A Coloron Model with a Decay to a Single Top Quark
This model introduces a heavy scalar color octet, the coloron. It is produced through gluon fusion and decays 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)
- Devin G. E. Walker (SLAC National Accelerator Laboratory)
- Jiang-Hao Yu (The University of Texas at Austin)
Other Contributors
- Joseph Nutter (Michigan State University)
- R. Sekhar Chivukula (Michigan State University)
- Elizabeth H. Simmons (Michigan State University)
Description of the Model
The color octet (GH) is a neutral heavy hadronic resonance. The Feynman diagram for the production of GH and its decay to a single top quark and a charm quark is shown below. The single production of GH can be described by the effective coupling
$-\frac{1}{4} C_{ggG} d_{abc} G^a_{\mu\nu} G^{\mu\nu b} G^c_H$
with
$C_{ggG}=\sqrt{\frac{1}{6}}\frac{\alpha_s}{\pi }\frac{\mu}{M^2_{G_H}}\left(\frac{\pi^2}{9}-1\right) \ .$
Note that single production is suppressed by a factor
$(\pi^2/9 -1)^2$,
which is an accidental suppression factor coming from the loop. Above the threshold for decays into a single top quark, GH has two main decay modes: the decay into gluons, which occurs at loop-level similar to single coloron production, and the flavor-violating decay into tc. The corresponding rates are:
$\Gamma \left[G_H \to (\bar{c}_L t_R +\bar{t}_R c_L )\right] =\left(V_{cb}\right)^2 \frac{M_{G_H}}{16 \pi} \frac{m^2_t}{u^2}\left(1-\frac{m^2_t}{M^2_{G_H}}\right)^2 \,, $ \newline $\Gamma \left[G_H \to gg \right]=\frac{5 \alpha^2_s}{1536 \pi^3}\frac{\mu^2}{M_{G_H}}\left(\frac{\pi^2}{9}-1\right)^2 \,.$
We set u=mu (the stability of the potential forbids mu>u); and consider for simplicity the set of
$(M_{G_H}, \mu)$
values that give a 50% GH decay into tc and 50% into gg. GH is a very narrow resonance, with a width of the order of 10-4 GeV.
See more details in
Model Files
- proc_card: for generation of 500 GeV coloron (place in Cards/)
- run_card: for generation of 500 GeV coloron (place in Cards/)
- Octet-tcgg: the model
Generation specifics
In 1409.7607v2, the samples were generated with the coloron 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 for 500 GeV mass included above. The specific generations run were
p p > GH, GH > b c~ l+ vl @1 GHT=1 QED=2 p p > GH, GH > b~ c l- vl~ @2 GHT=1 QED=2
To generate the settings for a specific coloron mass, use the appropriate model directory contained in the Octet-tcgg zip file. Parameter card files are included for the combination of settings that gives a branching ratio of 0.5 to tc. For other BR values, please see 1409.7607v2.
Related Models
Attachments (8)
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Coloron.png
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Feynman Diagram 1
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ColoronDouble1.png
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Feynman Diagram 2
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ColoronDouble2.png
(2.7 KB
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Feynman Diagram 3
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Colorong.png
(2.1 KB
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Feynman Diagram 4
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Colorong2.png
(2.5 KB
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Feynman Diagram 5
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proc_card_mg5.dat
(2.4 KB
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process card for a 500 GeV mass coloron
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run_card.dat
(13.8 KB
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run card for a 500 GeV mass coloron
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Octet-tcgg-new.zip
(163.9 KB
) - added by 9 years ago.
model
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