# Does a particle annihilate only with its corresponding antiparticle

## Main Question or Discussion Point

Does a particle annihilate only with its corresponding antiparticle,or with any anti particle?Also,as a photon is its own antiparticle,when one photon collides with another, they should annihilate,shouldn't they?

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Some thoughts(I could be wrong):

Annihilation is an event that only occurs with the direct interaction of charged particles.
Those charged particles must be of equal mass but opposite charge.
A photon has neither mass nor charge, therefore annihilation is not possible.

mathman
Annihilation occurs when a particle collides with its own antiparticle. These can be neutral, such as neutron and antineutron, although this is not too likely. Charged particles and antiparticles have opposite charge, so they attract, while neutral particles don't.

Photons are their own antiparticle. They don't annihilate - in fact when annihilation occurs, photons are produced. You need something to conserve momentum and energy.

Photons do not annihilate because they do not interact directly -- there is no such term in the QED lagrangian.
On the other hand, total aanihillation of neutron and anti-neutron is as likely as the annihilation of proton and anti-proton -- you have to arrange for interaction of three quark-antiquark pairs.

In general, particle and antiparticle annihilate when it's allowed by the corresponding term in the interaction lagrangian of the theory. For instance, electron and positron can always turn into photons, while quark and antiquark would turn into photons if their color quantum numbers match (but they can annihillate into gluons though). In the Standard Model you can even annihilate quarks of different flavors (for instance, b and anti-u) -- this process is called weak annihilation and happens in the decays of B-mesons.

HybriDeuteron...

I presume that particle annihilation is primarily driven by the subnuclear properties of any particle.

For example, one may suggest that a HybriDeuteron (proton+anti-neutron, anti-proton+neutron) nucleus would be stable because the proton and anti-neutron are not mirror images.

HybriDeuteron:
$$D_h = p(uud)+ \overline{ n}(\overline{ udd}) = p \overline{ n}$$

However, because of their subnuclear properties $$p(uud)+ \overline{ n}(\overline{ udd})$$, the primary decay method would be the annihilation of $$u+ \overline{ u}$$ or $$d+ \overline{ d}$$ or $$ud + \overline{ ud}$$, because they are mirror images, resulting in Meson production.

$$D_h( p \overline{ n}) -> \pi ^+ + E$$
$$D_h( p \overline{ n}) -> \pi ^0 + E$$

Probability:
$$p(uud)+ \overline{ p}(\overline{ uud})$$
$$n(udd)+ \overline{ n}(\overline{ udd})$$
$$p(uud)+ \overline{ n}(\overline{ udd})$$

Given that $$p(uud)+ \overline{ p}(\overline{ uud})$$ and $$n(udd)+ \overline{ n}(\overline{ udd})$$ annihilation processes are the most probable because they are mirror images, it is reasonable that HybriDeuteron annihilation $$p(uud)+ \overline{ n}(\overline{ udd})$$ is a less probable process, therefore has a greater nuclear 'lifetime'.

Photons and anti-Photons can annihilate because Photons share a common particle-wave duality.

Annihilation processes primarily occur between mirror particles and anti-particles on a subnuclear scale.

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jimmy p
Gold Member
I was told that a particle can be annihilated by any anti-particle...well i suppose if they had opposite charge or whatever. I mean why cant a proton be annihilated by an anti-neutron?

All annihilation and decay processes obey the full spectrum of Conservation Laws where applicable, i.e conservation of spin, charge, mass, energy, momentum, quantum states, colours, etc.

Dirac Theory:
A Fermion is all particles with half integral spin:
$$s = \frac{1}{2}$$

The Dirac Fermion Theory was derived from the Time-independent Schrodinger equasion.

Time-independent Schrodinger equasion:
$$\frac{ \vartheta ^2 \psi}{ \vartheta x^2} = - \frac{ 2 m E}{ \hbar ^2} \psi$$

Dirac Fermion Spin equasion:
$$S = \sqrt{ s(s + 1)} \hbar = \frac{ \sqrt{ 3}}{ 2} \hbar$$
Spin angular momentum of Fermion.

According to Dirac Fermion Theory, all Fermions and anti-Fermions can only be created and destroyed in pairs.
$$\gamma -> e^- + e^+$$
$$e^- + e^+ -> \gamma$$

According to Dirac Hadron Theory, all Hadrons and anti-Hadrons can only be created and destroyed in pairs.
$$\gamma -> p^+ + \overline{ p} ^-$$
$$p^+ + \overline{ p} ^- -> \gamma$$

$$\gamma -> n + \overline{ n}$$
$$n + \overline{ n} -> \gamma$$

All Fermions have an anti-Fermion.
Exceptions are the photon and Meson neutral pion $$( \pi ^0)$$ and eta $$( \eta ^0)$$.
The Meson pion and eta are their own anti-particles.

Dirac Theory obeys the Pauli Exclusion Principle.

Pauli Exclusion Principle:
No two Fermions in a volume can ever be in the same quantum state; no two Fermions in the same volume can have the same set of quantum numbers $$(n, l, m_l, m_s)$$.

Protons and anti-Neutrons cannot spontaneously annihilate because they are not conserved Dirac Fermion or Hadron Pairs.

However they do annihilate, but it is not a complete annihilation.

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