Transcript Standard Model is an Effective Theory

Anticipating New Physics @ the LHC
• Why the Terascale?
• Scenarios for Electroweak Symmetry Breaking and
the Gauge Hierarchy
– LHC Signatures
– Connection to Dark Matter
• Summary: Discoveries are only months away!
APS April Meeting, 2007
J. Hewett, Stanford Linear Accelerator Center
Why the Terascale?
• Electroweak Symmetry breaks at
energies ~ 1 TeV
(Higgs or ???)
• Gauge Hierarchy: Nature is fine-tuned or
Higgs mass must be stabilized by
New Physics ~ 1 TeV
• Dark Matter: Weakly Interacting Massive
Particle must have mass ~ 1 TeV to
reproduce observed DM density
The LHC is turning on!
The anticipation
has fueled many
ideas!
A Cellar of New Ideas
’67
The Standard Model
’77
Vin de Technicolor
’70’s
Supersymmetry: MSSM
’90’s-now SUSY Beyond MSSM
a classic!
aged to perfection
better drink now
mature, balanced, well
developed - the Wino’s choice
svinters blend
CP Violating Higgs
all upfront, no finish
lacks symmetry
’98
Extra Dimensions
bold, peppery, spicy
uncertain terrior
’02
Little Higgs
’90’s
’03
’03
’04
’05
Fat Higgs
Higgsless
Split Supersymmetry
Twin Higgs
complex structure
young, still tannic
needs to develop
sleeper of the vintage
what a surprise!
finely-tuned
double the taste
J. Hewett
Discoveries at the
LHC will find the
vintage nature has
bottled.
The Standard Model of Particle Physics
Building Blocks of Matter:
Symmetry:
SU(3)C x SU(2)L x U(1)Y
QCD
Electroweak
Spontaneously Broken
to QED
This structure is
experimentally confirmed!
The Standard Model Higgs Boson
Economy: 1 scalar doublet
Higgs Potential:
V() = 22/2 + 4/4
Spontaneous Symmetry Breaking
Chooses a vacuum v = 0||0
and shifts the field  =  - v
V() = m22/2 + v3 + 4/4
gives 1 physical Higgs scalar with m = 2 v
Masses of electroweak gauge bosons proportional to v
We need to discover the Higgs and experimentally
test this potential and the Higgs properties!
Higgs Mass Upper Bound: Gauge Boson Scattering
Higgs
Higgs
Bad violation of unitarity
 ~ E2
Restores unitarity
Expand cross section into partial waves
Unitarity bound (Optical theorem!)  |Re a0| < ½
Gives mH < 1 TeV
LHC is designed to explore this entire region!
Present Limits:
Direct Searches at LEP:
mH > 114.4 GeV
Indirect Searches at
LEP/SLC:
mH < 150-200 GeV
@ 95% CL
Higgs
Z
Z
Z
Higgs @ the LHC:
Production mechanisms & rates
Signal determined by final
state versus background
Higgs Search Strategies
Low: MH < 140 GeV
Medium: 130<MH<500 GeV
High: MH > ~500 GeV
The Hierarchy Problem
Energy (GeV)
Planck
GUT
10
Weak
Quantum Corrections:
Virtual Effects drag
Weak Scale to MPl
desert
1019
1016
Future
Collider
Energies
3
mH2 ~
All of
known
physics
10-18
Solar System
Gravity
~ MPl2
The Hierarchy Problem: Supersymmetry
Energy (GeV)
Planck
GUT
Quantum Corrections:
Virtual Effects drag
Weak Scale to MPl
desert
1019
1016
Future
Collider
Energies
boson
10
3
Weak
fermion
mH2 ~
All of
known
physics
10-18
~ MPl2
mH2 ~
Solar System
Gravity
~ - MPl2
Large virtual effects cancel
order by order in
perturbation theory
Supersymmetry:
•Symmetry between fermions and bosons
•Predicts that every particle has a superpartner of
equal mass (  SUSY is broken: many competing models!)
•Suppresses quantum effects
•Can make quantum mechanics consistent with
gravity (with other ingredients)
Supersymmetry at the LHC
SUSY discovery generally
‘easy’ at LHC
Cut: ETmiss > 300 GeV
LHC Supersymmetry Discovery Reach
Model where gravity
mediates SUSY breaking
– 5 free parameters at
high energies
Squark and Gluino
mass reach is
2.5-3.0 TeV @ 300 fb-1
MSSM only viable for mh < 135 GeV
Carena, Haber hep-ph/0208209
MSSM: tension with fine-tuning
Competing factors:
– Mass of lightest higgs
mh < MZ at tree-level
large quantum corrections from top sector
< (130 GeV)2
If stop mass ~ 1 TeV
– Stability of Higgs mass
stops cut-off top contribution to quadratic divergence
 stops can’t be too heavy
– Z mass relationship
Resolve Fine-Tuning: Extend the MSSM
• NMSSM (Next-to Minimal SSM)
Dermisek, Gunion, …
– Add a Higgs Singlet
- Evade LEP bounds – minimize fine-tuning!
- Regions where Higgs discovery is difficult @ LHC
• MNMSSM (Minimally Non-minimal MSSM)
– Lightest higgs < 145 GeV
– Observable @ LHC
• Gauge Extensions of MSSM
– Mh < 250 (350) GeV
• Split Supersymmetry
Panagiotakopoulos, Pilaftis
Batra, Delgado, Kaplan, Tait
Dark Matter in Supersymmetry
•A component of Dark Matter could be the Lightest
Neutralino of Supersymmetry
- stable and neutral with mass ~ 0.1 – 1 TeV
•In this case, electroweak strength annihilation gives
relic density of
ΩCDM h2 ~
m2
(1 TeV)2
Fraction of total Dark Matter density
Mass of Dark Matter Particle from Supersymmetry (TeV)
Determination of Dark Matter Density @ LHC
• Measure SUSY
properties @ LHC
• Benchmark point
SPS1a
• Dependence on Stau
mass determination
Baltz, Battaglia, Peskin, Wizansky hep-ph/0602187
The Hierarchy Problem: Extra Dimensions
Energy (GeV)
Planck
GUT
Simplest Model:
Large Extra Dimensions
desert
1019
1016
Future
Collider
Energies
10
3
Weak – Quantum Gravity
= Fundamental scale in
4 +  dimensions
MPl2 = (Volume) MD2+
All of
known
physics
Gravity propagates in
D = 3+1 +  dimensions
10-18
Solar System
Gravity
Arkani-Hamed, Dimopoulis, Dvali
Kaluza-Klein Modes in a Detector
Indirect Signature
Missing Energy Signature
pp  g + Gn
Events / 50 GeV / 100 fb-1
LHC
102
10
1
10-1
10-2
JLH
Mee [GeV]
Vacavant, Hinchliffe
Graviton Exchange Modified with Running
Gravitational Coupling
t=
SM
1
0.5
Insert Form Factor in
coupling to parameterize
running
M*D-2 [1+q2/t2M*2 ]-1
Could reduce signal!
D=3+4
M* = 4 TeV
JLH, Rizzo, to appear
Black Hole Production @ LHC:
Dimopoulos, Landsberg
Giddings, Thomas
Black Holes produced when s > M*
Classical Approximation:
E/2
b
[space curvature << E]
b < Rs(E)  BH forms
E/2
Geometric Considerations:
Naïve = Rs2(E),
details show this holds up to a factor
of a few
Production rate is enormous!
Determination of Number
of Large Extra Dimensions
1 per sec at LHC!
JLH, Lillie, Rizzo
hep-ph/0503178
Black Hole event simulation @ LHC
The Hierarchy Problem: Extra Dimensions
Energy (GeV)
Planck
GUT
desert
1019
1016
Future
Collider
Energies
Model II:
Warped Extra Dimensions
strong
curvature
10
3
Weak
wk = MPl e-kr
All of
known
physics
10-18
Solar System
Gravity
Randall, Sundrum
Kaluza-Klein Modes in a Detector: SM
on the brane
Number of Events in Drell-Yan
For this same model
embedded in a string
theory: AdS5 x S
Davoudiasl, JLH, Rizzo
Kaluza-Klein Modes in a Detector: SM
off the brane
Fermion wavefunctions in the bulk:
decreased couplings to light
fermions for gauge & graviton KK
states
gg  gn  tt
gg  Gn  ZZ
Lillie, Randall, Wang, hep-ph/0701164
Agashe, Davoudiasl, Perez, Soni hep-ph/0701186
Issue: Top Collimation
g1 = 2 TeV
gg  gn  tt
g1 = 4 TeV
Lillie, Randall, Wang, hep-ph/0701164
The Hierarchy Problem: Little Higgs
Energy (GeV)
Planck
GUT
Little Hierarchies!
desert
1019
1016
Future
Collider
Energies
104
New Physics!
10
Weak
3
Simplest Model:
The Littlest Higgs with
 ~ 10 TeV
No UV completion
All of
known
physics
10-18
Solar System
Gravity
Arkani-Hamed, Cohen, Katz, Nelson
The Hierarchy Problem: Little Higgs
Energy (GeV)
1019
1016
.
.
.
Future
Collider
Energies
Planck
GUT
106
105
104
New Physics!
New Physics!
New Physics!
10
Weak
3
All of
known
physics
10-18
Solar System
Gravity
Stacks of Little
Hierarchies
Simplest Model:
The Littlest Higgs with
1 ~ 10 TeV
2 ~ 100 TeV
3 ~ 1000 TeV
…..
Little Higgs: The Basics
• The Higgs becomes a component of a larger
multiplet of scalars, 
•  transforms non-linearly under a new global
symmetry
• New global symmetry undergoes SSB
 leaves Higgs as goldstone
• Part of global symmetry is gauged
 Higgs is pseudo-goldstone
• Careful gauging removes Higgs 1-loop divergences
 mh2 ~
2
(162)2
,
 > 10 TeV,
@ 2-loops!
3-Scale Model
 > 10 TeV: New Strong Dynamics
Global Symmetry
f ~ /4 ~ TeV:
v ~ f/4 ~ 100 GeV:
Sample Spectrum
Symmetires Broken
Pseudo-Goldstone Scalars
New Gauge Fields
New Fermions
Light Higgs
SM vector bosons & fermions
Little Higgs Gauge Production
WZ  WH  WZ  2j + 3l + 
Azuelos etal, hep-ph/0402037
Birkedal, Matchev, Perelstein, hep-ph/0412278
The Hierarchy Problem: Higgsless
Energy (GeV)
Planck
GUT
desert
1019
1016
Future
Collider
Energies
Warped Extra Dimensions
strong
curvature
10
3
Weak
wk = MPl e-kr
With NO Higgs boson!
All of
known
physics
10-18
Solar System
Gravity
Csaki, Grojean,Murayama, Pilo, Terning
Framework: EW Symmetry Broken by Boundary
Conditions
SU(2)L x SU(2)R x U(1)B-L in 5-d Warped bulk
Planck
brane
TeV-brane
SU(2)L x SU(2)R
SU(2)R x U(1)B-L
U(1)Y
WR, ZR get
Planck
scale masses
SU(2)D
BC’s restricted by variation
of the action at boundary
SU(2) Custodial Symmetry
is preserved!
W, Z get TeV scale masses
 left massless!
Unitarity in Gauge Boson Scattering: What do
we do without a Higgs?
Exchange gauge
KK towers:
Conditions on KK masses & couplings:
Csaki etal, hep-ph/0305237
(g1111)2 = k (g11k)2
4(g1111)2 M12 = k (g11k)2 Mk2
Necessary, but not sufficient, to guarantee perturbative unitarity!
Production of Gauge KK States @ LHC
gg, qq  g1  dijets
Davoudiasl, JLH, Lilllie, Rizzo
Balyaev, Christensen
The Hierarchy Problem: Who Cares!!
Planck Scale
Gauge Hierarchy Problem
Weak Scale
Cosmological Constant Problem
Cosmological
Scale
We have much bigger Problems!
Split Supersymmetry:
Energy
(GeV)
Arkani-Hamed, Dimopoulis hep-ph/0405159
Giudice, Romanino hep-ph/0406088
MGUT ~ 1016 GeV
MS : SUSY broken at high scale ~ 109-13 GeV
Scalars receive mass @ high scale
Mweak
1 light Higgs + Fermions
protected by chiral
symmetry
Collider Phenomenology: Gluinos
•
•
•
•
Pair produced via strong interactions as usual
Gluinos are long-lived
No MET signature
Form R-hadrons
q
Gluino pair + jet cross section
1 0
~
~
g
q
q
100 fb-1
Rate ~ 0, due to heavy
squark masses!
JLH, Lillie, Masip, Rizzo hep-ph/0408248
Density of Stopped Gluinos in ATLAS
Arvanitaki, etal hep-ph/0506242
See also ATLAS study, Kraan etal hep-ph/0511014
This is a Special Time in Particle Physics
• Urgent Questions
Provocative discoveries lead to urgent questions
• Connections
Questions seem to be related in fundamental, yet
mysterious, ways
• Tools
We have the experimental tools, technologies, and
strategies to tackle these questions
We are witnessing a Scientific Revolution
in the Making!
The LHC is Turning On!!!!!!!!
And we are ready!
Higgs Coupling Determinations @ LHC
Duhrssen, Heinemeyer, Logan,
Rainwater, Weiglein, Zeppenfeld
Observed Channels:
–
–
–
–
gg  H  ZZ, WW, 
qqH  qqZZ, qqWW, qq, qq
WH  WWW, W; ZH  Z
ttH, with H  WW, , bb
Theoretical Assumption:
Employ Narrow Width Approx:
(H) B(Hxx) =
(H)SM p x
V  VSM , V=W,Z
pSM
tot