WIN 05

WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN

WIN 05

• Inclusive signatures: discovery, fast but not unambiguous

• Exclusive final states & long term measurements: towards understanding the underlying model

Supersymmetry searches at the LHC

Filip Moortgat, CERN


Why SUSY is a good idea

One of the most appealing extensions of the Standard Model:

TeV-scale supersymmetry

Solves several problems at once:

• dark matter candidate (e.g. lightest neutralino)• opening towards a theory of gravity• unification of gauge couplings• hierarchy problem• allows to explain why the Higgs mechanism works

[= a symmetry between fermions and bosons, duplicates the SM particle spectrum, but not the couplings]


SUSY models

• In general MSSM: many allowed soft SUSY breaking parameters (124) due to unknown nature of SUSY breaking mechanism

= difficult to work with

use more constrained models

• Most popular: mSUGRA

• Also mGMSB, AMSB

m0 , m1/2 , A0 , tan , sign(


The Large Hadron Collider

(8 T !!)

yr/fb 100 20

scm10102. L

TeV14:

1-

1-2-3433

spp

also AA and pA collisions; for PbPb : 5.5 TeV/nucleon and L = 1027 cm-2s-1


Generic SUSY signatures

General characteristics of R-parity conserving SUSY:

• sparticles pair produced and LSP stable large amount of missing transverse energy

• coloured sparticles are copiously produced and cascade down to the LSP with emission of many hard jets and often leptons

Generic SUSY signatures are ET

miss + multi-jets (and multi-leptons)


Inclusive SUSY

• jets + ETmiss

• 1,2,3 lepton + ETmiss

• opposite sign (OS) or same sign (SS) di-leptons

• often several topologies simultaneously visible


Jet + MET

Signature: ETmiss + jets

• ~ 1 pb at 1 TeV → physics for startup

• significant reach after 1 yr

• with 300 fb-1, reach squarks and gluinos up to ~ 2.5 TeV

• (need good understanding of detector and backgrounds!)


Variable that gives information on the “SUSY scale”:

Et sum

SM background

SUSY (700 GeV)

[Branson et al, ATLAS]

Warning: model dependent plot!


Same-sign dileptons

Lpp gu X 1 d

L

01

1t t1 b

L 01

Signal:

pp tt X W b

Y

W b

Background:

[Drozdetski et al, CMS] ask for 2 SS leptons + hard jets + ETmiss

_


Exclusive final states

• so far: inclusive measurements fast discovery, but does not unambiguously single out SUSY

• need to reconstruct sparticle decay chains and masses involved need to be prepared for all possible final states

• goal is to measure cross sections, BR’s ( couplings) and even spin of the sparticles LHC can not only discover SUSY, but also MEASURE its properties (if nature is kind)


Coloured sparticle decays

qqqqg ~,~~)~()~( qmgm Region

1

Region 2, e.g.

bbbbgqgqL ~

,~~,~~

Region 3 )~()~( gmqm qqgqgq ~,~~

[Pape, CMS]


Neutralino2 decay signatures

01

002 Z

01

02 ll

ll ~0

2

01

002 h

[Pape, CMS]

02q q~

Significant fraction of


Decay chain to dileptons

g~ q~

q q

02 l

~

l

missTE0

1

l

• 2 high pt isolated leptons• 2 high pt jets• missing Et

Final state:


Kinematic endpoints

Kinematic endpoint technique: construct lepton/quark upper/lower endpointsand relate them to the masses in the decay chain

E.g.:

4 unknown masses: 4 endpoints:

all masses can be determined

maxmaxmaxmax )(,)2(,)1(,)( llqMqlMqlMllM01

02

,,, ~~ MMMM

lq

q~ q02

01 ~

Usually non-linear relations all masses, not just differencesExtra endpoints, or start from gluino constraints


Final states with dileptons (1)

M(ll): very sharp end point, triangular shape (due to spinless

slepton)

)1)(1(2~

2

2

2~max

01

02

02

l

lll M

M

M

MMM

%1.0/ MM

[Biglietti et al, ATLAS][Chiorboli et al, CMS]


Final states with dileptons (2)

M(l1q):

M(l2q):

Can distinguish M(l1q)max from M(l2q)max

M(llq):

)1)(1(2~

2

2~

2

~max2

01

02

lqqql M

M

M

MMM

)1)(1(2

2~

2~

2

~max1

02

02

M

M

M

MMM l

qqql

)1)(1(2

2

2~

2

~max

02

01

02

M

M

M

MMM

qqllq

M(llq)[ATLAS]


Gluino reconstruction

Choose dilepton pairs close to the edge; then

pMMp )/1( 0

102

~~

can reconstruct and qM ~ qg MM ~~

[Chiorboli et al, CMS]

assuming can be at 01

~02

~rest in the frame of


Final state with taus

• often decays to taus instead of electrons/muons

• can we use hadronic tau final states?

[Biglietti et al, ATLAS]

endpoint smeared out

02

~


Decay chain to h0 or Z0

g~ q~

q q

02

missTE0

1

00 , Zh


Final states with h0 or Z0

Higgs peak can be reconstructed from 2 b-jets

could be a h0 discovery channel !

(even for light H0 and A0)

Z0 reconstructed from di-lepton decay

Decay chain is shorter than for di-leptons

e.g. start from gluinoM(q1h0),M(q2h0),M(qq),M(qqh0)to determine 4 masses

M(bb)

[Paige, ATLAS]

[Moortgat, CMS]h0

A0,H0


GMSB signatures

In GMSB, the light gravitino is the LSP

Who is NLSP?

Neutralino is NLSP

Stau is NLSP

ETmiss + , or long-

lived particles

G~0

1

G~~

1

dE/dx and TOF

TOF measurement in the CMS muon DT’s

[Wrochna, CMS]


SUSY spin measurement

[Barr, ATLAS]Lq~ L

02 q

~

R

01

)( qlM

qlql and

qlql and

Make use of spin correlations in decay of squark:

no spin correlations


SUSY spin measurements (2)

washes out for antisquarks, but in pp colliders more squarks produced than antisquarks

Visible asymmetry: (500 fb-1)

[Barr, ATLAS]

no spin correlations


Conclusions

• If TeV-scale SUSY exists, its discovery at the LHC should be (relatively) fast, using inclusive signatures

• The LHC can measure sparticle properties: reconstruction of masses in sparticle decay chains, mainly using kinematic endpoints

• Ultimately would like to measure spins and couplings (WIN 05 WINO 5?)

• only 750 days to startup … so focusing on being ready for first day physics now!


Backup


Cross sections @ the LHC

“Well known”processes,don’t need to keep all of them …

New Physics!!This we want to keep!!


CMS


ATLAS


Civil Engineering

UXC 55

USC 55


Higgs to sparticles

If accessible, we may exploit the sparticle decay modes:

A, H 20 2

0 4l + ETmiss

Documents

WIN 05