studying the fundamental structure of matter...of elementary particles: quarks and leptons...
TRANSCRIPT
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Studying the fundamental structure of matter
Ming‐chung Chu 朱明中Hoi Tik Alvin Leung 梁凱迪
Department of Physics, The Chinese University of Hong Kong
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Hong Kong Science Museum Jan 16, 2016
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Structure of matter
2https://www.youtube.com/watch?v=bhofN1xX6u0
From the elementary particles (R
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Searching for the fundamental structure of matterWhat’s inside?
image by Cliparts.co
until the atoms are found
image by AIP
for the ultimate ‘atom’ and the rules that govern the structures
could be a mess ...
image by Cliparts.co
Image credit: ETH Zurich, Institute for Particle Physics.
and we keep looking ...
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Standard Model of Particle Physics
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• All matter are composed of elementary particles: quarks and leptons (structureless, R
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Probing the structures of matter
image by Cliparts.co
3 ideas:
2. scattering散射: send interactive particles in and see how they are deflected eg. X‐ray
3. collisions 撞擊: break it up!
image by Cliparts.co image by Cliparts.co
1. emission 放射: measure what comes out
image by Cliparts.co
Image by CERN
Image by Gael du Plessix
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Studying the fundamental structure of matter
• I. Neutrino astrophysics• II. Gravitational wave astrophysics• III. Electron microscopy• IV. Crystallography• V. High energy particle collisions at LHC
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I. Neutrino Astrophysics
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• Elementary particles• 3 types﹕• No electric charge• Interact only via weak and gravity forces• Finite but tiny masses (m
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Solar Neutrinos
Earth: 4x1011 e/s/cm2
1016 e passes through your body every s!
~ 2x1038 e/s!
Stars turn matter into neutrinos and photons (m E). Neutrinos penetrate the entire star, but not the photons.
ee 22HeH44
Signals from the solar core!
Fusion energy from the sun:
e
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“for the discovery of neutrino oscillations, which shows that neutrinos have mass"
Nobel Prize in Physics 2015http://www.nobelprize.org/nobel_prizes/physics/laureates/2015/
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Arthur B. McDonald
Photo: K. MacFarlane. Queen's University /SNOLAB
Takaaki KajitaPhoto © Takaaki Kajita
SNO
http://snoplus.phy.queensu.ca/Home.html
Super Kamiokande (SK)
http://www‐sk.icrr.u‐tokyo.ac.jp/sk/index‐e.html
梶田隆章
Solar neutrinos measured well by neutrino observatory, agree with solar theory
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http://wwwlapp.in2p3.fr/neutrinos
Supernova neutrinos
Animation by STScI/NASA
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超新星 Supernova
‐Massive stars (M > 3Mo) die as supernovae‐ As bright as 109 ‐1010 x Sun. Releases 1046 J ~ 1012 yr of solar
energy in days; T ~ 1011 K! Produce ~1058 ’s in seconds.
‐ ~10% rest mass of the star → neutrinos‐ > 90% energy carried away by neutrinos
‐ Supernova neutrinos: observed, new tool?
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http://www‐sk.icrr.u‐tokyo.ac.jp/doc/sk/index.htmlhttp://cupp.oulu.fi/neutrino/nd‐sn.html
Supernova neutrinos
Superkamiokande and IMB detected neutrinos from SN1987A
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@Anglo‐Australian Observatory
SN1987A Neutrino signals can help to study explosion mechanism
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Daya Bay Neutrino Experiment
13Far Hall: 4 x 80 ton‐detectors Daya Bay Near Hall: 2 x 80 ton‐detectors
We are ready: Supernova Early Warning Network
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Primordial neutrinos
Figure courtesy NASA/WMAP
Hot, dense cold
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13.8 billion years
Cosmological neutrinos
~ 300/cm3 Big Bang neutrinos everywhere, signals from first seconds of Big Bang
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II. Gravitational Astrophysics
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Gravitational Waves
• Einstein: matter/energy deforms space‐time→ space‐time = deformable medium可變形介質
• Ma er accelera on → waves in space‐time • = gravitational waves (重力波)• Predicted by Einstein’s General Relativity 100 years ago• Travels at speed of light• Displaces space‐time positions ofmatter
Wave motion in a string
A 2‐d analogy of Einstein’s space‐time16
‘Space‐time tells matter how to move; matter tells space‐time how to curve.’ – J. Wheeler
2 modes as seen by test masses
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Gravitational wave sources
• Violent motions of strong gravitational sources• black holes黑洞、neutron stars中子星 oscillations 振盪,
mergers 結合• Supernovae 超新星• Big Bang • But: very weak signals• Eg.: orbiting of 2 neutron stars 2 million light years away →
gravitational wave amplitude ~ 10‐18m
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2 10‐Mo black holes merging
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Gravitational wave observation –what can we learn?
Strong‐field tests of General Relativity
Nature of Black Holes
Physics of dense matter inside neutron stars
How supernovae explodeAdapted from Prof. Tjonnie Li’s talk
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LIGO
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Otto Lau at LIGO Hanford
Prof. Tjonnie Li 黎冠峰
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Ken
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III. Electron microscopy
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Some physical properties of wavesReflection Refraction
Interference Diffraction
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Photo credit: Todd Allen Photo credit: Crok Photography
Photo credit: Rolf Muller Photo credit: Thirteensteps13, flickr
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Optical microscope uses light waves!
• Visible lights are used.• Optical lenses are used to refocus
the light.
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Photo credit: Nikon
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We commonly use optical microscopes to view biological samples.
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… but can we see individual atoms with optical microscopes directly?
25Image credit: ETH Zurich, Institute for Particle Physics.
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Unfortunately not……because diffraction and interference come into play.
26Photo source: http://zeiss‐campus.magnet.fsu.edu/articles/basics/resolution.htmlhttp://www.cambridgeincolour.com/tutorials/diffraction‐photography.htm
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Unfortunately not……because diffraction and interference come into play.
Large Aperture
Light bends when passes through a small opening (aperture)
Small Aperture
Photo source: http://zeiss‐campus.magnet.fsu.edu/articles/basics/resolution.htmlhttp://www.cambridgeincolour.com/tutorials/diffraction‐photography.htm
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d d dWhat you put on a microscope slide
What you see through
the lens in a microscope
The two objects are resolved
The two objects are still resolved
The two objects are NOT resolved
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Unfortunately not……because diffraction and interference come into play.
Photo credit: Spencer Bliven
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The resolution of a microscope is limited by the wavelength used
d d dWhat you put on a microscope slide
The two objects are resolved
The two objects are still resolved
The two objects are NOT resolved
Resolution of a microscope:
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What you see through
the lens in a microscope
Photo credit: Spencer Bliven
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Wave‐particle duality• In 1924, de Broglie proposed that any moving
particle or object had an associated wave. • The de Broglie wavelength λ of a particle with a
momentum p is given by:
• Electrons, protons and neutrons also exhibit wave properties!
where h is called the Planck constant. h has a value of 4.1 x 10‐15 eVs
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Photo credit: Encyclopædia Britannica, Inc
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What is the wavelength of a 1 keVelectron?
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Electron microscopes
• In 1931, Max Knoll and Ernst Ruska built the first electron microscope.
• In late 1930, electron microscopes with theoretical resolutions of 10 nm were being designed and produced.
• The best resolution achieved to date is 0.05 nm.
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Photo credits: the Ernst Ruska Archive
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Electron microscopesSimplified version of scanning electron microscope (SEM)
Simplified version of transmission electron microscope (TEM)
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Pictures from http://www.britannica.com/technology/transmission‐electron‐microscopehttp://www.britannica.com/technology/scanning‐electron‐microscope
(‐ve terminal)
(+ve terminal)
(+ve terminal)
(‐ve terminal)
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Comparison of TEM and SEM
Transmission EM Scanning EM
Detection of electrons Based on transmitted electrons
Based on scattered electrons
Accelerating voltage higher lower
Resolution 0.2 nm 10 nm
Sample preparation Thin slide Can be thicker
Electron beam Can be broader Need to focus to a fine point
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Application of electron microscopes in Chemistry and Biology
Influenza virus particle
Photo Credit: Cynthia Goldsmith, Centers for Disease Control and Prevention
Scanning electron micrograph of HIV‐1 budding from cultured lymphocyte
Photo Credit: Cynthia Goldsmith, Centers for Disease Control and Prevention
Atomic resolution EM image of nanoscale precipitates in an Al‐Cu‐Li‐Mg‐Ag aerospace alloy.
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SuperSTEMimage of the novel nano‐iron Supplement (ferrihydrite)
Powell et al., Nanomedicine 2014
Oct;10(7):1529‐38.
Photo Credit: M. Weyland, Monash university
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Question: What is this?
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Answer: this is the famous “Photograph 51” , a x‐ray crystallography diffraction pattern of DNA
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IV. Crystallography
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How does crystallography work?• Crystallography is a common technique to determine the
arrangement of atoms in the crystalline solids.• You need a crystal (a solid material whose constituents are
arranged in a highly ordered microscopic structure)
• AND a wave source
39Photo source: http://www.atomsinmotion.com/book/chapter4/salts
-x-ray (x-ray diffraction), most commonly used -Electron wave (electron diffraction)-Neutron wave (neutron diffraction
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Crystallography was used to solve many problems in the last century!
Structure of Hemoglobin by x-ray diffraction
Hexamethylbenzene
Photo source: http://www.differencebetween.info/difference‐between‐blood‐and‐haemoglobin
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Bragg spectrometer
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Diffraction pattern
Picture source: http://hyperphysics.phy‐astr.gsu.edu/hbase/quantum/bragg.htmlhttp://education.mrsec.wisc.edu/supplies/DNA_OTK/
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Diffraction grating pattern
42Photo source: http://physics‐animations.com/Physics/English/DG10/DG.htmhttp://www.physicsoftheuniverse.com/images/quantum_double_slit_photon.jpg
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Diffraction grating pattern
43Photo source: http://www.doitpoms.ac.uk/tlplib/diffraction/diffraction3.php
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Diffraction Demonstration
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Image credit: University of Wisconsin‐Madison
Diffraction grating 1
Diffraction grating 2
Diffraction grating 3
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Bragg’s law
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ϴ ϴ
d
d sin Ѳ
Path A
Path B
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Determination of structure from diffraction patterns
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Measure diffraction pattern for different
values of Ѳ
Fourier transform
(Mathematical operation)
Molecular structure
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Comparison between x‐ray, electron and neutron diffraction
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X‐ray diffraction Electron diffraction Neutron diffraction
Interact with electron cloud
Interact with the electron clouds and
protons
Highly penetrating
Interact with heavy elements as they
have larger electron cloud
Scatter strongly by matter
Scatter from both light and heavy
atoms, differentiate between different
isotopes
Smaller amount of sample
Even smaller amountof sample
Larger amount of sample
Lower cost Medium cost High cost (Require nuclear
reactors/particle accelerator to
generate neutrons)
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Take‐home message
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Electron microscopeOptical microscope
Electron diffractionNeutron diffraction
Electron microscope
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VI. High energy particle collisions at LHC
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Protons accelerated to v = 99.999999% c (6.5 TeV)
http://lhc‐machine‐outreach.web.cern.ch/lhc‐machine‐outreach/
Large Hadron Collider (LHC)CERN: largest fundamental physics lab. LHC: most powerful accelerator in the world
LHC: US$8.75 billion
High energy collisions: recreate conditions at early universe, produce hidden particles, look for fundamental constituents of matter
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Why high energy collisions?
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‐ Recreate conditions at early universe (the Big Bang): evolution of the universe/physics from high T/E to low T/E
‐ Probe deeper into structure of matter: look for fundamental constituents
‐ Provide enough energy to create massive but hidden particles (eg. Dark matter)
Figure courtesy NASA/WMAP
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Higher energy further back in time
Higher energy deeper in space
Credit: CERN
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The ATLAS Experiment
http://www.atlas.ch/photos/full‐detector.html#52
Cost: 550M Swiss Francs
44m
25m
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The ATLAS Detector
37 m
Water Tow
er, N
ew Asia
College
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ATLAS detector
Fig. by CERN
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ATLAS Collaboration
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~ 3,000 scientists,
38 countries/regions,
174 institutions
06/14 +3: CUHK, HKU, HKUST
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LHC Run II
03/06/2015http://www.atlas.ch/LHC‐and‐ATLAS‐Restart/
CERN control room
ATLAS control room
Photos/animation by CERN
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56Fig. by CERN
13 TeV proton collisions
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Elementary particles基本粒子
57Figure from Wikimedia
Carrier of Electromagnetic force
Carriers of weak force
Carrier of strong force
Why are the masses so different?
Why are and gmassless while Wand Zmassive?
Gauge bosons
What’s the origin of these masses?
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Masses of elementary particles
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‐ Sizes of atoms (everything) determined by meR 1/meEg. If me halved, everything doubles in size
‐ binding energy of electrons in atoms me If me reduced, atoms can be ionized much easier, becomes relatively unstable
‐ Range of force 1/mass of gauge bosonEg.: EM force carried by photons (m = 0) range = Weak force by W, Z; mW, mZ >> mp range
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Mass
E = mc2 mass includes kinetic energy (KE) and interaction energy
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m m
M1 = 2m
v=0
Even if m = 0, M2 , M4 > 0 Eg. Proton mass mp ~ 1 GeV/c2:Masses of u, d quarks mq (a few MeV/c2)
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Lattice potential ~ Higgs field
Higgs Field 希格斯場
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vacuum真空 = filled with Higgs field = medium介質
Spontaneous Symmetry Breaking自發對稱性破缺
Elementary particles acquire masses
e‐
+++
+
effective mass for e‐
Excited states of Higgs field = Higgs particles
Vacuum = lowest energy state, could be full of particles/energy
Eg.: the effective mass of electron in a crystal
Particle mass: interaction energy mass (E = mc2)
Higgs mechanism: interaction with medium → mass
Different interactions with the medium → different masses
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Higgs = 5th force!
weak force
matter
EM strong
Higgs Field
Animation from CERN
Higgs opens a new window to study elementary particle physics!
Precision measurement of Higgs properties constrain/discover physics beyond Standard ModelHong Kong team: significant contributions to measuring Higgs couplings, mass, spin and parity.
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Other searches in LHC
• Super Symmetry (boson‐fermion) 超對稱 (Samuel + Wolf + others)• Other Higgs particles, non‐standard Higgs coupling (Haonan + Sze
Ning + Flora + Tak + others)• Other gauge bosons (Terry + Ka Wa + others) • Quantum black holes (Zihui + Terry + Ka Wa + others)• Dark matter particles 暗物質• ….
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Any discovery will revolutionize our understanding of elementary particles and the universe!
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Simulated decay of a mini black hole in LHC
Mini black holes?
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Extra dimensions (多餘維度)
Why is gravity so weak? gravity/EM ~10‐38unnatural!
Brane Model (膜世界理論): only gravity can propagate to extra spatial dimensions
If gravity = EM, LHC may produce 1 mini black hole per second with R ~10‐19m!
Dimopoulos + Landsberg (2001):
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If r < a, G →Go: gravity becomes strong!
No. of spatial dimensions n → F 1/rn-1 spread uniformly over the surface of a sphere with radius r
-m1m2Go/rn-1-m1m2(Go/an-3)/r2 (r > a)
(r < a)F = small effective G
G
If true, very important for quantum gravity!
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HK ATLAS team
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‐ 2‐4 undergrads + several grad students/yr‐ 2015: 20 members/alumni at CERN
‐ Supported by a RGC CRF (HK$8.661M, ’14 ‐’17)
ATLAS detector
06/14
05/14
Part of HK team, 2015
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Studying the fundamental structure of matter
• I. Neutrino astrophysics• II. Gravitational wave astrophysics• III. Electron microscopy• IV. Crystallography• V. High energy particle collisions at LHC
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Studying the fundamental structure of matter
Ming‐chung Chu 朱明中Hoi Tik Alvin Leung 梁凱迪
Department of Physics, The Chinese University of Hong Kong
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Hong Kong Science Museum Jan 16, 2016