what prospects for supersymmetry at the large hadron collider ? a brief introduction to the...

What prospects for Supersymmetry at the Large Hadron Collider ?

A brief introduction to the techniques with which ATLAS and CMS intend

to constrain Supersymmetry

Christopher.Lester @ cern.ch

July 2001 HEP2001 : SUSY at the LHC : [email protected] 2

LHC & Supersymmetry

What can the LHC provide if SUSY exists?

DISCOVERY ? ………………………………. YES!• Excellent prospects• Might even be “easy” !• Largely model-independent

PRECISE MEASUREMENTS ? …….... Plenty!• but more likely to be model-dependent


What do we want to know?

M.S.S.M. Squark masses

(12) The gluino mass (1) Slepton masses (9) Neutralino masses (4) Chargino masses (2) Mixing matrices (?) Phases (?) …..

(plenty)

Other models: RP-Violating M.S.S.M.

RPV couplings (45) mSUGRA model

m0, m1/2, A0, tan β, sgn μ (5)

A.M.S.B. model m0, m3/2, tan β, sgn μ (4)

G.M.S.B. model λ, Mmes, N5, tan β, sgn μ, Cgrav (6)

There is no shortage of parameters which need to be determined!


Which can we measure?

The kinds of measurements which can be made, very much depend on the SUSY model which nature has chosen!

It is important to understand the physical effects of R-Parity conservation (or non-conservation) in SUSY models, before discussing measurements.

“Lots, but it depends…”


Two main SUSY scenarios: (RPV/RPC)

RP-Conserving RP-Violating

R-Parity: Conservation/Violation

(L.S.P. = “lightest SUSY particle”)

How stable is thelightest SUSYparticle (L.S.P.) ?

Largemissingenergy?

Event can bereconstructedfully?

Sparticleproduction

RPC Stable Yes Usually not Only in pairs

RPV Unstable(decays to leptons or jets)

No Yes Either singly,or in pairs

R=+1 for Standard Model particles R= -1 for SUSY particles

sLBR 2)(3)1(


R-Parity Conservation RPC

L.S.P. stable and weakly interacting, and so “goes missing”• Missing energy signature• Usually incomplete event

reconstruction• Need to rely on long decay chains and

kinematic variables (endpoints and distributions)

Sparticles are only produced in pairs• double the trouble!

L.S.P. = lightest SUSY particle


(GeV)effM

even

ts

Signal

Squark/gluon mass scale RPC

i

iEM || jetT

missingTeff p

Peak of Meff distribution correlates well with

squark/gluon mass scale for mSUGRA and GMSB

models.

S.M. Background

SU

GR

A R

each

(CM

S)

RPC


Kinematic edges: l+l- edge RPC

The l+l- invariant mass from the decay chain (right) has a kinematic endpoint.

For 100 fb-1, edge measured at 109.10±0.13(stat) GeV

Dominant systematic error on lepton energy scale also ~0.1%

In progress:• incorporation of widths,• decay matrix elements,• polarisations,• photon radiation, etc


Coverage of l+l- edge RPC

However ... … different processes can produce the same final state.

Can the process be identified?• Detailed study of the shape of the

mll distribution can provide clues

Likely coverage?• Lepton edge observable over

significant region of m0, m1/2 parameter space (CMS plot left)

Likely outcome? Precise sparticle mass differences When chains are long enough, resolution

on absolute mass scale improves and can measure mass of L.S.P.


R-Parity Violation RPV

RP-Violating: L.S.P. decays into leptons or jets:

• If L.S.P. lifetime is short:Multi-jet or multi-lepton signatureNo missing energy, so reconstruct full event

• If L.S.P. lifetime is long: looks like RPC scenario

Sparticles may be produced singly



Lepton number violating RPV

λ’ijk couples a slepton to two quarks

Can have resonant sneutrino production

Cross section can place lower bound on λ’ijk

Expect to observe (within 3 years) either 900 GeV neutrino if λ’211>0.05

350 GeV neutrino if λ’211>0.01 (present limit: )

GeV) 100/( 60.0 ~211'

RdM

λ’ijk =0.09

Reconstructed neutralino mass peak in mjjμ invariant mass distribution


Baryon number violating RPV

Each L.S.P. decays to three quarks (u,d,s) forming three jets (jjj)

Require 2 leptons and at least 8 jets: (j+jjj)+(j+ll+jjj)

Look for L.S.P. / chargino peak in mjjj / m jjjll plane

msquark L= 638 ± 5 ±12 GeV

mneutralino 2 = 212 ± 0.3 ± 4 GeV

mslepton R= 155 ± 3 ± 3 GeV

mneutralino 1 = 117 ± 3 ± 3 GeV


Conclusions

We can expect ATLAS and CMS to Observe squarks and gluons

below 2.5 TeV andobserve sleptons below 300 GeV in inclusive measurements.

Accurately measure squark, slepton and neutralino masses using cascade decays (provided chains are sufficiently long and rates are favourable)

Success is expected in both RPV and RPC scenarios

Precise measurements: many can be made in principle, but which of them can measured in practice will depend strongly on the model which nature has chosen

Other areas of completed and ongoing research which there was not time to discuss:

N.L.S.P. lifetime in G.M.S.B. models (Non-pointing photons / slow heavy leptons) A.M.S.B. models Lepton flavour violation (via slepton mixing) Measuring the gaugino mixing matrix Direct slepton production Non-minimal models SUSY Higgs sector Everything else which I have forgotten to mention ...

CMS


R=+1 for Standard Model particles R= -1 for SUSY particles

R-Parity: conservation/violation

Two main SUSY scenarios: RPV/RPC

RP-Conserving: RP-Violating:

sLBR 2)(3)1(


R-Parity: conservation/violation


L.S.P. Largemissingenergy?

Event can bereconstructedfully?

Sparticleproduction

RPC Stable Yes Usually not Only in pairs

RPV Unstable(decays to leptons or jets)

No Yes Either singly,or in pairs

what prospects for supersymmetry at the large hadron collider ? a brief introduction to the...

Documents