Quantum Diaries

This fantastic event takes place every year at the university, where local A level students from different schools attend a cram-packed day of particle physics. First, PhD students and staff give talks about the different kinds of particle physics detectors, the physics of the Standard model and what is being searched for by the LHC experiments the group is working on (ATLAS and ALICE), and more about how the LHC itself works. I love this part of the day because it is a fantastic example of physics communication done well - the students are keen to take in whatever can be thrown at them, and the talks are carefully put together and well rehearsed to ensure they are given as much as clearly as possible. My supervisor, Dr David Evans, is particularly good at this, bringing the subject to life, highlighting its immediate apparentness in our world, and aiding the students to visualise some of the extreme large and small scales involved.

The next part of the day involves careful preparation - the students are given the opportunity to try to identify and classify particular events. In the past, this used real data from the LEP (Large Electron Positron collider at CERN) experiments, and involved identifying Z boson decays to charged leptons (the electron and muon having rather different characteristic traits in a particle detector) or quark-antiquark pairs (that become two back-to-back jets in the detector). This gave students an exciting insight into how events are really chosen, and also how the first handful of events were, historically, analysed.

Now simulated events for the ATLAS detector are analysed by the students, thanks to the university’s Mark Stockton, who developed the visualisation software and spent alot of time preparing suitable tasks for this purpose. Here, the students get a closer insight into the challenge of the LHC - proton collisions are much messier than electron-positron collisions! This part of the day gets alot of the department involved, helping to moderate, as students pair up and work through event by event looking for particular decays, and at one stage, searching for the Higgs Boson. They learn brilliant problem solving skills here, surprisingly quickly picking up where to look when they see something unusual like missing transverse energy or a distracting spray of particles from a jet.

Next comes the part of the day I mentioned in my post, Communicating Science: 1. Small groups of students are placed with a member of staff or PhD student and and split up (in this year’s case, around the grass on campus). The students get the opportunity to discuss what they have learned, ask any questions and think process the information of the day. This year, the teachers made up their own small group too. The big questions that come up are then written down, ready for the grand finale of the day.

Once everyone is back in the main lecture theatre, a live video link-up to CERN is made, and questions are put to an expert. This year, the University’s Dave Charlton, Physics co-ordinator of ATLAS, was there to answer questions. However, even for him, some curiously difficult questions popped up. I love hearing all of the different things people want to ask about - everything from personal experience of the job to ethical and political queries, as well as a baracade of unusual physics questions. I always find that the younger you are, the better questions you ask about the world, so A level students are my favourite people to talk to because they have the curiosity to ask you something killer but have the maturity, interest and patience to take a full and detailed answer. Finally, Mick Storr, also connected via video link, usually gives us a tour from down in the tunnels. This year though, he was positioned just beside the ATLAS detector as something very exciting was happening. The students got to watch as the end-cap of the detector was slowly moved back into position after maintenance work. The scale is quite overwhelming - I remember my first visit to CERN in 2001 seeing the world’s largest (at the time, anyway) warm dipole magnet being moved by a crane above my head at ALICE. It takes your breath away.

And here I am, back to CERN! In the past weeks I spent most of my time traveling and attending conferences, which is one exciting component of our job. The IFAE (Italian Conference of High Energy) was held in Bari, located in the South of Italy.

Its fame in the world comes not only from the wonderful cathedral,but mainly from the “orecchiette”, the Puglia’s traditional ear-shaped pasta. As well   known, you can get “orecchiette” while walking through the narrow and charming streets of the old town!

(These nice pictures are from good friends of mine whom I had the pleasure to see again)

The conference covered a broad range of physics results, spanning from astrophysics to nuclear physics and finally to particle physics. Let me spend some time now to explain how we actually carry out a data analysis and produce our results. The process is long and complex, involving data taking, high level programming and final extensive data understanding. First the events are collected on tape, i.e. all signals from all sub-detectors are saved and used for so called “reconstructing” the objects in the event (from a set of hits recorded by the muon chamber we can infer that a muon passed through that given chamber, for instance). At this stage we know the nature of the object (being muon or electron, etc) at high level of confidence. Once we have such pictures of all events, we select those events which resemble the event we look for. If the particle we hunt for decayed into two muons and two neutrinos, we would select only events with two muons and missing transverse energy (neutrinos translate into missing transverse energy in the detector language). However, not only the particle we look for decays into two muons and two neutrinos, but also many other (non-interesting) ones. And generally the non-interesting processes happen at higher rate than the interesting ones! We might be left with millions of possible (candidate) events while we expect our particle to contribute with just hundreds events (or less). How do we dig these events out ? For each given event, we don’t know which process it corresponds to. We only know the rates of processes. Our approach needs to be probabilistic. In this framework, we then look for deviation from the rates we expect. Typically we measure the rates of the background processes that populate our pool of candidate events. The rate are known within some uncertainty. In most of the current searches the uncertainty is larger than the signal itself. The plot below gives you an example.

The histogram presents the number of candidate events we observe in data (black marker) compared to the number of events we expect from out background model (the meaning of the x-axis is not crucial now). The dashed area indicates the uncertainty on the prediction. If we focus on the first bin, we expect  a number of events varying between 2800 and 4000 and we observe 3600.  If the signal causes a deviation of - say - 50 events we would not be able to see it by simple counting.

To overcome this experimental limitations, advanced analysis techniques have been studied and finally, after careful consideration, deployed in the searches. Those techniques are not new, but were imported in the field fairly recently. They are machine learning tools, ranging from Neural Network to Boosted Decision Tree. Let me steal from Wikipedia a concise description: “machine learning is the sub-field of artificial intelligence that is concerned with the design and development of algorithms that allow computers to improve their performance over time based on data, such as from sensor data or databases. A major focus of machine learning research is to automatically produce (induce) models, such as rules and patterns, from data. Hence, machine learning is closely related to fields such as data mining, statistics, inductive reasoning, pattern recognition, and theoretical computer science.”
The basic idea is to teach an artificial brain to distinguish the signal from the background to levels that the experiments could not reach. This gave a boost to the sensitivity of the current experiments at the Tevatron. The top quark is mainly produced in pairs from a gluon at high rate; however it can also be singly produced in processes involving the exchange of the W boson. While in the first case we end up with high energy events containing a large number of jets (experimental manifestation of quarks in this case) and leptons, in the second case the amount of energy is smaller and the number of objects is reduced (one top quark decays instead of two top quarks). As a consequence the second process is extremely challenging from experimental point of view. The Tevatron experiments, CDF and D0, invested the past years in looking for that process!
Teams of physicists analyzed the data produced in proton-antiproton collisions to build the basis of background modeling and construct a solid “single top” search. Depending on the mode in which the single top decays, they could look for electrons, or muons or jets and missing transverse energy. Each decay mode needs to be distinguished from a different background source, due to other un-interesting processes or detector mis-measurements. Finally the separate analyzes are combined in a single sensitive search using machine learning techniques. The observation was announced in March, 15 years after the pair production of top quark pairs was firstly observed! The measured rate of single top production is in agreement with the Standard Model expectations.

We’ve already seen how important, and sometimes subtle, names for experiments and collaborations can be. In bigger collaborations, finding a name can also be a source of seemingly endless debate. The planned high-luminosity successor experiment to the currently still running Belle experiment at KEK in Japan just went through this process, with thankfully a final outcome now… Well, I do hope it is final, just to save my email inbox from more suffering! For quite a while now, this new experiment has been referred to as SuperBelle, in particular among the new European collaborators. But as usual, not everybody was happy with the name, so a name-finding process was initiated. I was actually surprised at the number of suggested names, ranging from perfectly reasonable to utterly crazy, and about one suggestion per each four collaboration members.

Anyway, a very good habit for future name searches is to just enter the suggestions into Google. If you can not bring the results up on your laptop while sitting in a crowded room without being seriously embarrassed or even risking to get your computer banned from the network because of violation of the network user agreement, the name might not be such a good idea after all…

After what felt like a thousand emails (probably more like a hundred or so), two names emerged as the ones with the most support: SuperBelle and Belle-II. I think both names would have been good choices, since they keep the already well known (and highly successful) Belle as part of the name. SuperBelle seemed to me slightly better, since it sounds more like a major step ahead. After all, this new experiment is aiming for a factor of 50 increase in the amount of collected data, compared to Belle. Following the discussion, I was surprised at the unbelievable childishness of some grown-up physicists: Threatening to leave the collaboration if the name SuperBelle is chosen? Shouldn’t science be the thing that drives your decision to participate in an experiment? Apparently not everybody thinks so. Well, anyway, after a shoot-out vote, Belle-II was chosen by a narrow margin.

So, now that we have a name, I think it is time to get back to work on making this new experiment happen, but then, we will also need a new logo. So there might be more fun discussions ahead!

S. Ramanujan( from http://www.math.rochester.edu/u/faculty/doug/)

I was asked by a friend of mine to read the blog to give him an example that numbers are interesting. It reminds me a very famous episode of S. Ramanujan, who was an Indian mathematician in the early 20th cent. He found tremendous numbers of mathematical formulas or relationships among numbers. When he was in the bed of a hospital, an English mathematician, G.H. Hardy visited his room, and said that he took a taxi of which plate number was 1729, and that this number was quite trivial one. But Ramanujan immediately answered that 1729 was quite interesting one, because it was the minimum number which could be presented by the sum of two cubic numbers in two ways, as follows;

1729 = 12^3 + 1^3 = 10^3 + 9^3.

It is natural to have a question why Ramanujan so quickly remembered 12^3=1728. Those days, Fermat’s Last Theorem, relating to cubic numbers, was one of the center problems among mathematicians. So it is not so strange, in some sense.

R.P. Feynman( photo by Magnus Waller)

This question is, however, solved by R.P. Feynman who was an American physicist, establishing the theory of electron and photon, quantum electrodynamics(QED) in the middle of 20th cent. Almost the same number appears in the book, ‘Surely you are joking, Mr. Feynman!’ That number is 1729.03.

At a restaurant in Brazil, Feynman had to compete against a Japanese who was very good at counting on the abacus. The problem was to calculate cubic root of 1729.03. Feynman immediately remembered 1728 = 12^3 because a cubic foot is 1728 cubic inches. Then Feynman used Taylor expansion to get better accurate solution, 12.002, before the Japanese got a result with his abacus. We, Japanese, do not use inch-feet system. But we can learn from this story that 1 foot is 12 inches! I wonder a large fraction of Europeans or Americans must know well about 1728=12^3.

But it was just Ramanujan who realized 1729 had such an interesting nature. Especially it is not trivial to prove 1729 is the minimum one. In this context, it is natural to agree with another English mathematician, J.E. Littlewood to say “Every positive integer is one of Ramanujan’s personal friends”.

このブログを読んでくださっている知り合いの方から、数字に関する面白い話はありますか？と聞かれました。それで思い出したのが、20世紀前半に活躍したインドの数学者のラマヌジャンのとても有名は話です。彼は次々と新しい公式や、数の関係を証明無しで量産しました。彼が入院していたとき、彼をイギリスに呼んだ数学者のハーディが見舞いに訪れたときの話です。ハーディの乗ったタクシーのナンバーが1729で、なんということもない数だね、と言ったところ、ラマヌジャンは直ちに、1729は2通りの仕方で2つの立方数の和となっている最小の数という面白い数です。と答えたというのです。

1729=12^3+1^3=10^3+9^3．

この話で思うのは、ラマヌジャンは何故12^3=1728を憶えていたのだろう、ということです。ただ当時は立方数に関係のあるフェルマーの最終定理がまだ証明されておらず、ラマヌジャンもいろいろと計算していたということなので、憶えていてもそんなに奇妙ではないということはあります。

ところが、この疑問に答えていたのが、20世紀に活躍したアメリカの物理学者、ファインマンでした。彼は電子と光の量子力学、量子電磁気学（ＱＥＤ）を構築した一人として有名です。その彼の著書「ご冗談でしょ、ファインマンさん！」の中で、ほとんど同じ数のエピソードがでてきているのです。彼の本の中での数は、1729.03なのですが。

ファインマンがブラジルのとあるレストランで食事を取ろうとしたとき、そのレストランにいた算盤がたいへん得意な日本人と計算の競争をする羽目になります。その計算問題とは、129.03の立方根をどちらが早く計算できるか？といった競争でした。ファインマンはすぐに、1立方フィートが1728立方インチであることを思い出し、その答えが12に近いはずとし、より正確な答えを求めるために、テイラー展開により補正を計算し、算盤の名人よりも素早く12.002を求めたのでした。我々日本人はインチやフィートを使っていないので知らないのは当たり前なのですが、この話から、１フィートが12インチであることがわかります。つまり、ヨーロッパやアメリカの人にとっては12の3乗が1728であることはよく知られていることなのでは、ということなのです。

しかし、逆に言えば、12の3乗が1728ということが知られていても、1729が面白い数だと最初にきがついたのはラマヌジャンだったということです。特に、1729がそういった性質をもつ最小の数であることを示すのは結構厄介です。この1729のエピソードを聞いたハーディの友人で、やはり数学者のリトルウッドは「どの正の整数もまことにラマヌジャンの親友のようなものだな」と言ったということに素直にうなずけます。

It is time to come back to my work on calorimetry, following my previous post, before I get distracted again by other things. This time I’m blogging on the couch, not on a plane, though.

So, where did I leave off last time? One of the key goals for ILC calorimeters is to achieve unprecedented jet energy resolution. The calorimeters developed by the CALICE collaboration rely in Particle Flow Algorithms (PFA) to achieve this goal, as discussed in my last post. What is needed to make PFA work? First and foremost: Extremely granular detectors, with high 3D resolution to provide a detailed image of the particle showers.

Particle Flow at work: Separating energy deposits of individual particles.

This is needed to provide what is most important for PFA: The separation of individual particles in a shower. The PFA principle is simple: Measure each particle in the jet (actually, each particle in the event) as good as you can. This will then give you the best possible jet energy resolution. Depending on the particle type, this measurement comes from different detectors. Charged particles are best measured in the tracking detectors, photons (mostly from the decay of neutral pions) in the electromagnetic calorimeter, and neutral hadrons in the hadron calorimeter. Now, the problem is that charged hadrons also give a signal in the calorimeters, and to make PFA work, the deposits of each of these particles has to be separated. This is only possible with very granular detectors, as illustrated in the figure on the right.

That is why, in CALICE, we are studying the best technique to build highly granular calorimeters optimized for this new idea. I am currently focusing on an idea for the hadronic calorimeter, based on small scintillator cells read out with tiny, novel photo detectors.

But that again is the topic for another post. For now, I have to get ready for a workshop on pixel detectors, a completely different part of modern particle physics detectors.

Sometimes, living and working abroad to follow your career passion has its difficulties, specifically concerning the people you leave behind. Of course you make new friends and associates, but your old friends and your family are the constants in your life that make it hard to be afar from. My Mother and sister live 7,000 km from me, and 8 time zones away in Edinburgh, while my Father lives even further in southern Spain and 9 time zones away. My greatest friends also all still live in Edinburgh. This makes it difficult to see everyone as often as I would like, as I very often have to make a choice between the UK or Spain each year, whether to see my Father or my Mother and Sister. Of course nowadays with Skype and other such devices, it is easy to talk face-to-face on a regular basis, and in fact I probably have more talk time with my parents than I did when I lived in the same city as them. However there is no freedom to have the kind of spontaneous family and friend activities that  one likes. 

So this year I am in luck. It just so happens that I will take a vacation to Spain in June for two weeks to stay at my Father’s house, where my Sister will come down to join us. This will be the first time I have seen my Father in the flesh for two years. Also, a few days later one of my good oldest friends from Scotland will join us for his vacation. It doesn’t end there. My Mother just happens to be vacationing in the North of Spain for a week at the same time, so I will also get to see her for a couple of days! There’s more: my friend from Jordan will be in Spain at the same time and would like to join us also. I feel an embarrassment of riches all of a sudden. So long have I felt that I don’t see all of the people I miss enough, and they are all going to be packed into the same two weeks! Amazing!

I may also be extending my stay to work on some particle detector tests in Madrid, with a group of collaborators, if they manage to book beamtime at the small accelerator there, so I could very well end up staying for up to 30 days in Spain, half vacationing, half working. I am very privileged to work in a job which is international by its nature and requirements. Physicists need to travel all over the world as members of collaborations and groups all working towards a common goal. In fact we travel less than the typical business traveler, but we may go to a more diverse range of countries to attend meetings and conferences where we share the latest knowledge, hatch plans to improve existing experiments or come up with novel ones. The internationality of science is what makes it tick - everyone brings different skills and ideas to the table. Governments pledge funding for different aspects of projects. The LHC is a good example, as is TRIUMF, where we receive scores of international scientists visiting us each year to help advance our knowledge in certain areas of physics. 

All this said, I do enjoy travel not connected to work, where I can dissociate myself from work for at least….oh a few days, and enjoy the warm pleasantness of the country where I was born. I am very much looking forward to it.  :)

Today I saw the personalized signature of my sister on QQ (the most popular instant messenger in China), saying “God could not be everywhere and therefore he made mothers.” Obviously she cites this Jewish Proverb for the coming Mother’s day. So I said, if God stays absolutely at rest, his location is totally uncertain according to the Quantum Theory. Therefore he could be everywhere. This is Uncertainty Principle introduced by Heisenberg, whose epitaph reads “He lies here, somewhere”.

“But God could not appear everywhere at the same, could he?”

“Eh~, that’s true. If you see God somewhere, to keep unitarity, he can not be elsewhere. But before you see God, he could be everywhere”

上帝不能到处都在

今天看到我妹妹在QQ个性签名上用英语写着“上帝不能到处都在，所以他创造了母亲”。显然是为了迎接母亲节引用的一句犹太格言。我跟她开玩笑说，如果上帝保持绝对静止的，根据量子力学，他的位置完全不可确定，在任何地方都有出现的几率。提出这个“测不准原理”的人叫海森堡，他的墓碑上写着“他长眠于此处，某个（不确定的）地方”。

“那上帝不能同时出现在所有的地方吧？”

“那倒是！如果你看见了上帝，那么根据幺正性，他不会同时出现在别的地方。不过在你看到上帝之前，他还是到处都在。”

KITP is very quiet during weekends. I am in my office, but no sound in KITP.  Normally in weekdays, I can hear many discussions here and there, but in weekends, silence has come. I bought my lunch at university center, and is waiting for my collaborator to come. 

In Japan, it is not like this in universities. In weekends, I can find many people working, not only grad students but also professors: they are so busy with lectures and administrative duties during weekdays, so they just enjoy physics in the weekends. Here the situation seems to be a little different.

Any physicists needs discussions, and also silence like this. It is very important to develop one’s own ideas gradually. And also for calculations. Some of my friends told me that they listen to music when they calculate, but I cannot believe it. I tried it many times, but it ended up with just finding that the music came to the end before I noticed it. 

This morning, here at KITP, I enjoyed the silence for thinking about various possibilities for developping my little idea. I walked in the office, I read some papers, and found out that one idea didn’t work easily, and some other ideas were already studied 3 years ago by other physicists. Good papers. It was a joyful moment to explore physics like this!

Just outside of the window is the beautiful sea. Quiet offices plus insightful discussions, plus wonderful seminars, all of these are combined here organiclly into a single institute — that is one of the perfect styles of physics institutes. Blackboards: everywhere. Anywhere one can start discussions. And seminars. The seminar by Joe Polchinski  was beautiful. Next week, I am going to provide a seminar here and at Caltech. I know I cannot go that high, but I will try my best. Rather than going to deliver technical physics, I will try to express my enthusiasm and excitement which I felt during the collaboration. Can a Japanese who is not good at exposing feelings do that? Well, let’s see how it goes.

It’s been a while since my last post as it’s all go here at the lab right now in preparation for a busy month of running.
Desperately trying to finish off the analysis of our last radioactive beam fusion experiment (the fusion of magnesium-23 with hydrogen in novae), I’m also in preps for three other experiments coming up imminently.

The first, a test experiment, starts on monday when we intend to implant stable aluminium into very thin carbon targets to prove that we can eventually use this method to create radioactive aluminium targets. This is a fairly trivial exercise but we’re short-staffed to do this simple job so it will be a busy few days.
Soon after, TRIUMF’s ISOL system will start up with a silicon-carbide production target and a ‘FEBIAD’ (Forced Electron Beam Ion-Arc Discharge) ion source to produce an intense radioactive fluorine-18 beam for two astrophysics experiments. The first of these is an elastic scattering experiment designed to probe quantum energy levels in neon-19 (which is what is made when fluorine-18 fuses with hydrogen) of astrophysical interest. The second is a DRAGON experiment where we will measure directly the fusion of fluorine-18 with hydrogen, and experiment that has not been done before due to lack of an intense enough beam.
So expect radio silence from me at least until mid-next week, but then I shall be blogging about the daily activities of the fluorine-18 experiments and you will hopefully get an insight into the drama, banality, trials, fortunes, etc…of a nuclear physics experiment!

Yesterday I had the pleasure of meeting with a group of 8th graders from a local middle school.  They were visiting the lab on a field trip and, as is custom for tours, arrangements were made near the end of their visit to meet with an employee from the lab - this time me.   I do this once or twice a month and many other people at the lab participate as well, as there are many tour groups that visit Fermilab.

It’s not a presentation, but rather a Question & Answer session, so it requires no preparation on my part other than to be in the right room at the right time.  The free form of these sessions, I think, is what makes it so much fun for me.  This week I was asked everything from how long I had to go to school to do my job here (that one always gets their attention!) to whether the protons and antiprotons make any sound when they collide at such high energy.  I mean, that’s a really great question!  I usually have to be coerced by the tour docents to stop taking questions 10 minutes past the allotted time.  I think they remind me a little why I ultimately wanted to become a scientist in the first place - there are so many great questions out there to be answered - and I always come away from these sessions feeling refreshed and enthusiastic.  That’s a pretty remarkable result from a 30 minute session squeezed into a packed schedule between lunch and some afternoon meeting.  I only hope the students get a fraction of what I do out of our brief discussions.