Beyond the Terascale with muons
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Transcript of Beyond the Terascale with muons
Beyond the Terascale with muons
Fermi National Accelerator Laboratory
Peter Skands
Theoretical Physics Dept
Fermilab Accelerator Physics and Technology Seminar / Low-Emittance Muon Collider Workshop, Fermilab, February 2006
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OverviewOverview• Introduction: the Standard Model
– What works– What doesn’t
• Beyond the Standard Model– Open-minded model building– Inspirational examples
• Collider Physics in the post-LHC era
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Below the TerascaleBelow the Terascale
D. B. Leinweber, hep-lat/0004025
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• Relativistic Quantum Field Theory w/ Poincare Inv.
• 45 matter particles (fermions)– 36 quarks– 9 leptons (incl. neutrinos)
• 3 Forces (gauge bosons)– Gauged U(1):
electromagnetism– Gauged SU(2): weak force– Gauged SU(3): strong force
The Standard Model (s.m.)The Standard Model (s.m.)What works …What works …
symmetry breaking
masses•1 Higgs boson (scalar)
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What worksWhat worksdatadata Standard ModelStandard Model
. . . etc. . . etc
But is that all?But is that all?
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What Doesn’tWhat Doesn’t• The Standard Model does face a few problems:
– A few experiments …
– Some mathematics …
– Some cosmetics …
is the TeV scale inhabited?
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A Few ExperimentsA Few Experiments““I have done a Terrible Thing, I have invented I have done a Terrible Thing, I have invented a particle that cannot be detected.”a particle that cannot be detected.”
W. PauliW. Pauli
What is giving mass to neutrinos?What is giving mass to neutrinos?
Nobel 2002: Raymond Davis Jr., Masatoshi KoshibaNobel 2002: Raymond Davis Jr., Masatoshi Koshiba
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A Few ExperimentsA Few Experiments
What’s causing this? (Dark Matter?)What’s causing this? (Dark Matter?)
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A Few ExperimentsA Few Experiments
What’s causing What’s causing thisthis? (Dark Energy?)? (Dark Energy?)
The Supernova Cosmology The Supernova Cosmology Project:Project:
Type Ia supernovae = extragalactic Type Ia supernovae = extragalactic ‘standard candles’‘standard candles’
The Supernovae are The Supernovae are too dim!too dim!
Universe accelerates!Universe accelerates!
Einstein’s Cosmological Einstein’s Cosmological constant constant ΛΛ ≠ 0 ≠ 0
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+ Muons …+ Muons …
(problematic)
• Muon spin precession
• Ability to control & handle muons to extreme precision may already be informing against the Standard Model:
muon storage ring (BNL)Is mu is, or is mu ain’t? Is mu is, or is mu ain’t?
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• WLWL scattering
• Pertubative scattering P > 1for s ~ 1 TeV2 • Need something (e.g. Higgs) to unitarize theory.
+ Some Mathematics+ Some Mathematics
¾» GF s16¼
(See also Bogdan’s talk)
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• The Standard model isn’t natural! – The Higgs is special, it’s the only (spin 0)– In QFT, the mass of a scalar gets huge contributions
from high-energy quantum fluctuations
+ Some Mathematics+ Some Mathematics
fluct. to top quark etc…
scalar
–But indirectly we know
There must be a spectacular cancellation occurring for this to happen THE HIERARCHY PROBLEM
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• Gravity does not fit in the Standard Model!– The graviton is special, it’s the only (spin 2)
– General Relativity: metric gμν describes curvature of space-time a mixture of S=0, S=1, and S=2 fields.
– In QFT, S=2 is no sense!
– Also, Gravity appears very weak compared to the other forces Does that mean anything?
+ Some Mathematics+ Some Mathematics
tensor
non-renormalizable
Gravity appears to be fundamentally incompatible with Quantum Field Theory!
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• Why more matter than antimatter?• Why 3 generations of quarks and leptons?• Why 3 forces?• Why 3 spatial dimensions?• Are particles really pointlike?• + your children’s favourite questions …
+ Some Aesthetics+ Some Aesthetics
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Open-minded model Open-minded model buildingbuilding
• So: we ask ourselves. Maybe …
Matter
Matter
–There could be new fundamental matter?– Is Dark Matter made of Particles? What are they like? WIMPS?
(Bogdan)
– How About Dark Energy? – More than 3 Generations of Fermions? – More Higgs Fields? 2HDM? radion? NMSSM?
– New Exotic Particles? With new quantum numbers?– Instantons? Cosmic Strings? Monopoles? …
–‘Fundamental’ Matter Might Be Composite?– Are Quarks or Leptons Composite? (excited fermions? top?)
– Is the Higgs particle a Composite? (Technicolor? Top seesaw?)
– Is Matter Made up of Strings?
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Open-minded model Open-minded model buildingbuilding
ForceForce
–There could be new fundamental interaction(s)?–New Short-range Gauge Forces? (Z’ / W’ ? Technicolor?)
–Could there be Lepton or Baryon Number Violation?
Matter
• So: we ask ourselves. Maybe …
(Bogdan)
GG
p ¡ gdx4³R ¡ ¹ 4n + 2
aR 2+bR ¹ º R ¹ º +cR ¹ º ¾½R ¹ º ¾½
´–What is gravity, at the fundamental level?– Deviations from Einstein Gravity? – What is The Quantum Description Of Gravity? – String Theory?
– Known forces might not be fundamental? – Grand Unification One Single Primeval Force?
[SU(5), SO(10), Supersymmetric Grand Unification, … ]
– ‘Stepwise unification’ ? Left-Right symmetry, flipped SU(5), …
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Open-minded model Open-minded model buildingbuilding
Spacetim
eS
pacetime
–There could be new symmetries of space-time?– Is There a Supersymmetry (SUSY) in Nature? (Probably most well-studied BSM possibility)
Matter
Force
• So: we ask ourselves. Maybe …
SUSY generators anticommute:
They relate particles of different spin:
Every SM state must have one (or more)
spin-partners!
scalar quarks and leptons, gluino,
gauginos, higgsinos
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Open-minded model Open-minded model buildingbuilding
Spacetim
eS
pacetime
–There could be new symmetries of space-time?– Is There a Supersymmetry (SUSY) in Nature? (Probably most well-studied BSM possibility)
Matter
Force
• So: we ask ourselves. Maybe …
Why should Nature have this weird symmetry?• SUSY is largest possible symmetry of space-time• Stabilises the Higgs mass no hierarchy problem• Good dark-matter candidate: lightest neutralino• SM GUT’s don’t work. SUSY GUT’s do• SUSY is the “super” in superstrings• (Gives experimentalists something to look for)
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Open-minded model Open-minded model buildingbuilding
Spacetim
eS
pacetime
–There could be new symmetries of space-time?– Is There a Supersymmetry (SUSY) in Nature? (Probably most well-studied BSM possibility
Matter
Force
• So: we ask ourselves. Maybe …
– Known symmetries might break down?– Is Lorentz Symmetry Violated to some Small Extent?
–There could be extra dimensions?– How Many are There? – What Do They Look Like? (Flat / Curved? Big / Small?)Big / Small?)– What Lives in Them? (All Matter / Gravity / Exotics /Exotics / Branes?)Branes?)
(Randall, last week)
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What can we say beforehand?What can we say beforehand?
Spacetim
eM
atterForce
• A] A complete theory should:– explain the origin of mass– explain dark matter and dark energy– explain neutrino masses– unitarize WW scattering– agree with all measurements so far– address the hierarchy problem– incorporate quantum gravity
• B] A complete theory could:– involve grand unification (we have hints of it)– involve a deviation from the SM (g-2)mu – be aesthetic and natural– be simple
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What can we say beforehand?What can we say beforehand?
Spacetim
eM
atterForce
• On one hand, we may roughly say– Simplest explanation for neutrino masses
involves no new observable physics – Quantum Gravity extremely difficult to probe
experimentally, due to smallness of hG – Dark Energy: no great ideas at the moment
• But!– Best Dark Matter candidate is a weakly-
interacting particle with <~ TeV-scale mass – WW scattering must be unitarised below the TeV
scale, probably by Higgs or similar – If Higgs is there, then hierarchy problem means
something new likely at TeV scale
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Collider physics in the post-Collider physics in the post-LHC eraLHC era
• We believe TeV scale to be inhabited
Textbook
Real life is more
complicated
–LHC: powerful machine, good discovery potential. Large backgrounds. Composite initial state. Strong-interaction debris, QCD radiation, beam remnants. Difficult to reach high precision.
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High Precision is *High Precision is *importantimportant*!*!• (apologies) ILC propaganda (but also works for MC!):
• High precision allows us to extrapolate to fundamental scales GUT? Superheavy intermediate physics?
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Collider physics in the post-Collider physics in the post-LHC eraLHC era
• ILC: precision machine. Below ~ 0.5 TeV.
• NB for SUSY: WMAP
COBECOBE
WMAPWMAPWilkinson Microwave Anisotropy Probe
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1 TeV1 TeV
??
Collider physics in the post-Collider physics in the post-LHC eraLHC era
• ILC: precision machine. Below ~ 0.5 TeV.
• WMAP killed the bulk
• CLIC: technically challenging, but serious alternative.
• Both are e+e- , muons are different.
–(E.g. intermediate SUSY Higgs factory at 500GeV?)
–Neutrino Factory
–Probe new physics differently
(talk by D. Cline)
(talk by B. Dobrescu)
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A Note on LuminosityA Note on Luminosity• Goal: L=1035 cm-2s-1 (acc. units)
L ~ 1000 fb-1 / yr 100 evts/yr for σ > 0.1 fb
• But lots of physics potential with smaller luminosity as well σ > “a few” fb.
• Physics case exists also for L=1032,33,34 cm-2s-1, due to high energy.
• (Large lumi still needed for precision)
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Outlook for the TeV scale and Outlook for the TeV scale and the muon colliderthe muon collider
• We believe the TeV scale to be inhabited
• The LHC is a powerful machine, but difficult to get high precision
• And high precision is important!
• If built, ILC will add immensely to our knowledge no matter what, but need higher energy if LHC indicates new physics is heavy
• Even if new physics is within ILC reach, it is likely only the top of an iceberg. Higher energies will still be needed to probe the full spectrum!