Searches for long lived particles at the Tevatron Page: 3 of 5
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integrated luminosity [11].
The analysis looks for stopped gluinos which decay into a gluon and a neutralino ( -
gXt). The typical signature consists largely of an empty event with a single large transverse
energy deposit in the calorimeter, reconstructed as a jet, and large missing transverse energy.
No evidence for a signal was found and upper limits were placed on the stopped gluino cross
section as a function of the gluino mass for three different assumptions of neutralino mass
(see Fig. 2). Also shown in the figure are the predicted cross sections for stopped gluinos
which include both the production rate and as well as its probability to stop. Figure 2 (left)
assumes a small gluino lifetime (< 3 hours) while Fig. 2 (right) shows the 95% C.L. upper
limits for different assumptions of gluino lifetime with the limits becoming weaker for very
large lifetimes owing to the fact that signal events are not recorded between accelerator
stores.
aD0, L-410p~ a DO, L=410 pb1
E 4, aE
w J
o Expected Limit a . 100 hours
--Observed Limit 1 18 hours
UO <O hours
N 1 u
o o
150 200 250 300 350 400 450 500 550 600 10 150 200 250 300 350 400 450 500 550 600
Gluino Mass (GeV) Gluino Mass (GeV)
Figure 2: Left: The expected and observed upper limits on the cross section of stopped
gluinos for three choices of the X mass (50, 90 and 200 GeV, from left to right). A 100%
branching rate of g -> g4 and a small gluino lifetime are assumed. Right: Upper limits
on the cross-section of stopped gluinos for various assumptions of the gluino lifetime, for a
X4 mass of 50 GeV. Also shown on the plots (dashed red lines) are the theoretical stopped
gluino cross sections for varying assumptions of the neutral to charged R-hadron conversion
cross section (0.3, 3, and 30 mb).
The above results exclude a cross section of ~ 1 pb for gluinos stopping in the D0
calorimeter and later decaying to a neutralino and a gluon. For a neutralino mass of 50 GeV,
stopped gluinos with mass less than 270 GeV can be excluded, assuming a gluino lifetime
of less than 3 hours, a 100% branching fraction for , and a neutral to charged R-hadron
conversion cross section of 3 mb.
2.3 Neutral long lived particles
D0 has searched for light, neutral, long-lived particles (NLL) that are pair-produced in
pp collisions using 380 pb-- of integrated luminosity [12]. The search was inspired by an
excess of di-muon events observed by the NuTeV experiment [13]. The final state studied
by D0 involved the decay of an NZL into two muons and possibly a neutrino after the
N2L had traveled at least 5 cm. Since no signal was found a limit was set. Fig. 3 shows
the 95% (99%) C.L. limit on the cross section o-(pp - NL NL X times the branching
fraction (N2LpJ + X) as a function of lifetime. The 95% C.L. limit for a mass ofDIS 2008
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Bose, Tulika & U., /Brown. Searches for long lived particles at the Tevatron, article, April 1, 2008; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc930557/m1/3/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.