2 march 2011modern physics iii lecture 812 march 2011modern physics iii lecture 81modern physics iii...

2 March 2011 Modern Physics III Lecture 8 12 March 2011 Modern Physics III Lecture 8 1Modern Physics III Lecture 6 1

Modern Physics for Frommies IIIA Universe of Leptons, Quarks and

Bosons; the Standard Model of Elementary Particles

Lecture 8

Fromm Institute for Lifelong Learning, University of San Francisco

2 March 2011 Modern Physics III Lecture 8 22 March 2011 Modern Physics III Lecture 8 2

Agenda• Administrative Matters• CP Violation• Neutrino Oscillations• Beyond the Standard Model


Administrative Matters

•Full schedule of colloquia is posted on the Wiki and should be posted in Fromm Hall. Next colloquium is 9 March•A list of popular books pertaining to Elementary Particle Physics is posted on the Wiki. It was updated recently•A sort of Glossary or at least a listing of particle types with examples has been posted on the Wiki. Revised version (R1) now posted.•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• Repeat starting with Relativity again• Some combination of the above


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.


C. S. Wu 1912 - 1997


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


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


------ time


More Violations

CP 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.

2 March 2011 Modern Physics III Lecture 8 10

1964: V. Fitch, J. Cronin et al. provided evidence that CP symmetry could be broken also.

Val Fitch James Cronin

Nobel Prize in Physics 1980


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


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


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


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.


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.


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)


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.


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.


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


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


Original retains its flavor

Original changes its flavor


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


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.


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 RH. 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.


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


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 .


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


Time

Modern Physics III Lecture 8


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


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.

2 march 2011modern physics iii lecture 812 march 2011modern physics iii lecture 81modern physics iii...

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nuclear physics

molecular physics

elementary particle

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time slide

standard model slide

parity violation

nevis cyclotron slide