SPS5 SUSY STUDIES AT ATLAS Iris Borjanovic Institute of Physics, Belgrade

SUPERSYMMETRY EXTENSION of the SM EXTENSION of the SM EVERY SM PARTICLE HAS ITS SUSY PARTNER EVERY SM PARTICLE HAS ITS SUSY PARTNER UNIFICATION OF ALL INTERACTIONS UNIFICATION OF ALL INTERACTIONS SUSY IS BROKEN SUSY IS BROKEN IF EXIST AT THE TeV SCALE IT IS LIKELY TO BE DISCOVERED AT LHC IF EXIST AT THE TeV SCALE IT IS LIKELY TO BE DISCOVERED AT LHC

MSSM Higgs sector Electroweak gauge bosons Right helicity matter Left helicity matter Gluon SPIN 0SPIN 1/2SPIN 1 Mixings: 128 free parameters

R-parity R=(-1) 3(B-L)+2S SM particles R=+1, SUSY particles R=-1 SM particles R=+1, SUSY particles R=-1 R-parity conservation (multiplicative QN): - SUSY particles are produced in pairs - SUSY particles are produced in pairs - LSP is absolutely stable and present - LSP is absolutely stable and present in the final state of every SUSY decay in the final state of every SUSY decay LSP : colorless, uncharged, interacts weakly → SUSY events with large E T missing

SUSY breaking mechanism mass of SM particle ≠ mass of SUSY partner mass of SM particle ≠ mass of SUSY partner SUGRA SUGRA GMSB GMSB AMSB AMSB BRANE MODELS BRANE MODELS Number of free parameters is significantly reduced !!! Which is the right one ?

mSUGRA R-parity conserving, LSP is lightest neutralino SCALAR MASS PARAMETER - m 0 SCALAR MASS PARAMETER - m 0 GAUGINO MASS PARAMETER – m 1/2 GAUGINO MASS PARAMETER – m 1/2 TRILINEAR COUPLING – A 0 TRILINEAR COUPLING – A 0 RATIO OF THE HIGGS VACUM EXPECTAION VALUES – tan(β) RATIO OF THE HIGGS VACUM EXPECTAION VALUES – tan(β) HIGGS MASS PARAMETER – sign(μ) HIGGS MASS PARAMETER – sign(μ) Parameters at Planck scale Parameters at EW scale SUSY masses, BR, decays RGE

“ SNOWMASS POINTS AND SLOPES” - new set of benchmark points - Point m 0 m 1/2 A 0 tan(β) sign(μ) 1a b SPS 5 SPS 5

SUSY masses SUSY masses heaviest lightest light stop

SUSY decays gluinos decays strongly squarks decay weakly stop always decay to

SUSY production For L=30 fb -1, N=1.2 x 10 6 SUSY events Squark and gluino production dominate

KINEMATIC ENDPOINTS RPC models missing LSP, invariant mass formed from final state particles has no peaks RPC models missing LSP, invariant mass formed from final state particles has no peaks Relativistic kinematics invariant masses have maximums and minimums (kinematic endpoints ) which are function of SUSY masses. From endpoints measuremnets SUSY masses can be extracted. Relativistic kinematics invariant masses have maximums and minimums (kinematic endpoints ) which are function of SUSY masses. From endpoints measuremnets SUSY masses can be extracted.

Example Example C Q + B, B P + A C Q + B, B P + A C Q B A P Maximum PQ invariant mass P and Q are back to back in the B rest frame

Characteristics of SUSY events Large missing transverse energy E T miss Large missing transverse energy E T miss High p T jets High p T jets Large multiplicity of jets Large multiplicity of jets Large Large M eff = E T miss + p T (j 1 ) + p T (j 2 ) + p T (j 3 ) + p T (j 4 ) M eff = E T miss + p T (j 1 ) + p T (j 2 ) + p T (j 3 ) + p T (j 4 ) - SM background reduced by hard kinematics - large SUSY background

MONTE CARLO ISAJET 7.64 ISAJET 7.64 HERWIG 6.5 HERWIG 6.5 ATLFAST ATLFAST Generated: Generated: fb -1 of SUSY events fb -1 of SUSY events - 10 fb -1 of top-antitop pairs - 10 fb -1 of top-antitop pairs

LEFT SQUARK CASCADE DECAY Left squark production : Left squark production : directly or from gluino decay directly or from gluino decay Event signature : Event signature : - 2 SFOS leptons (natural trigger) high p T jet from left squark decay - large missing transverse energy - one more high high p T jet from the decay of squark/gluino the decay of squark/gluino produced with left squark produced with left squark

ENDPOINTS Final state particles: l +, l -, q Invariant masses: l + l -, l + l - q, l ± q 5 ENDPOINTS - l + l - maximum - l + l - maximum - l + l - q maximum - l + l - q maximum - l + l - q minimum - l + l - q minimum - maximum for larger l ± q mass - maximum for larger l ± q mass - maximum for smaller l ± q mass - maximum for smaller l ± q mass

ENDPOINTS ARE FUNCTION OF 4 SUSY MASSES GeV GeV GeV 320 GeV 470 GeV 225 GeV lepton and quark masses were neglected while deriving formulas

EVENT SELECTION E T miss > 100 Gev E T miss > 100 Gev n(jet) ≥ 4 n(jet) ≥ 4 p T (j 1 ) > 150 GeV, p T (j 2 ) > 100 GeV, p T (j 1 ) > 150 GeV, p T (j 2 ) > 100 GeV, p T (j 3, j 4 ) > 50 GeV p T (j 3, j 4 ) > 50 GeV 2 SFOS leptons (e + e -, μ + μ - ) with 2 SFOS leptons (e + e -, μ + μ - ) with p T > 10 GeV p T > 10 GeV + additional cuts for every distributions + additional cuts for every distributions SM background is negligible !!!

SUSY BACKGROUND background : SFOS leptons from two independent decays SFOS-OFOS subtraction removes background, applied on all mass distributions N(SFOS)=N(OFOS), identical shape of mass distributions SFOS-OFOS ll invariant mass SFOS OFOS M ll (GeV)

FITTED ENDPOINTS llq lq high ll lq low M(GeV) L=300 fb -1

FIT RESULTS ENDPOINT THEORY FIT STATISTIC SYSTEMATIC ERROR ERROR ERROR ERROR ll max llq max lq high max lq low max llq min % for jets, 0.1% for leptons up to 2% Good agreement between theory and fit Energy scale error Fit error

MASS RECONSTRUCTION 5 endpoint measurements and 4 unknown masses over constrained system of equations is solved numerically by minimising χ 2 Only one set of endpoint measurement, one set of SUSY masses ansambl of endpoint set of measurements is modeled, mass distributions Endpoints are function of SUSY masses Modeled experimental endpoint value Random numbers

RECONSTRUCTED MASSES NEUTRALINO 1 LEFT SQUARK M(GeV) ENTRIES

RESULTS Particle m nom (GeV) m rec (GeV) σ (GeV) σ/m rec neutralino % right slepton % neutralino % left squark % calculated value reconstructed mean value ANSAMBL OF 1000 EXPERIMENTS

LIGHT STOP SQUARK Mixture of left and right stop Mixture of left and right stop Mass: 236 GeV Mass: 236 GeV Higgs mass depends on stop mass Higgs mass depends on stop mass Production: Production: Decay: Decay:

STOP PAIRS 50% of all SUSY production 50% of all SUSY production 2 low p T b quarks 2 low p T b quarks No detectable signal !!! No detectable signal !!! =15 GeV p T (GeV) Entries

tb + E Tmiss channel 14% 38%tb edge structure Kinematically equivalent to decay (1) if M(bW)~M(t) 38% 2% 14% (1) (2) (3) Decay (1) can be isolated !!! Hadronic top(W) decay →bjj

TOP-BOTTOM ENDPOINT Maximum occurs for bottom and top back to back in the stop rest fr GeV GeV 2 Maximum occurs for bottom and top back to back in the sbottom rest frame Decay (1) Decay (2)

M(tb) from HERWIG M ( GeV ) Events/4 GeV (1) (2) (3)

Event signature low p T b quark from stop low p T b quark from stop b quark from top decay b quark from top decay two light (u,d,s,c,) quarks from W decay two light (u,d,s,c,) quarks from W decay high p T quark from left/right squark produced with gluino high p T quark from left/right squark produced with gluino LSP from chargino decay and large missing energy LSP from chargino decay and large missing energy

EVENT SELECTION E T miss > 200 GeV E T miss > 200 GeV n jet n jet ≥ 3 ( ≠ b, τ jets), p T > 30 GeV, |η| 300 GeV p T > 30 GeV, |η| 300 GeV n(b jet)=2 n(b jet)=2 30< p T (b 1 ) <150 GeV, 30< p T (b 2 ) <50 GeV 30< p T (b 1 ) <150 GeV, 30< p T (b 2 ) <50 GeV no leptons no leptons

TOP-BOTTOM MASS RECONSTRUCTION Excluding j 1, jj → :|m jj - m W |< 15 GeV Excluding j 1, jj → :|m jj - m W |< 15 GeV bjj minimizing | m bjj - m t | + p T (b ’ ) < 50 GeV bjj minimizing | m bjj - m t | + p T (b ’ ) < 50 GeV Scaling m jj = m W, m bjj recalculated, Scaling m jj = m W, m bjj recalculated, |m bjj - m t |< 30 GeV |m bjj - m t |< 30 GeV m bjj + b jet → m tb m bjj + b jet → m tb ΔR(tb) < 2 ΔR(tb) < 2 ‘Sideband’ subtraction ‘Sideband’ subtraction

SIDEBAND METHOD Some jj pairs accidentally have masses in W zone W :|m jj - m W |< 15 GeV A :| m jj – (m W -30)| <15 GeV B :| m jj – (m W +30)| <15 GeV W-0.5(A+B) subtraction A WB jj mass M(GeV) Events/5 GeV/300 fb -1

TOP MASS TOP MASS L=300 fb -1

TOP-BOTTOM MASS L=300 fb -1 W0.5(A+B) signal W-0.5(A+B)

M(tb) shape linear part for background gaus smeared triangular shape

M(tb) FIT M(tb) fit = ± 0.3(stat.) ± 2.6(syst.) GeV M(tb) th = 255 GeV This measurement puts contraints on the stop, gluino and chargino masses !!! Good agreement between fit and theory M (GeV) L=300 fb -1

CONCLUSION If SUSY particles with SPS5 characteristics exist, it will be possible to: - identify SUSY particles - reduce SM and SUSY background - measure SUSY masses with ATLAS detector at LHC