What Particle PhysicistsWant to Know

Hitoshi MurayamaLetters & Science Forum

December 2, 2002

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We are interested inthings we don’t see

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Energy budget of Universe

• Stars and galaxies are only ~0.5%• Neutrinos are ~0.3–10%• Rest of ordinary matter (electrons and protons) are

~5%• Dark Matter ~30%• Dark Energy ~65%• Anti-Matter 0%• Higgs condensate ~1062%??

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The Cosmic Questions

• What is Dark Matter?• What is Dark Energy?• How much is Neutrino component?• Is Higgs Boson really there?• Where did Anti-Matter go?

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Einstein’s Dream

• Is there an underlying simplicity behind vast phenomena in Nature?

• Einstein dreamed to come up with a unified description

• But he failed to unify electromagnetism and gravity (GR)

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History of Unification

gravity

electric magnetic

-decay

-decay

-decay

planets apple

electromagnetiesm

atoms

Quantum mechanicsmechanics

Special relativity

Quantum ElectroDynamics Weak force

Strong forceElectroweak theory

Grand Unification?

GR

String theory?

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We are just about to achieveanother layer of unification

• HERA ep collider • Unification of electromagnetic and weak forces electroweak theory

• Long-term goal since ‘60sWe are getting there!

• The main missing link: Higgs boson

EMweak

What are they?

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“Wimpy and Abundant”Neutrinos are Everywhere

• They come from the Big Bang:– When the Universe was hot, neutrinos were created equally with

any other particles– They are still left over: ~300 neutrinos per cm3

• They come from the Sun:– Trillions of neutrinos going through your body every second

• They are shy:– If you want to stop them, you need to stack up lead shield up to

three light-years

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Neutrinosfrom backstage to center stage

• Pauli postulated neutrinos in order to save the energy conservation in nuclear -decay in 1930

• Finally discovered by Cowan and Reines using a nuclear reactor in 1958

• Massless Neutrinos in the Standard Model (‘60s)

• Evidence for neutrino mass from SuperK (1998) and SNO (2002)

• First evidence that the minimal Standard Model of particle physics is incomplete!

• 2002 Nobel to pioneers: Davis and Koshiba

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Neutrinos Have Mass

SuperKamiokande

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Raised More Questions

• Why do neutrinos have mass at all?

• Why so small?– At least million times

smaller than the lightest particle: electron

• We have seen mass differences. What are the masses? ~m/15eV

• Are neutrinos and anti-neutrinos the same?

• How do we extend the Standard Model to incorporate massive neutrinos?

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Evidence for Dark Matter

• Galaxy and cluster of galaxies are held together by mass far bigger than all stars combined

• Crucial ingredient in the “standard cosmology” and structure formation

• It is not dim small stars (e.g., MACHOs)

• WIMPs (Weakly Interacting Massive Particle) strongly favored

• Stable heavy particle produced in early Universe, left-over from near-complete annihilation

• TeV=1012eV (or T=1016 degrees): the correct energy scale to produce them

Giacconi2002 NobelFather of X-ray astronomy

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Type-IA Supernovae

• Type-IA Supernovae “standard candles”

• Brightness not quite standard, but correlated with the duration of the brightness curve

• Apparent brightness how far (“time”)

• Know redshift expansion since then

Expansion of Universe is accelerating

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Accelerating Universe

• Einstein’s equation:

• If the energy dilutes as Universe expands, it must slow down

• Need something that gains in energy as Universe stretches

i.e, negative pressure• The cosmological constant has

the equation of state w=p/=–1• Generically called “Dark

Energy”

€

˙ R R( )

2= 8π

3 GN ρ

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Embarrassment with Dark Energy

• A naïve estimate of the cosmological constant in Theory: ~MPl

4=GN–2~10120 times observation

The worst prediction in theoretical physics!• People had argued that there must be some

mechanism to set it zero• But now it seems finite???

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Cosmic Coincidence Problem

• Why do we see matter and cosmological constant almost equal in amount?

• “Why Now” problem• Actually a triple

coincidence problem including the radiation

• If there is a deep reason for ~ GN

2(TeV)8, coincidence natural Arkani-Hamed, Hall, Kolda, HM

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What is the Dark Energy?

• We have to measure w• For example with a

dedicated satellite experiment

Domain wall

Friedland, HM, PerelsteinSNAP

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Mystery of the “weak force”

• Gravity pulls two massive bodies (long-ranged)

• Electric force repels two like charges (long-ranged)

• “Weak force” pulls protons and electrons (short-ranged) acts only over 10–16 cm [need it for the Sun to burn!]

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Something is in the Universe

• There is something filling our Universe• It doesn’t disturb gravity or electric force• It does disturb weak force and make it short-ranged• No longer go with speed of light, acquire a mass• “Mother of mass” of all elementary particles

– Electron, quarks, muon, …• What is it??

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Cosmology and Particle Physicsmeet at TeV scale

• Dark MattermWIMP~TeV

• Fermi (Higgs) scalev~1/4 TeV

• Dark Energy~(2meV)4 vs GN

–1/2(TeV)2~0.5meV• Neutrino

(m2LMA)1/2~7meV vs GN

–1/2(TeV)2~0.5meV TeV-scale physics likely to be rich

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LHC

• Large Hadron Collider• 14 TeV pp• CERN (Geneva)

• Under construction • LHC would discover

Standard Model Higgs boson of any mass within 3 years!

• Measure mass, some ratio of couplings

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LC

• Linear e+e– Collider• 0.5–1.5 TeV• International Project• Planning stage• Tests if Higgs Boson

is the “Mother of Mass”

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Dark Matter:The Missing Link?

• Dark Matter likely to be TeV-scale electrically neutral weakly interacting particle (e.g., LSP, Lightest KK)

• Then accessible at accelerators (LHC & LC)• Precision measurement at LC of its mass, couplings

in order to calculate its cosmic abundance• If it agrees with cosmological observations, we

understand Universe back to 10–10 sec after the Big Bang

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Where Did Anti-Matter Go?

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Matter and Anti-MatterEarly Universe

q q

10,000,000,001 10,000,000,000

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Matter and Anti-MatterCurrent Universe

q q

The Great Annihilation

1

us

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Baryogenesis

• What created this tiny excess matter? • Necessary conditions for baryogenesis (Sakharov):

– matter number non-conservation– CP violation

(subtle difference between matter and anti-matter)– Non-equilibrium (B>0) > (B<0)

• Possible new consequences in– Matter instability– CP violation

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Do We Exist Thanks to Neutrino Mass?

• Plans to shoot neutrino beams over thousands of kilometers to see this

• CP-violation may be observed in neutrino oscillation

It’s of course completely safe!

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Conclusion

• What is Universe made of?• Einstein’s Dream towards unified description• Physics at TeV scale likely to be rich• LHC & LC: major assault on physics at TeV-scale• Many cosmic questions accessible experimentally

– Dark Matter, Dark Energy, Higgs Condensate, Anti-Matter