8.3 Interpretation
8.3.2 Simplified models
Figure 62 shows the observed (red) and expected (black) mass limits in the Simplified model assuming gluino pair productions and a LSP mass of 60 GeV. The x-axis shows gluino mass and they-axis repre-sentsx≡(mχ˜±1 −mχ˜0
1)/(mg˜−mχ˜0
1). Estimation error, including systematic and statistical uncertainties, is shown by the yellow band. The magenta, blue and green lines show separate limits of the Tight, Loose and Soft Signal Regions. Combined limit is basically driven by the Tight Signal Region, which is be-cause a gluino pair production generally accompanies a large number of jets. The Loose Signal Region has a good sensitivity in highxregime, where gluino and chargino masses become degenerate. In most ofxrange (0.3<x<0.8), a gluino mass up to 1200 GeV is excluded. This is an improvement of 300 GeV from the previous limit [78] shown in the light blue area. For a severe condition ofx>0.1, a gluino mass up to 1000 GeV is excluded.
Sensitivity loss in highxregion formg˜>1000 GeV is caused by softer jet pTspectra, thus the number of jet condition of the Tight Signal Region becomes hard to be satisfied. Instead, the Loose Signal Region gains sensitivity, though not enough to fully compensate the sensitivity loss of the Tight Signal Region.
On the other hand, in low x region aroundmg˜ = 1000 GeV, a chargino ˜χ±1 tends to have a large transverse momentum compared with the chargino mass, hence the decay products of the chargino, especially a lepton and a LSP, have a smaller opening angle. Resultant softermTleads to the sensitivity loss. This tendency is also seen in Fig. 39, where the signals with low-x(light magenta and light cyan) seem to have softermT distributions than those of high-xsignals (dark magenta and dark cyan).
Figure 63 shows mass limits in the Simplified model assuming gluino pair productions with varying gluino and LSP masses. A chargino mass is set halfway between them. Thex-axis shows gluino mass and
they-axis represents LSP mass. In the region where gluinos are much heavier than LSPs, the sensitivity
is solely driven by the Tight Signal Region. When gluino and LSP degenerates and the mass splitting comes down to 100 GeV, the Tight Signal Regions looses the sensitivity due to an acceptance loss at the lepton selection. The Soft Signal Region covers the degenerate region until the mass difference becomes 30 GeV. Below the mass difference, we loose the sensitivity completely because the lepton emitted from decay often fall below our lowest lepton threshold, 6 GeV. Since no lepton is reconstructed in such a region, it should be covered by 0-lepton analysis [79].
A LSP mass up to 500 GeV is excluded in a wide range belowmg˜=1000 GeV. Assuming a chargino ˜χ±1 is produced at rest and Wmass is negligible compared with LSP mass, the following equation gives a rough estimation of the LSP momentum:
pLSP∼ mχ˜±1
2
1−
mχ˜0
1
mχ˜±1
2
. (78)
pLSPT is suppressed by the second term as LSP mass increases, which results in softerEmissT . Another impact of heavy LSP appears inmeff, which becomes smaller for heavy LSPs because some fraction of the energy is consumed to create heavy LSPs. We perform a binned fit onmeff to cope with such signals, however, lowmeff region is suffered from a large background thus we loose sensitivity. The sensitivity loss inmχ˜0
1>500 GeV is mainly explained by these two reasons.
Figure 64 shows mass limits in the Simplified model assuming squark pair productions and a fixed LSP mass of 60 GeV. They-axis representsx≡(mχ˜±1−mχ˜0
1)/(mq˜−mχ˜0
1). Both the Tight and Loose Signal Regions equally contributes to the combined limit. The observed limit reaches to 750 GeV, which is lower than the gluino limit because: (1) the cross-section of squark pair production is about 10 times lower than that of gluino around m˜q=mg˜=750 GeV (see Fig. 30). (2) the acceptance of squark pair production is lower because the decay chain starting from squark has a smaller number of jets.
Forx>0.2,m˜q<700 GeV is excluded. The sensitivity loss in low-xregion is explained in a similar way as gluino pair-production case.
Finally, Fig. 63 shows mass limits in the Simplified model assuming squark pair productions with varying gluino and LSP masses. A chargino mass is set halfway between them. Both the Tight and the Loose Signal Regions equally contribute to the combined limit. The Soft Signal Region recovers the sensitivity in the degenerate region aroundm˜q=300 GeV. The combined limit exclude a LSP mass up to 200 GeV form˜q<750 GeV.
[GeV]
g~
m
400 600 800 1000 1200 1400
) 1
0 χ∼- m g~) / (m 1
0 χ∼- m 1±χ∼(m
0 0.2 0.4 0.6 0.8 1 1.2 1.4
=60GeV
1 χ0
,m∼ 1
χ∼0 1
χ∼0
qqqqWW
→ g~
-~g
= 8TeV s
-1, L dt = 20.3fb
∫
All limits at 95% C.L.
Obs. Limit (2011)
theory) σSUSY
±1 Observed limit (
exp) σ
±1 Expected limit (
Tight SR Loose SR Soft SR
Figure 62: Observed and expected mass limits onmg˜ andx=(mχ˜±1 −mχ˜0
1)/(mg˜−mχ˜0
1) for the Simplified Model with ˜g-˜gproduction.mχ˜01 is fixed at 60 GeV. The black line and the yellow band show the expected limit and its uncertainty (±1σ). The solid red line shows the observed limit obtained by combining all the Signal Regions. The dotted red lines specify the impact of signal cross-section and acceptance uncertainties. The magenta, blue and green lines show separate limits of the Tight, Loose and Soft Signal Regions. The light blue area shows the previous limit [78] for reference.
[GeV]
g~
m
400 600 800 1000 1200 1400
[GeV] 10χ∼m
100 200 300 400 500 600 700 800 900 1000
, x=1/2
1
χ∼0 1
χ∼0
qqqqWW
→ g~
-~g
= 8TeV s
-1, L dt = 20.3fb
∫
All limits at 95% C.L.
Obs. Limit (2011)
1 0χ
<m∼
~g
m
theory) σSUSY
1
± Observed limit (
exp) σ
±1 Expected limit (
Tight SR Loose SR Soft SR
Figure 63: Observed and expected mass limits onmg˜ andmχ˜0
1for the Simplified Model with ˜g-˜g produc-tion. x=(mχ˜±1 −mχ˜0
1)/(mg˜−mχ˜0
1) is fixed at 1/2. The black line and the yellow band show the expected limit and its uncertainty (±1σ). The solid red line shows the observed limit obtained by combining all the Signal Regions. The dotted red lines specify the impact of signal cross-section and acceptance un-certainties. The magenta, blue and green lines show separate limits of the Tight, Loose and Soft Signal Regions. The light blue area shows the previous limit [78] for reference.
[GeV]
q~
m
400 600 800 1000 1200 1400
) 1
0 χ∼- m q~) / (m 1
0 χ∼- m 1±χ∼(m
0 0.2 0.4 0.6 0.8 1 1.2 1.4
=60GeV
1 χ0
,m∼ 1
χ∼0 1
χ∼0
qqqqWW
→ q~
-~q
= 8TeV s
-1, L dt = 20.3fb
∫
All limits at 95% C.L.
Obs. Limit (2011)
theory) σSUSY
±1 Observed limit (
exp) σ
±1 Expected limit (
Tight SR Loose SR Soft SR
Figure 64: Observed and expected mass limits onm˜qandx=(mχ˜±1 −mχ˜0
1)/(mq˜−mχ˜0
1) for the Simplified Model with ˜q-˜q production.mχ˜01 is fixed at 60 GeV. The black line and the yellow band show the expected limit and its uncertainty (±1σ). The solid red line shows the observed limit obtained by combining all the Signal Regions. The dotted red lines specify the impact of signal cross-section and acceptance uncertainties. The magenta, blue and green lines show separate limits of the Tight, Loose and Soft Signal Regions. The light blue area shows the previous limit [78] for reference.
[GeV]
q~
m
400 600 800 1000 1200 1400
[GeV] 10χ∼m
100 200 300 400 500 600 700 800 900 1000
, x=1/2
1
χ∼0 1
χ∼0
qqqqWW
→ q~
-~q
= 8TeV s
-1, L dt = 20.3fb
∫
All limits at 95% C.L.
Obs. Limit (2011)
1 0χ
<m∼
~q
m
theory) σSUSY
1
± Observed limit (
exp) σ
±1 Expected limit (
Tight SR Loose SR Soft SR
Figure 65: Observed and expected mass limits onm˜qandmχ˜0
1for the Simplified Model with ˜q-˜q produc-tion. x=(mχ˜±1 −mχ˜0
1)/(mq˜−mχ˜0
1) is fixed at 1/2. The black line and the yellow band show the expected limit and its uncertainty (±1σ). The solid red line shows the observed limit obtained by combining all the Signal Regions. The dotted red lines specify the impact of signal cross-section and acceptance un-certainties. The magenta, blue and green lines show separate limits of the Tight, Loose and Soft Signal Regions. The light blue area shows the previous limit [78] for reference.