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A1261399556tZlka

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Title: A1261399556tZlka


1
Measuring Symmetry at the Energy
Frontier Themis Bowcock University of Liverpool
Department of Physics
2
Outline
  • Introduction
  • Symmetries in Particle Physics
  • The Energy Frontier
  • New Horizons

Introduction
3
Vertical Questions
  • Charge Quantization
  • Gauge Structure for forces
  • Unification of all Forces
  • MwltltMPl(Hierarchy)

Introduction
4
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
5
Ubiquitous
  • Continuous Symmetries
  • Discrete Symmetries
  • Broken Symmetries
  • Manifest themselves at almost all energies in
    most systems
  • Cosmological
  • Particle, Nuclear, Atomic
  • DNA
  • Chaotic systems

Introduction
6
According to ..
  • Symmetry Physics 1,560,000
  • Physics 55,800,000
  • Football 92,600,000
  • All pages 4,000,000,000

Introduction
7
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

8
But not all is simple symmetry
Introduction
9
Particle Physics
  • C, CP, T, CPT
  • Gauge Symmetries
  • Broken Symmetries
  • Supersymmetry
  • Lorentz Invariance

Symmetries
10
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
11
P operator
  • Changes r?-r
  • Clockwise spin

Symmetries P
  • Clockwise spin

12
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
13
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
14
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
15
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
16
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
17
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).

18
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
19
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
20
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
21
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
22
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
23
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
24
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
25
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
26
Analogy(1) conservation
Symmetries CP
x
27
Analogy(1) violation
Symmetries CP
x
28
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
29
Neutral Kaon decays
  • and both decay via the weak
    interaction into the same end products.

Symmetries CP
30
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
31
Kaon mixing
  • These have even and odd CP symmetry respectively

Symmetries CP
32
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
33
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
34
Results
  • The branching ratio for this decay is
  • Because CP is not conserved, the states and
    can be written as

Symmetries CP
35
Indirect CP
  • Cronin and Fitch had observed indirect CP
  • The weak eigenstates were admixtures of CP
    states

Symmetries CP
36
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
37
CP with quarks
  • Classically to see CP we need 2 or more
    interfering phases and identical final states

Symmetries CP
i
p
38
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
39
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
40
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
41
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
42
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

43
(No Transcript)
44
BaBar
  • B-meson factory
  • First observation of CP violation in B-system

Symmetries CP
45
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
46
Standard Model
Symmetries CP
47
Matter Anti Matter Asymmetry
Symmetries CP
48
Baryon asymmetry
  • No Anti-matter

49
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
50
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
51
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
52
CPT and Lorentz
  • Anti-protonic Helium Spectroscopy
  • Neutral-Meson oscillations
  • QED in Penning Trap
  • Muon spin precession
  • Cosmological Birefringence

Tests of Symmetries
53
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
54
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
55
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
56
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
57
CPLEAR T-Violation
Symmetries T
58
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
59
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
60
Large Hadron Collider
  • International Collaboration

Energy Frontier LHC
61
Large Hadron Collider
Energy Frontier LHC
62
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
63
Collisions of great complexity
Energy Frontier
64
Detectors
Energy Frontier LHC
65
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
66
LHCb detector
Energy Frontier
67
Forward Physics
Energy Frontier
68
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
69
Experiments
  • General Purpose Detectors
  • CMS, ATLAS
  • Biggest experiments ever built
  • Complement CP studies

Energy Frontier
70
Restoring Symmetry
  • Broken symmetries
  • Gauge theories
  • Higgs
  • Running coupling constants
  • Supersymmetry

Energy Frontier
71
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. 
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