title: Laser spectroscopy of muonic deuterium.
abstract: The deuteron is the simplest compound nucleus, composed of one proton and one neutron. Deuteron properties such as the root-mean-square charge radius rd and the polarizability serve as important benchmarks for understanding the nuclear forces and structure. Muonic deuterium μd is the exotic atom formed by a deuteron and a negative muon μ(-). We measured three 2S-2P transitions in μd and obtain r(d) = 2.12562(78) fm, which is 2.7 times more accurate but 7.5σ smaller than the CODATA-2010 value r(d) = 2.1424(21) fm. The μd value is also 3.5σ smaller than the r(d) value from electronic deuterium spectroscopy. The smaller r(d), when combined with the electronic isotope shift, yields a "small" proton radius r(p), similar to the one from muonic hydrogen, amplifying the proton radius puzzle.
authors: Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany. pohl@uni-mainz.de.
authors: Randolf
authors: R
authors: Pohl
authors: Laboratoire Kastler Brossel, UPMC-Sorbonne Universités, CNRS, Ecole Normale Supérieure-PSL Research University, Collège de France, 75005 Paris, France.
authors: François
authors: F
authors: Nez
authors: LIBPhys, Department of Physics, University of Coimbra, 3004-516 Coimbra, Portugal.
authors: Luis M P
authors: LM
authors: Fernandes
authors: LIBPhys, Department of Physics, University of Coimbra, 3004-516 Coimbra, Portugal.
authors: Fernando D
authors: FD
authors: Amaro
authors: Laboratoire Kastler Brossel, UPMC-Sorbonne Universités, CNRS, Ecole Normale Supérieure-PSL Research University, Collège de France, 75005 Paris, France.
authors: François
authors: F
authors: Biraben
authors: LIBPhys, Department of Physics, University of Coimbra, 3004-516 Coimbra, Portugal.
authors: João M R
authors: JM
authors: Cardoso
authors: I3N, Departamento de Física, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
authors: Daniel S
authors: DS
authors: Covita
authors: Physics Department, Yale University, New Haven, CT 06520-8121, USA.
authors: Andreas
authors: A
authors: Dax
authors: Physics Department, Yale University, New Haven, CT 06520-8121, USA.
authors: Satish
authors: S
authors: Dhawan
authors: Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany.
authors: Marc
authors: M
authors: Diepold
authors: Institut für Strahlwerkzeuge, Universität Stuttgart, 70569 Stuttgart, Germany. Dausinger + Giesen GmbH, Rotebühlstrasse 87, 70178 Stuttgart, Germany.
authors: Adolf
authors: A
authors: Giesen
authors: LIBPhys, Department of Physics, University of Coimbra, 3004-516 Coimbra, Portugal.
authors: Andrea L
authors: AL
authors: Gouvea
authors: Institut für Strahlwerkzeuge, Universität Stuttgart, 70569 Stuttgart, Germany.
authors: Thomas
authors: T
authors: Graf
authors: Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany. Ludwig-Maximilians-Universität, Munich, Germany.
authors: Theodor W
authors: TW
authors: Hänsch
authors: Laboratoire Kastler Brossel, UPMC-Sorbonne Universités, CNRS, Ecole Normale Supérieure-PSL Research University, Collège de France, 75005 Paris, France.
authors: Paul
authors: P
authors: Indelicato
authors: Laboratoire Kastler Brossel, UPMC-Sorbonne Universités, CNRS, Ecole Normale Supérieure-PSL Research University, Collège de France, 75005 Paris, France.
authors: Lucile
authors: L
authors: Julien
authors: Département de Physique, Université de Fribourg, 1700 Fribourg, Switzerland.
authors: Paul
authors: P
authors: Knowles
authors: Institute for Particle Physics, ETH Zurich, 8093 Zurich, Switzerland.
authors: Franz
authors: F
authors: Kottmann
authors: Laboratoire Kastler Brossel, UPMC-Sorbonne Universités, CNRS, Ecole Normale Supérieure-PSL Research University, Collège de France, 75005 Paris, France.
authors: Eric-Olivier
authors: EO
authors: Le Bigot
authors: Physics Department, National Tsing Hua University, Hsinchu 300, Taiwan.
authors: Yi-Wei
authors: YW
authors: Liu
authors: LIBPhys, Department of Physics, University of Coimbra, 3004-516 Coimbra, Portugal. Instituto Politécnico de Coimbra, ISEC, 3030-199, Portugal.
authors: José A M
authors: JA
authors: Lopes
authors: Département de Physique, Université de Fribourg, 1700 Fribourg, Switzerland.
authors: Livia
authors: L
authors: Ludhova
authors: LIBPhys, Department of Physics, University of Coimbra, 3004-516 Coimbra, Portugal.
authors: Cristina M B
authors: CM
authors: Monteiro
authors: Département de Physique, Université de Fribourg, 1700 Fribourg, Switzerland. Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany. I3N, Departamento de Física, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
authors: Françoise
authors: F
authors: Mulhauser
authors: Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany.
authors: Tobias
authors: T
authors: Nebel
authors: Department of Chemistry, Princeton University, Princeton, NJ 08544-1009, USA.
authors: Paul
authors: P
authors: Rabinowitz
authors: LIBPhys, Department of Physics, University of Coimbra, 3004-516 Coimbra, Portugal.
authors: Joaquim M F
authors: JM
authors: dos Santos
authors: Département de Physique, Université de Fribourg, 1700 Fribourg, Switzerland.
authors: Lukas A
authors: LA
authors: Schaller
authors: Institute for Particle Physics, ETH Zurich, 8093 Zurich, Switzerland. Dausinger + Giesen GmbH, Rotebühlstrasse 87, 70178 Stuttgart, Germany. Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
authors: Karsten
authors: K
authors: Schuhmann
authors: Laboratoire Kastler Brossel, UPMC-Sorbonne Universités, CNRS, Ecole Normale Supérieure-PSL Research University, Collège de France, 75005 Paris, France.
authors: Catherine
authors: C
authors: Schwob
authors: Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
authors: David
authors: D
authors: Taqqu
authors: I3N, Departamento de Física, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
authors: João F C A
authors: JF
authors: Veloso
authors: Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany. Institute for Particle Physics, ETH Zurich, 8093 Zurich, Switzerland. Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
authors: Aldo
authors: A
authors: Antognini