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Les Houches

2019 Session

Wikis of Previous sessions

Les Houches Themes



Simplified Models for Vector-Like quarks

We chose to represent two different classes of models:

* Simple VL quarks/top partners on a multiplet by multiplet basis

* VL quarks with Minimal Flavour Violation couplings

see below for the two projects (model files, who's doing what, etc…)

Task assignment/volunteering and projects

Status of the projects:

  1. - Models in FeynRules/Madgraph: DONE. All model files can be found below or on the FeynRules models web pages.
  2. - Event generation: DONE. If you need a sample write to to have the password.

Please, add your name, or project you'd like to be involved in.

  1. - Implementation in Feynrules and validation: Giacomo, Aldo, Andreas, Veronica - DONE
  2. - Event generation: Jose - DONE
  3. - Study of the 3(2)-jet resonance in single production (MFV): Jose, Veronica
  4. - QQbar → semileptonic decays: Jose
  5. - Combination of searches in pair production: Sasha, Giacomo, Luca Panizzi, Aldo, Asesh, Tobias, Guillaume
  6. - Sensitivity to single production/combination: Minho, Sasha, Giacomo, Mathieu Buchkremer
  7. - New signals in single production (other than 3j resonance): Tobias, Giacomo, Asesh, Aldo, Lorenzo, Seung Lee
  8. - Limits on single production from single top measurements: Sasha
  9. - Flavour constraints, effective operator based, compute Wilson coefficients in simplified models: Guillaume, Nazila, Giacomo, Aldo
  10. - Boosted analysis in pair production, QQ → Vj Vj (Jose, …)

Note: individual pages for each projects can be created and linked here. Please contribute!

Simple VL quarks/top partners

* Single VL representation that mixes to SM quarks via Yukawa couplings. Coupling to light generations not set to zero.

* Parameters:

  1. - mQ, VL quark mass (MC default: mQ = 1 TeV)
  2. - RL, rate of decays into light quarks (MC default: RL = 0.5)
  3. - g*, coupling strength entering single production (MC default, g* = 0.1 g)

References: 1305.4172, 1007.2933, hep-ph/0007316 (and many others)

* Model files (Aldo and Giacomo's version with CalcHep and Madgraph implementation, also on the FeynRules web site) :

  1. - Standard doublet (T,B): FeynRules, CALCHEP, MADGRAPH
  2. - Singlet T: FeynRules, CALCHEP, MADGRAPH
  3. - exotic doublet (X,T): FeynRules, CALCHEP, MADGRAPH
  4. - remaining possibilities (more constrained): exotic doublet (B,Y), triplet (X,T,B) and (T,B,Y).

* Remarks: T has charge +2/3, B charge -1/3, X charge +5/3, Y charge -4/3. For the Standard doublet, only mixing in the up sector has been considered (see case lambda_d=0 of Table 2 in 1305.4172), because mixing in the down sector is strongly constrained by flavour (and less motivated by naturalness). Note that the pattern of decays change significantly if a sizeable mixing in the down sector is added. The remaining cases are general. For some multiplets the quantum numbers do not allow some couplings (ex. in the exotic doublet (X,T) there is no coupling T'W and standard quark, just to Z and h). See table 1 of 1305.4172 for a complete list.

* Note : updated versions of CalcHep model files using version 1.7.178 of FeynRules (solves a small issue with the latest version of CalcHep), UFO model files from Feynrules 1.4.9 (there is a known issue with the UFO files due to MadGraph which is fixed in the forthcoming version 1.5.11) Thanks Benjamin for the information. Quick fix in the meantime if you generate yourself the model files from the FeynRules model: edit and replace all occurences of 'goldstone' by 'GoldstoneBoson'.

MFV with rho

* VL quarks with MFV yukawa couplings to SM quarks, large coupling to a (heavy) spin-1 resonance rho. Main decay of the VL quark is 2 jets (chromomagnetic operator) or 3 jets(virtual rho).

* Parameters:

  1. - mQ, VL quark mass (MC default, mQ = 1.6 TeV)
  2. - mρ, rho mass (MC default, mρ = 3 TeV)
  3. - gρ, coupling to the rho, (MC default, gρ = 3)
  4. - θuR, mixing angle for up-type (MC default, θuR = 0.7)
  5. - θdR, mixing angle for down-type (MC default, θdR = 0.7)

References: 1305.3818

* The UFO file is here: and a consistent parameter card is here (GammaSpin1 = 642.091 GeV and GammaHeavyUp = 0.0786164 GeV).

Things to do, and think of

- FeynRules implementation of the toy models (with parameters as in this page);

- find processes not covered by present searches (prospects at 13 TeV)

  1. - decays into 3(2) jets
  2. - mixed decays in pair production (i.e. Q Qbar → qV tV)
  3. - single production with decays in third generation (?)

- interpretation of present searches in the simplified models (combination of various channels, single + pair)

- Please add more proposals!


Model files and additional material (events?) will be made available asap (Dropbox?).

- Comment from Benj: maybe not the events (too huge files after PS/hadr.).

17th June discussion : we go both for the “generic” model on a multiplet by multiplet basis to test the cases with 1st and 3rd generation mixings and also MFV with rho, which is a case with t-channel resonance. Aldo and Giacomo provide Madgraph and Calchep model files for the first case, Veronica for the second. Analysis following the suggestions and benchmark decided last Saturday.

Discussion of June 20th, whiteboard topics and tasks:

2013/groups/np/simplivl.txt · Last modified: 2013/07/30 08:46 by ruiz_alvarez.jose_david