# Presentation: 336471

## 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

## Overview

- 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

- Beyond the Terascale with Muons

## Below the Terascale

- D. B. Leinweber, hep-lat/0004025

- Beyond the Terascale with Muons

## 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

- _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.)

- What works ...

- Beyond the Terascale with Muons

## What works

- data

- Standard Model

- . . . etc

- But is that all?

- Beyond the Terascale with Muons

## What Doesn’t

- The Standard Model does face a few problems:
- A few experiments ...
- Some mathematics ...
- Some cosmetics ...

-  is the TeV scale inhabited?

- Beyond the Terascale with Muons

## A Few Experiments

- “I have done a Terrible Thing, I have invented a particle that cannot be detected.”
- W. Pauli

- What is giving mass to neutrinos?

-     Nobel 2002:  Raymond Davis Jr., Masatoshi Koshiba

- Beyond the Terascale with Muons

## A Few Experiments

- What’s causing this? (Dark Matter?)

- Beyond the Terascale with Muons

## A Few Experiments

- What’s causing *this*? (Dark Energy?)

- The Supernova Cosmology Project:
- Type Ia supernovae = extragalactic ‘standard candles’
- The Supernovae are too dim!
- Universe accelerates!

-  Einstein’s Cosmological constant Λ ≠ 0

- Beyond the Terascale with 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?

- Beyond the Terascale with Muons

## WLWL scattering

Pertubative scattering P > 1for s ~ 1 TeV2 
Need something (e.g. Higgs) to unitarize theory.

- Pertubative scattering P > 1for s ~ 1 TeV2
- Need *something* (e.g. Higgs) to unitarize theory.

- + Some Mathematics

- (See also Bogdan’s talk)

- Beyond the Terascale with Muons

## 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

- 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

-  fluct. to top quark etc...

- scalar

- Beyond the Terascale with Muons

## 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?

- 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

- tensor

- non-renormalizable

- Gravity appears to be fundamentally incompatible with Quantum Field Theory!

- Beyond the Terascale with Muons

## 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 ...

- 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

- Beyond the Terascale with Muons

## Open-minded model building

- So: we ask ourselves. Maybe ...

- (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_?

- Beyond the Terascale with Muons

## Open-minded model building

- Force

- 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)

-  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), ...

- Beyond the Terascale with Muons

## Open-minded model building

- Spacetime

- 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 ...

- Beyond the Terascale with Muons

## Open-minded model building

- Spacetime

- 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)

- Beyond the Terascale with Muons

## Open-minded model building

- Spacetime

- 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?)
-  What Lives in Them? 			(All Matter / Gravity / Exotics / Branes?)

- (Randall, last week)

- Beyond the Terascale with Muons

## What can we say beforehand?

- Spacetime

- Matter

- Force

- 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

- Beyond the Terascale with Muons

## What can we say beforehand?

- Spacetime

- Matter

- Force

- 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 

- Beyond the Terascale with Muons

## Collider physics in the post-LHC 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.

- Beyond the Terascale with Muons

## 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?

- Beyond the Terascale with Muons

## Collider physics in the post-LHC era

- ILC: precision machine. Below ~ 0.5 TeV.
- NB for SUSY: WMAP

- COBE

- WMAP
- Wilkinson Microwave Anisotropy Probe

- Beyond the Terascale with Muons

## 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 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)

- Beyond the Terascale with Muons

## A 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)

- Beyond the Terascale with Muons

## 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!

- Beyond the Terascale with Muons