Discovering walking technirho mesons at the LHC

We formulate a scale-invariant hidden local symmetry (HLS) as a low-energy effective theory of walking technicolor (WTC) which includes the technidilaton, technipions, and technirho mesons as the low-lying spectra. As a benchmark for LHC phenomenology, we in particular focus on the one-family model of WTC having eight technifermion flavors, which can be—at energy scales relevant to the reach of the LHC—described by the scale-invariant HLS based on the manifold $[\mathrm{SU}(8{)}_L\times \mathrm{SU}(8{)}_R{]}_{\text{global}}\times \mathrm{SU}(8{)}_{\text{local}}/\mathrm{SU}(8{)}_V$, where $\mathrm{SU}(8{)}_{\text{local}}$ is the HLS and the global $\mathrm{SU}(8{)}_L\times \mathrm{SU}(8{)}_R$ symmetry is partially gauged by the $\mathrm{SU}(3)\times \mathrm{SU}(2{)}_L\times U(1{)}_Y$ of the standard model. Based on the scale-invariant HLS, we evaluate the coupling properties of the technirho mesons and place limits on the masses from the current LHC data. Then, implications for future LHC phenomenology are discussed by focusing on the technirho mesons produced through the Drell-Yan process. We find that the color-octet technirho decaying to the technidilaton along with the gluon is of interest as the discovery channel at the LHC, which would provide a characteristic signature to probe the one-family WTC.

Figure 1

An illustration of the relevant LHC production and two-body decay processes for ${\rho }_{\theta }^0,{\rho }_P^0,{\rho }_{\mathrm{\Pi }}^{\pm ,3}$.

Figure 2

The total widths (normalized by each mass) of the isosinglet technirho mesons, ${\rho }_{\theta }^0$ (left panel) and ${\rho }_P^0$ (right panel), as functions of respective technirho masses. Here we take the masses of the relevant technipions, $M_{T^{3,0,\pm }}$, to be 2 TeV.

Figure 3

The total widths (normalized by each mass) of the isotriplet technirho mesons, ${\rho }_{\mathrm{\Pi }}^3$ (left panel) and ${\rho }_{\mathrm{\Pi }}^{\pm }$ (right panel), as functions of respective technirho masses. Here we take the masses of the relevant technipions as $(M_{T^{3,0,\pm }},M_{P^{\pm ,3}})=(2\mathrm{TeV},1\mathrm{TeV})$.

Figure 4

The branching ratios of the isosinglet technirho mesons, ${\rho }_{\theta }^0$ (left panel) and ${\rho }_P^0$ (right panel), as functions of respective technirho masses. Here we take the masses of the relevant technipions, $M_{T^{3,0,\pm }}$, to be 2 TeV. Note that $j$ and $l$ in the figure represent the sum of light quarks $(j=u,d,s,c)$ and that of leptons $l=(e,\mu )$, respectively.

Figure 5

The branching ratios of the isotriplet technirho mesons, ${\rho }_{\mathrm{\Pi }}^3$ (left panel) and ${\rho }_{\mathrm{\Pi }}^{\pm }$ (right panel), as functions of respective technirho masses. Here we take the masses of the relevant technipions as $(M_{T^{3,0,\pm }},M_{P^{\pm ,3}})=(2\mathrm{TeV},1\mathrm{TeV})$. Note that $j$ and $l$ in the figure represent the sum of light quarks $(j=u,d,s,c)$ and that of leptons $l=(e,\mu )$, respectively.

Figure 6

The LHC production cross sections of the isosinglet technirho mesons, ${\rho }_{\theta }^0$ (left panel) and ${\rho }_P^0$ (right panel), as functions of respective technirho masses. Here we take the masses of the relevant technipions as $(M_{T^{3,0,\pm }},M_{P^{\pm ,3}})=(2\mathrm{TeV},1\mathrm{TeV})$. The solid and dashed curves correspond to $\sqrt{s}=8$ and 14 TeV, respectively.

Figure 7

The LHC production cross sections of the isotriplet technirho mesons, ${\rho }_{\mathrm{\Pi }}^3$ (left panel) and ${\rho }_{\mathrm{\Pi }}^{\pm }$ (right panel), as functions of respective technirho masses. Here we take the mass of the relevant technipion, $M_{T^{3,0,\pm }}$, to be 2 TeV. The solid and dashed curves correspond to $\sqrt{s}=8$ and 14 TeV, respectively.

Figure 8

Left panel: ${\sigma }_{\mathrm{DY}}(pp\to {\rho }_{\theta }^0\to qq)$, multiplied by the acceptance $A\simeq 0.6$ [39, 44], for $q=u,d,s,c$, in units of pb as a function of $M_{{\rho }_{\theta }^0}$. The black curve (smooth decreasing function) corresponds to the prediction of the one-family model for $\sqrt{s}=8\mathrm{TeV}$. The 95% C.L. upper limit on a generic cross section times the acceptance set by searches for a new resonance in the dijet mass distribution by the CMS experiment with $\sqrt{s}=8\mathrm{TeV}$ [39] is shown by the red curve (nonsmooth line). Right panel: ${\sigma }_{\mathrm{DY}}(pp\to {\rho }_P^0\to l^{+}{l}^{-})$ with $l=e,\mu$ as a function of $M_{{\rho }_P^0}$. The black curve (smooth decreasing function) corresponds to the prediction of the one-family model for $\sqrt{s}=8\mathrm{TeV}$. The 95% C.L. upper limits on the $Z^{\prime }\to l^{+}{l}^{-}$ cross section reported by the ATLAS [40] and CMS [41] experiments are shown by the blue and red curves (upper and lower of two nonsmooth lines), respectively.

Figure 9

Left panel: ${\sigma }_{\mathrm{DY}}(pp\to {\rho }_{\mathrm{\Pi }}^3\to l^{+}{l}^{-})$ with $l=e,\mu$ as a function of $M_{{\rho }_{\mathrm{\Pi }}^3}$. The black curve (smooth decreasing function) corresponds to the prediction of the one-family model for $\sqrt{s}=8\mathrm{TeV}$. The 95% C.L. upper limits on the $Z^{\prime }\to l^{+}{l}^{-}$ cross section reported by the ATLAS [40] and CMS [41] experiments are shown by the blue and red curves (upper and lower of two nonsmooth lines), respectively. Right panel: ${\sigma }_{\mathrm{DY}}(pp\to {\rho }_{\mathrm{\Pi }}^{\pm }\to W^{\pm }Z)\times \mathrm{BR}(W^{\pm }\to l^{\pm }\nu )\times \mathrm{BR}(Z\to l^{+}{l}^{-})$ with $l=e,\mu$. The black curve (smooth decreasing function) corresponds to the prediction of the one-family model for $\sqrt{s}=8\mathrm{TeV}$. The 95% C.L. upper limits on the $W^{\prime }/\rho \to WZ$ cross section reported by the ATLAS [42] and CMS [43] experiments are shown by the blue and red curves (middle and upper curves at the right edge of the plot), respectively.

Figure 10

DY production of the technirho meson which decays into the Higgs (TD) and the SM gauge boson.

Figure 11

Left panel: ${\sigma }_{\mathrm{DY}}(pp\to {\rho }_{\theta }^0\to \varphi g)\times \mathrm{BR}(\varphi \to gg)$ in units of fb as a function of $M_{{\rho }_{\theta }^0}$. Right panel: ${\sigma }_{\mathrm{DY}}(pp\to {\rho }_P^0\to \varphi \gamma )\times \mathrm{BR}(\varphi \to gg)$ in units of fb as a function of $M_{{\rho }_P^0}$. In both plots, the solid and dashed curves correspond to cross sections for $\sqrt{s}=8$ and 14 TeV, respectively. Also, the branching ratio of the TD decaying into two gluons is taken to be $\mathrm{BR}(\varphi \to gg)=75\%$ [10].