A Kaluza-Klein Gluon Model with FCNC Decay to a Single Top Quark

This model allows for FCNC interactions of the Kaluza-Klein gluon and in particular focuses on the flavor-violating decay of the KKg to a top quark and a charm quark.

Corresponding Authors

• Elizabeth Drueke (Michigan State University)
• Reinhard Schwienhorst (Michigan State University)
• Natascia Vignaroli (Michigan State University)

Other Contributors

• Joseph Nutter (Michigan State University)
• Devin G. E. Walker (SLAC National Accelerator Laboratory)
• Jiang-Hao Yu (The University of Texas at Austin)
• R. Sekhar Chivukula (Michigan State University)
• Elizabeth H. Simmons (Michigan State University)

Description of the Model

Colored vector bosons from new strong dynamics, Kaluza-Klein gluons or KKg’s (G*) in a dual 5D picture, have been searched for mainly in the t-tbar channel. The analysis in ​1409.7607v2 analyzes the tc decay as depicted below: The benchmark adopted here is a simple renormalizable model of an extended color gauge sector, which realizes next-to-minimal flavor violation (NMFV). In this model, the third generation quarks couple differently than the light quarks under an extended

$SU(3)_1 \times SU(3)_2$

color gauge group. The mixing between light and third generation quarks is induced by the interactions of all three generation quarks with a set of new heavy vector-like quarks. Gluon-gluon fusion production is forbidden at tree level by SU(3)_C gauge invariance.

The G* decay widths are:

$\Gamma[G^{*} \to t\bar t] = \frac{g^2_s}{24\pi} M_{G^{*}}\cot^2\omega \sqrt{1-4 \frac{m^2_t}{M^2_{G^{*}}}} (1+2\frac{m^2_t}{M^2_{G^{*}}}),$ \newline
$\Gamma[G^{*} \to b\bar b] = \frac{g^2_s}{24\pi} M_{G^{*}}\cot^2\omega,$ \newline
$\Gamma[G^{*} \to j j] = \frac{g^2_s}{6\pi} M_{G^{*}}\tan^2\omega.$

Additionally, the NMFV flavor structure of the model generates a G* to tc flavor violating decay with rate

$\Gamma[G^{*} \to t_L \bar c_L]=\Gamma[G^{*} \to c_L \bar t_L]\simeq \left(V_{cb}\right)^2 \frac{g^2_s}{48\pi} M_{G^{*}} \left( \cot\omega+\tan\omega \right)^2,$

where

$V_{cb}=0.0415$

is the CKM matrix element.

The default value is

$\cot\omega=2.6$,

which corresponds to a width of about 25% of the KKg mass.

See more details in

• ​1409.7607v2
• ​1412.3094

Model Files

• proc_card​: for generation of 500 GeV KKg (place in Cards/)
• run_card​: for generation of 500 GeV KKg (place in Cards/)
• kkg_FV​: the model and parameter cards for specific mass generations

Generation specifics

In ​1409.7607v2, the samples were generated with the KKg mass as the scale, dsqrt_q2fact1, and dsqrt_q2fact2 in the run_card.dat file. These samples were also generated without MadGraph cuts as demonstrated in the run_card.dat file for 500 GeV mass included above. The specific generations run were

p p > kkg > b~ c l- vl~ @1
p p > kkg > b c~ l+ vl @2

To generate the settings for a specific KKg mass, change the param_card.dat in the generation directory to the card of the appropriate mass in the param_cards directory (included as part of the model zip file). It is important to do this immediately before generating events.

Related Models

• modcolorS_trip
• Octet_tcgg
• W-prime