What’s the Matter With Antimatter? Dr. Natalie A. Roe Lawrence Berkeley National Laboratory
1900 - 1920’s: Development of relativity, quantum mechanics 1928: Paul Dirac’s relativisitic equation of motion for the electron Predicted the positron, antimatter partner of the electron Predicted that negative protons must also exist Speculated that half the stars may be made of antimatter 1933 Nobel Prize in Physics The Prediction of Antimatter
1936 Nobel Prize in Physics The Discovery of Antimatter • The positron was discovered in 1932 in cosmic rays by Carl Anderson
What is a Fundamental Particle? • Greeks: Earth, Air, Fire, Water • 1800’s: Periodic table of the elements • 1897: Thomson discovers the electron • 1911: Rutherford discovers the nucleus • 1919: Rutherford discovers the proton • 1932: Chadwick discovers the neutron • 1967: Kendall, Friedman and Taylor discover quarks in electron-nucleon scattering experiments at SLAC. • Quarks • are fractionally charged • occur in pairs or in triplets, never singly • are point-like objects (to the limit of our ability to measure)
Quirks of quarks … • Two types of quarks are needed to make our world, “up” and “down” • proton = (uud) and neutron = (udd) • protons and neutrons form nuclei • add electrons to form neutral atoms • neutrinos are emitted in nuclear processes that power the sun • 4 fundamental particles are building blocks of our world Charge +2/3 -1/3 0 -1 • 2 additional generations of particles have been discovered • Why 3 generations? • What determines their masses? • What determines their decays? Increasing Mass --> • Do all particles have antimatter partners?
Discovery of the Anti-proton at Berkeley Lab in 1955 Surrounding Edward Lofgren (center), head of the Bevatron, are discoverers of the antiproton, (left to right) E.Segre, C.Wiegand, O. Chamberlain and T.Ypsilantis. E.O. Lawrence, inventor of the cyclotron and founder of Berkeley Lab 1939 Nobel Prize in Physics 1959 Nobel Prize in Physics
The Mirror Universe • All fundamental particles have anti-matter partners • The neutrino ( n ) may be its own anti-particle • Quark and anti-quarks form bound states called mesons • p+ = ud K0= ds • B0= bd B0= bd The “Standard Model” particles
Energy can also materialize as particle-antiparticle pairs • This is what happened in the “Big Bang” e- g g e+ Feynman diagram e- g e+ Matter and Energy • Einstein first realized the equivalence of matter and energy • When matter and antimatter meet, they annihilate into energy
Gamma Ray emission from Solar flare on July 23, 2003 Blue = 0.3 - 0.5 MeV Purple = 0.7 - 1.4 MeV Red = 2.2 MeV Antimatter Production in the Sun • Every second, thermonuclear reactions in the sun convert 600 million tons of hydrogen into 595 million tons of helium, and 5 million tons of mass is converted to energy • p + p => pn (deuterium) + e+ + n • pn + p => 3He + g • 3He + 3He => 4He + p + p • Solar flares accelerate particles, producing electron-positron pairs. • ~ 0.5 kg antimatter produced in large flare! • Image of flare by RHESSI satellite (PI Bob Lin of UC Berkeley/SSL)
Where is all the Antimatter? • No antimatter within our galactic cluster • Can Universe be a quilt of matter & antimatter domains? • Gamma ray spectrum in space rules out antimatter domains smaller than ~1000 Mpc • No evidence yet for antimatter in primordial cosmic rays • The AMS experiment will search for primordial antimatter from its orbit on the International Space Station
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Energy budget of Universe Dark Energy: ~70% Dark Matter: ~25% Antimatter: 0% ~25% ~70%
e- e+ + - e- e- g g e+ e+ Symmetries of Matter: C, P and T C = Charge conjugation: particle antiparticle P = Parity (mirror reflection): x -x C and P together change matter to antimatter; T = Time reversal: t -t The product CPT: always invariant!!! CP Mirror
1957 Discovery of Parity Violation ne Co60 n -> p e-n B field e- Beta Decay of Co60 C.S. WU The Universe knows its right hand from its left!
Another way to look at CP Violation Left-handed particle => Right-handed anti-particle Bob Cahn
An Unexpected Discovery In 1964 1980 NOBEL PRIZE V. Fitch J.Cronin Cronin and Fitch discovered CP violation in the decay of the long-lived, CP-odd neutral K meson into a CP-even final state: Br(KL -> p+p- ) ~ 0.2% There is a difference between matter and antimatter! “We are hopeful… that at some epoch, perhaps distant, this cryptic message from nature will be deciphered.” J. Cronin
Alpha Test Trap and Superconducting Magnet Prototype built at LBNL Prototype for a next generation experiment to trap anti-hydrogen and characterize with laser spectorscopy. J. Fajans, J. Wurtele et al Discovery of CPT violation would be revolutionary! CP Violation => T Violationunless CPT is also violated! Antiproton Decelerator at CERN Anti-hydrogen annihilation near walls of trap ATHENA experiment
(nB - nB )/ ng= 6.1 x 10-10 Sakharov’s Recipe for BAU (1967)(Baryon Asymmetry of the Universe) Necessary ingredients are: • Baryon number violation • Thermal non-equilibrium • C and CP violation • Do we understand the cause of CP violation in particle interactions? • Can we calculate the BAU from first principles? All of these ingredients were present in the early Universe! 1975 Nobel Peace Prize
u d cs t b An Astounding Connection • In 1973, M. Kobayashi and T. Maskawa predicted: CP violation third generation of quarks! • Subsequent discoveries confirmed the prediction: • b quark was discovered in 1977 at Fermilab by Lederman et al • t quark was discovered in 1994 at Fermilab by CDF and D0 • The three-generation Standard Model naturally includes CP violation in certain particle decays. e e quark doublets lepton doublets Standard Model Particles
An Asymmetric B Factory to Study CP Violation • CP violation in K0 (= sd) meson decays was exhaustively studied for over three decades • the effects are very small, and hard to interpret theoretically • In B0 (= bd) meson decays, the Kobayishi- Maskawa theory predicts large CP violation effects • besides being large, the effects are theoretically clean • But - the decay rates are small => need to produce millions of B mesons in a B “factory” • To observe the CP asymmetry between B and anti-B mesons, a special type of e+e- collider is required with unequal beam energies - the Asymmetric B Factory
PEP-II Stanford Linear Accelerator Center, Stanford, California Approved as a Presidential Initiative in 1993; completed in 1999. Reached full design luminosity in 2000. Japanese B Factory has also been built with similar design.
The BaBar Detector The BaBar Collaboration: ~600 physicists from 73 institutions and 9 countries
B0 B0 B0(t) B0(t) fCP fCP B0 B0 Measuring CP Violation with B0s Not equal – CP Violation! CP violation occurs in the interference between mixing and decay to a CP eigenstate, eg B0-> p+ p -
d B0 b B0B0 Mixing • Matter-antimatter oscillations occur in neutral K0 and B0 mesons • Mixing adds CP violating couplings, with time dependence • Observation of the time dependence requires the use of asymmetric energy beams • this boosts the B mesons so they travel a measurable distance before decaying • measuring the B decay vertices establishes when the B decayed t B0 W- W- d b t first - third generation coupling the mixing “box” diagram
e+ e-->U(4S) ->BB decay of B “tag” B ->CP eigenstate Dt µDz The Asymmetric B Factory Concept 3 GeV e+ 9 GeV e-
Golden Mode for CP Violation in B decay • B0J/Y Ks is the best decay mode to measure the CP violating angle b , the phase due to the mixing diagram • B0J/Y Ks also has a relatively large branching ratio (1 per million) and is “easy” to reconstruct b c J/Y c W+ s Ks d d
Recipe for Measuring CP Violation in B Meson Decays • Produce many B0 B0 pairs (hundreds of millions) • Reconstruct one B in a special decay called a CP eigenstate • “Tag” the other B0 to make the matter/antimatter distinction • Determine the time between the two B0 decays, Dt • Compare Dt distributions for B0 and B0 tagged events; the difference measures CP violation, the difference between matter and antimatter B tagged B tagged Dt (ps)
270 Million BB pairs produced since 1999 and recorded by the BaBar detector Year
How to “tag” a B or anti-B meson:The DIRC Detector Quartz bar Active Detector Surface Particle Cherenkov light n e+ K+ B0 B0-> D* e n D 0 p - p - • Angle of Cherenkov light is related to particle velocity • Transmitted by internal reflection • Detected by~10,000 PMTs
How to measure the decay times:The Silicon Vertex Tracker (SVT) Uses five layers of silicon microstrip detectors to measure B decay vertices to better than 0.1 mm and determine the time between the two B meson decays.
Latest results from BaBar on difference of matter and antimatter: Sin2220400.023
What does this result mean? sin2b=0.72±0.04 • Maximum asymmetry => sin2b = 1 • Zero asymmetry => sin2b = 0 • Much larger asymmetry than in K0 decays (72% vs 0.2%); combined experimental plus theoretical error is small • The result is consistent with the prediction of the three-generation Standard Model • But: our best calculations of early Universe do not produce enough excess matter - off by 10 orders of magnitude!
What is the Matter with Antimatter? • How can a parameter between 0 and 1 provide the missing 10 orders of magnitude? • It can’t • New particles can provide the required CP violation • The effects of new particles may be observable in B decays…
sin 2b in a different mode • sin2b measured in final states with charm agrees with the Standard Model predictions • sin2b can also be measured in other “penguin” decays and should agree within a few percent • New physics could enter in loops! , f b c J/Y c W+ s Ks d d tree diagram penguin diagram
World average for sin2b in “penguins” compared to J/Y Ks … hint of new physics, or a statistical fluctuation?
Future Prospects for BaBar… • The BaBar experiment has published ~ 150 papers so far in refereed journals on a wide variety of topics • Expect to collect ~4x more data over next 3-4 years => statistical errors will decrease by x2 • In a race with the Japanese B Factory • behind right now in total luminosity • advantage in the ability to confirm any unexpected results • The Large Hadron Collider at CERN will turn on in 2007, data taking by 2008 • could directly produce new particles
Summary • Antimatter exists and can be created at accelerators; but there is very little antimatter naturally occurring in our Universe • CP violation is required in any theory starting from the Big Bang to explain the dominance of matter over antimatter • CP symmetry between matter and antimatter is violated at the quark level, as measured by BaBar - but not enough ! • More detailed measurements may give clues to new physics beyond the Standard Model
Antimatter engines on Starship Enterprise were powered by p + p annihilation! Penn State Univ Penning Trap Penning Trap The Anti-Hydrogen Economy? • Distinguish between energy source and method to store and transport energy - • Creating, storing antiprotons requires a lot of energy, and trapping them is also very inefficient • All the antiprotons created in one year at Fermilab would only power a 100 watt bulb for 30 minutes, even with 100% trapping and conversion efficiency! • Cost: $62.5 trillion per gram!
What’s the Matter with Antimatter? • Our present view of matter - the “Standard Model” of particle physics • The amazing prediction and discovery of antimatter • Is antimatter useful, Dr. Spock? • Colliding matter and antimatter • What happened to all the antimatter ? - the search for CP Violation • Why does it matter?
Latest result: Sin2