18 february 2015modern physics iii lecture 71modern physics iii lecture 8modern physics iii lecture...
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18 February 2015 Modern Physics III Lecture 7 1Modern Physics III Lecture 8Modern Physics III Lecture 6
Modern Physics for Frommies IIIA Universe of Leptons, Quarks and
Bosons; the Standard Model of Elementary Particles
Lecture 7
Fromm Institute for Lifelong Learning, University of San Francisco
18 February 2015 Modern Physics III Lecture 7 2
Agenda• Administrative Matters• CP Violation• Neutrino Oscillations• Finding the Higgs at the LHC
18 February 2015 Modern Physics III Lecture 7 3
Administrative Matters
•Full schedule of colloquia is posted on the next slide and should be posted in Fromm Hall.
– Colloquium #3 is today, 3:30 – 5:00 PM, LSCSI 210. Dr. Calvin Berggren, Texas Lutheran University, Particle Physics Simulations.
– Colloquium #4 is Wed. 25 March, Dr. Stephen Bailey, Lawrence Berkeley Lab
How to Make a 3-D Map of the Universe (and Why)
•Please give some thought as to what you would like me to teach next time. Give me feed back via e-mail ([email protected]).
• A mixture of Modern Physics stuff: Atomic and molecular physics, nuclear physics, solid state physics, etc.
• Cosmology• Gravity, the fourth and most mysterious force• Start over with relativity
18 February 2015 Modern Physics III Lecture 7 4
USF Physics and Astronomy Colloquium Series Spring 2015Date (Wed 3:30 - 5 PM) Speaker Topic/Title Location Affiliation Personal/Research Website
28-Jan Xiaosheng Huang Course policy and schedule LCSI 2104-Feb James Jee Weak Gravitational Lensing LCSI 210 UC Davis http://www.physics.ucdavis.edu/~mkjee/
11-Feb Alexander Grutter Neutron Reflectometry LCSI 210 NIST http://www.ncnr.nist.gov/programs/reflect/18-Feb Calvin Berggren Particle Physics Theory LCSI 210 Texas Lutheran U.25-Feb Stephen Bailey Baryon Acoustic Oscillations LCSI 210 LBNL https://www.sdss3.org/surveys/boss.php
4-Mar Jennie Guzmann Atomic Physics LCSI 210 Cal State East Bay http://crf.sandia.gov/combustion-research-facility/about-us/crf-staff-2/wdts/dr-jennie-guzman/11-Mar John McGuire Condensed Matter/Nonlinear Optics LCSI 210 Michigan State http://www.pa.msu.edu/~mcguire/18-Mar spring break25-Mar No Talk Scheduled1-Apr No Talk Scheduled8-Apr Daniel Fisher Bio/Condensed Matter Physics LCSI 210 Stanford http://web.stanford.edu/dept/app-physics/cgi-bin/person/fisher-daniel-s/
15-Apr Student Seminars22-Apr Student Seminars29-Apr Aaron Parsons Astrophysics LCSI 210 Berkeley http://astro.berkeley.edu/people/faculty/parsons.html6-May Student Seminars
18 February 2015 Modern Physics III Lecture 7 5
A set of particles is invariant under a parity invariant interaction process must not change if the handedness of every particle is changed
OR
Characteristics of a process change when all spins are flipped parity is not conserved.
C. S. (“Madame”) Wu at Columbia and E. Ambler at NBS60 6027 28Co Ni ee Nucleons align so net nuclear spin = 5 ħ
Using a strong magnetic field and extremely low temperature it was possible to polarize the 60Co sample, i.e. most of the nuclear magnetic moments aligned with the field.
Violation of Conservation of Parity Redux
18 February 2015 Modern Physics III Lecture 7 6
Beta Decay
1P P
P P
W WN N eP D e
1
P P
P P
W WN N eP D e
Early work on radioactivity observed 3 forms of decay designated andraysThese were later identified as:
= Helium nucleus (2p + 2n) = e = high energy photon from nuclear transition
60 6027 28Co Ni ee
Why the neutrinos?
n p p n
18 February 2015 Modern Physics III Lecture 7 7
To avoid violating conservation of energy, W. Pauli postulated the existence of the “little neutral one”.
F. Reines and C. Cowan actually detect the (anti) neutrino in 1956
e p n e
e p n e
18 February 2015 Modern Physics III Lecture 7 8
C. S. Wu 1912 - 1997
Characteristics of a process change when all spins are flipped parity is not conserved.
18 February 2015 Modern Physics III Lecture 7 9
T. D. Lee and C. N. Yang Nobel Prize 1957
The Wu experiment showed WI have a strong penchant for LH particles How strong is this preference?
1957: R. Garwin et al. looked at decay at the Nevis cyclotron
18 February 2015 Modern Physics III Lecture 7 1010
stopped in carbon absorber.
Measure angle of e- emission w.r.t flight direction
2 for RH only# forward
1 for no preference# backward
1 2 for LH only
Measured ratio: 1/2 10 %
WI has only LH currents. Note, antiparticles are RH
Note that the universe is matter rather than antimatter.
Parity violation is maximal for WI
is now known as 0
via WIK us
18 February 2015 Modern Physics III Lecture 7 11
------ time
18 February 2015 Modern Physics III Lecture 7 12
More ViolationsCP Violation:
Product of 2 symmetries, C for charge conjugation, transforms a particle into its antiparticle, and P for parity, which creates a mirror image of a physical system.
C symmetry requires, among other things, that a particle and its antiparticle have identical masses.
C, like P, is conserved by strong and EM interactions. Again, like P there is violation by WI.
Following C. S. Wu’s discovery that WI violate P symmetry it was proposed that the combined symmetry, CP, might restore order.
C acting on LH LH but WI acts only on RH antiparticles
18 February 2015 Modern Physics III Lecture 7 13
1964: V. Fitch, J. Cronin et al. provided evidence that CP symmetry could also be broken.
Val Fitch James Cronin
Nobel Prize in Physics 1980
18 February 2015 Modern Physics III Lecture 7 14
The kaons:
Contain strange quarks and antiquarks.
1947: Cosmic rays in cloud chambers Neutral → 2 charged pions charged → charged pion + neutral
Decays slow 10-10 sec
Production fast 10-23 sec
Abraham Pais postulated new quantum number, “strangeness”, conserved by SI but violated by WI.
pp ppK K K
Associated production
0 0
K su K su
K sd K sd
We’ve seen the charged kaons rôle in the puzzle, now the neutrals
18 February 2015 Modern Physics III Lecture 7 15
Unlike the , the neutral kaon cannot be its own antiparticle (s = 2)
Assume for now that CP is conserved.
Kneutral → are the most prominent decay channels. These final states have CP = +1
0 0 0 0 0 0Under CP , i.e. and CPK K K K K K
Linear combinations can be formed which are CP eigenstates with eigenvalues of ±1
0 01
1 CP = +1
2K K K
0 02
1 CP = -1
2K K K
The 2decay modesare allowed for K1 but not for K2 This results in K2 having a lifetime 100 times longer than K1
Rename the CP states: K1 = Ks and K2 = KL
18 February 2015 Modern Physics III Lecture 7 16
So a test of CP conservation is to look for the CP violating decay
LK
K0 beam, production target is many Ks decay lengths upstream
Magnetic spectrometers
32.0 0.4 10 all charged modes
L
L
K
K
=> Maybe our identification of KS and KL with the CP eigenstates should be modified.
2 32 1 where 2 10LK K K
18 February 2015 Modern Physics III Lecture 7 17
Consequences of CP Violation: CPT theorem, CP violation T violation
• CP violation is incorporated in the standard model by including a complex phase in the CKM (quark mixing) matrix.
• Necessary condition is at least 3 generations of quarks
• Decay width of Z0 3 is enough
• Strong CP problem
• Experiments have found no CP violation in QCD yet terms in QCD should lead to large breaking of CP
• Best known solution is the Pecci – Quinn mechanism, involving new scalar particles called axions.
• Matter – antimatter imbalance in the universe
• WI CP violation as measured by experiment can account for only a small portion of the observed imbalance.
18 February 2015 Modern Physics III Lecture 7 18
CPT Theorem:
The CPT theorem is a very general theoretical result linking Lorentz and CPT symmetry.
Roughly, it states that certain theories (local quantum field theories) with Lorentz symmetry must also have CPT symmetry.
These theories include all the ones used to describe known particle physics (e.g. electrodynamics or the Standard Model)
They also include many proposed theories (e.g. Grand Unified Theories).
18 February 2015 Modern Physics III Lecture 7 19
Friends don’t let friends break Lorentz symmetry
18 February 2015 Modern Physics III Lecture 7 20
Neutrino OscillationsWhere are the solar neutrinos?
1 1 21 1 1 0.42 MeV
2 1.02 MeV
eH H H e
e e
2 1 31 1 2
3 3 4 12 2 2 1
5.49 MeV
2 12.86 MeV
H H He
He He He H
Late 1960’s Raymond Davis Jr. (BNL) looked for them.
100,000 gal. of dry cleaning fluid (C2Cl4) 4850 ft. underground in the Homestake gold mine in Lead, SD. 25% of the Cl are 37Cl.
37 3717 18e Cl Ar e e n p e
Collect 37Ar by bubbling He thru fluid and look for radioactive decay of 37Ar with counters.
18 February 2015 Modern Physics III Lecture 7 21
Solar models predict the number of neutrinos one should detect
Davis detected less than half the predicted number!
Possibilities: Experiment wrong.But, many subsequent experiments, using both radiochemical and water Čerenkov techniques confirmed the deficit
Models wrongBut, nobody could come up with one agreeing with Davis’ results.
Experiment and models right but something else is going on.
Sun has gone out but we don’t know it.
Or, neutrino oscillations (finally verified 2001)
18 February 2015 Modern Physics III Lecture 7 22
Neutrino oscillations are a phenomenon, predicted by Bruno Pontecorvo, where a neutrino created with a specific lepton flavor , e.g. e , can later be measured to have a different flavor, e.g. or .
Classical analogue: Coupled pendulums
Let k be small, weak coupling
Set 2 in motion while 1 begins at rest.
Over time 1 begins to swing under influence of the spring, while 2’s amplitude decreases as energy is transferred to 1.
Eventually, all of the energy is transferred to 1 and 2 is at rest. The process then reverses.
The energy oscillates between 1 and 2 repeatedly until it is lost to friction.
18 February 2015 Modern Physics III Lecture 7 23
This behavior can be understood by looking at the normal modes of oscillation.
Lower frequency, doesn’t involve spring
Higher frequency, involves spring
Any motion of the system is a combination of both normal modes. Due to the intermodal frequency difference, the modes drift in and out of phase as time passes, leading to back and forth transfer of energy between the pendulums.
18 February 2015 Modern Physics III Lecture 7 24
Things are somewhat more complicated if the pendulums are not identical, but we can in general write
1 in
2 out
Transformation
or Mixing
2 2 Matrix
t t
t t
Analogous to PMNS1 matrix describing -mixing
Analogous to mass basis of s
Analogous to flavor basis of s
_____________________________________________________________________________
1. PMNS = Pontecorvo-Maki-Nakagawa-Sakata
For 2 oscillators (particles) the transformation is that of a simple rotation through a mixing angle m
1 in
2 out
cos sin
sin cosm m
m m
t t
t t
18 February 2015 Modern Physics III Lecture 7 25
If we increase the number of oscillators (particles) to 3 as we must for neutrinos, a single angle no longer suffices; 3 (Euler) angles are required.
.
1 2 3 1
1 2 3 2
1 2 3 3
e e e eU U U
U U U
U U U
or flavor flavor mass massmass
U
For solar neutrinos we can get away with a 2 approximation, e ↔ X
where X is some superposition of and Then the mixing matrix is just cos sin
sin cosm m
m m
The probability of a neutrino changing its flavor is
2
2 2, sin 2 sin 1.267m
m LP
E
18 February 2015 Modern Physics III Lecture 7 26
Original retains its flavor
Original changes its flavor
18 February 2015 Modern Physics III Lecture 7 27
If there is a mass difference between neutrinos ( at least one m ≠ 0) then we can explain the low number of solar neutrinos.The solar models are correct and predict the correct number of e
During their flight from the Sun to the Earth, some of the e convert to other flavors.
Davis and others measure a correct, but reduced from expected, number of e.
Raymond J. Davis Jr. 1914 – 2006 Nobel Prize in Physics 2002
18 February 2015 Modern Physics III Lecture 7 28
Bruno Pontecorvo 1913 -1993
Origins of neutrino mass:
Standard model Higgs mechanism. Requires both left and right handed particles. Interactions with Higgs bosons flip handedness. No RH observed so far. Massless neutrinos go hand in hand with the absence of RH neutrinos.
Two problems:Exclusive handedness vs, mass
Why are mso small? me > 500,000 m from indirect measurements.
18 February 2015 Modern Physics III Lecture 7 29
Need to extend Standard Model to make neutrinos massive.
If is a Dirac particle (like e only chargeless) let the interactions of RH be 10-26 as strong as LH. This allows Higgs generation of m but does not resolve the smallness issue.
There is an argument invoking extra dimensions, borrowed from string theory, which can explain the non-observation of RH and why their interactions with the Higgs are so weak.
If is a Majorana particle, i.e it is its own antiparticle, we no longer have to invoke RH s with ultra-weak interactions, but we give up some of the fundamental distinction between matter and antimatter. This can work because the has no electric charge (no violation of charge conservation)
Lorentz invariance requires that a Majorana neutrino have mass.
18 February 2015 Modern Physics III Lecture 7 30
Ettore Majorana 1906 - 1938
Neutrinoless double – decay:
1
192
Normal β - decay: 12 yr. for Tritium
Double β - decay: 2 2 10 yr.
A AZ Z
A AZ Z
X Y e
X Y e
1Neutrinoless double β - decay: 2A AZ ZX Y e
18 February 2015 Modern Physics III Lecture 7 31
Claimed observation in 2001 by a Heidelberg – Moscow collaboration. H.V. Klapdor-Kleingrothaus, Mod. Phys. Lett. A 16 (2001) 2409
76 25
2
10 yr.
0.11 0.56 eV
Ge
m c
This claim has been criticized by a lot of people.
Seesaw mechanism: How Majorana neutrinos can help.
Absence of RH s 0.
If then 0 to allow helicity flip
m
m
RH s can have a mass of their own outside the Higgs
mechanism, They are not tied to the Higgs mass scale .
18 February 2015 Modern Physics III Lecture 7 32
RHLH RH is very very largeH m
So large that energy is not conservedDo the “Heisenberg embezzlement”
2
RH
tm c
LHRH LH LH has now picked up a mass H m
2
Averaging over time: = LH
RH
mm
m
very large as predicted by GUTs and particularly by
SUSY GUTs. RH
m
18 February 2015 Modern Physics III Lecture 7 33
Time
Modern Physics III Lecture 7
18 February 2015 Modern Physics III Lecture 7 34
The Future
It’s dangerous to make predictions, especially about the future. -Yogi Berra
(1) (2) (3)
EM WI(2) SIcolorU SU SU
Electroweak
GUTs ??
What about gravity ??
0
331 2Super Kamiokande lower limit 3 10 yrs.
p e
String theoryLoop quantum gravityIs gravity a force at all??
Too many free parameters
18 February 2015 Modern Physics III Lecture 7 35
Supersymmetry (SUSY): Every fermion has a supersymettric partner boson and vice-versa.
LHC and other facilities:HiggsLightest SUSY particlesBetter understanding of CP, sNucleon decayAxionsGravitational wavesWeird stuff that may or may not show up.