Future Directions in Particle Physics

Physical and Biological Sciences Staff Lecture, UCSC

Michael DineMay 2006

http://www4.nationalacademies.org/news.nsf/isbn/0309101948?OpenDocument

Particle physics is a major activity in this division, centered around the Santa

Cruz Institute for Particle Physics, SCIPP

•Experiment: 5 regular faculty, 3 adjuncts, 10 postdocs, researchers, 12 graduate students, 5 technical staff•Theory: 3 faculty, two postdocs, 5 graduate students•Staff: 2(These are rough numbers)

What is particle physics?

Particle physics is just that – the study of particles. What are the proton and neutron? What are they made of? What about the electron? How do all of these particles interact with each other? The tools: mainly big machines, particle accelerators.

Why Bother?

No direct applications in the forseeable future (spinoffs include accelerator technologies in medicine, WWW, but one doesn’t engage in such an endeavor to produce spinoffs).• Learning about the elementary particles, we learn what are the laws of nature which operate at very small distance scales.• Knowing the laws allows us to understand the universe

Gravitation

Newton: F=ma = mM/R2

Probably the most famous physical laws. UNIVERSAL

Laws of Nature:

Newton could use his laws to explain the motion of the planets, the moon. Haley – comets.

Electricity and Magnetism:Faraday

Conducted experiments which showed that a changing electric field produces a magnetic field and vice versa, and that a changing magnetic field induces current (generators)

Electricity and magnetism aspects of one related set of phenomena: ELECTROMAGNETISM.

Laws of Nature:

Electricity and Magnetism:Maxwell

Wrote down the laws of electricity and magnetism; Maxwell’s equations. Light, radio waves (Maxwell predicted), and other radiation all part of the same set of phenomena.

Laws of Nature:

HERTZ: RADIO WAVES

The end of the 19th century saw the discovery of the first elementary particle, by Thompson – the electron.

EINSTEIN

Excited by Maxwell’s equations and also puzzled. There seemed to be a maximal speed at which light could travel.Puzzled, also by the problem of the photoelectric effect – the emission of electrons by light. 1905: SPECIAL RELATIVITY: time and space are relative concepts, depend on the observer. But the speed is absolute; all observers agree about it. Not important when v ¿ c, but very important in the day-to-day lives of particle physicists.

Laws of Nature:

General RelativityNow, a deeper understanding of the laws of electricity and magnetism. But Einstein didn’t know how to reconcile Newton’s laws with the rules of relativity.

Einstein’s clue: the equality of gravitational and inertial mass: F=ma FG= mM/R2

Inertia – something to do with space and time. So gravity?

Einstein and the General Theory of Relativity

After almost eleven years of struggle, Einstein announced his general theory of relativity in 1916. A theory in which gravity arises as the distortion of space and time by energy. Proposed three experimental tests:

•Bending of light by the sun•Perihelion of Mercury•Red Shift•Recent years: pulsar timing (Thorsett), LIGO (Barish, Seiden)

LIGO (searching for gravitational waves) [Barish, Seiden]

New particles, new laws

• 1911 - discovery of the atomic nucleus

• 1920’s – quantum mechanics

• 1930’s – the neutron, and understanding of the atomic nucleus.

• 1930’s – discovery of antimatter.

Rutherford’s Discovers the Nucleus (not quite an accelerator)

"It was quite the most incredible event that ever happened to me in my life. It was almost as incredible as if you had fired a 15-inch shell at a piece of tissue paper and it came back and hit you."

LOOKING STILL DEEPER

By the 1940’s, much progress, but much not well understood:

• Photons• The precise laws underlying the nuclear

forcesTo go further: theoretical developments Experiments probing distances smaller than the size of nuclei

Quantum Electrodynamics

Feynman, Schwinger, Tomanaga: detailed understanding of how quantum mechanics and electricity and magnetism work together. Predictions with awesome precision. E.g. the magnetism of the electron explained in terms of the electron’s charge and mass to one part in 1012.

The Accelerator Era

The late 1940’s launched the era of large particle accelerators. Some of the important discoveries (also cosmic rays):

• Particles like the electron, but heavier: • Three kinds of neutrino

• Neutrons, protons made up of quarks

Stanford Linear Accelerator

Quarks were discovered at SLAC, in an experiment much

like Rutherford’s.

SPEAR collided electrons and positrons (anti-electrons) producing a previously unknown

form of matter, made of a new type of quark, the charmed quarks (1974).

Experiments at SLAC and other accelerators established the full Standard model:•Brookhaven, Fermilab: more quarks (b,t)•SLAC, LEP: The Z boson (Lidtke, Johnson, Schumm, Coyne, Seiden, Sadrozinski, …)•SLAC: Studies of the asymmetry between antimatter and matter (BaBar – Schumm, Seiden….)

quantum field theory, describing interactions between quantum field theory, describing interactions between pointlike spin-1/2 particles (quarks and leptons) pointlike spin-1/2 particles (quarks and leptons) via exchange of spin-1 vector bosons (photon, W and Z, gluon)via exchange of spin-1 vector bosons (photon, W and Z, gluon)

fundamental particles (fermions)fundamental particles (fermions) 2 (particle pair) * 2 (particle pair) * 3 (generations)* 3 (generations)* 2 (anti-particles) 2 (anti-particles) 19951995

20002000

The Standard Model (I)The Standard Model (I)

electrical chargeelectrical charge +2/3+2/3 -1/3-1/3 -1/3-1/3 -1/3-1/3+2/3+2/3 +2/3 (?)+2/3 (?)

1 GeV= proton mass1 GeV= proton mass

quark massesquark massesand breaking of symmetry ?and breaking of symmetry ?

The Standard Model (II)The Standard Model (II)

why thiswhy thispatternpattern

... weakest force ...... weakest force ...

... irrelevant in... irrelevant in microcosm ...microcosm ...

Fundamental InteractionsFundamental Interactions

9.

Mw=82;Mz=91

Back to theory.

Theorists played crucial role in development of the Standard Model:•Feynman, Gell-Mann: quarks•Gross, Politzer, Wilczek, ‘t hooft: developed and understood detailed theory of interactions•Local theorists – Banks (work on how quarks are bound into protons and neutrons), Dine (calculation of total rate of electron-positron collisions at SLAC), Haber (Higgs phenomenology), Primack (high energy interactions of quarks)– all made contributions (in their youths!)

Are we satisfied with the Standard Model? -- Yes and no. Incredibly successful. At this moment, no interesting discrepancies in hundreds of measurements, many to part in 1000.

Electroweak Precision DataElectroweak Precision Data

... need to consider... need to consider quantum fluctuations ...quantum fluctuations ...

MMZZ22 = = MMZZ

2 0.order2 0.order

comparison :comparison :precision measurement precision measurement ⇔⇔ correction correction⇨⇨prediction of mass of prediction of mass of top quarktop quark

ΔΔ ... ... mmtt22 ... + ... ... + ... ln mln m

hh ... ...

MMZZ22 = = MMZZ

2 0.order2 0.order / (1 - / (1 - ΔΔ))

But puzzles:

•Many parameters (masses of the particles, strengths of the interactions between particles). Where do they come from?•The mass of the Higgs particle is very difficult to understand. We know it’s not much heavier than the W and Z. But according to principles of quantum mechanics, it should be much heavier.•General relativity – gravitation – can’t be sensibly combined. Some have even argue that General Relativity shows that quantum mechanics must be incomplete.

One proposal for new physics: Supersymmetry

A possible new symmetry of nature. Explains why Higgs is light; explains strength of the strong interactions. Makes dramatic predictions for experiments.

A symmetry between ``bosons” (photon, gluons, W’s and Z’s) and ``fermions” (electrons, quarks, neutrinos…).

An attractive Extension: SupersymmetryAn attractive Extension: Supersymmetry

... doubled particle spectrum ... ☹... doubled particle spectrum ... ☹

Symmetry betweenSymmetry between

FermionsFermions ↔↔ BosonsBosons(m(matteratter)) (force carrier)(force carrier)

Extensive searches; so far haven’t seen.

g

g

q

q~

q~

The theorists at UCSC have all worked on supersymmetry, and made significant contributions:•Dine: one of the first to build models of supersymmetry and consider their phenomenology at accelerators; developed the theory of supersymmetry breaking•Haber: developed the phenomenology of supersymmetry at accelerators in some detail•Banks: models of supersymmetry, supersymmetry breaking, connections to string theory (more later)•Primack: more in a moment

Back to Experiment

Many other ideas to address these problems. All suggest new particles with masses of order 1000 times mp, or about 1 TeV (mc2).

Where to find them? The LHC. Beginning operation in late 2007. If supersymmetry, other hypotheses are correct, we will know in a few years.

The TEVATRON at FermilabThe TEVATRON at Fermilab

60 km60 km

Main Injector & Recycler

Tevatron

Booster

p p

p source

Chicago

_

_

p

s =1.8 - 1.96 TeV, Δt = 396 nsRun I 1987 (92)-95 LRun I 1987 (92)-95 L

intint ~ 125 pb ~ 125 pb-1-1

Run II 2001-09 4-9 fbRun II 2001-09 4-9 fb-1-1

p _

CDF & DCDF & DØ data taking Ø data taking εε ~90% ~90%

~ 1.5 fb~ 1.5 fb-1-1

delivereddelivered

~ 1.2 fb~ 1.2 fb-1-1

recordedrecorded

Recent Results from the Tevatron -Selected Highlights- 2.11.2005, Arnulf Quadt Seite 38

9.March 2006: Hadron Collider Physics - Arnulf Quadt – UCSC Colloquium Page 38

The Large Hadron Collider - LHCThe Large Hadron Collider - LHC

LHC dipolesLHC dipoles LHC quadrupolesLHC quadrupoles

ATLASATLAS

CMSCMS

The The LLarge arge HHadron adron CCollider:ollider: proton-proton collider (no p)proton-proton collider (no p) ⇨⇨2 separate beampipes2 separate beampipes first collisions in 2007first collisions in 2007 high energy: high energy: s = 14 TeVs = 14 TeV 40 Mio. collisions per second40 Mio. collisions per second 4 experiments:4 experiments: ATLAS, CMS, ALICE, LHC-BATLAS, CMS, ALICE, LHC-B 10 fb10 fb-1-1 per year per year

__

9.March 2006: Hadron Collider Physics - Arnulf Quadt – UCSC Colloquium Page 39

The CDF & DThe CDF & DØØ Experiment Experiment

9.March 2006: Hadron Collider Physics - Arnulf Quadt – UCSC Colloquium Page 40

Precise tracking and vertexingPrecise tracking and vertexing new bigger silicon/fiber tracker, new drift chamber, TOFnew bigger silicon/fiber tracker, new drift chamber, TOF Upgraded calorimeter and muon systemUpgraded calorimeter and muon system Upgraded DAQ/triggerUpgraded DAQ/trigger ~670 - 750 physicists~670 - 750 physicists

resolutions:resolutions:EM: EM: σσEE/E = 13.5 - 15% / sqrt(E)/E = 13.5 - 15% / sqrt(E)HAD: HAD: σσEE/E = 50 – 80 % / sqrt(E)/E = 50 – 80 % / sqrt(E)

The CDF & DThe CDF & DØØ Experiment Experiment

9.March 2006: Hadron Collider Physics - Arnulf Quadt – UCSC Colloquium Page 41

Precise tracking and vertexing Precise tracking and vertexing silicon pixel and strip detectors & transition radiation det.silicon pixel and strip detectors & transition radiation det. 2 & 4 T solenoid and toroid magnets (air core or iron core)2 & 4 T solenoid and toroid magnets (air core or iron core) EM & Had Calorimeters and muon systemsEM & Had Calorimeters and muon systems Fast DAQ/triggerFast DAQ/trigger ~~ 1 600 physicists each 1 600 physicists each

resolutions:resolutions:EM: EM: σσEE/E = 0.5 - 10% / sqrt(E)/E = 0.5 - 10% / sqrt(E)HAD: HAD: σσEE/E = 50 – 70 % / sqrt(E)/E = 50 – 70 % / sqrt(E)

The ATLAS & CMS ExperimentThe ATLAS & CMS Experiment

9.March 2006: Hadron Collider Physics - Arnulf Quadt – UCSC Colloquium Page 42

weightweightheightheightlengthlengthmagnet magnet (solenoid)(solenoid)

7 000 t7 000 t22 m22 m42 m42 m

2 Tesla2 Tesla

weightweightheightheightlengthlengthmagnet magnet (solenoid)(solenoid)

12 500 t12 500 t15 m15 m22 m22 m

4 Tesla4 Tesla

The ATLAS and CMS ExperimentThe ATLAS and CMS Experiment

9.March 2006: Hadron Collider Physics - Arnulf Quadt – UCSC Colloquium Page 43

Particle Physics and the Big Bang

These are puzzles in our understanding of the laws. There are also puzzles in our understanding of the universe.

Don’t have time to describe the Big Bang, but this is an area where UCSC theorists spend much of their research time (Aguirre, Banks, Dine, Primack). Here just note that from detailed astronomical and astrophysical observations we know that the universe, billions of years ago, was smaller and very hot. In the last decade we have learned a great deal about the composition of the universe:

COMPOSITION OF THE UNIVERSE

From studies of CMBR, of distant Supernova explosions, and from Hubble and Ground-Based observations we know:

• 5% Baryons (protons, neutrons)• 30% Dark Matter [???] (zero pressure)• 65% Dark Energy [????] (negative pressure)

New York Times: April, 2003

Reports a debate among cosmologists about the Big Bang.

lll1.html

Rounding out the field were Dr. Lee Smolin, a gravitationaltheorist at the Perimeter Institute for Theoretical Physicsin Waterloo, Ontario, whom Dr. Tyson described as "alwaysgood for an idea completely out of left field - he's hereto stir the pot";

But Dr. Smolin said the 20th-century revolution was not

complete. His work involves trying to reconcile Einstein's

general relativity, which explains gravity as the

"curvature" of space-time, with quantum mechanics, the

strange laws that describe the behavior of atoms.

"Quantum mechanics and gravity don't talk to each other,"

he said, and until they do in a theory of so-called quantum

gravity, science lacks a fundamental theory of the world.

The modern analog of Newton's Principia, which codified the

previous view of physics in 1687, "is still ahead of us,

not behind us," he said.

Although he is not a cosmologist, it was fitting for him to

be there, he said, because "all the problems those guys

don't solve wind up with us."

But Smolin is wrong. The proper address is particle physics.•Origin of the baryons: again, can be understood if supersymmetry (Dine).•Dark matter: we know that this is some new type of elementary particle. In supersymmetry, automatically a particle which plays this role (Primack; Banks, Dine, Haber). Another candidate: axions (Dine). Both subject of experimental search.•Dark energy: much harder. Only theoretical structure currently available: string theory (Aguirre, Banks, Dine)

String Theory

Smolin states we don’t know how to reconcile quantum mechanics and general relativity. But we have known for a long time that a theory where the basic entities are strings (rather than point particles) looks a lot like the Standard Model plus general relativity. Obeys all of the rules of quantum mechanics.

Strings colliding

At first glance, the theory is very attractive. Has Einstein’s theory, quarks, leptons, gauge bosons. Much pretty mathematics. Pretensions to explain all of the parameters of the Standard Model (masses and couplings). Has supersymmetry, candidates for dark matter and dark energy. Some very interesting physics and mathematics. But much which is not understood.

Banks, Dine: focus on how to extract predictions for processes which can be studied in accelerators or the cosmos. Esp. supersymmetry in accelerators, and cosmology of the extremely early universe.

The future: The ILCe+ e-

10-20 km

long linac constructed of many RF accelerating structures

typical gradients range from 2560 MV/m

single shot

One working machine SLC at SLAC proof of principle

International Linear Collider

Aug 2004: Technology decision

• Baseline: 200 GeV < √s < 500 GeV Integrated luminosity ~ 500 fb-1 in 4 years80 % e- beam polarisationUpgrade to 1TeV, L = 1 ab-1 in 3 years2 interaction regionsConcurrent running with the LHC from 2015

PDG Wall Chart

Detailed study of the CMBR:

From satellites and earth based (balloon) experiments. Most recently the WMAP satellite.

Detailed information about the universe: