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PPT – SUSY at the LHC PowerPoint presentation | free to download - id: 7645f8-YzliN

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Alan Barr

Just find SM Higgs

Was it reallySUSY?

How can we discovery SUSY at LHC?

What can we sayabout what wevefound?

Your mission

SM

SUSY

quarks (LR)leptons (LR) neutrinos (L?)

squarks (LR)sleptons (LR)sneutrinos (L?)

Spin-1/2

Spin-0

AfterMixing

?Z0 W gluon

BinoWino0Wino gluino

BW0

Spin-1

4 x neutralino

Spin-1/2

gluino

h0 H0 A0 H

H0H

2 x chargino

Spin-0

Extended higgs sector (2 doublets)

Features of RP SUSY?

Production part

standard

2 exotics

Time

- RPV as a conserved QN
- Events build from blobs with 2 exotic legs
- A pair of cascade decays results
- Complicated end result

General features

- Complicated cascade decays
- Many intermediates
- Typical signal
- Jets
- Squarks and Gluinos
- Leptons
- Sleptons and weak gauginos
- Missing energy
- Undetected LSP
- Model dependent
- Various ways of transmitting SUSY breaking from a

hidden sector

typical susy spectrum(mSUGRA)

LHC Pt5

What do we see?

Lifetimes short -gt look for Standard Model decay

relics missing energy

Example of a search topology

LSP

q

squark

q

_

q

_

BACKGROUND topology (QCD)

q

(and similar)

LSP

- No unique choice of sensitive topology
- Complementary information/sensitivity
- Expect SM backgrounds with similar

characteristics to signal - Need to search for excesses

SIGNAL topology

Practical Problems

- See only SM decay products
- Expect short lifetimes
- Lose information about order of decays
- Jets (other than b and t) indistinguishable
- Loose flavour information for other squarks
- Missing momentum from neutralinos only

determined perpendicular to beam - Individual LSP momenta not individually

measurable - Z-momentum of initial state unknown (PDFs)
- Cant reconstruct from final state
- Forward jets lost down beam pipe
- Cant form invariant masses of sparticles
- No clean mass peaks for resonances

Precise measurement of SM backgrounds the problem

Rediscover

Lower backgrounds

- SM backgrounds are not small
- There are uncertainties in
- Cross sections
- Kinematical distributions
- Detector response

WW

ZZ

Discover

Higher backgrounds

Just look for jets?

Big QCD background

Scalar sum of transverse energy / GeV

Add some missing energy

- Look for events with jets and missing energy
- Cuts
- at least two jets with
- ETJet1,2 gt 150,100 GeV
- ?Jet1,2 lt 2.5

Meff ?Jets pTi MET

- But with addition of some other cuts
- ? Missing transverse momentum gt 100

GeV - ? cuts based on ??i ?(Jet,i)-?(MET))
- R1 ?(??22(?-??1)2) gt 0.5 rad
- R2 ?(??12 (?-??2)2) gt 0.5 rad
- no jet with ??i lt 0.5 rad

QCD dijets

Kill events with missing energy from

miss-measured jets

SUSY

No MT2Dijet cuts MET ??

Two-Jet

Scalar sum of transverse energy / GeV

Expect discovery distribution to be of something

like this form Excess of some sort of new

physics about SM backgrounds.

Importance of detailed detector understanding

Et(miss)

Lesson from the Tevatron

- GEANT simulation already shows events with large

missing energy - Jets falling in crack region
- Calorimeter punch-through
- Vital to remove these in missing energy tails
- Large effort in physics commissioning

Rare occurrences hurt

Inclusive reach in mSUGRA parameter space

- Map of discovery potential corresponding to a 5s

excess above background in mSUGRA m0 m1/2

parameter space for the ATLAS experiment.

L 1033 cm-2 s-1

jets ETmiss channel

1 year ? 2200 GeV

1 month ? 1800 GeV

few days (lt one week) ? 1300 GeV

Health warning expecting SUSY discovery in a

few days will seriously damage your credibility

Different searches

- We will be looking in many different channels
- n jets m leptons missing energy
- - b-jets (common at large tan ß)
- - tau-jets ( )
- Charged stable particles
- NLSP -gt photon gravitino (GMSB)
- R-parity violating modes
- R-hadrons

What might we then know?

- Can say some things
- Undetected particles produced
- missing energy
- Some particles have mass 600 GeV, with

couplings similar to QCD - Meff cross-section
- Some of the particles are coloured
- jets
- Some of the particles are Majorana
- excess of like-sign lepton pairs
- Lepton flavour conserved in first two

generations - e vs mu numbers
- Possibly Yukawa-like couplings
- excess of third generation
- Some particles contain lepton quantum numbers
- opposite sign, same family dileptons

- Assume we have MSSM-like SUSY with

m(squark)m(gluino)600 GeV - See excesses in these distributions
- Cant say we have discovered SUSY

Slide based on Polesello

Mapping out the new world

LHC Measurement SUSY Extra Dimensions

Masses Breaking mechanism Geometry scale

Spins Distinguish from ED Distinguish from SUSY

Mixings, Lifetimes Gauge unification? Dark matter candidate? Gauge unification? Dark matter candidate?

- Some measurements make high demands on
- Statistics (gt time)
- Understanding of detector
- Clever experimental technique

Constraining masses

Frequently- studieddecay chain

- Mass constraints
- Invariant masses in pairs
- Missing energy
- Kinematic edges

Observable

Depends on

Limits depend on angles betweensparticle decays

Mass determination

Measure edges

Try various masses in equations

Variety of edges/variables

- Basic technique
- Measure edges
- Try with different SUSY points
- Find likelihood of fitting data
- Event-by-event likelihood
- In progress

C.G. Lester

- Narrow bands in ?M
- Wider in mass scale
- Improve using cross- section information

SUSY mass measurements

Tryvariousdecaychains

- Extracting parameters of interest
- Difficult problem
- Lots of competing channels
- Can be difficult to disentangle
- Ambiguities in interpretation
- Lots of effort has been made to find good

techniques

Look forsensitive variables (many of them)

Extractmasses

SUSY mass measurements

- LHC clearly cannot fully constrain all parameters

of mSUGRA - However it makes good constraints
- Particularly good at mass differences O(1)
- Not so good at mass scales
- O(10) from direct measurements
- Mass scale possibly best measured from

cross-sections - Often have gt1 interpretation
- What solution to end-point formula is relevant?
- Which neutralino was in this decay chain?
- What was the chirality of the slepton ?
- Was it a 2-body or 3-body decay?

SUSY spin measurements

- The defining property of supersymmetry
- Distinguish from e.g. similar-looking Universal

Extra Dimensions - Difficult to measure _at_ LHC
- No polarised beams
- Missing energy
- Indeterminate initial state from pp collision
- Nevertheless, we have some very good chances

Measuring spins of particles

- Basic recipe
- Produce polarised particle
- Look at angular distributions in its decay

spin

?

Revisit Typical sparticle spectrum

Left Squarks-gt strongly interacting -gt large

production -gt chiral couplings

LHC point 5

?20 neutralino2gt (mostly) partnerof SM W0

Right slepton(selectron or smuon) -gt

Production/decay produce lepton -gt chiral

couplings

Right slepton(selectron or smuon) -gt

Production/decay produce lepton -gt chiral

couplings

mass/GeV

?10 gt Stable -gt weakly interacting

?10 neutralino1gt Stable -gt weakly interacting

Some sparticles omitted

Spin projection factors

P

S

Chiral coupling

Approximate SM particles as massless -gt okay

since m p

Spin projection factors

P

S

S0

S

Spin-0

Produces polarised neutralino

Approximate SM particles as massless -gt okay

since m p

Spin projection factors

Fermion

?

p

S

Scalar

Polarisedfermion

Approximate SM particles as massless -gt okay

since m p

Spin projection factors

P

mql measure invariant mass

S

?

p

S

Approximate SM particles as massless -gt okay

since m p

lnearq invariant mass (1)

Back to backin ?20 frame

quark

Probability

?

l

lepton

Phase space

Invariant mass

l-

m/mmax sin ½?

- Phase space -gt factor of sin ½?
- Spin projection factor in M2
- lq -gt sin2 ½?
- l-q -gt cos2 ½?

Production Asymmetry

Twice as much squark as anti-squark pp collider ?

Good news!

Squark

Anti-squark

Note opposite shapes in distributions

After detector simulation (ATLFAST)

Change in shape due to charge-blind cuts

l-

parton-level 0.6

Events

Charge asymmetry,

spin-0

SUSY

l

detector-level

Invariant mass

-gt Charge asymmetry survives detector

simulation-gt Same shape as parton level (but

with BG and smearing)

? detector effects ? cuts to greatly reduce

SM

Interesting questions

- Can we test gaugino universality?
- Can we constrain the neutralino mass mixing

matrix? - Can we measure sparticle splittings?
- JMR Htt coupling interesting
- Can we predict/confirm dark matter density?
- Can we measure mass scale to better than 10
- Precision measurement/prediction for

cross-sections? - Can we confirm spin(s)?

Extras

Standard Model backgrounds measure from LHC DATA

Measure in Z -gt µµ

Use in Z -gt ??

R Z -gt nn B Estimated

- Example SUSY BG
- Missing energy jets from Z0 to neutrinos
- Measure in Z -gt µµ
- Use for Z -gt ??

- Good match
- Useful technique
- Statistics limited
- Go on to use W gt µ? to improve

W contribution to no-lepton BG

Oe, Okawa, Asai

- Use visible leptons from Ws to estimate

background to no-lepton SUSY search

Normalising not necessarily good enough

Distributions are biased by lepton selection ?

Need to isolate individual components

Then possible to get it right

Similar story for other backgrounds control

needs careful selection

Direct slepton spin determination

- Spin important in slepton production
- Occurs through s-channel spin-1 process only
- Characteristic angular distribution in production

Distributions _at_ parton level

Parallel

Parallel

Perpendicularto beam

redUED

- Spin-0
- SUSY
- Sleptons
- perpendicular to beam
- Spin-½
- UED
- KK leptons
- parallel to beam

bluePS

stotal not to scale

blackSUSY

Sensitive variables?

- cos ?lab
- Good for linear collider
- Not boost invariant
- Missing energy means Z boost not known _at_ LHC
- Not sensitive _at_ LHC
- ??
- Boost invariant
- Sensitive
- Not easy to compare with theory
- cos ?ll
- 1-D function of ??
- All benefits of ??
- Interpretation as angle in boosted frame
- Easier to compare with theory

(A)

(B)

boost

(C)

N.B. ignores azimuthal angle

Some results

- SPS5 point
- Below spectrum
- Right results
- Good stat. discrimination

Data inclusive SUSY after cuts