I want to know, quantitatively, how strange I am.

August 22, 2011 9:46 AM

How many strange quarks are in my body at any given time, on average?

I know that most of my body is made up of protons, neutrons, and electrons. So it is largely composed of up and down quarks, and mix of leptons and the occasional photon here and there. However, what I would like to know is how many strange quarks there are in there.

To the best of my recollection, strange particles are usually produced from either weak decay or from high energy interactions of some kind, and I'm pretty sure that neither of those really occur that often in our body. While we have some radioactive material (at least carbon-14), I'm under the vague impression that it decays via alpha decay, and so... shouldn't produce any strange quarks?

So not counting the occasional cosmic high-energy particle passing through (and not interacting---if they do interact and leave me some strange-ness, I guess that counts?), how many strange quarks are inside me at any given time? All I'm looking for is order-of-magnitude type answers.

Bonus points if you can tell me how charming I am as well, or how much of a top/bottom I am.

posted by vernondalhart to Science & Nature (3 answers total)

Enough to make about a 10% contribution to the charge/magnetization distribution of all the protons in your body? (And presumably an approximately similar amount for all other particles, other than the proton, in your body.) See this article:

The G-Zero researchers were particularly interested in these strong force energy fields. The energy from these fields appears in the form of particles inside the proton called “sea particles.” These particles bubble up for the briefest of moments before melting back into energy fields.

The sea particles, also called virtual particles, can take the form of quark pairs. Pairs of up quarks and pairs of down quarks are the most likely pairs to appear briefly in this sea, because they are the lightest of quarks. The proton’s permanent quarks consist of two up quarks and a down quark.

The next-heaviest quarks, strange quarks, are also thought to be present in the sea as virtual particles. G-Zero scientists proposed their experiment in 1993 to measure what effect these temporary residents of the proton have deep inside the proton. . . .

These results indicate strange quarks make small, less than 10 percent contributions, to the charge/magnetization distributions. Ten percent compared to the total charge and magnetization distribution. . . .

The G-Zero scientists say that this is surprising, since other experiments give strong indications that there are a significant number of strange quarks in the proton, and early theoretical calculations suggested that the strange quarks could contribute significantly more than 10% of the proton’s charge or magnetization at the level they measured.

Presumably that means that somewhere more than 10% of the virtual particles are strange quarks, since quite a few of them will come in pairs that will stay close together and mostly cancel each other's charge/magnetization effect out. But as an order-of-magnitude approximation, there you are . . .
posted by flug at 12:22 PM on August 22, 2011

There are beta decay processes that will occur in your body: potassium-40, for example, is a pretty significant radiation source, and C-14 undergoes beta decay as well (alpha decays tend to happen in heavier nuclei, as it involves losing 4 nucleons, rather than just converting a p to n or n to p). However, the strange quark masses ~100 MeV, compared to 2-4 MeV for u and d quarks (those later two masses aren't very well defined, by the way). Looking at C14 decay, it goes to N14+ e- + \bar{nu}, and the mass difference between C14 and N14 is 14.003241u-14.00307u=0.00171u = .15 MeV. So there isn't enough energy available to create a strange quark. So most radioactive decay in your body won't create strangeness (at these energies, they convert u to d or vice versa, along with an electron and neutrino pair).

This brings up the biggest problem to answering your question. What do you mean by a "strange quark?" If you want to only count "real" strange quarks, then my educated guess is zero strangeness. Nuclear decays won't create any strangeness, and if it did, the strange quarks would decay immediately (into light quarks and an electron/neutrino pair). There are strange quarks created in atmospheric interactions of cosmic rays, and these will filter down and pass through your body, as well as strange quarks created in your body from cosmic rays. But you didn't want to count those, and any created strange quarks will decay and/or escape your body pretty quickly.

However, if you want to count "virtual" quarks, then you're sort of in luck. See, a proton isn't 2 ups and 1 down quark (or 1 up and 2 downs for the neutron). It's 2 up and 1 down valance quarks, and a sea of gluons and quark/antiquark pairs that pop in and out of existence continually. It's this sea that makes up the majority of the mass of the nucleon. So, you contain a significant proportion of heavy quark flavors in your body at any given time, but you also contain a significant proportion of heavy anti-quark flavors, and statistically, these two cancel out, leaving you with (on average) zero strangeness, charmness, bottomness and topness. If you want to count both s and \bar{s} (strange and anti-strange) as having the same "strangeness" (which you shouldn't, but let's run with it), then I could try one of two things. First, I can look at the parton distribution functions (p.d.f.s) used by the collider experiments (Tevatron and LHC) to predict the results of proton-antiproton or proton-proton collisions. They need to know the probability of finding a u,d,s... quark or gluon with a given energy "inside" a proton. These p.d.f.s were originally normalized using other proton/electron collider experiments, and depend on the energy of the proton in a given frame of reference. I tried playing with the p.d.f.s I have for Tevatron/LHC calculations, and get a strange component of about 6% of the up+down component at low energies. But I'm not sure I trust this, since the p.d.f. isn't really intended to be used in this energy regime and it might just be giving me crap results.

There's one other thing that can be tried. Dark matter collision experiments often rely on hitting the heavy quark content in the nucleon, rather than the u or d components. So we can try to the calculated values for the strange quark matrix element to get an estimate - this has the advantage of being relevant at zero momentum transfer. When I do this, I get something like 3% (with considerable uncertainties - the strange component of this calculation is very tricky to determine), though this number probably isn't answering your question (just answering a vaguely related one).

So, to sum up: you have no strangeness from nuclear decays in your body. Any "real" strange quarks in your body are transients passing through on their way from the upper atmosphere or created in your body from high energy cosmic rays (sorry, I'm not calculating this number; I don't have the relevant spectrum of cosmic rays or required nuclear cross sections handy. If you're interested, what you want is the kaon spectrum from cosmic rays). If you want to count the strange/antistrange sea quarks in your nucleons, then an extremely rough estimate puts it at ~5% of the total number of valance quarks. But this contributes zero net strangeness, since half is strange and half is antistrange, and any strange quark "created" this way will disappear back into the gluon/quark sea very quickly.
posted by physicsmatt at 1:01 PM on August 22, 2011 [2 favorites]

I asked a couple of physicist friends.

Physicist A: "hmmm, strange quarks aren't usually laying around, I don't think; I'm going to take a potshot and guess at zero :)"

Physicist B: "I think she's right, except for times like when you're standing inside a particle accelerator, or maybe on a supernova"

And to them we say … Thanks guys!
posted by krilli at 4:35 PM on August 22, 2011