The DØ Experiment Don Lincoln Fermilab ‘Physics for Everyone’

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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 HeliumNeon u d u u d d Proton Neutron Electron Gluons hold quarks together Photons hold atoms together

Consider an Ice Cube Heat it and it –Melts –Boils –Turns to steam –H 2 O 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 ( seconds) Quarks differentiate ( seconds?) ??? (Before that) Fermilab 4× seconds LHC 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 Currently DØ has two co-spokesmen who stand for re-election every three years

January 2001

550 scientists involved17 countries63 institutions400 authors

DØ History First Meeting Stony Brook July 1983 Baseline Approval from DOE November 1984 Design Collision Hall, Do Detector R&D (First Calorimeter Using Liquid Argon) Peak Construction Roll In February 1992 Good Beam September 1992 Fall 1993, First DØ Paper (Leptoquarks) March 1995, Discovery of Top Fall 2000, 100 th DØ Paper (W Boson) 130 th Ph.D. Data Taking Upgrade Detector to Utilize Main Injector Upgrade 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 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 (1,000,000,000,000,000) bytes in the next run (1 PetaByte). 30’ 50’

DØ vs. Borg Coincidence? Or just another cool thing about DØ? f

Highlights from 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 ~ 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 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

We’re in luck! Quarks can’t exist, except when they are confined Miracle q As 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 qq bbe jj jje jj jje jj jje “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 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 ~  “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 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  The Main Ring upgrade was completed in  The new accelerator increases the number of possible collisions per second by  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 Fermilab Tevatron will deliver times as many collisions per second as Run I. The DØ detector required an overhaul in order to cope.

Eight cylinders covered with scintillating fiber are read out with a novel light detector (VLPCs). VLPCs DØ Fiber Tracker See the Display!

1.25 m p p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 c 2 Energy is Matter Matter is Energy Lots of energy makes lots of matter and vice versa!!!!!!

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

Acceleration Particle Acceleration Linear Accelerator (LINAC) Particle Acceleration Electric Field Synchrotron (Fermilab) Electric Field

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 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.