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Kaplan Muonium Gravity Talk Mu2e-II-Snowmass.Pdf MAGE: Probing Antimatter Gravity MICE-U.S. Plans withDaniel Muons M. Kaplan US Spokesperson, MICE Collaboration Daniel M. Kaplan Mu2e-II Snowmass 2021 Workshop MuTAC Review 26 Aug.Fermilab 2020 16–17 March, 2006 Outline • Motivation: Some history • Experimental approach • Required R&D • Conclusions D. M. Kaplan, IIT: Mu2e-II Snowmass Talk Probing an*ma,er gravity with muons 8/26/20 2/20 Brief History generalantiparticles a } phenomenon • 1928: Dirac postulates antielectrons • 1932: Anderson discovers positron • 1955: Chamberlain & Segrè discover antiproton • 1956: M. Goldhaber notes “baryon asymmetry of the universe” (BAU) - now generally believed BAU arose through CP violation (discovered 1964) - but, pre-1964, more plausible to postulate gravitational repulsion between matter and antimatter – “antigravity”! D. M. Kaplan, IIT: Mu2e-II Snowmass Talk Probing an*ma,er gravity with muons 8/26/20 3/20 Brief History Led to Witteborn–Fairbank experiment: F. C. Witteborn & W. M. Fairbank, • “Experimental Comparison of the Gravitational Force on Freely measure direction of “falling” positrons Falling Electrons and Metallic Whitteborn & FairbanksElectrons,” Expt PRL 19,1049 (1967) - preliminary e– test ended inconclusively, e+ neverFamous attempted experiment attempted to measure gravitational force • LANL-ledon team positrons. proposed (1986) p̄ gravity experiment at LEAR ➢electrons in copper drift tube - also inconclusive➢measured – stray maximum EM forces TOF on charged particles too challenging? Only managed to set a limit on • Moral: needelectrons: neutral Fantimatter < 0.09mg - H̅ at AD:Never ALPHA, published AEgIS, GBAR (made?) : - Muoniummeasurement at PSI (FNAL)? withVirtue positrons No hadronic uncertainty PRL 19,1049 (1967) D. M. Kaplan, IIT: Mu2e-II Snowmass Talk Probing an*ma,er gravity with muons 8/26/20 4/20 Thomas Phillips Friday, October 26, 2012 25 Studying Antimatter Gravity C. Amole et al., “Description and Experimentally, still unknown if antimatter first application of a new technique • to measure the gravitational mass of antihydrogen,” Nature Comm. 4 falls up or down! Or whether ḡ – g = 0 or ε (2013) 1785: –65 < ḡ/g < 110 T. J. Phillips, “Antimatter gravity - in principle a simple interferometric studies with interferometry,” Hyp. measurement with slow antihydrogen beam: Int. 109 (1997) 357 Mask Time- de Broglie grating ½ gt2 = 5 µm waves of- !"=# interfere Flight Detector - well within v ~ 103 m/s interferometry H̅ state of the art e+ p̄ ~ 1 m ~ 1 m In either case, Equivalence Principle - if ḡ = – g, antigravity as discussed above must be modified! Thomas Phillips Preliminary Draft - if ḡ = g ± ε, need to modify theory Dofuke Ugravityniversity (scalar5 + vector + tensor), or add “5th force” to the known 4 D. M. Kaplan, IIT: Mu2e-II Snowmass Talk Probing an*ma,er gravity with muons 8/26/20 5/20 Studying Antimatter Gravity • Besides antihydrogen (and maybe positronium), only one other antimatter system conceivably amenable to gravitational measurement: • Muonium (M or Mu) — ‣ hydrogenic atom with µ+ replacing the proton o easy to produce but hard to study! • Measuring muonium gravity — if feasible — could be1st (only?) gravitational measurement of a ⎧lepton ⎩2nd-generation particle D. M. Kaplan, IIT: Mu2e-II Snowmass Talk Probing an*ma,er gravity with muons 8/26/20 6/20 Muonium • Much is known about muonium... - a purely leptonic atom, V. W. Hughes et al., “Formation of Muonium and Observation discovered 1960 of its Larmor Precession,” Phys. Rev. Lett. 5, 63 (1960) February4,2008 14:21 ProceedingsTrimSize: 9inx6in hughes˙mem˙KJ˙muonium τM = τµ = 2.2 µs 2 2 2 P3/2 F=2 + 74 MHz readily produced when µ stop in matter 2 F=1 - 2 S 10922 MHz 1/2 F=1 558 MHz 1047 MHz F=0 F=1 chemically, almost identical to hydrogen 187 MHz - λ= 244 nm 2 F=0 2 P1/2 atomic spectroscopy well studied 2 455 THz - λ= 244 nm forms certain compounds (MuCl, NaMu,...) F=1 - 2 4463 MHz 1 S1/2 F=0 Figure 1. Energy levels of the hydrogen-like muonium atom for states with principal quantum numbers n=1 and n=2. The indicated transitions couldbeinducedtodateby “ideal testbed” for QED, search for newmicrowave forces, or laser spectroscopy. precision High accuracy has been achieved for the transitions - which involve the ground state. The atoms can be produced mostefficiently for n=1. measurement of muon properties, etc. charge and spin carrying constituents inside the proton are not known to sufficient accuracy. D. M. Kaplan, IIT: Mu2e-II Snowmass Talk Probing an*ma,er gravity with muons 8/26/20 High energy scattering experiments7/20 have shown for leptons nostructure down to dimensions of 10−18 m. They may therefore be considered ”point- like”. As a consequence, complications as those arising fromthestructure of the nucleus in natural atoms and such artificial systems that contain hadrons are absent in the muonium atom (M = µ+e−), which is the bound state of two leptons, a positive muon (µ+)andanelectron(e) 1,2.Itmay be considered a light hydrogen isotope. The dominant interaction within the muonium atom (see Fig. 1)iselec- tromagnetic. In the framework of bound state Quantum Electrodynamics (QED) the electromagnetic part of the binding can be calculated to suffi- ciently high accuracy for modern high precision spectroscopy experiments. There are also contributions from weak interactions arisingthroughZ0- boson exchange and from strong interactions owing to vacuum polarization Studying Muonium Gravity arXiv:physics/0702143v1 [physics.atom-ph] Testing Gravity with Muonium K. Kirch∗ Paul Scherrer Institut (PSI), CH-5232 Villigen PSI, Switzerland (Dated: February 2, 2008) − Recently a new technique for the production of muon (µ+)andmuonium(µ+e )beamsofun- precedented brightness has been proposed. As one consequence and using a highly stable Mach- Zehnder type interferometer, a measurement of the gravitational accelerationg ¯ of muonium atoms at the few percent level of precision appears feasible within100daysofrunningtime.Theinertial mass of muonium is dominated by the mass of the positively charged - antimatter - muon. The measurement ofg ¯ would be the first test of the gravitational interaction of antimatter, of a purely leptonic system, and of particles of the second generation. 2 ity experiment, then there would be no telling what ex- PACS numbers: citing physics could follow.” L ~ 1.4 cm x The muonium experiment appears feasible now be- cause of two recent inventions: (i) a new technique to ~ 43 mrad stop, extractThe and gravitational compress a high acceleration intensity beam of pos- of antimatter has notΘ Matomscomesfromthefactthattheinertialmassof itive muons, to reaccelerate the muons to 10 keV and fo- w<100 µ m cusbeen them into measured a beam spot so of far. 100 µmdiameteroreven An experiment with antiprotons the muon is some 207 times larger than the one of the d~100 nm less(see [14]; and [1] (ii) and a new references technique to therein) efficiently convert did not succeed because electron, thus, muonium is almost completey, to 99.5%, the muons to M atoms in superfluid helium at or below 0.5of K in the which extreme they thermalize diffi andculty from to which suffi theyciently get Source shield theInterferometer inter- antimatter. Detection An interesting feature is that M atoms are boostedaction by 270K region perpendicular from to electromagnetic the surface when they fields. For a simi- almost exclusively produced at thermal energies by stop- leave into vacuum [15]. lar reason, results of measurements withFIG. electrons 1: Scheme of [2] the experimental are ping setup:µ the+ Min beam matter comes which they often leave again as ther- Assuming an existing surface muon beam of highest from the cryogenic µ+ beam target on the left hand side, intensity as input, see e.g. [16], it should be possible discussed veryD. M. Kaplan, IIT: Mu2e-II Snowmass Talk controversial and the planenters to andProbing an*ma,er gravity with muons eventuallypartially traverses themalized, interferometer hydrogen-like, and reaches8/26/20 M atom. However,8/20 up to until re- to obtain an almost monochromatic beam of M atoms the detection region on the right hand side. The dimensions (∆E/Ecompare0.5/270) with with positrons a velocity of was about never 6300 m/s realized.are not to Not scale a andffected the diffractioncently, angle θ is in a reality gravitational smaller experiment with muonium would (corresponding≈ to 270 K or a wavelength λ 5.6A)˚ and than the divergence. by these problems are neutral≈ systems like antihydrogen have been science fiction. The reason for this publication a1-dimensionaldivergenceof!∆E/E 43 mrad at a rateand, of about consequently, 105 s−1 Matoms[15].Thisisamanyorders considerable≈ effort today is devoted is, that there is now the real chance to perform such an of magnitudeto the preparation brighter beam than of available suitable up to samples now. ferometer. of antihydrogen The gravitational phaseexperiment shift to be observed within the next few years. Following(compare the approach [1]). A of possibility [5, 6, 8, 9] a Mach-Zehnder to measureis the (using effect the notation of grav- of [9]) type interferometer should be used in the muonium ex- An experiment with M atoms would constitute the 2π 2 periment.itation The on principle neutral with particles the source, the is three via grat- a phase acquired inΦg = the g τ first0.003. test of the(3) gravitational interaction of antimatter inggravitational interferometer and potential the detection in region a suitably is sketched built interferometer,d ≈ in Fig. 1. We assume here three identical gratings and This is rather small but still an orderwith of magnitudematter. larger It would also be the first and probably usedemonstrated the first two for setting in the up the classic interference Colella–Overhauser–Werner pattern than the phase shift due to theunique acceleration test induced of particles of the second generation. While which(COW) is scanned experiment by moving the third [3].
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