Beyond the Terascale with muons Fermi National Accelerator Laboratory Peter Skands Theoretical Physics Dept Fermilab Accelerator Physics and Technology

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

Beyond the Terascale with Muons 2

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


Below the TerascaleBelow the Terascale

D. B. Leinweber, hep-lat/0004025


• 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)


What worksWhat worksdatadata Standard ModelStandard Model

. . . etc. . . etc

But is that all?But is that all?


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?


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


A Few ExperimentsA Few Experiments

What’s causing this? (Dark Matter?)What’s causing this? (Dark Matter?)


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


+ 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?


• 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)


• 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


fluct. to top quark etc…

scalar

–But indirectly we know

There must be a spectacular cancellation occurring for this to happen THE HIERARCHY PROBLEM


• 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?


tensor

non-renormalizable

Gravity appears to be fundamentally incompatible with Quantum Field Theory!


• 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


Open-minded model Open-minded model buildingbuilding

• So: we ask ourselves. Maybe …

Ma

tterM

atter

–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?



Fo

rceF

orce

–There could be new fundamental interaction(s)?–New Short-range Gauge Forces? (Z’ / W’ ? Technicolor?)

–Could there be Lepton or Baryon Number Violation?

Ma

tter


(Bogdan)

GG

p¡ gdx4

³R ¡ 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), …



Sp

acetim

eS

pace

time

–There could be new symmetries of space-time?– Is There a Supersymmetry (SUSY) in Nature? (Probably most well-studied BSM possibility)

Ma

tterF

orce


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



Sp

acetim

eS

pace

time

–There could be new symmetries of space-time?– Is There a Supersymmetry (SUSY) in Nature? (Probably most well-studied BSM possibility)

Ma

tterF

orce


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)



Sp

acetim

eS

pace

time

–There could be new symmetries of space-time?– Is There a Supersymmetry (SUSY) in Nature? (Probably most well-studied BSM possibility

Ma

tterF

orce


– 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)


What can we say beforehand?What can we say beforehand?

Sp

acetim

eM

atter

Fo

rce

• 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


What can we say beforehand?What can we say beforehand?

Sp

acetim

eM

atter

Fo

rce

• 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


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.


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?



• ILC: precision machine. Below ~ 0.5 TeV.

• NB for SUSY: WMAP

COBECOBE

WMAPWMAPWilkinson Microwave Anisotropy Probe


1 TeV1 TeV

??


• 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)


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)


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!

Documents

Beyond the Terascale with muons Fermi National Accelerator Laboratory Peter Skands Theoretical Physics Dept Fermilab Accelerator Physics and Technology