Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to...
Transcript of Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to...
![Page 1: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/1.jpg)
1
Introduction to the
Standard Model
Quarks and leptons
Bosons and forces
The Higgs Bill Murray,
RAL,
March 2002
![Page 2: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/2.jpg)
2
Outline:
An introduction to particle
physics
What is the Higgs Boson?
Some unanswered questions
![Page 3: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/3.jpg)
3
From you to the quark
Electrons
orbiting
nucleus
d type
quark
u type
quarks
![Page 4: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/4.jpg)
4
d
The Matter Particles
e
Neutrino
Electron
Proton Mass: 1.7 10-27 kg
charge: +1
Mass: ~<10-9 proton mass?
Charge: 0
Mass: 0.0005 proton mass
charge: -1
u
u d
Neutron Charge: 0 u
d
![Page 5: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/5.jpg)
5
How do we know about quarks?
Stanford Linear Accelerator Centre,
California
Fire electrons at protons: See big deflections!
Rutherford found a nucleus in the atom by firing
alpha particles at gold and seeing them bounce back
Late 1960’s
![Page 6: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/6.jpg)
6
The particles of Matter
e
‘up’ quark
neutrino
e
u
d
Electron
‘down’ quark
u u
d d
Come in 3 versions,
known as colours
Exercise to check
this later
Why 3
colours?
![Page 7: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/7.jpg)
7
The particles of Matter
e
u
d
e
All ordinary matter is composed of these
(There is a corresponding antiparticle for each)
See Stefania’s talk later
![Page 8: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/8.jpg)
8
The Matter particles
u
d
e
1st Generation
Ordinary
matter
2nd Generation
Cosmic rays
s
c
3rd Generation
Accelerators
b
t
Why 3
generations
?
![Page 9: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/9.jpg)
9
The Matter particles
e
u
d
e
1st Generation
2nd Generation
s
c
3rd Generation
b
t
0.1GeV
1.7GeV
4.5GeV
175GeV
E=mc2
1GeV~Proton Mass
1.7GeV
Others are lighter
![Page 10: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/10.jpg)
10
The Matter particles
u
d
e
1st Generation
2nd Generation
s
c
3rd Generation
b
t
1974
1977
2000 1995
1975 1897
![Page 11: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/11.jpg)
11
How do quarks combine?
u
u d
A proton:
two ‘u’ quarks and one ‘d’ quark
d
u d
A neutron:
2 ‘d’ quarks and 1 ‘u’
quark
u
d
Mesons have a quark and an
anti-quark - Many created,
not stable
With 6 quark
types there are
hundreds of
combinations
![Page 12: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/12.jpg)
12
Can we see a quark?
Probably not
The picture shows
the result of making
a pair of quarks at
LEP, CERN
The quarks are not
seen: A jet of
‘hadrons’ is instead
![Page 13: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/13.jpg)
13
+
Forces in Ordinary Physics
Classically, forces are described by
+
Field
charges and fields
+ +
![Page 14: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/14.jpg)
14
Continuous field exchange of quanta
+ +
For Electromagnetism
The quanta are photons,
High energies and small distances quantum mechanics
Forces in Particle Physics
![Page 15: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/15.jpg)
15
The Forces of Nature
Force Realm Particle
Electro-magnetism
Magnets, DVD players
Strong Fusion Gluon
Weak -decay, (sunshine)
W+,W
-,
Z0
Gravitation Not in the same framework
Higgs may give
a link?
![Page 16: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/16.jpg)
16
The Forces of Nature
Force Mass, GeV Particle
Electro-magnetism
0
Strong 0 Gluon
Weak
W’s Z
Gravitation Not in the same framework
![Page 17: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/17.jpg)
17
Feynman
Diagram
Positron
(anti-electron)
Mediation of the Forces
Electron
At each ‘vertex’
charge is
conserved.
Heisenberg
Uncertainty
allows energy
borrowing.
![Page 18: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/18.jpg)
18
Particles and forces
‘u’ quarks ‘d’ quarks electron neutrino
E.M.charge
+2/3
Strongforce
yes yes no no
Weakforce
yes yes yes yes
Heavier generations have identical
pattern
![Page 19: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/19.jpg)
19
What is the Higgs boson?
The equations describing the forces and
matter particles work well.
Unfortunately they demand that they all
weigh nothing
– We know this is not true
Prof. Higgs proposed an addition which
corrects this.
Together Known
as…
The Standard
Model
![Page 20: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/20.jpg)
20
The Waldegrave Higgs challenge
In 1993, the then UK Science Minister,
William Waldegrave, issued a challenge to
physicists to answer the questions:
'What is the Higgs boson, and why do we
want to find it?’
on one side of a sheet of paper. David Miller of UCL won a bottle of champagne for
the following:
![Page 21: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/21.jpg)
21
The Waldegrave Higgs challenge
Imagine a room full of
political activists
![Page 22: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/22.jpg)
22
The Waldegrave Higgs challenge
The Prime Minister
walks in
![Page 23: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/23.jpg)
23
The Waldegrave Higgs challenge
He is surrounded by a
cluster of people Analogous to
generation of Mass
![Page 24: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/24.jpg)
24
The Waldegrave Higgs challenge
Imagine the same room
again
![Page 25: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/25.jpg)
25
The Waldegrave Higgs challenge
A interesting rumour is
introduced
![Page 26: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/26.jpg)
26
The Waldegrave Higgs challenge
Thanks to
D. Miller
and CERN
Soon we have a cluster
of people discussing it Analogous to Higgs
boson
©
Photo
CERN
![Page 27: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/27.jpg)
27
What does Higgs theory imply?
Higgs’ mechanism gives
mass to W and Z bosons,
and to the matter particles.
Mass of the W predicted
We can
check it
The Higgs
Boson mass is
not predicted
It also predicts one
extra particle:
The Higgs boson
![Page 28: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/28.jpg)
28
The W, the top quark and Higgs
We can calculate the mass of the W
boson
Need the mass of the Z and the
strength of the forces; these are well
known
It is also affected by:
– Top quark mass: Weak effect
–Higgs mass: Tiny effect
![Page 29: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/29.jpg)
29
The W, the top quark and Higgs
The W mass is
about 80GeV/c2
![Page 30: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/30.jpg)
30
The W, the top quark and Higgs
Expanded
scale
The W mass
depends upon the
top and Higgs
masses
![Page 31: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/31.jpg)
31
CERN’s Collider ring
LEP : e+e-, Ecms~ 210 GeV LHC : pp, Ecms~ 14000 GeV
CERN
4 LEP experiments: 2 LHC experiments
DELPHI
©
Photo
CERN
![Page 32: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/32.jpg)
32
What are LEP and LHC?
LEP LHC
Beams of Electrons Protons
Energy, GeV 208 14,000
Max. Higgs
Mass
115 ~1000
Detailed? Yes No
Operation 1989-2000 2006-
Complementary machines – but needing the same tunnel
Work
started
1980’s
![Page 33: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/33.jpg)
33
In the LEP tunnel
27km of
vacuum
pipe and
bending
magnets
©
Photo
CERN
![Page 34: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/34.jpg)
34
Now to be the LHC tunnel
27km of
vacuum
pipe
8.3Tesla
bending
magnets,
3o above
absolute
zero
©
Photo
CERN
![Page 35: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/35.jpg)
35
One experiment: ‘OPAL’
One of
four
rather
similar
detectors
Assembly in 1989 Note the
people
©
Photo
CERN
![Page 36: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/36.jpg)
36
An LHC experiment: ATLAS
In construction Note the
people
©
Photo
CERN
![Page 37: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/37.jpg)
37
Z studies at LEP
From 1989 to 1995
LEP created
20,000,000 Z bosons
These were used for
detailed studies of its
properties
Here you see the
analysis which
established the number
of neutrinos as 3
They can say
something about the
Higgs too.
Peak at
Z mass,
91GeV
![Page 38: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/38.jpg)
38
Positron
Feynman Diagram for Z production
Electron
Z Cannot see the Z
Only its decay
products
![Page 39: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/39.jpg)
39
Indirect Search for the Higgs Boson
Basic Feynman
diagram
top
Properties of the Z boson changed by ‘loop’ effects:
Higgs
What is affected?
Z decay rate to b’s -
sensitive to top mass
Angular distributions -
sensitive to W & H mass
![Page 40: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/40.jpg)
40
Indirect Search for the Higgs Boson
%1
%1
0.1% Precision needed!
By carefully studying Z’s we:
• Predict mtop and mW;
Compare with measurements;
• Predict mH;
Compare with measurements.
top
Higgs
![Page 41: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/41.jpg)
41
How to recognize Z decays: e) Z-> -
Z qq: Two jets, many
particles
Z e+e-, -: Two
charged particles (e or .)
Z -: Each gives 1 or
3 tracks
-
![Page 42: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/42.jpg)
42
How to recognize Z decays: e) Z-> -
Z bb: Like qq events, with detached vertices,
measured in accurate vertex detectors
Z : Not detectable. -
-
-
(weak and slow decays to lighter quarks)
![Page 43: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/43.jpg)
43
One example Z distribution: Z Angular distributions
•This distribution depends
on the W mass DELPHI
1993-1995
46GeV
45GeV
47GeV
Many things are used:
Z mass,
Several angular
distributions,
Z decay fraction to bb Cos( ) of outgoing
![Page 44: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/44.jpg)
44
The W, the top quark and Higgs
The W and top
masses from Z
studies agree
with theory
i.e. they lie on the
curves
Result from Z studies
They can be
checked by
direct
measurement
![Page 45: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/45.jpg)
45
The W, the top quark and Higgs
W mass from
LEP and
Tevatron
Completely
consistent!
This suggested the
top quark had a
mass of 175GeV
before it had been
discovered
![Page 46: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/46.jpg)
46
The W, the top quark and Higgs
Top mass
from
Tevatron
Again,
incredible
consistency
The top mass
directly measured
agrees completely
with the predicted
one
![Page 47: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/47.jpg)
47
The W, the top quark and Higgs
Scale has
been
expanded
further
The data
(especially if they
are averaged)
suggest a Higgs
mass around
100GeV
This procedure
worked for the top
quark. Will it work
again?
10GeV 100GeV
1000GeV
![Page 48: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/48.jpg)
48
Summary of model
W mass agrees with Higgs theory
– to 1 part in 1000
Electro-weak corrections verified:
– W mass agrees with prediction
– Top mass agrees with prediction
Higgs mass should be:
GeV54
3485
![Page 49: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/49.jpg)
49
The Search for the Higgs
In the late 1990’s ‘LEP’ at CERN ran
with enough energy to make W pairs
There was also hopes it might make
a Higgs.
![Page 50: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/50.jpg)
50
The W pairs:
W’s produced by
reactions like this one
Each W decays in ~10-26 seconds
Or quarks
(2 sorts)
e-,
e
Into leptons
(3 sorts)
![Page 51: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/51.jpg)
51
W+W-: What do we see?
A
muo
n
An
electron
Both W’s decayed to
leptons
![Page 52: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/52.jpg)
52
W+W-: What do we see?
A quark
A jet from
a quark
A muon
One W as 2 quarks, the
other as leptons.
The nicest signature
![Page 53: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/53.jpg)
53
W+W-: What do we see?
A jet
from a
quark
A quark
A quark
A quark
Both W’s
decayed to 2
quarks
![Page 54: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/54.jpg)
54
How could LEP make a Higgs ?
Make a Higgs and
a Z together
So need Energy
greater than Higgs
mass plus Z mass
Predicted LEP events,
4 experiments
![Page 55: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/55.jpg)
55
tau
b quarks
gluons
WW
other
Higgs and Z decay channels
Higgs decay modes
taus
quarks
neutrinos
electrons
muons
Z decay modes
e.g. ZH bb All Z decay modes used
Higgs only into b-quarks
B quarks Any quark
WW
Recall: Both Z & H are made
![Page 56: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/56.jpg)
56
First data above 206 GeV: First Serious Candidate
(14-Jun-2000, 206.7 GeV)
• Mass 114.3 GeV/c2; • Good HZ fit; • Poor WW and ZZ fits; • P(Background) : 2% • s/b(115) = 4.6
The purest candidate event ever!
b-tagging (0 = light quarks, 1 = b quarks)
• Higgs jets: 0.99 and 0.99;
• Z jets: 0.14 and 0.01.
e+e- bbqq _ _
Missing Momentum
High pT muon
![Page 57: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/57.jpg)
58
Combined Mass Plot Distribution of the
reconstructed Higgs
boson mass with
increasing purity
for a signal with
mass 115 GeV/c2
Essential to
understand the
background if we
want to claim
something new
Yellow: background
Red: Higgs
![Page 58: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/58.jpg)
59
What is the position?
We look to the future to solve this question.
LEP closed in 2000
mH 53 to 141 GeV/c2
mH = 115.6 GeV/c2 - 0.8 + 0.8
•Precision studies of Z,W and top DEMAND a Higgs: •MW agrees with Higgs’ predictions to 1 per mille, • Direct Searches (4 in 100 effect)
Is this a
coincidence?
![Page 59: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/59.jpg)
60
What happens next?
s = 2000 GeV
The Tevatron:
• A pp collider, near Chicago;
• run II started in 2001 – collecting
far more data than before
•Can probably find a 115GeV
Higgs by 2007
![Page 60: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/60.jpg)
61
What happens next?
The LHC:
• CERN’s future pp collider;
• Designed to find the Higgs, it
can do it!
•First chance in 2007
s = 14000 GeV
![Page 61: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/61.jpg)
62
What happens next?
TESLA:
• A Proposed e+e- collider -
CLEAN
• 500-800GeV, very high
rate
•Find the Higgs in ½ a
day: study it carefully
s = 800 GeV
![Page 62: Introduction to the Standard Modelbanburytuition.coffeecup.com › Physics A Level...Introduction to the Standard Model Quarks and leptons Bosons and forces The Higgs Bill Murray,](https://reader033.fdocuments.in/reader033/viewer/2022052611/5f04905f7e708231d40e97b3/html5/thumbnails/62.jpg)
63
Some Unanswered Questions Does the Higgs exist? If not, how do you
explain mass?
Where is all the anti-matter?
– See Stefania’s talk
What about Gravity
– Why do we get the cosmological constant
wrong by 10120?
Why are there 3 generations of
particles? And 3 colours?