Inflation, String Theory, Andrei Linde Andrei Linde and Origins of Symmetry.
What is the Matter with Them? Andrei Gritsan Johns Hopkins ...
Transcript of What is the Matter with Them? Andrei Gritsan Johns Hopkins ...
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Matter and Anti-MatterWhat is the Matter with Them?
Andrei Gritsan
Johns Hopkins University
August 2006
QuarkNet Seminar
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OUTLINE
• What is matter: molecules, atoms, nucleus, etc
• What is anti-matter: positron vs. electron
• Prediction and observation of anti-matter
• Anti-matter in our every-day life
• Creation of anti-matter in a laboratory
• Why does matter dominate in our Universe
• Time-reversal symmetry violation as a condition
• Summary
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Part I: Matter and anti-matter around us
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What We Know about Matter: Molecules
• Everything around us is made from molecules
(including us)
• Example of water molecule: H2O (e.g Cavendish, 1781)
– molecules (solids) made of atoms
– “chemistry” can break molecules
• Atoms cannot be broken through “chemistry”
• Periodic table of atomic elements (Mendeleev, 1868)
– about 100 elements
– need Quantum Mechanics (1920) to understand the structure
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What We Know about Matter: Atoms
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What We Know about Matter: Nucleus
Atom: nucleus and electrons
Nucleus: protons and neutrons
Protons and neutrons: quarks
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What We Know about Matter: Quarks/Electrons
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Matter and Anti-Matter
• For each Quark or Lepton (like electron): Anti-particle
matter anti-matterquarks leptons anti-quarks anti-leptons
d
s
b
u
c
t
e
µ
τ
νe
νµ
ντ
d
s
b
u
c
t
e
µ
τ
νe
νµ
ντ
-e/3 2e/3 -e 0 charge e/3 -2e/3 e 0
�e� e� • “Forces” are the same for matter and anti-matter:
Electromagnetic (γ)
Gravity (graviton ?)
Weak (Z0, W±)
Strong (gluons)
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The Simplest Anti-Matter: Positron
• Electron e− - simplest matter (all around us)
– Positron (or Anti-Electron) - simplest anti-matter
– anti-matter has opposite charge: e+
• What happens if matter and anti-matter meet:
– they annihilate into energy (e.g. photon, ∆E∆t ∼ h)
• We do not encounter anti-matter around us (fortunately!)
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Matter-Anti-Matter Annihilation
• Famous Einstein’s mass-energy:
E = mc2
• Matter-Anti-Matter is the most efficient “bomb”
• More efficient than atomic/H bomb
– nucleus binding energy
fraction of proton/neutron mass
• Matter-Anti-Matter “bomb” is not practical
– nearly impossible to store anti-matter
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Prediction of Anti-Matter: Positron
• Dirac equation (1928)
H = α0mc2 +
∑
αipic
Quantum Mechanical operator H for e− wave-function ψ(x)
Hψ(x) = Eψ(x)
• Solution (compare Einstein’s mass-momentum-energy):
E = ±√
(mc2)2 +∑
(pic)2
Negative solution E = −√... is a “hole” or e+
• Dirac was not confident enough to call it e+
suggested it was a proton p+ (wrong)
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Observation of Anti-Matter: Positron
• Observation by C.D. Anderson in Cosmic Rays:
“The Positive Electron” Physical Review 43, 491 (1933)
cloud chamber
in magnetic field
(Nobel Prize in 1936)
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Anti-Matter in a Classroom
• Cloud chamber
• Two sources:
(1) Radioactive isotopes,
22890 Th→ ...→ 212
84 Po+6α3β
(2) Cosmic rays
example: 2211Na → 22
10Ne + νe + e+
deep: (bound) p→ n+ νe + e+
deeper: (bound) u→ d+ νe + e+
deepest: u→ d+W+;W+ → νe + e+
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Cosmic Rays: Source of Anti-Matter
• Observed muon µ± like electron/positron, just heavy
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Anti-Matter from Cosmic Rays
• Incoming cosmic particles are matter (e.g. protons)
• Large energy transformed into
new matter-anti-matter (e.g. mesons qq)
E = mc2
• Eventually anti-matter interacts or decays
annihilates
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Anti-Matter as Part of Energy from the Sun
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Anti-Matter in Accelerators
Smash at high energy
E = mc2
Stanford Linear Accelerator Center
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Observation of Anti-Matter: Anti-proton
• Collide proton (p) with a target (proton/neutrons p/n)
p+ p→ p+ p+ p+ p ...
Observation of Antiprotons
Phys. Rev. 100, 947 (1955)
(Nobel Prize 1959)
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Anti-Matter in Accelerators
• Modern accelerators: e+e− and pp
– most efficient utilization of energy E = mc2
– kind of matter-anti-matter “bomb”
e+ c, b, µ+, ...
e− c, b, µ−, ...
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Building up Anti-Matter
• Put together anti-proton and positron (p−e+)
– anti-Hydrogen atom (anti-atom)
• 1995 PS210 experiment (CERN, Europe)
– high-energy (“hot”) anti-H
• 2002 the ATHENA project (CERN, Europe)
– “cold” anti-H
– neutral anti-atoms impossible to store
annihilate with walls
• No attempts to create anti-molecules
or anti-nucleus
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Part II: Why we are made of matter
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Anti-Matter Universe?
• A science fiction story:
– parallel Universe made of anti-matter, possibly with anti-humans
– annihilate if try to meet, but can send radio-waves (γ)
– how do we tell we are matter and they are anti-matter ?
– impossible? Only Particle Physics gives an answer (tell you later)...
• Reality:
– no evidence for Anti-Matter Universe
– would see “explosions” e+e− → γγ, pp... on the boundaries
– visible universe is predominantly matter over anti-matter
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Why Matter Dominates Over Anti-Matter
• Start with symmetric Big Bang
– end up with matter asymmetry
• Why does MATTER dominate
(Sakharov, 1966):
– CP -asymmetry
– baryon non-conservation
– non-equilibrium
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Fundamental Symmetries
• Symmetries ⇒ conservation laws
Charge + Parity (mirror) transformation
Matter⇐⇒ Antimatter
�d0L uLW���d0R �uR
W+
• CP asymmetry⇐⇒ matter and antimatter difference
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Time Reversal
• Fundamental CPT Theorem
– all physics laws are invariant under CPT transformation:
Charge + Parity + T ime reversal
• T ime reversal symmetry (“backwards movie”)
– symmetric in most interactions (EM, gravity, strong)
– second law of thermodynamics (entropy increase)
is simply probability
not microscopic process dynamics
– BUT: T (and CP ) violated in weak interactions (with W±)
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What is Special about Weak Interactions
• Weak • EM (photon) • Strong (gluon)
�d dZ�d d
�d d
g
• Weak interactions are special:
(1) change of quark “flavor” (e.g. b→u)|d′〉 = Vud · |d〉+ Vus · |s〉+ Vub · |b〉
(2) couple “left-handed” fermions
helicity λ = spin·direction = −1
2
• Violate Charge and Parity symmetry
might violate CP (?)
�d0L uLW�
��d0R �uRW+
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Example of CP Symmetry Violation
B0 (anti-matter) = bd B0 (matter) = bd
B0 → K+ + π− B0 → K− + π+
(bd)→ (su) + (ud) (bd)→ (su) + (ud)
10% more often
• Observed 10% difference in 2004 (BABAR and BELLE)
• First CP violation ∼ 0.2% in K0L
decays in 1964
• Cosmological question: how to tell matter vs anti-matter
– communicate results to another Universe
choice of “+” and “−” is arbitrary
– we are made of d and u quarks
which are more frequent in B → K±π∓ decays
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Example of CP Violation: How It Works
B0 → K+ + π−
(bd)→ (su) + (ud)
Feynman diagrams of decay
VtdVtb*
VcdVcb*
α=ϕ2β=ϕ1
γ=ϕ3
VudVub*
�W+�t gd�b
d�uu�s
Penguin
�W+d �b d�u
�suTree
Probability from complex numbers
“amplitudes” (A) are vectors
Probability ∝ |A|2 = |AP + AT |2
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Example of CP Violation: How It Works
B0 → K+ + π− B0 → K− + π+
(bd)→ (su) + (ud) (bd)→ (su) + (ud)
larger probability smaller probability
• Need overall “phase” difference (δ) between Penguin and Tree
• Angle (γ) changes sign under CP , “interference” of two amplitudes:
|A|2 = |AP + AT |2 > |A|2 = |AP + AT |2
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Observation of CP Violation
• Evidence for the 2π Decay
of the K02 Meson (1964)
(Nobel prize 1980)
K02 → π+ + π− (?)
(CP = −1)→ (CP = +1)
�u; ; t Wu; ; tWdK0(B0)�s(�b)s(b)�K0( �B0)�d
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Summary: Do We Understand Matter Dominance?
• CP symmetry violation can separate matter and anti-matter
– the known source in Standard Model is still not enough !
• Baryon non-conservation needed
– not allowed in Standard Model
• We still do not know all the answers
– expect answers Beyond the Standard Model
e− u
X
d u
example Baryon number violation
mass(X)> 1014×mass(p)
would allow proton decay
p→ π0 + e+ (not seen yet)
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Part III: Back-up slides
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Access to New Particles
• Brute force: new particles at highest energy (e.g. CMS, CDF)
(exceed current E = mc2 ∼ 100 GeV)
• Virtual production: ∆E∆t ∼ h (e.g. BABAR and CDF)
Standard Model new particles in loops
�b s�ss
gt
W − �b s�ssg
t
H− �b s�ss
gq
W
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Producing New Matter: Near Future
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Detecting Particles
• Example: B meson decay products on BABAR at SLAC
e.g. B0 → φK0 → (K+K−)(π+π−)
• Different detector subsystems
K−
K+
π+
π−
K− K+
π+ π−
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Detecting Particles at CMS
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CMS Experiment
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How It Looks: CDF Experiment
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BABAR Silicon Vertex Detector Assembly
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Modern Tracking Detectors
← CMS tracker
(>20,000 sensors)
↓ BABAR silicon
(340 sensors, R∼15cm)
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Example: CMS Forward Pixel Detector
• CMS Forward Pixel (optical survey at Fermilab):
– 3 or 4 sensors on a panel
– 2 panels back-to-back in a blade = 7 sensors
– 12 blades in a half-disk
– half-disks in a cylinder, cylinder in CMS
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Need Good Vertex Resolution
• Silicon “alignment” with particle tracks
crucial for precise particle detection: BABAR and CMS
• Other technical aspects of detector operation
µ+
µ- µ-
µ+
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What We Study
• Analysis of decay products:
at BABAR at CMS
K+
K Φθ1 K∗ φ θ2
Bπ
K−
e+
µ+ φθ1 Z Z θ2
Hµ−
e−
��
K�B W+�u; � ; �t gu; d�b
u; d�ss�s
�H ZZ
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More information (and some graphics in this talk) on particle physics:
http://particleadventure.org/particleadventure/
http://pdg.lbl.gov/
http://www2.slac.stanford.edu/vvc/
http://public.web.cern.ch/Public/Welcome.html
http://www.fnal.gov/
http://en.wikipedia.org/wiki/