SUSY searches with the SUSY searches with the

Jet Gamma Balance method in CMSJet Gamma Balance method in CMS

Eleni Ntomari (PhD Thesis work),T.G., Kostas Theofilatos (ETH Zurich)

26 April 2013

Theodoros GeralisInstitute of Nuclear and Particle PhysicsNCSR Demokritos, HEP2013, EESFYE, Chios

Why SUperSYmmetryWhy SUperSYmmetry Standard Model weknesses:

—Hierarchy problem: large contributions to W, Z and Higgs masses from new physics at the Planck scale. —Distinct coupling constants: for Electromagnetic, Weak and Strong interactions— Non Unification of interactions— Too many papameters (19)

- SUSY solves the hierarchy problem

—One-loop quantum corrections in Higgs (mH2) mass from a Dirac

Fermion (left) and from a scalar (right) from new physics at the Planck scale (ΛUV ~ Planck scale)

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— Solves the hierarchy problem by introducing a symmetry between fermions and bosons and doubling the number of particles fermion boson — Possible unification of coupling constants at ~1016 GeV

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Why SUperSYmmetryWhy SUperSYmmetry

Gauge mediation is used for the soft SUSY symmetry breaking in the MSSM (arXiv:0801.3278v3)

—Gravitino is the LSP → experimental signature: Missing transverse energy (MET)

—Neutralino is the NLSP

Work hypothesis is the R-parity conservation: two LSP's per event

Challenge: understanding the background

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Gauge Mediating SUSY breakingGauge Mediating SUSY breaking

Bino-like NLSP → decays to gravitino και γ/Z

χ10 → γ+G or χ1

0 → Z0+G

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Typical Feynman diagrmas for final states with (a) one or (b) two photons, as they are provided by GGM for the bino-like neutralino case

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WhyWhy γγ ++ jetsjets ++ ΜΕΤΜΕΤ;;

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Typical Feynman diagrmas for final states with one photon as they are provided by GGM for the bino-like neutralino case 66Eleni Ntomari - NCSR Demokritos

WhyWhy γγ ++ jetsjets ++ ΜΕΤΜΕΤ;;

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Wino-like (co-)NLSP

—Neutral winos:

χ10 → Z0+G ή χ1

0 → γ+G

—Charged winos:

χ1± → W±+G

~ ~ ~ ~

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Photons are important ingredients in SUSY final states

We would like to exploit our sensitivity to detect Photons (Excellent detection, reconstruction efficiency and Energy resolution of the CMS ECAL detector: O(0.5%)) → clean experimental signature

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WhyWhy γγ ++ jetsjets ++ ΜΕΤΜΕΤ;;

Reconstruction of EM objectsReconstruction of EM objects Combine information from the Calorimeters and the tracking detectors

– Superclusters of energy deposition in ECAL

• Photons: equivalently low energy in HCAL

– Tracks are reconstructed from their trace at the Si CMS tracker (pixel + strips)

• Combines superclusters with tracks• Existence of track → electron• NO track → photon

Pixeldetector

TrackerStrips

ET

pT

e+

γ

Jet reconstructionJet reconstructionThe Particle Flow algorithm is used for the evaluation of the missing transverse energy

– It combines information from all the CMS subdetectors

– It creates a list of Particle Flow objects• Photons, electrons, muons, charged & neutral hadrons

– This list is used as input to jet algorithms (jet clustering) anti-kT

– It provides the direction of the invisible particles like neutrinos and the lightest supersymmetric particles.

→

|| n

i

iT

missT pE

Event selectionEvent selection

Cuts variables Photons Electron

σiηiη <0.011

Η/Ε <0.05

ΝpixelSeeds* 0 1

Isolation criteria Photons Electrons

CombIso* <6 GeV

*CombIso=EcalIso+HcalIso+TrackIso•Corrected for the pileup

Photon (electron) selection criteria

– At least one tight photon

• pT > 80 GeV, for the most energetic photon

• pT > 35 GeV, for the rest of the photons

– |η|<1.4442

Selection criteria ΗΤ

– ΗΤ>460 GeV

• ΗΤ: scalar sum of calo jets (CaloJets)

with pT > 40 GeV, |η|≤3.0

Jets selection criteria

– At least 3 PF jets :

• pT > 100 GeV, for the 3 most energetic jets

• pT > 30 GeV, for the rest

– |η| < 2.6

– Cut on the minimum distance between the selected photon and the jets ΔR=(Δη2+Δφ2)1/2<0.4

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Ei: Energy of ith crystal Ε: Total energy in 5x5 crystals

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• SUSY signal : γ + jets + Gravitinos (MET)

•Standard Model backgrounds:

— Dominant background without missing transverse energy (MET)

•QCD: γ + jets (fake MET because of the detector resolution)

— Sub-dominant background: processes with true missing transverse energy (MET).

•W(→eν) + jets, ttQ + jets (with fe→γ )

-SM Background simulation with MadGraph Monte Carlo samples

All simulated data (signal & SM background) are normalized to the total data integrated luminosity. They are used only for the evaluation of the method (MC Closure Test)

11114Eleni Ntomari - NCSR Demokritos

SUSY signal and SUSY signal and Standard Model backgroundStandard Model background

Experimental Data samplesExperimental Data samples The data were recorded by the CMS detector during 2011, from proton proton collisions

provided by the LHC accelerator at 7 TeV:

– They correspond to 5.1 ± 0.1 fb-1

– Good quality data were used for this analysis (CMS data quality group) Photon triggers were used with rather loose criteria

– Presence of a photon with Energy above a threshold.

• Thresholds are ajusted according to the luminosity in order to keep up

with the trigger rates.

• ET > 70 GeV and ΗΤ>300 GeV for the first runs (subsequently increased to ΗΤ>400 GeV)

• Criteria for Photon identification and isolation

The Jet Gamma BalanceThe Jet Gamma Balance (JGB) variable(JGB) variable

The JGB method’s essentials:

— Standard Model background processes mostly present a symmetric around zero JGB distribution.

Backgrounds:

γ + jets, W + jets, ttbar + jets

DY + jets , γV + jets

— Supersymmetric processes with long decay chains tend to present non symmetric JGB distributions, with long tail tail in its positive side.

pfJGB|||| T

jetsT ppJGB

The Jet Gamma BalanceThe Jet Gamma Balance (JGB) variable(JGB) variablepfJGB||||

Tjets

T ppJGB

The JGB method’s essentials:

— Standard Model background processes mostly present a symmetric around zero JGB distribution.

Backgrounds:

γ + jets, W + jets, ttbar + jets

DY + jets , γV + jets

— Supersymmetric processes with long decay chains tend to present non symmetric JGB distributions, with long tail in its positive side.

The SM background prediction is performed using real data (data driven), and is based on the Jet Gamma Balance variable distribution. (Jet-Gamma Balance, JGB)

– The method is inspired from an equivalent analysis in SUSY final states to Z, jets and missing transverse energy where the balance between Jets and Z is used (Jet-Z Balance, JZB)• CMS Collaboration, “Search for physics beyond the standard model in events with a Z boson, jets, and missing transverse energy in pp collisions at sqrt(s) = 7 TeV” (2011) arXiv:1204.3774

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Standard Model backgroundStandard Model background

Background due to electron misidentification as a photon in Standard Model processes is estimatied using only data (data driven method).

— Use Zee events in which one electron has a tight selection and the second is not required to have pixel hits. We thus estimate the electron identification efficiency.

Background calculation fromBackground calculation fromelectron misidentficationelectron misidentfication e→e→γγ

Background due to electron misidentification as a photon in Standard Model processes is estimatied using only data (data driven method).

— Comparison of data events Z→ee with the corresponding Z→eγ

— Misidentification rate is thus estimated

To be :

fe→γ~ 0.006 ± 0.003

— The background is calculated by reweighting

Electron + Jet events by the above factor.

γe

γγ 2 ee

ee NN

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Background calculation fromBackground calculation fromelectron misidentficationelectron misidentfication e→e→γγ

Twofold profit from JGB:

Event selection with JGB>0, rejects ~50% of the SM background while retains greatest part of the signal.

Estimation of the total background in the JGB >0 region, without being based in simulation.

– Backgrounds with symmetric JGB:

• JGB distribution for events with ≥1 photons and ≥3 jets

• ”folding” the region with JGB<0

– Backgrounds with asymmetric JGB distribution:

• JGB distribution for events with ≥1 electrons and ≥3 jets

• Normalized using the electron misidentification rate fe→γ~ 0.006 ± 0.003 (for pT>80GeV )

• ”folding” of the region with JGB<0 and subtraction from the region with JGB>0

The The JGB methodJGB method

Background only hypothesis

Background Estimation as stated in the previous slide with MC data

JGB method validation withJGB method validation with MCMC

JGBJGB method capability method capability to discover a signalto discover a signal

Signal+Background hypothesis

Repeat the previous exercise by adding a SUSY signal (msquark:750 GeV / mgluino:700 GeV / mneutralino:225 GeV) in order to test the signal + background hypothesis and to prove the existence of the signal

The agreeement between Data and MC simulation events is good even though simulated events are not used for the background calculation. The leading photon Pt spectrum is shown for data and MC for the same integrated luminosity.

Applying JGB Applying JGB on experimental dataon experimental data

● The JGB distribution for experimental data (black circles) and the corresponding estimated background (red line). The shaded surfaces represent the total uncertainty (left). The ratio of the two Is shown in the right plot.

Applying JGB Applying JGB on experimental dataon experimental data

Applying JGB Applying JGB on experimental dataon experimental data

Run= 176797, Lumi= 180, Run= 176797, Lumi= 180, Event_Number= 282232912Event_Number= 282232912

2404/21/23

η = 1.35238Φ = -1.98983

2424

#pfJets=5, #γ= 1, pfMET= 303.887, H/E= 0, σiηiη= 0.00759025, R9=0.857648, EcalIsoDR04= 2.695, HcalIsoDR04= 0.3708, TrkIsoDR04= 0

pfJets

Major sources of systematic errors are:– Luminosity

• ±2.2%– Jet Energy Scale

• ± 2%– Photon efficiency

• ± 4 %– Acceptance PDF uncertainty

• ± 0.03-78% (εξάρτηση από τις μάζες των SUSY σημάτων – αυξάνεται με την ταυτόχρονη αύξηση της μάζας των gluino και squark)

Systematic uncertaintiesSystematic uncertainties

Uncertainty in the background yield

80-100 GeV 100-120 GeV >120 GeV

JGB uncertainty: 40% ± 39 % ± 38 % ± 32 %

fe→γ : 34% ± 1 % ± 2 % ±10 %

Exclusion limitsExclusion limits

Eclusion limits at 95% CL using the JGB method and the isolation sideband analysis (SUS-12-001), for the bino-like (left, middle) and wino-like (right) neutralino The limits estimation was performed using three bins: [80,100), [100,120) and [120,inf)

ConclusionsConclusions

No SUSY signal detected in the final state γ + Jets + MET using the 2011 data at 7 TeV in CMS

The measurement is compatible with the Standard Model

We have set new more stringent limits on the parameter space

More data at 8 TeV are available and are being analyzed

The results are public and have been presented in major conferences

ConclusionsConclusions— Presentations:

• Hadron Collider Physics Symposium 2012, Kyoto, Japan • Invited talk on “Search for SUSY in final states with photons at CMS”, (speaker: Eleni

Ntomari on behalf of CMS)• LHC Days 2012, Split, Croatia

• Poster on “SUSY Search in Photon(s)+jets+MET final states with the Jet-Gamma Balance method in CMS”, (speaker: Eleni Ntomari on behalf of CMS)

• SUSY 2012, 20th International Conference on Supersymmetry and Unification of Fundamental Interactions, Peking, China

• Invited talk on “Searches for SUSY in final states with photons at CMS”, (speaker: Konstantinos Theofilatos on behalf of CMS)

— Documentation:• [3] Eleni Ntomari, et. al CMS Collaboration, "SUSY Search in Photon(s)+jets+MET final

state with the Jet-Gamma Balance method", CMS-PAS-SUS-12-013, (2012)• [4] Eleni Ntomari on behalf of the CMS Collaboration, “Search for SUSY in final states

with photons at CMS”, EPJ Web of conferences, DOI: TBA• [5] Eleni Ntomari, Theodoros Geralis, Kostantinos Theofilatos, "SUSY Searches in the

Photon(s)+jets+MET final state in 7TeV pp collisions with the JGB method", CMS Internal Note AN/2012-180

This research has been co-financed by the European Union (European Social Fund – ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program: Thales. Investing in knowledge society through the European Social Fund.