# Presentation: 400194

## The DØ Experiment

- Don Lincoln
- Fermilab
- ‘Physics for Everyone’

## Approved

**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 made
- of protons, neutrons
- and electrons

- Helium

- Neon

- Proton

- Neutron

- Electron

- Gluons hold quarks together
- Photons hold atoms together

## Slide 5

## 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)

- Fermilab
- 4×10-12 seconds
- LHC
- 10-13 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 stand
- for re-election every three years

## January 2001

## Slide 11

## DØ History

- 1985

- 1990

- 1995

- 2000

- First Meeting
- Stony Brook
- July 1983

- Baseline
- Approval from
-  DOE
- November 1984

- Design Collision
- Hall, 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
- 			*C**oolest *
*	**	**	**	**D**etector *
*	**	**	**	**      **at *
*	**	**	**	**	** **F**ermilab*
*Rejected due to copyright infringement*

## Why DØ?

- Second name
- 			*B**est *
*	**	**	**	**F**ermilab *
*	**	**	**	**	** **D**etector*
*Rejected by directorate.*

## Why DØ?

- Third name: Ask famous Hollywood Star
*And it stuck.......*

## Why DØ?   The Real Reason

## 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’

## Slide 18

## 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

***Theorist’s View***

## 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

- 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

## Top Facts

- 6 quarks

- 2 quarks
- 2 leptons
- 2 neutrinos

- Tau
- stuff
- (hard)

- 4 quarks
- 1 lepton
- 1 neutrino

- The types of
- collisions one gets
- in top-creating
- collisions are not
- unique to top.
- In fact, there are many other
- ways 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

- Very messy collisions
- Hundreds of objects after collision
- Need to simplify the measurement

***Experimentalist's View***

## We’re in luck!

- Quarks can’t exist, except when they are confined

- Miracle

- As quarks leave a collision, they change into a ‘shotgun blast’ of particles called a *‘jet’*

- 

## Where Did the Energy Go?

## Combining Viewpoints

## “God”

- “God”

- t

- t

- b

- W

- e

- 

- b

- W

- q

- q

- “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 

- 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*.

- Undiscovered!

## “LEP observes significant Higgs

- “LEP observes significant Higgs
- candidates for a mass of 115 GeV
- with a statistical significance of
- 2.7 and compatible with the
- expected rate and distribution of
- search channels.”
- Chris Tully, Fermilab Colloquium
- 13-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.

##   The Main Ring upgrade was completed in 1999.

**Increasing ‘Violence’ **
**of Collision **

**Expected**
**Number**
**of**
**Events**

**Run II**

**Run I**

**Increased reach **
**for discovery physics**
**at highest masses**

**Huge statistics **
**for precision physics**
**at low mass scales**

**Formerly rare processes**
**become high statistics**
**processes**

- 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

## In Run II (March 1, 2001), the Fermilab

- Tevatron will deliver 10-20 times as
- many collisions per second as Run I.
- The DØ detector required an overhaul
- in order to cope.

## DØ Fiber Tracker

- covered with
- scintillating fiber
- are read out with
-     a novel light
-     detector (VLPCs).

- VLPCs

- See the Display!

## 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

- 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

- E = m c2

- Energy is Matter
- Matter is Energy

- Lots of energy makes
- lots of matter
- and vice versa!!!!!!

## Particle Acceleration

- _Vocabulary_

- electron

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

## Particle Acceleration

- Linear Accelerator (LINAC)

- Particle
- Acceleration

- Electric Field

- Synchrotron   (Fermilab)

- Electric Field

## Slide 47

## Slide 48

## Measuring Momentum

- r

- ×

- ×

- ×

- ×

- ×

- ×

- r = radius of curvature
- p = momentum (~energy)
- q = electrical charge
- B = magnetic field
- The use of a magnet makes
- the path of the particle bend.
- Thus we can measure the
- momentum (related to the
- velocity in HS physics)

- Magnetic Field
- points into screen

- Wires or
- Scintillating
- Fibers

*Equations!*

- High
- Momentum

- Low
- Momentum

- ×

- ×

- ×

- ×

## Calorimetry: Measuring Energy

- E                    2×E/2       4×E/4        8×E/8      16×E/16

- 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.