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(Phys.org) —Officially, the radius of a proton is 0.88 ± 0.01 femtometers (fm, or 10-15
m). Researchers attained that value using two methods: first, by
measuring the proton's energy levels using hydrogen spectroscopy, and
second, by using electron scattering experiments, where an electron beam
is shot at a proton and the way the electrons scatter is used to
calculate the proton's size.
But when trying to further improve the precision of the proton
radius value in 2010 with a third experimental technique, physicists
got a value of 0.842 ± 0.001 fm—a difference of 7 deviations from the
official value. These experiments used muonic hydrogen, in which a
negatively charged muon orbits around the proton, instead of atomic
hydrogen, in which an electron orbits around the proton. Because a muon
is 200 times heavier than an electron, a muon orbits closer to a proton
than an electron does, and can determine the proton size more precisely.
This inconsistency between proton radius values, called the "proton
radius puzzle," has gained a lot of attention lately and has led to
several proposed explanations. Some of these explanations include new
degrees of freedom beyond the Standard Model, as well as extra
dimensions.
Now in a new paper published in EPL, physicist Roberto Onofrio
at the University of Padova in Padova, Italy, and the
Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts,
has suggested that the muonic hydrogen experiment may be providing a
hint of quantum gravity. He has proposed that the proton radius puzzle
can be solved by considering a new theory of quantum gravity that is
based on the unification of gravity and the weak force, also called
"gravitoweak unification."
In this theoretical scenario, conventional Newtonian gravity holds at
large distances, but morphs into a different kind of gravitational
interaction at very small scales. Specifically, the strength of the
gravitational interactions is equal to the strength of the weak charged
interactions that occur among subatomic particles. The weak charged
interactions can be considered as manifestations of the quantized
structure of gravity at or below the Fermi scale.
As Onofrio theoretically shows in his paper, quantum gravity of this
nature contributes an additional binding energy to the muonic hydrogen
experiments, which explains the smaller proton radius value. In these
experiments, the proton radius value was measured in terms of an energy
difference between two energy levels, called the Lamb shift.
Onofrio calculated that the gravitational energy contribution in the
atomic hydrogen experiments is about two orders of magnitude smaller
than in the muonic hydrogen experiments, due to the electron's smaller
mass compared to the muon. Onofrio evaluated that the energy
contribution should be noticeable when measuring the Lamb shift of atomic hydrogen,
and its absence in the data could imply the presence of a
flavor-dependent interaction, similar to what happens already for the
well-known charged weak interaction.
"Muonic hydrogen is unique in that it probes small distances at an
unprecedented precision, so it may pick up any small force acting
between the constituents," Onofrio told Phys.org. "Since the
explanation I provide relies on the mass of the nuclei, complementary
tests may be performed on variants of muonic hydrogen currently under
experimental study, more specifically the measurement of the Lamb shift
in muonic deuterium, and muonic helium spectroscopy. In the EPL paper, I make a definite prediction for muonic deuterium, for instance."
Perhaps the most exciting outcome of this work is that it shows that muonic hydrogen may be used to test possible scenarios of gravitoweak unification, with weak interactions providing evidence of gravity's effects at very small scales.
"This work shows that the combination of high-precision spectroscopy
and the use of exotic atoms with size in between ordinary atoms and
nuclei may open a novel way to test physics at the attometer scale, a
scale at which, according to my conjecture developed in a former paper, quantum gravity is acting also under the form of what we now know as weak interactions," Onofrio said.
Onofrio plans to continue to pursue the gravitoweak conjecture in
various directions, and to investigate how it matches with what we know
from the Standard Model of particle physics in which weak interactions
are mixed with electromagnetic ones. He has outlined the future research
landscape in a second paper, listed below.
International team of physicists confirms surprisingly small
proton radius with laser spectroscopy of exotic hydrogen. The initial
results puzzled the world three years ago: the size of the proton (to be
precise, its charge ...
(Phys.org) —Researchers have made the first experimental
determination of the weak charge of the proton in research carried out
at the Department of Energy's Thomas Jefferson National Accelerator
Facility ...
Scientists lobbed a bombshell into the world of sub-atomic
theory on Wednesday by reporting that a primary building block of the
visible Universe, the proton, is smaller than previously thought.
By delving into the interactions between a hydrogen molecule and
muonic hydrogen, the heaviest hydrogen isotope to date, a team of
researchers from academia and Pacific Northwest National Laboratory
created ...
(Phys.org) —Quantum electrodynamics (QED) – the relativistic
quantum field theory of electrodynamics – describes how light and matter
interact – achieves full agreement between quantum mechanics and ...
Scientists and engineers working on the design of the particle
detector for the proposed Long-Baseline Neutrino Experiment celebrated a
major success in January. They operated for the first time a 35-ton ...
If you think it's been cold outside this winter, that's nothing
compared to the deep freeze setting in at the Relativistic Heavy Ion
Collider (RHIC), the early-universe-recreating "atom smasher" at the
U.S. ...
Around 100 years ago a father and his son in north England
conducted an experiment that would revolutionise the way scientists
study molecules. A refined version of their method still remains one of
the most ...
(Phys.org) —The same physics that gives tornadoes their
ferocious stability lies at the heart of new University of Washington
research, and could lead to a better understanding of nuclear dynamics
in studying ...
(Phys.org) —Officially, the radius of a proton is 0.88 ± 0.01 femtometers (fm, or 10-15
m). Researchers attained that value using two methods: first, by
measuring the proton's energy levels using hydrogen spectroscopy, and
second, by using electron scattering experiments, where an electron beam
is shot at a proton and the way the electrons scatter is used to
calculate the proton's size.
(Phys.org) —Officially, the radius of a proton is 0.88 ± 0.01 femtometers (fm, or 10-15
m). Researchers attained that value using two methods: first, by
measuring the proton's energy levels using hydrogen spectroscopy, and
second, by using electron scattering experiments, where an electron beam
is shot at a proton and the way the electrons scatter is used to
calculate the proton's size.
(Phys.org) —Officially, the radius of a proton is 0.88 ± 0.01 femtometers (fm, or 10-15
m). Researchers attained that value using two methods: first, by
measuring the proton's energy levels using hydrogen spectroscopy, and
second, by using electron scattering experiments, where an electron beam
is shot at a proton and the way the electrons scatter is used to
calculate the proton's size.
(Phys.org) —Officially, the radius of a proton is 0.88 ± 0.01 femtometers (fm, or 10-15
m). Researchers attained that value using two methods: first, by
measuring the proton's energy levels using hydrogen spectroscopy, and
second, by using electron scattering experiments, where an electron beam
is shot at a proton and the way the electrons scatter is used to
calculate the proton's size.
(Phys.org) —Officially, the radius of a proton is 0.88 ± 0.01 femtometers (fm, or 10-15
m). Researchers attained that value using two methods: first, by
measuring the proton's energy levels using hydrogen spectroscopy, and
second, by using electron scattering experiments, where an electron beam
is shot at a proton and the way the electrons scatter is used to
calculate the proton's size.
The quark structure of the proton. Credit: Arpad Horvath / Wikipedia.
(Phys.org) —Officially, the radius of a proton is 0.88 ± 0.01 femtometers (fm, or 10-15
m). Researchers attained that value using two methods: first, by
measuring the proton's energy levels using hydrogen spectroscopy, and
second, by using electron scattering experiments, where an electron beam
is shot at a proton and the way the electrons scatter is used to
calculate the proton's size.
The quark structure of the proton. Credit: Arpad Horvath / Wikipedia.
(Phys.org) —Officially, the radius of a proton is 0.88 ± 0.01 femtometers (fm, or 10-15
m). Researchers attained that value using two methods: first, by
measuring the proton's energy levels using hydrogen spectroscopy, and
second, by using electron scattering experiments, where an electron beam
is shot at a proton and the way the electrons scatter is used to
calculate the proton's size.
The quark structure of the proton. Credit: Arpad Horvath / Wikipedia.
(Phys.org) —Officially, the radius of a proton is 0.88 ± 0.01 femtometers (fm, or 10-15
m). Researchers attained that value using two methods: first, by
measuring the proton's energy levels using hydrogen spectroscopy, and
second, by using electron scattering experiments, where an electron beam
is shot at a proton and the way the electrons scatter is used to
calculate the proton's size.
The quark structure of the proton. Credit: Arpad Horvath / Wikipedia.
(Phys.org) —Officially, the radius of a proton is 0.88 ± 0.01 femtometers (fm, or 10-15
m). Researchers attained that value using two methods: first, by
measuring the proton's energy levels using hydrogen spectroscopy, and
second, by using electron scattering experiments, where an electron beam
is shot at a proton and the way the electrons scatter is used to
calculate the proton's size.
The quark structure of the proton. Credit: Arpad Horvath / Wikipedia.
(Phys.org) —Officially, the radius of a proton is 0.88 ± 0.01 femtometers (fm, or 10-15
m). Researchers attained that value using two methods: first, by
measuring the proton's energy levels using hydrogen spectroscopy, and
second, by using electron scattering experiments, where an electron beam
is shot at a proton and the way the electrons scatter is used to
calculate the proton's size.
The quark structure of the proton. Credit: Arpad Horvath / Wikipedia.
(Phys.org) —Officially, the radius of a proton is 0.88 ± 0.01 femtometers (fm, or 10-15
m). Researchers attained that value using two methods: first, by
measuring the proton's energy levels using hydrogen spectroscopy, and
second, by using electron scattering experiments, where an electron beam
is shot at a proton and the way the electrons scatter is used to
calculate the proton's size.
(Phys.org) —Officially, the radius of a proton is 0.88 ± 0.01 femtometers (fm, or 10-15
m). Researchers attained that value using two methods: first, by
measuring the proton's energy levels using hydrogen spectroscopy, and
second, by using electron scattering experiments, where an electron beam
is shot at a proton and the way the electrons scatter is used to
calculate the proton's size.
(Phys.org) —Officially, the radius of a proton is 0.88 ± 0.01 femtometers (fm, or 10-15
m). Researchers attained that value using two methods: first, by
measuring the proton's energy levels using hydrogen spectroscopy, and
second, by using electron scattering experiments, where an electron beam
is shot at a proton and the way the electrons scatter is used to
calculate the proton's size.
(Phys.org) —Officially, the radius of a proton is 0.88 ± 0.01 femtometers (fm, or 10-15
m). Researchers attained that value using two methods: first, by
measuring the proton's energy levels using hydrogen spectroscopy, and
second, by using electron scattering experiments, where an electron beam
is shot at a proton and the way the electrons scatter is used to
calculate the proton's size.
Jan 24, 2013
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