GRAVITY AND ANTIMATTER: THE AEGIS EXPERIMENT AT CERN DAVIDE PAGANO UNIVERSITÀ DEGLI STUDI DI BRESCIA & INFN PAVIA on behalf of the AEgIS collaboration TAUP 2017 - XV International Conference on Topics in Astroparticle and Underground Physics
THE WEAK EQUIVALENCE PRINCIPLE 2 • Universality of free fall (UFF) established by Galileo and Newton so m i ¼ m g Weak equivalence principle (WEP) electric field: gravitational field: F = q · E F = m · G • Unique behavior: | E | ∼ Q | G | ∼ M ∝ ∝ r 2 r 2 ∝ | a | ∼ q | a | � = F ( m ) , a = const. = const | a | = • Einstein Equivalence Principle : • WEP • Local Lorentz Invariance (LLI) • Local Position Invariance (LPI)
� TEST OF THE EEP 3 • EEP is the “heart and soul” of General Relativity (GR) : • EEP valid → gravity is governed by a “metric theory of gravity” R. Dicke, Les Houches Summer School of Theoretical Physics: Relativity, Groups and Topology , pp. 165–313, CNUM: C63-07-01 (1964) C. Will, Living Rev. Relativity 17 (2014) • EEP extensively tested experimentally: LLI δ = | c − 2 − 1 | > 10 -23 Isotropy of atomic energy levels: WEP Gravitational red shift: 10-8 Matter waves E¨ otv¨ os LPI Renner Free-fall ∆ ν = (1 + α ) ∆ U 10-9 > 10 -6 Fifth-force c 2 searches 10-10 ν Boulder Princeton E¨ ot-Wash 10-11 E¨ ot-Wash Moscow 10-12 LLR Torsion balance: WEP 10-13 a 1 − a 2 �� a 1 -a 2 > 10 -13 η = (a 1 +a 2 )/2 10-14 ( a 1 + a 2 ) / 2 1 1 1 1 1 1 1 2 2 9 9 9 9 9 9 9 0 0 0 2 1 4 6 7 8 9 0 0 0 0 0 0 0 0 0 0
WEP FOR ANTIMATTER: THE CURRENT PICTURE 4 • Some arguments would suggest the WEP holds for antimatter • Strong theoretical arguments only apply to the idea of antigravity • Morrison (1958), Schiff (1958), Good (1961), etc… • none of them necessarily requires m antimatter = m matter i g • On the experimental side: • neutrinos detected from Supernova 1987A S. Pakvasa et al. , Phys. Rev. Lett. D. 39, 6 (1989) • Shapiro delay of relativistic particles not a test for the EEP G. T. Gillies, Class. Quantum Grav. 29 (2012) ω c − ¯ ω c • p-p cyclotron frequency comparisons: < 9 × 10 − 11 G. Gabrielse et al. , PRL 82 (3198) (1999) ω c • Model dependent, CPT assumption, absolute potentials, … • and others…but none of them is conclusive
WEP FOR ANTIMATTER: WHY TO TEST IT? 5 • Our attempts for a quantum theory of gravity typically result into new interactions which violate the WEP (ex. KK theory ) Int. J. Mod. Phys. D18 , 251–273 (2009) • Some open questions (like dark matter and baryogenesis ) could benefit from a direct measurement Astrophys. Space Sci. 334 , 219–223 (2011) JHEP 1502 , 076 (2015) • Because it’s possible and no direct measurements are available • Previous attempts: • 1967 : Fairbank and Witteborn tried to use positrons Phys. Rev. Lett. 19 , 1049 (1967) • 1989 : PS-200 experiment at CERN tried to use (4 K) p Nucl. Instr. and Meth. B , 485 (1989) • Problem with charged particles: stray E and B fields m g /m i • 2013 : ALPHA experiment at CERN set limit on for H Nature Communications 4, 1785 (2013) m g /m i • > 110 excluded at 95% CL
AEGIS COLLABORATION 6 19 institutes and ~80 people University of University of University of Genova Brescia Bergen CERN, Geneva Max Planck Institute for Nuclear Physics, Heidelberg University College Heidelberg University London University of Lyon 1 Institute of Nuclear Research of the Russian Academy University of Politecnico di University of of Science, Moscow Milano Milano Oslo University Paris-Saclay University of Czech Technical University of and CNRS Pavia University, Prague Trento INFN Sections of Genova, Milano, Padova, Pavia, ETH Zurich Trento Stefan Meyer Institute, Vienna
GRAVITY MEASUREMENT WITH AEgIS EXPERIMENT 7 • The main goal of AEgIS is a direct measurement of the Earth’s local gravitational acceleration g on “cold” beam of H atoms • using a moiré deflectometer • relative intensity relative intensity 0.02 0.04 0.06 0.02 0.04 0.06 0 position-sensitive detecto 0 -1.0 -1.0 “falls” by detector grating 1 grating 2 grating 1 grating 2 grating 3 “falls” by � 2 � L � � -0.5 -0.5 δx = − g δ x � � � � δ position (grating units) position (grating units) v � � � � δ � � � � δ 0 0 � � 0.5 0.5 L L L L atomic atomic beam beam 1.0 1.0 • For H at very low temperature a precision of the order of few – percent can be reached – – “Self focusing” effect (works with – “Self focusing” effect (works with – – −4 σ −4 σ
AEgIS APPARATUS 8 (Over)Simplification of the experimental setup Antiproton traps Deflectometer Positronium p converter p p a r t n o r t i e + s o P � � p � � � � Ps H �
ANTIHYDROGEN PRODUCTION STRATEGY 9 • Cold Rydberg H* atoms can be produced via charge exchange Ps ∗ + ¯ H ∗ + e − p → ¯ n 4 σ ∝ n 4 P s ~ 20 - 30 • P s • Temperature of H given by the temperature of p • Rydberg H: strong dipole moment → Stark acceleration • p are provided from the Antiproton Decelerator (AD) at CERN and are cooled down (electron cooling) in electromagnetic traps
POSITRONIUM FORMATION AND EXCITATION 10 • The second ingredient for our H recipe is the Rydberg positronium which is an exotic atom composed by an e - and a e + e + • para-Ps (125 ps) and ortho-Ps (142 ns) SiO 2 e + • Ps produced via electron capture of e + e + within a nanoporous silica target Si e + AEgIS status: Positrons • e + source: 440 MBq (current 15mCi) transfer line 22 Na e + source plus • Accumulation accumulator bunches of ~10 7 e + moderator up to 8x10 8 e + transfer ε > 0.8
• λ ≈ 1670 nm τ ≈ 10 ns σ � λ ≈ 205 nm τ ≈ 3 ns • � � POSITRONIUM FORMATION AND EXCITATION 11 Excitation efficiency ≈ 30% • • Two-step excitation of Ps: IR fiber Ps target • UV n = 1 3 e + trap • IR n = 3 Rydberg UV prism continuum PHYSICAL REVIEW A 94 , 012507 (2016) (1650 nm) 0.75 eV Laser excitation of the n = 3 level of positronium for antihydrogen production n = 35 n = 3 (205 nm) 6.05 eV n = 2 n = 1
DETECTOR TESTS 12 • Two candidates detectors are currently under investigation: nuclear emulsions 1 and Timepix 2 (from Medipix collaboration) 1) S. Aghion et al. , JINST 12 (2017) P04021 2) N. Pacifico et al. , NIM A 831 (2016) 12–17 • Nuclear emulsions provide excellent position resolution (~2 μ m) but require a very long time to be processed • Timepix is a silicon detector composed a matrix of 256 by 256 pixels which allows a spatial resolution of ~25 μ m
RESULTS: (MINI) MOIRÉ TEST WITH ANTIPROTONS 13 • AEgIS experiment is taking data (H production expected in 2017) • Small-scale test of the Moiré deflectometer with p was performed a M o i r é Contact 12 μ m 40 µ m 25 mm ARTICLE 25 mm emulsions Received 5 Nov 2013 | Accepted 27 Jun 2014 | Published 28 Jul 2014 OPEN DOI: 10.1038/ncomms5538 ´ deflectometer for antimatter A moire Matter moiré antiprotons light
RESULTS: (MINI) MOIRÉ TEST WITH ANTIPROTONS 14 • 146 antiprotons recorded 1 c 50 9.8 µ m 0.8 40 y position (mm) Antiprotons Light 30 0.6 Hits 20 0.4 10 0.2 0 0 d /2 d 0 0 0.2 0.4 0.6 0.8 1 y position x position (mm) as a reference for the alignement (grating shadow) ed! � y = 9.8 ± 0.9(stat) ± 6.4(syst) µm � ured magnetic field of ~10 G at the t ¼ B ~ 10 G measured at of F ¼ 530 ± 50 aN (stat.) ± 350 aN (syst.). • the Moiré position important to note that the mere observation of • consistent with a B ~ 7.4 G
CONCLUSIONS AND FUTURE PLANS 15 • AEgIS aims at probing the WEP on antimatter Goal • No direct measurement so far • AEgIS is taking data Results • The working principle tested using antiprotons • Stray B field → no gravity measurement possible on p Future plans • H production expected to be achieved later this year • First gravity measurements planned for the next years • Longer term plans also include H-H spectroscopy
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