Transcript Gabrielsex
Gabrielse High Precision, Low Energy Tests of the Standard Model and Its Symmetries Gerald Gabrielse, Leverett Professor of Physics, Harvard University Spokesperson of the CERN ATRAP Collaboration Testing the Most Precise Prediction of the Standard Model Electron magnetic moment Testing Standard Model Extensions (e.g. Supersymmetry) Electron electric dipole moment Testing the Symmetries of the Standard Model Q/M for the antiproton and proton Antiproton and proton magnetic moments Positron and electron magnetic moments (underway) Antihydrogen and hydrogen structure (still in the future) Comparing Antimatter and Mater Gravity Gravitational Redshift of the Antiproton and Proton Supported by US NSF and AFOSR. Antiprotons from CERN Gabrielse Low Energy Particle Physics AMO Physics, Particle Physics, Plasma Physics methods and funding can’t avoid goals and facility 2Mp c2 LEAR and AD 1010 TRAP 4.2 K 0.3 meV 70 mK, lowest storage energy for any charged particles Gabrielse Gabrielse Electron Magnetic Dipole Moment • Most precisely measured property of an elementary particle • Most precise prediction of the standard model • Most precise confrontation of theory and experiment • Greatest triumph of the standard model Gabrielse The Amazing Electron Electron orbits give atoms their size, but the electron itself may actually have “no size” R 2 10 20 m m* 10.3 TeV / c 2 mass of “ingredients” is 20 million times more than the mass 0.5 MeV/c2 Electron has angular momentum (spin) even though it has no size and nothing is rotating: S m R 2 Magnetic dipole moment: S /2 IA ~ R 2 What about electric dipole? S d d /2 Gabrielse Standard Model Prediction 1 C2 C4 C6 C8 C10 ... B 2 e 2m 3 4 5 a hadronic aweak anew physics e2 1 Fine structure constant: 4 0 c 137 1 1 Dirac QED essentially exact Hadronic Weak aweak smaller Gabrielse Probing 10th Order and Hadronic Terms Dirac QED Gabrielse David Hanneke G.G. Shannon Fogwell Gabrielse Need Good Students and Some Time 20 years 8 theses Elise Novitski Joshua Dorr Shannon Fogwell Hogerheide David Hanneke Brian Odom, Brian D’Urso, Steve Peil, Dafna Enzer, Kamal Abdullah Ching-hua Tseng Joseph Tan N$F Gabrielse Cylindrical Penning Trap V ~ 2 z 2 x2 y 2 • Electrostatic quadrupole potential good near trap center • Control the radiation field inhibit spontaneous emission by 200x (Invented for this purpose: G.G. and F. C. MacKintosh; Int. J. Mass Spec. Ion Proc. 57, 1 (1984) Trap with charges Gabrielse One Electron Quantum Cyclotron ------- f c 150 GHz n=4 n=3 n=2 n=1 n=0 y 2 hc 7.2 kelvin y ------- B 6 Tesla Need low temperature cyclotron motion T << 7.2 K 0.1 m 2 0.1 m Gabrielse Quantum Measurement of the Electron Magnetic Moment E ms s (n 1/ 2) c Spin flip energy: s B 2 B eB Cyclotron energy: c 2 B B m (the magnetometer) S /2 s c B Bohr magneton e 2m Need to resolve the quantum states of the cyclotron motion Relativistic shift is 1 part in 109 per quantum level Gabrielse Quantum Jump Spectroscopy • one electron in a Penning trap • lowest cyclotron and spin states “In the dark” excitation turn off all detection and cooling drives during excitation QND – quantum non-demolition detection s c B Gabrielse Inhibited Spontaneous Emission excite, measure time in excited state t = 16 s 20 10 0 0 10 20 30 40 50 60 15 12 9 Y Axis 2 30 axial frequency shift (Hz) number of n=1 to n=0 decays Application of Cavity QED 6 3 0 -3 0 100 200 time (s) decay time (s) many other new methods 300 Most precisely measured property of an elementary particle Electron Magnetic Moment Determined to 3 x 10-13 2.8 10 13 (improved measurement is underway) Gabrielse Gabrielse from measured fine structure constant From Freeman Dyson – One Inventor of QED Gabrielse Dear Jerry, ... I love your way of doing experiments, and I am happy to congratulate you for this latest triumph. Thank you for sending the two papers. Your statement, that QED is tested far more stringently than its inventors could ever have envisioned, is correct. As one of the inventors, I remember that we thought of QED in 1949 as a temporary and jerry-built structure, with mathematical inconsistencies and renormalized infinities swept under the rug. We did not expect it to last more than ten years before some more solidly built theory would replace it. We expected and hoped that some new experiments would reveal discrepancies that would point the way to a better theory. And now, 57 years have gone by and that ramshackle structure still stands. The theorists … have kept pace with your experiments, pushing their calculations to higher accuracy than we ever imagined. And you still did not find the discrepancy that we hoped for. To me it remains perpetually amazing that Nature dances to the tune that we scribbled so carelessly 57 years ago. And it is amazing that you can measure her dance to one part per trillion and find her still following our beat. With congratulations and good wishes for more such beautiful experiments, yours ever, Freeman. Gabrielse Test for Physics Beyond the Standard Model g 1 aQED ( ) aSM :Hadronic Weak aNew Physics B 2 Does the electron have internal structure? m* total mass of particles bound together to form electron R 5 10 19 m R 2 1019 m m 360 GeV / c 2 a m m* 1 TeV / c 2 a m* limited by the uncertainty in independent value if our uncertainty was the only limit Not bad for an experiment done at 100 mK, but LEP does better R 2 1020 m m* 10.3 TeV / c 2 LEP contact interaction limit > 20,000,000 electron masses of binding energy Gabrielse Gabrielse Electron Electric Dipole Moment (EDM) • Most precise test of extensions to the standard model • 12 times more precise than previous measurements Magnetic moment: S /2 Well measured Electric dipole moment: S d d /2 Does this also exist? Gabrielse Particle EDM Requires Both P and T Violation Magnetic moment: S /2 P T Electric dipole Moment: S d d /2 If reality is invariant under parity transformations P d=0 If reality is invariant under time reversal transformations T d=0 Gabrielse Standard Model of Particle Physics Predicts a Non-zero Electron EDM Standard model: d ~ 10-38 e-cm Too small to measure by orders of magnitude best measurement: d ~ 2 x 10-27 e-cm Weak interaction couples quark pairs (generations) CKM matrix relates to d, s, b quarks (Cabibbo-Kabayashi-Maskawa matrix) almost the unit matrix four-loop level in perturbatio theory Gabrielse Extensions to the Standard Model Much Bigger, Measureable Electron EDM An example Low order contribution larger moment Low order contribution vanishes From Fortson, Sandars and Barr, Physics Today, 33 (June 2003) Gabrielse Improved Electron Electric Dipole Moment and What is Next Gerald Gabrielse Leverett Professor Physics, Harvard University Advanced Cold Molecule EDM Science 343, 269 (2014) NSF, and NIST Gabrielse ACME Collaboration Joint effort of 3 research groups Gerald Gabrielse (Harvard) David DeMille (Yale) John Doyle (Harvard) ACME PhD Ben Spaun Chris Panda Nick Hutzler Adam West Brendon O’Leary Paul Hess Jacob Baron Elizabeth Petrik Earlier: Amar Vutha, Yulia Gurevich, Emil Kirilov, Ivan Kozyreyv, Wes Campbell Gabrielse Before Our ACME Measurement of Electron EDM Before ACME ACME aspiration for first 5 years W. Bernreuther, M. Suzuki, Rev. Mod. Phys. 63, 313 (1991) Gabrielse How to Measure an Electron EDM Put the EDM in an Electric Field bigger is better H d E Measure the energy shift for the system Cannot Use Electric Field Directly on an Electron or Proton Gabrielse Simple E and B can be used for neutron EDM measurement (neutron has magnetic moment but no net charge) Electric field would accelerate an electron out of the apparatus Electron EDM are done within atoms and molecules (first molecular ion measurement is now being attempted) Gabrielse Schiff Theorem – for Electron in an Atom or Molecule Schiff (1963) – no atomic or molecular EDM (i.e. linear Stark effect) • from electron edm • nonrelativistic quantum mechanics limit Sandars (1965) – can get atomic or molecular EDM (i.e. linear Stark effect) • from electron edm • relativistic quantum mechanics • get significant enhancement (D >> d) for large Z Commins, Jackson, DeMille (2007) – intuitive explanation Schiff Lorentz contraction of the electron EDM in lab frame Schiff, Phys. Rev. Lett. 132, 2194 (1963); Sandars, Phys. Rev. Lett. 14, 194 (1965); ibid 22, 290 (1966). Commins, Jackson, DeMille, Am. J. Phys. 75, 532 (2007). Gabrielse Why Use a Molecule? To Make Largest Possible Electric Field on Electron Tl atom (best EDM limit till YbF) Elab 123 kV/cm E eff 72 MV/cm ThO molecule Elab 100 V/cm Eeff 100 GV/cm Molecule can be more easily polarized using nearby energy levels with opposite parity (not generally available in atoms) Gabrielse Still, the EDM Gives Tiny Shift of Energy Levels E 7 1018 eV 2 mHz 7 1027 GeV Not so easy to resolve 7 1030 TeV To detect let a prepared wave function evolve for time T | (0) |1 | 2 | (T) |1 e i | 2 E large as possible T T 1.1 ms 11106 0.6 103 degrees Example is for an electron edm equal the ACME upper limit. Gabrielse Detect a Small Phase Shift set by choice of direction of the first of the two orthogonal detection laser polarizations set by choice of dark state m 1 e io m 1 m 1 e time in E, B 2 i ( o 1 ) m 1 2 ( B d E)t y x T 1.1 ms 11106 0.6 103 degrees Example is for an electron edm equal the ACME upper limit. Gabrielse Experiment in Two Labs – 100 Meters Separated Harvard Jefferson Building Harvard LISE Building 100 m optical fibers Lasers, Iodine Clock, Comb ThO Source and Interaction Chamber (2 floors down Gabrielse ThO Molecular Beam Pulse Tube Cooler Molecular Beam Source “Interaction Region”: Efield plates inside, Bfield shields and coils outside Pulsed YAG Prep Lasers Probe Lasers Lasers 100m away 34 Gabrielse Magnetic Field Coils and Shielding mu metal endplates ThO beam Cos(theta) coils to provide transverse B field 5 shields (no shown) ~ 10-5 shielding Interaction chamber inside 200 mG with uniformity of 10-3 over 26 cm Gabrielse Detect the Tiny Phase Shift Interference set by choice of dark state m 1 eio m 1 set by choice of direction of the first of the two orthogonal detection laser polarizations m 1 ei ( o 1 ) m 1 2 2 ( B d E)t maximize sensitivity to d E t 11106 Gabrielse Detecting an EDM ground state superposition evolve: E + edm cold ThO source combine emit E B electric field plates magnetic field light detector apparatus control and data acquisition Gabrielse Total Phase Equation: 𝜙 𝑁, 𝐸, 𝐵 = 𝑔 + Δ𝑔 𝑁 𝐵0 + 𝐵𝑛𝑟 𝐵 + 𝐵𝑙𝑒𝑎𝑘 𝐸 𝜇𝐻 𝜏 + 𝑑𝑒 𝐸𝑒𝑓𝑓 𝐸 𝑁 ++- B0 g t +-+ Bleak g t +-- 0 -++ Bnr g t -+- B0 g t --+ de Eeff t B0 η Enr t phase (rad) Bnr g t + θnr 3±5 x 10-5 rad block (~1 min) phase (rad) +++ --- single block 10 blocks averaged Derived quantities 392 ± 5 x 10-5 rad block (~1 min) phase (rad) Parity sum (NEB) ??? ± 5 x 10-5 rad block (~1 min) phase (rad) single block 10 blocks averaged block (~1 min) B0 g t +-+ Bleak g t +-- 0 -++ Bnr g t -+- B0 g t --+ de Eeff t --- B0 η Enr t phase (rad) ++- -3590 ± 5 x 10-5 rad -2 ± 5 x 10-5 rad block (~1 min) phase (rad) Bnr g t + θnr phase (rad) Derived quantities +++ -1530 ± 5 x 10-5 rad 4±5 x 10-5 rad block (~1 min) phase (rad) Parity sum (NEB) Gabrielse -1 ± 5 x 10-5 rad block (~1 min) Gabrielse Gabrielse Constraining New Physics on the 1 to 3 TeV Scale for weak interactions ~4/137 prefactor conservative difficult to suppress new CP violating phase mass scale of new particles couples to weak interaction via n=1 or n=2 loop diagrams 3 TeV 1 TeV Probing same mass scale as the LHC Gabrielse We need molecular theory to get the effective electric field We actually constrain the EDM and CS Assuming d=0 Gabrielse New ACME Electron EDM Measurement New ACME Result Gabrielse How Big is 8 x 10-29 e cm? How sensitive was our princess to the hidden pea? Scale size of the polarization cloud around the electron earth Shift in earth center by 2 nm earth-sized polarization cloud around electron (scale classical electron radius) Gabrielse Relationship to LHC Physics The LHC is exciting and important but EDMs also play a role • should get an improved electron EDM on the LHC time scale • If the LHC sees new particles, is CP violation involved? • If the LHC sees nothing, EDM game is the only one in town • Would be great to use LHC results and ours together to see what we have learned together about Standard Model extensions Gabrielse https://twiki.cern.ch/twiki/pub/AtlasPublic/CombinedSummaryPlots/AtlasSearchesSUSY_SUSY2013.pdf Gabrielse Gabrielse Testing the Standard Model’s Fundamental Symmetry and Comparing Antimatter-Matter Gravity Gabrielse Single Particle Measurements Have Three Big Advantages Can be done with antiparticles Can reach a much higher precision Direct measurement same measurement and apparatus is used with a particle and antiparticle Gabrielse Most Stringent Tests of the Standard Model (and Gravity) with Antiprotons Q/M of Antiproton and Proton – most stringent test of the Standard Model’s CPT theorem with baryons Comparison of Antiproton and Proton Gravity 680 Times Improved Comparision of the Antiproton and Proton Magnetic Moments Gabrielse Embarrassing, Unsolved Mystery: How did our Matter Universe Survive Cooling After the Big Bang? Big bang equal amounts of matter and antimatter created during hot time As universe cools antimatter and matter annihilate Big Questions: • How did any matter survive? • How is it that we exist? Our experiments are looking for evidence of any way that antiparticles and particles may differ Gabrielse Our “Explanations” are Not so Satisfactory Baryon-Antibaryon Asymmetry in Universe is Not Understood Standard “Explanation” • CP violation • Violation of baryon number • Thermodynamic non-equilibrium Alternate • CPT violation • Violation of baryon number • Thermo. equilib. Bertolami, Colladay, Kostelecky, Potting Phys. Lett. B 395, 178 (1997) Why did a universe made of matter survive the big bang? Makes sense look for answers to such fundamental questions in the few places that we can hope to do so very precisely. Bigger problem: don’t understand dark energy within 120 orders of magnitude _ _ Gabrielse Why Compare H and H (or P and P)? Reality is Invariant – symmetry transformations P parity CP charge conjugation, parity CPT charge conjugation, parity, and time reversal CPT Symmetry Particles and antiparticles have • same mass • same magnetic moment • opposite charge • same mean life Atom and anti-atom have same structure Looking for Surprises • simple systems • extremely high accuracy • comparisons will be convincing • reasonable effort • FUN Gabrielse Comparing the CPT Tests 3 fundamentally different types of particles Warning – without CPT violation models it is hard to compare CPT Test Measurement Accuracy Accuracy Free Gift _ K0 K0 2 x 10-18 Mesons 2 x 10-3 1015 e+ e2 x 10-12 Leptons 2 x 10-9 103 improve with antihydrogen _ PP 9 x 10-11 baryons 9 x 10-11 1 Gabrielse I Came to CERN First in 1986 to Compare the Antiproton and the Proton Started cold antiproton and antihydrogen physics Now a dedicated storage ring and 6 international collaboration (still amazes me) Gabrielse Accumulating Low Energy Antiprotons: Basic Ideas and Demonstrations (1986 – 2000) TRAP Collaboration at CERN’s LEAR 1 cm magnetic field 21 MeV antiprotons _ • Slow antiprotons in matter • Capture antiprotons in flight • Electron cooling 4.2 K • 5 x 10-17 Torr + _ 10-10 energy reduction Now used by 5 collaborations at the CERN AD ATRAP, ALPHA, ASACUSA, AEGIS, BASE Gabrielse Highest Precision Test of Baryon CPT Invariance by TRAP at CERN q / m (antiproton) 0.99999999991(9) q / m (proton) 9 1011 90ppt (most precise result of CERN’s antiproton program) Goal at the AD: Make CPT test that approach exceed this precision Gabrielse We Improved the Comparison of Antiproton and q / m (antiproton) 6 0.99999999991(9) Proton by ~10 q / m (proton) 9 1011 90 ppt most stringent CPT test with baryons 6 105 100 antiprotons and protons G. Gabrielse, A. Khabbaz, D.S. Hall, C. Heimann, H. Kalinowsky, W. Jhe; Phys. Rev. Lett. 82, 3198 (1999). Gabrielse Seek to Improve Lepton and Baryon CPT Tests antiproton moment ATRAP members R [H] m[e ] R [H] m[e ] 2 2 q[e ] q[ p ] 1 m[e ] / M [ p ] q[e ] q[ p ] 1 m[e ] / M [ p ] Gabrielse Gabrielse Direct Comparison of Antimatter and Matter Gravity Does antimatter and matter accelerate at the same rate in a gravitational field? g antimatter g matter acceleration due to gravity for antimatter acceleration due to gravity for matter Gabrielse The Most Precise Experimental Answer is “Yes” to at lease a precision of 1 part per million / g h / c 2 Gravitational red shift for a clock: Antimatter and matter clocks run at different rates if g is different for antimatter and matter c c U 3( 1) 2 c for tensor gravity (would be 1 for scalar gravity) Hughes and Holzscheiter, Phys. Rev. Lett. 66, 854 (1991). grav. pot. rnergy difference between empty flat space time and inside of hypercluster of galaxies Experiment: TRAP Collaboration, Phys. Rev. Lett. 82, 3198 (1999). c c 10 10 1 ( 10 ) 6 Gabrielse Gravity and Antihydrogen Gabrielse May be Hard to Get the Part per Million Precision of the Redshift Limit with Antihydrogen and Hydrogen g antimatter g matter Gravitational redshift: c c 10 10 1 ( 10 ) 6 Worthy goal for AEGIS and GBAR can they get a part per million ALPHA trapped antihydrogen released (2013): 110 (108 times less precise) Gabrielse Sometimes It is Said that this Redshift Measurement is not so Valid Because it “Assumes CPT Invariance” • Does not assume CPT invariances in the gravity sector of course • Only assumes that CPT violations in the Standard Model (if they exist) do not cancel the CPT violations in gravity (if they exist) • Does not seem likely to me that CPT violations in the Standard Model would be just the right size to cancel differences in gravitational redshifts of the antiproton and proton (at our location in space-time). Gabrielse Antiproton Magnetic Moment Gabrielse Proton and Antiproton Magnetic Moments are Much Smaller than the Electron Moment Harder: nuclear magneton rather than Bohr magneton Gabrielse Phys. Rev. Lett. 180, 153001 (2012) Earlier contributions Later measurement with similar methods Gabrielse Gabrielse Resonance Lines to Determine the “Two” Frequencies square of extra width Brown-Gabrielse Invariance Theorem Gabrielse First One-Particle Measurement of the Antiproton Magnetic moment 680 times lower than previous Gabrielse 680 – Fold Improved Precision ASACUSA 680 2013 plausible aspiration ATRAP, Phys. Rev. Lett. (2013). Gabrielse Proton Spin Flip Report Similar proton result from Mainz group in same issue Gabrielse Gabrielse Antihydrogen Hope for the Future Note: no scientifically interesting tests of fundamental symmetries have yet taken place with antihydrogen – beware the hype Gabrielse Proposal to Trap Cold Antihydrogen – 1986 • Produce cold antihydrogen from cold antiprotons “When antihydrogen is formed in an ion trap, the neutral atoms will no longer be confined and will thus quickly strike the trap electrodes. Resulting annihilations of the positron and antiproton could be monitored. ..." • Trap cold antihydrogen • Use accurate laser spectroscopy to compare antihydrogen and hydrogen “For me, the most attractive way ... would be to capture the antihydrogen in a neutral particle trap ... The objective would be to then study the properties of a small number of [antihydrogen] atoms confined in the neutral trap for a long time.” Gerald Gabrielse, 1986 Erice Lecture (shortly after first pbar trapping) In Fundamental Symmetries, (P.Bloch, P. Paulopoulos, and R. Klapisch, Eds.) p. 59, Plenum, New York (1987). Use trapped antihydrogen to measure antimatter gravity Gabrielse Most Trapped Antihydrogen in Its Ground State 5 +/- 1 ground state atoms simultaneously trapped ATRAP, “Trapped Antihydrogen in Its Ground State”, Phys. Rev. Lett. 108, 113002 (2012) Gabrielse ATRAP Collaboration Gabrielse Ultimate Goal: Hydrogen 1s – 2s Spectroscopy (or similar tests of ground state hyperfine structure) (Haensch, et al., Max Planck Soc., Garching) http://www.mpq.mpg.de/~haensch/hydrogen/h.html Many fewer antihydrogen atoms will be available Gabrielse Two Methods Produce Slow Antihydrogen 1. In a nested Penning trap, during positron cooling of antiprotons Device and technique – ATRAP Used to produce slow antihydrogen – ATHENA and ATRAP Variations: Basic (ATRAP initially, ATHENA-ALPHA) Driven (ATRAP before 2007) Adiabatic well depth change (ATRAP 2007) 2. Laser-controlled resonant charge exchange ATRAP Anti-H Method 1: Nested Penning Trap Gabrielse 3-Body “Recombination” Nested Penning Trap 3-Body “Recombination” Positron Cooling of Antiprotons in a Nested Penning Trap Gabrielse p + e TRAP/ATRAP Develops the Nested Penning Trap Proposed nested trap as a way to make antihydrogen "Antihydrogen Production Using Trapped Plasmas" G. Gabrielse, L. Haarsma, S. Rolston and W. Kells Physics Letters A 129, 38 (1988) "Electron-Cooling of Protons in a Nested Penning Trap" D.S. Hall, G. Gabrielse Phys. Rev. Lett. 77, 1962 (1996) "First Positron Cooling of Antiprotons" ATRAP Phys. Lett. B 507, 1 (2001) Gabrielse Anti-H Method II: Antihydrogen Via Laser-Controlled Resonant Charge Exchange 852 nm 510.6 nm ATRAP, Phys. Rev. Lett. 93, 263401 (2004) 1986 Gabrielse 2012 1 Collaboration 4 Collaborations Following the 1986 plan: Variations cold antiprotons cold antihydrogen trap antihydrogen colder antihydrogen extract from trap precise laser spectroscopy laser spectroscopy interferometry ATRAP and ALPHA ASACUSA AEGIS Gabrielse Gabrielse First Generation Penning-Ioffe Apparatus Gabrielse ATRAP – observed the production of antihydrogen atoms in the fields of a Ioffe trap (PRL 2008) Less than 20 atoms were being trapped per trial ALPHA – did similar production the following year two directions ATRAP Try to make more atoms 5 +/- 1 per trial ALPHA Try to detect fewer atoms 0.7 +/- 0.3 per trial Gabrielse 1.2 K Electrodes and Millions of Antiprotons 1.2 K Using Pumped Helium Gabrielse ATRAP More Antiprotons, Much Colder, More Simultaneously Trapped Atoms • Lowered electrode temperature to 1.2 K • Started measuring antiproton temperatures • Developed new pbar cooling methods First antiprotons cold enough to centrifugally separate from the electrons that cool them Phys. Rev. Lett. 105, 213002 (2010). Two new cooling methods for antiprotons -- embedded electron cooling -- adiabatic cooling Phys. Rev. Lett. 106, 073002 (2011). 3 million antiprotons at 3.5 K Gabrielse Gabrielse Particle Physics at Low Energy Gerald Gabrielse Leverett Professor of Physics, Harvard University Spokesperson of the CERN ATRAP Collaboration Testing the Most Precise Prediction of the Standard Model Electron magnetic moment Testing standard model extensions Electron electric dipole moment Testing the Symmetries of the Standard Model Q/M for the antiproton and proton Antiproton and proton magnetic moments Positron and electron magnetic moments (underway) Antihydrogen and hydrogen structure (still in far future) Comparing Antimatter and Mater Gravity Gravitational Redshift of the Antiproton and Proton Supported by US NSF and AFOSR Gabrielse Summary Low energy particle physics produces the most stringent tests of the standard model, its extensions and its fundamental symmetries - electron magnetic dipole moment - electron electric dipole moment - comparison of antiproton and proton charge-to-mass ratios - comparison of antiproton and proton gravity - comparison of antiproton and proton magnetic moments Antihydrogen – now have cold trapped antihydrogen atoms in their ground states, but not enough atoms yet – no interesting tests of fundamental symmetries yet, but big hopes for the future