Antihydrogen Physics with ALPHA CERN – May 2014 Mike Charlton, Physics, Swansea University UK Antihydrogen Physics with ALPHA

CERN – May 2014 Summary of the Talk Introductory Remarks - The Hydrogen/Antihydrogen Playground Antihydrogen Production: Formation Processes Antihydrogen Production for Trapping ALPHA -Antihydrogen Trapping and Physics ALPHA - What’s Next? Introductory Remarks - The Hydrogen/Antihydrogen Playground Antihydrogen Production: Formation Processes Antihydrogen Production for Trapping ALPHA -Antihydrogen Trapping and Physics ALPHA - What’s Next?

Antihydrogen Physics with ALPHA CERN – May 2014 The Hydrogen/Antihydrogen Playground From R. Ley, Appl. Surf. Sci. 194 (2002) 301 1S-2S transition in H; Parthey et al. PRL 107 (2011) (10) Hz, or 4.2 parts in Ground State Hyperfine transition in H; Essen et al. Nature 229 (1971) (9) Hz, or 6.4 parts in 10 13

Antihydrogen Physics with ALPHA CERN – May 2014 The Hydrogen/Antihydrogen Playground GravityGravity … plus Charge Neutrality …

Antihydrogen Physics with ALPHA CERN – May 2014 Antihydrogen Production: Formation Processes Plasma self electric field Plasma parameters Tangential drift speed low high > 10 3 s -1

Antihydrogen Physics with ALPHA CERN – May 2014 Antihydrogen Production: Formation Processes The TBR is a quasi-elastic encounter of 2 positrons in the vicinity of an antiproton. Energy exchange ~ k B T e, which will be the same order of the binding energies. Thus, these are very weakly bound states which are strongly influenced by the ambient fields. Many are field ionized. The TBR is a quasi-elastic encounter of 2 positrons in the vicinity of an antiproton. Energy exchange ~ k B T e, which will be the same order of the binding energies. Thus, these are very weakly bound states which are strongly influenced by the ambient fields. Many are field ionized. Antihydrogen binding energies as the atoms leave the positron plasma n e = m -3 (x); n e = 5 x m -3 (+) c.f. Antihydrogen binding energies on detection n e = m -3 (+); 5 (○), 2 (Δ) and 1 (□) x m -3 and 5 x m -3 (x) Results of simulations: Jonsell et al. J.Phys B. 42 (2009)

Antihydrogen Physics with ALPHA CERN – May 2014 Antihydrogen Production: Formation Processes Radial distribution of antihydrogen formation positions at different time intervals T e = 15 K n e = m -3 n e = 5 x10 13 m -3 short (x), medium (Δ) and long (□) times NB at m -3 a “long” time is > 1ms Repeated antihydrogen formation and destruction cycles in the plasma transport the antiprotons to the outer edge of the plasma Results of simulations: Jonsell et al. J.Phys B. 42 (2009)

Antihydrogen Physics with ALPHA CERN – May 2014 Antihydrogen Production: Formation Processes So … want high positron density and low temperatures to drive 3-body reaction to form antihydrogen efficiently, but:- Field ionization … Cross-field antiproton transport driven by the antihydrogen production mechanism … Higher tangential drift speeds at higher radius and density … To say nothing of plasma expansion effects, which are most deleterious at high densities …

Antihydrogen Physics with ALPHA CERN – May 2014 Antihydrogen Production for Trapping We have machines to manipulate and capture positrons and antiprotons using a raft of long- established techniques These are then fed into a central apparatus where – eventually – they are mixed to form antihydrogen. A small fraction of the anti-atoms (to date at least) may then be trapped … The manipulations of the positrons and antiprotons before, and upon, mixing are crucial to this achievement

Antihydrogen Physics with ALPHA CERN – May 2014 Antihydrogen Production for Trapping Classic Ioffe-Pritchard Geometry Solenoid field is the minimum in B B quadrupole winding mirror coils N.B. Well depth ~ 0.7 K/T for the ground state N.B. Well depth ~ 0.7 K/T for the ground state THE CHALLENGE ALPHA’S Octupolar magnet for radial field minimum

Antihydrogen Physics with ALPHA CERN – May 2014 Antihydrogen Production for Trapping From the AD e + from accumulator 3-layer silicon antiproton annihilation vertex detector surrounding the mixing region is not shown

Antihydrogen Physics with ALPHA CERN – May 2014 Antihydrogen Production for Trapping

Antihydrogen Physics with ALPHA CERN – May 2014 Antihydrogen Production for Trapping Sympathetic compression of an antiproton cloud by electrons – uses rotating electric fields Andresen et al., PRL, 101 (2008) To reduce tangential drift speeds at high radius and promote overlap with the positron plasma

Antihydrogen Physics with ALPHA CERN – May 2014 Antihydrogen Production for Trapping Andresen et al., PRL 105 (2010) K 325 K 57 K 23 K 19 K 9 K Typically (9 ± 4) K is lowest achievable at the lowest well available at which (6 ± 1) % of the initial antiprotons remain Evaporative cooling of antiproton and positrons to lower temperatures prior to mixing

Antihydrogen Production for Trapping Antihydrogen Physics with ALPHA CERN – May 2014 Andresen et al. PRL (2011) Chirped driven harmonic oscillator Autoresonant injection of antiprotons in to the positron plasma to achieve robust mixing with minimum added kinetic energy

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics 30,000 pbars at 200K 2M positrons at 40 K (evaporatively cooled) Auto-resonant injection and mix for 1 sec. Clear the charge particles Turn off the neutral trap (1/e time ~ 9 ms) Search for pbar annihilations from Hbar (bias fields to eject any charged particles still trapped) 30,000 pbars at 200K 2M positrons at 40 K (evaporatively cooled) Auto-resonant injection and mix for 1 sec. Clear the charge particles Turn off the neutral trap (1/e time ~ 9 ms) Search for pbar annihilations from Hbar (bias fields to eject any charged particles still trapped) Neutral trap depth ~ 0.5 K

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics Searching for trapped antihydrogen Shut off magnetic minimum trap (1/e time ~ 9 ms) Interrogate output of vertex detector in 30 ms time window after the shut off Apply cuts to data to reject cosmic ray events Searching for trapped antihydrogen Shut off magnetic minimum trap (1/e time ~ 9 ms) Interrogate output of vertex detector in 30 ms time window after the shut off Apply cuts to data to reject cosmic ray events a) Antiproton annihilation b) Cosmic ray

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics Initial success – just 38 events Published in Nature 468 (2010) 673

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics 309 events – Nature Physics 7 (2011) 558

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics Time release distribution and various fits

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics Magnetic Field map of the antihydrogen trap Note the small red box near the field minimum, close to 1 T

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics On resonance – 15 MHz scan width for 15 s each – 6 repeats

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics On resonance – 15 MHz scan width for 15 s each – 6 repeats Off resonance – B shift

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics On resonance – 15 MHz scan width for 15 s each – 6 repeats Off resonance – B shift On resonance – frequency shift

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics Extra annihilations on resonance – the microwaves force the antihydrogen into the untrapped states First observation of a resonant quantum transitions in an anti- atom: Nature 483 (2012) 439

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics Microwave experiments (ALPHA- type) limited by:- Statistics (no lineshape scan) B-field and variation across “sample” Magnetometry (in-situ) issues …

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics F = M g /M, ratio of grav. to inertial mass F = 1 F = 100 Analysis of the up/down annihilation positions versus time (red dots, data: green dots, simulations) during the magnet shutdown

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics ALPHA’s reverse cumulative average analysis Data Red: y-direction Green: x-direction (for comparison) Simulations Dash: “antigravity” at given |F| Line: gravity at given |F| Grey bands: 90% confidence limits on simulations

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics Possibilities with cooled antihydrogen atoms … reverse cumulative averages from simulation Majenta: F =-1 Red: F = 0 Green: F = 1 N.B. Field shut down slowed by a factor of 10 Thin black line is fraction escaped versus time Dark yellow s/n (cosmic) > 5 for current trapping rate: light yellow for trapping rate x10 Grey bands – 90% conf. limits for F = +/- 1

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics Limitations … Statistics – signal-to-noise at long times Systematics regarding magnetic effects; trajectories are complicated – need simulations to extract F Need cooled antihydrogen to get near F = 1; probably can’t get much further

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics To be published Electric fields used for “Bias-Left” and “Bias-Right” configurations Experimental data for Bias-Left and Bias-Right

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics Simulation of z-annihilation points for an antihydrogen charge, Q Effective potential, U, used to derive Q for E to left and right Experimental data ’s are average annihilation positions with fields to left and right Replace approximate result for Q with value of “sensitivity to charge” from simulation s = - (3.31 +\- 0.04) x mm -1 To be published

Antihydrogen Physics with ALPHA CERN – May 2014 ALPHA Antihydrogen Trapping and Physics Limitations and possibilities… Statistic and systematics … Laser cooling to 20 mK will improve by a factor of about 10 (lower neutral trap, lower mirror coil fields) Stochastic heating/acceleration … possible to achieve |Q| ~ : see preprint:- To be published

ALPHA – What’s Next? Antihydrogen Physics with ALPHA CERN – May 2014 Layout of ALPHA-2 Working on new apparatus to allow laser access for 1S-2S 2-photon transition (ALPHA-2) and to incorporate antihydrogen laser cooling Long term goals of the field For a discussion of laser cooling in an ALPHA-like trap; see Doonan et al. J. Phys. B, 46 (2013)

ALPHA – What’s Next? Antihydrogen Physics with ALPHA CERN – May 2014 Challenges … More trapped antihydrogen! (  cooler positrons) Optics/cavities and cryogenics Lasers for stringent spectroscopy/cooling requirements – challenging wavelengths

ALPHA – What’s Next? Antihydrogen Physics with ALPHA CERN – May 2014 A possible new venture – ALPHA-g: a vertical ALPHA with a long- term vision of performing antimatter interferometry For discussion of the concept see: Hamilton et al. PRL 112 (2014)

ALPHA – What’s Next? Antihydrogen Physics with ALPHA CERN – May 2014 A very bright and busy future awaits … CERN has started work on ELENA an extra ring to decelerate antiprotons to about 100 keV – this will increase our capture efficiency for low energy antiprotons by a factor of around 100.

Antihydrogen Physics with ALPHA CERN – May 2014 Acknowledgements – ALPHA circa University of Aarhus: J.S. Hangst, C. Rasmussen Auburn University/Purdue University: P.H. Donnan, F. Robicheaux University of British Columbia: N. Evetts, A. Gutierrez, W.N. Hardy, T.Momose University of Calgary: T. Friesen, R.I. Thompson University of California, Berkeley: M. Baquero-Ruiz, J. Fajans, A. Little, H. Mueller, C. So, T. Tharp, J.S. Wurtele CERN: E. Butler – now a JRF at Imperial College University of Liverpool: J.T.K. McKenna, P. Nolan, P. Pusa University of Liverpool/Cockcroft: S. Chattopadhyay University of Manchester/Cockcroft: W. Bertsche NRCN, Negev: E. Sarid Federal University of Rio de Janeiro: C.L. Cesar, D.M. Silveira Simon Fraser University : M.D. Ashkezari, M.E. Hayden York University, Toronto : C. Amole, A. Capra, S. Menary Swansea University: M. Charlton, D. Edwards, S.J. Eriksson, C.A. Isaac, S. Jones, N. Madsen, M. Sameed, D.P. van der Werf Stockholm University : S. Jonsell TRIUMF: M. C. Fujiwara, D.R. Gill, L. Kurchaninov, K. Olchanski, A. Olin, S. Straka