Vadym Zhuravlov

ATLAS MDT seminar 27 Nov 2007

Contents:

1.Introduction: what is SUSY and why SUSY2.Models, points, spectra3.Quasi-stable NLSP4.Missing Et signature5.Background6.Spin measurement7.Conclusion

•A symmetry which relates bosons and fernions and represented by operator

Q |BOSON> = |FERMION> and Q |FERMION> = |BOSON>

• Generalization of Poincare algebra links together representation with different spin

{Q Q} = 2σ P

• Q does not change the particle quantum numbers, except spin

• Even if there is no “WHY” still there is a question:

why there are two classes of particles in nature – bosons and fermions

• Invented more then 30 years ago and still not discovered ( Higgs also)

• Provides unification of gauge coulings: (requires SUSY masses below few TeV)

• Provides a good candidate for Dark Matter – lightest neutralino (R-parity is conserved)

ΔMHiggs ~ log Λ

ΔMHiggs ~ Λ2

ΔMHiggs ~ Λ• Solves “hierarchy” problem SM is effective theory at E<<Λ (~1019 GeV)

MHiggs(tree level) ~ 1038 GeV

Fine tuning needed!“Not natural…”

SUSY: = 0

Barnett Newman “Broken Obelisk”

SUSY fields and particles

•SM: 28 bosonic and 96 fermionic DOF – highly non-supersymmetric! •Fields -> superfields• 2 complex Higgs fields: h, H, A, H+, H- tanb = V1/V2

MSSM – 124 parameters.

SUSY is a broken symmetry.

• Non of MSSM fields can develop non-zero VEV to break SUSY. Hidden sector where SUSY is broken.

• Messenger: transmit broken SUSY to visible sector.

1. Gravity mediated SUSY breaking: gravitino mass ~ EW mass

mSUGRA parameters: m0, m1/2, A0, tanb, sign(m)1. Gauge mediated SUSY breaking: messinger sector

consists of particles with SU(3)xSU(2)xU(1) quantum numbers

2. Gaugino mediation: SUSY is broken in another brane.

Our braneHidden

sector

BULK

gaugino

R = (-1)3(B-L)+2s

“+” for ordinary particles“-” for supersymmetrical partners

If R-parity is conserved, SUSY-particles are created in pairs, LSP is stable

Under R-parity the lepton and barion numbers are conserved

Rule to create SUSY Feynman vertex: take SM vertex and replace 2 legs by super-legs

GeV

Renorm. GroupEquations

Ellis et al. hep-ph/0303043

tanβ=10, μ>0

Old constrain0.1 < Ώh2 < 0.3

New constrain0.094 < Ώh2 <

0.129Favorite by g-2

STAU is NLSP

excluded by b→sγ

excluded by LEP

'Bulk' region: t-channel slepton exchange - LSP mostly Bino. 'Bread and Butter' region for LHC Expts.

'Focus point' region: significant h component to LSP enhances annihilation to gauge bosons

Slepton Co-annihilation region: LSP ~ pure Bino. Small slepton-LSP mass difference makes measurements difficult.

SUSY Dark Matter

Quasi- stable STAU

Production:

10 fb-1 Mτ = 160 GeV tanβ=10340 STAUs

Experimental signatures:

1. Lifetime > 10-8 : slow muon-like particle

2. 10-10 < Lifetime < 10-8 : kink tracks

3. Lifetime < 10-10 : muons with large impact parameter

A.Gladyshev hep-ph/0509168

• A charged particle passing the MDT will leave clusters of ionized atoms

• The electrons drift to the wire in the center of each tube

• The radius from which the electrons drift to the wire is calculated from a time measurement

• t0 is estimated for a muon traveling at the speed of light

• The segment is tangent to the radii

• Some hits from “noise” are ignored

t0

tmeasured=t0+tdriftR=R(tdrift)=R(tmeasured-t0)

tdrift

Segment reconstruction

S. Bressler

• The long time window of the MDT guarantees that data of low particles will be saved.

• The measured hit radius is incorrect

• We want to estimate t

• Larger radii result in

• Badly fitted segment

• Wrong direction of segment

t0(slow particle)

=t0+ttmeasured=t0+t+tdri

ft

Rmeasured = R(tmeasured-t0) = R(tdrift+t) > R

tdrift

Segment reconstruction

S. Bressler

• Relies on long time window of MDT and BCID from ID

• Identify penetrating particle by associating muon hits and segments with extrapolated ID track

• Loop over possible t

• Change MDT digits’ time and hence radii

• Create MDT segments from the re-timed digits• Estimate t0 (TOF) from the t that minimizes the 2

• Include information from segmentsin trigger chambers• RPC tof

• TGC direction

• Calculate and M

S. Bressler

misal1_mc12.005414.GMSB5_jimmy.susy.digit.RDO.v12000502part of MuGirl

M=P/βγ

Hiroshi Nomoto

0-lepton mode

MET > 100 GeV1 jet with Pt>100 GeV4 jets with pt>50 GeVTransv. Spher. > 0.2

1-lepton mode

MET > 100 GeV1 jet with Pt>100 GeV4 jets with pt>50 GeVTransv. Spher. > 0.2m or e pt > 20 GeV

2-lepton mode

MET > 100 GeV1 jet with Pt>100 GeV4 jets with pt>50 GeV2 m or e pt>20 GeVTransv. Spher. > 0.2

TDR cuts – 10 years old!!!

pg

Lq 02

R

01

qq

no interaction with detector ET,miss

qX

Meff = Sjjets|Pt| + Et miss correlated to MSUSY

MSUSY = SMisi / Ssi

ATLAS TDR

S/B = 10S/B = 2

Matrix Element calculation VS Parton Showering

No lepton mode

Estimate background from data

Bad knowledge of:

• Underlined Event

• Cross-sections

• Parton Distribution Functions

• Detector Calibration (jets, MET)

• statistics of Monte Carlo

QCD Background

• Two main sources:– fake ET

miss (gaps in acceptance, dead/hot cells, non-gaussian tails etc.)

– real ETmiss (neutrinos from b/c quark decays)

• Simulations require detailed understanding of detector performance (not easy with little data).

• Huge cross-section – need of Fast Shower Simulation

• Estimate background using data: jet smearing function

Pythia dijets

SUSY SU3

QCD Background• Step 1: Measure jet smearing function from data

– Select events: ETmiss > 100 GeV, (ET

miss, jet) < 0.1

– Estimate pT of jet closest to EtMiss as

pTtrue-est = pT

jet + ETMiss

• Step 2: Smear low ETmiss multijet events with

measured smearing function

MET

jets

fluctuatingjet

Njets >= 4, p

T(j1,j2) >100GeV,

pT(j3,j4) > 50GeV

ETmiss

NB: error bars expected errors on background.

ATLAS

Preliminary

ATLAS

Preliminary

No lepton channel: Z→νν background

Get Z from Zee, what are the steps :1. Take Zee events2. Correct for electron identification efficiency (measured with real data)3. Correct for acceptance cuts (with MC)4. Get Z distributions

Below is the formula summarizing the different steps :

)(

)())(())((

),(),(

))(()(

2,21,1 eeZBr

ZBrZPCZPC

PeffPeff

ZPNMETN TFiducialTKin

TT

TRawCorr

20.00%

3.36%

Z MET distribution

Correct for electron id efficiency (measured with data)factor 2

# branching ratios from PDGFactor 6

Correct for kinematics cuts (PT(lept) > 20 GeV/c) from MC20%

Correct for fiducial cuts (|(lept)| < 2.5) from MC15%

Background: ttbar -> lnln (one l is missing) and ttbar -> qqbar ln

How to get rid of semi-leptonic ttbar background?

MT (GeV) MT (GeV)

bbqql bbll

Transverse mass: Minv(Missing Pt and PtLepon)

W mass

di-leptonic ttbar: decay resimulation

1. Select pure biased di-leptonic ttbar sample: small MET (no susy signal) – seed events

2. Reconstruct kinematics. How? → coming soon

3. resimulate top decay (as many times as needed) and count events with large MET

no susy with susy

Background: ttbar->bblnln Bbqqln with second lepton from b/c decay

dileptonic ttbar background: clean bb lνlν sample

Clean di-leptonic ttbar sample

Missing ET

Number of pairs

Background in D = A x C/B

A

B C

D

N_pairs = 0

N_pairs > 0

No strong correlation between MET and N_pairs

ttbar background for 2 lepton search

background+

SUSY

1 lepton search: main background – dileptonic top.Why one lepton is missing?

• it is tau. Take one of the leptons of clean di-leptonic ttbar sample and replace it by tau. Decay tau and see what happens – change of MET, Njets, nLeptons. • it miss-identified. Drop on the two leptons of clean di-leptonic sample, re-weight events by miss-identification efficiency

Inclusive reach in mSUGRA parameter space

Reach sensitivity only weakly depends on tanb, A0 and m

SUSY spin measurement

ll

llA

Spin-0 flat

•If SUSY signals are observed at the LHC, it will be vital to measure the spins of the new particles to demonstrate that they are indeed the predicted super-partners•Angular distributions in sparticle decays lead to charge asymmetry in lepton-jet invariant mass distributions. The size of the asymmetry is proportional to the primary production asymmetry between squarks and anti-squarks

•charge asymmetry of lq pairs measures spin of c0

2

•shape of dilepton invariant mass spectrum measures slepton spin

Spin-½, mostly winoSpin-0

Spin-½

Spin-0

Spin-½, mostly bino

Polarise

MeasureAngle

stransverse mass

Transverse mass Mt– endpoint is a mass of decaying particle (W)Stransverse mass Mt2– endpoint is a mass of c

stransverse mass – direct slepton production

Signature: two opposite sign same flavor leptons and missing Et

Endpoint of stransverse mass is a function of mass difference of slepton and LSP

MT2

Other topics:

1. R-hadrons2. Tau-signatures3. Gaugino direct production4. Study of gauge-mediated SUSY5. R-parity violating processes6. Spectroscopy

Conclusion:

• LHC is last chance to discover SUSY• SM uncertainties in the BG estimation is a limiting factor• Many models, parameters, preferable points: lot of work

Backup slides

electri

“SUSY was invented more then 30 years ago and still not discovered”

but

Electron was invented more then 2 500 years before

Vision of Ezekiel… et a lumbis eius et sursum quasi aspectus splendoris ut visio