Search for Stopped Gluinos in pp collisions at sqrt s = 7 TeV

Abstract

The results of the first search for long-lived gluinos produced in 7 TeV pp collisions at the CERN Large Hadron Collider are presented. The search looks for evidence of long-lived particles that stop in the CMS detector and decay in the quiescent periods between beam crossings. In a dataset with a peak instantaneous luminosity of 10^{32} cm^{-2} s^{-1}, an integrated luminosity of 10 inverse picobarns, and a search interval corresponding to 62 hours of LHC operation, no significant excess above background was observed. Limits at the 95% confidence level on gluino pair production over 13 orders of magnitude of gluino lifetime are set. For a mass difference between the gluino and the neutralino greater than 100 GeV/c^2, and assuming a branching ratio for gluino to gluon+neutralino of 100%, gluinos of mass less than 370 GeV/c^2 are excluded for lifetimes from 10 microseconds to 1000 s.

Figures (4)

• Figure 1: Probability for a produced R-hadron to stop anywhere inside the CMS detector for different gluino masses and $\sqrt{s} = 7$ TeV. The solid line shows the stopping probability for the cloud model with both electromagnetic (EM) and nuclear interactions (NI), the dashed line is for the EM only model, and the dotted line is for the "neutral R-baryon" model in which only R-mesons stop Buccella:1985cs. Charge exchange reactions are considered NI.
• Figure 2: Expected and observed 95% C.L. limits on gluino pair production cross section times branching fraction using the "cloud model" of R-hadron interactions as a function of gluino lifetime from both the counting experiment and the time-profile analysis. Observed 95% C.L. limits on the gluino cross section for alternative R-hadron interaction models are also presented. The NLO+NLL calculation is for $m_{\tilde{g}} = 300$ GeV/$c^2$ from a private communication with the authors of Ref. Beenakker:2009ha.
• Figure 3: 95% C.L. limits on gluino pair production cross section times branching fraction as a function of gluino mass assuming the "cloud model" of R-hadron interactions (solid line) and EM interactions only (dot-dashed line). The $m_{\tilde{g}}-m_{\tilde{\chi}^0_1}$ mass difference is maintained at 100 GeV/$c^2$; results are only presented for $m_{\tilde{\chi}^0_1} > 50$ GeV/$c^2$. The NLO+NLL calculation is from a private communication with the authors of Ref. Beenakker:2009ha. The lifetimes chosen are those for which the counting experiment and time-profile analysis are most sensitive
• Figure 4: The top panel shows the in-orbit positions of 2 observed events in the subset of our data that was recorded during an LHC fill with 140 colliding bunches. The decay profile for a 1 $\mu$s lifetime hypothesis is overlaid. The bottom panels are zoomed views of the boxed regions around the 2 events in the top panel so that the exponential decay shape of the signal hypothesis can be seen.