Compositeness Processes

  1. Excited fermions, production processes
  2. Excited fermions, parameters
  3. Contact interactions, production processes
  4. Contact interactions, parameters
Compositeness scenarios may give rise to sharp resonances of excited quarks and leptons. An excited copy of the first generation is implemented, consisting of spin 1/2 particles. The possibility of contact interactions between SM fermions is also implemented in the context of 2 → 2 quark or fermion-lepton scattering.

Related to excited fermions, the current implementation contains gauge interaction production by quark-gluon fusion or lepton-photon fusion and contact interaction production by quark-quark or quark-antiquark scattering. For both the 2 → 1 and 2 → 2 processes a non-trivial angular dependence is included in the decay, however, only decays into gauge bosons are supported, i.e. not decays through contact interactions. In additions to the compositeness scale and couplings listed below, you are expected to change the excited-fermion masses in accordance with what is desired. See [Bau90] for conventions.

The contact interactions are implemented according to [Eic83]. The processes include the SM contributions as well as interference. For this reason the processes below converge toward the SM equivalents when the contact interaction contributions are close to zero, e.g. HardQCD:qq2qq and HardQCD:qqbar2qqbarNew in the case of quark scattering.

It should also be noted that the gamma*/Z/Z' production process available with NewGaugeBoson:ffbar2gmZZprime is prepared for pair-production of excited quarks and leptons, assuming the same gauge couplings as for the non-excited fermions. What is missing is the actual decay channels in the list of Z' decay modes, which have to be added by hand, e.g. by
32:addChannel = 1 1. 100 4000001 -4000001
You can use Zprime:gmZmode to decide which gauge boson propagators actually are included in the simulation, and thus e.g. switch off the Z' part of the propagator. You may also want to switch off other decay channels and set the minimal mass to be at the threshold for the studied pair production (or suitably below it, if the excited fermions have a non-negligible width).

Excited fermions, production processes

A few different production processes have been implemented, which normally would not overlap and therefore could be run together.

flag  ExcitedFermion:all   (default = off)
Common switch for the group of implemented processes that produce an excited fermion.

flag  ExcitedFermion:dg2dStar   (default = off)
Scatterings d g → d^*. Code 4001.

flag  ExcitedFermion:ug2uStar   (default = off)
Scatterings u g → u^*. Code 4002.

flag  ExcitedFermion:sg2sStar   (default = off)
Scatterings s g → s^*. Code 4003.

flag  ExcitedFermion:cg2cStar   (default = off)
Scatterings c g → c^*. Code 4004.

flag  ExcitedFermion:bg2bStar   (default = off)
Scatterings b g → b^*. Code 4005.

flag  ExcitedFermion:egm2eStar   (default = off)
Scatterings e gamma → e^*. Code 4011.

flag  ExcitedFermion:mugm2muStar   (default = off)
Scatterings mu gamma → mu^*. Code 4013.

flag  ExcitedFermion:taugm2tauStar   (default = off)
Scatterings tau gamma → tau^*. Code 4015.

flag  ExcitedFermion:qq2dStarq   (default = off)
Scatterings q q(bar) → d^* q(bar). Code 4021.

flag  ExcitedFermion:qq2uStarq   (default = off)
Scatterings q q(bar) → u^* q(bar). Code 4022.

flag  ExcitedFermion:qq2sStarq   (default = off)
Scatterings q q(bar) → s^* q(bar). Code 4023.

flag  ExcitedFermion:qq2cStarq   (default = off)
Scatterings q q(bar) → c^* q(bar). Code 4024.

flag  ExcitedFermion:qq2bStarq   (default = off)
Scatterings q q(bar) → b^* q(bar). Code 4025.

flag  ExcitedFermion:qqbar2eStare   (default = off)
Scatterings q qbar → e^*+- e^-+. Code 4031.

flag  ExcitedFermion:qqbar2nueStarnue   (default = off)
Scatterings q qbar → nu_e^* nu_ebar. Code 4032.

flag  ExcitedFermion:qqbar2muStarmu   (default = off)
Scatterings q qbar → mu^*+- mu^-+. Code 4033.

flag  ExcitedFermion:qqbar2numuStarnumu   (default = off)
Scatterings q qbar → nu_mu^* nu_mubar. Code 4034.

flag  ExcitedFermion:qqbar2tauStartau   (default = off)
Scatterings q qbar → tau^*+- tau^-+. Code 4035.

flag  ExcitedFermion:qqbar2nutauStarnutau   (default = off)
Scatterings q qbar → nu_tau^* nu_taubar. Code 4036.

flag  ExcitedFermion:qqbar2eStareStar   (default = off)
Scatterings q qbar → e^*+- e^*-+. Code 4051.

flag  ExcitedFermion:qqbar2nueStarnueStar   (default = off)
Scatterings q qbar → nu_e^* nu_e^*bar. Code 4052.

flag  ExcitedFermion:qqbar2muStarmuStar   (default = off)
Scatterings q qbar → mu^*+- mu^*-+. Code 4053.

flag  ExcitedFermion:qqbar2numuStarnumuStar   (default = off)
Scatterings q qbar → nu_mu^* nu_mu^*bar. Code 4054.

flag  ExcitedFermion:qqbar2tauStartauStar   (default = off)
Scatterings q qbar → tau^*+- tau^*-+. Code 4055.

flag  ExcitedFermion:qqbar2nutauStarnutauStar   (default = off)
Scatterings q qbar → nu_tau^* nu_tau^*bar. Code 4056.

Excited fermions, parameters

The basic couplings of the model are

parm  ExcitedFermion:Lambda   (default = 1000.; minimum = 100.)
Compositeness scale Lambda in GeV.

parm  ExcitedFermion:coupF   (default = 1.0; minimum = 0.0)
Strength f of the SU(2) coupling.

parm  ExcitedFermion:coupFprime   (default = 1.0; minimum = 0.0)
Strength f' of the U(1) coupling.

parm  ExcitedFermion:coupFcol   (default = 1.0; minimum = 0.0)
Strength f_c of the SU(3) coupling.

parm  ExcitedFermion:contactDec   (default = 1.0; minimum = 0.0)
Strength of contact-interaction decay channels, implemented as three-body decays l^* → l f fbar for excited leptons and neutrinos, where unity corresponds to the same normalization as for the production channels.

Contact interactions, production processes

The processes including contact interactions are

flag  ContactInteractions:QCqq2qq   (default = off)
Scatterings q q → q q including contact interactions. Code 4201.

flag  ContactInteractions:QCqqbar2qqbar   (default = off)
Scatterings q qbar → q' qbar' including contact interactions. Code 4202.

flag  ContactInteractions:QCffbar2eebar   (default = off)
Scatterings f fbar → e- e+ including contact interactions. Code 4203.

flag  ContactInteractions:QCffbar2mumubar   (default = off)
Scatterings f fbar → mu- mu+ including contact interactions. Code 4204.

flag  ContactInteractions:QCffbar2tautaubar   (default = off)
Scatterings f fbar → tau- tau+ including contact interactions. Code 4205.

Contact interactions, parameters

mode  ContactInteractions:nQuarkNew   (default = 3; minimum = 0; maximum = 5)
Number of allowed outgoing new quark flavours in the above q qbar → q' qbar' process. Similar to HardQCD:nQuarkNew for the QCD processes.

parm  ContactInteractions:Lambda   (default = 1000.; minimum = 100.)
Compositeness scale Lambda in GeV. Its overall normalization is largely a matter of convention. The choice made here for the q qbar → l- l+ processes is such that the pure contact interaction part of the left-left interactions (i.e. disregarding gamma^*, Z^0 and interference terms) has the form d(sigmaHat)/d(tHat) = pi * uHat^2 / (3 * sHat^2 * Lambda^4). The corresponding part of the q qbar → q' qbar' cross section is a factor 3 larger from colour.

mode  ContactInteractions:etaLL   (default = 0; minimum = -1; maximum = 1)
Helicity parameter.
option 1 :
option 0 :
option -1 :

mode  ContactInteractions:etaRR   (default = 0; minimum = -1; maximum = 1)
Helicity parameter.
option 1 :
option 0 :
option -1 :

mode  ContactInteractions:etaLR   (default = 0; minimum = -1; maximum = 1)
Helicity parameter.
option 1 :
option 0 :
option -1 :

mode  ContactInteractions:etaRL   (default = 0; minimum = -1; maximum = 1)
Helicity parameter. Implemented only for the q qbar → l- l+ process.
option 1 :