Why the puzzle existed: e-H vs muonic-H discrepancy

1:18:31Right. Okay. >> Okay. >> Yeah. Yeah. >> Proton size, >> right? Because because part of uh part of what I said earlier, which may or may not be true, it's like, you know, why do why can't we just measure it directly? >> Yeah. Well, I mean, how would you measure something that is a phentometer, >> right? But so like for someone who might not understand the scale of the problem set, it's like, well, why don't you just look at it? And it's like, well, the problem is you you it's it's what are we going to use to do that? >> Exactly. I mean I mean you could think, right? Like what if we just like set light? >> Okay. >> Okay. What if we just had like um light at a phentometer? >> Mhm. >> How I think I think that kind of light

1:19:13is extremely high frequency. >> Okay. >> Okay. Like a light at a wavelength of a phentoter. Yeah. >> Anything anything larger than the obstacle. If if I were to shine like visible light, which is like 400 nanome, >> right, >> on something that is a phento nan 400 nanome is 10 - 7 m. >> This thing is 10us 15. Imagine a giant ocean wave. >> Yeah. >> And then there's a pebble in the way. >> Okay. >> Is the ocean wave going to care? >> No. >> No. No. >> Right. The way we image things is that the the wavelength of light needs to be way smaller than the thing we're measuring because then the light bends and like refracts and like bounces off. This is important. >> But if it's like the you know

1:19:54>> the the object we're trying to measure is literally half the size of the wavelength of light we would send at it to even measure it. >> Yeah. Not even half. No, it's it's it's a th 10,000th >> 100,000 >> or a millionth the size. So it literally is it's a pebble >> with a tsunami >> like no a grain of sand versus like the Nazare you know the Portugal >> wave yeah the 100 foot wave in Nazare Portugal. Yes in Nazare Portugal. Do you think the Nazare Portugal wave cares about a tiny bit of grain of sand misplaced one way or the other? No, it really doesn't. So we got to get really clever with this kind of stuff. >> So we can't just image it the way we normally do optical imaging. It's just

1:20:36the scale is not uh it just it doesn't even make sense. >> It doesn't even make sense. Yeah. Exactly. And so people have done it before. People have measured the the size of a proton before. Yes. And it came out to about 0.8758 >> according to this giant consortium where where they they had like um electrons that would scatter off nuclei and then they would try to figure out okay like what is the what is the size of the proton in there. They also had something called electronic hydrogen spectroscopy. It's a traditional laser measurement kind of similar but like not as like insane as the one that we're going to talk about. And they got it to about 0.8758 phentometers. >> Right. >> Then in 2010 there was a bombshell.

1:21:17>> Right. >> Because some of the same guys in this current paper. >> Yeah. Yeah. >> Made an exotic hydrogen atom. They made a hydrogen atom out of muons. >> Okay. >> And they published a paper in nature called the size of the proton. This this was 15 16 almost 16 years ago. >> Almost 16 years ago, these guys published a hydrogen atom where instead of an electron moving around it, they've got a muon that moves around it. A muon is the close cousin of the electron, but it's 200 times more massive. >> And because it's 200 time more 200 times more massive, >> the atom that you create with a proton

1:21:58and a muon is going to be 200 times smaller. And we've got a little >> sort of like thing to show for that, right? The atom is going to be the muonic hydrogen is going to be 200 times smaller. If it's 200 times smaller, that muon effectively what we've done is take that giant stadium. >> Yeah. Yeah. >> And turn it into like, you know, a high school stadium. >> So, so >> now the the relationship between my muon and the proton is going to be a lot closer and my error bar is going to be smaller. the the the measurement we're trying to make is the distance between the electron and the grandstands and the proton at the 50 R. >> Yeah. Effectively, we're trying to get like the light that comes out of this atom. The smaller the atom is like the

1:22:41more we can sort of >> nail down exactly what that frequency is, >> right? The the the delta for error is much smaller. >> Yeah. Because we've effectively make made the atom smaller, >> right? Right. And this the the key idea here was the muon as the orbiting uh particle as opposed to a standard electron. It was much more massive which meant the proton necessarily need to be smaller which is what creates >> the atom needs to be smaller. >> Excuse me. The atom needs to be smaller which is what collapsed the surface area of the measurement to be this >> more dealwithable. >> Yes. >> Size. >> Yes. And we got a whole new number for the size of the proton there. 0.84 instead of 0.87. Okay.

1:23:23>> Already on the second significant figure, >> we're off. >> Okay. That is that is unheard of for physicists who are doing precision measurement. They're like, "This is this is absolutely awful." >> Okay. >> Okay. >> That's like a almost um >> that's almost 5% difference. >> Yeah. Well, that's unacceptable. >> That's unacceptable. Okay. In every sense of the word. [laughter] There's two there's two possibilities. >> Okay. >> Okay. Either our theory is wrong. Meaning lepttons are not universal. We used to think that the muon and the electron, the only thing that's different between them is the mass. >> Mhm. >> But what if there's new physics? >> Mhm. >> And the muon is actually behaving differently around my proton, which is

1:24:04why I'm getting this different >> measurement. >> Okay. Yeah. >> Either that or >> there's some undetected systematic error >> in the earlier measurement of the electron >> hydrogen. >> Basically, the first time we did it, something was wrong. >> Something was wrong. >> No one caught it at the time. But now we get it. >> Or there's literal new physics, >> right? It's one of the two. >> It's one of the two. And now you can see why this is such a big deal. >> We need to really figure out if that first measurement was actually wrong. >> Correct. Cuz that's that's actually a Okay. Yes. >> That would be a big deal. >> That would be a big deal because if the first measurement was correct, then this is a really big deal because then that means there is actually new physics. The muon and the electron are actually different somehow and there's like now

1:24:45the theorists are super happy. >> Right. >> Right. Right. or the experimentalists are not happy and these new experimentalists are happy because they like their muonic hydrogen measurement was actually correct and it's like everybody else >> oh theorist go back to the the chalkboard >> yeah yeah [laughter] it's not it's not a field day for you guys right and so that's where this current um experiment comes in >> oh this is fascinating they replicated that muon experiment >> okay from from 2010 >> from 2010 they've been working on it for 10 years >> to try and nail down this measurement using just normal storegrade hydrogen. >> Okay. >> Okay. And it's incredibly difficult.