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SPS5 SUSY STUDIES AT ATLAS. Iris Borjanovic Institute of Physics, Belgrade. SUPERSYMMETRY. EXTENSION of the SM EVERY SM PARTICLE HAS ITS SUSY PARTNER UNIFICATION OF ALL INTERACTIONS SUSY IS BROKEN IF EXIST AT THE TeV SCALE IT IS LIKELY TO BE DISCOVERED AT LHC. MSSM. SPIN 0. SPIN 1/2. - PowerPoint PPT Presentation
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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