Adrien Renaud (LAL-Orsay IN2P3/CNRS and Université Paris-Sud)for the Atlas collaboration.

Search for supersymmetry via resonant final states with the

ATLAS detector

HEP2012 – Valparaiso, Chile January 6, 2012

• PRL (arXiv:1103.5559)• EPJC (arXiv:1109.3089)• EPJCL (arXiv:1110.2693)

2

Overview

1) Introduction 2) RPV tau sneutrino search in the eμ final state3) Scalar gluon search in the four jets final state4) Conclusion

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Susy via Resonances ??MSSM:- particles with L or B numbers- renormalizable terms violate L or B

Potential disaster:- much too fast proton decay

RP conservation:- PR = (-1)2S • (-1)3(B-L)

- forbids L and B violating terms- PR= +1 (-1) for SM (SUSY) particles- LSP stable, in all cascade decays, DM

No resonances--> look for an excess in SM tail

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Susy via Resonances ??Beyond MSSM with RP conservation:

Extended supersymmetry: -- minimal ? new pheno ? flavor-violation ? dirac gauginos ? … -- new particles with PR = +1 --> resonances in RP conserved susy !

RP violated susy: -- B and L conservation ? neutrino masses and mixing ? …

-- some of the couplings have to be small --> stable proton

--> Scalar-gluon search

--> RPV tau sneutrino search

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Introduction to RPV Sneutrino search

Search for RPV sneutrino with lepton number violation decay:

- eμ clean signature with low SM background- previous limit from low energy tau branching ratio:

λ’311 < 0.11 and λ312 < 0.07 for Mslepton = Msquark =

100 GeV

λ’311 ≠ 0 and λ312 ≠ 0

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Event Selection

Using L=1.07 fb-1: 2011 dataSingle lepton (e, μ) trigger (100±1%)

Electron:-- pT > 25 GeV-- |η| < 1.37 or 1.42 < |η| < 2.47-- isolated in EM calorimeter-- shower shape requirements

Muon:-- pT > 25 GeV-- |η| < 2.4-- reconstructed in ID and MS-- isolated in the ID

- Exactly one muon and one electron with opposite-sign charge

- No requirements on #jets and ETmiss

Signal generated with HERWIG + JIMMY + NLO k-factor

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Highest invariant mass (662 GeV) eμ event

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Backgrounds Physics backgrounds (real leptons) -- Z/γ*->tau,tau top pair single top WW, WZ, ZZ -- Estimated using MC corrected for data/MC differences

Instrumental background (lepton faked by photon or jet) -- W/Z+γ estimated using MC -- SM multijet and W/Z+jets estimated using data-driven matrix method: 1) Define loose and tight lepton definitions 2) Apply on all events to get NTT,NTL,NLT,NLL

3) Determine efficiency (r) and fake rate (f) for a lepton that has passed the loose definition to also pass the tight definition 4) Solve the 4*4 matrix:

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Data / Background

Kolmogorov-Smirnov test probability: 56%Data consistent with absence of new physics

Final observable:

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Limits

Excluded @ 95% CL: - 135 fb @ 100 GeV - 4.5 fb @ 1 TeV

Excluded @ 95% CL: - 1.32 TeV for λ′311 = 0.10 and λ312 = 0.05 - 1.45 TeV for λ′311 = 0.11 and λ312 = 0.07

Bayesian method (uniform prior for signal cross section):

Best limits for: - Msneutrino > 270 GeV

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Introduction to scalar-gluon search

Non minimal realisations of SUSY:• Extended SUSY: hybrid N=1/N=2• Extended R-Parity: MRSSM

Sgluon = Scalar color-octet with SM-like PR

Production:

Decay:

Wojciech Kotlarski @7TeV

Pair production

Single production

A 4-jets final state:

Diff cross section from PL.B672,2009implemented as external process to PYTHIA

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Analysis strategy

4 jets pT > 0.55 * Msgluon

ΔRjj < 1.6

|Cos(θ*)| < 0.5 |M1–M2|/(M1+M2) <

0.075Look for an excess in the (M1+M2)/2 distribution.

Combinatory: Event selection:

Using L=34 pb-1: 2010 dataMultijet trigger: 4 jets pT > 55 GeV --> Low threshold = low mass~same amount recorded in 2011 for this threshold

Scalar production at rest suppressed by factor β -- > “ Slightly Boosted ” regime

Minimize :

| ΔRij – 1 | + |ΔRkl - 1|

Where ijkl are the 4 leading jets

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Multijet Event

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DATA-driven BGR estimation

ABCD method:• NA = NB * NC / ND

• Take shape of final

observable in region B via a fit:

JHEP09(2011)074

Only Simulation

BackgroundBackground estimationSignalBackground + Signal

|M1

–M2

|/(M

1+

M2

)

|Cos(θ*)|

C D

BA

0.5 0.7

7.5%

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ABCD results (1/2)

Prediction within1-2 sigma stat

Reasonably good fit

Good agreement A/B

Agreement between data and background prediction:

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ABCD results (2/2)

Systematic uncertainties

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Limits

Profile likelihood ratio and CLS approach :

Likelihood is the Product of : -- Poisson for each bin (shape analysis) -- Gaussian for each systematic uncertainty

Contamination in ABCD method. Correlations between systematic.

Excluded σ @ 95% CL :1 nb @ 100 GeV200 bp @ 200 GeV

Excluded @ 95% CL:• Sgluon : 100-185 GeV (except 5 GeV around 140 GeV)

L = 34 pb-1:

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ConclusionSearch for tau sneutrino decaying to eμ: -- limits for sneutrino mass vs coupling in RPV (0.1 – 2. TeV)

Search for pair-produced sgluon decaying to four-jets: -- limits for low mass colored scalar (100 – 200 GeV)

Other interpretations already available (LFV Z’, hypercolor).More to come with higher Luminosity, Energy, refined analysis

Already 3 published papers

Funny link between 2 analysis:

- slightly modified analysis to search for RPV stops !

qq

Λ’’313

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Spare

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The ATLAS detector

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Jet reconstruction

Jets : -- Anti-kt R=0.6

-- EM+JES calibration

-- pT > 20 GeV && |η| < 2.8

JER

JES

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RPV sneutrino search ET

miss not used in the analysis to make the search more generic

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Other interpretations

Z′ gauge bosons with lepton flavor

violating (LFV) interactions

--> Same analysis as for stau

sneutrino

Hypercolor model:

Hyperpion, scalar color octet

--> Same as analysis as sgluon

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Data / MC (1/2)

ALPGEN+HERWIG+JIMMYSM-multijet production

after pT cut(4 jets pT>55 GeV -> M=100GeV)

1) 4 jets pT > 0.55 * Msgluon

--> sliding cut

2) ΔR(jj) < 1.6

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Data/MC (2/2)

After pT cut and ΔR cuts

After all cuts but cos(θ*)

- Reasonably good description- Ratio compatible with 1 even without JES uncertainty - large MC stat uncertainty

3) |M1–M2|/(M1+M2) < 0.075

4) |Cos(θ*)| < 0.5

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Data / Background

Good agreement with SM prediction