Post on 31-Jan-2016
description
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 : Christopher.Lester@cern.ch 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
July 2001 HEP2001 : SUSY at the LHC : Christopher.Lester@cern.ch 3
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!
July 2001 HEP2001 : SUSY at the LHC : Christopher.Lester@cern.ch 4
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…”
July 2001 HEP2001 : SUSY at the LHC : Christopher.Lester@cern.ch 5
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(
July 2001 HEP2001 : SUSY at the LHC : Christopher.Lester@cern.ch 6
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
July 2001 HEP2001 : SUSY at the LHC : Christopher.Lester@cern.ch 7
(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
July 2001 HEP2001 : SUSY at the LHC : Christopher.Lester@cern.ch 9
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
July 2001 HEP2001 : SUSY at the LHC : Christopher.Lester@cern.ch 10
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.
July 2001 HEP2001 : SUSY at the LHC : Christopher.Lester@cern.ch 11
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
L.S.P. = lightest SUSY particle
July 2001 HEP2001 : SUSY at the LHC : Christopher.Lester@cern.ch 12
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
July 2001 HEP2001 : SUSY at the LHC : Christopher.Lester@cern.ch 13
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
July 2001 HEP2001 : SUSY at the LHC : Christopher.Lester@cern.ch 14
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
July 2001 HEP2001 : SUSY at the LHC : Christopher.Lester@cern.ch 15
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(
July 2001 HEP2001 : SUSY at the LHC : Christopher.Lester@cern.ch 16
R-Parity: conservation/violation
L.S.P. = lightest SUSY particle
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