JHEP05(2018)058
In final states with two LSPs and no other weakly interacting particles, the observable
R
ISR
can be written in the laboratory frame as
R
ISR
∼
~
6E
T
· ˆp
ISR
T
p
ISR
T
∼
M
˜χ
0
1
M
˜
P
+ O
p
˜
P
˜χ
0
1
2M
˜
P
q
p
ISR
T
2
+ m
2
˜
P
˜
P
p
ISR
T
sin Ω. (2.1)
This approximation is valid for the extremely compressed scenarios, hence in the limit of
a low-momentum of the LSP in the parent superparticle rest frame (p
˜
P
˜χ
0
1
) with respect to
the parent superparticle mass (M
˜
P
). In eq. (2.1), m
˜
P
˜
P
is the true mass of the S-system
and sin Ω is a quantity which is zero on average. The observable scales with the mass ratio
M
˜χ
0
1
M
˜
P
and width of order
p
˜
P
˜χ
0
1
2M
˜
P
in the limit p
ISR
T
m
˜
P
˜
P
. When visible decay objects are not
reconstructed in the V-system, or additional neutrinos in the final state contribute to the
missing transverse momentum, R
ISR
is expected to assume values between the mass ratio
and unity, while the last term in eq. (2.1) decreases.
3 Compressed electroweakino production in leptonic channels
Simulated Monte Carlo (MC) samples of Standard Model backgrounds and SUSY sig-
nals are used to study distributions of the performance of the RJR observables. The SM
background processes expected to be the largest contributions have been generated else-
where [23]. These samples are proton-proton collisions at
√
s = 14 TeV generated with
MadGraph 5 [24]. The parton shower and hadronization is performed with Pythia 6 [25]
followed by a detailed detector simulation with Delphes 3 [26]. The parameterization incor-
porates the performance of the existing ATLAS [27] and CMS [28] experiments. Jets are
reconstructed by the anti-k
T
clustering algorithm [29] with R = 0.5 and p
min
T
= 20 GeV,
implemented with the FastJet [30] package. The simulation procedure involves generation
of events at leading order in bins of the scalar sum of the generator level particles trans-
verse momenta, with jet-parton matching and corrections for next-to-leading order (NLO)
contributions [31].
The same procedure and parametrization are used to generate the signal samples.
The topologies considered are associated chargino-neutralino production and chargino pair
production assuming degenerate masses, M
˜χ
±
1
= M
˜χ
0
2
, M
˜χ
+
1
= M
˜χ
−
1
, in the range 100 GeV
≤ M
˜
P
≤ 500 GeV. The compressed regime is probed: the mass splittings considered are in
the range 15 GeV≤ ∆M ≤ 75 GeV.
The cross sections for pure wino chargino pair production and chargino-neutralino
associated production at
√
s = 13 TeV at NLL can be found elsewhere [32, 33], with relative
uncertainties in the range 4.5% . ∆σ . 9% for the masses investigated. We estimate the
NLL cross sections at
√
s = 14 TeV, evaluating the NLO cross sections for the wino-like
electroweakino pair production at 13 and 14 TeV with MadGraph, and assuming the same
NLL/NLO k-factors for the corrections. The resulting NLL cross sections are shown in
figure 2a and used as inputs for the analysis of the simplified supersymmetric topologies.
This procedure provides small corrections (. 5%) from the k-factors, and it is a check for
– 4 –
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