The DØ Experiment

Don Lincoln

Fermilab

‘Physics for Everyone’

Approved

Don’s Mom

Feb 2000

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What’s the Point?High Energy Particle Physics is a study of the smallest pieces of matter.

It investigates (among other things) the nature of the universe immediately after the Big Bang.

It also explores physics at temperatures not common for the past 15 billion years (or so).

It’s a lot of fun.

Periodic Table

All atoms are madeof protons, neutronsand electrons

Helium Neon

u

du u

d d

Proton NeutronElectron

Gluons hold quarks togetherPhotons hold atoms together

Consider an Ice Cube• Heat it and it

– Melts– Boils– Turns to steam

– H2O breaks up into hydrogen and oxygen atoms

– The electrons get ripped off the atoms and electrons and atomic nuclei scurry around

– Atomic nuclei get broken up into protons and neutrons– Protons and neutrons get ripped apart into particles called

quarks.

• So lots of energy means very hot temperatures, which in turn means you can look at very small objects.

Now (15 billion years)

Stars form (1 billion years)

Atoms form (300,000 years)

Nuclei form (180 seconds)

Protons and neutrons form (10-10 seconds)

Quarks differentiate (10-34 seconds?)

??? (Before that)

Fermilab4×10-12 seconds

LHC10-13 Seconds

What is DØ?• One of two large multi-purpose particle detectors

here at Fermilab.

• Designed to record collisions of protons colliding with antiprotons at nearly the speed of light.

• It’s basically a camera.

• It lets us look back in time.

Rogue’s Gallery

1983-1996

1996-

1993-1999

1999-

Currently DØ has two co-spokesmen who standfor re-election every three years

January 2001

550 scientists involved 17 countries63 institutions400 authors

DØ History1985 1990 1995 2000

First MeetingStony Brook

July 1983

Baseline Approval from

DOENovember

1984Design CollisionHall, Do Detector

R&D (First Calorimeter Using

Liquid Argon)1985-1987

Peak Construction 1988-1991

Roll In

February 1992

Good Beam

September 1992

Fall 1993, First DØ Paper (Leptoquarks)

March 1995, Discovery of Top

Fall 2000, 100th DØ Paper (W Boson)

130th Ph.D.

Data Taking 1992-1996

Upgrade Detector

to Utilize Main

Injector Upgrade

1996-2000

Roll In January 2001

Why DØ? Initial name

Coolest

Detector

at

Fermilab

Rejected due to copyright infringement

Why DØ? Second name

Best

Fermilab

Detector

Rejected by directorate.

Why DØ? Third name: Ask famous Hollywood Star

And it stuck.......

Why DØ? The Real Reason

AØ: The High Rise

BØ: The Competition

CØ: Future BTeV

FØ: The RF

EØ: This Space For Rent

DØ: Fermilab’s Best Detector

DØ Detector: Run II

• Weighs 5000 tons• Can inspect 3,000,000

collisions/second• Will record 50

collisions/second• Records

approximately 10,000,000 bytes/second

• Will record 1015 (1,000,000,000,000,000) bytes in the next run (1 PetaByte).

30’

30’

50’

DØ vs. Borg

Coincidence? Or just another cool thing about DØ?

f

Highlights from 1992-1996 Run

• Limits set on the maximum size of quarks (it’s gotta be smaller than 1/1000 the size of a proton)

• Supported evidence that Standard Model works rather well (didn’t see anything too weird)

• Studied quark scattering, b quarks, W bosons

• Top quark discovery 1995

The Needle in the Haystack: Run I• There are 2,000,000,000,000,000 possible

collisions per second.

• There are 300,000 actual collisions per second, each of them scanned.

• We write 4 per second to tape.

• For each top quark making collision, there are 10,000,000,000 other types of collisions.

• Even though we are very picky about the collisions we record, we have 65,000,000 on tape.

• Only 500 are top quark events.

• We’ve identified 50 top quark events and expect 50 more which look like top, but aren’t.

Run II

×10

Top Facts• Discovery

announced March 1995

• Produced in pairs

• Decays very rapidly ~10-24 seconds

• You can’t see top quarks!!!

• Six objects after collision

• In each event, a top and anti-top quark is created.

• ~100% of the time, a top quark decays into a bottom quark and a W boson.

• A W boson can decay into two quarks or into a charged lepton and a neutrino.

• So, an event in which top quarks are produced should have:– 6 quarks

– 4 quarks, a charged lepton and a neutrino

– 2 quarks, 2 charged leptons and 2 neutrinos

Top Facts

6 quarks

2 quarks2 leptons

2 neutrinos

Taustuff

(hard)

4 quarks1 lepton

1 neutrino

The types ofcollisions one gets

in top-creating collisions are not

unique to top.

In fact, there are many otherways that one can make top-like

collisions.

You have to figure out how to pick the ones you want.

1,000,000 to 1

20 to 1

3 to 1

Top Facts

Top Facts• Very messy

collisions

• Hundreds of objects after collision

• Need to simplify the measurement

We’re in luck!

Quarks can’t exist, except when they are confined

MiracleqAs quarks leave a collision, they change into a ‘shotgun blast’ of particles called a

‘jet’

q

Where Did the Energy Go?

Combining Viewpoints

“God”

t

t

b W

e

b W

q q q q b b e

j j j j e

j j j j e

j j j j e

“Us”

Top Quark Run I: The Summary• The top quark was discovered in 1995• Mass known to 3% (the most accurately known

quark mass) • The mass of one top quark is 175 times as heavy

as a proton (which contains three quarks)

Why??

?

In 1964, Peter Higgs postulated a physics mechanism which gives all particles their mass.

This mechanism is a field which permeates the universe.

If this postulate is correct, then one of the signatures is a particle (called the Higgs Particle). Fermilab’s Leon Lederman co-authored a book on the subject called The God Particle.

top

bottom

Undiscovered!

“LEP observes significant Higgscandidates for a mass of 115 GeVwith a statistical significance of 2.7 and compatible with theexpected rate and distribution ofsearch channels.”

Chris Tully, Fermilab Colloquium13-Dec-2000

PFE Translation:

Maybe we see something, maybe we don’t.

What we see is consistent with being a Higgs Particle. But it could end up being nothing.

It’s Fermilab’s turn.

Is a Fermilab Higgs Search Credible?

• LEP incorrect Rule out with 95% certainty by ~2003

• LEP correct Similar quality evidence ~2004-2005 “Discovery” quality evidence ~2007

• Higgs exists but is heavier than LEP suggests Depends on how heavy DØ has a good shot on seeing ‘maybe’ and

possibly ‘absolutely’ quality evidence

Is a Fermilab Higgs Search Credible?: Good News/Bad News

• Good News ×10 more data than Run I

• Bad News ×1/10 less likely to be created than top quark

• So it’s a wash...similar problem to Run I top search

• Except... Events which look like Higgs but aren’t are much

more numerous. An irony...top quarks are a big piece of the ‘noise’

obscuring Higgs searches.

Increasing ‘Violence’ of Collision

ExpectedNumber

ofEvents

Run II

Run I

Increased reach for discovery physicsat highest masses

Huge statistics for precision physicsat low mass scales

Formerly rare processesbecome high statisticsprocesses

1

10

100

1000

The Main Ring upgrade was completed in 1999.

The new accelerator increases the number of possible collisions per second by 10-20.

DØ and CDF have undertaken massive upgrades to utilize the increased collision rate.

Run II begins March 2001

Calorimeters Tracker

Muon System

Beamline Shielding

Electronics

protons antiprotons

66 feet

In Run II (March 1, 2001), the FermilabTevatron will deliver 10-20 times asmany collisions per second as Run I.

The DØ detector required an overhaulin order to cope.

Eight cylinders covered withscintillating fiberare read out with a novel light detector (VLPCs).

VLPCs

DØ Fiber Tracker

See the Display!

1.25 mp

p

DØ Silicon Tracker

• 800,000 distinct detector elements

• Very complex (fragile)• Absolutely crucial for viewing

the details of how particles behave near the collision.

• Particles that don’t come from the collision point serve as ‘flags’ of interesting physics.

DØ Muon System

• Muons provide a signature of many interesting physics events.

• Muons penetrate dense material for long distances.

• Thus muon detectors are outside the large amount of metal that makes the rest of the detector.

• The muon system consists of many different detector technologies, and is the physically largest system.

Data-Model Comparison

Run II: What are we going to find?

I don’t know!

Improve top mass and measure decay modes.

Do Run I more accurately

Supersymmetry, Higgs, Technicolor, particles smaller than quarks, something unexpected?

Thanks!

Backup Slides

E = m c2

Energy is MatterMatter is Energy

Lots of energy makes lots of matter

and vice versa!!!!!!

Particle AccelerationAccelerationVocabulary

1 eV (electron volt) is the amount of energy carried by aparticle with the same charge as an electron, when accelerated by a 1 volt battery.

electron

1 keV (kilo electron volt) 1,000 x-rays, TV1 MeV (mega electron volt) 1,000,000 Gamma rays1 GeV (giga electron volt) 1,000,000,000 Big gamma rays1 TeV (tera electron volt) 1,000,000,000,000 Fermilab!

Particle AccelerationAcceleration

Linear Accelerator (LINAC)

ParticleAcceleration

Electric Field

Synchrotron (Fermilab)

Electric Field

Measuring Momentum

)/(qBpr

qVBF

r×

×

××

××

r = radius of curvaturep = momentum (~energy)q = electrical chargeB = magnetic field

The use of a magnet makesthe path of the particle bend.Thus we can measure themomentum (related to the velocity in HS physics)

Magnetic Fieldpoints into screen

Wires orScintillatingFibers

Equations!

High Momentum

Low Momentum

× ×× ×

Calorimetry: Measuring Energy

E 2×E/2 4×E/4 8×E/8 16×E/16

Dense Stuff Undense Stuff

A particle hits some dense stuff (like metal) and creates more particles, each of which have less energy. In the undense material you count particles. The number of particles is proportional to the energy.