Evaluation of the Sensitivity of Existing Searches toHiggsino Models

Veronika Kratzer

Ludwig-Maximilians-Universitaet Muenchen, Germany

Supervisors: Sonia Carrà, Federico Meloni

September 4, 2019

Abstract

A search for Supersymmetry was performed by the ATLAS collaboration on asimplified model of the χ±1 χ0

2 pair production with W/Z boson mediated decaysinto a three lepton and missing energy final state. The χ±1 and χ0

2 were assumedto be a pure wino-like state. Since no signal was observed, exclusion limits on aportion of the phase space have been set. Since the higgsino case is also of interest,a dedicated study to investigate the sensitivity of the search to such a model wasdeveloped. In this project the acceptances obtained from the existing search havebeen compared to a model with three production processes: χ±1 χ0

2, χ±1 χ03 and

χ02 χ0

3. The acceptances have been compared for signal samples with two differentmass splittings between the χ±1 , χ0

2, χ03 and the χ0

1. The acceptances obtained inthis study for the higgsino sample are comparable to the acceptances for the winosample found in the existing search.

Contents

1 Introduction and Motivation 3

2 Supersymmetry 52.1 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.1.1 Minimal Supersymmetric Standard Model . . . . . . . . . . . . . 52.1.2 Neutralinos and charginos . . . . . . . . . . . . . . . . . . . . . . 6

2.2 Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3 ATLAS Experiment 9

4 Method 114.1 Monte Carlo Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 114.2 Standard Model background . . . . . . . . . . . . . . . . . . . . . . . . . 114.3 Variables definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124.4 Preselection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164.5 Signal regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

5 Results 18

6 Conclusion and Outlook 21

Bibliography 22

2

1 Introduction and MotivationThe Standard Model (SM) is a theory describing the particles that matter consists ofand their interactions very well. However, it is known that the theory is not completesince it does not provide an explanation for many observed phenomena, for example thenature of dark matter [1, 2, 3].Supersymmetry (SUSY) could provide a solution to various of the open questions andprovide a dark matter candidate in the form of the lightest supersymmetric particle.Therefore searches for supersymmetric particles are of great interest in modern particlephysics.

A lot of searches for SUSY have been performed by the ATLAS collaboration targetingdifferent possible realisations of the SUSY models and many different signatures. Inthis project a specific model in the pMSSM and a specific signature are considered. Anexisting search on χ±1 χ0

2 pair production was performed [4]. A simplified model [5] forthe decay of these SUSY particles into a χ0

1 and W or Z boson was considered. Thebosons decay further leptonically. The final state is three leptons and missing energyin which leptons refer to either electrons or muons. The process is shown in figure 1.1.The χ±1 and the χ0

2 were considered to have the same mass and to be pure wino-like, theχ0

1 is pure bino state, as it will be described in section 2.2.

Figure 1.1: χ±1 χ02 pair production. The χ±1 decays into a χ0

1 and a W boson and the χ02

into a χ01 and a Z boson. The W boson decays into a lepton and a neutrino.

The Z boson decays into two leptons [4].

3

1 Introduction and Motivation

Figure 1.2: Exclusion limits on SUSY simplified models for a chargino-neutralino pairproduction with decay via W/Z bosons [4].

For this final state signal regions were defined and the search was performed on 36.1fb−1 of proton-proton collisions with

√s = 13 TeV collected by the ATLAS detector.

Since no excess has been observed, mass exclusion limits on the masses have been setfor the considered model. They are shown in figure 1.2.

Since the mixing of the wino, higgsino and bino superfields into the charginos andneutralinos is unknown, it is important to look not only at wino-like χ±1 and χ0

2 as donein the search discussed so far but also at the pure higgsino-like state.The goal of this project is to determine the sensitivity of the search to a higgsino model.Therefore acceptance of the signal region (SR) of the existing search for the wino modelwill be compared with the acceptances for the model with higgsino-like particles withthe same final state. In the higgsino case three production processes are considered: χ±1χ0

2, χ±1 χ03 and χ0

2 χ03. The χ±1 , χ0

2, χ03 are considered to be higgsino-like and decay into

a χ01 and leptonically via a W, Z or Higgs boson. The χ0

1 is considered to be bino-like.

4

2 Supersymmetry

2.1 TheoryTo understand the basic concept of Supersymmetry a brief overview of the theory willbe given in this chapter. Since charginos and neutralinos are of special interest for thisproject they will be explained in section 2.1.2.

2.1.1 Minimal Supersymmetric Standard ModelSupersymmetry introduces a new symmetry between fermionic and bosonic particles. Inthe SUSY theory each Standard Model field has a SUSY counterpart, a so-called super-field. These fields mix into mass eigenstates. The result is a new set of particles witha different spin number, which are the SUSY particles in the Minimal SupersymmetricStandard Model (MSSM). The mass eigenstates are shown in table 2.1.

Table 2.1: Mass eigenstates in the MSSM. There are five Higgs bosons, squarks, sleptons,neutralinos, charginos, the gluino and the goldstino (gravitino) [3].

Names Spin Mass EigenstatesHiggs bosons 0 h0 H0 A0 H±

uL uR dL dRsquarks 0 sL sR cL cR

t1 t2 b1 b2eL eR νe

sleptons 0 µL µR νµτ1 τ2 ντ

neutralinos 1/2 χ01 χ

02 χ

03 χ

04

charginos 1/2 χ±1 χ±2gluino 1/2 g

goldstino (gravitino) 1/2 (3/2) G

The SM contains the B, W and Higgs fields, the MSSM contains their superpartners,the bino, wino and higgsino fields [3].

5

2.2 Models

2.1.2 Neutralinos and charginosThe four neutralinos χ0

1, χ02, χ0

3 and χ04 are a mix of the neutral higgsino, the neutral

wino and the bino fields. The numbering of the neutralinos follows the convention thatthe masses are higher with ascending number: mχ0

1< mχ0

2< mχ0

3< mχ0

4. In this work

the χ01 is considered to be the lightest supersymmetric particle. It is considered to be

stable and weakly interacting. It is a dark matter candidate and escapes the detectorwithout interacting [3].The charged higgsinos and the charged winos mix into the four charginos χ±1 and χ±2 .The χ±2 is the heavier eigenstate compared to the χ±1 .

2.2 ModelsSince the mixing of the higgsino, wino and bino superfields, leading to the neutralinosand charginos, is unknown, searches on chargino and neutralino pair production not onlywith wino-like particles but also with higgsino-like particles should be performed.

The existing search considered a simplified model with the masses of the SUSY par-ticles as the only free parameters [5]. The model that was used is the χ±1 χ0

2 pairproduction with wino-like χ±1 and χ0

2 and a bino-like χ01. The χ±1 and the χ0

2 have thesame masses. All the other SUSY particles are considered to have much higher massesand are therefore not relevant for this model [6]. The χ±1 decays into a χ0

1 and a W bosonthat decays further into a lepton and a lepton neutrino. The χ0

2 decays into a χ01 and a

Z boson which itself decays into two leptons. The final state contains three leptons andmissing energy. A diagram of this decay is shown in figure 1.1

To validate the analysis in this project, the same model is used to create the valida-tion sample with wino-like χ±1 and χ0

2 and bino-like χ01.

In case of the models with the higgsino-like χ±1 , χ02 and χ0

3 the masses of these threeSUSY particles have very similar values. The χ±2 and the χ0

4 are assumed to be muchheavier and will not be accessible [6]. In this case three different pair production pro-cesses are possible:

• χ±1 χ02

• χ±1 χ03

• χ02 χ

03

The first process is similar to the wino-like particles. The differences are that the χ02 can

also decay via a Higgs boson and the cross section is smaller (see also table 2.3). In thecase of the χ±1 χ0

3 production the χ±1 also decays via a W boson and the χ03 decays via a

Z or Higgs boson. The third process is the χ02 χ

03 pair production. Both, the χ0

2 and theχ0

3, can decay via a Z or a Higgs boson and into a χ01. This process does not necessarily

6

2.2 Models

have a three lepton final state. It can have a four lepton final state if both neutralinosdecay into a χ0

1 and a Z boson which decays into two leptons. A four lepton final statecould for example pass the selection if one lepton is too soft to be identified as lepton.All three production processes are shown in figure 2.1.

[h]

(a) χ±1 χ02 pair production

3

3 [h]

(b) χ±1 χ03 pair production

[h]

[h]

(c) χ02 χ0

3 pair production

Figure 2.1: SUSY processes for the higgsino models considered in this project

The masses are free parameters in the SUSY models. Since the values are unknownseveral mass configurations have to be considered. The mass spectrum affects the kine-matics of the signal events. In this project two different mass splittings are considered:a small mass splitting and a large mass splitting. The masses are listed in table 2.2.In case of the wino signal the χ±1 and the χ0

2 are mass-degenerate. The difference be-tween the χ±1 / χ0

2 and the χ01 is about 100 GeV for the small mass splitting and about

200 GeV for the large mass splitting.In the higgsino case the masses of the χ±1 , the χ0

2 and the χ03 are not exactly the same

Table 2.2: Mass configurations of the SUSY particles used in the models considered inthe existing search, in the validation wino sample and in the higgsino sample.For each model a small and a large mass splitting is considered.

small mass splitting large mass splittingMasses Wino Wino Higgsino Wino Wino Higgsinoin GeV (paper [4]) (validation) (paper [4]) (validation)χ0

3 - - 163.5 - - 260.4χ0

2 175 155 160.1 275 257 259.2χ±1 175 155 154.1 275 257 255.7χ0

1 75 75 74.7 75 80 79.4

but very close. The χ03 is the heaviest of the three SUSY particles, followed by the χ0

2and the χ±1 . For this model the difference in the masses for the small mass splitting is

7

2.2 Models

also about 100 GeV and for the large mass splitting about 200 GeV.

Whether the χ±1 , χ02 and χ0

3 are considered to be wino-like or higgsino-like affects theproduction cross section. The cross section also depends on the masses of the SUSYparticles that are produced in the proton-proton collision.

The cross sections for the pair production processes are shown in table 2.3.Looking at the χ±1 χ0

2 pair production with the χ±1 and χ02 with masses between 154

GeV and 160 GeV, one finds, that the cross section for the wino case is with 4.60 pbabout four times larger than for the higgsino case, that has a cross section of 1.05 pb.The higgsino cross section for the χ±1 χ0

3 production is assumed to be exactly the same.For the χ0

2 χ03 production it is again smaller with 0.72 pb. In the higgsino case three

production processes are considered and as a consequence the acceptance is increased inthis case.

Table 2.3: Cross Sections for the production processes

Masses χ03, χ0

2 , χ±1 in GeV -, 155, 155 164, 160, 154 -, 257, 257 260, 259, 256Cross sections in pb Wino Higgsino Wino Higgsino

χ±1 χ02 4.60 1.05 0.70 0.16

χ±1 χ03 - 1.05 - 0.16

χ02 χ

03 - 0.72 - 0.10

8

3 ATLAS ExperimentThe search described in chapter 1 was performed using the data collected by the ATLAS(A Torodial LHC ApparatuS) experiment at the LHC [7]. A brief overview of thedetector will be given in this chapter. Its structure is shown in figure 3.1.

Figure 3.1: Schematic view of the ATLAS detector [7]

The innermost part, the inner tracker, consists of a pixel detector, a strip detector anda transition radiation tracker. A superconducting solenoid surrounds it, providing themagnetic field necessary for momentum measurement.The next layers are the electromagnetic and hadronic calorimeters that sit both in thebarrel and in the endcaps. The electromagnetic calorimeter is used to measure the en-ergy of electrons, positrons and photons. The hadronic calorimeter measures energies ofhadrons.The outermost part of the detector is the muon spectrometer. Three superconducting

9

3 ATLAS Experiment

toroids provide the magnetic field.

The origin of the coordinate system used in this experiment is the nominal interac-tion point. The z-axis is along the beam direction and the x-y plane is the transverseplane with respect to it. φ is the azimuthal angle around the beam direction and θ isthe polar angle measured between the beam axis and the direction of the particle.

10

4 MethodIn this chapter the method used to determine the sensitivity of the existing search tothe higgsino models is discussed. The Monte Carlo simulation, the Standard Modelbackgrounds and the kinematic variables are described. The preselection and the signalregions are defined.

4.1 Monte Carlo SimulationIn this project Monte Carlo simulations at particle level, i. e. without the simulationof the effects of the ATLAS detector, are used. The background samples are generatedusing Sherpa [8]. For the generation of the SUSY samples MadGraph and Pythia areused [9, 10].

4.2 Standard Model background

Figure 4.1: Observed data and expected SM background yield for the search in reference[4]. The signal regions of interest in this project are WZ-0Ja, WZ-0Jb andWZ-0Jb. The dominating backgrounds are the diboson (VV) and triboson(VVV) productions.

11

4.3 Variables definition

One of the crucial points in all SUSY searches is the extraction of the supersymmetricsignal from the large SM background. According to the analysis described in the in-troduction, the dominating background are the diboson (VV) productions, in particluarthe WZ process, and triboson (VVV) productions.This can be seen in figure 4.1. It shows the observed data and expected SM backgroundsfor the searches performed in the paper. For this project only the signal regions WZ-0Ja,WZ-0Jb and WZ-0Jc, specified in section 4.5, are relevant. Here it can clearly be seenthat the VV and the VVV backgrounds are the largest contributors. Therefore in thisproject only these two backgrounds are considered.

4.3 Variables definitionThe variables described in this section are defined according to the existing search to beable to reproduce the signal regions.

Lepton pseudorapidity

Instead of using the polar angle θ introduced in chapter 3, the pseudorapidity

η = −ln(tan

(θ

2

))(4.3.1)

is used.

Lepton transverse momentum

The transverse momentum pT is the component of the momentum of a particle inthe plane perpendicular to the beam axis. In this search selections on the transversemomenta of the leptons in the event are performed (see section 4.4). The leptons areordered by the value of their pT . In the following they are refered to as “leading“ ,“subleading“ and “third “ lepton.The distributions of the transverse momenta of the signals with both mass splittings andthe background samples for the leading, the subleading and the third lepton are shownin figure 4.2. In all plots the VV background is dominating, while the VVV backgroundis of the same order of magnitude as the wino validation sample and the higgsino signalsample.

Number of leptons

The variable nleptons gives the number of leptons in the event.

12

4.3 Variables definition

lept1 [GeV]T

p

0 50 100 150 200 250 300 350

entr

ies

1−10

1

10

210

310

410

m(C1, N2)=155 m(N1)=75wino C1N2

m(C1)=155 m(N2)=160 m(N3)=164 m(N1)=75higgsino C1N3 C1N2 N2N3

VVV

VV

(a) leading lepton, small mass splitting

lept1 [GeV]T

p

0 100 200 300 400 500 600 700

entr

ies

1−10

1

10

210

310

410

m(C1, N2)=257 m(N1)=80wino C1N2

m(C1)=256 m(N2)=259 m(N3)=260 m(N1)=79higgsino C1N3 C1N2 N2N3

VVV

VV

(b) leading lepton, large mass splitting

lept1 [GeV]T

p

0 50 100 150 200 250 300 350

entr

ies

1−10

1

10

210

310

410

m(C1, N2)=155 m(N1)=75wino C1N2

m(C1)=155 m(N2)=160 m(N3)=164 m(N1)=75higgsino C1N3 C1N2 N2N3

VVV

VV

(c) subleading lepton, small mass splitting

lept2 [GeV]T

p

0 100 200 300 400 500 600 700

entr

ies

1−10

1

10

210

310

410

m(C1, N2)=257 m(N1)=80wino C1N2

m(C1)=256 m(N2)=259 m(N3)=260 m(N1)=79higgsino C1N3 C1N2 N2N3

VVV

VV

(d) subleading lepton, large mass splitting

lept3 [GeV]T

p

0 20 40 60 80 100 120 140 160 180

entr

ies

1−10

1

10

210

310

410

m(C1, N2)=155 m(N1)=75wino C1N2

m(C1)=155 m(N2)=160 m(N3)=164 m(N1)=75higgsino C1N3 C1N2 N2N3

VVV

VV

(e) third lepton, small mass splitting

lept3 [GeV]T

p

0 50 100 150 200 250 300 350

entr

ies

1−10

1

10

210

310

410

m(C1, N2)=257 m(N1)=80wino C1N2

m(C1)=256 m(N2)=259 m(N3)=260 m(N1)=79higgsino C1N3 C1N2 N2N3

VVV

VV

(f) third lepton, large mass splitting

Figure 4.2: Distributions of the transverse momenta of the leptons with applied pres-election for the signal and background samples. The distributions for theleading, the subleading and the third lepton for the signal models with thesmall mass splitting (4.2a, 4.2c, 4.2e) and the large mass splitting (4.2b, 4.2d,4.2f) are shown.

13

4.3 Variables definition

Number of jets

The jets are classified as b-tagged jets and non b-tagged jets. nb−tagged jets is the numberof jets per event that are found to originate from a b quark. nnon−b−tagged jets is the num-ber of all other jets respectively. For both variables the jets have to have a transversemomentum larger than 20 GeV.

Missing transverse energy

Missing transverse energy is expected in the signal. It is defined as

EmissT = |Emiss

T | =√

(Emissx )2 + (Emiss

y )2 (4.3.2)

withEmissx(y) = −

∑i∈{hard objects}

px(y),i −∑

i∈{soft items}px(y),i (4.3.3)

where px(y) are the components of the transverse momentum vectors of the objects. Hardobjects are all the reconstructed particles and jets in the detector [11].

The distributions for the signal and the background samples are shown in figure 4.3.

[GeV]missTE

0 50 100 150 200 250 300 350

entr

ies

1−10

1

10

210

310

410

m(C1, N2)=155 m(N1)=75wino C1N2

m(C1)=155 m(N2)=160 m(N3)=164 m(N1)=75higgsino C1N3 C1N2 N2N3

VVV

VV

(a) small mass splitting

[GeV]missTE

0 100 200 300 400 500 600 700

entr

ies

1−10

1

10

210

310

410

m(C1, N2)=257 m(N1)=80wino C1N2

m(C1)=256 m(N2)=259 m(N3)=260 m(N1)=79higgsino C1N3 C1N2 N2N3

VVV

VV

(b) large mass splitting

Figure 4.3: Distributions of EmissT with applied preselection for the background and the

signal samples with the small (4.3a) and the large (4.3b) mass splittings.

In plot 4.3b it can be seen that the background has a maximum very close to zero whilethe SUSY signal distributions are slightly shifted towards higher values of Emiss

T . Thisis reasonable because the expected missing energy is higher for the SUSY samples dueto the χ0

1.

14

4.3 Variables definition

Invariant mass of a SFOS lepton pair

For the supersymmetric signal three leptons are expected in the final state. Two ofthem, having the same flavour and opposite sign (SFOS), originate from the Z or Higgsboson decay. Combining two of the leptons fulfilling the SFOS requirement and calcu-lating the invariant mass of the SFOS pair gives the new variable mSFOS.

[GeV]SFOSm

0 50 100 150 200 250 300 350

entr

ies

1−10

1

10

210

310

410

m(C1, N2)=155 m(N1)=75wino C1N2

m(C1)=155 m(N2)=160 m(N3)=164 m(N1)=75higgsino C1N3 C1N2 N2N3

VVV

VV

(a) small mass splitting

[GeV]SFOSm

0 100 200 300 400 500 600 700

entr

ies

1−10

1

10

210

310

410

m(C1, N2)=257 m(N1)=80wino C1N2

m(C1)=256 m(N2)=259 m(N3)=260 m(N1)=79higgsino C1N3 C1N2 N2N3

VVV

VV

(b) large mass splitting

Figure 4.4: Distributions of the mSFOS variable after applying the preselection for thebackground and the SUSY samples with the small (4.4a) and the large (4.4b)mass splittings.

The distributions of the variable mSFOS with applied preselection can be seen in figure4.4. The background distributions clearly peak at the mass of the Z boson.

Minimal transverse mass

The lepton not associated with the Z boson is used together with the missing energy tobuild the transverse mass

mT =√

2(EmissT El

T − pmissT · plT)

(4.3.4)

where ElT is the energy of the lepton in the transverse plane and pmissT · plT is the

scalar product of the missing transverse momentum and the transverse momentum ofthe lepton.If there are more than one SFOS pairs, the lepton giving the minimum of the transversemass mmin

T is chosen for the transverse mass and the other two leptons are used toconstruct mSFOS.The plots presenting the mmin

T variable are shown in figure 4.5. The distribution of thediboson background drops rapidly at about 80 - 100 GeV. For the SUSY samples thedistributions decrease much slower. Therefore this observable can be used to suppress

15

4.4 Preselection

[GeV]minTm

0 50 100 150 200 250 300 350

entr

ies

1−10

1

10

210

310

410

m(C1, N2)=155 m(N1)=75wino C1N2

m(C1)=155 m(N2)=160 m(N3)=164 m(N1)=75higgsino C1N3 C1N2 N2N3

VVV

VV

(a) small mass splitting

[GeV]minTm

0 100 200 300 400 500 600 700

entr

ies

1−10

1

10

210

310

410

m(C1, N2)=257 m(N1)=80wino C1N2

m(C1)=256 m(N2)=259 m(N3)=260 m(N1)=79higgsino C1N3 C1N2 N2N3

VVV

VV

(b) large mass splitting

Figure 4.5: Distributions ofmminT with applied preselection for the background and signal

samples with the small (4.5a) and large (4.5b) mass splittings.

background if a selection mminT > 110 GeV is performed.

4.4 PreselectionA requirement the selected events have to fulfil is that the number of leptons in oneevent is exactly three.As mentioned in section 4.3 the leptons have to fulfil certain criteria. Using the exactsame selection as for the existing search, the leading and the subleading lepton haveto have pT > 25 GeV, the third lepton pT > 20 GeV. They also have to be within theangular acceptance of the inner tracking detector, i. e. electrons with |η| < 2.47 andmuons with |η| < 2.5 are accepted.The threshold for jets, both, b-tagged or not, to be counted is pT > 20 GeV.

4.5 Signal regionsThe goal of this project is to make statements about the sensitivity of the existing searchto the model with higgsino-like χ±1 , χ0

2 and χ03. Therefore the signal regions used in this

project are the same as those used in the search. The selection criteria for the threerelevant signal regions are listed in table 4.1.For all three signal regions the number of jets is required to be zero. The invariant massof the SFOS pair must be consistent with an on-shell Z boson. The minimal transversemass has to be larger than 110 GeV in order to suppress diboson background. The signalregions are binned in the missing transverse energy. The events are required to have atleast Emin

T > 60 because larger missing transverse energy is expected from the signal [4].

16

4.5 Signal regions

Table 4.1: Signal region requirements as defined in the existing search. The SR is binnedin the missing transverse energy.

SR nnon−b−tagged jets nb−tagged jets mSFOS [GeV] mminT [GeV] Emiss

T [GeV]SR3-WZ-0Ja 0 0 81.2 - 101.2 > 110 60 - 120SR3-WZ-0Jb 0 0 81.2 - 101.2 > 110 120 - 170SR3-WZ-0Jc 0 0 81.2 - 101.2 > 110 > 170

17

5 ResultsIn figure 5.1 the distributions of the missing transverse energy in the signal regions areshown. The SUSY signals with the large mass splitting (5.1b) are now at the same orderof magnitude as the diboson background. This shows that relatively more backgroundthan signal can be suppressed. For both signal samples a significant number of eventsenters the signal regions.In figure 5.1a the distributions of the signals with the small mass splitting is showntogether with the distributions of the background. For the signal with the higgsino-likeparticles no event enters the signal region. For the validation sample with the wino-likeparticles only a few events are found in SR3-WZ-0Ja. The yields from the plot are alsoreported in table 5.1.The defined signal regions are effective for the SUSY signals with the large mass splittingbut no higgsino signal with the small mass splitting survives the selection.

SR3-WZ-0Jc

(a) small mass splitting

SR3-WZ-0Jc

(b) large mass splitting

Figure 5.1: Distributions of EmissT in the signal regions for the background samples and

the signal samples with the small (5.1a) and the large (5.1b) mass splittings.

To compare the sensitivity of the existing search for the wino and the higgsino caseand to validate the analysis used in this project, the acceptance defined as

α = number of events in SR

total number of events(5.0.1)

18

5 Results

Table 5.1: Number of events in each signal region for the samples with wino-like orhiggsino-like χ±1 , χ0

2 and χ03 with both mass splittings.

small mass splitting large mass splittingNumber of Events Wino Higgsino Wino Higgsino

SR3-WZ-0Ja 0.3 0 49.1 12.6SR3-WZ-0Jb 0 0 48.9 12.5SR3-WZ-0Jc 0 0 34.4 9.0

is used. In table 5.2 the acceptances for the existing search, the validation wino sampleand the higgsino sample are summarized.For the large mass splitting the numbers obtained from the search provided on the HEPData website [12] and the numbers for the validation wino sample are in the same orderof magnitude for each of the three SRs. The values from the search are 0.04 - 0.05 % andso are the values for the validation sample. This is reasonable and therefore this validatesthe search in this work. Looking at the higgsino signal sample, a similar observationcan be made. The numbers for this sample are also in the same order of magnitude.For this case 0.04 - 0.06 % are obtained. This means that the search with this SRs isexpected to be equally sensitive to the higgsino sample as to the wino sample. Though,the higgsino sample contains three production processes in contrast to the wino samplethat just contains one process.

For the SUSY signals with the small mass splitting the numbers obtained in the

Table 5.2: Signal region acceptances for the wino sample provided by the existing search,for the validation wino sample and for the higgsino sample.

small mass splitting large mass splittingAcceptances Wino Wino Higgsino Wino Wino Higgsino

in % (search [12]) (validation) (search [12]) (validation)SR3-WZ-0Ja 0.01 0.00005 0 0.04 0.05 0.06SR3-WZ-0Jb 0.0009 0 0 0.05 0.05 0.06SR3-WZ-0Jc 0.0005 0 0 0.04 0.04 0.04

performed search differ significntly from the numbers for the validation signal. For thelatter only for SR3-WZ-0Ja a number different from zero is found. It is 0.00005 % whichis still three orders of magnitude smaller than the number from the existing search 0.01%. The other signal regions have 0.0009 % or 0.0005 % acceptance for the wino samplefrom the existing search but 0 for the wino validation sample. For the higgsino sample

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5 Results

only acceptances equal to zero can be found. In this case the analysis in this project isnot validated. Further research concerning the validation needs to be done. Currentlyno statements about the acceptances and therefore the sensitivity can be made.

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6 Conclusion and OutlookIn this project the acceptances for the existing search considering a pair production ofpure wino-like χ±1 and χ0

2 were compared with those for a sample with higgsino-likeSUSY particles. For the latter three production processes have been considered: χ±1 χ0

2pair production, χ±1 χ0

3 pair production and χ02 χ

03 pair production. The signal regions

were chosen the same in the existing search and in this project.The results showed that the acceptances are comparable in the wino case and in thehiggsino case with the three different processes and the larger mass splitting. For thesignal samples with the smaller mass splitting some discrepancies in the numbers for thevalidation wino sample and the existing search have been found. Therefore no state-ments can be made on the sensitivity of the search to the higgsino sample in this case.

For the SUSY signals with the larger mass splitting the next steps could be to re-cast the limits obtained for the wino case to the higgsino case. The acceptance obtainedfor the higgsino sample and the cross section of the higgsino processes could be used todetermine what the expected sensitivity for the higgsino case would be.For the smaller mass splitting the next step would be to trace back the origin of thediscrepancy of the acceptances found in the existing search and for the wino validationsample.

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