Stopping gluinos

Long-lived gluinos are the trademark of split supersymmetry. They form $R$-hadrons that, when charged, efficiently lose energy in matter via ionization. Independent of $R$-spectroscopy and initial hadronization, a fraction of $R$-hadrons become charged while traversing a detector. This results in a large number of stopped gluinos at present and future detectors. For a 300 GeV gluino, ${10}^6$ will stop each year in LHC detectors, while several hundred stop in detectors during Run II at the Tevatron. The subsequent decays of stopped gluinos produce distinctive depositions of energy in calorimeters with no activity in either the tracker or the muon chamber. The gluino lifetime can be determined by looking for events where both gluinos stop and subsequently decay.

Figure 1

The gluino production cross section as a function of mass at the LHC (solid, red line) and Tevatron Run II (dashed, green line).

Figure 2

The distribution of gluino velocities at the LHC (right) and Tevatron (left). In each case we have shown the distribution for multiple gluino masses. At the Tevatron, we show $m_{\tilde{g}}=200$, 300, 400 GeV as a dashed (blue) line, dotted (green) line, and solid (black) line, respectively. At the LHC, we show the distribution for $m_{\tilde{g}}=300$, 800, 1100 GeV as dashed (blue) line, dotted (green) line, and solid (black) line, respectively.

Figure 3

The distribution of gluino velocities at the LHC for $m_{\tilde{g}}=300\mathrm{GeV}$ as a function of rapidity. Shown are curves for $0<|\eta |<0.5$ (dashed, blue line), $0.5<|\eta |<2.0$ (dotted, green line), $2<|\eta |<3.5$ (solid, black line).

Figure 4

The number of $R$-hadrons stopped after two meters of iron in Mass Region 1. This plot convolutes the velocity distribution at production with conversion processes and matter and ionization losses. The upper set of curves is for the LHC for a total accumulated luminosity of $100{\mathrm{fb}}^{-1}$, equivalent to a year of running at high luminosity. The lower set is for the Tevatron Run II, assuming a total of $2{\mathrm{fb}}^{-1}$. In each set the curves correspond to a meson to baryon conversion cross section, ${\sigma }_0=30\mathrm{mb}$, 3 mb, and 0.3 mb from top to bottom.

Figure 5

The fraction of gluinos stopped per 10 cm as a function of distance in the case where the isosinglet hadron is the lightest (Mass Region 1). There are three curves in each plot representing different cross sections for $R$-meson to $R$-baryon conversion. The different colors represent different cross sections for meson to baryon conversion ($\sigma v_{\mathrm{rel}}=30\mathrm{mb}$ (solid, blue line), $\sigma v_{\mathrm{rel}}=3\mathrm{mb}$ (dashed, red line), $\sigma v_{\mathrm{rel}}=0.3\mathrm{mb}$ (dotted, green line)). The left plot is for the Tevatron and gluino mass of 300 GeV while the right plot is for the LHC and a mass of 1100 GeV.

Figure 6

The density of stopped gluinos in the ATLAS detector for $m_{\tilde{g}}=300\mathrm{GeV}$ at the LHC, assuming a $100{\mathrm{fb}}^{-1}$ of data. Note the increased density of stopped gluinos at low pseudorapidity. The vertical lines represent the start of the end cap calorimeter.