SLHA (=SUSY Les Houches Accord) file, which defines a parameter point of a supersymmetric model. Let's study it!

  • Can you find out the meaning of the various SLHA blocks? E.g., what is encoded in the Blocks SMINPUTS; EXTPAR and MINPAR and MSOFT; MASS, DECAY?
    In the Block MASS, after the comment character '#', the nomenclature of the sfermion masses MSf(s,t,g) means s=1,2 sfermion index; t=1..4 sfermion type (nu, e, u, d), g=1..3 generation index. The sfermion index simply labels the lighter (1) and heavier (2) sfermion (i.e. mass ordering). The first column gives the PDG number.
  • Can you find out the masses of the light and heavy scalar top quark (stop)?
  • What are the masses of the staus?
  • What are the masses of the neutralinos and charginos?
  • What are the masses of the Higgs bosons?
    Let's study the DECAY blocks at the bottom of the file. The header of each block gives the PDG number of the decaying particle and the decay width (in GeV). Each row then contains the value of the branching ratio, the number of final state particles of the decay, and then the PDGs of the final state particles. The comment (after "#") gives a human readable expression.
  • First of all: How do we calculate the lifetime (in seconds) from the decay width?
  • Let's look at the branching fractions of the light Higgs boson (PDG 25). How do the decays to photons, ZZ and bb compare to the SM prediction (see above)?
  • Let's look at the heavier Higgs bosons (H and A, denoted here as HH and A0 with PDGs 35 and 36). What are the dominant decay modes? What are the branching fractions into gauginos and/or staus?


  • No labels