susy studies with atlas experiment 2006 texas section of the aps joint fall meeting october 5-7,...

SUSY Studies with ATLAS Experiment

2006 Texas Section of the APS Joint Fall MeetingOctober 5-7, 2006Arlington, Texas

Nurcan OzturkUniversity of Texas at Arlington

ATLAS Collaboration

TSAPS 2006 - Arlington Nurcan Ozturk - UTA 2

Outline

Introduction Why Supersymmetry SUSY Particle Spectrum SUSY Signatures at the LHC Data Challenge Activities Results from Full Simulation Conclusions


Introduction• Large Hadron Collider (LHC) is a 14 TeV proton-proton collider at CERN in Switzerland. LHC will start taking data in 2007.• Luminosity goals: 10 fb-1/year (first 3 years)

100 fb-1/year (subsequently)• Five experiments will operate: ALICE, ATLAS, CMS, LHC-B, TOTEM.• Supersymmetry will be explored primarily in ATLAS and CMS experiments.

A Toroidal LHC ApparatuS

ATLAS Detector

Five-story-high7000 tons


Why Supersymmetry?

Supersymmetry (SUSY) is one of the most attractive extensions of the Standard Model (SM) that pairs fermions and bosons.

Hierarchy Problem: SUSY stabilizes Higgs mass against loop corrections (gauge hierarchy/fine-tuning problem) leads to Higgs mass ≤ 135 GeV.

Good agreement with LEP constraints from EW global fits.

Grand Unification: SUSY modifies running of SM gauge couplings ‘just enough’ to give Grand Unification at single scale.

Dark Matter: R-Parity (R = (-1)3B+2S+L) conservation causes the lightest supersymmetric particle (LSP) to be stable provides a solution to dark matter problem of astrophysics and cosmology.


SUSY Particle Spectrum

SUSY partners have opposite spin-statistics but otherwise same quantum numbers


SUSY Signatures at the LHC

Gll ~~

Heavy strongly interacting sparticles (gluinos and squarks) produced in initial interaction

Long decay chains and large mass differences between SUSY states; many high PT objects are observed (lepton, jets, b-jets)

If R-Parity is conserved cascade decays to stable undetected LSP (lightest SUSY particle; neutralino in mSUGRA); large ET

miss signatures If the model is GMSB, LSP is gravitino. Additional signatures from NLSP (next-to-

lightest SUSY particle) decays; for example photons from and leptons from

If R-parity is not conserved LSP decays to 3-leptons, 2leptons+1jet, 3 jets; ETmiss

signature is lost

lqql

g~ q~ l~

~

~p p

A typical decay chain of supersymmetric particles in a proton-proton collision:

G~~01


mSUGRA Framework The minimal SUSY extension of the SM (MSSM) brings 105 additional free

parameters preventing a systematic study of the full parameter space. Assume a specific well-motivated model framework in which generic signatures

can be studied. mSUGRA framework: Assume SUSY is broken

by gravitational interactions unified masses and couplings at GUT scale gives five free parameters: m0, m1/2, A0, tan(β), sgn(µ)

Reach sensitivity only weakly dependent on A0, tan(β), sgn(µ). R-parity assumed to be conserved. Multiple signatures on most of parameter space:

ETmiss (dominant signature), ET

miss with lepton veto, one lepton, two leptons same sign (SS), two leptons opposite sign (OS)

Choose benchmark points in mSUGRA plane to study SUSY exclusively

5exclusion contours


Data Challenge Activities (1) Goal:

Provide simulated data to optimize the detector Validate Computing Model, the software, the data model, and to ensure the

correctness of the technical choices to be made

Analyzing SUSY events is important to test the reconstruction software since typical SUSY events contain the complete set of physics objects that can be reconstructed in the detector

SUSY in ATLAS Data Challenges: DC1: July 2002 – March 2003

Bulk region point, similar to LHCC Point 5 DC2: June 2004 – December 2004

DC1 bulk region point (validation of Geant4 and new reconstruction) Coannihilation point


Data Challenge Activities (2) Data Challenge for Rome ATLAS Physics Workshop: January- June 2005

SU1 sample: Coannihilation point m0 =70 GeV, m1/2 = 350 GeV, A0 = 0 GeV, tanβ = 10, sgn(µ) = +

SU2 sample: Focus point m0 = 3350 GeV, m1/2 = 300 GeV, A0 = 0 GeV, tanβ = 10, sgn(µ) = +

SU3 sample: DC1 bulk region point m0 =100 GeV, m1/2 = 300 GeV, A0 = -300 GeV, tanβ = 6, sgn(µ) = +

SU4 sample: Low mass point m0 = 200 GeV, m1/2 = 160 GeV, A0 = -400 GeV, tanβ = 10, sgn(µ) = +

SU5 sample: Scan of parameter space SU5.1: m0 = 130 GeV, m1/2 = 600 GeV, A0 = 0 GeV, tanβ = 10, sgn(µ) = +

SU5.2: m0 = 250 GeV, m1/2 = 600 GeV, A0 = 0 GeV, tanβ = 10, sgn(µ) = + SU5.3: m0 = 500 GeV, m1/2 = 600 GeV, A0 = -400 GeV, tanβ = 10, sgn(µ) = + SU6 sample: Funnel region point

m0 = 320 GeV, m1/2 = 375 GeV, A0 = 0 GeV, tanβ = 50, sgn(µ)


Data Challenge Activities (4) Data Challenge for Computing System Commissioning (CSC): December 2005-ongoing

K.De, Software workshop, Sept. 2006

Some Results from Full Simulation


Missing ET Distributions – Rome Data (1)

ReconstructedMonte Carlo

after selection cuts normalized to 5 fb^-1

Top

W+jets

Z+jets

SU1

SU3

SU4

SU6

SU2

As expected, missing ET

provides powerful handle against SM backgrounds


Z+jetsTopSU1SU2SU3SU4SU6

Selection cuts applied to enhance SUSY signal:

• 4 jets with PT > 50 GeV• 2 jets with PT > 100 GeV• ET miss > 100 GeV

Missing ET Distributions – Rome Data (2)

after selection cuts normalized to 5 fb^-1


Dilepton Invariant Mass – Rome Data (1)

Z+jets

W+jets

SU3

SU1

Excellent discovery channel!

Top

SU6

SU4

before selection cutsnormalized to 5 fb^-1

SU2

e+e- + µ+µ- - e+-µ-+

llll 01

02

~~~


Dilepton Invariant Mass – Rome Data (2)

Z+jet

W+jets

SU3

SU1Top

SU6

SU4

after selection cutsnormalized to 5 fb^-1

But need lots of data!

SU2


Conclusions The LHC will be the place to search for SUSY If TeV scale SUSY exists, ATLAS should find it Big challenge for discovery will be understanding the performance of

the detector SUSY discovery is possible in other models which I have not covered

here, however some of UTA group members have been involved: Gauge Mediated Supersymmetry Breaking (GMSB) Anomaly Mediated Supersymmetry Breaking (AMSB) R-Parity Violation

Currently a great effort is being taken in Data Challenges to understand different SUSY models, and to test the reconstruction software

Exciting times ahead of us with the LHC turn on!

Backup Slides


Statistics – Rome DataSample sigma x BR (pb) Number of AOD files Integrated

Luminosity (pb-1)

Top 577 6793 577

W+4jets 2400 3693 76

Z+jet : ZJ1ee ZJ1mumu ZJ1nunu

4730, eff = 0.10034730, eff = 0.10586140, eff = 0.115

177517851976

184175137

SU1 6.8 3668 26600

SU2 4.9 1156 11555

SU3 19.3 1728 4377

SU4 280 1070 187

SU6 4.5 1308 14293

• Top sample’s cross section is calculated by using what is given in the wiki page: 10K events corresponds to an integrated luminosity of 17.34 pb-1 • Each AOD file has 49 events• Each sample is normalized to 5000 pb-1 in all plots


Event Selection Two different sets of cuts applied

‘before selection cuts’, which includes some default cuts ‘after selection cuts’ – additional cuts to enhance SUSY signal

Default cuts: Pseudorapidity cuts: ElectronEtaCut: 2.5, MuonEtaCut: 2.5, JetEtaCut: 5.0,

TauEtaCut: 2.5, PhotonEtaCut: 2.5 Transverse momentum cuts: ElectronPtCut: 10 GeV, MuonPtCut: 10 GeV,

JetPtCut: 10 GeV, TauPtCut: 10 GeV, PhotonPtCut: 10 GeV TauLikelihoodCut: 4 Isolation cuts: 5 GeV for electrons and muons. For muons chi2<20

Selection cuts: 4 jets with PT > 50 GeV 2 jets with PT > 100 GeV ET miss > 100 GeV

Cone 4 jets (R=0.4) are used


mSUGRA Points for Rome Data (1)

DC1 bulk region point (new underlying event in generation) m0 =100 GeV, m1/2 = 300 GeV, A0 = -300 GeV, tanβ = 6, sgn(µ) = + LSP is mostly bino, light lR enhance annihilation. ‘Bread and butter’ region

for the LHC experiments llq distributions, tau-tau measurements, third generation squarks (both tau

identification and B tagging improved) Coannihilation point

m0 =70 GeV, m1/2 = 350 GeV, A0 = 0 GeV, tanβ = 10, sgn(µ) = + LSP is pure bino. LSP/sparticle coannihilation .Small slepton-

LSP mass difference gives soft leptons in the final state Focus point

m0 = 3350 GeV, m1/2 = 300 GeV, A0 = 0 GeV, tanβ = 10, sgn(µ) = + LSP is Higgsino, near µ2=0 bound. Heavy sfermions; all squarks and

sleptons have mass >2 TeV, negligible FCNC, CP, gµ-2, etc. Complex events with lots of heavy flavor

~

101~~


mSUGRA Points for Rome Data (2)

Funnel region point m0 = 320 GeV, m1/2 = 375 GeV, A0 = 0 GeV, tanβ = 50, sgn(µ) = + Wide H, A for tanβ >> 1 enhance annihilation. Heavy Higgs resonance

(funnel); main annihilation chain into bb pairs Dominant tau decays

Low mass point at limit of Tevatron RunII reach m0 = 200 GeV, m1/2 = 160 GeV, A0 = -400 GeV, tanβ = 10, sgn(µ) = + Big cross section, but events rather similar to top Measure SM processes in presence of SUSY background to show

detector is understood Scan of parameter space (11 different model points)

mSUGRA points near search limit of 10 fb-1

Understand limitation of fast simulation analyses; detector backgrounds, pileup, reconstruction errors, etc

susy studies with atlas experiment 2006 texas section of the aps joint fall meeting october 5-7,...

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