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Beyond the Terascale with muons

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Fermilab Accelerator Physics and Technology Seminar / Low-Emittance Muon ... Why more matter than antimatter? Why 3 generations of quarks and leptons? Why 3 forces? ... – PowerPoint PPT presentation

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Title: Beyond the Terascale with muons


1
Beyond the Terascale with muons
Fermilab Accelerator Physics and Technology
Seminar / Low-Emittance Muon Collider Workshop,
Fermilab, February 2006
Peter Skands Theoretical Physics Dept
Fermi National Accelerator Laboratory
2
Overview
  • Introduction the Standard Model
  • What works
  • What doesnt
  • Beyond the Standard Model
  • Open-minded model building
  • Inspirational examples
  • Collider Physics in the post-LHC era

3
Below the Terascale
D. B. Leinweber, hep-lat/0004025
4
The Standard Model (s.m.)
What works
  • 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

5
What works
data
Standard Model
. . . etc
But is that all?
6
What Doesnt
  • The Standard Model does face a few problems
  • A few experiments
  • Some mathematics
  • Some cosmetics
  • ? is the TeV scale inhabited?

7
A Few Experiments
I have done a Terrible Thing, I have invented a
particle that cannot be detected. W. Pauli
Nobel 2002 Raymond Davis Jr., Masatoshi
Koshiba
What is giving mass to neutrinos?
8
A Few Experiments
Whats causing this? (Dark Matter?)
9
A Few Experiments
  • The Supernova Cosmology Project
  • Type Ia supernovae extragalactic standard
    candles
  • The Supernovae are too dim!
  • Universe accelerates!

? Einsteins Cosmological constant ? ? 0
Whats causing this? (Dark Energy?)
10
Muons
  • Muon spin precession
  • Ability to control handle muons to extreme
    precision may already be informing against the
    Standard Model

(problematic)
Is mu is, or is mu aint?
muon storage ring (BNL)
11
Some Mathematics
  • WLWL scattering
  • Pertubative scattering P gt 1for s 1 TeV2
  • Need something (e.g. Higgs) to unitarize theory.

(See also Bogdans talk)
12
Some Mathematics
  • The Standard model isnt natural!
  • The Higgs is special, its the only
    (spin 0)
  • In QFT, the mass of a scalar gets huge
    contributions from high-energy quantum
    fluctuations

scalar
fluct. to top quark etc
13
Some Mathematics
  • Gravity does not fit in the Standard Model!
  • The graviton is special, its the only
    (spin 2)
  • General Relativity metric gµ? describes
    curvature of space-time ? a mixture of S0, S1,
    and S2 fields.
  • In QFT, S2 is
    ? no sense!
  • Also, Gravity appears very weak compared to the
    other forces ? Does that mean anything?

tensor
non-renormalizable
Gravity appears to be fundamentally incompatible
with Quantum Field Theory!
14
Some Aesthetics
  • Why more matter than antimatter?
  • Why 3 generations of quarks and leptons?
  • Why 3 forces?
  • Why 3 spatial dimensions?
  • Are particles really pointlike?
  • your childrens favourite questions

15
Open-minded model building
  • So we ask ourselves. Maybe
  • How About Dark Energy?
  • More than 3 Generations of Fermions?
  • More Higgs Fields? 2HDM? radion? NMSSM?
  • New Exotic Particles? With new quantum numbers?

(Bogdan)
  • 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?

16
Open-minded model building
  • So we ask ourselves. Maybe
  • There could be new fundamental interaction(s)?
  • New Short-range Gauge Forces? (Z / W ?
    Technicolor?)
  • Could there be Lepton or Baryon Number Violation?

Matter
(Bogdan)
  • 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),

Force
17
Open-minded model building
  • So we ask ourselves. Maybe
  • There could be new symmetries of space-time?
  • Is There a Supersymmetry (SUSY) in Nature?
    (Probably most well-studied BSM possibility)

Matter
Force
Spacetime
18
Open-minded model building
  • So we ask ourselves. Maybe
  • There could be new symmetries of space-time?
  • Is There a Supersymmetry (SUSY) in Nature?
    (Probably most well-studied BSM possibility)

Matter
  • 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 GUTs dont work. SUSY GUTs do
  • SUSY is the super in superstrings
  • (Gives experimentalists something to look for)

Force
Spacetime
19
Open-minded model building
  • So we ask ourselves. Maybe
  • There could be new symmetries of space-time?
  • Is There a Supersymmetry (SUSY) in Nature?
    (Probably most well-studied BSM possibility

Matter
  • Known symmetries might break down?
  • Is Lorentz Symmetry Violated to some Small
    Extent?

Force
  • There could be extra dimensions?
  • How Many are There?
  • What Do They Look Like? (Flat / Curved? Big /
    Small?)
  • What Lives in Them? (All Matter / Gravity /
    Exotics / Branes?)

(Randall, last week)
Spacetime
20
What can we say beforehand?
  • 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

Matter
Force
Spacetime
21
What can we say beforehand?
  • 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 ?

Matter
Force
  • But!
  • Best Dark Matter candidate is a
    weakly-interacting particle with lt 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 ?

Spacetime
22
Collider physics in the post-LHC era
  • We believe TeV scale to be inhabited
  • LHC powerful machine, good discovery potential.
    Large backgrounds. Composite initial state.
    Strong-interaction debris, QCD radiation, beam
    remnants. Difficult to reach high precision.

Real life is more complicated
Textbook
23
High Precision is important!
  • (apologies) ILC propaganda (but also works for
    MC!)
  • High precision allows us to extrapolate to
    fundamental scales ? GUT? Superheavy intermediate
    physics?

24
Collider physics in the post-LHC era
  • ILC precision machine. Below 0.5 TeV.
  • NB for SUSY WMAP

COBE
WMAP Wilkinson Microwave Anisotropy Probe
25
Collider physics in the post-LHC era
  • ILC precision machine. Below 0.5 TeV.
  • WMAP killed the bulk ?
  • CLIC technically challenging, but serious
    alternative.
  • Both are ee- , 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)
26
A Note on Luminosity
  • Goal L1035 cm-2s-1 (acc. units)
  • ? L 1000 fb-1 / yr ? 100 evts/yr for s gt 0.1 fb
  • But lots of physics potential with smaller
    luminosity as well ? s gt a few fb.
  • Physics case exists also for L1032,33,34
    cm-2s-1, due to high energy.
  • (Large lumi still needed for precision)

27
Outlook for the TeV scale and the 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!
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