Could atoms be formed from other quarks than up and down?

[elcaro]

TL;DR Summary

Normal atoms consist of up and down quarks, gluons and electrons. Under what conditions (different physics constant, different vacuum energy?) would atoms be formed from the other quarks (strange/charm, top/botton).

Is it possible - perhaps in a different universe with different physical constant and vacuum energy - that atoms can be formed from strange/charm or top/bottom quarks?

 

[Vanadium 50]

A. Not in this universe,
B. See https://www.physicsforums.com/threads/what-is-made-up-of-all-the-rest-quarks.1006836/ if you want a scientific discussion.
C. Other universes are filled with invisible pink unicorns. Prove they aren't!

 

[elcaro]

A. Not in this universe,
B. See https://www.physicsforums.com/threads/what-is-made-up-of-all-the-rest-quarks.1006836/ if you want a scientific discussion.
C. Other universes are filled with invisible pink unicorns. Prove they aren't!

a. That's why I asked under different physics conditions ie. other values for the physics constants ie in a different universe
b. Not much of a discussion there
c. The invisible pink unicorns got extinct, eaten up by invisible dragons, thought you knew that!

 

[elcaro]

Maybe I rephrase my question, if we were allowed to fiddle with the physics constants, could we make atoms made from strange/charm quarks or top/bottom quarks stable, is there anything in the standard model that would allow for that hypothetically?

 

[Gaussian97]

Is the Kaonic hydrogen valid?

 

[ohwilleke]

Outline

The basic obstacle is that hadrons other than protons and bound neutrons aren't stable (see primarily the list of baryons with three valence quarks and the list of mesons with two valence quarks, although these lists exclude excited states of hadrons and hadrons with four or more valence quarks or otherwise exotic structures).

There are a variety of things that could be tweaked in the properties of our observable universe to change that.

To set this up, I provide a few background terms and a fun fact regarding the terminology used for what you are asking about.

Then, I consider four of the least noticeable changes that could accomplish this change in the way the universe works, plus one very notable change (which I mention before pointing out why it doesn't work), and one unrelated notable bonus tweak, which I discuss below, because its a neat thought experiment of the same variety as the question you are asking.

I'm sure that someone more creative than I could come up with additional approaches.

Finally, I explain that, in a certain sense, higher generation quarks are actually already present in ordinary protons and neutrons.

Background

Here is some additional background to bring this post closer to the basic level of this thread:

* a hadron is a set of fundamental particles bound by the strong force which is transmitted by massless bosons called gluons.

* quarks and gluons at moderate temperatures (below the much hotter than the Sun temperature needed to form "quark-gluon plasma" a.k.a. QGP) are always "confined" within hadrons, except top quarks, which decay via the weak force (99%+ of the time into bottom quarks) before they have time to join a hadron.

* the weak force which is mediated by W and Z bosons (like heavy photons in analogy to the electromagnetic force) converts one kind of particle into another a different flavor of particle of the same type - it can turn up type quarks into down type quarks and visa versa, and can change the flavor of charged leptons (i.e. electrons, muons and tau leptons).

* Particle physicists like to describe mass in terms of electron volts divided by the speed of light squared, although they suppress the c² term under the convention that c=1 that is used for simpler notation. The usual metric abbreviations (m for milli, M for mega, G for giga, T for tetra) are used with electron volt masses.

Fun Fact

Composite particles of hadrons other than protons and neutrons are usually called "molecules" in high energy physics (as in "meson molecules") rather than atoms, even though they are more analogous to atoms (which are hadrons bound to each other by the residual strong force) and not to chemical molecules (which are atoms made of protons and/or neutrons that are bound electromagnetically to each other).

1. A Supersymmetric Solution

There is a class of beyond the Standard Model theories called supersymmetric theories in which there is a new boson particle for every known fundamental quark and lepton, and a new fermion particle for every known fundamental boson. A few adjustments required in these theories because of how quantum particles act so that the correspondence between Standard Model fundamental particles and their "sparticles" is not quite one to one.

This class of theories is mathematically elegant and a low energy assumption of string theory. Basically, it provides a reason for the laws of the Nature to look like they do in a way that many theoretical physicists find to be more beautiful than the Standard Model. There is no positive evidence for it, but it is one of the main things that the Large Hadron Collider was invented to look for.

Some supersymmetry motivated theories suppose that there is a quantum number that is conserved called R-parity. The idea is that ordinary quarks and leptons and fundamental bosons of the Standard Model have one R-parity (+1), and supersymmetric partners of quarks and leptons and fundamental bosons (sparticles) have another R-parity (-1), and that all interactions must preserve R-parity, which is a conserved quantity, just like charge, or mass-energy, or baryon number minus lepton number.

In this scheme, the hadrons at the bottom of the sparticle decay chain would be, like protons and electrons, stable because there would be nothing else they could decay into. They could plausibly form a dark sector that interacts only weakly or not at all with regular matter. This dark sector could include composite particles and atoms made up of the lightest supersymmetric fermions that are stable.

Of course, since the new atoms would be a form of dark matter, we'd never see them in this scenario.

2. Tweaking The Weak Force

If you want higher generation fundamental particles to stick around, one way to do that is to gum up the weak force which permits them to decay into lower generation particles, to make it less efficient at doing so.

You could do this by tweaking the mass of the carrier bosons that transmit the weak force, by weakening the strength of the force itself with its coupling constant, or by tweaking the width of the carrier bosons (which is another way of saying that you are tweaking their mean lifetime).

W and Z Boson Mass

You could get "metastable" heavy quark atoms by dramatically weakening the weak force. One way to do this would be by increasing the mass of the W and Z bosons from 80.35 GeV and 91.2 GeV to 803.5 TeV and 912 TeV.

We'd have the same CKM matrix (discussed below) and proportionately similar decays of Standard Model fundamental particles, but they'd happen a lot less frequently, although even that much of a difference might not be enough to produce very long lived heavy quark atoms.

Weak Force Coupling Constant

A coupling constant is the strength of a force in dimensionless terms.

Alternately, you could make the weak force coupling constant (which is proportionate to the Fermi constant) a lot weaker than it already is now, perhaps a trillion times smaller than the electromagnetic coupling constant instead of a million times smaller.

Weak Force Boson Width

Yet another possibility would be to keep the coupling constant and W and Z boson masses the same, but to dramatically reduce the W and Z boson widths from say 2 GeV and 2.5 GeV respectively, to say, 2 and 2.5 meV (i.e. a factor of 10¹² smaller).

This would make the mean lifetime of the muon about 1,000,000 seconds (about 11 days), and would make other hadrons other than the proton and neutron much more long lived, surely enough to form atoms, although still highly unstable.

For example, the positively charged sigma baryon, which is a just like a proton except that it has a strange quark instead of a down quark, would have a mean lifetime of about 88 seconds and a mass that is 27% greater than a proton, if the weak force boson widths were a factor of 10¹² smaller.

This tweak would also make hadrons including top quarks (which are possible in theory now, but undetectably rare and incredibly short lived) viable in systems with high enough energies.

Caveat

All of this analysis is a very crude first order approximation. To really do it right you'd have to consider all of the secondary and indirect effects of these changes (and any other tweaks to the laws of physics proposed elsewhere in this post).

For example, while I make a crude estimate of the lifetime of the positively charged sigma baryon if the W boson width were different, this doesn't fully consider impacts on strong force interactions and electromagnetic interactions of this baryon that would be too minor to consider with the real laws of physics, and doesn't take into account the issue that slowing down the process of decay via the weak force would also make it much harder to produce such hadrons in the first place.

3. Tweaking the Quark Masses

If the quark masses were nearly degenerate (i.e. almost the same), higher generation hadrons and atoms made from those hadrons could be stable.

For example, suppose that the charm quark was just 1% more massive than an up quark, and that a top quark was just 2% more massive than an up quark, while a strange quark was just 1% more massive than a down quark and a bottom quark was just 2% more massive than a down quark.

Also, we could make the weak force stronger instead of weaker, causing more transitions to happen between quark flavors via W bosons.

In this situation, very minimal additional energy would be necessary to sustain higher generation quarks in metastable or dynamically stable hadrons and atoms made of those hadrons.

Of course, if that happened, the reality would be almost indistinguishable from a world in which there were just two kinds of quarks instead of six. All up type quarks are identical except for their mass and CKM mixing rates, and all down type quarks are identical except for their mass and CKM mixing rates, so it would be phenomenologically almost identical to a world with one generation of quarks and three generations of leptons. The telltale difference would be in the relative frequency of W and Z boson decays to different quark types v. lepton types which would stay the same as they are now, except that top quark decays would be facilitated because top quarks would be less massive than W and Z bosons.

Also, note that in the current Standard Model, a tweak to the quark masses is really a tweak to the Higgs field coupling strengths called Yukawas of the quarks, and so this could be described as a change in the properties of the Higgs boson as well.

4. Tweaking the CKM matrix

The CKM matrix is the part of the Standard Model that tells us the probability of a quark of one flavor turning into a quark of another flavor mass-energy conservation permitting when quarks have weak force interactions.

For example, in real life, top quarks almost always decay to bottom quarks, even though they can decay to strange quarks or down quarks.

Tweaking these probabilities would change the mix of quark flavors in the universe.

The goal here would be to replicate the feat that the neutron achieves - making neutrons stable in a bound state, even though free neutrons are only metastable with a mean lifetime on the order of a quarter hour. Bound neutrons are stable because in an atomic nucleus, neutrons change into protons at the same rate that protons turn into neutrons in a process triggered by the decay products of a neutron.

For example, if you had universal transition probabilities for quarks in the CKM matrix akin to charged lepton universality (in which the decay probability of a fundamental particle to another flavor of fundamental particle was independent of its flavor) you could have far more transitions from up to bottom and back, from down to top and back, and so on.

This would, in high energy systems that weren't conservation of mass-energy limited, allow the quark content of atoms to be dynamically stable with a significant proportion of second and third generation quarks.

But, these atoms would still only be possible in extremely high energy particle collider-like environments to allow heavy fermions and light ones to shift back and forth. As noted below in tweak number five, this actually wouldn't work because it would be so hot that the quarks wouldn't stick together in hadrons. So, while you might get more atoms with strange quark hadrons in them, you probably wouldn't get many more atoms with heavy quarks in them.

Also, in order for top quarks to hadronize, they would need to have a much smaller width (i.e. a much longer mean lifetime).

5. A Very Energetic Solution

In real life, the Big Bang cooled down so fast that the ultrahigh temperatures there that permitted higher generation quarks to stick around, didn't even last long enough for meaningful numbers of hadrons to form.

If the universe had temperatures comparable to moments after the Big Bang all the time (roughly the first 20 microseconds), and stayed in a confined space rather than expanding rapidly as it did, second and third generation quark atoms would be viable. This would be because new second and third generation quarks would be created as quickly as they decayed.

The other problem is that it would be so hot, that quarks and gluons wouldn't be confined in hadrons and instead everything would be a quark gluon plasma. So, actually, the fifth tweak doesn't really work because the universe wouldn't settle down enough to allow atoms to form.

6. Bonus Tweak - Changing the Pion Mass To Get A Stable Neutron

While not precisely on point to your question, it is well known that if the pion mass (the least massive hadron and the main carrier of the residual strong force between protons and neutrons in an atomic nucleus, which are made up of first generation quarks bound by gluons) was greater (they are roughly 138 MeV in the real world, about 1/6th of the mass of a proton), free neutrons, and atomic nuclei with neutrons but no protons, would be stable. See here.

QCD for quantum chromodynamics, is the physics of the strong force that hold protons and neutrons and other hadrons together and residually binds atoms in atomic nuclei together. Lattice QCD calculations are an iterative discrete mathematical method necessary to do low energy QCD interactions that aren't accurately described by perturbative methods which are done using calculus, such as the internal behavior of hadrons as opposed to the behavior of them smashing together at nearly the speed of light.

This comes up rather often because lattice QCD calculations often consider non-physical pion masses and evaluate how strong force interactions change with differing pion masses to create a trend line to predict the behavior of the system at the physical pion mass (since this is computationally easier in many cases than doing the calculations with physical masses).

A Footnote on Sea Quarks: In A Sense What You Are Imagining Is Already True.

The basic way to explain the structure of protons and neutrons describes them as three valence quarks (two up and one down, or one up and two down, respectively) bound together by gluons. This simple model is good enough for lots of purposes, like determining the electromagnetic charge and spin of a hadron.

But, this model isn't actually entirely true. At a deeper level, a proton or neutron is a sea of quarks of all flavors that nets out to the three valence quarks.

If you smash a proton against something else with enough energy, you will sometimes get strange quarks, charm quarks, bottom quarks, and top quarks out of the debris of the collision and not just up or down quarks. This is how we know that they exist at all. The comic below (from here) illustrates just how weird an idea this is with a "fruit collider" analogy:

So, in a sense, which can be quantified quite precisely using a tool known as a Parton Distribution Function (a.k.a. PDF), you can determine what percentage of the time a proton smashed at a particular energy will produce a particular kind of quark. (In theory, PDFs can be calculated from first principles, but in practice, scientists usually just keep a running log of what they see and compile it into a graph that summarizes their data.)

So, it isn't entirely wrong to say that a certain small percentage of the ordinary stuff of the universe in protons and neutrons is actually made of strange, charm, bottom and top quarks.

At a practical level, this general idea of one kind of matter turning into something else at low probabilities comes up, for example, in calculating from first principles the magnetic moment of the muon, which includes tiny probabilities (relevant at parts per billion levels) that a muon has a W boson interaction that forms quarks that form hadrons and decay back into a muon. Getting this part of the calculation right is the main reason that this property of a heavy electron is so hard to calculate accurately from first principles and is the main source of uncertainty in the calculation (although scientists have gotten very close).

So, even muons are impacted in their day to day behavior ever so slightly by the possibility that they turn into or produce quarks (usually "virtual ones" that don't and can't appear in an end state of an interaction).