The AE¯gIS experiment at CERN’s Antiproton Decelerator is set up to precisely measure the gravitational interaction between matter and antimatter. For this purpose, antihydrogen will be formed from cold antiprotons and positronium, the hydrogen-like bound state of an electron and a positron. Subsequently,

the free-fall acceleration of a cold horizontal beam of antihydrogen will be measured by a deflectometer. The present status, recent experimental progress and the medium-term plan of the AE¯gIS experiment are presented

Aghion, S.

Amsler, C.

Antonello, M.

Belov, A.

Caravita, R.

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DOI 10.1393/ncc/i2019-19123-9Colloquia: EuNPC 2018IL NUOVO CIMENTO 42 C (2019) 123The AEgIS experiment at CERN: Probing antimatter gravityR. Caravita(1), S. Aghion(2)(3), C. Amsler(4), M. Antonello(3)(5),A. Belov(6), G. Bonomi(7)(8), R. S. Brusa(9)(10), M. Caccia(3)(5),A. Camper(1), F. Castelli(3)(11), G. Cerchiari(12), D. Comparat(13),G. Consolati(2)(3), A. Demetrio(14), L. Di Noto(15)(16), M. Doser(1),C. Evans(2)(3), M. Faǹı(1)(15)(16), R. Ferragut(2)(3), J. Fesel(1),A. Fontana(8), S. Gerber(1), M. Giammarchi(3), A. Gligorova(4),F. Guatieri(9)(10), P. Hackstock(1), S. Haider(1), A. Hinterberger(1),H. Holmestad(1), A. Kellerbauer(12), O. Khalidova(1), D. Krasnický(16),V. Lagomarsino(15)(16), P. Lansonneur(17), P. Lebrun(17), C. Malbrunot(1)(4),S. Mariazzi(9)(10), J. Marton(4), V. Matveev(6)(18), S. R. M’́uller(14),G. Nebbia(19), P. Nedelec(17), M. Oberthaler(14), D. Pagano(7)(8),L. Penasa(9)(10), V. Petracek(20), F. Prelz(3), M. Prevedelli(21),B. Rienäcker(1), J. Robert(13), O. M. Røhne(22), A. Rotondi(8)(23),H. Sandaker(22), R. Santoro(3)(5), L. Smestad(24), F. Sorrentino(15)(16),G. Testera(16), I. Tietje(1), M. Vujanovic(1), E. Widmann(4),P. Yzombard(12), C. Zimmer(1), J. Zmeskal(4) and N. Zurlo(8)(25)(The AEgIS Collaboration)(1) Physics Department, CERN - 1211 Geneva 23, Switzerland(2) Politecnico of Milano - Piazza Leonardo da Vinci 32, 20133 Milano, Italy(3) INFN Milano - via Celoria 16, 20133, Milano, Italy(4) Stefan Meyer Institute for Subatomic Physics, Austrian Academy of SciencesBoltzmanngasse 3, 1090 Vienna, Austria(5) Department of Science, University of Insubria - Via Valleggio 11, 22100 Como, Italy(6) Institute for Nuclear Research of the Russian Academy of Science - Moscow 117312,Russia(7) Department of Mechanical and Industrial Engineering, University of Bresciavia Branze 38, 25123 Brescia, Italy(8) INFN Pavia - via Bassi 6, 27100 Pavia, Italy(9) Department of Physics, University of Trento - via Sommarive 14, 38123 Povo, Trento,Italy(10) TIFPA/INFN Trento - via Sommarive 14, 38123 Povo, Trento, Italy(11) Department of Physics, University of Milano - via Celoria 16, 20133 Milano, Italy(12) Max Planck Institute for Nuclear Physics - Saupfercheckweg 1, 69117 Heidelberg,Germany(13) Laboratoire Aimé Cotton, Université Paris-Sud, ENS Cachan, CNRS, Université Paris-Saclay - 91405 Orsay Cedex, France(14) Kirchhoff-Institute for Physics, Heidelberg University - Im Neuenheimer Feld 227, 69120Heidelberg, Germany(15) Department of Physics, University of Genova - via Dodecaneso 33, 16146 Genova, Italy(16) INFN Genova - via Dodecaneso 33, 16146 Genova, Italy(17) Institute of Nuclear Physics, CNRS/IN2p3, University of Lyon 1 - 69622 Villeurbanne,FranceCreative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 R. CARAVITA et al.(18) Joint Institute for Nuclear Research - 141980 Dubna, Russia(19) INFN Padova - via Marzolo 8, 35131 Padova, Italy(20) Czech Technical University, Prague - Bøehová 7, 11519 Prague 1, Czech Republic(21) University of Bologna - Viale Berti Pichat 6/2, 40126 Bologna, Italy(22) Department of Physics, University of Oslo - Semælands vei 24, 0371 Oslo, Norway(23) Department of Physics, University of Pavia - via Bassi 6, 27100 Pavia, Italy(24) The Research Council of Norway - P.O. Box 564, NO-1327 Lysaker, Norway(25) Department of Civil Engineering, University of Brescia - via Branze 43, 25123 Brescia,Italyreceived 5 February 2019Summary. — The AEḡIS experiment at CERN’s Antiproton Decelerator is set upto precisely measure the gravitational interaction between matter and antimatter.For this purpose, antihydrogen will be formed from cold antiprotons and positro-nium, the hydrogen-like bound state of an electron and a positron. Subsequently,the free-fall acceleration of a cold horizontal beam of antihydrogen will be mea-sured by a deflectometer. The present status, recent experimental progress and themedium-term plan of the AEḡIS experiment are presented.1. – IntroductionProbing experimentally the antimatter gravitational acceleration with a pulsed beamof cold antihydrogen is the ambitious goal of the AEḡIS collaboration at CERN [1],aiming to use a moiré deflectometer [2] to detect its vertical displacement due to the free-fall with a position-sensitive detector [3]. Pulsed antihydrogen production has not beenexperimentally achieved yet, and will be realized in AEḡIS with a double charge-exchangereaction between trapped antiprotons (p̄) and laser-excited Rydberg Positronium (Ps)atoms [4] obtained from the conversion of positrons (e+) in a matter e+-Ps converter:e− + e+ −→ Ps Ps productionPs + γ205 nm + γ1700 nm −→ Ps∗ Laser excitationp̄− + Ps∗ −→ H̄∗ + e− Charge exchange.Many progresses towards a first milestone pulsed production of H̄ have been recentlypursued by AEḡIS: the preparation of a dense, cold plasma of p̄; the efficient production ofPs by the matter converter designed for cryogenic high-vacuum use; efficient Ps Rydberglaser-excitation.A sketched scheme of the current setup of the experiment is shown in Fig. 1. Ananoporous silicon positron-Ps converter developed for cryogenic use [7] is placed 1.5 cmabove a Malmberg-Penning trap for p̄ storage [6]. Positrons (e+) implanted with KeVenergy are efficiently converted into Ps atoms - immediately re-emitted into vacuum afterTHE AEgIS EXPERIMENT AT CERN: PROBING ANTIMATTER GRAVITY 3Figure 1. – Cut-open schematic view of the AEgIS experiment, highlighting the most crucialcomponents. Inset: zoom on the antihydrogen production region.cooling by collisions in the material porosities (electrochemically-etched nanochannels[8]). Two laser pulses are sent from the side of the converter to excite the emitted fractionof Ps first to n = 3 (205.045 nm) then to Rydberg levels (1700 nm) [10]. Rydberg Psatoms, having a lifetime longer than 10μ s, fly towards the p̄ storage trap and produceH̄ by the charge-exchange reaction with the p̄ in the cold plasma.2. – Antiproton plasma preparationAbundant cold p̄ were prepared in the final trap based on a procedure constitued byseveral plasma manipulations. First, ∼ 1% of the 3 · 107 5.3 MeV antiprotons in eachspill of the Antiproton Decelerator were captured and cooled in AEḡIS catching traps(using a matter energy degrader and electron sympathetic cooling [6]). Subsequently, themixed p̄ - e− plasma was radially compressed to high densities, using the rotating-walltechnique [11], to  mm [12]. Finally, the antiprotons were transferred ballistically to theH̄ production trap by applying fast potential pulses on the trap end-caps [13]. Stackingof several p̄ spills was shown possible, allowing 6− 7 · 105 antiprotons to be stored in thetrap with long plasma lifetimes (> 1 h).3. – Positronium production and Rydberg excitationIn parallel, Ps production and emission into vacuum from the mesoporous silicontargets designed for AEḡIS was shown to have high (∼ 35%) efficiency [5]. Ps wassubsequently laser-excited to the Rydberg levels spanning from n = 15 to n = 17 [14] withan overall laser excitation efficiency of ∼ 8% [15], demonstrating the proof-of-principlelaser excitation for H̄ production. An alternative way to increase the Ps lifetime wasalso investigated, i.e. Ps laser excitation to the 23S metastable state, revealing to be apossible candidate for future inertial experiments on Ps itself [16].4 R. CARAVITA et al.4. – ConclusionsAEgIS entered its data taking period with both antiprotons and positrons at thebeginning of 2015. Since then, significant progress towards a first experimental demon-stration of pulsed antihydrogen formation was obtained. This experiment, now withinreach, is the crucial milestone towards conducting a first gravity measurement on anti-hydrogen.REFERENCES[1] Doser M. et al. (AEgIS Collaboration), Class. Quantum Grav., 18 (2012) 183009[2] Aghion S. et al. (AEgIS collaboration), Nat. comms., 5 (2014) 4538[3] Aghion S. et al. (AEgIS collaboration), J. Instrum., 9 (2014) P06020[4] Krasnický, D., Caravita R., Canali C. and Testera G., Phys. Rev. A, 94 (2016)022714[5] Aghion S. et al. (AEgIS collaboration), Nucl. Instrum. Methods Phys. Res., Sect.B, 362 (2015) 86-92[6] Krasnický D. et al. (AEgIS collaboration), AIP Conf. Proc., 1521 (2013) 144[7] Mariazzi S., Bettotti P., Larcheri S. Toniutti L. and Brusa R. S., Phys. Rev. B,81 (2010) 235418[8] Mariazzi S., Bettotti P. and Brusa R. S., Phys. Rev. Lett., 104 (2010) 243401[9] Cialdi S., Boscolo I., Castelli F., Villa F. and Giammarchi M. G., Nucl. Instrum.Methods Phys. Res., Sect. B, 269 (2011) 1527-1533[10] Cialdi S., Boscolo I., Castelli F., Villa F. and Giammarchi M. G., Nucl. Instrum.Methods Phys. Res., Sect. B, 269 (2011) 1527-1533[11] Huang X.-P., Anderegg F., Hollmann E. M., Driscoll C. F. and O’Neil T. M.,Phys. Rev. Lett, 78 (1997) 875[12] Aghion S. et al. (AEgIS collaboration), Eur. Phys. J. D, 72 (2018) 76[13] Caravita R., Towards measuring gravity on neutral antimatter, Ph.D. thesis (2017)http://cds.cern.ch/record/2640201?ln=en[14] Aghion S. et al. (AEgIS collaboration), Phys. Rev. A, 94 (2016) 012507[15] Caravita R. et al. (AEgIS collaboration), Acta Phys. Polon. B, 48 (2017) 1583[16] Aghion S. et al. (AEgIS collaboration), Phys. Rev. A, 98 (2018) 013402

The AEgIS experiment at CERN: Probing antimatter gravity

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The AEgIS experiment at CERN: Probing antimatter gravity

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