The Super-K detector

Super-Kamiokande is a 50~kiloton water Cherenkov detector located at the Kamioka Observatory of the Institute for Cosmic Ray Research, University of Tokyo. It was designed to study neutrino oscillations and carry out searches for the decay of the nucleon. The Super-K experiment began in 1996 and in the ensuing years of running has produced extremely important results in the fields of atmospheric and solar neutrino oscillations, along with setting stringent limits on the decay of the nucleon and the existence of dark matter and astrophysical sources of neutrinos. Perhaps most crucially, Super-K for the first time definitively showed that neutrinos have mass and undergo flavor oscillations.

This facility is in the Mozumi mine of the Kamioka Mining Company in Gifu prefecture, in the Japanese alps. Super-K consists of two concentric, optically separated water Cherenkov detectors contained in a stainless steel tank 42 meters high and 39.3 meters in diameter, holding a total mass of 50,000 tons of water. The inner detector is comprised of 11,146 Hamamatsu~R3600 50~cm diameter photomultiplier tubes (PMTs), viewing a cylindrical volume of pure water 16.9~m in radius and 36.2~m high.

A famous neutrino letter: “Dear Radioactive Ladies and Gentlemen,”


The most famous document in neutrino physics is the letter Wolfgang Pauli sent explaining the idea for the particle.  It begins “Dear Radioactive Ladies and Gentlemen,” and due to his embarrassment at proposing something that seemed crazy and probably not-observable he gives an excuse for not attending the meeting in person:

“Unfortunately, I cannot personally appear in Tübingen since I am indispensable here in Zürich because of a ball on the night from December 6 to 7.”

No such reticence occurs today (also physicists don’t usually attend balls due to their typically poor waltzing skills).

Symmetry Magazine had a nice picture and exposition of the original letter, explaining what various parts mean, and Kurt Riesselmann’s translation from that article is below.


Physics Institute of                                          Zürich, Dec. 4, 1930
the ETH Zürich

Dear Radioactive Ladies and Gentlemen,

As the bearer of these lines, to whom I graciously ask you to listen, will explain to you in more detail, because of the “wrong” statistics of the N- and Li-6 nuclei and the continuous beta spectrum, I have hit upon a desperate remedy to save the “exchange theorem” (1) of statistics and the law of conservation of energy. Namely, the possibility that in the nuclei there could exist electrically neutral particles, which I will call neutrons, that have spin 1/2 and obey the exclusion principle and that further differ from light quanta in that they do not travel with the velocity of light. The mass of the neutrons should be of the same order of magnitude as the electron mass and in any event not larger than 0.01 proton mass. – The continuous beta spectrum would then make sense with the assumption that in beta decay, in addition to the electron, a neutron is emitted such that the sum of the energies of neutron and electron is constant.

Now it is also a question of which forces act upon neutrons. For me, the most likely model for the neutron seems to be, for wave-mechanical reasons (the bearer of these lines knows more), that the neutron at rest is a magnetic dipole with a certain moment μ. The experiments seem to require that the ionizing effect of such a neutron can not be bigger than the one of a gamma-ray, and then μ is probably not allowed to be larger than e • (10-13cm).

Therefore one should seriously discuss every way of rescue. Thus, dear radioactive people, scrutinize and judge.


I admit that my remedy may seem almost improbable because one probably would have seen those neutrons, if they exist, for a long time. But nothing ventured, nothing gained, and the seriousness of the situation, due to the continuous structure of the beta spectrum, is illuminated by a remark of my honored predecessor, Mr Debye, who told me recently in Bruxelles: “Oh, It’s better not to think about this at all, like new taxes.” Therefore one should seriously discuss every way of rescue. Thus, dear radioactive people, scrutinize and judge. – Unfortunately, I cannot personally appear in Tübingen since I am indispensable here in Zürich because of a ball on the night from December 6 to 7. With my best regards to you, and also to Mr. Back, your humble servant

signed W. Pauli

Roger is in Canada!

Roger is in Canada.  He is spending six weeks working on the HALO experiment. Underground in asia got boring so he is checking out the north american underground.

Alex Himmel joins group

Alex Himmel

Alex Himmel officially joins the group as a postdoctoral researcher this month. He got his Ph.D. working on the MINOS experiment at Caltech.



Poem: Cosmic Gall


Neutrinos, they are very small.
They have no charge and have no mass
And do not interact at all.
The earth is just a silly ball
To them, through which they simply pass,
Like dustmaids through a drafty hall
Or photons through a sheet of glass.
They snub the most exquisite gas,
Ignore the most substantial wall,
Cold-shoulder steel and sounding brass,
Insult the stallion in his stall,
And scorning barriers of class,
Infiltrate you and me! Like tall
And painless guillotines, they fall
Down through our heads into the grass.
At night, they enter at Nepal
And pierce the lover and his lass
From underneath the bed-you call
It wonderful; I call it crass.

John Updike

Exciting new T2K Results!

A T2K candidate electron neutrino event

After many years of work in T2K we are excited to report our first indications of electron neutrino appearance!

Read more on Chris Walter’s website here.
Read the official T2K press release here and the Duke Today story here.



The T2K experiment is a “long-baseline” neutrino experiment where neutrinos are produced in an accelerator north of Tokyo and then shot across Japan to the Super-Kamiokande detector underneath the Japanese Alps.  Super-Kamiokande is a giant underground water Cherenkov experiment, designed to capture neutrinos from the Sun and sky: the 11,000 inner detector photomultiplier tubes (PMTs) record photons from the charged products of neutrino interactions in the ultra-pure water.  In the T2K experiment, Super-K acts at the far target of the neutrino beam.

In 1998, Super-K showed that muon neutrinos produced by cosmic ray collisions in the Earth’s atmosphere “disappear” by changing to almost-invisible tau flavor: the neutrinos “oscillate” from one flavor to another by interference of mass states.  Such flavor change is only possible if neutrinos have mass.  Neutrino masses and the parameters which govern neutrino flavor oscillation are deeply connected to both fundamental particle physics and cosmology. Over the next few years, the Super-K atmospheric neutrino result was confirmed by other experiments.  The beam neutrinos “went missing” in exactly the numbers expected, and with exactly the expected energy dependence predicted by the oscillation hypothesis.

The next physics quest for Super-K is the search for  the unknown neutrino oscillation parameter, “Theta _13” as part of the T2K experiment.  The signature of non-zero Theta_13 is a tiny amount of electron neutrino appearance in a beam of muon neutrinos.  The T2K experiment is designed to measure this parameter by looking for muon neutrinos produced in an accelerator at the JPARC center north of Tokyo to transform into electron neutrinos after they travel 295 km across Japan.  Since this is a very small effect, a powerful beam is needed to create just a few of these events.

In the latest T2K results, the accelerator made a beam pulse of neutrinos over two million times.   Six events consistent with an electron neutrino were observed, although only 1.5 events would have been seen if muon neutrinos don’t oscillate into electron neutrinos.  The probability that the observation is just due to a chance fluctuation is less than 1%.





Duke at Super-K

Super-K is located near Toyama city in Japan.  In fact, Toyama is a sister city of Durham . Home to Toyama bay, firefly squid and excellent Buri, you can be there in a short 20 hours from Durham!

Members of the group make frequent trips to the experiment and some are based there.  We have been and are involved in both the physical construction and maintenance of the experiment, and data analysis from both Super-K and T2K.