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Nuclear and Particle Physics 3 Nuclear and Particle Physics 3 = Particle Physics 2= Particle Physics 2

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TopicsTopics

Recap of SM particles and forces Symmetry How to do a particle physics

experiment Fermilab, TeVatron collider DØ experiment

detector discovery of top quark

experimental tests of the SM Beyond the SM The Future: CERN, LHC, CMS Summary

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u u u d d d e

b b b

c c c s s s

g g g g g g g g

Z W+/-

e

Quarks Leptons+2/3 -1/3 -1 0

I

II

III

Boso

ns

Ferm

ions

Particles of Standard ModelParticles of Standard Model

t t t

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“every-day” matter

Proton

d u

d

e

Neutron

e

u d

u

Electron Electron Neutrino

Photon

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Forces (interactions)Forces (interactions) Strong interaction 1

Binds protons and neutrons to form nuclei

Electromagnetic interaction 10-2

Binds electrons and nuclei to form atoms Binds atoms to form molecules etc.

Weak interaction 10-10

Causes radioactivity

Gravitational interaction 10-40

Binds matter on large scales

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What holds the world together?What holds the world together?

interaction

participants

relative strength

field quantum(boson)

strong

quarks

1

ggluon

electro-magnetic

charged particles

10-2

photon

weak

all particles

10-10

W± Z0

gravity

all particles

10-40

Ggraviton

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Beta decay

d u

d

Neutron

Proton

u d

u

e

Electron e

Anti-electron Neutrino

W

Mean lifetime of a free neutron ~ 10.3 minutes Mean lifetime of a free proton > 1031 years!QuestionQuestion: Why doesn’t the neutron in the deuteron decay? Hint: deuteron mass = 1875.6 MeV/c2

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SymmetrySymmetry

An object is called symmetric if one can do something with/to it (“perform a transformation”) without having changed it when one is finished with the procedure.

“symmetry” in physics: invariance under a transformation laws of nature are invariant under

certain transformations electromagnetic theory has

“gauge symmetry” which is related to charge conservation

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The Noether-TheoremThe Noether-Theorem

Emmi Noether (1882-1935)

Symmetry Conservation Law Symmetry Conservation Law

Laws of physics are independent of...Laws of physics are independent of...

origin of time axis energy conservation

origin of spatial axes momentum conservation

orientation of spatial axes angular mom. conservation

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““Gauge Transformations”Gauge Transformations”

Hermann Weyl (1920): noted scale invariance of electromagnetism tried to unify general relativity and

electromagnetism conjectured that “Eichinvarianz”) (scale

invariance) may be also a local gauge theory of general relativity – did not work out

later realized that requiring the Schrödinger equation to be invariant under a local gauge (phase) transformation leads naturally to electromagnetic field and gives the form of the interaction of a charged quantum particle

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Global and local gauge Global and local gauge transformationstransformations

global transformation: same transformation carried out at all space-time

points (“everywhere simultaneously”) local transformation:

different transformations at different space-time points

globally invariant theories in general not invariant under local transformations

in quantum field theory, can restore invariance under local gauge (phase) transformation by introducing new force fields that interact with the original particles of the theory in a way specified by the invariance requirement

i.e. in this sense the dynamics of the theory is governed by the symmetry properties

can view these force fields as existing in order to permit certain local invariances to be true

electroweak interaction theory as well as QCD follow from gauge invariance which is a generalization of the gauge invariance of Maxwell’s equations

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Particle physics experimentsParticle physics experiments Particle physics experiments:

collide particles to o produce new particles o reveal their internal structure and laws of their

interactions by observing regularities, measuring cross sections,...

colliding particles need to have high energy o to make objects of large mass o to resolve structure at small distances

to study structure of small objects:o need probe with short wavelength: use particles

with high momentum to get short wavelength o remember de Broglie wavelength of a particle

= h/p in particle physics, relativistic effects

important; mass-energy equivalence plays an important role; in collisions, kinetic energy converted into mass energy;

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How to do a particle physics How to do a particle physics experimentexperiment

Outline of experiment: get particles (e.g. protons, antiprotons,…) accelerate them throw them against each other observe and record what happens analyze and interpret the data

ingredients needed: particle source accelerator and aiming device detector trigger (decide what to record) recording device sufficiently many people to:

o design, build, test, operate accelerator o design, build, test, calibrate, operate, and understand

detectoro analyze data

lots of money to pay for all of this

p p

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Testing the Standard Model: Testing the Standard Model: Requirements for experimentsRequirements for experiments

Use highest available energy higher cross sections of rare processes can probe smaller distances

Be sensitive to rare processes Deviations from SM are rare (would have been seen

otherwise) need high beam intensities (“luminosity”) and detectors that can cope with this.

Detectors: Precise momentum measurement of charged particles Energy and direction measurement of neutral particles

and “jets” (from quarks and gluons) Identify leptons (e, μ, τ) all of this in whole solid angle -- detector should be

“hermetic” (be able to measure “missing energy” as signature of production of weakly interacting particle(s)

development of big “general-purpose” detectors Need to be able to recognize “new” phenomena among

huge background of “standard” processes need to understand background very well

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How to get high energy qq How to get high energy qq collisionscollisions

Need Ecm to be large enough to o allow high momentum transfer (probe small distances)o produce heavy objects (top quarks, Higgs boson)o e.g. top quark production: e+e- tt, qq tt, gg tt, …

Shoot particle beam on a target (“fixed target”): o Ecm = 2Emc2 ~ 20 GeV for E = 100 GeV, m = 1 GeV/c2

Collide two particle beams (“collider”) :

o Ecm = 2E ~ 200 GeV for E = 100 GeV

__

__________

-- __ __ __

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DetectorsDetectors use characteristic effects from interaction of particle with matter to detect, identify and/or measure properties of particle;

“transducer” to translate direct effect into observable/recordable (e.g. electrical) signal

example: our eye is a photon detector; “seeing” is performing a photon scattering

experiment:o light source provides photonso photons hit object of our interest -- absorbed, some

reemitted (scattered, reflected)o some of scattered/reflected photons make it into eye;

focused onto retina;o photons detected by sensors in retina (photoreceptors

-- rods and cones) o transduced into electrical signal (nerve pulse)o amplified when neededo transmitted to brain for processing and interpretation

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Bend angle momentumMuon

Experimental signature of a quark or gluon

Jet

Hadronic layers

Magnetized volumeTracking system

EM layersfine sampling

CalorimeterInduces shower

in dense material

Innermost tracking layers

use siliconMuon detector

Interactionpoint Absorber

material

“Missing transverse energy”

Signature of a non-interacting particle

Electron

Typical particle physics detector system

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Fermi National Accelerator Fermi National Accelerator LaboratoryLaboratory

(near Batavia, Illinois)(near Batavia, Illinois)

Main Injector

Tevatron

DØCDF

Chicago

_ p source

Booster

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FermilabFermilab

Fermi National Accelerator Laboratory (http://www.fnal.gov/) Founded 1972 One of the top laboratories for high energy

physics Near Batavia, Illinois (45 mi West of Chicago) presently world’s highest energy accelerator:

Tevatron = proton synchrotron, Emax=900GeV

Operated as collider: proton – antiproton collisions at Ecm = 1.9 TeV

Physics Program Collider experiments CDF, DØ, CMS neutrino physics: Minos, Mini-Boone Astrophysics: Auger Observatory, Sloan Sky

Survey ………….

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FermiNational AcceleratorLaboratory

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The The TeVTeVatron Collideratron Collider

Tevatron collider Colliding bunches of protons and anti-

protons; bunches meet each other every 396 ns

in the center of two detectors (DØ and CDF)

steered apart at other places Each particle has ~ 980 GeV980 GeV of energy,

so the total energy in the center of massis 1960 GeV = 1.96 TeV1960 GeV = 1.96 TeV

About 2,500,000 2,500,000 collisions per second

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peak luminosity 1032 cm-1s-1 (5X1032 cm-1s-1 ) energy in c.m.s. 1.9 TeV, bunch crossing

time 396 ns expect integrated luminosity 6fb-1

Turn-on March 1, 2001 First collisions April 3, 2001

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Collisions at the TevatronCollisions at the Tevatron

we are interested in what’s inside the proton and antiproton “soft collisions” – peripheral

collisions – do not really probe internal structure

“hard collisions”: constituents interact

p p collisions qq(g) interactionsUnderlyingEvent

u

u

d

gq

q u

u

d

Hard Scatter

_ _

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~700 scientists

and engineers

82 institutions

20 countries

140 Ph.D.

Dissertations

150 papers

published

The DØ CollaborationThe DØ Collaboration

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The old DØ detector (before 1996)The old DØ detector (before 1996)

CalorimeterUranium-liquid Argon60,000 channels

Muon System1.9T magnetized Fe,Prop. drift tubes40,000 channels

Central Tracking

Drift chambers, TRD

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DØ DØ CalorimeterCalorimeter

Uranium-Liquid Argon sampling calorimeter Linear, hermetic About 55000 cells

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DDØ Ø Control Room 1993Control Room 1993

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the upgraded DØ detectorthe upgraded DØ detector

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DDØ Ø Detector in hall January 2001Detector in hall January 2001

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DDØ Ø Detector in hall January 2001Detector in hall January 2001

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The Discovery of Top QuarkThe Discovery of Top Quark

1977 – 1992 Many null

results

1992 – 1993 A few

interesting events show up

1994, DØmt > 131

GeV/c2

1994, CDFFirst evidencemt ~ 170

GeV/c2

1995 – CDF, DØDiscovery!

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e u c

e d s

e u c

e d s

PP

t2 3/

t 2 3/

W b1 3/

W

b 1 3/

Creating Top Anti-Top Quark pairsCreating Top Anti-Top Quark pairs

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Artist’s impression of a top eventArtist’s impression of a top event

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What do we actually “see”What do we actually “see”

Jet-1

Jet-2

Muon

Electron

Missing energy

jetsett _

jetsett _

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““event display” of a event display” of a DØ top eventDØ top event

jetse tt -

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Standard model vs experimentStandard model vs experiment

Theory works embarrassingly well! Has been tested by many hundreds of

precision measurements over last decade – very few measurements differ by more than 1 or 2 standard deviations

Even some amount of frustration – always hope to see experimental result in disagreement with theory

In electroweak theory, three parameters can be used to calculate

any electroweak quantity (use the three known best!)

lots more than three have been measuredo theory is over-constrained

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Luminosity and cross Luminosity and cross sectionsection

Luminosity is a measure of the beam intensity (particles per area per second) ( L~1031/cm2/s )

“integrated luminosity” is a measure of the amount of data collected (e.g. ~100 pb-1)

cross section is measure of effective interaction area, proportional to the probability that a given process will occur.

o 1 barn = 10-24 cm2

o 1 pb = 10-12 b = 10-36 cm2 = 10- 40 m2

interaction rate: LdtnLdtdn /

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Experimental tests of standard Experimental tests of standard modelmodel

we are interested in the “hard scattering processes”, i.e. central head-on collisions, since high momentum transfer probes small distances

most of the “hard scatters” are due to strong interactions between partons (quarks, gluons) leading to two ore more “jets” in the final state

such reactions represent a source of “background” to the search for other (rarer) processes that we want to study need to understand this background

in addition, measuring the cross section for these events is a test of QCD

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Jet productionJet production

measured jet production cross section vs pt of the jet varies by 9 orders of magnitude over measured range;

good agreement with prediction

from QCD

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Photon productionPhoton production photon production probes directly the quark

content of the proton:

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Photon production vs theory predictionPhoton production vs theory prediction

good agreement over 6 orders of magnitude

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W, Z productionW, Z production

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W propertiesW properties

W width: upper points:

measured lowest two points

(“LEP1/SLD..”: calculated within SM from all other measured parameters

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The SM works very well Why aren’t we satisfied ?The SM works very well Why aren’t we satisfied ?

SM, developed in the 1970’s, has been thoroughly tested in many experiments -- describes data extremely well

Why are we not happy with it? Lots of parameters

o Masses of charged leptons, neutrinos, quarks, W, Z, ….. not predicted by theory

o Where do they come from ? -- would like theory which predicts all of these parameters from first principles

EW. symmetry breaking mechanism via Higgs Boson is “put in by hand”

Higgs mass calculation within SM is not stable – “quadratic divergences”

Haven’t seen evidence for Higgs Boson yet SM becomes inconsistent at very high energies SM does not include gravity

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What about gravity? Why three generations?

with different masses so many elementary particles

Why is the top quark so heavy? Why are W and Z bosons heavy and

’s light? No dark matter candidate

Open questionsOpen questions

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… … would like “theory of would like “theory of everything”everything”

Looking for the “Theory of Everything” (TOE) that contains SM as approximation while solving SM

shortcomings many extensions proposed and considered:

o GUTs, technicolor, SUSY, … superstring theory,… Theorists need guidance from experiment to nail down

choice Frantically looking for deviations from SM unification

Electricity

Magnetism

Weak force

Strong force

Gravity string theory...

electromagnetism

electroweak force

GUTs

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What do we need to do?What do we need to do? further refine tests of SM, hope to see deviations

from SM: higher energy increased precision and higher sensitivity

o More precision will constrain SM more tightly (e.g. SM relation between masses of top, W, Higgs)

new measurements that were not possible before Something new must show up at scale of 1 TeV

look for “new phenomena” (not predicted within SM): Supersymmetry Technicolor, compositeness,

new vector bosons, extra dimensions …. Higgs boson:

Mass expected below 200 GeV If seen, is it “SM Higgs”?

(mass, decay modes,… as predicted by SM?)

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The Higgs ParticleThe Higgs Particle electroweak symmetry breaking

accomplished by Higgs field -- particles acquire mass by interaction with Higgs Field

Particle manifestation of Higgs Field (its “quantum”) is the Higgs Boson (spin 0)

Search for Higgs particle is one of the main motivations for research programs at present and future colliders: Fermilab (DØ and CDF) -- ongoing Large Hadron Collider at CERN

(from 2009) Next Linear Collider (planned)

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Searches for the Higgs Searches for the Higgs BosonBoson

Searches for Higgs have been going on for a decade at LEP (CERN) and the Fermilab TeVatron collider direct searches for Higgs

production at LEP exclude mH < 114 GeV.

precision measurements of parameters of the W and Z bosons, combined with Fermilab’s top quark mass measurements

mH <~ 159 GeV. CDF and DØ exclude Higgs

mass range 159 to 170 GeV at 95% C.L.

159 @95% . .Hm GeV C L

GeVmH362787

)(114 directGeVmH

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MMtoptop, M, MWW, M, MHiggsHiggs

relation between Mtop, MW, MHiggs measurement of Mtop, MW constrains MHiggs

Constraint on the mass of the Higgs boson: MH = 80+36

-27 GeV(within SM)

Light Higgs preferred by the SM with latest top and W mass

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MMtoptop, , MMWW, ,

MMHiggsHiggs

Mtop (GeV)

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Higgs – exclusion limitsHiggs – exclusion limits

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Supersymmetry Supersymmetry

Symmetry between bosons and fermions such that all the presently observed particles have new, more massive super-partners (SUSY is a broken symmetry) Fermions have partners with spin 0 called “sfermions” :

squarks, selectrons, sneutrinos, … bosons have partners with spin ½ called “-inos”: photinos,

charginos, neutralinos 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

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Unification of forcesUnification of forces Unification of forces

Gauge couplings of em, weak and strong interactions vary

with log E within SM, they do not

become equal with SUSY corrections,

they coincide at E 1016 GeV (“GUT scale”

strong

weak

EM

cou

plin

g

log(energy)

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Or…Extra Dimensions!?Or…Extra Dimensions!? Superstring theory:

can accommodate four forces (including gravity) need 11 dimensional world (time, 3 space + 7

“compacted dimensions” (very small -- less than 1mm in size))

Only gravity can communicate with/to other dimensions, its “strength” is diluted in ours (its influence is spread among all 10 spatial dimensions)

Experiments are underway searching for signals of these

dimensions.

The “other” dimensions

“Our World”

q

graviton

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Status of searchesStatus of searches

Searches for SUSY, extra dimensions, other exotic particles predicted by extensions of standard model have been done during last decade at most HEP laboratories -- no evidence yet

Hope is to find Higgs, SUSY,… at the LHC

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CERN CERN (Conseil Europ(Conseil Europééen pour la Recherche Nuclen pour la Recherche Nuclééaire)aire)

European Laboratory

for Particle Physics,

near Geneva,

Switzerland

(about 9km West of

Geneva, between

Meyrin,

and St.Genis,

straddling the Swiss-

French border)http://www.cern.ch

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LHC ExperimentsLHC Experiments

Atlas

CMS

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Large Hadron Collider (LHC)

Proton beams travel around the 27 km ring

in opposite directions, separate beam pipes.

In ultrahigh vacuum, 10-10 Torr. time for a single orbit, 89.92 μs.

beams controlled by superconducting electromagnets

o 1232 dipole magnets, 15 m each, bends beam.

o 392 quadrupole magnets, 5-7 m, focus beams.

o 8 inner triplet magnets are used to 'squeeze' the particles closer for collisions. Similar to firing needles 10 km apart with enough precision to meet in the middle.

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LHC DetectorsLHC Detectors

ATLAS

CMS

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CMS CollaborationCMS Collaboration

Slovak Republic

CERN

France

Italy

UK

Switzerland

USA

Austria

Finland

Greece

Hungary

Belgium

Poland

Portugal

Spain

Pakistan

Georgia

Armenia

UkraineUzbekistan

CyprusCroatia

China, PR

TurkeyBelarus

Estonia

India

Germany

Korea

Russia

Bulgaria

China (Taiwan)

IranSerbia

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The CMS DetectorThe CMS Detector

HF

HOHB

HE

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Transverse slice through CMS detectorClick on a particle type to visualise that particle in CMS

Press “escape” to exit

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CMS Assembly HallCMS Assembly Hall

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Megatile Scanner & DAQ at CERNMegatile Scanner & DAQ at CERNBuilt by Florida State HEP3Built by Florida State HEP3

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Laser calibration and monitoring for Laser calibration and monitoring for HCALHCAL

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CMS Physics outlookCMS Physics outlook

LHC started end 2009, but running at half design energy and low luminosity

Global fit of electroweak data to theory suggests mass of Higgs 100 to 200 GeV

LEP results of mass of Higgs > 114 GeV; latest CDF and DØ results indicate MHiggs < 159GeV

Standard model breaks down at E ~ 1 TeV New physics is expected at TeV scale. Discoveries should revolutionize

particle physics & provide window to physics at unification.

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Accelerators Accelerators discoveries discoveries

1981 - 1987: CERN pp colliderE = 540 GeV W± (80 GeV),

Z0 (91 GeV) 1989 - 2011: Fermilab Tevatron

pp colliderE=1.8 (now 1.96) TeV

top quark (175 GeV) 2009: CERN LHC pp collider

E=7 TeV 14 TeV (in 2011?) discover SUSY and Higgs?

????: Linear e+e- ColliderE=1-2 TeV study Higgs in detail

_

_

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1897 – ELECTRON J.J. Thomson + others 1909 – PROTON E. Rutherford 1932 – NEUTRON J. Chadwick 1964 – QUARK M. Gell-Mann, G. Zweig 1974 – CHARM S. Ting (BNL) , B. Richter

(SLAC) 1977 – BOTTOM L. Lederman (Fermilab) 1979 – GLUON1979 – GLUON JADE, Mark J, TASSO (DESY)JADE, Mark J, TASSO (DESY) 1983 – W, Z BOSONS1983 – W, Z BOSONS UA1, UA2 (CERN) (C. Rubbia)UA1, UA2 (CERN) (C. Rubbia) 1995 – TOP1995 – TOP DDØØ & CDF (Fermilab) & CDF (Fermilab)

2012 – HIGGS BOSON ? 2013 – SUPERSYMMETRY ? 2015 – GRAVITON ? 2020 – EXTRA DIMENSIONS ?

Summary -- outlookSummary -- outlook

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What do HEP experimenters do?What do HEP experimenters do? Conceptual design of experiments and detectors

Simulation of physics reactions Simulation of detector response to background and

signal Design and construction of detectors and electronics

In close collaboration with engineers and technicians

Find compromise between desired performance and technical and financial constraints

Install, test, debug, calibrate detectors Study their performance Develop software tools for reconstruction and analysis Operate the detectors -- data taking

Shifts to ensure good data quality Maintenance, repair

Do physics analysis – discover things (sometimes), measure, test theory

Write and publish papers, present results at conferences and meetings