Smashing the Standard Model: Physics at the CERN LHC Kenneth Johns University of Arizona.

Smashing the Standard Model:

Physics at the CERN LHC

Kenneth JohnsUniversity of Arizona

2

Outline Opening remarks – 5 min

Destroyed magnets, black hole video Standard model and Higgs – 12 min CERN and LHC accelerator – 8 min ATLAS detector – 5 min October disaster – 5 min Higgs – 12 min

Production Decay Discovery potential

Other LHC physics and conclusions – 5 min Total UA contributions

3

First Beam in the LHCSept 10, 2008 in the ATLAS control

room

4

First Beam in the LHCNo black hole or stranglet production

5

First Beam in the LHCNo black hole or stranglet production

6

First Malfunction at the LHCSept 19, 2008 in the LHC tunnel

7

Physics at the LHC

“There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know.” Donald Rumsfeld

8

Fundamental Forces

8

9

Fundamental Particles

10

Fundamental Particles

Or just another pattern to unravel?

11

Standard ModelThe Standard Model unifies the strong,

weak, and electromagnetic interactions in the sense that they all arise from a local symmetry principle Local gauge invariance A minor problem is that the symmetries of

the Standard Model do not allow for massive gauge bosons

There are no experimental contradictions to the predictions of the Standard Model, which is complete in that its mathematical structure allows calculations to be carried out Tested to a high precision (1 part in 1000)

12

Standard ModelLocal gauge invariance

We first ask is the theory (L) invariant under global gauge transformations?

We next ask is the theory (L) invariant under local gauge transformations?

ψψmψγψiL μμ

by given is n Lagrangia Diracparticle free The

xexx i

xexx xi

13

Standard ModelWe can make the theory locally gauge

invariant by introducing a gauge covariant derivative that includes a gauge field

Now our Lagrangian does remain invariant under local gauge transformations Using this derivative leads directly to QED! And tells us that the photon is massless!

xe

AAA

ieAD

1

where

AeψψmψγψiL μ

μ

14

Standard Model

We could apply the same idea to the weak interaction Lagrangian (SU(2)) We’d find the need for three gauge

covariant derivatives containing three gauge bosons

We’d like to identify them as the W+, W-, and Z except they too are massless

15

Standard ModelSpontaneous Symmetry Breaking (SSB)

occurs when a Lagrangian is invariant under some symmetry but the ground state (vacuum) is not Pencil falling

Heisenberg ferromagnet

2008 Nobel Prize to Nambu for discovering SSB

16

Standard ModelHiggs mechanism

We have SSB when a Lagrangian is invariant under some symmetry but the ground state (vacuum) is not

If the broken symmetry is a continuous symmetry, then there necessarily exists one or more massless spin 0 particles (Goldstone bosons)

If the broken symmetry is a local gauge symmetry, then the Goldstone bosons get absorbed (eaten) by the massless gauge bosons thereby acquiring mass

17

Standard ModelConsider a charged self-interacting

complex scalar field (the Higgs field) Require the Lagrangian to be locally gauge

invariant

For 2 > 0 we have QED of charged scalars For 2 < 0 we have SSB and a continuum of

degenerate vacuum states

2*222

2

1 DL

22

22

0

2 v

18

Standard ModelThe Lagrangian for small perturbations

about the ground state

.interact2

22

1L

ation transformgauge specifica usingafter And

2/For

2222

AAvq

iv

A massive scalar (Higgs) with

A massive gauge boson with

And no massless Goldstone boson

22 2 m222 vqmA

19

Standard Model

SummaryHiggs

Mechanism

MassiveGaugeBosons

LocalGauge

Invariance

MassiveHiggs Boson

20

Standard ModelAn often used

analogy for mass generation

21

Standard Model SuccessesTested from 10-17 to 1022 cmNo significant deviations (including

quantum corrections) at the 10-3 levelPredicted weak neutral currents –

discoveredRequired the existence of W, Z –

discoveredNecessitated charm and top –

discoveredPredicts only 3 neutrino families

22

Standard Model Successes

There are no experimental discrepancies with Standard Model predictions

But no Higgs boson observation either

23

Standard Model Parameters

On the other hand, the Standard Model does contain a lot of parameters

24

The basic constituents of matter are the 6 quarks and the 6 leptons, and the 4 carriers of the fundamental forces. The three quark and lepton generations have very similar properties.

All the particles we know of (protons, neutrons, nuclei, atoms are made from these simple building blocks.

As far as we know, there are no smaller units than quarks and leptons.

Seeking the underlying patterns of matter

2525

Fundamental Forces

Interactions arise from Fields (classical field theory) Exchanged quanta (quantum field

theory)

2626

Fundamental Fermions

There are three families of leptons and quarks

27

Fundamental Particles

Or just another pattern to unravel?

ee

e

e L

L

d

u

d

u

d

u

uuu

ddd

s

c

s

c

s

c

ccc

sss

b

t

b

t

b

t

ttt

ttt

0ZW

Wg

28

So what is this thing called the Standard Model we are trying to smash – and why

Let’s start with the fundamental particles and their interactions

You’ve seen this many times so I won’t linger here

29

One of the goals of physics is to understand the common elements of these forces and particles

Perhaps they can be unified in the sense that electricity and magnetism are unified as electromagnetism

And in fact, in the 1960’s it was shown that the electromagnetic force and weak force had a common origin