From Newsgroup: sci.physics
Jan Panteltje <
alien@comet.invalid> wrote or quoted:
This rare phenomenon, known as light-on-light scattering, challenges the classical idea
that light waves pass through each other untouched.
Generated by AI, read below:
1. About light-on-light scattering
2. What the Scientists in the report found out
3. Some terms explained for laymen
4. "2." explained for laymen
1. About light-on-light scattering
The concept of light-by-light scattering - that is, photons
interacting with each other indirectly through quantum
effects - has been predicted by quantum electrodynamics (QED)
since the 1930s. The theoretical foundation was laid soon after
QED itself was developed in the late 1920s and early 1930s, with
the understanding that photons can scatter off one another via
virtual charged particles, even though classical electromagnetism
says light beams pass through each other without interaction.
However, the actual experimental observation of light-by-light
scattering is extremely challenging due to the effect's
tiny probability. It was only very recently - in 2017 - that the
ATLAS and CMS experiments at the Large Hadron Collider (LHC)
at CERN reported the first direct observation of elastic
light-by-light scattering in ultraperipheral heavy-ion
collisions, confirming the decades-old theoretical prediction
2. What the Scientists in the report found out
The authors identify that tensor mesons (particles with spin-2)
generate an infinite tower of excitations in holographic QCD,
and their contributions have not been adequately included in
previous calculations. Excitations of tensor mesons contribute
specifically to the symmetric short-distance region, where
all photon virtualities are large, thus directly addressing the
noted deficit. Including these tensor meson towers can "fill
the gap" left by the axial-vector sector
Quantitative analysis demonstrates that tensor mesons chiefly
contribute at low energies (photon virtualities below 1.5 GeV),
with this positive contribution being significant. At intermediate
("mixed") energies, their effect is smaller, and at very high
energies, it becomes negligible. When this component is included,
it bridges the gap seen between the most recent dispersive
calculations and lattice QCD results for the total hadronic
light-by-light contribution to the muon's anomalous magnetic
moment, potentially resolving a notable portion of the discrepancy
3. Some terms explained for laymen
A meson is a type of subatomic particle made from one quark
and one antiquark held together by the strong force. Mesons
are strongly interacting particles, and they help hold
together protons and neutrons inside atomic nuclei.
Spin is a fundamental property of particles, similar to electric
charge or mass. For elementary (and composite) particles, spin
refers to a type of intrinsic angular momentum. It's measured in
units of the reduced Planck constant. For example, photons have
spin 1, electrons have spin 1/2, and tensor mesons have spin 2.
Holographic QCD is a theoretical framework inspired by string
theory that approaches the strong force (which binds quarks
in protons, neutrons, and mesons) using ideas from gravity
in higher-dimensional spaces. It often predicts many related
particle "states" called a tower of excitations, much like
a string that can vibrate at multiple frequencies.
In quantum mechanics, "light-by-light scattering" refers to photons
interacting with each other via virtual charged particles like
mesons. This effect makes a tiny but important contribution to the
muon's anomalous magnetic moment ("g-2") - an ultra-precise property
of the muon that serves as a critical test of particle physics.
In particle physics, a "virtual" photon is a photon that doesn't
behave quite like ordinary light. It's a mathematical way to
describe force-carrying particles in quantum field theory, and
its "virtuality" means the amount by which its energy and
momentum differ from what a real photon would have.
4. "2." explained for laymen
When physicists use the holographic QCD approach, they not only
get contributions from certain types of mesons (like axial-vector
mesons), but also from a whole set - called an "infinite tower"
- of tensor mesons, which are mesons with spin-2 (think of them
as more complex cousins of particles like the pion). Previous
calculations did not include the effects of all these tensor
mesons. However, in situations where all the interacting photons
are behaving very "off-shell" (meaning all have high virtuality),
these tensor mesons start to matter a lot. Their collective
contributions help to correct a shortfall that arises if you
only consider the more basic meson types. By including this
infinite series of tensor mesons, scientists can better match
the calculations to what is expected from the fundamental QCD
theory, "filling the gap" that was left in earlier models that
considered only a finite set or just the axial-vector mesons.
This improvement helps ensure that theoretical predictions for
the muon's magnetic properties are more accurate and reliable.
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