Presentation at Sonoma State “What Physicists Do” SeriesMichael Dine, University of California, Santa Cruz, Feb., 2009

Einstein spoke of the “incomprehensible comprehensibility” of nature. Consciously or not, this viewpoint drives much of what we do in science, especially in astronomy, astrophysics and particle physics. When we see surprising or interesting features in nature, we believe we should be able, over time, to understand them. This view has historical support. LHC/Fermi-GLAST – two instruments to extend our understanding.

Aerial view of LHC

Muon Toroids

Muon superconductingToroids in the ATLAS Detector at the LHC

GLAST (Fermi) launch, June

What are we hoping to learn with these instruments?

Convergence of particle physics, astrophysics and cosmology:1.What are the basic laws of nature: an ingredient in any study of the universe (compare nuclear physics, stars)?2.What is the composition of the universe?3.How did the universe get to be as it is?

Particle physicists, in the past few decades, have determined completely the laws of nature which govern phenomena on scales as small as 10-17 cm. Embodied in the Standard Model, which describes the strong nuclear force, the weak nuclear force, and electromagnetism (light, electricity, magnetism…)

This model has been subjected to stringent tests.

PDG Wall Chart

Previous generation of instruments: Stanford Linear Accelerator

Quarks were discovered at SLAC

Later, precision studies of quarks, leptons, W, Z, gluons at CERN, SLAC, Fermilab

1. CERN (Geneva, site of LHC): LEP collided electrons, positrons. Precision studies of the weak interactions. [In same tunnel as LHC]

2. SLAC: SLAC Linear collider, new technology, beams smaller than human hair collided with enormous energies. Similar studies.

3. Fermilab: collide protons, antiprotons at very high energies. Precision studies of the strong interactions.

The TEVATRON at FermilabThe TEVATRON at Fermilab

60 km60 km

Main Injector & Recycler

Tevatron

Booster

p p

p source

Chicago

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_

p

s =1.8 - 1.96 TeV, t = 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 13

9.March 2006: Hadron Collider Physics - Arnulf Quadt – UCSC Colloquium Page 13

By 1995, the strong and weak interactions were understood and tested with high precision. Closely parallel to the triumph of Quantum Electrodynamics, associated with Feynman, Schwinger, Tomanaga, Lamb. No interesting discrepancies.

Puzzles with this picture:

1.Many ``fundamental constants” – masses of quarks and leptons, strength of the interactions (17 in all). Shouldn’t it be possible to understand these?2.Einstein’s General Theory of Relativity is not compatible with this structure, but we know that this describes gravitation in the universe very well.3.Related to (2), we don’t understand why gravity is so “weak”.4.Some of the constants in (1) are very surprising. E.g. there is one called µ, which is just a pure number, but µ < 10-9

Possible solutions (much more about these shortly):

1.For the puzzle of the weakness of gravity, a hypothetical new symmetry of nature, called supersymmetry. Turns out to also explain some of the constants: the strength of the strong interactions related to the strength of the electromagnetic and weak interactions.2.For the puzzle of quantum gravity, string theory.3.For the question of µ, a hypothetical particle called the axion (subject of searches at Livermore)4.For the puzzle of the many constants, string theory again.

Meanwhile, over the same period, astronomers and astrophysicists established:

1.The big bang really happened. The universe (at least what we can hope to see of it) is 15 billion years old; its history is well understood from three minutes until the present. We have some evidence of phenomena at much earlier times (10-25 sec after the big bang).2.The universe consists of about 5% baryons (protons and neutrons), 25% dark matter, 70% dark energy.

Detailed study of the CMBR:

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

Detailed information about the universe:

Questions:1.What is the dark matter?2.What is the dark energy?3.Why is there matter at all?4.What happened at the very early stages of the big bang (something called inflation, but what is it?)5.What came before?

None of these questions can be answered within our present knowledge of the laws of nature!

All of our cosmic questions are tied to the questions from particle physics:

Supersymmetry ! Dark Matter

Supersymmetry ! Baryons

Axions ! Dark Matter

String theory ! Possible explanation of inflation

String theory ! Possible explanation of dark energy

String theory ! May explain what came before

Magnet Pictures 2 in 1 superconductingdipole magnet beinginstalled in the CERN tunnel

LHC dipoles waiting to be installed.

Detecting Particle Collisions

When high energy particles collide, they produce many more particles. 00ZZHgg

Simulation of an eventin ATLAS detector.White lines are the fourmuons. The other tracksare due to particlesfrom quarks in theprotons.

ATLAS Detector

Tracker Pictures

Tracker Inserting silicon detector into tracker

Inserting solenoid into calorimeter

Calorimeter Installation

Muon Toroids

Muon superconductingtoroids.

Endcap muon sectorEndcap Muon Sectors

The stored energy in the beams is equivalent roughly to the kinetic energy of an aircraft carrier at 10 knots (stored in magnets about 16 times larger)

There will be about a billion collisions per second in each detector.

The detectors will record and stores “only” around 100 collisions per second.

The total amount of data to be stored will be 15 petabytes (15 million gigabytes) a year.

It would take a stack of CDs 20Km tall per year to store this much data.

SCALE OF THE PROJECT

Collide two protons each with energy 7TeV.

(1TeV is roughly the kinetic energy of a flying mosquito. This energy is squeezed into a region 10-12

of a mosquito.)

32

The total energy in the beam is comparable to an aircraft carrier moving at about 10 knots.

LHC Accident: Fall 2008

Electrical failure at a magnet junction: damage to several magnets, large release of helium; design flaws exposed, currently being assessed. Delay of a few to many months possible, situation should be clearer this week.

Information on the machine status is available on the web

LHC Commissioning - home.htmhttp://lhc-commissioning.web.cern.ch/lhc-commissioning/

cern_lhc_page.htmhttp://lhc.web.cern.ch/lhc/

Update from the DG (edited)

Subject:     LHC Performance Workshop, Chamonix 2009 - Message from the Director-General - Message du Directeur général Date:     Fri, 6 Feb 2009 19:17:41 +0100 From:     Rolf Heuer <rolf.heuer@cern.ch> To:     cern-personnel <cern-personnel@cern.ch> Many issues were tackled in Chamonix this week, and important recommendations made. Under a proposal submitted to CERN management, we will have physics data in late 2009, and there is a strong recommendation to run the LHC through the winter and on to autumn 2010 until we have substantial quantities of data for the experiments. With this change to the schedule, our goal for the LHC's first running period is an integrated luminosity of more than 200 pb-1 operating at 5 TeV per beam, sufficient for the first new physics measurements to be made. This, I believe, is the best possible scenario for the LHC and for particle physics. Since the incident, enormous progress has been made in developing techniques to detect any small anomaly. These will be used in order to get a complete picture of the resistance in the splices of all magnets installed in the machine. This will allow improved early warning of any additional suspicious splices during operation. The early warning systems will be in place and fully tested before restarting the LHC.

What Might the LHC Discover?

The short answer: we don’ t know!

But there are plenty of speculations, motivated by the questions on our lists. We can’t review them all, and it is likely that none of our guesses are right. But, as a prototype, we’ll consider the most popular one: Supersymmetry.

What is supersymmetry?What is supersymmetry?

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

Symmetry betweenSymmetry between

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

Why supersymmetry (maybe?)

Higgs field: very heavy, mass > 116 GeV (more than 100 times mp). Can’t be too much more.

Real question: why so light?Dimensional analysis: mH ¼ Mp = 1018 GeV.

In quantum field theory, there really are contributions to the Higgs mass which are this large unless either1.The Higgs particle is a composite, with a size a ¼ 1/mH,

2.Nature is supersymmetric

Why Supersymmetry Solves this “Hierarchy Problem”

Lorentz: Model for electron as a blob of charge of size r. Ecoul = e2/r

But we know r < 10-17 cm me > 10 ¼ 10 mp!Dirac theory of electron fixes this (Weisskopf) – roughly speaking the positrons cancel off the big contribution of the Coulomb field.

In supersymmetry, the extra particles cancel the big contributions to the Higgs particles if their masses are not too different than mH.

Einstein: Energy = mass £ c2; me = {e2/r c2}

If supersymmetry is there, LHC will find it! (Fermilab has looked and will continue)

Discovery of Supersymmetry is Likely to Answer Several Questions in Our Lists

1. Explain why gravity is weak (mH ¿ Mp)2. Supersymmetry -- (almost) for free – explains the value of

the strong coupling in terms of the couplings of weak interactions and electromagnetism.

3. Supersymmetric theories – for free – almost always possess a candidate for the dark matter, a WIMP (weakly interacting massive particle).

4. Supersymmetry can readily explain the excess of matter over antimatter.

If supersymmetry accounts for the dark matter, we ought to be able to find it

1. Search in mines for (rare) collisions of dark matter particles with ordinary particles.cdms.html http://astro.fnal.gov/projects/cdms.html

2. Dark matter particles might annihilate frequently near the galactic center – see energetic particles in Fermi/GLAST.

FERMI-GLAST

If dark matter particles are from supersymmetry, they will sometimes meet and annihilate in areas where they are most dense; the products of these annihilations can be seen by GLAST, other instruments. Already some tantalizing evidence (esp. from an Italian satellite, PAMELA) for such phenomena.

Being greedy, physicists speculate about the other questions on the list. The structure with the potential to address all of them: Sting Theory

A contentious subject.•What has it explained?•When will it be tested?

String Theory

•For reasons that are still not understood, assuming that the fundamental entities are strings rather than point particles automatically gives a sensible quantum theory of gravity (General Relativity). •At the same time, these theories automatically give structures which look remarkably like the Standard Model.

As so often, the issues are exaggerated and misrepresented by the antagonists.

But trust me; I speak with authority (I hang out with string theorists and I went to high school with Smolin)

•String theory has taught us that quantum mechanics and gravity can get along – something not widely believed before (e.g. Hawking). Smolin is wrong when he says he has an alternative which accomplishes this, but this is not really so important.

•What theorists have studied – string theory and related objects – are definitely unrealistic models. They have the right to believe that more realistic theories exist and to speculate on their properties, but at the moment they are groping. Only some inklings of the underlying structure.

Could the LHC discover string theory?

Maybe. String theory may predict supersymmetry, the spectrum (masses) of the new particles. It might predict (a real long shot, but terribly exciting if true) extra dimensions of space which could be observed, black holes…

So now we wait and see. Theorists, experimentalists, working hard to be ready to interpret the data as it starts to come in, hopefully within less than a year!

Extra Slides

Bq

pR

At the LHC, the desired beam energy 7 TeV and thestate of the art dipole magnets have a field of 8 Tesla.Plugging in and converting units gives a radius of 3 kmand a circumference of 18 km.

In a magnetic field B, a particle of charge q and momentum p travels in a circle of radius R given by