Loading...

PPT – A1261399556tZlka PowerPoint presentation | free to download - id: 24a10d-ZDc1Z

The Adobe Flash plugin is needed to view this content

Measuring Symmetry at the Energy

Frontier Themis Bowcock University of Liverpool

Department of Physics

Outline

- Introduction
- Symmetries in Particle Physics
- The Energy Frontier
- New Horizons

Introduction

Vertical Questions

- Charge Quantization
- Gauge Structure for forces
- Unification of all Forces
- MwltltMPl(Hierarchy)

Introduction

Horizontal Questions

- Why are there three generations?
- What determines the pattern of quark lepton

masses and mixing? - What is the origin of matter anti-matter

asymmetry? - What is the origin of CP violation?

Introduction

Ubiquitous

- Continuous Symmetries
- Discrete Symmetries
- Broken Symmetries
- Manifest themselves at almost all energies in

most systems - Cosmological
- Particle, Nuclear, Atomic
- DNA
- Chaotic systems

Introduction

According to ..

- Symmetry Physics 1,560,000
- Physics 55,800,000
- Football 92,600,000
- All pages 4,000,000,000

Introduction

Beauty of Symmetry

Introduction

- We seem compelled to look for patterns and

symmetries as our guide for appreciating and

understanding nature - Even sexual attraction seems driven by symmetry

But not all is simple symmetry

Introduction

Particle Physics

- C, CP, T, CPT
- Gauge Symmetries
- Broken Symmetries
- Supersymmetry
- Lorentz Invariance

Symmetries

Parity and Common Sense

- Despite biological evidence (Thanks to Frank

Close!) - Isomers, were found to rotate polarized light in

two different directions --- one to the left, the

other to the right. - Pasteur observed as well that living organisms

were able to synthesize and use only one isomer

and never the other. But nature itself appeared

to have no preference over which form it produced

--- in reactions the isomers were produced in

equal quantities. That is, nature appears to

exhibit complete symmetry between the left and

right. - Until 1957 physicists believed this symmetry to

hold for all physical processes. A mirror image

of any reaction should be identical in every way

to the actual reaction. This idea was intuitive

to the physicist --- what could it mean if nature

preferred left over right or vice-versa?

Symmetries P

P operator

- Changes r?-r

- Clockwise spin

Symmetries P

- Clockwise spin

Parity

- A quantum number describing the symmetry of the

mirror reflection. - The parity operation reverses the sign of the

spatial coordinates of the wavefunction - P? (r,t)? (-r,t). Parity is even if P? ? ,

parity is odd if P? -? . For a state with

orbital angular momentum l the parity is (-1)l. - Parity reverses momenta and positions but not

angular momenta (or spins). Spin is an axial

vector and does not change sign under parity

operation. - Parity reverses helicityv

Symmetries P

Yang and Lee

- The events which led to the publication of Lee

and Yang's historic paper, Question of Parity

Conservation in Weak Interactions, began at the

International Conference on High Energy Physics

at the University of Rochester in April 1956. - Feynman said, "I thought the idea (of parity

violation) unlikely, but possible, and a very

exciting possibility." Indeed Feynman later made

a fifty dollar bet with a friend that parity

would not be violated 6.

Symmetries P

Proposed Parity Violation

- They proposed several experiments
- beta decay of cobalt-60. The idea involved

orienting cobalt nuclei with a strong magnetic

field so that their spins are aligned in the same

direction. Beta rays (electrons) are emitted at

the poles of the nuclei. - A mirror image of the system would also show beta

rays being emitted from the poles of the mirror

cobalt nuclei, the only difference being that the

north and south poles of the mirror nuclei would

be reversed since they spin in opposite direction

of their real counterparts. - Parity conservation demands that the emitted beta

rays be equally distributed between the two

poles. If more beta particles emerged from one

pole than the other, it would be possible to

distinguish the mirror image nuclei from their

counterparts. Thus an anisotropy in the emitted

beta rays would be tantamount to parity

violation. - T.D. Lee, C.N. Young, Phys. Rev. 104, 254 (1956)

Symmetries P

Discovery of P

- C.S. Wu in beta-transition of polarized Cobalt

nuclei. - Charged weak current, acting in Beta-transitions,

couples only to left-handed states (particles

with projection of their spin

Symmetries P

Wus experiment

- Beta-decay of 60Co to 60Ni. The excited 60Ni

decays to the ground state through two successive

g emissions with g energies 1.173 and 1.332 MeV. - National Bureau of Standards (Ambler et al.) -

nuclear polarisation through spin alignment in a

large magnetic field at 0.01oK. At low

temperature thermal motion does not destroy the

alignment. Polarisation was transferred from 60Co

to 60Ni nuclei. Degree of polarisation was

measured through the anisotropy of gamma-rays. - Beta particles from 60Co decay were detected by a

thin anthracene crystal (scintillator) placed

above the 60Co source. Scintillations were

transmitted to the photomultiplier tube (PMT) on

top of the cryostat.

Symmetries P

Anti-neutrinos

Magnetic field

Electrons

Wus experiment

Symmetries P

- Photons were detected by two NaI crystals

(scintillators). Difference in the counting rate

(g anisotropy) showed the degree of polarisation. - The time of experiment - several minutes (before

the set up warmed up and the polarisation

disappeared). - Polarising magnetic field was applied in both

directions (up and down).

Wus results

- Graphs top and middle - gamma anisotropy

(difference in counting rate between two NaI

crystals) - control of polarisation bottom - b

asymmetry - counting rate in the anthracene

crystal relative to the rate without polarisation

(after the set up was warmed up) for two

orientations of magnetic field. - Similar behaviour of gamma anisotropy and beta

asymmetry. - Rate was different for the two magnetic field

orientations. - Asymmetry disappeared when the crystal was warmed

up (the magnetic field was still present)

connection of beta asymmetry with spin

orientation (not with magnetic field).

Symmetries P

Parity violation

- C.S. Wu et al., Phys. Rev. 105, 1413 (1957)
- Isador Rabi said, "A rather complete theoretical

structure has been shattered at the base and we

are not sure how the pieces will be put together"

6

Symmetries P

Parity violation in ?? ?? e decay

- Positrons from muon decay were detected by a

telescope 3-4, which required particles of range

gt8 g/cm2 (25 MeV positrons). - Events concidence between counters 1-2 (muon)

plus coincidence between counters 3-4 (positron)

delayed by 0.75-2.0 ms. - Goal to measure I(q) for positrons.
- Conventional way move detecting system

(telescope 3-4) around carbon target measuring

intensities at various q. But very complicated. - More sophisticated method precession of muon

spin in magnetic field. Vertical magnetic field

in a shielded box around the target. - The intensity distribution in angle was carried

around with the muon spin.

Symmetries P

Results of the experiment by Garwin et al.

- Changing the field (the magnetising current),

they could change the rate (frequency) of the

spin precession, which will be reflected in the

angular distribution of the emitted positrons. - Garwin et al. plotted the positron rate as a

function of magnetising current (magnetic field)

and compared it to the expected distribution - The agreement proved the initial assumption

about parity violation.

Symmetries P

To celebrate

- ...Hudson brought out a bottle of Chateau

Lafite-Rothschild, 1949, and they drank to the

overthrow of the law of parity"

Symmetries P

Parity

- Core collapse supernovae are gigantic explosions

of massive stars that radiate 99 of their energy

in neutrinos. This provides a unique opportunity

for large scale parity or charge conjugation

violation - Only left-handed neutrinos exist and right-handed

anti-? - asymmetry of charge is an observed fact. Thus,

the violation of C-symmetry is considered a

fundamental physical property of the universe.

Symmetries P

Charge Conjugation

- asymmetry of charge is an observed fact. Thus,

the violation of C-symmetry is considered a

fundamental physical property of the universe.

Symmetries C

CP

- Application of C and P to a system
- E.G. a negative helicity proton under CP becomes

a positive helicity antiproton - This was believed to be the symmetry!

Symmetries CP

Analogy(1) conservation

Symmetries CP

x

Analogy(1) violation

Symmetries CP

x

Discovery of CP Violation

- J.H. Christenson, J.W. Cronin, V.L. Fitch, and R.

Turlay, Phys. Rev. Lett. 13, 138-140 (1964)

Symmetries CP

Neutral Kaon decays

- and both decay via the weak

interaction into the same end products.

Symmetries CP

Kaon mixing

- As and decay to the same state, they

can mix - This can be expressed as
- and are not CP eigenstates, however,

linear combinations of these can be constructed

to satisfy this

Symmetries CP

Kaon mixing

- These have even and odd CP symmetry respectively

Symmetries CP

Short and Long Kaons

- In 1956, two neutral Kaon decay modes were

observed experimentally - The large difference in the lifetimes of these

particles are the origin of the names long and

short. - These decays would suggest that
- due to their corresponding CP symmetries

Symmetries CP

Observation of CP Violation

- However, in 1964, Christenson, Cronin and Fitch

discovered that the long lived Kaon also decayed

into two pions - If as originally thought, then CP

symmetry had been violated - If, as first thought
- And
- Then CP is violated

Symmetries CP

Results

- The branching ratio for this decay is
- Because CP is not conserved, the states and

can be written as

Symmetries CP

Indirect CP

- Cronin and Fitch had observed indirect CP
- The weak eigenstates were admixtures of CP

states

Symmetries CP

Direct CP

- Another route was possible
- K2 supposedly 3 pions only could decay directly

to 2 pions - Direct CP violation
- NA31 1988 (CERN)
- Fermilab and CERN in late 90s

Symmetries CP

CP with quarks

- Classically to see CP we need 2 or more

interfering phases and identical final states

Symmetries CP

i

p

CKM Matrix

- CKM matrix links the weak charged currents to the

quarks - Mass eigenstates to weak eigenstates
- Uintary matrix 3 amplitudes and a phase

diversion

Vtb

t

b

CKM matrix

- Only source for predicting CPV
- CKM matrix
- Linked to other decays and weak processes
- CP Symmetry intrinsically linked with our

understanding of Standard Model

diversion

Standard Model

- Symmetry breaking in QCD
- chiral perturbation theory
- Strong CP(axion) and instantons
- Symmetry breaking in Electro-Weak
- Masses of W, Z, photons, Higgs Mechanism
- CP violation in quark and lepton sector
- Broken Symmetries seem to be an inevitable

by-product of fundamental dynamics.

Symmetries

B/meson factories

Symmetries CP

U.S. Department of Energy Secretary Bill

Richardson symbolically initiates the operation

of the new PEP-II B Factory at SLAC on October

23, 1998

Pier Oddones Idea (1987) asymmetric energy

beams

Exclusive B Meson Reconstruction

B-Flavor Tagging

- 9GeV e- on 3.1GeV e
- Y(4S) boost bg0.56

(No Transcript)

BaBar

- B-meson factory
- First observation of CP violation in B-system

Symmetries CP

Direct CP

- BaBar has now discovered direct CP violation for

B mesons. - Bs into Kpi- pairs and anti-Bs into K-pi pairs.
- According to theory, CP symmetry would dictate

that the two events have the same odds of

happening. - Hence, by starting with equal numbers of Bs and

anti-Bs one should end with equal numbers of

Kpi- and K-pi pairs. However, the BaBar

collisions produced 910 Kpi- pairs but only 696

K-pi pairs.

Symmetries CP

Standard Model

Symmetries CP

Matter Anti Matter Asymmetry

Symmetries CP

Baryon asymmetry

- No Anti-matter

Sakharov Conditions

- The first requirement was that the proton the

bedrock particle of nuclear matter should be

unstable. - The second was that there would be interactions

violating C and CP, that would open up the

possibility that the universe's initial exact

matterantimatter symmetry could be upset. - The third condition was that the universe would

undergo a phase of extremely rapid expansion - If a cosmological matterantimatter asymmetry

could be built up in this way, all of the

remaining antimatter particles would annihilate

later in the history of the universe, leaving

behind matter particles and radiation, as

observed today.

Symmetries CP

Classical Symmetries CPT

- Consequences
- Locality
- Lorentz invariance
- http//www.physics.indiana.edu/Local Quantum
- Field Theories ? CPT invariance Luders-Pauli

theorem, 1955 - If T is violated then CP compensates

Symmetries CPT

Lorentz

- Rotations and boosts
- Physical sources of Lorentz Symmetry violation
- Vacuum destabilization(Spontaneously broken or

otherwise) - Implications (Coleman, Glashow)
- Muon radiative decays
- Neutrino oscillations modified
- High Energy Cosmic Rays

Symmetries

CPT and Lorentz

- Anti-protonic Helium Spectroscopy
- Neutral-Meson oscillations
- QED in Penning Trap
- Muon spin precession
- Cosmological Birefringence

Tests of Symmetries

EDM

- Under time reversal the direction of the spin

changes, since it is an axial vector, while the

charge distribution does not change. - The electric dipole moment, which is a vector,

has to be parallel to the spin, since it is the

only available vector in the rest frame of the

particle. - Therefore, if time reversal is a good symmetry,

the electric dipole moment must be zero.

Symmetries T

Electric Dipole Moments

- A long experimental campaign currently led by an

experiment at ILL Grenoble limits this to less

than 6x10-26 e cm, analogous to the Earth's

surface being smooth and symmetric to less than 1

µm.

Symmetries CP

KTEV CPLEAR

- Both CPLEAR and KTeV observed T violation
- Transformation of matter into antimatter is

asymmetrical in time compared with the reverse

process. - Incidentally,
- The Alien test....

Symmetries T

CPLEAR

- pp? K-pK0
- pp? Kp-K0
- The strangeness of the neutral kaon - that is,

whether it is kaon or antikaon- at the time of

production can be "tagged" by the charge of the

second kaon produced in the collision. - The strangeness of the kaon at the moment of

decay can be tagged through its decay products

kaon particles decay into a positron, negative

pion and a neutrino, while antikaon particles

decay into an electron, positive pion and

anti-neutrino. - If there is an asymmetry, AT, between the number

of initial antikaon decaying into positrons and

the number of initial kaon decaying into

electrons,this is a measure of the violation of

time-reversal symmetry in the sense described

above - AT (6.6 1.3stat 1.0syst) X 10-3 (A

Angelopoulos et al . 1998 Physics Letters B at

press).

Symmetries T

CPLEAR T-Violation

Symmetries T

C,P,CP,T and CPT

- Violations of all the symmetries C,P,CP,and T are

possible within the Standard Model - Only CPT is required (by Standard Model) to be an

exact symmetry of nature - Implications
- Masses of particles and anti-particles equal.
- Charges of particles and anti-particles exact

opposites. - C,P,CP and T may be observed

Symmetries

Precision and Energy

- Testing of Standard Model for consistency
- Rare decays accessing all possible modes and

interference diagrams - Lower energy machines usually buy simplicity and

access to higher energies - large statistics
- Measurement
- B-factories
- Higher Energies e.g. LHC
- Observation/discovery
- Attempt to use for measurement
- Discovery?Measurement?Calibration!

Energy Frontier

Large Hadron Collider

- International Collaboration

Energy Frontier LHC

Large Hadron Collider

Energy Frontier LHC

A few statistics

- Takes 0.1ms for a particle travelling at the

speed of light to go round! - Current in one beam approx 0.5A
- 3.2 1014p
- Energy in one proton 1TeV (??1000)
- Person would weight 100Tonnes at this velocity!
- Wavelengths10-18m
- Explode to sun 1m?1AU wavelength still less than

0.1micron - Energy in one beam
- 362MJ
- Mass of Boeing laden 747350Tonnes
- Travelling at 45m/s (163km/h at landing -

normally 230)

Energy Frontier LHC

Collisions of great complexity

Energy Frontier

Detectors

Energy Frontier LHC

LHCb

- CP violation in B-physics
- Ultimate Standard Model Checker
- Precision trackers
- Particle ID
- Sophisticated Trigger
- Huge Rate of events
- Rare B-decays
- New Physics Reach

Energy Frontier

LHCb detector

Energy Frontier

Forward Physics

Energy Frontier

LHCb What will we learn?

- Enormous production rate at LHCb 1012 bb

pairs per year - much higher statistics than the current B

factories - O(100,000)/s
- CP in K was 1/1000
- Energy Frontier has bought us this gift

Energy Frontier

Experiments

- General Purpose Detectors
- CMS, ATLAS
- Biggest experiments ever built
- Complement CP studies

Energy Frontier

Restoring Symmetry

- Broken symmetries
- Gauge theories
- Higgs
- Running coupling constants
- Supersymmetry

Energy Frontier

Warnings

- Ernst Mach's "Even instinctive knowledge of so

great a logical force as the principle of

symmetry ... may lead us astray ... The

instinctive is just as fallible as the distinctly

conscious. Its only value is in provinces with

which we are very familiar" - Physicists' assume that nature will present a

simple model - Chen Ning Yang "In the study of nature, one

believes in something simple underlying all". - Madame Wu "One hopes that nature possesses an

order that one may aspire to comprehend. When we

arrive at an understanding, we shall marvel how

neatly all the elementary particles fit into the

great scheme.