Mass measurement in boosted decay systems at hadron colliders

We report a new possibility of using the $M_{CT2}$ (Constransverse mass) variable for mass measurement in single step decay chains involving missing particles with moderate transverse momentum. We show that its experimental feasibility is enhanced compared to the corresponding $M_{T2}$-kink method. We apply this method to reconstruct a pair of chargino decay chains.

Figure 1

a) $M_{CT2}^{\max }(\chi )$ for $(m_Y,m_X)=(130,100)\mathrm{GeV}$ and ${\delta }_T^{*}=247.9\mathrm{GeV}$ with ${\delta }_T=20\mathrm{GeV}$ (${\chi }_{*}=21.8\mathrm{GeV}$) b) $M_{CT2}(\chi )$ distribution for ${\delta }_T=250\mathrm{GeV}$ (No ${}^2\mathrm{BK}$).

Figure 2

a) Ratios of ${\delta }_T$-shift between $M_{CT2}^{\max }$ and $M_{T2}^{\max }$ with respect to ${\delta }_T/M_Y$ for various mass spectrums, $M_X/M_Y$. b) ${\delta }_T$-shift of $M_{CT2}^{\max }-M_{CT2}^{\max }(m_X=0)$ for $m_X=(10–190)\mathrm{GeV}$ with the ${\alpha }_0=62.4\mathrm{GeV}$ and the trial LNP mass, $\chi ={\chi }_{*}+50\mathrm{GeV}$.

Figure 3

Contour plots of the SS SUSY dileptonic events surviving the event selection cuts in $M_{CT2}(\chi )-\chi$ vs $\chi$ plane for $|{\delta }_T^{\max }|=({50}_{\mathrm{Top}-\mathrm{Left}},{160}_{\mathrm{Top}-\mathrm{Right}},{300}_{\mathrm{Bottom}-\mathrm{Left}},{400}_{\mathrm{Bottom}-\mathrm{Right}})\mathrm{GeV}$.

Figure 4

a) Top-Left $|{\delta }_T|$ distribution of the SS dilepton $+{\cancel{E}}_T$ system surviving the cuts. b) Top-Right $M_{CT2}$ and c) Bottom-Left $M_{CT2}$ distributions. d) Bottom-Right Consistent mass ranges in $M_Y-M_X$ vs $M_X$ plane.