02/21/2003Physics at DZERO1 Exploring the Microscopic Structure of the University with DZero??

02/21/2003 Physics at DZERO 1

Exploring the Microscopic Structure of the University with

DZero??


Exploring the Microscopic Structure of the Universe with

DZero

Jerry BlazeyNorthern Illinois University


The Standard Model

• Simple: “Bits of matter stick together by exchanging stuff.”

• The crowning achievement of particle physics is a model that describes all particles and particle interactions. The model includes:– 6 quarks (those little fellows in the nucleus) and

their antiparticles.– 6 leptons (of which the electron is an example) and

their antiparticles– 4 force carrier particles

• More Precise: “All known matter is composed of composites of quarks and leptons which interact by exchanging force carriers.”


The Quarks*• Three pairs of quarks.• The up and down are

the constituents of protons (= uud) and neutrons (= udd), and make up most matter.

• The other particles are produced in energetic subatomic collisions from cosmic rays or in accelerators, where they are also studied.*The name comes from James’s Joyce’s Finnegan’s Wake,

“Three quarks for Muster Mark!”


Leptons*• Leptons are generally lighter

particles and are most commonly observed in radioactive decays.

• The best example is neutron decay into a proton, an electron, and a neutrino:

*Greek for “small mass”


Periodic Table of Fundamental ParticlesAll point-like (down to

10-18 m) spin-1/2Fermions

Families reflectincreasing mass and

a theoreticalorganization

u, d, , e are “normal matter”

These all interact by exchanging spin 1

bosons…

-1

+2/3

-1/3

0

Mass


SM Interactions• Electroweak interaction

– Photons, W, and Z: all spin-1 bosons

• Strong interaction (QCD)– Gluons: all spin-1 bosons

• Three lepton generations (e,,,’s) – feel electroweak interaction only

• Three quark generations (u,d,s,c,t,b)– feel electroweak, strong interactions


We could stop here but…..

Explained by Standard Model10-37 weakerthan EM, not

explained


Two Compelling Unsolved Questions

(there are many others)

•How do particles get mass?

•How does gravity fit into all of this?


The Higgs Particle• The electroweak unification postulates the existence

of the Higgs field. (Named after a Scottish physicist who first hypothesized its existence.)

• This field interacts with all other particles to impart mass - think of walking through molasses.

• The Higgs field is a microscopic property of space-time, but at least one real particle will result.

• The experimental program at Fermilab, the Large Hadron Collider in Europe, and the next Linear Collider are dedicated, in part, to the search for this particle.

• It’s discovery would be an achievement of the highest order - an understanding of the origins of mass!


Beyond That?• Even with the Higgs, the Standard

Model requires fine tuning of parameters to avoid infinite Higgs masses from quantum corrections – the theory is “ugly.”

• Leads to strong belief that the SM is merely a low energy or effective theory valid up to some scale, where additional physics will appear.

• Most popular theoretical option:

Supersymmetry or SUSY.


SUSY• In SUSY every particle and force

carrier has a massive partner: Squarks, slectrons, gluinos…

• Since they are massive they’ve not been produced in current machines.

• The discovery requires more energetic accelerators – something which is being enthusiastically pursued.


Or…Extra Dimensions!?• Amazingly enough an 11 dimensional world

(time, 3-D & 7 very small less than 1mm in size) can accommodate a theory with all four forces.

• Only gravity can communicate with/to other dimensions, it’s “strength” is diluted in ours. That is, the graviton, or gravity carrier can spread it’s influence among all 10 spatial dimensions.

• Experiments are underway searching for signals of these dimensions.The “other”

dimensions

“Our World”

qgraviton


How do we test these theories?


The Two Basic Ideas: – Find a source of particles with

high kinetic energy.– Study the debris resulting from

collisions inside detectors.

The Sources:– Cosmic Rays– Accelerators – The higher the energy the more

numerous the number and types of particles.

The Detectors:– A series of special purpose devices that

track and identify collision products

p p


Fermilab Proton-Antiproton Collider

Main Injector & Recycler

Tevatron

Booster

p p

DØ

DØDØ

p source

Batavia, Illinois Chicago

1)Hydrogen Bottle2)Linear Accelerator3)Booster4)Main/Injector5)Tevatron

You are here


Physics Goals of a Detector

Precise study of the known quanta of the Standard ModelWeak bosons, top quark, QCD, b-quark

Search for particles and forces beyond those knownHiggs, supersymmetry, extra dimensions, other new phenomena

Driven by these goals, A detector emphasizes– Electron,

muon and tau identification

– Jets (q and g) and missing transverse energy

– Flavor tagging through displaced vertices and leptons


A Schematic detector

Hadronic

layers

Tracking system Magnetized volume

CalorimeterInduces shower

in dense material

Innermost tracking layers

use silicon

Muon detector

Interactionpoint

Absorber material

Bend angle momentum

Electron

Experimental signature of a quark or gluon

Muon

Jet: q or g

“Missing transverse energy”

Signature of a non-interacting (or weaklyinteracting) particle like a neutrino

EM layersfine sampling

p p


A Real Detector: D0muon system

electronics

• Proposed 1982

• First Data: 1992-1995

1.8 TeV• Upgrade:

1996-2001• Run II:

2002-2008 2.0 TeV


Any resemblance betweenDZero and the Borg Home ship is purely a coincidence.


Calorimeters Tracker

Muon System

Beamline Shielding

Electronics

protons antiprotons

20 m


International

• 18 countries• 77 institutions• 650+ physicists


Run I (1992-6) Results

• 140+ reviewed articles– Discovery of the top quark– Precision measurements of particle

masses and cross sections– Limits on new physics

• 100/year presentations• 100+ Ph.D./Master’s Students each

with an separate data stream, topic, and analysis


About the Detector: Silicon Microstrip Tracker

• 1M Channels• Four barrel layers• Axial and stereo

layers• Disks for

Forward/Backward Coverage


Scintillating Fiber Tracker

• 100k Channels in eight layers

• Scintillating Fiber

• Clear Fiber• Solid State

Visible Light Photon Counters at 9 Kelvin


Fiber Tracker Readout3-FRONT

4-FRONT

D3

-G4

B 1

5A 5B

E 3

R99.000

A2

-G5

A 2

G 5

C 3

E 4

C3

-E4

A 1

H 5

A1

-H5

B 2

F 4

123

ONE HALF CONNECTOR IN SECTOR 3 ONLY WITH FULL SHAREDCONNECTORS AT SECTORS 1 & 2, AND SECTORS 4 & 5.

4 5

B2

-F4

274

296

232

135

177

SECTORS 1 THRU 5 (5 SPLIT)CABLE ROUTES3/4 DIA. BUNDLES HELD AT R58 AND

CONTINUING ON TO THE TOP OF THE NOTCHES575eith3card.dwg

SCALE: 1/8(LOOKING AT SOUTH FACE OF CC)

B 3

H 6

B3

-H6

D4

-F5

D 4

F 5

B 5

B5

-H1

1

F 9

G 1 0

H 1 1

F9

-G1

0

D 7

E 8

D7

-E8

C 6

H 1 0

B1

-E3

C 2

F 3

H 4

D 2

C2

-H4

D2

-F3

D 3

G 4

C6

-H1

0

G 9

A 4

A4

-G9

E 7

G 3

H 3

G3

-H3

E2

-F2

E 2

F 2

F 8

E7

-F8

D 6

H 9

D6

-H9

C 5

G 8

C5

-G8

E 6

F 7

E6

-F7

B 4

H 8

B4

-H8

G 7

D 5

D5

-G7

A 3

F 6

A3

-F6

C 4

H 7

C4

-H7

E 5

G 6

E5

-G6

C1

-D1

C 1

D 1

E 1

F 1

G 1

H 1

H 2

G 2

E1

-G1

F1

-H2

G1

-H1

C.P.S

.

C.P.S

.

H 1 2

H 1 3

H 1 4

H 1 5

H 1 6

H 1 7

G 1 1

G 1 2

G 1 3

G 1 4

G 1 5

F 1 0

F 1 1

F 1 2

F 1 3

F 1 4

E 9

E 1 0

E 1 1

E 1 2

D 8

D 9

D 1 0

D 1 1

C 7

C 8

C 9

B 6

B 7

B 8

A 5

A 6

H 1 8

H 1 9

H 2 0

H 2 1

H 2 2

G 1 6

G 1 7

G 1 8

G 1 9

G 2 0

G 2 1G 2 2

F 1 5

F 1 6

F 1 7

F 1 8

F 1 9

F 2 0

E 1 3

E 1 4

E 1 5

E 1 6

E 1 7 E 1 8

D 1 2

D 1 3

D 1 4

D 1 5

D 1 6

C 1 0

C 1 1

C 1 2

C 1 3

C 1 3

B 9

B 1 0

B 1 1B 1 2

A 7

A 8

A 9

A 1 0

B 1 3

C 1 4

C 1 5

D 1 7

D 1 8

E 1 9

E 2 0

F 2 1

F 2 2

F 2 3

G 2 3

G 2 4

G 2 5

H 2 3

H 2 4 H 2 5

H 2 6

H 2 7

H 2 8

B6

-C8

-F1

0-H

12

E9

-G1

1

Readout under detector

Photoelectron peaks 1 pe ~ 7 fC


Liquid Argon Calorimeter

Z

y

x

p

p

69.0GeV, 472

69.0GeV, 47522

11

T

T

E

E

Highest ET jet event in Run 1

• 50k Channels• Liquid argon

sampling with Ur absorber


Muon System

Connect tracks

J/ +-

scintillator

Match to CFT

tracks = 83 MeV

Resolutions ~ 20% better in MC than data

shielding


Run II: 24/7 Event Collection• Proton-antiprotons collide at 7MHz

or seven million times per second• Tiered electronics pick

successively more interesting events– Level 1 10 kHz– Level 2 1 kHz

• About 100 crates of electronics readout the detectors and send data to a Level 3 farm of 100 CPUs that reconstruct the data

• Per second: 50 events or 300 Mbytes of data to tape.

• Per year: 10 million events or 30 Terabytes of data.


Physics: Event Analysis• Events are “reconstructed”

offline by farms of ~100 CPUs.

• Each detector samples position, energy, or momentum, 1M+ channels

• Then computers build or reconstruct full event characteristics based upon these samples

• Interesting events or signals are culled from the background usually 100’s out of millions.


Sample Run II Event: Ze+e- p

pZ

qq’

l

l


Sample Distributions: Ze+e-

1) Collect events2) Calculate mass for each event3) Plot distributions4) Statistically measure mass or production rate as a function of brightness or luminosity (1pb-1 means 1 event of cross section 1 pb will be produced.)5) Test predictions of Standard Model


Prospects for W mass and width

Current knowledge of mW:• DØ: 80.483 ± .084 GeV• World: 80.451 ± .033 MeV

Run II prospects for mW

• 2 fb-1 ±27 MeV• 15 fb-1 ±15 MeV

To improve measurements will require ~ fb-1 datasets or several years of Tevatron running.

p

pW

qq’

e


Top Mass Measurement

Discovered at Tevatron in 1995

Expected top mass accuracy by the end of Run II : ~ 1.4 GeV


W and Top Measurements

Indirectly constrain mass of The Higgs

Top quark mass (GeV)

W m

ass

(GeV

)

2001

mt 2 GeVmW 15 MeV

Stand

ard

Mod

elSuper

sym

met

ry


114 GeV 193 GeV

Past Searches for the Higgs

Over the last decade, experiments at the CERN e+e–

collider ( European Laboratory for Particle Physics) have been searching for the Higgs– direct searches for Higgs

production exclude mH < 114 GeV.

– precision measurements of parameters of the W and Z bosons, combined with Fermilab’s Run I top quark mass measurements, set an upper limit of mH ~ 193 GeV.


Higgs Hunting at the Tevatron• For any given Higgs mass,

the production cross section, decays are calculable within the Standard Model Inclusive Higgs cross section ~ 1pb

• A good search bet below ~ 140 GeV is associated production with W or Z– e or decays of W/Z

help give the needed background rejection

– cross section ~ 0.2 pb

p

pW*

qq’

H

W


“The Tevatron’s a Good Bet!”“We find it or eliminate it”

15 fb-1

110-190 GeV

Combined Channel/Experiments Higgs Mass Reach


Well actually… there’s at least

one Higgs!


Supersymmetry

• Postulates a symmetry between bosons and fermions such that all the presently observed particles have new, more massive super-partners (SUSY is a broken symmetry)

• Theoretically attractive:– additional particles cancel divergences in mH

– SUSY closely approximates the standard model at low energies

– allows unification of forces at much higher energies– provides a path to the incorporation of gravity and

string theory: Local Supersymmetry = Supergravity– lightest stable particle cosmic dark matter

candidate• masses depend on unknown parameters, but expected

to be 100 GeV - 1 TeV


Supersymmetry signatures• Squarks and gluinos are the most copiously produced

SUSY particles• As long as the associated new quantum number “R-

parity” is conserved, cannot decay to normal particles • Missing transverse energy from escaping (lightest

supersymmetric particle or LSP)

Possible decay chains always end inthe LSP:

Which leaves missingTransverse Energy in the DetectorSearch region typically > 75 GeV


Past Searches at the Tevatron• In Run I DØ carried out extensive

searches for SUSY

– Squarks/gluinos Missing ET + jets (+ lepton(s))

– Charginos/neutralinos multileptons

– GMSB Missing ET +photon(s)

• Searches for other new phenomena – leptoquarks, dijet resonances,

W’,Z’, massive stable particles, extra dimensions . . .

Now sign of new physics:DØ analysed 32 final states containing electrons, muons, photons, jets, W’s, Z’s and missing ET Find an 89% CL for agreement with the Standard Model (PRD 64 012004)

Run II prospect:gluino mass ~ 400 GeV

Run I excluded


Searches for Extra Dimensions

Standard Model

ExtraDimensions

DATA

Instrumental background (from data)

Extra Dimensions

Run II limits frompp ee,, MS(GRW) > 0.92 TeV (ee/)

MS(GRW) > 0.50 TeV () (first limit from a hadron collider in this channel)less than 1 mm depending on the number of extra dimensions.

p

G

qq

p


New York Times


Closing Comments: Prospects• Over the next several years DZero and the

Tevatron will explore the microscopic universe:– Constrain the SM and place limits on the

Higgs mass or – Discover the Higgs, and perhaps– Discover new physics, extra dimensions….

• It is an exciting, challenging program that asks two of the most fundamental questions: – What is the structure of the universe? – What is the history of the universe?“To the

Microscopic Universe….and beyond!”


Now (15 billion yrs)

Stars form (1 billion yrs)

Atoms form (300,000 yrs)

Nuclei form (180 seconds)

Protons and neutrons (10-10 s)

Quarks differentiate (10-34 s)

Fermilab4×10-12 seconds

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02/21/2003Physics at DZERO1 Exploring the Microscopic Structure of the University with DZero??

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