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Our group is part of the GBAR collaboration (Gravitational Behavior of Antihydrogen At Rest), whose aim is to measure the effect of gravity on antihydrogen atoms by letting them fall in the gravitational field of the Earth. This international collaboration (involving research groups from France, Switzerland, UK, Russia, and Japan) was approved by CERN in May 2012, and is to be run at the CERN Antiproton Decelerator (AD) at the start of the new ELENA ring in 2014.

The production of a significant amount of antihydrogen goes through a series of steps involving the creation, trapping, and cooling of positrons and antiprotons, as well as the formation of positronium atoms (neutral particles composed of one electron and one positron). As a byproduct, significant amounts of cold and dense anti-particles are expected to be created and trapped for relatively long times, opening up the possibility to study "exotic" states of (anti)matter.

Our group is involved in the following research topics:

  • The determination of the cross-sections of the antiproton-positronium reactions that should produce positively charged antihydrogen ions. These reactions constitute a crucial step in the production of antihydrogen for the GBAR experiment.
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  • The investigation of "exotic" states of antimatter under extreme conditions of temperature and density. In particular, we have studied the static and dynamical properties of small (nanometric) electron-positron clusters, for which the density is so high that these systems display a "metallic" character. We are currently studying the dynamical formation of Bose-Einstein condensates of positronium atoms trapped in porous silica materials. Our results indicate that the BEC formation should occur on a timescale faster than the lifetime of ortho-positronium (142 ns).


Gravity, antimatter and the Dirac-Milne universe.
G. Chardin and G. Manfredi, preprint (2018).

Cosmological structure formation with negative mass.
G. Manfredi, J.-L. Rouet, B. Miller, G. Chardin, Phys. Rev. D 98, 023514 (2018).

Towards a test of the Weak Equivalence Principle of gravity using anti-hydrogen at CERN. Banerjee, D., Biraben, F., Charlton, M., Clade, P., Comini, P., Crivelli, P., … Yamazaki, Y. In CONFERENCE ON PRECISION ELECTROMAGNETIC MEASUREMENTS (CPEM 2016). 345 E 47TH ST, NEW YORK, NY 10017 USA: IEEE (2016).

"Resonant antihydrogen formation in antiproton–positronium collisions", R. Lazauskas, P.-A. Hervieux, M. Dufour and M. Valdes, J. Phys. B 49, 094002 (2016).

"Bose–Einstein condensation of positronium: modification of the s-wave scattering length below the critical temperature", O. Morandi, P.-A. Hervieux and G. Manfredi, J. Phys. B: At. Mol. Opt. Phys. 49, 084002 (2016).

"The GBAR antimatter gravity experiment"
P. Perez et al., Hyperfine Interactions 233, 21 (2015).

"Theoretical study of the thermalization of the positronium interacting with heavy mass atoms"
O. Morandi and P.-A. Hervieux, J. Phys.: Conf. Ser. 618, 012011 (2015).

"Hbar+ production from collisions between positronium and keV antiprotons for GBAR",
P. Comini, P. -A. Hervieux and F. Biraben, Hyperfine Interactions 228, 159 (2014).

"Study of the quenched lifetime of an interacting positronium gas",
O. Morandi, P. -A. Hervieux, and G. Manfredi, J. Phys. B: At. Mol. Opt. Phys. 47 , 155202 (2014).

"Study of the positronium thermalization in porous materials",
O. Morandi, P. -A. Hervieux, and G. Manfredi, Eur. Phys. J. D 68, 84 (2014).

"The Gbar project, or how does antimatter fall?",
P. Indelicato et al., Hyperfine Interactions 228, 141 (2014).

"Bose-Einstein condensation of positronium in silica pores",
O. Morandi, P. -A. Hervieux, and G. Manfredi, Phys. Rev. A 89, 033609 (2014).

"Hbar+ production from collisions between antiprotons and excited positronium: cross sections calculations in the framework of the GBAR experiment"
Pauline Comini and Paul-Antoine Hervieux, New J. Phys. 15, 095022 (2013).

"Bose-Einstein-condensation dynamics with a quantum-kinetic approach"
O. Morandi, P. -A. Hervieux and G. Manfredi, Phys. Rev. A 88, 023618 (2013).

"Hbar and Hbar+ production cross sections for the GBAR experiment"
P. Comini and P. -A. Hervieux, J. Phys.: Conf. Ser. 443 , 012007 (2013).

"Gravitational behavior of antihydrogen at rest"
P. Debu et al. (GBAR Collaboration), Hyperfine Interactions 212, 51 (2012).

"Adiabatic Cooling of Trapped Non-Neutral Plasmas"
G. Manfredi and P. -A. Hervieux, Phys. Rev. Lett. 109, 255005 (2012).

"Nonlinear dynamics of electron–positron clusters"
G. Manfredi, P. -A. Hervieux and F. Haas, New J. Phys. 14, 075012 (2012).