# B What happens during electron capture physically?

#### intothefire

I wonder if someone could explain what is known about electron capture in which a proton captures an electron which then becomes a neutron? I have read that a proton which has two up quarks and a single down quark will have the the creation and destruction of multiple quark - antiquark pairs within the diameter of the proton happening.

But an electron is also a fundamental particle so, what happens there?

Does for example, the electron knock out one of the up quarks which allows a down quark - antidown quark pair to take advantage of the situation? Such that, the down quark remains in the particle and the antidown quark goes away with the up quark as a meson with up quark - antidown quark character? What happens to the electron though? It is a fundamental particle and cannot be destroyed correct?

thanks

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#### vanhees71

Gold Member
It's a weak interaction via a charged current. On the fundamental level it's $u+e \rightarrow \nu_e+d$.

#### Nugatory

Mentor
It is a fundamental particle and cannot be destroyed correct?
Not correct. “Fundamental” means (loosely) “isn’t made of anything smaller”, but fundamental particles can be created and destroyed. For example, an electron and a positron can turn into photons, and under the right circumstances (google for “pair production”) a photon can produce an electron-positron pair.

Thus, the interaction here is just as vanhees says above: an electron and an up quark turn into a down quark and electron neutrino. The electron is no more, the neutrino heads off into empty space, and where we had an up quark we now have a down quark.

(Although electrons can be created and destroyed, electric charge and something called “lepton number” must be conserved. The electron and the neutrino both have lepton number one, so the interaction is allowed)

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#### intothefire

thanks everyone,

But to pursue this a bit farther - are there any situations where quarks combine together, perhaps to form heavier quarks? Perhaps this might happen in a neutron star?

#### vanhees71

Gold Member
Everything around us is made of quarks combining to colorless bound states. A single quark cannot be observable since it's a gauge-dependent object since it carries non-zero color charge.

#### intothefire

Can the down quark combine with an electron to make another heavier quark? Where could I find more information about the types of interactions that vanhees71 cited? Is there some layman's book that discuss the various types of electron capture in these terms? thanks

#### vanhees71

Gold Member
I'm not sure whether it covers electron capture in great detail, but on a popular-science level I found Lederman's "The God Particle" quite well and amusing to read. Another one is Veltman, Facts and mysteries of elementary particle physics.

#### snorkack

Can the down quark combine with an electron to make another heavier quark?
No.
Electron is negative.
All quarks other than down are either same charge as down or else more positive.

#### intothefire

But what about these more positive quarks such as charm and top (truth) quarks? Can they combine with the electron?

Incidentally, anyone know why top and bottom are more popular names than truth and beauty? I rather like the latter names.

#### snorkack

But what about these more positive quarks such as charm and top (truth) quarks? Can they combine with the electron?
For the charmed lambda (charmed sigmas are resonances), semileptonic decay modes are in percents:
page 4 quotes 2,1 % for Λe+νe
What are the branching factors for electron captures:
Λc+e+=Λ+νe
Λc+e+=n+νe
?

#### snorkack

Λc+e+=Λ+νe
Λc+e+=n+νe
Sorry, seems cannot edit,
Of course
Λc+e-=Λ+νe
Λc+e-=n+νe

#### intothefire

So what is happening here?: Λc+e-=n+νe

The charm quark is heavier than the down quark so if the charm quark becomes a down quark does that mean that the neutron and electron neutrino are moving with great momentum?

Sorry about the superscripts and subscripts. I can't seem to find the LaTeX controls.

#### snorkack

So what is happening here?: Λc+e-=n+νe

The charm quark is heavier than the down quark so if the charm quark becomes a down quark does that mean that the neutron and electron neutrino are moving with great momentum?
Yes.
Sorry about the superscripts and subscripts. I can't seem to find the LaTeX controls.
I found subscripts and superscripts from above the edit window, the icon with three dots and arrow. Opening the arrow.

#### PeterDonis

Mentor
Moderator's note: Moved thread to high energy physics forum.

#### mfb

Mentor
But to pursue this a bit farther - are there any situations where quarks combine together, perhaps to form heavier quarks? Perhaps this might happen in a neutron star?
All the heavier quarks are produced in reactions of lighter quarks or leptons.

What B-factories like SuperKEKB routinely do: $e^- e^+ \to b \bar b$, a pair of bottom and anti-bottom created from leptons (via a virtual photon).
Very common reactions at the LHC: $g + g \to b \bar b$ or $u + \bar u \to b \bar b$ or $d + \bar d \to b \bar b$ or any other quark/antiquark pair.
The charm quark is heavier than the down quark so if the charm quark becomes a down quark does that mean that the neutron and electron neutrino are moving with great momentum?
Yes. It is like a super energetic variant of regular electron capture.

To use LaTeX formulas just put ## before and after them.