Adrien Renaud (LAL-Orsay IN2P3/CNRS and Université Paris-Sud)
for the Atlas collaboration.
Search for supersymmetry viaresonant final states with theATLAS 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 state
3) Scalar gluon search in the four jets final state
4) Conclusion
3
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
4
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 data
Single 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.B672,2009
implemented 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) < 0.075
Look for an excess in the (M1+M2)/2 distribution.
Combinatory:
Event selection:
Using L=34 pb-1: 2010 data
Multijet 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
Background
Background estimation
Signal
Background + Signal
|M1–M2|/(M1+M2)
|Cos(θ*)|
C
D
B
A
0.5 0.7
7.5%
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ABCD results (1/2)
Prediction within
1-2 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 ABCDmethod.
Correlations betweensystematic.
Excluded σ @ 95% CL :
1 nb @ 100 GeV
200 bp @ 200 GeV
Excluded @ 95% CL:
• Sgluon : 100-185 GeV(except 5 GeV around 140 GeV)
L = 34 pb-1:
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Conclusion
Search 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 !
q
q
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
ETmiss not used in the analysis
to make the search moregeneric
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Other interpretations
Z′ gauge bosons with lepton flavorviolating (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+JIMMY
SM-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 evenwithout 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 SMprediction