Measuring the gravitational acceleration of antimatter with an antihydrogen interferometer

The gravitational force on antimatter has never been directly measured. A method is suggested for making this measurement by directing a low-energy beam of neutral antihydrogen atoms through a transmission-grating interferometer and measuring the gravitationally-induced phase shift in the interference pattern. A 1% measurement of the acceleration due to the Earth's gravitational field (¯ g) should be possible from a beam of about 10⁵ or 10⁶ atoms. If more antihydrogen can be made, a much more precise measurement of¯ g would be possible. A method is suggested for producing an antihydrogen beam appropriate for this experiment.     

The AEgIS antihydrogen gravity experiment

The experimental program of the AEgIS experiment at CERN’s AD complex aims to perform the first measurement of the gravitational interaction of antimatter, initially to a precision of about 1%, to ascertain the veracity of Einstein’s Weak Equivalence Principle for antimatter. As gravity is very much weaker than electromagnetic forces, such an experiment can only be done using neutral antimatter. The antihydrogen atoms also need to be very cold for the effects of gravity to be visible above the noise of thermal motion. This makes the experiment very challenging and has necessitated the introduction of several new techniques into the experimental field of antihydrogen studies, such as pulsed formation of antihydrogen via 3-body recombination with excited state positronium and the subsequent acceleration of the formed antihydrogen using electric gradients (Stark acceleration). The gravity measurement itself will be performed using a classical Moire deflectometer. Here we report on the present state of the experiment and the prospects for the near future.     

A possible gravity measurement with antihydrogen

A neutral probe such as antihydrogen offers appealing experimental advantages, compared to a charged probe such as antiproton, for a measurement of the gravitational behaviour of antimatter. The feasibility of this approach is preliminarily investigated. A direct extension of the sextupolar ring technique used by Paul is not feasible but the use of a straight sextupole seems to be promising.     

Possible measurements of the gravitational acceleration with neutral antimatter

The interest in measuring the gravitational acceleration using neutral antimatter is discussed as well as the advantages compared with using charged antimatter, and a few possible experimental schemes are briefly discussed.     

A Proposal to Measure Antimatter Gravity Using Ultracold Antihydrogen Atoms

The gravitational acceleration of antimatter has never been measured directly. Antihydrogen atoms, being both stable and neutral, are an ideal system for investigating antimatter gravity. Ultralow temperatures in the 10–100 K range are desirable for practical experiments. It is proposed to cool positive antihydrogen ions using laser-cooled ordinary ions. Ultracold neutral antihydrogen atoms might then be obtained by photodetachment. The gravitational acceleration can readily be determined from the time-of-flight between the photodetachment laser pulse and an annihilation detector.     

Gravitational repulsion and Dirac antimatter

Based on an analogy with electron and hole dynamics in semiconductors, Dirac's relativistic electron equation is generalized to include a gravitational interaction using an electromagnetic-type approximation of the gravitational potential. With gravitational and inertial masses decoupled, the equation serves to extend Dirac's deduction of antimatter parameters to include the possibility of gravitational repulsion between matter and antimatter. Consequences for general relativity and related antigravity issues are considered, including the nature and gravitational behavior of virtual photons, virtual pairs, and negative-energy particles. Basic cosmological implications of antigravity are explored—in particular, potential contributions to inflation, expansion, and the general absence of detectable antimatter. Experimental and observational tests are noted, and new ones suggested.     

Elementary Process Theory: a formal axiomatic system with a potential application as a foundational framework for physics supporting gravitational repulsion of matter and antimatter

Theories of modern physics predict that antimatter having rest mass will be attracted by the earth's gravitational field, but the actual coupling of antimatter with gravitation has not been established experimentally. The purpose of the present research was to identify laws of physics that would govern the universe if antimatter having rest mass would be repúlsed by the earth's gravitational field. As a result, a formalized axiomatic system was developed together with interpretation rules for the terms of the language: the intention is that every theorem of the system yields a true statement about physical reality. Seven non‐logical axioms of this axiomatic system form the Elementary Process Theory (EPT): this is then a scheme of elementary principles describing the dynamics of individual processes taking place at supersmall scale. It is demonstrated how gravitational repulsion functions in the universe of the EPT, and some observed particles and processes have been formalized in the framework of the EPT. Incompatibility of Quantum Mechanics (QM) and General Relativity (GR) with the EPT is proven mathematically; to demonstrate applicability to real world problems to which neither QM nor GR applies, the EPT has been applied to a theory of the Planck era of the universe. The main conclusions are that a completely formalized framework for physics has been developed supporting the existence of gravitational repulsion and that the present results give rise to a potentially progressive research program.     

What Would Be Outcome of a Big Crunch?

I suggest the existence of a still undiscovered interaction: repulsion between matter and antimatter. The simplest and the most elegant candidate for such a force is gravitational repulsion between matter and antimatter. I argue that such a force may give birth to a new Universe; by transforming an eventual Big Crunch of our Universe, to an event similar to Big Bang. In fact, when a collapsing Universe is reduced to a supermassive black hole of a small size, a very strong field of the conjectured force may create particle-antiparticle pairs from the surrounding quantum vacuum. The amount of antimatter created from the physical vacuum is equal to the decrease of mass of “black hole Universe” and violently repelled from it. When the size of the black hole is sufficiently small, the creation of antimatter may become so huge and fast, that matter of our Universe may disappear in a fraction of the Planck time. So fast transformation of matter to antimatter may look like a Big Bang with initial size about 30 orders of magnitude greater than the Planck length, questioning the need for inflation. In addition, a Big Crunch, of a Universe dominated by matter, leads to a new Universe dominated by antimatter, and vice versa; without need to invoke CP violation as explanation of matter-antimatter asymmetry. Simply, our present day Universe is dominated by matter, because the previous Universe was dominated by antimatter.     

反质子间相互作用的研究

随着对反物质研究的深入,人们需要迫切知道反质子之间的相互作用力是怎样的,是否与质子之间的作用是对称的。对这个作用力的测量,有助于我们理解反物质原子核的形成机制以及对物质-反物质对称性的理解。为此,STAR合作组利用相对论重离子加速器中金核-金核碰撞中产生的丰富的反质子,通过反质子-反质子动量关联函数的测量,并扣除了通过其他粒子衰变过来的次级反质子与其他反粒子关联的污染,精确地构建了反质子-反质子关联函数。然后,结合量子多粒子关联理论,定量提取出反质子-反质子的有效力程和散射长度这两个基本作用参数。研究表明,在实验精度内,反质子间的相互作用与正质子保持一致。反质子-反质子之间的强相互作用存在着吸引,它们可以克服由于同号（负电荷）的反质子-反质子之间的库仑排斥而结合成反物质原子核。这项研究首次实现了对反物质间相互作用力的测量,为进一步研究反原子核的形成和属性奠定了基础。同时为CPT对称性的检验提供了一种新的方式,对人类深刻认识物质世界的构成及其运动规律具有重要意义。With undergoing researches on antimatter physics, it is crucial to understand what the interaction between antiprotons is. Is it the same as the interaction between protons? This measurement will definitely help us to understand the formation mechanism of antimatter nuclei as well as the symmetry of matter and antimatter. In this context, our STAR collaboration measured the correlation function of antiproton-antiproton pairs from 200 GeV/c Au+Au collisions. After substracting the residual correlation due to the secondary antiprotons that decayed from other particles, the primary antiproton-antiproton correlation function is extracted. By applying the quantum theory of multi-particle correlation, two key parameters that characterize the corresponding strong interaction:namely, the scattering length (f₀) and effective range (d₀) were obtained. Within error bars, it is found that the f₀ and d₀ for the antiproton-antiproton interaction are consistent with their antiparticle counterparts -the ones for the proton-proton interaction. Like the force that holds ordinary protons together within the nuclei of atoms, the force between antiprotons is attractive and strong, which overcomes the tendency of the like (negatively) charged particles to repel one another, and allows the antiprotons to bind to form antinucleus. The current measurement is for the first time to measure the interaction between antimatter, it offers a foundation to understanding the structure of more-complex antinuclei and their properties. Also our measurement offers a new way to test the CPT symmetry, which has an important impact for human beings to understand the law of motion in our world.     

Particle manipulation techniques in AEgIS

The AEgIS experiment (http://aegis.web.cern.ch) will measure the gravitational acceleration g of antihydrogen. Once performed this could be the first direct test of the gravitational interaction between matter and antimatter. In the AEgIS experiment a beam of antihydrogen will travel horizontally along a path of about 1 m trough a moir?? deflectometer followed by a position sensitive detector. The g value will be obtained measuring the vertical displacement of the annihilation patterns. Before producing the beam, several tasks have to be performed mainly involving positron and electron plasma manipulation and particles cooling in Malmberg-Penning traps. The AEgIS experiment is currently under construction at CERN, meanwhile several tests involving particle manipulation and particle cooling are in progress. In this report some experimental results involving diocotron manipulation of plasma will be presented.     

Quark deconfinement in antiproton annihilation at rest on light nuclei

The production of low-energy antimatter provides unique opportunities to search for new physics in an unexplored regime. Testing gravitational interactions with antimatter is one such opportunity. Here a scenario based on Lorentz and CPT violation in the Standard-Model Extension is considered in which anomalous gravitational effects in antimatter could arise.     

ALPHA: antihydrogen and fundamental physics

Detailed comparisons of antihydrogen with hydrogen promise to be a fruitful test bed of fundamental symmetries such as the CPT theorem for quantum field theory or studies of gravitational influence on antimatter. With a string of recent successes, starting with the first trapped antihydrogen and recently resulting in the first measurement of a quantum transition in anti-hydrogen, the ALPHA collaboration is well on its way to perform such precision comparisons. We will discuss the key innovative steps that have made these results possible and in particular focus on the detailed work on positron and antiproton preparation to achieve antihydrogen cold enough to trap as well as the unique features of the ALPHA apparatus that has allowed the first quantum transitions in anti-hydrogen to be measured with only a single trapped antihydrogen atom per experiment. We will also look at how ALPHA plans to step from here towards more precise comparisons of matter and antimatter.     

The matter‐antimatter interpretation of Kerr spacetime

Repulsive gravity is not very popular in physics. However, one comes across it in at least two main occurrences in general relativity: in the negative‐r region of Kerr spacetime, and as the result of the gravitational interaction between matter and antimatter, when the latter is assumed to be CPT‐transformed matter. Here we show how these two independent developments of general relativity are perfectly consistent in predicting gravitational repulsion and how the above Kerr negative‐r region can be interpreted as the habitat of antimatter. As a consequence, matter particles traveling along vortical geodesics can pass through the throat of a rotating black hole and emerge as antimatter particles (and vice versa). An experimental definitive answer on the gravitational behavior of antimatter is awaited in the next few years.

     

AEGIS at CERN: Measuring Antihydrogen Fall

The main goal of the AEGIS experiment at the CERN Antiproton Decelerator is testing fundamental laws such as the weak equivalence principle (WEP) and the CPT symmetry. In the first phase of AEGIS, a beam of antihydrogen will be formed whose fall in the gravitational field is measured in a Moirè deflectometer; this will constitute the first test of the WEP with antimatter.     

Antihydrogen production and precision experiments. The ATHENA collaboration

The study of CPT invariance with the highest achievable precision in all particle sectors is of fundamental importance for physics. Equally important is the question of the gravitational acceleration of antimatter. In recent years, impressive progress has been achieved at the Low Energy Antiproton Ring (LEAR) at CERN in capturing antiprotons in specially designed Penning traps, in cooling them to energies of a few milli-electron volts, and in storing them for hours in a small volume of space. Positrons have been accumulated in large numbers in similar traps, and low energy positron or positronium beams have been generated. Finally, steady progress has been made in trapping and cooling neutral atoms. Thus the ingredients to form antihydrogen at rest are at hand. We propose to investigate the different methods to form antihydrogen at low energy, and to utilize the best of these methods to capture a number of antihydrogen atoms sufficient for spectroscopic studies in a magnetostatic trap. Once antihydrogen atoms have been captured at low energy, spectroscopic methods can be applied to interrogate their atomic structure with extremely high precision and compare it to its normal matter counterpart, the hydrogen atom. Especially the 1S-2S transition, with a lifetime of the excited state of 122 ms and thereby a natural linewidth of 5 parts in 10¹⁶, offers in principle the possibility to directly compare matter and antimatter properties at a level of 1 part in 10¹⁸. Additionally, comparison of the gravitational masses of hydrogen and antihydrogen, using either ballistic or spectroscopic methods, can provide direct experimental tests of the Weak Equivalence Principle for antimatter at a high precision. This revised version was published online in August 2006 with corrections to the Cover Date.     

Prospects for antiproton experiments at Fermilab

Fermilab operates the world’s most intense antiproton source. Newly proposed experiments can use those antiprotons either parasitically during Tevatron Collider running or after the end of the Tevatron Collider program. For example, the annihilation of 5 to 8 GeV antiprotons is expected to yield world-leading sensitivities to hyperon rare decays and CP violation. It could also provide the world’s most intense source of tagged D ⁰ mesons, and thus the best near-term opportunity to study charm mixing and, via CP violation, to search for new physics. Other measurements that could be made include properties of the X(3872) and the charmonium system. An experiment using a Penning trap and an atom interferometer could make the world’s most precise measurement of the gravitational force on antimatter. These and other potential measurements using antiprotons offer a great opportunity for a broad and exciting physics program at Fermilab in the post-Tevatron era.     

Does antimatter emit a new light?

Contemporary theories of antimatter have a number of insufficiencies which stimulated the recent construction of the new isodual theory based on a certain anti-isomorphic map of all (classical and quantum) formulations of matter called isoduality. In this note we show that the isodual theory predicts that antimatter emits a new light, called isodual light, which can be distinguished from the ordinary light emitted by matter via gravitational interactions (only). In particular, the isodual theory predicts that all stable antiparticles such as the isodual photon, the positron and the antiproton experience antigravity in the field of matter (defined as the reversal of the sign of the curvature tensor). The antihydrogen atom is therefore predicted to: experience antigravity in the field of Earth; emit the isodual photon; and have the same spectroscopy of the hydrogen atom, although subjected to an anti-isomorphic isodual map. In this note we also show that the isodual theory predicts that bound states of elementary particles and antiparticles (such as the positronium) experience ordinary gravitation in both fields of matter and antimatter, thus bypassing known objections against antigravity. A number of intriguing and fundamental, open theoretical and experimental problems of “the new physics of antimatter” are pointed out. This revised version was published online in August 2006 with corrections to the Cover Date.     

Measurement of the gravitational acceleration of antihydrogen

The gravitational force acting on antiparticles has never been directly measured to date. A method for measuring the gravitational effects on antihydrogen by equilibrating the gravitational force with a magnetic gradient is discussed. The systematic and statistical errors inherent to the measurement will be presented. It will be shown that a measurement of gravity at 1% can be realised using ∼ 5 × 10⁵ antihydrogen atoms. The production of antihydrogen atoms in conditions suitable for the measurement is also discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Outline of a classical theory of quantum physics and gravitation

It is argued that in the manner in which the Galilean-Newtonian physics may be said to have explained the Ptolemaic-Copernican theories in terms which have since been called classical, so also Milner's theories of the structure of matter may be said to explain present day quantum and relativistic theory. In both cases the former employ the concept of force and the latter, by contrast, are geometrical theories. Milner envisaged space as being stressed, whereas Einstein thought of it as strained. Development of Milner's theory from criticisms and suggestions made by Kilmister has taken it further into the realms of quantum and gravitational physics, where it is found to give a more physically comprehensible explanation of the phenomena. Further, it shows why present day quantum theory is cast in a statistical form. The theory is supported by many predictions such as the ratio of Planck's constant to the mass of the electron, the value of the fine structure constant and reason for apparent variations in past measurements, the magnetic moment of the electron and proton of the stable particles such as the neutron Λ and Σ together with the kaon, and a relation between the universal gravitational constant and Hubble's constant—all within published experimental accuracy. The latest results to be accounted for by the theory are the masses of the newly discovered ψ particles and confirmation of the value of the decay of Newton's gravitational constant obtained from lunar measurements. While this paper is being typed, new particles are rapidly being discovered—the latest being a neutral ψ particle. A short Appendix discusses the significance of these.     

Possible measurement of the gravitational acceleration of antiprotons in the presence of “strong” patch effect electrical fields

The role of electrical fields due to the patch effect in a Penning trap used to measure the Earth's gravitational accelerationg on antiprotons is analyzed. Theg measurement method is based on the study of the gravity-induced shift of the center of the radial orbits of particles stored in a Penning trap having the magnetic field perpendicular to the direction of the force of gravity. The analysis of the radial motion shows that forces originating from patch effect electrical fields about ten times stronger than the force of gravity, still allow a differential measurement ofg for antiprotons and matter particles (H^–). As the precision of the measurement is affected by the particle axial energy distribution, particular care must be devoted to injecting antiprotons and H^– ions into the trap with very similar initial conditions.