Physics Perspectives for the LHC - IPMU March 12th, 2008
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Physics Perspectives for the LHC
IPMU
March 12th, 2008
The Standard Model
= Cosmic DNA
The matter particles
The fundamental interactions
Gravitation electromagnetism weak nuclear force strong nuclear forceStatus of the Standard Model
• Perfect agreement with all confirmed
accelerator data
• Requires a missing ingredient
• Consistency with precision electroweak data
(LEP et al) only if there is a Higgs boson
• Agreement seems to require a relatively light
Higgs boson weighing < ~ 150 GeV
• Raises many unanswered questions:
mass? flavour? unification?Open Questions beyond the
Standard Model
• What is the origin of particle masses?
due to a Higgs boson? + other physics?
solution at energy < 1 TeV (1000 GeV) LHC
• Why so many types of matter particles?
matter-antimatter difference? LHC
• Unification of the fundamental forces?
at very high energy ~ 1016 GeV?
probe directly via neutrino physics, indirectly via masses,
couplings LHC
• Quantum theory of gravity?
(super)string theory: extra space-time dimensions? LHCSome particles have mass, some do not
Where do the masses
come from?
Newton: photon
Weight proportional
0 to Mass
Mass 0
Einstein: W+ Z 0 W -
Energy
+1related
0 to-1 Mass
Mass 80.419 91.188 80.419
Neither explained origin of Mass
Are masses due to Higgs boson?
(yet another particle)And Supersymmetry?
• Would unify matter particles and force particles
• Related particles spinning at different rates
0 - ! - 1 - 3/2 - 2
Higgs - Electron - Photon - Gravitino - Graviton
(Every particle is a ‘ballet dancer’)
• Would help fix particle masses
• Would help unify forces
• Predicts light Higgs boson
• Could provide dark matter wanted by
astrophysicists and cosmologistsLoop Corrections to Higgs Mass2
• Consider generic fermion and boson loops:
∀ 4
• Each is quadratically divergent: ! d k/k2
2
• Leading divergence cancelled if
x 2 Supersymmetry!Other Reasons to like Susy
It enables the gauge couplings to unify
It predicts mH < 150 GeV
As suggested
by EW data
Erler: 2006
JE, Nanopoulos, Olive + Santoso: hep-ph/0509331Lightest Supersymmetric Particle
• Stable in many models because of conservation of R
parity: Fayet
R = (-1) 2S –L + 3B
where S = spin, L = lepton #, B = baryon #
• Particles have R = +1, sparticles R = -1:
Sparticles produced in pairs
Heavier sparticles ! lighter sparticles
• Lightest supersymmetric particle (LSP) stableDark Matterininthe
Dark Matter theUniverse
Universe
Astronomers say
that most of tell
Astronomers the
matter
us in theof the
that most
Universe
matter is
in the
universe
invisibleis
invisible
Dark Matter
‘Supersymmetric’ particles ?
We will look for it
We shall look for
with the
them LHC
with the
LHCHow do Matter and Antimatter Differ?
Dirac predicted the existence of antimatter:
same mass
opposite internal properties:
electric charge, …
Discovered in cosmic rays
Studied using accelerators
Matter and antimatter not quite equal and opposite: WHY?
Why does the Universe mainly contain matter, not antimatter?
Experiments at LHC and elsewhere looking for answersUnify the Fundamental Interactions:
Einstein’s Dream …
∀ … but he never succeededThe Large Hadron Collider (LHC)
Proton- Proton Collider
7 TeV + 7 TeV
1,000,000,000 collisions/second Primary targets:
•Origin of mass
•Nature of Dark Matter
Connections with big issues in cosmology •Primordial Plasma
•Matter vs AntimatterA Simulated Higgs Event @ LHC
When will the LHC discover the Higgs boson?
• A Standard Model Higgs 1 ‘year’ @ 1033
boson could be discovered
with 5-∀ significance with
5fb-1, 1fb-1 would be
sufficient to exclude a
‘month’ @ 1033
Standard Model Higgs boson
at the 95% confidence level
• Signal would include ##, ∃∃,
bb, WW and ZZ
‘month’ @ 1032
• Will need to understand
detectors very well
Blaising, JE et al: 2006The Stakes in the Higgs Search
• How is gauge symmetry broken?
• Is there any elementary scalar field?
• Would have caused phase transition in the Universe
when it was about 10-12 seconds old
• May have generated then the matter in the Universe:
electroweak baryogenesis
• A related inflaton might have expanded the Universe
when it was about 10-35 seconds old
• Contributes to today’s dark energy: 1060 too much!
Do not take the Higgs for granted!Classic Supersymmetric Signature
Missing transverse energy
carried away by dark matter particlesPossible Nature of LSP
• No strong or electromagnetic interactions
Otherwise would bind to matter
Detectable as anomalous heavy nucleus
• Possible weakly-interacting scandidates
Sneutrino
(Excluded by LEP, direct searches)
Lightest neutralino % (partner of Z, H, ∃)
Gravitino
(nightmare for astrophysical detection)Constraints on Supersymmetry
• Absence of sparticles at LEP, Tevatron
selectron, chargino > 100 GeV
squarks, gluino > 300 GeV
• Indirect constraints 3.3 ∀
effect in
Higgs > 114 GeV, b & s ∃ gµ – 2?
• Density of dark matter
lightest sparticle %:
0.094 < ∋%h2 < 0.124Implications of LHC Search for LC
In CMSSM
LHC gluino
mass reach
Corresponding sparticle
thresholds @ LC
LHC will tell LC
where to look
‘month’ @ 1032 ‘month’ @ 1033 1 ‘year’ @ 1033 1 ‘year’ @ 1034
Blaising, JE et al: 2006m (ll) spectrum Reconstruction of `Typical’ m (llj)min spectrum
end-point : 109 GeV end-point: 552 GeV
precision ~ 0.3% Sparticle Decay Chain precision ~1 %
~
q L ! q ∀02
~
l R l
l ∀01
m (llj)max spectrum
threshold: 272 GeV m (l±j) spectrum
exp. precision ~2 % Msquark = 690 end-point: 479 GeV
M÷’ = 232 exp. precision ~1 %
Mslepton = 157
M÷ = 121
(GeV)
Erice. Sept. 2, 2003 L. Maiani: LHC Status
ATLAS 14Supersymmetric Benchmark Studies
Lines in
susy space Specific
allowed by benchmark
accelerators, Points along
WMAP data WMAP lines
Sparticle Calculation
detectability of relic
Along one density at a
WMAP line benchmark
point
Battaglia, De Roeck, Gianotti, JE, Olive, PapeSummary of LHC
Scapabilities
… and Other
Accelerators
LHC almost
`guaranteed’
to discover
supersymmetry
if it is relevant
to the mass problem
Battaglia, De Roeck, Gianotti, JE, Olive, PapeAfter LHC @ CERN - CLIC? Electron-Positron collisions up to 3 TeV
The Stakes in the SUSY Search • A novel symmetry of Nature? • Circumstantial hint for string theory? • Stabilize the hierarchy of mass scales in physics? • Explain 90% of the matter in the Universe? • Leads to unification of the fundamental forces?
Search for a ‘Theory of Everything’
• Two greatest achievements of early 20th-
century physics still not combined:
– Quantum theory, gravity
• String theory ‘only game in town’
– Needs SUSY, suggests extra dimensions
• Powerful new theoretical toolbox
– >> traditional quantum field theory
• Many other potential applications
– Quark-gluon plasma, …How large could extra Dimensions be?
• 1/TeV?
could break supersymmetry, electroweak
• micron?
can rewrite hierarchy problem
• Infinite?
warped compactifications
• Look for black holes, Kaluza-Klein
excitations @ colliders?And if gravity becomes strong at the TeV scale …
Black Hole Production at LHC?
Multiple jets,
leptons from
Hawking
radiationBlack Hole Decay Spectrum
Deviations from
black-body
could probe string theory
Cambridge: al et WebberSummary
• The origin of mass is the most pressing in particle
physics
• Needs a solution at LHC energy
Higgs? Supersymmetry?
LHC will tell!
• Lots of speculative ideas for other physics beyond the
Standard Model
Grand unification, strings, extra dimensions? …
LHC may also probe these speculations
We do not know what the LHC will find
Its discoveries will set agenda for future projectsThe Big Questions in Particle Physics
and Cosmology
Where are we coming from?
What are we? LHC
Where are we going?You can also read
