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 Muons2 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 Muons3 Below the Terascale D. B. Leinweber, hep-lat/

Beyond the Terascale with Muons4 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.) What works … symmetry breaking masses 1 Higgs boson (scalar)

Beyond the Terascale with Muons5 What works dataStandard Model... etc But is that all?

Beyond the Terascale with Muons6 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 Muons7 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 Nobel 2002: Raymond Davis Jr., Masatoshi Koshiba

Beyond the Terascale with Muons8 A Few Experiments What’s causing this? (Dark Matter?)

Beyond the Terascale with Muons9 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 Muons10 + 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 Muons11 W L W L scattering Pertubative scattering P > 1for s ~ 1 TeV 2 Need something (e.g. Higgs) to unitarize theory. + Some Mathematics ¾ » G F s 16 ¼ (See also Bogdan’s talk)

Beyond the Terascale with Muons12 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 fluct. to top quark etc… scalar – –But indirectly we know There must be a spectacular cancellation occurring for this to happen  THE HIERARCHY PROBLEM

Beyond the Terascale with Muons13 Gravity does not fit in the Standard Model! –The graviton is special, it’s the only (spin 2) –General Relativity: metric g μν 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 Muons14 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

Beyond the Terascale with Muons15 Open-minded model building So: we ask ourselves. Maybe … 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?

Beyond the Terascale with Muons16 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) G p ¡ g d x 4 ³ R ¡ ¹ 4 n + 2 a R 2 + b R ¹º R ¹º + c R ¹º¾½ R ¹º¾½ ´ – –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), …

Beyond the Terascale with Muons17 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 … 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

Beyond the Terascale with Muons18 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 Muons19 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? – Big / Small?) – What Do They Look Like? (Flat / Curved? Big / Small?) – Exotics /Branes?) – What Lives in Them? (All Matter / Gravity / Exotics / Branes?) (Randall, last week)

Beyond the Terascale with Muons20 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 Muons21 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 Muons22 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 Muons23 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 Muons24 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 Muons25 1 TeV ? 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 Muons26 A Note on Luminosity Goal: L=10 35 cm -2 s -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=10 32,33,34 cm -2 s -1, due to high energy. (Large lumi still needed for precision)

Beyond the Terascale with Muons27 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!