Debjyoti Bardhan

Research Scholar

Theoretical Physics

TIFR

INSPIRE CAMP TALK

6th October, 2012

The ‘backbone’ of particle physics

Explains forces, particles and their interactions

Unites The

Three Forces of Nature

Examples

And Jealous!

Examples

And Co-operative!

Make up matter Carry forces

Electrons Protons

Neutrons

PhotonsGluons

W, Z Bosons

Only one

per level

As many

per level

Quarks…

BoseFermi

Indivisible Can be broken down

to simpler parts

No substructure!Made up of fundamental

particles

Concept of the atom around

since Dalton (1808)

1911: Structure of the

Atom

e p

1932: Chadwick discovers neutrone p n

1932 : Positron discovered by Carl Anderson

e pe np n

Electron

Positron

Some neutral

particle

Scattered

electron

Another

Electron-positron

pair

1931: Neutrino hypothesis by Wolfgang Pauli

1937: Muon discovered in Cosmic Rays

e

n

p n

e m

ne nm

p n

e m

ne nm

p n

1947-64 : Many particles were discovered

K+ K0 K0 K-

p+ p0 p- L0

1964 : Quark/Parton Model proposed by

Gell-Mann, Feynman & Zweig

At least 3 quarks!e m

ne nm

p n

K+ K0 K0 K-

p+ p0 p- L0u

ds

1969 : Quarks u,d,s discovered in SLAC

e m

ne nm

u

d

s

1969 : Fourth quark predicted

e m

ne nm

u

d

s

c

1st Gen2nd Gen2nd Gen1st Gen

u

u d dd

u

Proton Neutron

1974 : Fourth quark – charm – discovered

c

1975 : Tau discovered

e m

ne nm

t

1973 : Kobayashi & Maskawa predict 3rd generation

of quarks

u

d

c

s

?

?

1977 : Bottom quark discovered at Fermilab

u

d

c

s b

e m

ne nm

t

1995 : Top Quark discovered at Fermilab2000 : Tau Neutrino directly observed at Fermilab

u

d

c

s b

te m

ne nm

t

ntFERMIONS

1979 : Gluon discovered at DESY1983 : W, Z Bosons discovered at CERN

g

ZW+ W-

ge m

ne nm

t

nt

u

d

c

s b

t

u

d

c

s b

te m

ne nm

t

nt

g

ZW+ W-

g

Leptons Quarks

FERMIONS

BOSONS

H

Higgs

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

1897

1923

1937

1955

1962

1969

1974

1975

1977

1983

1979

1995

2012

e m

ne nm

t

nt

u

d

c

s b

t

g

ZW+ W-

g

H

2000

If enough energy is packed

into a small space, previously

absent particles can come into

existence

Now you see it,

now you don’t

High data production rate

from LHC

Finicky scientists

g

gSomethin

g

HappensH

d

u

W+

Somethin

g

Else

Happens

H

W+

Gluon

Fusion

Higgs-

strahlung

HSomethin

g

Happens

g

g

H

Golden

Channels

Pick the ones

with just the right length

Photo Credit: CERN

Photo Credit: CERN

Photo Credit: CERN

Photo Credit: CMS

Photo Credit: CERN

Perfect

L-R

Symmetry

Right biased Left biased

You can choose only one!

R L

Every valid mathematical description

should lead to the

same physical prediction.

- Gauge Symmetry Principle

Gauge symmetry implies

no mass!

Keep gauge symmetry…

The Higgs field does the dirty job!

later break it!

n tn m

n ee

td

uc

H

Higgs

is the

Keystone

Spread over all space and time

Has a value at each point of space and time

Interactions between fields are INTERESTING!

Identical particles

Higgs Field

Heisenberg’s

Uncertainty

Principle

from

Frank Wilczek’s

Nobel Lecture,

2004

Particles are excitations of the field!

Everything is just excited vacuum!

Right biased Left biased

Been there, seen that!

R L

But the Universe was cooling…

At the Big Bang, all particles were masslessThe Higgs field condensed as the Universe cooled.

Particles which interact or collect more particles are heavier

Massless particles don’t interact with the Higgs field

We have observed a new boson with a mass of 125.3

Rolf Heuer,

Director General, CERN

Brout

Englert Goldstone Higgs

Kibble

1. Standard Model explains a lot, but cannot explain mass

3. Higgs Field gives mass by breaking gauge symmetry2. Gauge Symmetry prevents mass terms

4. Higgs Boson is an excitation of the Higgs Field5. The Higgs Boson has been discovered!!

Thank You