CERN Breakthrough: Tracking an Extremely Fragile Atomic Nucleus

CERN scientists have successfully tracked an extremely fragile atomic nucleus, offering new insights into nuclear stability and fundamental forces of nature.

Table of Contents

Context

ALICE experiments show fragile deuterons form after violent LHC collisions via short-lived resonances.

ALICE Collaboration

The ALICE Collaboration (A Large Ion Collider Experiment) is one of the four major particle physics experiments at the CERN Large Hadron Collider. It focuses on studying the physics of strongly interacting matter at extreme energy densities to understand the early universe’s conditions and the formation of quark–gluon plasma.

Key facts

Founded: 1993
Headquarters: Geneva, Switzerland
Member institutions: ~175 from 39 countries
Primary goal: Study of quark–gluon plasma via heavy-ion collisions

About the Experiment

- The experiment sought to resolve the mystery of how deuteron, a fragile particle, does not break apart immediately in LHC collisions. But they are regularly observed in LHC experiments.

Two Possible Theories

Direct emission: Deuterons form immediately during collision.
Coalescence: Proton and neutron form first, then join later.

- Outcome of the experiment: ALICE found that pions and deuterons often appeared with linked motion. This meant the deuteron was formed after the Δ(1232) particle decayed, using the proton or neutron produced in that decay. Because this happens slightly later and away from the most violent region, the fragile deuteron survives.

Important Result
About 62% of deuterons are formed after Δ decays.
Including other resonances, nearly 80% formed via coalescence.

What are Pions

Pions are the lightest mesons, made of one quark and one antiquark.
It acts as a force carrier between protons and neutrons inside atomic nuclei.
Commonly produced in high-energy particle collisions and cosmic-ray interactions.
Important in particle physics experiments and in explaining nuclear binding.

About Δ(1232) resonance

It is a very short-lived excited version of a proton or a neutron that quickly decays.
It decays into a pion and a proton or a neutron
Produced in high-energy particle collisions, such as those at the LHC.
Plays a key role in nuclear and particle interactions, especially in pion production.
Important for studying the strong nuclear force and nucleus formation mechanisms.

Significance of the ALICE Experiment

Improved understanding of nucleus formation: The experiment shows that deuterons form after collisions via coalescence, correcting earlier assumptions about the instantaneous formation of nuclei in high-energy reactions.
More accurate cosmic-ray models: Knowing how light nuclei form helps scientists realistically model cosmic-ray collisions with interstellar matter and interpret observational data more accurately.
Better interpretation of telescope data: Clear formation mechanisms allow researchers to identify which detected particles originate from cosmic rays rather than instrumental or background processes.
Stronger dark-matter signal identification: Accurate models prevent confusing ordinary nuclear production with rare dark-matter signatures, reducing false positives in indirect dark-matter searches.
Link between collider physics and space phenomena: Results connect laboratory experiments at the LHC with natural high-energy processes occurring throughout the universe.
Resolution of a long-standing physics puzzle: Explaining deuteron survival in extreme environments strengthens confidence in nuclear and particle physics theories.
Broader impact on astrophysics and cosmology Insights improve understanding of matter formation in the universe and support studies of cosmic evolution and fundamental forces.

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