Simone Amoroso

Inclusive searches for squarks and gluinos with the ATLAS detector

Albert Ludwigs Universität Freiburg

On behalf of the ATLAS collaboration

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the ATLAS detectorS

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SUSY at collidersS

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SUSY at the weak scale provides:Higgs mass stabilization

Gauge coupling unification

Dark Matter candidate

Theoretically appealing and with a very rich phenomenology to explore

R-parity conserving (RPC) signatures

Sparticles are produced in pairs, with each decay ending with an LSP, mostly the lightest neutralino or the gravitino

Squarks and gluinos production through strong interaction are prime candidates for discovery due to highest production cross sections

R-parity violating (RPV) signatures

Resonances or multi-jets/leptons, from production of single sparticles and LSP decays

Displaced vertices from late LSP decays

high-ETmiss

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How do we search for SUSY?S

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In realistic SUSY models with many parameters mostly only a few are relevant

Searches are interpreted in Simplified Models in which only one decay is allowed

Only a few parameters/masses, easier to study mass dependences

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Natural S

USY{

ATLAS SUSY resultsS

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talk of F. C.

Ungaro

talk of V. Lang

this talk

this talk

Natural S

USY{

Focusing on the most recent results using the full 8TeV dataset

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0L + [2-6] jets + ETmiss

SUSY “flagship” analysis, sensitive to many scenarios

squark-squark squark-gluino gluino-gluino

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experimental + MC stat +theory

meff = ETmiss +ΣpTjet

Defines 10 SR with different jet multiplicities and hard cuts on meff and ETmiss/meff

ATLAS-CONF-2013-047

SR SR

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Dominant at low Njets

Important for high Njets

}

Constrain main backgrounds to control regions (CR) in a combined fit:4 CR for each of the signal regions

Multijet shape determined with a data-driven method (jet smearing)

No deviations observed, limits set on 𝛔(vis)

before fit before fitbefore fit

0L + [2-6] jets + ETmissATLAS-CONF-2013-047

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InterpretationsS

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ATLAS-CONF-2013-047

Exclusion limits with CLs and profile likelihood ratio test statistics

Squark/Gluino pair production, with direct decays to the LSP; all other SUSY particles decoupled

Gluino (Squark) masses of 1.25 (1.4) TeV are excluded for all Squark (Gluino) masses and a massless 𝜒0

Expected limit

Yellow band ±1𝝈 experimental uncertainties

Observed limit

±1𝝈 signal theory uncertainty

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0L + [7-10] jets + ETmiss

Focus on long decay chains, many jets and lower ETmiss

Interpretation in several models with intermediate χ0, χ+/- or stops

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Main discriminating variable ETmiss/√HT (similar to ETmiss resolution)

Flavour stream:

Separate b-tag categories (0, 1 or ≥2 b-jets)

Targeting gluino mediated 3rd generation scenarios (in F. Ungaro talk)

Fat-jet stream:

Reclustering all Anti-Kt, R=0.4 jets with pT>20GeV into R=1 fat jets

Take the sum of fat-jet masses as discriminating variable:

JHEP 10 (2013) 130

MJΣ = ΣmR=1.0,pT>100GeV

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Multijets dominant background, but ETmiss/√HT independent of Njets

The shape of multijets is extracted from data at lower jet multiplicities

The same number of b-jets in CR and SR is used to get the template.

Other main backgrounds normalized in 1/2L CR:

MT and ETmiss (1L) or mll (2L) selections are applied to enhance background purity

Control Region (7 jets) Signal Region (≥10 jets)

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JHEP 10 (2013) 130

0L + [7-10] jets + ETmiss

Multijets

W+jetsTtbar /

No excess observed, limits on 𝛔(vis)

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Sim

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JHEP 10 (2013) 130

Interpreted in 1- or 2-step simplified models

1L CR, ≥2 b-tag

Interpretations

for decays with stops/sbottoms see F. Ungaro talk

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1L + [3-6] jets + ETmissATLAS-CONF-2013-062

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Mostly targeting 1- and 2-step gluino decays

Leptonic decays of χ0, χ+/-, sleptons, sneutrinos directly or through intermediate steps

Soft lepton [6-25 GeV] Hard lepton [>25 GeV]

Common discriminating variables ETmiss, mT, meff and ETmiss/meff

W/Z+jets and Ttbar backgrounds normalized to data in dedicated CR

Fake leptons obtained from data with the “matrix-method”

meff = ETmiss+ΣpTjet+pTlep mT = √2ETmisspTlep [1-cosΔ∆ɸ(pTmisspTlep)]

recovers sensitivity for compressed scenarios for large mass splittings

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InterpretationsS

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hard 1Lsoft 1L

ATLAS-CONF-2013-062

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2L RazorS

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ATLAS-CONF-2013-089

Search in dileptonic final states without a Z boson using the Razor variable

Makes use of symmetry in SUSY decay chains when sparticles are pair produced

Longitudinal:

Transverse:

SR are defined with cuts on R, M’R veto on Z candidates

Main backgrounds normalized to data in simultaneous fit, fakes data-drivenBinned fit in M’R , shape powerful discriminant against backgrounds

low for SM background

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2L RazorS

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ATLAS-CONF-2013-089

Search in dileptonic final states without a Z boson using the Razor variable

Build two mega-jets from the visible decay products:Longitudinal:

Transverse:

SR are defined with cuts on R, M’R veto on Z candidates

Main backgrounds normalized to data in simultaneous fit, fakes data-driven

Binned fit in M’R , shape powerful discriminant against backgrounds

Limits are extended to smaller mass splittings

1L 3-6 jets 1L 3-6 jets

low for SM background

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Msugra/Cmssm

higgs a

Higgs aware MSUGRA/CMSSM:

accomodates a lighest Higgs boson mass of 125

GeV

Gluinos below 1.35 TeV are excluded for any

squark massSim

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Tau+Jets+EtmissTargeting GMSB SUSY with stau NLSP

1 (≥2) had. 𝞽 with pT>30(20) GeV, no additional leptons

Dominant Backgrounds:W/Z+jets and Ttbar - 2D CR (mT vs nb-tags)

Multijets - (ABCD 𝞽ID vs Δɸ)

After all selections but final HT cutSim

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ATLAS-CONF-2013-026

Sensitive to baryon number violating coupling λ”UDD

Allow the LSP to decay to 3 quarks → many jets in the final state

Huge combinatorics prevents bump search; looks for an excess in events with with >6 or >7 high pT jets (>80GeV) for various b-tag multiplicities

Multijet background estimated by projecting from lower jet multiplicity bins

Set 95% CL upper limits on cross section, for 6- and 10-quark models, and different assumed branching ratios

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Multijet RPVS

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ATLAS-CONF-2013-091

Sensitive to baryon number violating coupling λ”UDD

Allow the LSP to decay to 3 quarks → many jets in the final state

Huge combinatorics prevents bump search; looks for an excess in events with with >6 or >7 high pT jets (>80GeV) for various b-tag multiplicities

Multijet background estimated by projecting from lower jet multiplicity bins

Set 95% CL upper limits on cross section, for 6- and 10-quark models, and different assumed branching ratios

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Multijet RPVS

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ATLAS-CONF-2013-091

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DV+muon

Control Region (7 jets)

Search for a long-lived χ0 decaying to a muon and jets → Uses dedicated reconstruction of tracks and vertices

Trigger on one high-pT muon (>55 GeV)

DV search within r<180mm |z|<300mm, mDV>10GeV and >4 tracks

Vertices from regions of the detector with high material density are vetoed to reduce the background from hadronic interactions

Very low expected background (0.02±0.02 events), 0 observed

1TeV squarks excluded for 1.5<ct<156mm (100% BR to a muon)

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ATLAS-CONF-2013-092

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R-hadrons search

Uses run scheduleUse bunch structure

Year

MonthDay

HourRevolution period

Search for long-lived stopped R-hadrons, decaying in the detector beyond the time between bunches

Triggers on empty bunch crossings with calorimeter activity

Leading jet |η|<1.2, pT>100, 300 GeV

Strong model dependence in the signal stopping fraction

Main backgrounds: Cosmics (measured in low-lumi runs)

Beam-halo (measured in unpaired bunches)

No excess is observed

Limits:

For mχ0=100 GeV mg<832 GeV is

excluded for lifetimes between 10μs and 1000 s

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Phys.Rev.D 88, 112003 (2013)

SR1 SR2

SR2

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SummaryS

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ATLAS has performed a broad search for SUSY

Inclusive analysis have been extended to cover challenging scenarios

Mass limits pushed further in the TeV region

Gluino masses up to 1.3 TeV

Squark masses up to 740 GeV

Complete the exploitation of the 8TeV dataset

Leave no stone unturned!

Looking forward to the new possibilities of LHC Run2

But no excess observed so far!

Backup

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0L + [2-6] jets + ETmiss

mUED

NUHMGtt

gluino 1-step

gluino 1-step

squark 1-step

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Matrix method