Flavor violating gluino three-body decays at the LHC

We study the effect of squark generation mixing on gluino production and decays at LHC in the minimal supersymmetric standard model for the case that the gluino is lighter than all squarks and dominantly decays into three particles, $\tilde{g}\to q\overline{q}{\tilde{\chi }}_k^0$, $q{\overline{q}}^{\prime }{\tilde{\chi }}_l^{\pm }$. We assume mixing between the second and the third squark generations in the up-type and down-type squark sectors. We show that this mixing can lead to very large branching ratios of the quark-flavor violating gluino three-body decays despite the strong constraints on quark-flavor violation (QFV) from the experimental data on B mesons. We also show that the QFV gluino decay branching ratios are very sensitive not only to the generation mixing in the squark sector, but also to the parameters of the neutralino and chargino sectors. We show that the branching ratio of the QFV gluino decay $\tilde{g}\to c\overline{t}(\overline{c}t){\tilde{\chi }}_1^0$ can go up to $\sim 40\%$. Analogously, that of the QFV decay $\tilde{g}\to s\overline{b}(\overline{s}b){\tilde{\chi }}_1^0$ can reach $\sim 35\%$. We find that the rates of the resulting QFV signatures, such as $pp\to tt\overline{c}\overline{c}{E}_{\mathrm{T}}^{\mathrm{mis}}$, can be significant at LHC. This could have an important influence on the gluino searches at LHC.

Figure 1

Feynman diagrams for $\tilde{g}\to c\overline{t}{\tilde{\chi }}_i^0$.

Figure 2

(a) Up-type squark and gluino masses and (b) flavor decomposition of ${\tilde{u}}_1$ [i.e. $|R_{15}^{\tilde{u}}{|}^2\equiv |{\tilde{c}}_R\mathrm{\text{component}}{|}^2$ (full red line) and $|R_{16}^{\tilde{u}}{|}^2\equiv |{\tilde{t}}_R\mathrm{\text{component}}{|}^2$ (dashed blue line)] as functions of the QFV parameter ${\delta }_{23}^{uRR}$, with the other QFV parameters being zero, for the scenario of Table . In Fig 2a the horizontal line around 1000 GeV shows the gluino mass and those around 3000 GeV show the masses of ${\tilde{u}}_{3,4,5,6}$.

Figure 3

Contours of the QFV decay branching ratio $B(\tilde{g}\to ct{\tilde{\chi }}_1^0)$ in the ${\delta }_{23}^{LL}–{\delta }_{23}^{uRR}$ plane with the other QFV parameters being zero, for the scenario of Table  (solid lines). Also shown are the contours of $\Delta M_{B_s}=21.1{\mathrm{ps}}^{-1}$ and ${10}^4\times B(b\to s\gamma )=4.23$ (dashed lines). The region between the two dashed lines is allowed by all the constraints mentioned in Sec. 2, including those from $\Delta M_{B_s}$ and $B(b\to s\gamma )$.

Figure 4

The branching ratios of the decays $\tilde{g}\to c\overline{t}{\tilde{\chi }}_1^0+\overline{c}t{\tilde{\chi }}_1^0$, $\tilde{g}\to c\overline{c}{\tilde{\chi }}_1^0$ (upper dashed line) and $\tilde{g}\to t\overline{t}{\tilde{\chi }}_1^0$ (lower dashed line) as functions of ${\delta }_{23}^{uRR}$ for the other QFV parameters being zero and the other parameters are fixed as in Table .

Figure 5

Contours of the QFV decay branching ratio $B(\tilde{g}\to sb{\tilde{\chi }}_1^0)$ in the ${\delta }_{23}^{LL}–{\delta }_{23}^{dRR}$ plane, with the other QFV parameters being zero for the scenario of Table , but with the values of $M_{U\alpha \alpha }^2$ and $M_{D\alpha \alpha }^2$ interchanged (solid lines). Also shown are the contour lines for $\Delta M_{B_s}=14.5{\mathrm{ps}}^{-1}$ and $\Delta M_{B_s}=21.1{\mathrm{ps}}^{-1}$ (dashed lines). The region between the two dashed lines is allowed by all the constraints mentioned in Sec. 2, including the $\Delta M_{B_s}$ constraint.

Figure 6

Contour plot for $B(\tilde{g}\to ct{\tilde{\chi }}_1^0)$ (solid lines) in the $\mu -M_2$ plane for ${\delta }_{23}^{uRR}=0.8$, the other QFV parameters being zero, and the other parameters specified as in Table  with $M_1=139\mathrm{GeV}$. Region (A): binolike LSP region; region (B): winolike LSP region; region (C): Higgsino-like LSP region. The point “X” corresponds to our reference scenario given in Table : $M_2=264\mathrm{GeV}$, $\mu =1000\mathrm{GeV}$.

Figure 7

The $\mu$ dependence of the QFV and QFC gluino decay branching ratios for ${\delta }_{23}^{uRR}=0.8$, the other QFV parameters being zero, for the scenario given in Table . (a) Branching ratios of the decays $\tilde{g}\to c\overline{t}{\tilde{\chi }}_i^0+\overline{c}t{\tilde{\chi }}_i^0$, $i=1,\dots ,4$ as a function of $\mu$. Note that $B(\tilde{g}->c\overline{t}{\tilde{\chi }}_1^0+\overline{c}t{\tilde{\chi }}_1^0)>B(\tilde{g}->c\overline{t}{\widetilde{chi}}_2^0+\overline{c}t{\tilde{\chi }}_2^0)$ for $\mu \gtrsim 250$. (b) Branching ratios of the decays $\tilde{g}\to c\overline{c}{\tilde{\chi }}_1^0$, $\tilde{g}\to t\overline{t}{\tilde{\chi }}_1^0$, $\tilde{g}\to c\overline{t}{\tilde{\chi }}_1^0+\overline{c}t{\tilde{\chi }}_1^0$ and $\tilde{g}\to c\overline{t}{E}_{\mathrm{T}}^{\mathrm{mis}}+\overline{c}t{E}_{\mathrm{T}}^{\mathrm{mis}}$ as a function of $\mu$.

Figure 8

The $M_2$ dependence of the QFV gluino decay branching ratios for $M_1=264\mathrm{GeV}$, $\mu =600\mathrm{GeV}$, ${\delta }_{23}^{uRR}=0.8$, the other QFV parameters being zero, and the other parameters fixed as in Table . (a) Branching ratios of the decays $\tilde{g}\to c\overline{t}{\tilde{\chi }}_i^0+\overline{c}t{\tilde{\chi }}_i^0$, $i=1,\dots ,4$ as a function of $M_2$. (b) Branching ratios of the decays $\tilde{g}\to c\overline{b}{\tilde{\chi }}_k^{-}+\overline{c}b{\tilde{\chi }}_k^{+}$, $k=1$, 2 as a function of $M_2$.

Figure 9

Signal rates for $pp\to \tilde{g}\tilde{g}X$ at $\sqrt{s}=14\mathrm{TeV}$ where at least one of the gluinos decays as $\tilde{g}\to c\overline{t}(\overline{c}t){\tilde{\chi }}_1^0$, as a function of ${\delta }_{23}^{uRR}$ with the other QFV parameters being zero and the other parameters fixed as in Table . Shown are the rates for the final states with $cc\overline{t}\overline{t}{E}_{\mathrm{T}}^{\mathrm{mis}}$ (lower solid line), $c\overline{c}t\overline{t}{E}_{\mathrm{T}}^{\mathrm{mis}}$ ($\mathrm{QFV}+\mathrm{QFC}$) (upper solid line), $c\overline{c}t\overline{t}{E}_{\mathrm{T}}^{\mathrm{mis}}$ (QFC only) (upper dashed line), $ct\overline{t}\overline{t}{E}_{\mathrm{T}}^{\mathrm{mis}}$ (lower dashed line), $cc\overline{c}\overline{t}{E}_{\mathrm{T}}^{\mathrm{mis}}$ (middle solid line).

Figure 10

Invariant mass distributions of two up-type quarks from the decay $\tilde{g}\to u_j{\overline{u}}_k{\tilde{\chi }}_1^0$, with ${\delta }_{23}^{uRR}=0.8$, the other QFV parameters being zero, and the other parameters fixed as in Table .