The hadrons, i.e. the particles made of components bound together by the so-called strong nuclear forces are partitioned into 3 groups: particles made of 3 quarks, particles made of 3 anti-quarks and particles made of 1 quark together with 1 anti-quark.
Particles made from more quarks than in these 3 groups are possible in principle, but they would disintegrate extremely quickly, i.e. in times many orders of magnitude less than 1 nanosecond.
The reasons why only those 3 kinds of hadrons are normally encountered is that exactly like the electric forces attempt to neutralize the electric charge and prevent the negative charges to separate from the positive charges, the strong nuclear forces also try to neutralize a similar quantity, with the difference that this quantity is 2-dimensional, unlike the electric charge, which is 1-dimensional.
The condition of neutralizing that 2-dimensional quantity can be satisfied by the 3 kinds of quark combinations listed above.
The lightest hadron made of 3 quarks is the proton and the lightest hadron made of 3 anti-quarks is the anti-proton.
The proton and the similar hadrons can be considered as matter and the anti-proton and similar hadrons can be considered as anti-matter.
None of these hadrons made of either 3 quarks or 3 anti-quarks can switch between matter and anti-matter and this remains true for their compounds, like nuclei or anti-nuclei.
On the other hand, the 3rd kind of hadrons, which are usually named mesons, and which are made from 1 quark and 1 anti-quark, are in fact neither matter nor anti-matter.
The article linked here refers to a particle of this kind, where the total number of quarks is +1 -1 = 0.
So in mesons it is possible that the pair of 1 quark + 1 anti-quark will transform in another pair of 1 quark + 1 anti-quark, but where the quarks are different types of quarks than before the transformation. This transformation is possible because the total number of quarks is 0, both before and after the transformation, so any such transformation is possible as long as the new types of quarks are such so that the electrical charge remains the same.
The compositions of mesons can oscillate between different pairs quark + anti-quark, but the heavier mesons decay extremely fast so it is exceedingly difficult to observe such oscillations.
The linked article reports the experimental observation of such an oscillation, which was known as possible since decades ago, but it was not seen in experiments due to technical difficulties.
So in these transformations some quarks and anti-quarks appear and disappear, but the total quantity of matter and anti-matter is the same before and after, which is why the title is misleading.
This experiment says when they bump into each other ones spinning a certain direction always have a little spin to it left over. A tiny bit of fun still exists.
That little bit of fun is all physical matter in the universe.
Not unrelated, HN has a few actual subject matter experts who are often aghast at how wrong HN tends to be about any field or subject not directly related to programming, and how often their confidence is in inverse proportion to their knowledge.
You can safely assume that while there may be actual, credible particle physicists on HN, their voices are likely to be drowned out by armchair expositors of bullshit ranting about dark matter being a hoax perpetrated by cultural Marxists or somesuch. Do the work yourself. Read the article yourself. Enrich your own mind and satisfy your own intellectual curiosity, don't expect HN to do it for you, or to be better than the mainstream in terms of general expertise, or you'll be misled and disappointed more often than not.
I'm not putting aside skepticism and intellectual rigour when I read the comments here.
I also think you're wrong about the members of this community. There are a tremendously wide assortment of backgrounds represented here.
I come to Hacker News mostly for, not in spite of, the comments.
I think telling people to not ask questions is dangerous. The person I originally responded to was not doing that exactly, but it felt borderline enough to remind them that the community here is filled with experts and teachers.
It's also worth pointing out that we shouldn't silence curiosity. Attacking what you perceive as a lazy mind can only harm the desire to learn.
But HN does have a problem in that no one believes reading the article is worth the effort, and everyone prefers to just read the comments. The end result of that is a negative feedback loop of insularity and incuriosity, more people only engaging with the subject (or what they believe the subject is based on their reading of the title) on a superficial level rather than real intellectual discussion.
HN and Reddit are filled with people sneering at how dumb everyone else on HN and Reddit are. It makes for tedious reading, and a cringeworthy "I'm superior because I see how dumb everyone else is" status grab. If something is wrong, correct it or downvote it or ignore it; don't conjour up some imaginary mind-reading fantasy about how great the author must think they are and then sneerily tear down the strawman.
The one where instead of saying "here's a good book", you side-eye your friends and say "OMG Becky can you believe it, they are reading Twilight! THEY think it's a GOOD BOOK! a-haw-HAW-haw-HAW!", where the purpose is not to enjoy whatever book you are reading, or to share good books with other people and why you think they are good, not to improve the quality of books in general or to observe and people-watch with curiosity, but to re-inforce that people who read Twilight are inferior and therefore your group is superior.
From a PG essay[1] "When you tread water, you lift yourself up by pushing water down. Likewise, in any social hierarchy, people [...] will try to emphasize [their status] by maltreating those they think rank below. But I think the main reason other kids persecute nerds is that it's part of the mechanism of popularity. Popularity is only partially about individual attractiveness. It's much more about alliances. To become more popular, you need to be constantly doing things that bring you close to other popular people, and nothing brings people closer than a common enemy."
The status grab is "I must be superior to those people, because I'm here, and they are there so I'm not part of them, and they are inferior".
> "The only thing that's going to happen here is that I get aggressively downvoted and the problems I'm complaining about will continue unabated, because mentioning them makes for "tedious reading."
That will continue regardless; a big part of your rant was that Dunning-Kruger dross about how people who write a comment on the internet without adding a pile of IMHO to it must be cock-sure idiots who don't know how dumb and wrong they are. If that's correct and they don't know how wrong they are, how are they going to identify as the target of your rant and change? If they are "soooo confident", why would they know to change their belief?
The only thing that's going to change it is people pointing out incorrectness in a way that helps (i.e. without closing off avenues to change with insults), or downvoting it to hide it so it doesn't spread. In the "be the change you want to see in the world" sense.
Except the entire point of my comment (fairly, rant) was to tell the people who refuse to read Twilight that they should actually try reading Twilight instead of asking their circle of friends who probably haven't read Twilight but insist that it's garbage because all modern literature is infantile commercial pap whether it's worth reading.
>If that's correct and they don't know how wrong they are, how are they going to identify as the target of your rant and change?
They won't. They'll do what you're doing, attack me personally and lecture me and, ironically, attempt the exact same "status grab" you're accusing me of. Except something tells me you'll wind up with far more invisible kudo points at the end of the day than I will, because defending Hacker News and refusing to admit its flaws is always a better social strategy than criticizing it. Who's pushing whom under the water here?
I'm attacking one specific comment (yours), linking to the HN guidelines to say why.
You're ranting about "armchair expositors of bullshit ranting about dark matter being a hoax perpetrated by cultural Marxists" [any examples of this happening?], claiming that posting a comment on the internet means the author "believes they are a subject matter expert", presumably reasoning that "posting on the internet" is something only people who believe they are experts do? Claiming that people "wear their ignorance as a badge of elitism", because "not clicking a link" is somehow a claim of eliteness? You're accusing people of "thinking themselves superior", because "not clicking a link" is the same as saying "people who read the link are plebian"? (This isn't encouraging people to read articles, this is "everyone else is so dumb, eyeroll").
In your terms, you're pushing everyone under the water. I'm pushing you and people who post similar "everyone except me is dumb" rants, under the water.
But after reading twice, what seems to be going on is that a particle has a slightly different mass from its antiparticle. (That is the most unbelievable sentence I have written so far this year! It's just... wow. I didn't think that was even theoretically possible.)
This is not the case, and that would violate CPT symmetry.
There are two states with different masses (the mass eigenstates) but they are not antiparticles of eachother. They are linear superpositions of the flavour eigenstates:
|D1> = p|D⁰> + q|D̅⁰>
|D2> = p|D⁰> − q|D̅⁰>
where p and q are complex coefficients.
The difference in mass between D1 and D2 is directly proportional to the oscillation frequency.
If p/q ≠ 1, you have CP violation in this mixing. The amount of CP violation in this measurement was found to be consistent with zero.
But... having flavor eigenstates not being mass eigenstates is almost as mind-blowing to me. How is that possible?
And, by "p/q ≠ 1", I presume you meant their norms?
You get CP violation even if |p/q|=1 but Arg(p/q)≠0.
Some things are indeed too complicated to be explained in simple terms and analogies.
ELI5 what implications does that have?