Neutron to Proton Change: The Role of the W Boson

[jal]

My search for the understanding of neutrons converting to protons, which is neutron beta decay (n → p + e− + ¯ν) and the reverse, electron capture (e− + p → n + ν), has lead me to Ultra-cold neutrons (UCN), slow neutrons experiments.
The following review paper highlights the cutting edge.
There is a lot that I did not understand in the paper.
Now … I have more questions
I assume that this paper is all “old news” for people like CarlB
http://arxiv.org/abs/nucl-ex/0612022
Experiments in Fundamental Neutron Physics
Authors: J. S. Nico, W. M. Snow
(Submitted on 20 Dec 2006)
Abstract: Experiments using slow neutrons address a growing range of scientific issues spanning nuclear physics, particle physics, astrophysics, and cosmology. The field of fundamental physics using neutrons has experienced a significant increase in activity over the last two decades. This review summarizes some of the recent developments in the field and outlines some of the prospects for future research.
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p. 11 The substantial difference between the neutron lifetime of PDG average and that of Serebrov et al. is not understood. It is essential to resolve the disagreement.
ref.
http://arxiv.org/abs/nucl-ex/0702009
Neutron lifetime measurements using gravitationally trapped ultracold neutrons
Authors: A. P. Serebrov, V. E. Varlamov, A. G. Kharitonov, A. K. Fomin, Yu. N. Pokotilovski, P. Geltenbort, I. A. Krasnoschekova, M. S. Lasakov, R. R. Taldaev, A. V. Vassiljev, O. M. Zherebtsov
(Submitted on 6 Feb 2007 (v1), last revised 26 Jul 2007 (this version, v2))

Experiment using gravitationally trapped ultracold neutrons (UCNs) to measure the neutron lifetime is reviewed. The precise value of the neutron lifetime is of fundamental importance to particle physics and cosmology. In our experiment, the UCN storage time is brought closest ever to the neutron lifetime: the probability of the UCN loss from the trap was only 1% of that for neutron beta-decay. The neutron lifetime obtained, 878.5+/-0.7stat+/-0.3sys s, is the most accurate one to date.
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How does a lower lifetime affect other process/calculations?
jal

 

[Vanadium 50]

0.14% of W boson is huge uncertainity ...(around 60 Mev)

If you are going to post nonsense, at least be arithmetically correct about it. 60/80,400 = 0.075%, not 0.14%. A bonus would be to use the correct number of 29 MeV, not 60. That gets you to 0.036%.

There have been more W bosons observed (in no fewer than eight experiments) than the number of major league baseball games that have been played. Nobody doubts the existence of baseball.

 

[jal]

I like to phrase my questions so that an amateur can understand?
Is neutron beta decay (n → p + e− + ¯ν), happening faster, ( the W boson doing its job) lowering the life time of the free neutrons, when the neutrons are gathered together as a gas in a container?
How many neutrons do you need to make a sufficient defence (phalanx) against the W boson?
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http://arxiv.org/abs/0802.4029
The Nuclear Physics of Neutron Stars
Authors: J. Piekarewicz
(Submitted on 27 Feb 2008)
A neutron star is a gold mine for the study of the phase diagram of cold baryonic matter.
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[malawi_glenn]

jal, other conditions such as temperature, presurre etc does not affect the life time of particles, same holds for nuclei. A U-235 nucleus has same lifetime as in gas form as in solid form. And so on.

However, neutrons bound inside nuclei does not decay in the same way as a free neutron.

 

[jal]

Hi malawi_glenn!
Your points seem to be the concensus.
I would like to read some experiments that could back up that point of view. Free neutrons seem to break that rule. They are theorized to be able to avoid the W boson transformation within 15 minutes and to stay stable. (Neutron stars)
Maybe there are still unknowns ( neutron skin?) in the nuclear data of neutrons that would affect "neutron star models".
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http://arxiv.org/abs/0805.1007
Two-fluid models of superfluid neutron star cores
Authors: N. Chamel
(Submitted on 7 May 2008)
A neutron star is mainly composed of three distinct regions: an outer crust, an inner crust characterized by the presence of a neutron ocean and a liquid core which might be solid in the deepest regions (Haensel, Potekhin & Yakovlev 2006). Microscopic calculations of dense nuclear matter suggest that the matter inside neutron stars is superfluid (Dean & Hjorth-Jensen 2003).
We consider a mixture of superfluid neutrons and superconducting protons at zero temperature, taking into account mutual entrainment effects.
With the nuclear models considered in this work, we have found that the neutron relativistic effective mass is even greater than the bare neutron mass in the liquid core of neutron stars.
We have constructed new relativistic mean field models that yield a much better agreement with nuclear data than those considered by Comer & Joynt (2003).

jal

 

[malawi_glenn]

Sorry I seems to have misunderstood your question.

The thing is that you can't bind neutrons toghether using the strong nuclear force (nucleon-nucleon force), since the only bound nucleon nucleon system is the deutron (proton + neutron) - and it has only ONE bound state! (no excitation spectra). So you can't have a neutron ball consisting of 300 neutrons, and so on.

In a neutron star, the force responsible is gravity. In ordinary quantum mechanical systems, we ignore gravity since it is so weak in comparison with the other 3forces (strong(colour), electromagnetic & weak nuclear force).

And since the mass of a bound neutron is less than a free neutron, this affects the lifetime of it. This is also the reason why free protons don't decay, while a proton 'inside' a proton-rich nucleus can 'decay' (Beta plus decay).

I am just a novice in Neutron Star (NS) physics, so i don't know if the neutrons in a NS are stable or undergo decay aswell.

Interresting article, (The Nuclear Physics of Neutron Stars, Authors: J. Piekarewicz) will read it tonight (have not much job to do now) but i prefer reading good ol textbooks in a subject before diving into articles that has not been published.

 

[jal]

So you can't have a neutron ball consisting of 300 neutrons, and so on.

You can have neutron rich nucleons.
I believe that you said that you were on a trip at CERN. Enjoy your stay at CERN.
If you bump into someone from "SIRIUS", they may be more informed and willing/open to a discussion over a beer.
Can I be your waiter?
http://www.sirius.ac.uk/
jal

 

[malawi_glenn]

jal, there exists a thing called "neutron dripline" in nuclear physics. You must have HUGE gravity (and preasure) just as in a NS to make such nuclei bind more neutrons, we can't do it in lab here on earth. (http://en.wikipedia.org/wiki/Neutron_drip_line )

(Yes I am on CERN now, one of the labs where occupied, so we couldn't make more optical fibres =( .. so we are a bit delayed.. I work with beam radiation monitoring group at CMS experiment)

I must check if Sirius is a good place... have never heard of it yet.

 

[jal]

When I start a search I never know where I'll end up.
As a result I found myself searching for the following "terms"
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http://arxiv.org/find/all/1/all:+AND+Holographic+QCD/0/1/0/all/0/1
Holographic and QCD
results 1 through 25 (of 160 total)
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http://arxiv.org/find/all/1/all:+AND+AdS%2FQCD+models/0/1/0/all/0/1
results 1 through 25 (of 47 total)
AdS/QCD models
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http://arxiv.org/abs/0806.3114
Holographic deconfinement temperature at finite densities
Authors: Kyung-il Kim, Youngman Kim, Su Houng Lee
(Submitted on 19 Jun 2008)
Dense matter is one of the most challenging problems of modern physics. Understanding
the properties of such matter is important for the physics of relativistic heavy-ion collisions and dense stellar objects such as neutron stars.
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Understanding Confinement and Deconfinement seems to be the key to see "new physic".
Does anyone have a favorite paper to recommend?

 

[jal]

http://arxiv.org/abs/0805.3491v1
S-pairing in neutron matter. I. Correlated Basis Function Theory
Authors: Adelchi Fabrocini, Stefano Fantoni, Alexey Yu. Illarionov, Kevin E. Schmidt
(Submitted on 22 May 2008)
Superfluidity in neutron matter has been a fascinating topic in many–body physics and astrophysics ever since Migdal [2] proposed the possibility of superfluid matter in neutron stars. In the inner crust of the star, 1S0 pairing in the low density neutron gas permeating the lattice of neutron rich nuclei may occur and peak at densities much lower than the empirical nuclear matter saturation density, ρ0 = 0.16 fm−3. A similar pairing may take place for the low concentration proton component in the highly asymmetrical nuclear matter in the star’s interior. At higher interior densities, neutrons may also pair in the anisotropic 3P2–3F2 partial wave. A realistic evaluation of the density regimes where superfluidity takes place and of the strength of the connected energy gaps is needed for a quantitative understanding of important features of neutron stars, such as the cooling rate[3, 4] and the post–glitch relaxation times [5, 6].
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http://arxiv.org/abs/0805.2513
Equation of state of superfluid neutron matter and the calculation of $^1S_0$ pairing gap
Authors: S. Gandolfi, A. Yu. Illarionov, S. Fantoni, F. Pederiva, K. E. Schmidt
(Submitted on 16 May 2008)
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I assume that the next step, after pairing of neutron, would be a phase change to Quark-gluon liquid.

 

[Atakor]

Hello !

Perturbation theory may or may not be a good approximation. Strictly speaking, Feynman diagrams are (space-time) topological equivalent classes of terms, in an expansion of a scattering amplitude in momentum space. They should certainly not be considered as real processes in general. However, we do speak in those terms on a daily basis, and some might forget the grain of salt they should be taken with.

In another thread, we discussed about how real can a particle be if its mass is comparable to its width for instance.

Humanino, what do you mean by the bolded sentence ??
do you mean that feynman diagrams are just a mathemagical artifact ?

Can you give me the link for that thread too ?

Thanks !

 

[humanino]

Humanino, what do you mean by the bolded sentence ??

It was a while ago
I meant that Feynman diagrams are individual terms in an infinite series, and as such should be considered with caution. At first there is nothing more to my statement : if you are to calculate any observable, you'd better calculate it up to the next relevant order, that is up to when your calculation does not improve the result anymore.

do you mean that feynman diagrams are just a mathemagical artifact ?

No, that would be oversimplifying. Particle detected, I know what that is, and scattering matrix. Anything beyond is calculation.

Let me give you an example.

In the business of nucleon structure with an electromagnetic probe, people have assumed 1-photon exchange was a good enough approximation for a long time. And they extract particular form factors. Lately, people found a discrepancy in two ways to extract the ratio of the electric and magnetic form factors. Several possibilities exist to explain this, and it is not yet clear whether those possibilities are equivalent to one another. Anyway, the first thing people came up with is two-photon exchange, which people have written to be negligible (for such and such reason) for years (decades).

This is merely one example.

Another example, people use the optical theorem all the time, where we calculate a probability for a real process as an amplitude for an impossible process. Here again, you'd better not take the Feynman diagram as a real process !

My first example was rather extraordinary event, my second example is rather trivial. My remark applies possibly only at an elementary level. Let me go back to the tree level amplitude for electron-positron scattering. As explained by John Baez
Some frequently asked questions about virtual particles
attraction in the one photon exchange stems from the interference term with nothing happening ! So if you ask very basic questions about interpretations of Feynman diagrams, you sometimes should expect complicated answers.

 

[jal]

If I understood the following paper correctly, they are searching for the decay of a free neutron that does not involve the W boson.
Is that correct?
http://arxiv.org/abs/0710.1389
Comparison of two experiments on radiative neutron decay
Authors: R. U. Khafizov, S. V. Tolokonnikov, V. A. Solovei, M. R. Kolhidashvili
(Submitted on 6 Oct 2007)

First, the results from the first experiment aiming to observe the as yet undiscovered radiative decay mode of the free neutron are reported. Although the experiment could not be performed under ideal conditions, the data collected still allowed one to deduce the B.R. = (3.2±1.6) · 10-3 (99.7 % C.L.) for the branching ratio of radiative neutron decay in the gamma energy region greater than 35 keV. This value is in agreement with the theoretical prediction based on the standard model of weak interactions.
Secondly, the average B.R. value we obtained deviates from the standard model, but because of the presence of a significant error (50%) we cannot make any definite conclusions. Taking into account the fact that the experimental conditions can still be significantly optimized, an e-p coincidence count rate of 5-10 events per second is within reach. Together with the standard model prediction for the branching ratio of this decay mode, this would correspond to a triple e-p-γ coincidence rate of several events per 100 seconds. This can easily be observed with the current experimental set-up, which is now being optimized with a view to performing such an experiment. The aim of that experiment will then not only be to establish the existence of radiative neutron beta decay, but also to study B.R. in more detail. This, in turn, would allow to discover the deviation from standard electroweak theory. According to our estimates, we will be able to make more definite conclusions about deviation from the standard electroweak theory at the precision level of less than 10%.

 

[daschaich]

If I understood the following paper correctly, they are searching for the decay of a free neutron that does not involve the W boson.
Is that correct?
...

Doesn't look like it to me. They are searching for neutron $$\beta$$decays in which a photon is radiated,
$$n \to p + e + \overline{\nu} + \gamma.$$
They compare their results with "the theoretical prediction based on the standard model of weak interactions", which of course involves the W boson.

 

[Atakor]

Thanks Humanino for the answer.

Still, I have a problem relative to the interpretation.
I know the use of feynman diagrams to calculate cross-sections and it is of course a matter of precision to stop at a certain level in the development.
But, why can't we say that the real process involves all the different possibilities ? or .. paths to use another term ?

thanks.

 

[Atakor]

Doesn't look like it to me. They are searching for neutron $$\beta$$decays in which a photon is radiated,
$$n \to p + e + \overline{\nu} + \gamma.$$
They compare their results with "the theoretical prediction based on the standard model of weak interactions", which of course involves the W boson.

Hello daschaich, where does that $$\gamma$$ come from ?

 

[daschaich]

Hello daschaich, where does that $$\gamma$$ come from ?

That's a photon, which can be radiated by any electrically charged particle -- the proton, electron, intermediate W boson, probably even the individual quarks in the initial-state neutron. The paper jal posted discussed experiments trying to determine how likely it is for such a photon (with an energy of at least 35 keV) to be emitted during $$\beta$$ decay.

 

[jal]

In our case, when proton kinetic energy was 25 keV, the final velocity was 0.006 c, and its average velocity along the trajectory was 0.003 с. On Fig. 6, which shows the spectrum of the electron-proton coincidences, the peak of these coincidences is located in the 120th channel, which corresponds to proton delay of 500 ns on average or the distance between the point of decay and the proton detector in 40-50 cm. The estimate obtained is quite good and coincides with the real distance between the proton detector and the axis of neutron beam in our equipment with precision of ten-twenty per cent.

In the paper, they were able to position the detectors so that they were able to detect the proton, the photon, then the electron.
My understanding is that they captured some free neutron in a “cold thermos bottle”. They did some calculation to arrive at neutrons at rest, and measured “decayed/changed” to a proton. By measuring the time of flight they were able to determine that an electron and a neutrino, were formed from the “Fermi sea” (to make sure that there is conservation of energy).
In order for the electron to emit a photon it has to go from a “bigger orbit” to a “smaller orbit” around the proton.
The change in the orbit determines the “size” of the photon recorded on the detector.
Then, the electron was “pulled out” of orbit and into another detector.
Yes? No? … Okay! …. What really happened?

 

[jal]

I want to make a quote that explains, for most people, what scientists have concluded happens when a free neutron changes to a proton.
For me, it raises more questions and that’s why I searching for experimental evidence.

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Hydrogen: The Essential Element
John S. Rigden
2002


“p. 167
A static charge, like the electron, takes a new life in QED. An electron has a n electromagnetic field consisting of quantized photons. Thus, the electron is surrounded by a cloud of photons. This cloud of photons surrounding an electron effectively reproduces the 1/r^2 character of its measured electric field given by Coulomb’s law. The electron can interact with its own electromagnetic field; that is, with photons in the cloud surrounding it.
This interaction alters the behavior the electron would have in the absence of these interactions.
To give a complete theoretical account of the electron interaction with its own field, corrections must be made by QED; in fact by a new relativistic theory of QED. In the summer of 1947 Julian Schwinger … did with spectacular success during the next six months.
There is another consequence of the photon cloud around an electron. In this cloud of photons, the creation and annihilation of particles occur. It is these virtual particles, pairs of positive and negative particles, that lead to the polarization of the empty space surrounding the electron.
Thus, the charge of the electron is partially screened from an outside viewer and, from a distance, appears slightly different from what it really is.
Incidentally, quantum electrodynamics transcends the electron. In other words, the idea of QED go beyond the electron. For example the concept of a basic interaction being mediated by an exchange of particles has been extended to both the weak and strong interactions with mediated particles experimentally identified.”
----------
So my original questions, “Why does the change need to include the intermediate step of the heavy W boson?
Where did all the W boson mass come from and where did it go?” has been answered superficially.
Re-phrasing … QED … says so and it is assumed that it is the same for a free neutron.
but ... is it?