Waiting for the LHC: Exploring the Quantum Universe

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Waiting for the LHC Exploring the Quantum
Universe

• Sally Dawson
• BNL
• 2007

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What is the Quantum Universe?

• To discover what the universe is made of and how
  it works is the challenge of particle physics

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A Decade of Discovery

• Electroweak Theory
• Neutrino flavor oscillations
• Three separate neutrino species
• Understanding QCD
• Discovery of top quark
• B meson decays violate CP
• Flat universe dominated by dark matter energy
• Quarks and leptons structureless at TeV scale

Discoveries have us poised for next revolution
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Thesis of this talk.

• Particle physics has changed dramatically in the
  last 20 years
• And we expect the next few decades to be just as
  extraordinary
• Due to new experimental capabilities
• Due to theoretical advances

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Einsteins Dream

• Is there an underlying simplicity in the laws of
  nature?
• Einstein dreamed of a unified picture
• He failed to unify electromagnetism and gravity

The history of particle physics is the story
of the search for unification
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Electromagnetism and Radioactivity

• Maxwell unified Electricity and Magnetism with
  his famous equations (1873)

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Electromagnetic Theory

• Dirac introduced theory of electron - 1926

• Theoretical work of Feynman, Schwinger, Tomonga
  resulted in a theory of electrons and photons
  with precise predictive power
• Example magnetic dipole of the electron
  (g-2)/2 m g (eh/2mc) S

• current values of electron (g-2)/2
• theory 0.5 (a/p) - 0.32848 (a/p)2 1.19 (a/p)3
  .. (115965230 ? 10) x 10-11
• experiment (115965218.7 ? 0.4) x 10-11

We can calculate!
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Electromagnetism and Radioactivity

• Matter spontaneously emits penetrating radiation
• Becquerel found uranium emissions in 1896

• The Curies find radium emissions by 1898

Could this new interaction (the weak force) be
related to EM?
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Fermis Dream

• Fermi formulated the first theory of the weak
  force (1934)
• n ? p e- ne

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Electroweak Unification

• Glashow, Weinberg, and Salam realized that the
  field responsible for the EM force (the photon)
• And the fields responsible for the Weak force
• the yet undiscovered W and W- bosons
• Could be unified if another field existed
• the then undiscovered heavy neutral boson (Z)
• W and Z bosons discovered at CERN in 1983

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Unification is a Guiding Theme
HERA
Experimental evidence for the unification of the
weak and electromagnetic forces
Model requires Higgs boson or something like it
for consistency!
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The Quest for Unification

• Figure from H. Murayama

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Electroweak Theory is Predictive

• Theory has few free parameters
• Mass of the Z boson, MZ91.1875 ? .0021 GeV
• Strength of the coupling of the photon to the
  electron, ?1/137.0359895(61)
• Strength of the weak interactions (measured in
  muon decay) GF1.16637(1) x 10-5 GeV-2
• Then the W mass is predicted

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Tevatron is Worlds Highest Energy Accelerator
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Precise measurement of Mw
2007

• CDF has worlds most precise measurement of W
  mass MW80.413?0.048 GeV

• Predictions of
• electroweak theory

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Error on MW decreasing
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Standard Model doesnt explain the particle
spectrum
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Top Quark Discovered at Fermilab
CDF
Why is it so heavy?
DØ
Mt170.9?1.8 GeV
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Mt (and error) decreasing
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Why is Mass a Problem?

• Lagrangian for gauge field (spin 1)
• L-¼ F??F??
• F????A?-??A?
• L is invariant under transformation
• A?? (x) ?A?(x)-???(x)
• Gauge invariance is guiding principle
• Mass term for gauge boson ½ m2 A?A?
• Violates gauge invariance

• Solution requires physical scalar particle THE
  HIGGS BOSON

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Standard Model is Inconsistent Without a Higgs
boson

• Requires physical, scalar particle, h, with
  unknown mass
• Predictions are infinite without a Higgs boson
  (or something like it)
• Mh is ONLY unknown parameter of EW sector
• No evidence (yet) for existence of Higgs boson

Everything is calculable.testable theory
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LEP Looked for the Higgs

• Looked for ee- ? Z h
• Excluded a Higgs boson up to Mh114 GeV
• This limit assumes a Higgs boson with the
  properties predicted by the Standard Model

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Higgs at the Tevatron Very Hard!!!
?(gg?h)?1 pb ltlt ?(bb)
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SM Higgs Searches at Tevatron
Getting close!
Tevatron Expected
Tevatron Observed
LP07
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With precise measurements of MZ and ?, we can
predict MW
W Boson Mass
pa
MW2
v2GF (1 - MW2/MZ2)(1 - Dr)
?r Quantum corrections dominated by top/bottom
and Higgs loops
DMW µ Mt2
DMW µ ln (MH/MZ)
2
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Mt and MW Limit Higgs Mass

• Direct observation of W boson and top quark
  (blue)
• Inferred values from other measurements (red)

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Mt and MW Limit Higgs Mass

• LEP EWWG (July, 2007)
• Mt170.9 ? 1.8 GeV
• Mh7636-24 GeV
• Mh lt 144 GeV (one-sided 95 cl)
• Mh lt 182 GeV (Precision measurements plus direct
  search limit)

2007
Best fit in region excluded from direct searches
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Where is the Higgs ?

• We need to find the Higgs (Standard Model is
  theoretically inconsistent without it)
• We didnt find it at LEP
• We havent found it at Fermilab
• The end is in sight..if we dont find it at the
  LHC, the Standard Model as it stands cannot be
  the whole story (because precision measurements
  would be inconsistent)

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Livingstone PlotThe March of Progress

• Electron machines access full energy of
  collisions
• Quark and gluon interactions in a hadron machine
  access some fraction of total collision energy

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Science Timeline
Future ee- Collider
Tevatron
LHC
LHC Upgrade
2007
2008
2012
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Large Hadron Collider (LHC)

• proton-proton collider at CERN (2008)
• 14 TeV energy
• 7 mph slower than the speed of light
• cf. 2TeV _at_ Fermilab
• ( 307 mph slower than the speed of light)

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Stored Energy of Beams unprecedented

• Ebeam1.5 Giga Joule
• LHC beams have same kinetic energy as aircraft
  carrier at 15 knots!
• Largest scientific project ever attempted

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Requires Detectors of Unprecedented Scale

• CMS is 12,000 tons (2 xs ATLAS)
• ATLAS has 8 times the volume of CMS
• Collaborations have 2000 physicists each

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ATLAS Experiment at LHC
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CMS
ATLAS
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Particle Physics in the LHC/ILC Era

• Will be data driven

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LHC will find Standard Model Higgs
LHC Will find the Higgs if it exists
Consistency of SM REQUIRES a Higgs Boson or
something like it
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Higgs discovery at the LHC
Assumes well understood detector
Needed ?Ldt per experiment (fb-1)
Mh(GeV)
1 fb-1 95 C.L. exclusion 5 fb-1 5? discovery
J. Blaising et al, Eur. Strategy Workshop
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LHC and the Higgs

• LHC will discover Higgs boson if it exists
• Sensitive to Mh from 100-1000 GeV
• Higgs signal in just a few channels

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D

From the Tevatron to the LHC
High pT QCD Jets
LHC
Tevatron
Drell-Yan production of Ws Zs
? (nb)
Gluon fusion of 150 GeV Higgs
1 TeV squark/gluino pair production
?s (TeV)

• Large increase in cross sections as
• we go from the Tevatron to the LHC

F. Gianotti, Phys. Rep. 403, 379 (2004)
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Early Physics at the LHC

• O(100 pb-1) per experiment by early 2009

Channel Events/100 pb-1 at LHC Previous of Events
W??? 105 104 LEP, 106 Tevatron
Z ?ee- 105 107 LEP, 105 Tevatron
104 104 Tevatron
QCD jets, pTgt1 TeV gt103
1 TeV Gluino pairs 50

• Early data used to calibrate detectors
• Rediscover SM physics at ?s14 TeV W, Z, top, QCD

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Typical Collision Energy at LHC 1
TeV
b
W
t
p
p
t
W-
b
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Quantum Corrections Connect Weak and Planck Scales
Something new??
Tevatron/LHC Energy
Weak
GUT
Planck
1019 GeV
103 GeV
1016
Quantum corrections drag weak scale to Planck
scale
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Quantum Corrections to Higgs Mass

• Higgs mass grows quadratically with scale of new
  physics, ?

Mh ? 200 GeV requires ? TeV
Points to 1 TeV as scale of new physics
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We expect much at the TeV Scale

• Maybe a Higgs (or something like it)
• Maybe supersymmetry (lots of new particles)
• Supersymmetric models have at least 5 Higgs
  particles!
• Maybe extra dimensions
• Maybe other new symmetries

Were not sure what will be there, but were sure
there will be something!
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Possibilities galore

• H. Murayama

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More on Unification
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Einsteins Dream of Unification

• Coupling constants change with energy

Supersymmetric Model
Standard Model
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Supersymmetric Theories

• Predict many new undiscovered particles (gt29!)
• Very predictive models
• Can calculate particle masses, interactions,
  everything you want in terms of a few parameters
• Solve naturalness problem of Standard Model
• Instead of
• Supersymmetric models have

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Many New Particles in Supersymmetric Models

• Spin ½ quarks ? spin 0 squarks
• Spin ½ leptons ? spin 0 sleptons
• Spin 1 gauge bosons ?spin ½ gauginos
• Spin 0 Higgs ?spin ½ Higgsino
• Experimentalists dream.many particles to
  search
• for!
• What mass scale?
• Supersymmetry is broken.no scalar with mass of
  electron

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Supersymmetry at the LHC
?(pb)
M (GeV)

• Huge rates well defined signatures
• M(gluino, squark) ? 1 TeV gives 100 events with
  100 pb-1 at LHC

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Supersymmetry at the LHC

• LHC will find
• SUSY if it is
• at 1 TeV

M1/2 (GeV)
2009
M0(GeV)
Tevatron
Immediate improvements over Tevatron limits
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Supersymmetric Theories solve another problem
2006 Nobel Prize for COBE The first survey of
dark matter in the universe
We have a census of the universe
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Is Dark Matter a Particle?
The lightest supersymmetric particle has the
right properties to be dark matter
Can we produce dark matter in a collider and
study all its properties?
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Supersymmetry has Dark Matter Candidate

• Supersymmetric models have dark matter candidate
• Lightest supersymmetric particle (LSP) is neutral
  and weakly interacting
• On general grounds, LSP contributes correct
  amount of dark matter if its mass is 300 GeV-1
  TeV
• Supersymmetric particles within reach of the LHC

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Particle Dark Matter

• Wed like to detect dark matter particles in the
  lab
• To show theyre in the galactic halo
• And to produce them at an accelerator
• To measure their properties

WIMP Weakly Interacting Massive Particle aka
dark matter candidate
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If LSP is dark matter, LHC will observe
supersymmetric particles
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Conclusions
Discoveries coming soon