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
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. - PowerPoint PPT Presentation
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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
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 is2.5-3.0 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
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
< (130 GeV)2
Resolve Fine-Tuning: Extend the MSSM
• NMSSM (Next-to Minimal SSM)– Add a Higgs Singlet- Evade LEP bounds – minimize fine-tuning!- Regions where Higgs discovery is difficult @ LHC
•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
m2
ΩCDM h2 ~ (1 TeV)2
Dark Matter in Supersymmetry
Mass of Dark Matter Particle from Supersymmetry (TeV)
Fra
cti
on
of
tota
l D
ark
Matt
er
den
sit
y
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)
1019
1016
103
10-18Solar SystemGravity
Weak – Quantum Gravity
GUT
Planckd
ese
rt
Future Collider Energies
All of known physics
Simplest Model: Large Extra Dimensions
= Fundamental scale in 4 + dimensions
MPl2 = (Volume) MD
2+
Gravity propagates in D = 3+1 + dimensions
Arkani-Hamed, Dimopoulis, Dvali
Kaluza-Klein Modes in a Detector
Mee [GeV]
Eve
nts
/ 50
GeV
/ 1
00 f
b-1
102
10
1
10-1
10-2
LHC
Indirect Signature
Missing Energy Signature
pp g + Gn
JLH Vacavant, Hinchliffe
Graviton Exchange Modified with Running Gravitational Coupling
Insert Form Factor in coupling to
parameterize running
M*D-2 [1+q2/t2M*
2 ]-1
Could reduce signal!D=3+4M* = 4 TeV
SM
t=
1
0.5
JLH, Rizzo, to appear
Black Hole Production @ LHC:
Black Holes produced when s > M*
Classical Approximation: [space curvature << E]
E/2
E/2b
b < Rs(E) BH forms
Geometric Considerations:
Naïve = Rs2(E), details show this holds up to a
factor of a few
Dimopoulos, LandsbergGiddings, Thomas
Production rate is enormous!
1 per sec at LHC!
JLH, Lillie, Rizzohep-ph/0503178
Determination of Number of Large Extra Dimensions
Black Hole event simulation @ LHC
The Hierarchy Problem: Extra Dimensions
Energy (GeV)
1019
1016
103
10-18Solar SystemGravity
Weak
GUT
Planckd
ese
rt
Future Collider Energies
All of known physics
Model II: Warped Extra Dimensions
wk = MPl e-kr
strong curvature
Randall, Sundrum
Number of Events in Drell-Yan
For this same model embedded in a string theory: AdS5 x S
Kaluza-Klein Modes in a Detector: SM on the brane
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 ZZ
gg gn tt
Agashe, Davoudiasl, Perez, Soni hep-ph/0701186
-
Lillie, Randall, Wang, hep-ph/0701164
Issue: Top Collimation
Lillie, Randall, Wang, hep-ph/0701164
gg gn tt-
g1 = 2 TeV g1 = 4 TeV
The Hierarchy Problem: Little Higgs
Energy (GeV)
1019
1016
103
10-18Solar SystemGravity
Weak
GUT
Planckd
ese
rt
Future Collider Energies
All of known physics
Little Hierarchies!
104 New Physics!
Simplest Model: The Littlest Higgs with ~ 10 TeV
No UV completion
Arkani-Hamed, Cohen, Katz, Nelson
The Hierarchy Problem: Little Higgs
Energy (GeV)
1019
1016
103
10-18Solar SystemGravity
Weak
GUT
Planck
Future Collider Energies
All of known physics
Stacks of Little Hierarchies
104 New Physics!
Simplest Model: The Littlest Higgs with 1 ~ 10 TeV 2 ~ 100 TeV 3 ~ 1000 TeV …..
105
106
.
.
.
New Physics!
New Physics!
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