Map

Why look for SUSY?

What can we sayabout what we’vefound?

Anything unusual out there

Was it reallySUSY?

How

can

we

disc

over

SUSY

at LH

C?

Just find SM Higgs

Alan Barr

Dark Matter

• Atoms ~ 4%• Evidence for Dark Matter from

– Rotation curves of galaxies– Microwave background radiation– Galaxy cluster collision

Invisible mass

Visible mass

Particle physicists should hunt: Weakly Interacting, Stable, Massive Particles

Particle physicists should hunt: Weakly Interacting, Stable, Massive Particles

• If exotics can be produced singly they can decay– No good for

Dark Matter candidate

• If they can only be pair-produced they are stable– Only

disappear on collision (rare)

Producing exotics?

Time

standard

exotic

Time

standard

exotic

Time

standard

exotics

Time

standardexotics

Require an even number of exotic legs to/from blobs(Conserved multiplicative quantum number)

Require an even number of exotic legs to/from blobs(Conserved multiplicative quantum number)

How do they then behave?

• Events build from blobs with 2 “exotic legs”

• A pair of cascade decays results

• Complicated end result

• Events build from blobs with 2 “exotic legs”

• A pair of cascade decays results

• Complicated end result

Time

standard

2 exotics

Production part

Time

standard

heavyexotic lighter

exotic

Decay part Time

Complete event

= exotic= standard

Candidates?• New particles by a

symmetry:– Supersymmetry

• Relationship between particles with spins differing by ½h

– Spatial symmetry

• With extra dimensions

– Gauge symmetry

• Extra force interactions (and often matter particles)

electron

quarks

exoticpartners?

Force-carriers

Related bysymmetry

Related bysymmetry

neutrino

x3x2

…?

…?

…?

Alreadyobserved

_

What is supersymmetry?• Nature permits

various only types of symmetry:– Space & time

• Lorentz transforms• Rotations and

translations– Gauge symmetry

• SU(3)c x SU(2)L x U(1)– Supersymmetry

• Anti-commuting (Fermionic) generators

• Relationship with space-time

• Consequences:– Q(fermion)=boso

n– Q(boson)=fermio

n

• Equal fermionic and bosonic DF– Double particle

content of theory– Partners not yet

observed– Must be broken!

• Otherwise we’d have seen it

{Q,Q†} = -2γμPμ

Why SUSY?• Higgs mass2

– Quadratic loop corrections

– In SM natural scale• Λcutoff ~ Mplanck • v. high!

– Need m(h) near electroweak scale• Fine tuning• Many orders of

magnitude

top

Δm2(h) Λ2cutoff

higgs higgs

stop

higgs higgs

• Enter SUSY– 2 x Stop quarks– Factor of -1 from

Feynman rules– Same coupling, λ– Quadratic

corrections cancel

λλλ λ

What does SUSY do for us?• Coupling of stop to

Higgs– RGE corrections – Make mHH coupling

negative– Drives electro-weak

symmetry breaking

• Predicts gauge unification– Modifies RGE’s– Step towards

“higher things”

stop

higgs higgs

+SUSY

Log10 (μ / GeV)

Hit!

1/α

Extended higgs sector(2 doublets)

(S)particles

SM SUSY

quarks (L&R)leptons (L&R) neutrinos (L&?)

squarks (L&R)sleptons (L&R)sneutrinos (L&?)

Z0

W±

gluon

BW0

h0

H0

A0

H±

H0

H±

4 x neutralino

2 x chargino

AfterMixing

gluino

Spin-1/2

Spin-1

Spin-0

Spin-1/2

Spin-0

BinoWino0

Wino±

gluino

~

~

Proton on Proton at 14 TeV

40 million bunch crossings/minute

Something to see it with

General featuresMass/GeV

“typical” SUSY spectrum(mSUGRA)

• 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

SUSY event

Jets

Missing transverse momentum

LeptonsHeavy quarks

Cross-sections etc

Lower backgrounds

Higher backgrounds

“Rediscover”

“Discover”

ZZ

WW

Discovering SUSY with jets

• Select a small number of high PT jets– Large signal cross-section– Large control statistics– Relatively well known SM

backgrounds• Relatively “model independent”

– Does not rely on leptonic cascades– Does not rely on hadronic cascades

SIGNAL topology

BACKGROUND topology (QCD)

Importance of detailed detector understanding

Lesson from the Tevatron

Et(miss)

Geant simulation showingfake missing energy

Suppressing backgrounds

QCD SUSY

Jet

Jet

Remove events with missing energy back-to-back with leading jets

Measuring Backgrounds

• Example: SUSY BG– Missing energy + jets

from Z0 to neutrinos– Measure in Z -> μμ– Use for Z ->

• Good match– Useful technique

• Statistics limited– Go on to use W => μ

to improve

Measure in Z -> μμ

Use in Z -> νν R: Z

B: Estimated

R: Z

B: Estimated

Di-jets + MET measurement

)2(j(2)TT

)1(j(1)TT

T)2()1(T2 ,,,max

minpppp

ppp

mmM

• Keeping it simple– >=2 jets

– ET (J1,2) > 150 GeV; |η1,2| < 2.5 Cambridge “Stransverse mass”

Dijet inclusive: - No lepton veto- No b-jet veto- No multi-jet veto

Dijet inclusive: - No lepton veto- No b-jet veto- No multi-jet veto

Discovering SUSY with leptons

• Particularly important if strongly interacting particles are heavy

Small Standard Model Backgrounds

Golden channel @ Tevatron

Top pair backgrounds

Leptons from b-decayscontribute to background

Use track isolation to reduce these

e

Again: measure the background

Measure this backgroundin same-sign leptons in semi-leptonic b-decays

After 10 fb-1

• Great discovery potential here…• Lots of other channels:

– M jets + N leptons + missing transverse energy

“Standard” SUSY point Very light SUSY point

signal

signal

mSUGRA A0=0, tan(b) = 10, m>0

mSUGRA A0=0, tan(b) = 10, m>0

Slepton Co-annihilation region

Slepton Co-annihilation region

‘Bulk’ region: t-channel slepton exchange

‘Bulk’ region: t-channel slepton exchange

‘Focus point’ region: annihilation to gauge bosons

‘Focus point’ region: annihilation to gauge bosons

WMAP constraints

Rule out with 1fb-1

Reach in cMSSM?

Mass scale?

Spectrum SUSY kinematicvariable“MTGEN”

ET sum / 2

What might we then know?• “Discovered supersymmetry?”• Can say:

– Undetected particles produced• missing energy

– Some particles have mass ~ 600 GeV, with couplings similar to QCD

• MTGEN & 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

Perhaps notwhat we think!

Mapping out the new world

• Some measurements make high demands on:– Statistics (=> time)– Understanding of detector– Clever experimental technique

LHC Measuremen

tSUSY

Extra Dimensions

MassesBreaking

mechanismGeometry &

scale

SpinsDistinguish

from EDDistinguish from SUSY

Mixings,Lifetimes

Gauge unification?Dark matter candidate?

Constraining masses• Mass constraints• Invariant masses in

pairs– Missing energy– Kinematic edges

Observable: Depends on:

Limits depend on angles betweensparticle decays

Frequently-studieddecay chain

Mass determination

• Basic technique– Measure edges– Try with different SUSY

points– Find likelihood of fitting

data

• Event-by-event likelihood– In progress

Measureedges

Variety of edges/variables

Try variousmasses in equations

• Narrow bands in ΔM• Wider in mass scale• Improve using cross- section information

SUSY mass measurements• 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

Tryvariousdecaychains

Tryvariousdecaychains

Look forsensitive variables

(many of them)

Look forsensitive variables

(many of them)

Extractmasses

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 scale• [O(10%) from direct measurements]• Mass scale possibly best “measured” from cross-

sections– Often have >1 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 @ LHC– No polarised beams– Missing energy– Indeterminate initial

state from pp collision

• Nevertheless, we have some very good chances…

Universal Extra Dimensions• TeV-scale universal extra

dimension model• Kaluza-Klein states of SM

particles– same QN’s as SM– mn

2 ≈ m02 + n2/R2

[+ boundary terms]– KK parity:

• From P conservation in extra dimension

• 1st KK mode pair-produced

• Lightest KK state stable, and weakly interacting

• First KK level looks a lot like SUSY

• BUT same spin as SM

hep-ph/0205314 Cheng, Matchev

Radius of extra dimension ~ TeV-1

KK tower of masses n=0,1,…

Dubbed “Bosonic Supersymmetry”

R

S1/Z2

Spin 2 particle: looks same after 180° rotation

SPIN 2

Spin 1 particle : looks same after 360° rotation

SPIN 1

Spin ½ particle : looks different after 360° rotation indistinguishable after 720° rotation

SPIN ½

Measuring spins of particles

• Basic recipe:– Produce polarised particle– Look at angular distributions in its decay

spinθ

Left Squarks-> strongly interacting-> large production-> chiral couplings

mass/G

eV

Revisit “Typical” sparticle spectrum

Some sparticles omitted

10

–> Stable-> weakly interacting

Right slepton(selectron or smuon)-> Production/decayproduce lepton-> chiral couplings

LHC point 5

20 = neutralino2

–> (mostly) partnerof SM W0

10 = neutralino1

–> Stable-> weakly interacting

Spin projection factors

Approximate SM particles as massless-> okay since m « p

Lq~Lq

02

~1

0Lq

P

S

Chiral coupling

Spin projection factors

Lq~Lq

02

~

1

0~ LqP

S

0

1~02 S

Σ=0

Spin-0

Produces polarised neutralino

Approximate SM particles as massless-> okay since m « p

Spin projection factors

Approximate SM particles as massless-> okay since m « p

(near) Rl

θ*p

SLq~

Lq

Rl

~02

~Rl

Scalar

Fermion

Polarisedfermion

Spin projection factors

Approximate SM particles as massless-> okay since m « p

(near) Rl

θ*p

S

Lq~Lq

Rl

~02

~Rl

mql – measureinvariant mass

1

0~ LqP

S

lnearq invariant mass (1)

m/mmax = sin ½θ*

Back to backin 2

0 frame

θ*

quark

lepton

Phase space -> factor of sin ½θ*Spin projection factor in |M|2: l+q -> sin2 ½θ* l-q -> cos2 ½θ*

l+

l-

Phase space

Pro

bab

ility

Lq~ Lq

Rl

~02

~Rl

Invariant mass

After detector simulation

l+

l- parton-level * 0.6

-> Charge asymmetry survives detector simulation-> Same shape as parton level (but with BG and smearing)

detector-levelInvariant mass

Ch

arg

e a

sym

metr

y,

spin-0

Even

ts

SUSY

Change in shapedue to charge-blind cuts

Distinguishing between models

Sin (θ*/2)

dP/d

Sin

(θ*/

2)

SU

SY

No spin

UniversalExtra Dim.

ql+ or ql-_

dP/d

Sin

(θ*/

2)

Sin (θ*/2)

No spin

UniversalExtra Dim.

SUSY

ql- or ql+

As expected, UED differsfrom all-scalar (no-spin)and from SUSY

As expected, UED differsfrom all-scalar (no-spin)and from SUSY

Smillie et al.

What else can we do?

Predict WIMP relic density

Measure the invisible particle mass(WIMP mass)

Measure couplings from rates and branching ratios

Summary

• Discovering something new is an important step– Need to understand backgrounds and detector

very well

• Finding out what we have discovered is even more interesting!– Masses Spins Branching Ratios

• These tell us about– SUSY vs Extra Dimensions– Dark Matter– Unification– SUSY breaking

Extras

How is SUSY broken?• Direct breaking in

visible sector not possible– Would require

squarks/sleptons with mass < mSM

– Not observed!• Must be strongly

broken “elsewhere” and then mediated– Soft breaking terms

enter in visible sector

– (>100 parameters)

Stronglybrokensector

Weakcoupling(mediation)

Soft SUSY-breaking termsenter lagrangianin visible sector

Various models offer different mediation

mSUGRA – “super gravity”• A.K.A. cMSSM• Gravity mediated SUSY

breaking– Flavour-blind (no FCNCs)

• Strong expt. limits– Unification at high scales

• Reduce SUSY parameter space– Common scalar mass M0

• squarks, sleptons– Common fermionic mass

M½• Gauginos

– Common trilinear couplings A0

• Susy equivalent of Yukawas

Programs includee.g. ISASUSY,SOFTSUSY

1016 GeV

EW scale

Iterate usingRenormalisationGroupEquations

Unification of couplings

Correct MZ, MW, …

Production AsymmetryTwice as much squark as anti-squark pp collider Good news!

Squark Anti-squark

Note opposite shapes in distributions

Other suggestions• Gauge mediation

– Gauge (SM) fields in extra dimensions mediate SUSY breaking

• Automatic diagonal couplings no EWSB

– No direct gravitino mass until Mpl

• Lightest SUSY particle is gravitino• Next-to-lightest can be long-lived (e.g. stau or neutralino)

• Anomaly mediation– Sequestered sector (via extra dimension)

• Loop diagram in scalar part of graviton mediates SUSY breaking

• Dominates in absence of direct couplings– Leads to SUSY breaking RGE β-functions

• Neutral Wino LSP• Charged Wino near-degenerate with LSP lifetime • Interesting track signatures Not

exhaustive!

R-Parity

• Unrestricted couplings lead to proton decay:

LHUDDLQDLLEWRPV )(21

L-violating B-violating L-violating

General softbreaking terms include:

Pro

ton

u

d

u u_

e-Λ”112 Λ’112

s~_ P

ion Unacceptably high rate compared

to experimental limits (proton lifetime > 1033 years)

Strong limits on products ofcouplings

• Impose RP = (-1)3B+L+2S (by hand)

– Distinguishes SM from SUSY partners– Leads to stable LSP

• Required for dark matter

– Sparticles produced in pairs

Gauge Mediated SUSY Breaking

• Signature depends on Next to Lightest SUSY Particle (NLSP) lifetime

• Interesting cases:– Non-pointing

photons– Long lived staus

• Extraction of masses possible from full event reconstruction

• More detailed studies in progress by both detectors

R-hadrons

• Motivated by e.g. “split SUSY”– Heavy scalars– Gluino decay through

heavy virtual squark very suppressed

– R-parity conserved– Gluinos long-lived

• Lots of interesting nuclear physics in interactions– Charge flipping, mass

degeneracy, …

• Importance here is that signal is very different from standard SUSY

R-hadrons in detectors• Signatures:

1. High energy tracks (charged hadrons)

2. High ionisation in tracker (slow, charged)

3. Characteristic energy deposition in calorimeters

4. Large time-of-flight (muon chambers)

5. Charge may flip• Trigger:

1. Calorimeter: etsum or etmiss

2. Time-of-flight in muon system

– Overall high selection efficiency– Reach up to mass of 1.8

TeV at 30 fb-1

GEANT simulation of pair of R-hadrons

(gluino pair production)

Method 2: Angular distributions in direct slepton pair production

SUSY : qq slepton pair

UED : qq KK lepton pair

Phase Space :

Normalised cross-sections

AJB hep-ph/0511115

Sensitive variables?• cos θlab

– Good for linear e+e- collider

– Not boost invariant• Missing energy means Z

boost not known @ LHC• Not sensitive @ LHC

• cos θll*– 1-D function of Δη:

– Boost invariant– Interpretation as angle

in boosted frame– Easier to compare with

theory

N.B. ignore azimuthal angleN.B. ignore azimuthal angle

boos

t)tanh()tan2cos(cos 211* 2

1

ell

AJB hep-ph/0511115

l1l2

θ2lab

θ1lab

cos θlab

l1l2η2

lab

η1lab

ΔηΔη

l1Δη

l2

θl*θl

*

cos θ*ll

Slepton spin – LHC pt 5

• Statistically measurable

• Relatively large luminosity required

• Study of systematics in progress– SM background

determination– SUSY BG

determination– Experimental

systematics

Slepton spin AJB hep-ph/0511115

“Data” = inclusive SUSY after cuts

Snowmass points

SPS4 – non-universal cMSSMLarger mass LSPSofter leptonsSignal lost in WW background

SPS4 – non-universal cMSSMLarger mass LSPSofter leptonsSignal lost in WW background

SPS1a, SPS1b, SPS5mSUGRA “Bulk” pointsGood sensitivity

SPS1a, SPS1b, SPS5mSUGRA “Bulk” pointsGood sensitivity

SPS3 sensitiveCo-annihilation point(stau-1 close to LSP)Signal from left-sleptons

SPS3 sensitiveCo-annihilation point(stau-1 close to LSP)Signal from left-sleptons

Analysis fails in “focus point”region (SPS2). No surprise:Sleptons > 1TeV no xsection

Analysis fails in “focus point”region (SPS2). No surprise:Sleptons > 1TeV no xsection

Slepton spin AJB hep-ph/0511115

Statistical significance of spin measurementLHC design luminosity ≈ 100 fb-1 / year

Statistical significance of spin measurementLHC design luminosity ≈ 100 fb-1 / year

Smillie, Webberhep-ph/0507170

See also:Battaglia, Datta,De Roeck,Kong, Matchevhep-ph/0507284

SUSY vs UED: Helicity structure

• Both prefer quark and lepton back-to-back– Both favour large

(ql-) invariant mass

• Shape of asymmetry plots similar

Neutralino spin

SUSY case

UED case

Neutralino spin Smillie, Webberhep-ph/0507170

• For UED masses not measureable– Near-degenerate masses little asymmetry

• For SUSY masses, measurable @ SPS1a– but shape is similar– need to measure size as well as shape of asymmetry

Lepton non-universality• Lepton Yukawa’s

lead to differences in slepton mixing– Mixing measurable

in this decay chain

• Not easy, but there is sensitivity at e.g. SPS1a– Biggest effect for

taus – but they are the most difficult experimentally

Neutralino spin Goto, Kawagoe, Nojirihep-ph/0406317

Range of Validity• Limits:

– Decay chain must exist

– Sparticles must be fairly light

• Relatively small area of validity– ~ red +

orange areas in plot after cuts

Allanach & MahmoudiTo appear in proceedingsLes Houches 05

Decay chain kinematically forbidden

Spin Significance at the parton level – no cuts etc

Neutralino spin

Precise measurement of SM backgrounds: the problem

• SM backgrounds are not small

• There are uncertainties in– Cross sections– Kinematical

distributions– Detector response

W contribution to no-lepton BG

• Use visible leptons from W’s to estimate background to no-lepton SUSY search

Oe, Okawa,Asai

Normalising not necessarily good enough

Distributions arebiased by lepton selection

Distributions arebiased by lepton selection

Need to isolate individual components…

Then possible to get it right…

Similar story for other backgrounds – control needs careful selectionSimilar story for other backgrounds – control needs careful selection

Dark matter relic density consistency?• Use LHC measurements to

predict relic density of observed LSPs

• Caveats:– Can’t tell about lifetimes beyond

detector• To remove mSUGRA assumption

need extra constraints:1. All neutralino masses

• Use as inputs to gaugino & higgsino content of LSP

2. Lightest stau mass• Is stau-coannihilation important?

3. Heavy Higgs boson mass• Is Higgs co-annihilation important?

• More work is in progress– Probably not all achievable at LHC– ILC would help lots (if in reach)

mSUGRA

assumed

mSUGRA

assumed