It’s now been five years since the huge earthquake off the coast of Japan in 2011 and the subsequent tsunami and reactor meltdowns at the Fukushima Daiichi plant in Fukushima prefecture. Japan is just starting to try to turn some reactors back on and the Fukushima site still isn’t completely secured. The Fukushima Daiichi disaster is the second largest nuclear accident ever recorded (Chernobyl remains the worst). It’ll still be a long time before things are really cleaned up.
At the same time, there’s still plenty of fear-mongering about nuclear power. I’ve had people try to tell me that much of that region of Japan is now basically a radioactive wasteland (something that happens in a town like Boulder), which is very far from the truth. There is a closed zone around the plant (I’ve never been particularly close though) but even a few towns away things are safe.
A huge earthquake (greater than magnitude 8.0) shook Japan on Saturday, registering as much as a 5 on the Japanese earthquake scale in some places. Given the size of the earthquake, the shaking was actually pretty minor and little actual damage was caused. The epicenter was incredibly deep underground, so while the distance along the surface was fairly low, the earthquake was actually quite far away. In Shinjuku in central Tokyo, there wasn’t too much shaking (it wasn’t even noticeable to those walking around on the street) although objects rattling around made it clear that an earthquake was happening. Reportedly, things felt much scarier even just a few miles away in neighboring districts of the city.
This isn’t the only activity to hit Japan in recent weeks. There’s also been extra activity at Hakone and even right now a small volcano is erupting on an island in southern Japan.
T2K released a preprint today measuring the charged-current quasielastic scattering cross section of muon neutrinos on carbon using the ND280 off-axis near detector. The measurement reports the total cross section, the double-differential cross section using muon kinematic variables (muon momentum and angle with respect to the beam direction), and also reports a fit to the axial mass parameter of a theoretical model. There is good agreement between the measured flux-averaged cross section and the expectation from theory, and agreement between the measured and expected differential cross sections are also mostly good. The axial mass extraction is also reasonably consistent with expectations, so overall, everything seems to fit pretty well to expectations from the NEUT Monte Carlo generator and also from previous measurements.
While in Tokyo, I was able to do a bunch of touristy things. Here are some quick thoughts on a few of these:
- Edo-Tokyo Museum: This is a museum on the history of Tokyo. Admission is around $6 (not including special exibits). I thought this was a really nice museum. It includes artifacts from various periods of the city’s history, from the Edo period, where it was the capital of the Tokugawa shogunate to the present day, as well as reconstructions of different aspects of life in different periods. It also has performances at different times throughout the day. It’s maybe more akin to a natural history museum than an art museum but has a lot of stuff that you wouldn’t normally see, particularly in the US where you might only get some pottery and samurai equipment from Japan.
- National Museum of Modern Art: This is another nice and fairly small museum. Admission is only about $4 so it’s incredibly cheap. This has a number of 20th century works from both Japanese and non-Japanese artists. Not as big as something like the MoMA in New York but still a really good collection with a different focus (i.e. a lot from Japan) than US modern art museums.
- Tokyo Metropolitan Government Building Observation Deck: A free(!) observation deck on the 45th floor gives great views of the city and the surrounding area. It’s also at Shinjuku station so it’s more centrally located than, for example, the Tokyo Skytree.
- Imperial Palace East Gardens: The whole Imperial Palace area is very impressive. The gardens are accessible 6 days a week during daylight hours and are free. There are various little gardens, such as a pond with gigantic goldfish, an area with trees from each region of Japan, and fields with rare varieties of fruit. There are many varieties of flowers, so it probably looks amazing during the spring when everything blooms. At this time of year it was mostly just roses that were blooming. It’s also a very quiet space in the middle of central Tokyo.
- Meiji Shrine: Another nice quiet area near a very busy part of town. This is a Shinto shrine – with surrounding gardens and a forest – to the Meiji emperor, who overthrew the shogunate, started modernizing the country, and restored the imperial family to power. They’ve found mosquitoes with the Dengue fever virus in the area recently so be careful here right now.
I also walked around Ueno Park but didn’t have time to go to the museums there. Those museums are also supposed to be very impressive.
The winners of this year’s Nobel Prize in physics were announced a few hours ago. The prize went to three Japanese physicists for their work in developing blue LEDs, which apparently could have some nice properties in the future. I don’t think this was a very high profile topic that many people expected would win the prize. The committee mentions that this choice was motivated at least in part by the potential good LED technology could do in the future rather than basing the award on importance to physics research.
The SuperK collaboration has released a new proton decay search, looking for protons decaying to a neutrino and a kaon. SuperK (Super-Kamiokande) is a large water Cherenkov detector in the Kamioka mine near Toyama, Japan that has already been running for many years. In addition to results like this, SuperK is also used as the far detector for T2K.
Proton decay is not allowed by the Standard Model due to conservation of baryon number. Many extensions of the Standard Model, such as Grand Unified Theories (GUTs) that combine electroweak interactions with strong interactions at very high energy scales do have proton decay. GUTs typically propose that the new unified force have a larger symmetry group that breaks down through some process into the SU(3)xSU(2)xU(1) symmetry of the Standard Model. This is similar to how the SU(2) (weak isospin) x U(1) (hypercharge) symmetry group of the Standard Model is broken into two clearly distinct forces at energies much less than the electroweak scale of around 100 GeV. The W and Z bosons acquire masses (80.4 and 91.2 GeV, respectively) via the Higgs mechanism, while the choice of the Higgs vacuum expectation value (vev) and mixing angle between the weak isospin and hypercharge fields are chosen to give us a massless photon, a massive neutral Higgs, and massive W and Z bosons with different masses and couplings to other particles. The fact that the W and Z have mass and the photon does not ensures that below the electroweak scale, the weak force is much weaker than electromagnetism.
One of the simplest GUTs is an SU(5) symmetry, although this has been ruled out for some time. This theory has multiplets that include both leptons and quarks, and interactions conserve the difference between lepton number and baryon number rather than both separately. This allows for a proton to decay to modes including leptons. Other GUTs similarly include various channels for proton decay.
This result looks for a kaon in the final state and finds a lower limit on the proton lifetime through this channel of 5.9×1033 years: many orders of magnitude longer than the age of the universe.