Kaonic hydrogen
Encyclopedia
Kaonic hydrogen is an exotic atom
consisting of a negatively charged kaon
orbiting a proton
.
Such particles were first seen, through their X-ray
spectrum
, at the KEK
in Tsukuba
, Japan
. More detailed studies have been performed at DAFNE
in Frascati
, Italy
. Kaonium has been created in very low energy collisions of kaons with protons. In the experiments called DAFNE exotic atoms research (DEAR), kaons were produced by the decay of a φ meson
at the φ factory in DAFNE. The experiment saw X-rays from three states in kaonic hydrogen. The ground state binding energy
was measured to be 193 ± 37 (statistical) ± 6 (systematic) eV
.
Unlike in the hydrogen atom
, where the electron
and proton interact only through quantum electrodynamics
, kaons and protons interact also by nuclear force
s. This results in the atom being metastable, with a very small lifetime. This lifetime is given as a resonance width
of 249 ± 111 (statistical) ± 30 (systematic) eV
. The lifetime of kaonium is expected to be as low as .
Exotic atom
An exotic atom is an otherwise normal atom in which one or more sub-atomic particles have been replaced by other particles of the same charge. For example, electrons may be replaced by other negatively charged particles such as muons or pions...
consisting of a negatively charged kaon
Kaon
In particle physics, a kaon is any one of a group of four mesons distinguished by the fact that they carry a quantum number called strangeness...
orbiting a proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
.
Such particles were first seen, through their X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
, at the KEK
KEK
, known as KEK, is a national organization whose purpose is to operate the largest particle physics laboratory in Japan, which is situated in Tsukuba of Ibaraki prefecture. Established in 1997. The term "KEK" is also used to refer to the laboratory itself, which employs approximately 900 employees...
in Tsukuba
Tsukuba, Ibaraki
is a city located in Ibaraki Prefecture, Japan. It is known as the location of the , a planned city developed in the 1960s.As of 2008, the city has an estimated population of 207,394 and a population density of 730 persons per km². Its total area is 284.07 km².Mount Tsukuba, particularly well-known...
, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. More detailed studies have been performed at DAFNE
DAFNE
For the French collider DAPHNE, see Détecteur à Grande Acceptance pour la Physique Photonucléaire Expérimentale For "Dose Adjustment For Normal Eating", see Insulin therapy...
in Frascati
Frascati
Frascati is a town and comune in the province of Rome in the Lazio region of central Italy. It is located south-east of Rome, on the Alban Hills close to the ancient city of Tusculum. Frascati is closely associated with science, being the location of several international scientific...
, Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
. Kaonium has been created in very low energy collisions of kaons with protons. In the experiments called DAFNE exotic atoms research (DEAR), kaons were produced by the decay of a φ meson
Phi meson
In particle physics, the phi meson is a vector meson formed of a strange quark and a strange antiquark. It has a mass of .-Overview:-See also:*Charmonium*List of mesons*List of particles*Quark model...
at the φ factory in DAFNE. The experiment saw X-rays from three states in kaonic hydrogen. The ground state binding energy
Binding energy
Binding energy is the mechanical energy required to disassemble a whole into separate parts. A bound system typically has a lower potential energy than its constituent parts; this is what keeps the system together—often this means that energy is released upon the creation of a bound state...
was measured to be 193 ± 37 (statistical) ± 6 (systematic) eV
Electronvolt
In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
.
Unlike in the hydrogen atom
Hydrogen atom
A hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a single positively-charged proton and a single negatively-charged electron bound to the nucleus by the Coulomb force...
, where the electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
and proton interact only through quantum electrodynamics
Quantum electrodynamics
Quantum electrodynamics is the relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quantum mechanics and special relativity is achieved...
, kaons and protons interact also by nuclear force
Nuclear force
The nuclear force is the force between two or more nucleons. It is responsible for binding of protons and neutrons into atomic nuclei. The energy released causes the masses of nuclei to be less than the total mass of the protons and neutrons which form them...
s. This results in the atom being metastable, with a very small lifetime. This lifetime is given as a resonance width
Resonance (particle physics)
In particle physics, a resonance is the peak located around a certain energy found in differential cross sections of scattering experiments. These peaks are associated with subatomic particles and their excitations...
of 249 ± 111 (statistical) ± 30 (systematic) eV
Electronvolt
In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
. The lifetime of kaonium is expected to be as low as .