"Nobel 95
By Brian Tuffy
Nobel 95
The Royal Swedish Academy of Sciences has decided to award the 1995 Nobel Prize in Physics for pioneering experimental contributions to lepton physics with one half to Martin L. Perl, Stanford University, Stanford, California, USA for the discovery of the tau lepton and with one half to Frederick Reines, University of California, Irvine, California, USA for the detection of the neutrino.
Nobel 95
"for pioneering experimental contributions to lepton physics"
Nobel 95
"for pioneering experimental contributions to lepton physics“ 2. "for the discovery of the tau lepton" 3. "for the detection of the neutrino"
Questions scientists ask
What is the universe made of ?
Is there a single fundamental particle ?
How many fundamental forces are there ? Can we always divide a particle ?
What's a neutron made of ? What happened at the Big Bang ?
How many particles make an atom ?
Why is there so many particles ?
What's the smallest particle ever seen ?
Why do they react so quickly ?
Is it matter is it energy ?
Questions scientists ask
The Greeks, John Dalton, J.J. Thomson, Rutherford, Planck, Bohr, De Broglie…… … and many others have advanced our understanding of the atom and its sub atomic particles.
Today:
The Standard Model
The Standard Model
The
Theory of fundamental particles and how they interact.
6
Quarks 6 Leptons Force carrier particles
The Standard Model
The Theory of fundamenta l particles and how they interact.
The Standard Model
The Discovery of the Neutrino and the Tau.
Physics laureates 95
Martin L. Perl, for the discovery of the tau particle.
Frederick Reines, for the detection of the neutrino.
Frederick Reines → Neutrinos
• Frederick Reines Born 1918 Paterson, New Jersey Died Aug 26th 1998 • Professor Department of Physics University of California at Irvine
Frederick Reines → Neutrinos
In the 1950’s Frederick Reines together with Clyde L. Cowan, Jr., demonstrated experimentally the existence of the antineutrino of the electron.
The Hanford team in 1953. They called their experiment "Project Poltergeist." Cowan is far left and Reines is far right.
Frederick Reines → Neutrinos
• The neutrino was born as a hypothetical particle by wolfgang Pauli in 1950 to explain the missing energy in beta decay. • A particle which lacked electrical charge and reacted very little with its environment.
n →p +e +v e
0
+
−
• Pauli thought he had proposed a particle that could
“never be discovered” !
Frederick Reines → Neutrinos
• In 1953 Reines and Cowan proposed a nuclear reactor experiment to capture neutrinos. The reactor would produce a great intensity of anti-neutrinos. (Anti-neutrino) + (proton) → (neutron) + (positron)
ve + p →n + e
0
+
+
Frederick Reines → Neutrinos
• The target consisted of 400 litres of water containing cadmium chloride placed between large liquid scintillation detectors. • The detectors would record photons of light produced from the reactions in the chamber.
Reines inspecting the neutrino detection equipment at the East Rand Mine in South Africa 1965
Frederick Reines → Neutrinos
What happens in the chamber:
2. A neutrino collides with a proton in the water and creates a positron and a neutron. 3. The positron is slowed down by the water and destroyed together with an electron (matter meets antimatter) 4. Two photons are created which are recorded simultaneously in the two detectors.
1
2
3
Frederick Reines → Neutrinos
What happens in the chamber:
2. The neutron also loses velocity in the water and is eventually captured by a cadmium nucleus, photons are emitted. 3. These photons reach the detectors a microsecond later than those from the destruction of the positron.
4 5
Frederick Reines → Neutrinos
Although only a few events were recorded per hour Reines and Cowan succeeded in a feat considered to border on the impossible. They had raised the neutrino from its status as a figure of the imagination to its existence as a free particle.
The “Project Poltergeist” neutrino detection team at the Hanford Reactor site, 1953.
Frederick Reines → Neutrinos
The consequences of Reines work:
• • • Proved the existence of a virtually unobservable particle. Resolved the need for a new fundamental particle for the consistency of theory. Opened the door to the practical side of neutrino physics and future particle physics
These led to discoveries such as
• • • • Detection of neutrinos produced in the atmosphere Study of muons induced by neutrino interactions underground The first observation of the scattering of electron antineutrinos with electrons The first detection of neutrinos from a supernova ….and many others.
Frederick Reines → Neutrinos
• Reines pioneering contribution paved the way for the "impossible" neutrino experiments. These attempt to capture neutrinos from cosmic radiation. The neutrinos may originate in the sun or in supernovas. Their reluctance to react with atomic nuclei or electrons means that very large detector volumes are needed
• •
Underground detector tank for cosmic neutrino capture being examined by a diver.
Martin L. Perl → Tau particle
•Martin L. Perl Born 1927, New York. •Professor at Stanford Linear Accelerator Center Stanford University
Martin L. Perl → Tau particle
Between 1974 and 1977, Martin Perl and his colleagues discovered, through a series of experiments, at the Stanford Linear Accelerator Center (SLAC), that the electron has a relative some 3,500 times heavier! It is called the tau.
The SLAC Lab
Martin L. Perl → Tau particle
First sign of a “third family" of fundamental Particles. All of Earth’s matter is made from the first family! Tau has same charge as electron but 3,500 times heavier.
Martin L. Perl → Tau particle
Perl used the SPEAR collider (5GeV) to find new particles and after a few years they confirmed the discovery of a new lepton which they named after the Greek letter (τ). It stands for the first letter of the word triton meaning third.
Martin L. Perl → Tau particle
Collisions between electrons and positrons in the large cylindrical detector placed in a magnetic field revealed 24 events of the reaction:
or
electron + positron → electron + antimuon + neutrinos electron + positron → positron + muon + neutrinos
Applying the Conservation of Energy Law Perl concluded the production of at least 2 invisible particles
Martin L. Perl → Tau particle
The Explanation is the production of the tau lepton: …..Tau → electron (or muon) + neutrinos
electron + positron → Tau + anti-Tau ….. …..anti-Tau → antimuon (or positron) +
neutrinos
Which gives the Resultant:
or electron + positron → electron + antimuon + neutrinos electron + positron → positron + muon + neutrinos
Martin L. Perl → Tau particle
The Tau is discovered:
The muons, electrons, and positrons observed are the products of the Tau decay. After many years the Tau had passed the test and met all the possible requirements of a heavier relative of the electron. The tau also has its own neutrino - the tau neutrino. Perl said "The use of the discovery of basic particles is indirect. We have found that everything of a complicated nature is made from three basic families of particles. Eventually, this will lead to an improved understanding of energy and time. From that we hope will come new ideas that lead to applications like a source of cheap energy
Physics laureates 95
• Thanks to the contributions of
• They have proven the reliability and stability of today's Standard Model • Yet this model is incomplete it cannot explain why some particles exist as they do and doesn’t give us a pattern for particle masses. • We will need to extend the Standard Model with something totally new in order to thoroughly explain mass, gravity and other phenomena.
both Reines and Perl many discoveries and breakthroughs have been accomplished in lepton physics. • They set the groundwork for particle physics experiments for the future.
I wonder what I’ll decide to call the new theory that replaces the Standard Model! The Super-Standard Model? The New Revised Standard Model? The Very Standard Model?
..."
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