Meet Teppei Katori

22nd May 2017
Neutrino Interaction Physics

Hi everyone, my name is Teppei Katori! I am a lecturer at Queen Mary University of London, UK. My research topics include nuclear physics, particle physics, and astrophysics, both theory and experiment. Yes, I am the "Teppei of all trades, master of..." oops. But this also applies to my private side, I like dancing, music, reading, football..., and many others.

Two of my major interests are “neutrino interaction physics" and "test of Lorentz invariance with neutrinos". Three of my major collaborations are the T2K neutrino oscillation experiment in Japan, the IceCube Neutrino Observatory at the South Pole, and the NuSTEC (Neutrino Scattering Theory-Experiment Collaboration), at Fermilab. All of them are related by neutrinos. So clearly I consider neutrinos are the sexiest particles alive.

Today's talk is mostly about the neutrino interaction physics at the MiniBooNE neutrino experiment at Fermilab, USA. 

I did my undergrad at Tokyo Institute of Technology, Japan. All my undergrad time was dedicated to play football in the college league, men's choir, working in cafe, and other activities. So in the college I think I learnt a lot about the life, but not much about physics. My uncle did his PhD on atomic physics at University of Alberta (Canada). One day he said, "Teppei, you should leave this country, you are different and person like you never be successful in Japan. Go America, you may find American wife." So I went to America for my PhD. Although I didn't prepare much to apply, I managed to be accepted by Indiana University, Bloomington. I still don't understand why they accepted me. But anyway I started my new life in USA as a PhD student.

Bloomington is a typical college town, small, beautiful, lively, liberal, etc… and everyone loves it but I didn’t enjoy much because I struggled many years to communicate with people. Speaking English is an easy part, you can always express whatever you need to say and people listen carefully whatever they need to know, and you usually don’t have problems in language for your research. The problem comes every other place. Basically, you never follow any conversations at any places because of lack of background knowledge (movies, musics, etc) and difference of communication culture (distance with people, rhythm of conversation, hand and facial gestures, etc). So don't be harsh if your Asian colleagues look bored or not interactive, they may try hard but it’s not easy. Now my Japanese colleagues ask me how long did it take for me to speak English like this, and I usually say "4 years". My 4th year in USA, first time I felt I can speak comfortably with girls on the counter in a bar (which is a typical example of people not interested in your story!). But again this is not about my English skill, but more about cultural thing. There are tons of bars in front of the college but I've never been single one in my first 3-year life in America. It's bit scary for non-white person because I didn't feel welcomed. But all these are just cultural differences.

There is no better or bad culture, there is only a difference. I am so granted to be a Japanese, because Japan is a member of western world (=I can travel most of countries without visa) but very unique country. However, sometimes I feel Japan is too unique. When I first came to USA I was shocked how "the rest of the world" shares so many things but not with Japan. If you have Japanese colleges, ask them about 80's music. They (=including me) know none. Ask them about Star Wars or DC comics. Very few grew up with those, because we have too many our own stuffs. Somehow, Japan kept their uniqueness so well and that's cool thing (at least my wife thinks so, ah yes, my American wife), but it becomes little problem for Japanese to be assimilated with different environments. I gave a talk about my cultural experience in the "Story Collider" and a podcast is available.

So my time in Bloomington was bit isolated and bit sad, but because of this, I first time studied very hard. The topics I studied from two of my supervisors, Prof. Rex Tayloe (neutrino interaction physics) and Prof. Alan Kostelecky (violation of Lorentz invariance) are still my main topics through the T2K, IceCube, and NuSTEC.

I moved to Chicago to work further on the MiniBooNE experiment at Fermilab. This experiment uses a neutrino beam around 1 GeV. These muon neutrinos are created by decays of mesons, which are created by shooting 8 GeV protons extracted from the Fermilab Booster to a target. Muon neutrinos travel around 520 m and detected by the MiniBooNE Cherenkov detector. It measures neutrinos from an interaction called "charged-current quasi-elastic" (CCQE) interaction, where a neutrino collides (=exchange W-boson) with a neutron, and become a muon and a proton. This muon is energetic and makes characteristic Cherenkov radiation and by observing the Cherenkov light by an array of photo-multiplier tubes, we know neutrino interactions happen. CCQE is almost the simplest intersection you can imagine, but some reason simulation never agrees with our data. Rex was working on this problem, and I started to work with him, too. We needed a simulation to describe this interaction correctly, since if they don't agree we cannot measure the energy of neutrinos correctly. This means we cannot measure neutrino oscillations correctly and we would evaluate wrong neutrino masses. By the way neutrino oscillations and neutrino masses are topic of the Nobel Prize 2015 and the Breakthrough prize 2016. In order to describe our data by our simulation, we needed to tune a parameter called "axial mass (MA)" to be around 1.2 to 1.3 GeV (2007, but this parameter is known to be 1 GeV from other measurements. So something is not quite right…


Meantime, in Chicago, I met so many people and they are still my best friends, or Chicago became my hometown. In here, I met a band "Environmental Encroachment (EE)" (for example this I really liked it, so I started to follow their tours, and eventually I joined and started to play trombone. If you see a guy playing plastic pink trombone on streets in London, that’s me. The tours I made with EE are highlights of my life (the picture is from the Honk West 2012 festival, Seattle). I will talk about this more in other time...


Going back to my research, after many years of study, we concluded we didn't understand what was going on in our CCQE data, but we had multiple evidences this was not just a mistake of our experiment. So Rex, Dr. Sam Zeller (Fermilab), and Dr. Gerry Garvey (Los Alamos National Lab) came out the idea, we should publish the data but in the least model-dependent way so that any theorists can take a look and test their models directly (2009 ). Technically, we published the first flux-integrated double differential cross-section. That was a kind of game changing in this field, because back then everyone tried to figure out problems by themselves, and not openly discussed in the community to solve problems. You know, but some unknown theorists living in remote places might have better ideas to explain what's going on in the MiniBooNE CCQE data. So we bet our money on that possibility.

Teppi Katori and Kevin McFarland, class room of NuSTEC 2015

Shortly after (2009 ), theorists Dr. Marco Martini (the guy with me in the first picture) and others came out a solution. I don't describe here, but basically the problem was, we (=particle physicists) ignored nuclear physics, and nuclear effects modify the appearance of CCQE interaction. In CCQE, a neutrino hit a neutron, but neutrons are always in a nucleus. So we need to take account variety of effects, such as motion of nucleons (Fermi motion), suppression of nucleon kinematic phase space (Pauli blocking), overlaps of wave functions of nucleons in a nucleus (nucleon correlations), etc. Particle physicists tend to ignore nuclear physics because it looks messy and unsexy. But the importance of nuclear physics is increasing for neutrino physics. The main conference in neutrino-nucleus scattering community is the NuInt series, and in NuInt 2015 at Osaka, Japan, Prof. Kevin McFarland (University of Rochester) tore a T-shirts saying “MA=1.3” on the stage as a celebration of understanding of MiniBooNE CCQE puzzle.

In 2014, Dr. Jorge Morfin (Fermilab) and Dr. Luis Alvarez-Ruso (Valencia) formed a new collaboration called the "NuSTEC (Neutrino Scattering Theory-Experiment Collaboration)" to enhance further activities between nuclear and particle physicists, both theory and experiment. When they invited me to join, I joined immediately. Neutrino interaction physics has so many related topics, those are what you can see from my first picture. NuSTEC also organizes a school. This is a picture from the NuSTEC school 2015, Okayama university, Japan. It was unimaginable few years ago, that nuclear and particle physics PhD students, both theory and experiment, sit together to learn neutrino interaction physics! Our next NuSTEC school is coming on Nov. 7-15 at Fermilab, please feel free to join!

Class room of NuSTEC 2015

Another NuSTEC activity I am involved in is the NuSTEC News, which is the first kind of mailing list dedicated to the neutrino interaction physics, and in here we share latest news of neutrino interaction physics in the community. Clearly, this is inspired from the long-baseline newsletter made by Dr. Maury Goodman (Argonne National Lab). I also made a Facebook page for NuSTEC News, please “like” it today! I also encourage everyone to use hashtag #nuxsec for any news about neutrino interaction physics. So I am encouraging everyone to study neutrino interaction physics. It’s fun! We have real problems to solve. Please join us to make neutrino interaction physics great (I don’t say “great again”, because it’s never be great in the history of particle physics). If you want to learn this subject more, please read my review paper.

I picked up neutrino interaction physics for my research topic during my PhD, and I am still working on that. I didn't discuss my postdoc job, violation of Lorentz invariance, astrophysics, life in London... but I will talk more in the next time, ciao ciao!

High Energy Accelerator Research Organization (KEK)