SPS5 SUSY STUDIES AT ATLAS

SPS5 SUSY SPS5 SUSY STUDIES AT STUDIES AT

ATLASATLASIris BorjanovicIris Borjanovic

Institute of Physics, BelgradeInstitute of Physics, Belgrade

SUPERSYMMETRYSUPERSYMMETRY

EXTENSION of the SMEXTENSION of the SM EVERY SM PARTICLE HAS ITS SUSY EVERY SM PARTICLE HAS ITS SUSY

PARTNERPARTNER UNIFICATION OF ALL UNIFICATION OF ALL

INTERACTIONSINTERACTIONS SUSY IS BROKENSUSY IS BROKEN IF EXIST AT THE TeV SCALE IT IS IF EXIST AT THE TeV SCALE IT IS

LIKELY TO BE DISCOVERED AT LHCLIKELY TO BE DISCOVERED AT LHC

MSSM MSSM

Higgs sector

Electroweakgauge bosons

Right helicity matter

Left helicity matter

Gluon

SPIN 0 SPIN 1/2 SPIN 1

Mixings: 128 free parameters

R-parityR-parity

R=(-1)R=(-1)3(B-L)+2S3(B-L)+2S

SM particles R=+1, SUSY particles R=-1SM particles R=+1, SUSY particles R=-1

R-parity conservation (multiplicative QN):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 decayin the final state of every SUSY decay

LSP : colorless, uncharged, interacts weakly

→ SUSY events with large ET missing

SUSY breaking SUSY breaking mechanismmechanism

mass of SM particle ≠ mass of SUSY mass of SM particle ≠ mass of SUSY partnerpartner

SUGRASUGRA GMSB GMSB AMSBAMSB BRANE MODELSBRANE MODELS

Number of free parameters is significantly Number of free parameters is significantly reduced !!!reduced !!!

Which is the right one ?

mSUGRAmSUGRAR-parity conserving, LSP is lightest neutralinoR-parity conserving, LSP is lightest neutralino

SCALAR MASS PARAMETERSCALAR MASS PARAMETER - - mm00

GAUGINO MASS PARAMETERGAUGINO MASS PARAMETER – – mm1/21/2

TRILINEAR COUPLINGTRILINEAR COUPLING – – AA00

RATIO OF THE HIGGS VACUM EXPECTAION RATIO OF THE HIGGS VACUM EXPECTAION VALUESVALUES – – tan(tan(ββ))

HIGGS MASS PARAMETERHIGGS MASS PARAMETER – – sign(sign(μμ))

Parameters atPlanck scale

Parameters atEW scale

SUSY masses, BR, decays

RGE

““SNOWMASS POINTS AND SNOWMASS POINTS AND SLOPES”SLOPES”

- new set of benchmark points - new set of benchmark points --

PointPoint mm0 0 mm1/2 1/2 AA0 0 tan(tan(ββ) ) sign(sign(μμ))1a 100 250 -100 10 1a 100 250 -100 10 + +

1b 200 400 0 30 1b 200 400 0 30 + +

2 1450 300 0 10 2 1450 300 0 10 + +

3 90 400 0 10 3 90 400 0 10 + +

4 400 300 0 50 4 400 300 0 50 + +

5 150 300 -1000 5 5 150 300 -1000 5 + +

SPS SPS 5 5

SUSY massesSUSY masses

heaviest

lightest

light stop

SUSY decaysSUSY decays

gluinos decays strongly

squarks decay weakly

stop alwaysdecay to

SUSY productionSUSY production

For L=30 fb-1 , N=1.2 x 106 SUSY events

Squark and gluino production dominate

KINEMATIC KINEMATIC ENDPOINTSENDPOINTS

RPC models missing LSP , RPC models missing LSP , invariant mass formed from final invariant mass formed from final state particles has no peaksstate particles has no peaks

Relativistic kinematics Relativistic kinematics invariant masses have maximums invariant masses have maximums and minimums (kinematic endpoints ) and minimums (kinematic endpoints ) which are function of SUSY masses. which are function of SUSY masses. From endpoints measuremnets SUSY From endpoints measuremnets SUSY masses can be extracted.masses can be extracted.

ExampleExample C Q + B, B P + AC 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 Characteristics of SUSY eventsevents

Large missing transverse energy ELarge missing transverse energy ET T miss miss

High pHigh pTT jets jets Large multiplicity of jetsLarge multiplicity of jets Large Large

MMeffeff= E= ET T miss miss + + ppT T (j(j11) + p) + pT T (j(j22) + p) + pT T (j(j33) + p) + pT T

(j(j44) )

- SM background reduced by hard - SM background reduced by hard kinematicskinematics

- large SUSY background - large SUSY background

MONTE CARLOMONTE CARLO

ISAJET 7.64ISAJET 7.64 HERWIG 6.5HERWIG 6.5 ATLFASTATLFAST Generated:Generated:

- 300 fb- 300 fb-1-1 of SUSY events of SUSY events

- 10- 10 fbfb-1-1 of top-antitop of top-antitop pairspairs

LEFT SQUARK CASCADE LEFT SQUARK CASCADE DECAYDECAY

Left squark productionLeft squark production:: directly or from gluino decaydirectly or from gluino decay

Event signatureEvent signature::- 2 SFOS leptons (natural - 2 SFOS leptons (natural

trigger)trigger)

high phigh pTT jet from left squark jet from left squark decaydecay

- large missing transverse - large missing transverse energyenergy

- one more high high p- one more high high pTT jet jet fromfrom

the decay of squark/gluino the decay of squark/gluino produced with left squark produced with left squark

644 226

191

119

ENDPOINTSENDPOINTS

Final state particlesFinal state particles: : ll+ + , l, l- - , q, q

Invariant masses: lInvariant masses: l++ll- - , , ll++ll- - q , lq , l±±q q

5 ENDPOINTS5 ENDPOINTS - l- l++ll- - maximum maximum - l - l ++ll-- q maximum q maximum - l - l ++ll-- q minimum q minimum - maximum for larger l- maximum for larger l±± q mass q mass - maximum for smaller l- maximum for smaller l±± q mass q mass

ENDPOINTS ARE FUNCTION OF 4 ENDPOINTS ARE FUNCTION OF 4 SUSY MASSESSUSY MASSES

GeV93.4

511 GeV

GeV

320 GeV

470 GeV

225 GeV

lepton and quark masses were neglected while deriving formulas

EVENT SELECTIONEVENT SELECTION EET T miss miss > 100 Gev> 100 Gev n(jet) ≥ 4 n(jet) ≥ 4 ppT T (j(j11) > 150 GeV, p) > 150 GeV, pT T (j(j22) > 100 GeV, ) > 100 GeV, ppT T (j(j3 3 , j, j44) > 50 GeV) > 50 GeV 2 SFOS leptons (e2 SFOS leptons (e++ee-- , , μμ++μμ- - ) with ) with ppT T > 10 GeV > 10 GeV + additional cuts for every + additional cuts for every

distributionsdistributions

SM background is negligible !!!

SUSY BACKGROUNDSUSY BACKGROUNDbackground : SFOS leptons from two background : SFOS leptons from two

independent decaysindependent decays

SFOS-OFOS subtraction removes background, SFOS-OFOS subtraction removes background, applied onapplied on

all mass distributionsall mass distributions

N(SFOS)=N(OFOS), identical shape of mass distributions

SFOS-OFOS

ll invariant mass

SFOS

OFOS

Mll (GeV) Mll (GeV)

FITTED ENDPOINTSFITTED ENDPOINTS

llq llq

lq high

ll

lq low M(GeV) M(GeV)

M(GeV)

M(GeV) M(GeV)

L=300 fb-1

FIT RESULTSFIT RESULTS

ENDPOINTENDPOINT THEORYTHEORY FIT FIT STATISTIC STATISTIC SYSTEMATICSYSTEMATIC

ERRORERROR ERRORERROR

ll max 93.40 93.85 ll max 93.40 93.85 0.07 0.090.07 0.09

llq max 511 525 11 llq max 511 525 11 5 5

lqlqhighhighmax 470 472 1 max 470 472 1 5 5

lqlqlow low max 320 326 7 max 320 326 7 3 3

llq min 225 225 4 llq min 225 225 4 2 2

1% for jets,

0.1% for leptons

up to 2%Good agreement between theory

and fit

Energyscale errorFit error

MASS MASS RECONSTRUCTIONRECONSTRUCTION

5 endpoint measurements and 4 unknown masses 5 endpoint measurements and 4 unknown masses over constrained over constrained

system of equations is solved numerically by minimising system of equations is solved numerically by minimising χχ22

Only one set of endpoint measurement, one set of SUSY Only one set of endpoint measurement, one set of SUSY massesmasses

ansambl of endpoint set of measurements is modeled, ansambl of endpoint set of measurements is modeled, mass distributions mass distributions

Endpoints are function of SUSY masses

Modeled experimental endpoint value

Random numbers

RECONSTRUCTED RECONSTRUCTED MASSESMASSES

NEUTRALINO 1 LEFT SQUARK

M(GeV) M(GeV)

EN

TR

IES

EN

TR

IES

RESULTSRESULTS

Particle mParticle mnomnom (GeV) m (GeV) mrecrec(GeV) (GeV) σσ (GeV) (GeV)

σσ/m/mrecrec

neutralino 1 neutralino 1 119 116 119 116 33 28%33 28%

right slepton right slepton 191 186 191 186 33 18%33 18%

neutralino 2 neutralino 2 226 223 226 223 33 15%33 15%

left squark left squark 644 639 644 639 51 8% 51 8%

calculated value

reconstructed mean

value

ANSAMBL OF 1000 EXPERIMENTS

LIGHT STOP SQUARKLIGHT STOP SQUARK Mixture of left and right stopMixture of left and right stop Mass: 236 GeVMass: 236 GeV Higgs mass depends on stop Higgs mass depends on stop

massmass Production: Production:

Decay: Decay:

STOP PAIRSSTOP PAIRS

50% of all SUSY 50% of all SUSY productionproduction

2 low p2 low pT T b quarks b quarks No detectable signal !!!No detectable signal !!!

< pT(b) > =15 GeV

pT (GeV)

236 226

En

trie

s

tb + Etb + ETmiss Tmiss channelchannel

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 TOP-BOTTOM ENDPOINTENDPOINT

Maximum occurs for bottom and top back to back in the stop rest fr.

2552 GeV2

4622 GeV2

Maximum occurs for bottom and top back to back in the sbottom rest frame

Decay (1)

Decay (2)

M(tb) from HERWIGM(tb) from HERWIG

M (GeV)

Eve

nts

/4 G

eV

(1)

(2)

(3)

Event signatureEvent signature low plow pT T b quark from b quark from

stop stop b quark from top b quark from top

decaydecay two light (u,d,s,c,) two light (u,d,s,c,)

quarks from W decayquarks from W decay high phigh pT T quark from quark from

left/right squark left/right squark produced with gluinoproduced with gluino

LSP from chargino LSP from chargino decay and large decay and large missing energymissing energy

EVENT SELECTIONEVENT SELECTION

EET T miss miss > 200 GeV> 200 GeV

nnjet jet ≥ 3 ( ≠ b, τ jets),

ppTT > 30 GeV, | > 30 GeV, |ηη|<3 , |<3 , ppT T (j(j11) > ) > 300 GeV300 GeV

n(b jet)=2n(b jet)=2

30< p30< pT T (b(b11) <150 GeV, 30< p) <150 GeV, 30< pT T (b(b22) ) <50 GeV<50 GeV

no leptonsno leptons

TOP-BOTTOM MASS TOP-BOTTOM MASS RECONSTRUCTIONRECONSTRUCTION

Excluding jExcluding j1 1 , jj →, jj → :|m:|mjjjj - m - mWW |< 15 |< 15 GeVGeV

bjj minimizing | mbjj minimizing | mbjjbjj - m - mtt| + p| + pTT(b(b’ ’ ) < 50 ) < 50 GeVGeV

Scaling mScaling mjjjj = m = mW W ,, mmbjj bjj recalculated, recalculated,

|m|mbjjbjj - m - mtt |< 30 |< 30 GeVGeV

mmbjj bjj + b jet + b jet → m→ mtbtb

ΔΔR(tb) < 2R(tb) < 2

‘‘Sideband’ subtractionSideband’ subtraction

SIDEBAND METHODSIDEBAND METHOD

Some jj pairs Some jj pairs accidentallyaccidentally

have masses in W zonehave masses in W zone

W :|mW :|mjjjj - m - mWW |< 15 |< 15 GeVGeV

A :| mA :| mjjjj – (m – (mWW -30)| <15 -30)| <15 GeVGeV

B :| mB :| mjjjj – (m – (mWW +30)| <15 +30)| <15 GeVGeV

W-0.5(A+B) W-0.5(A+B) subtractionsubtraction

A W B

jj mass

M(GeV)E

ven

ts/5

GeV

/300 f

b-1

TOP MASSTOP MASS

L=300 fb-1

TOP-BOTTOM MASSTOP-BOTTOM MASS

L=300 fb-1

W 0.5(A+B)

signal W-0.5(A+B)

M(tb) shapeM(tb) shape

linear part forbackgroundgaus smeared triangular

shape

M(tb) FITM(tb) FIT

M(tb)fit = 258.7 ± 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

CONCLUSIONCONCLUSION

If SUSY particles with SPS5 If SUSY particles with SPS5 characteristics characteristics

exist, it will be possible to:exist, it will be possible to:

- identify SUSY particles- identify SUSY particles

- reduce SM and SUSY - reduce SM and SUSY backgroundbackground

- measure SUSY masses- measure SUSY masses

with ATLAS detector at LHCwith ATLAS detector at LHC