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The First Particle Physics Evidence of Physics Beyond the Standard Model?

Xerxes314 Re:No, there is no evidence of BSM yet (97 comments)

The SM doesn't specify what the neutrino masses are; they're free parameters just like the quark masses. Some people might be surprised that they're nonzero, but I'm not one of them. Personally, I think some of those some people are feigning surprise so they can pretend nonzero neutrino masses count as BSM, which is a bit silly.

about a month ago

The First Particle Physics Evidence of Physics Beyond the Standard Model?

Xerxes314 Re:No, there is no evidence of BSM yet (97 comments)

Actually, the good news is that the experiment is definitely happening! They moved the ring to Fermilab last year and are busy setting it up to run. You can read more about it here: Muon g-2 at Fermilab. They even have a Facebook page.

about a month ago

The First Particle Physics Evidence of Physics Beyond the Standard Model?

Xerxes314 No, there is no evidence of BSM yet (97 comments)

I am a particle physicist, and I have worked directly on this problem. The uncertainty in the hadronic contributions to the vacuum polarization and light-by-light scattering are large enough that the supposed BSM signal is not significant.

That is, you can do nice high-order paper-and-pencil calculations of Feynman diagrams when the particles involved are electrons and muons, but there are important cases where the particles contributing to this effect are composite: hadrons (which are made of quarks). Since you cannot do calculations on hadrons without considering how the hadron is composed of quarks, you can't avoid getting into strongly coupled quantum chromodynamics (QCD). See here for further discussion: Hadronic Light-by-Light.

That means you can't do your calculation on paper, you have to use a supercomputer and something called lattice QCD. Unfortunately, it's easier to crank out a thousand crappy model calculations of BSM that is supposedly showing up than to properly fund studies of the theory uncertainties. As a result, the precision of the theory values are not good enough to establish whether the muon magnetic moment is consistent with the Standard Model or not.

That said, it's still an interesting place to look, and somebody will work out all the uncertainties eventually. In a few years, there might be something to talk about seriously.

about a month ago

The People Who Are Still Addicted To the Rubik's Cube

Xerxes314 Random starting configuration, eh? (100 comments)

So the starting configurations for setting the Rubik's cube record are random. If I wait long enough, the starting configurations will randomly be the identity transformation, and I can solve the cube in 0 seconds. Therefore, in the infinite-time limit, I am the Rubik's cube champion with an unbeatable time. QED

about 5 months ago

Physics Forum At Fermilab Bans Powerpoint

Xerxes314 At my university, our group ended chalkboard talks (181 comments)

For our group meetings, we used to do chalkboard talks, and this year we ended them for all the same reasons. Without slides, the discussion tends to wander aimlessly, and the speaker does not get to talk about what she intended to talk about in the first place. It takes forever to sketch the simplest diagrams on a chalkboard, the resulting figure has little accuracy and the audience has to sit through a lot of pointless sketching where no information is being conveyed.

Most people still use LaTeX-Beamer rather than PowerPoint, but the latest versions of PPT actually have very good equation tools, so IMHO, there's little reason to favor one over the other. The days of academics trashing on PPT are long gone.

about 6 months ago

Physicists Test Symmetry Principle With an Antimatter Beam

Xerxes314 Re:Feynman tutored me in QM at Caltech (106 comments)

"MAYBE THERE'S JUST ONE ELECTRON!" Feynman once shouted.

Actually, that's basically right. Our current understanding (in quantum field theory) is that there's only one electron field, and all electrons and positrons are quantum excitations of that field. It's a bit more complicated, in that there are actually four electron fields, which cover left-handed/right-handed and electron/positron degrees of freedom. But if you think of those four fields as being the "one" electron, the idea works perfectly.

about 6 months ago

Wolfram Language Demo Impresses

Xerxes314 Re:missing the point (216 comments)

If you were to write a simple python program that uses say, the Panda package, would you include all the lines of code of that package when line counting your program? No.

Yes, as we all know, Hello World in C is actually thousands of lines long. (shakes head sadly) It's a terrible language.

about 7 months ago

Wolfram Language Demo Impresses

Xerxes314 Re:Not so sure about the language... (216 comments)

b) it is opaque, in the sense that there is little control on what code is doing what data: many of the functions act actually as black boxes and it is not straightforward to see how to actually get in control of the system and/or understand what is actually being done in order to provide an answer.

You can usually twiddle all the options in a function; the documentation is pretty good for most of the standard libraries. Of course, the demo doesn't look as slick if you have to use 6 lines of optional parameters to get the exact thing you want. Typically, the default options do a pretty good job, and there's a lot less typing for those cases.

Of course, it's also a universal language. You don't have to use the standard libraries; feel free to roll your own. I'm sure an hour later, you'll have a bit more respect for how well the default stuff works.

about 7 months ago

Quarks Know Their Left From Their Right

Xerxes314 Re:Spin (150 comments)

If the spin of the particle (electron in the summary) is germaine to the observed properties of the particle does that mean there are two different particles involved?

Yes! And there always has been. Left-handed particles are not the same as right-handed ones. Quarks in particular come in a dizzying amount of varieties. There are 6 flavors times 3 colors times 2 spins times 2 for regular/anti. So in total there are actually 72 kinds of quark!

But people find it easier to talk about there being fewer kinds and specifying the exact types only as necessary. That makes sense, because particles of one type can change into particles of another type pretty easily. For example, you could have a quark in a superposition of left- and right-handed states. Quarks are constantly changing their color as they exchange gluons with other quarks inside the proton. Flavor and regular/anti change the least, so you generally hear people talk about a "strange quark" or a "top antiquark". But all those other properties are always around.

about 7 months ago

China's PandaX Project Looks For Dark Matter In the Heart of a Marble Mountain

Xerxes314 XENON is US-led (62 comments)

Actually, XENON isn't a European project, it's an international collaboration with leadership in the United States and members in Europe and China. The device is in Europe, but that's sort of incidental. Here's the membership: XENON-100

about 8 months ago

3 Habitable-Zone Super-Earths Found Orbiting Nearby Star

Xerxes314 Re:All three planets are probably tidally locked (203 comments)

Well, they're all much bigger and closer than Mercury, which would amplify the effects of tidal drag. Mercury avoids full locking by having a large eccentricity. None of the planets in the habitable zone (c,e,f) have substantial measured eccentricity, but the uncertainty is large enough that it might be possible for them to get into a 3:2 resonance. Even in a 3:2, the planet would still face the star for weeks at a time; the resulting temperature fluctuations might actually be more inhospitable than full locking.

about a year ago

3 Habitable-Zone Super-Earths Found Orbiting Nearby Star

Xerxes314 All three planets are probably tidally locked (203 comments)

I'm not sure what difference this makes to the actual habitability of the planets, but all of these are tidally locked. That is, the same part of the planet is always facing the star (and thus baked) while the same part faces empty space (and thus freezes). A thick atmosphere might transport heat and make things more uniform, but none of these are what one would naively think of as "habitable". In fact, all planets in the "habitable" zone of such small stars are going to be tidally locked. Wikipedia actually has a nice summary of the problem of tidal locking in small stars.

On the other hand, they might have very interesting moons.

about a year ago

First Particle Comprising Four Quarks Discovered

Xerxes314 Re:Hang on (111 comments)

There's no real way to "confirm" the number of quarks. Quark number is not a conserved quantum number, so every particle exists as a superposition of different quark numbers. This is particularly problematic if you probe a particle at very high energies; at sufficiently high energies, every hadron (including the humble proton) appears to be a soup of quark-antiquark pairs bubbling out of the vacuum. However, you should be able to make predictions of what the particle's properties will be if it's mostly like a particle that has 4 quarks (really 2 quarks and 2 antiquarks) versus if it's mostly like a particle that is 2 loosely bound mesons (1 quark and 1 antiquark plus 1 quark and 1 antiquark). But there's no definitive way to distinguish between the two.

It's also noteworthy that neither tetraquarks nor mesonic molecules have been previously seen in two experiments. So no matter which it turns out to be mostly like, it's still a discovery.

about a year ago

Google and NASA Snap Up D-Wave Quantum Computer

Xerxes314 D-Wave still does not have a quantum computer (108 comments)

Anyone interested in the D-wave story should be reading this article where Scott Aaronson explains the meaning of D-Wave's current results.

The takeaway points are:

  1. D-Wave's machine does demonstrate entanglement and quantum annealing
  2. There is no speed advantage whatsoever for quantum annealing over classical simulated annealing
  3. A correctly optimized version of classical annealing is actually faster than D-wave's solution
  4. D-Wave will only be able to make this machine work as a quantum computer (with the attendant speed gains) by implementing error-correction and other improvements that D-Wave have been loudly deriding for their entire history

about a year ago

Ask Slashdot: Really Short Time Wasters?

Xerxes314 Learn Chinese! (279 comments)

Skritter is a game where you draw Chinese characters. Like anything you do repeatedly, they will burrow into your brain and take up residence. Result: you have learned Chinese on your lunch breaks.

about a year and a half ago

When Was the Last Time You Used a Landline Phone?

Xerxes314 Used or used as a phone? (329 comments)

I used a landline phone just recently. It made an excellent chew-toy, rattle, hammer, button pushing toy and number lesson for my baby daughter. It worked much better than my cell phone for these purposes too!

about a year and a half ago

Large Hadron Collider May Have Produced New Matter

Xerxes314 Re:No comments, then a flood of experts (238 comments)

Well, it's just cool because it probes new regions of the parameter space (temperature and density) of quantum chromodynamics (the fundamental theory of the strong nuclear force). Knowing what nuclear matter does under extreme conditions teaches us new things about what kinds of matter that might exist in the cores of neutron stars, whether there could be more compact kinds of stars between neutron stars and black holes and what conditions were like during the first moments after the Big Bang. It also gives us more data to compare against the predictions of quantum chromodynamics, which will help us make sure that that's actually the correct theory of the nuclear forces. I can't think of any practical applications (say, to fission cross-sections or something) off the top of my head, but that doesn't imply they don't exist.

about 2 years ago

Give me a solder gun, and I can produce ...

Xerxes314 Soldered our supercomputer back together (321 comments)

Back in my grad student days, we saved the early hardware for our supercomputer (a BlueGene precursor) by programming and soldering an EEPROM to every daughterboard. On a massively parallel machine, that was quite an undertaking, and given that we were all *theoretical* physicists, it was kind of a miracle that the thing worked when we were done.

more than 2 years ago

Is Jupiter Dissolving Its Rocky Core?

Xerxes314 Re:Silica? (181 comments)

According to TFA, the MgSiO3 dissociates into SiO2 and MgO under Jovian core conditions. They don't calculate what happens to the SiO2, but assume that its solubility is similar to the MgO component. So that would mean that the SiO2 also goes into solution in the Jovian core.

Also of interest (at least to me) but not addressed in this paper is what happens to the nickel-iron component of the core. Perhaps they figure Jovians don't have enough to worry about, since they form so far from the center of the protoplanetary disk?

more than 2 years ago

Dark Matter Hinted at Again at Cresst Experiment

Xerxes314 Don't bet your house on this result holding up (80 comments)

It's consistent with DAMA and Cogent in the sense that it's ruled out by those experiments at only a few sigma. It's "near" Cogent in the sense that 8 is "near" 25, and it's "near" DAMA in the sense that 35 is "near" 10; that is, it's not near at all. It's ruled out by Xenon by many orders of magnitude. My favorite theoretical model to explain these results is IDM (Italian Dark Matter), which consists of dark matter that only exists in Italy. Presumably similar particles are responsible for whatever makes Guinness taste better in Ireland.

about 3 years ago


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