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Alyssa Loos
• The Babar experiment
• Particles of matter
• CP Violation and Time asymmetry
• The positron-electron collision
• Babar Results
A. Loos, Seminar 730, 9-13-13 2
Source: Tim Gershon
A. Loos, Seminar 730, 9-13-13 3
Source: SLAC
• Located at SLAC in Menlo Park, California
• Took data between 1999 and 2008
• Billions of positron/electron collisions took place
• Designed to sort out properties of matter and anti-matter
A. Loos, Seminar 730, 9-13-13 4
Source: SLAC
Source: SLAC
• Quarks= elementary
particles
• Interact with the strong nuclear
force
• Leptons
• Do not interact with the strong
nuclear force
• Electrons and electron neutrinos
A. Loos, Seminar 730, 9-13-13 5
Source: Particle Central
• Baryons
• stable
• Made up of 3 quarks
• Neutrons and Protons
• Mesons
• short-lived
• Made up of 1 quark and one
antiquark
A. Loos, Seminar 730, 9-13-13 6 Source: Particle Central
• 15 billion years ago
• Anti-matter and matter existed in equal amounts
• Annihilated energy known as background cosmic radiation
• 1milifraction of a second
• Matter slightly outnumbered antimatter
• 1 second later…antimatter
disappears
A. Loos, Seminar 730, 9-13-13 7
Source: Melbourne University
• Matter vs. Anti-Matter
• Same masses, different
charges
• CP Violation
• CPT=Time asymmetry
A. Loos, Seminar 730, 9-13-13 8
Source: USAF
A. Loos, Seminar 730, 9-13-13 9
• Time asymmetry describes when the transition from one state to
another takes a different amount of time than the reversed
process Source Physics Today
Source: Tim Gershon
• Y(4S) meson is made
up of a quark and
anti-quark
• B0 and B0 Bar
Pair
• Eigenstates
A. Loos, Seminar 730, 9-13-13 10
Source: Gershon,Tim
• 1 in 10 tredecillion (10^43) or 14-sigma level of certainty
• Difference in time measurement for B0 meson pairs is not zero
• “Time arrow” is different for macroscopic and microscopic
reality source: The Reference Frame
A. Loos, Seminar 730, 9-13-13 11
• Plays a critical role in the early universe
• Important verification of quantum field theory
A. Loos, Seminar 730, 9-13-13 12
Source: SLAC
• Babar made the first direct measurement
• B0 mesons exhibit T violation
• Direction of the “time arrow” in microscopic situations is
different than macroscopic source The Reference Frame
A. Loos, Seminar 730, 9-13-13 13
1. “Elementary www.particlecentral.com/particle_page.html
2. Gershon,Tim . “A Triangle that Matters” PhysicsWorld.com.
(2007)
3. Pilsen, Lubos. “Babar directly measures time violation” The
Referance Frame(2012)
4. “Babar makes first direct measuresurement of time reversal
violation” Physics Today (2012)
5. SLAC National Linear Accelerator Website
6. USAF
A. Loos, Seminar 730, 9-13-13 14