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Archive for May, 2009

This week at CERN, Julie Peasley of LA came to tell us all about her subatomic-particle plushies – a way to make the abstract world of particle physics come to life. I love these adorable toys! They also have a facebook application, which is where I first found out about them.

Each one has been carefully designed to reflect the kind-of personality of the particle it represents. They are stuffed to have different relative weights depending on the masses of the particles. The quarks are triangular and point up or down depending on their position in the flavour heirarchy – a pair of each for each generation: down and up, strange and charm, bottom and top; so you can be reminded of their charges!

Higgs boson, right, and Dark matter, left, spotted at CERN! Heehee...

Higgs boson, right, and Dark matter, left, spotted at CERN! Heehee...

The charm quark has a charming rose on his collar, the strange quark (my favourite, and the most relevant to my analysis) is, well, strange! The neutrinos have black masks and look very ninja-like, which I think really reflects their elusive nature, and the W boson is double sided, reminding us that it comes in a positively and negatively charged form. You can even buy large proton and neutron plushies with three quarks and a gluon encased and zipped up safely inside them. If you buy the full set, you receive a booklet describing each of the particles in more detail.

Strange quark plushie!

Strange Quark Plushie!

All of these toys are handmade by Julie and her helper, Laura. So when you place your millions of orders as I am about to, spare a thought for them with their hands full. Thanks greatly Julie, this is truly inspired (and a great gift idea!)

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His Royal Highness Prince Edward, Duke of Kent visited CERN on Friday, and I was one of the students lucky enough to meet him.  He is President of the Royal Institution and has taken an interest in the LHC and the work being done at CERN.  In particular, as the former Special Representative for the International Trade and Investment,  he was interested to meet British young people being trained at CERN. During his visit, he was first given a tour of CMS (the Compact Muon Solenoid experiment).

His Royal Highness Price Edward Duke of Kent

His Royal Highness Price Edward Duke of Kent

A representative handful of students, post-docs and spokespersons were invited to gather for discussion with His Royal Highness, together with representatives for STFC (Science and Technology Facilities Council) and UK Trade and Investment. Prof. John Ellis was there to explain the more complex physics concepts, and some members of the IT side of CERN were there to discuss their skills and impact.

My father has met His Royal Highness twice, many years ago when he was a member of the Territorial Army. Apparently, they shared a plane. However, this was far from a familiar situation for me – I wasn’t sure of the right way to dress, act, stand or introduce myself. Everyone seemed to have this aura of nervousness. However, my concern was quickly dispelled as soon as His Royal Highness greeted me with a pleasant and relaxed “How do you do?” (I am still not sure if I was supposed to curtsey, but if I was, he didn’t seem to mind!)

I told him I was working on the ALICE experiment, which was understandably met with an inevitable confusion, because only last year he came across the ALiCE (Accelerators and Lasers In Combined Experiments) group, visiting the Linac at Daresbury Laboratory. However, he seemed very interested in hearing about the work that ALICE at CERN were doing, if a little blown away!

After the informal introductions and coffee, we were each seated around a large table in one of the Main Building’s meeting rooms. By chance, the students and most CERN staff lined up on the opposite side of the table to the visitors, which felt to me like we were more “on show”. I suppose we were, in a sense, but not in an intimidating way. We each then gave a more detailed description of ourselves, our work, and our roles here at CERN. I felt proud to be representing ALICE in this visit, and there seemed to be much interest in this unusual and lesser-known experiment. As usual, I basked in the opportunity to talk about my work!

The discussion that seemed to raise the most concern was on the topic of undergraduate technical training at CERN. The issue of too few UK technical students taking a year at CERN (an opportunity that I had never previously heard about) was illuminated, and it was not clear whether this was because of lack of knowledge or lack of opportunity. It seemed clear from the discussion that action was soon to be taken.

Finally, I feel I need to say my piece regarding a concern which was not raised but merely implied.The importance of innovation and development for the future of the UK was made clear. We were described as part of the solution to the economic problems, both in the advances and technology that falls from our work and the skills we acquire whilst working here. It is this second point that I felt left a strange feeling in the air. You see, most students working at CERN are enjoying their experience a great deal (myself included), and when asked by His Royal Highness, “Do you intend to stay here?”, almost every response was, “Yes, as long as I can”. Now, my answer to this was somewhat drowned out by these enthusiastic replies. I wanted to reiterate it at a later stage but never found a good moment. So, for the benefit of people who read these blogs, here it is:

I am from the UK, and have every intention of returning to work there permanently – it is my home. CERN is the most exciting place in the world to me right now and has been for many years, and to have the opportunity to conduct analysis for my PhD here makes me one of the luckiest people in the world. However, this is training I hope to be able to bring back to the UK.

So there it is. I want to bring my skills to the UK. In what field though, I am not sure. It does not seem too likely that I will be able to remain in my field of research in my country. In particle physics it is usually expected that you travel to many different countries on post-doc placements. However, that is not the only reason I will need to change direction.

Despite ALICE being one of the four large LHC experiments, the only institution in the UK working on the experiment is the University of Birmingham. This is not to say our contribution is small – our group contributes the Central Trigger Processor, an essential part of the ALICE detector that controls when each of its sub-detectors should send information about an event and when they should reject it. Our analysis is also important, and wide-ranging, from measurements of the very first few minutes of data to more long term detailed analyses. The problem is that we are low in number. As a result, heavy ion physics is not well known here, and I fear that defending its funding may be a struggle. Certainly finding myself a career in this field would mean working abroad for many many more years, if not indefinitely. In addition to this, mine is not the only field of research in which there is, not so much a shortage of UK studentships, but a very limited number of post-doc places.

It was mentioned in the meeting that the worth of a PhD student in the US is approximated to around 2 million dollars (apologies for not quoting the correct source of this, but I do not know what it is!). This indicates that training young scientists is a valuable INVESTMENT. The point I want to make is that, at least in my case, that is exactly what the UK is doing by allowing students to work here – INVESTING. CERN is a centre for knowledge and development and trains young people so that they can return to their home countries with these skills. I have learned so much being out here, I have developed in ways I never even expected. However, what I am yet to find out is, in what career my skills will be so useful, and in what way I will be part of “shaping the future”, as it is so often described. I am told that my skills are vital, but where?

Needless to say, some career-research needs to be done on my part, and I do have a fair idea already. I can tell from what I know so far that the possibilities are varied and almost endless. Another post, perhaps. As for where I myself will end up, time will tell, I suppose! All I know is, it is an exciting journey into the unknown. In the meantime, and perhaps for the rest of my life, I will continue to fight for fundamental research and its importance, and hopefully post-LHC discoveries, future generations may see improvement in opportunities in heavy ion and nuclear physics research in the UK. I can but hope (and do as much shouting about it as possible!) 😀

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My Daughter

Sunday, May 24th, 2009

keke

My daughter is 1.12 years old.

She likes books and reads aloud. But it is not easy to understand. Each sentence has 3-5 words. Probably she is speaking Korean.

She knows to say thanks. But it seems she doesn’t know who should say, the person receives something or the person gives. She often makes me awkward by giving me something and saying thanks.

Sleeping is an action, not a process. When I said “Keke, sleep”, she was docile enough to grovel on her pillow. After 3 seconds, she got up and continued to play. Yeah, sleeping is done.

Once she understand something is bad, not allowed to do, she will do it repeatedly, and smile evilly.

我女儿现在1.12岁了。

很喜欢翻着书大声朗读,不过听不太懂,三五个字一句,可能是韩语。

她知道说“谢谢”,但好像不清楚是拿东西的人应该说还是给东西的人说,经常递给我一件东西,然说说“谢谢”,弄得我很尴尬。

一旦她明白一件事是坏事,不许干的,她就会反复干,带着一脸贼笑。比如掰茶几的护角,在地板上撒水。

尿尿知道蹲下,叫人,或指尿盆。但帮助不大,因为经常谎报军情,有事没事蹲下嘴里“嘘嘘”。以后一定要多给她讲“狼来了”的故事。

睡觉是一个动作,不是一个过程。“柯柯,趴下睡觉”,她就很听话地趴到她的枕头上睡觉,三秒钟后爬起来接着玩,因为睡觉的指令已经执行完了。

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Uphill

Sunday, May 24th, 2009
View of the Tegernsee from the sumit of the Hirschberg

View of the Tegernsee from the summit of the Hirschberg

There is nothing like a day in the mountains to decompress from all the stress and excitement of shifts; well, maybe a day at the beach, but real beaches at some ocean are notoriously scarce in Munich. In the late spring, it is far too late in the season for skiing, but that’s not so bad, after all, hiking is also a good way to enjoy the mountains.

Hiking up through the snow.

Hiking up through the snow.

On Saturday morning, we headed south to the first ranges of the Alps, to hike up the Hirschberg, a mountain near the village of Kreuth in southern Bavaria. At an altitude of 1700 m ASL, it is not a really high alpine peak, but since the valley is around 730 m, it is quite a climb. The mountain is actually quite close to the castle Ringberg, where I spent a few days at a workshop recently.

After all the snow we had in late winter, there is still some left in the mountains, in particular on more protected north-facing slopes. So part of the way up turned into a slippery adventure. After a sweaty two and a half hours with the sun burning down from a cloudless sky, we reached the summit, and were rewarded with spectacular views of the beautiful lake Tegernsee below us and the high snow-covered peaks of the main range of the Alps in the distance.

Today I am quite sore, my body has to get used to this type of exercise. Nevertheless, inspired by the nice views from the top, new tours are already planned. One good candidate is the Rossstein and the Buchstein, the two rocky peaks in the foreground in the left part of the picture below.

View from Hirschberg towards the main range of the Alps. The Rossstein and Buchstein, potential targets for a future excursion, are visible in the foreground.

View from Hirschberg towards the main range of the Alps. The Rossstein and Buchstein, potential targets for a future excursion, are visible in the foreground.

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Public Science Day at IHEP

Sunday, May 24th, 2009

高能所公众科学日

上周末是中科院的公众科学日,高能所除了开放实验室供参观外,还安排了对撞机漫谈,探月工程, 高能物理中的超级计算机、中微子振荡与宇宙的物质-反物质不对称等四个讲座。两年前我曾在公众科学日做过一次关于中微子的讲座。虽然水平有待提高,对科普工作我一向是很热心的,宣传科学也是每个科学家的社会责任之一。现代科学离老百姓的生活太远,因此各种伪科学、反科学大行其道。俗话说,牛屎铺[1]这块阵地,无产阶级不去占领,资产阶级就一定会去占领。此次代表无产阶级前去占领阵地的是邢志忠。之前我还纳闷这个报告是谁去做的,问了大亚湾实验的几个人,都说不是。海报上没有说报告人,报告完了网上也找不到演示文件,说明这个宣传还不够到位,刚占领阵地又撤了下来。

[1]牛屎铺是网络史前用语,newsgroup的中文翻译,现在用google搜都不大容易找得到了。

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The “Wow” effect

Sunday, May 24th, 2009

googlelhc1A couple of days ago I read an interesting article on the Wall Street Journal, reporting about the HR strategy of Google. The driving principle of Google is a constant change and innovation which, in turns, should keep the
employees engaged. However, a flux of engineers, sales representatives etc takes place from Google to Facebook or Twitter. Why does it happen ? To tackle the problem, Google is developing the “Happiness algorithm”. Data extracted from progress reports, evaluation forms, etc. are crunched into a machinery which is supposed to output the level of commitment and  satisfaction the employee has. Not surprisingly the approach was not well received as it leads to reduce human brain and emotions into a set of data which are then
compared to some kind of template. Conclusions are drawn from there. Many of the Google employees stressed that the main reason for applying and working for Google is the “Wow effect” and since the beginning, the excitement faded and has being looked for somewhere else. Google should not invest in algorithms to predict the level of pattern of the engagement, but rather in new products and R&D which is what attracted good minds. This is bottom line expressed by its employees in return to the company decision.

Should we learn anything from the Google experience ? On one side the size of the LHC Experiments indicate a similarity between them and companies like Google. On the other hand, our aim is fundamental research and the management itself does not have profit as its goal. Nevertheless, we do encounter bumps in the road. In particular the life of a graduate student is very challenging now.  Besides the student type role of learning and producing results, the student is frequently a member of a larger group, learns how to interact, how to share the work and the reward, she/he is given the opportunity to present her/his job in front of the Collaboration and to International
Conferences. We should not forget that learning her/his subject means learning the theory behind the data analysis, the computational tools, the experimental probes available, the statistical interpretation of the results, all this along with hardware activities in most cases. Given the big challenge in front of each students, the mentors do have the responsibility of making the environment pleasant, of supporting students when needed and giving the appropriate guidance. No, algorithms should not be used!
It is a critical moment for all of us belonging to the LHC experiments. Great are the expectations, both in terms of discovery and in terms of personal interest given how sophisticated analyses will be carried out in this environment. Because of the delay in the past years and the accident of last September, the enthusiasm might be reduce. On top, student might be close to graduation, for which they planned of having a data analysis completed.
The management is doing a great job in holding the Collaboration together, keeping it engaged. Participation to meetings and understanding of what activities are on-going is in fact the best reward to the effort of their colleagues. Group conveners and mentors follow the lead. It is crucial that whoever experienced the beginning of an experiment share what it means, if unhappiness shows up along the way.  The LHC is the discovery machine once operational and the physics we’ll discover might change our view of the world. Yes, I know. This by itself does not help if you spend a couple of days debugging your code and you feel frustrated, I understand. Let me tell you how I felt when I arrived to Fermilab. I was freshly graduated in Italy (the system is different than US, our “laurea” is equivalent to the  master) and I was given the opportunity to spend three months at Fermilab. It was extremely exciting for me. And all my expectations were met, and what I found was even beyond that. As soon as I landed, I got engaged in some testing, cabling, services.  These activities are naturally not as intellectual as carrying out an analysis, but they do transfer ownership of the experiment. If you have the key to go into the pit at night (that was the case at CDF, the LHC experiments require more security checks), climb into the detector
sit with a handful of colleagues inside the detector, that detector will be yours. And no bumps in the road will mislead you, you will always be excited when it comes to maintain it operational and analyze the data it produces. When the first data event was recorded at CDF, people were emotional. Likewise to the LHC, physicists can work decades on the same project and bringing it to completion is a great satisfaction. We should all encourage the continuous effort in education, but we should also allow young collaborators to experience such a participation. Passion stems from understanding that you are contributing to an important project, that your effort is crucial to its progress
and success. Hardware activities and operations are a natural place where this can happen. Even if the LHC experiments will mainly operate remotely and most of people will be based at their home institutions, visiting CERN and devoting time to activities closely related to the detector constitutes a deep push. Many students in fact decide to join High Energy Physics soon after they spend time at the laboratory. The exciting field of study and the idea of participating to a unique and large project such as the LHC is a real motivation. The picture below was taken when beam circulated in the LHC last year and ATLAS recorded events. It’s happening soon!

acr

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Back at Riken.

Friday, May 22nd, 2009

After I came back to Japan, I have gone through hectic time, because of the Swine flu. Of course I didn’t caught the flu, but I and my family unfortunately got a different flu which has very similar symptom. You can imagine what happened to me, in this Japan where the goverment is very very sensitive to find the first patient in Tokyo  area. I won’t tell you more about this. But it was unfortunate that I couldn’t attend at interesting workshops held around Tokyo, one is the hot/dense QCD workshop at Hongo, the university of Tokyo, and the other is a focus week workshop on wall crossing at IPMU.

Today I got back to work, how happy I feel when I do calculations! For the previous few days I was on a bed, and could not think about any physics, because of the head ache. I really feel releaved that I could do calculations as before. So I started checking the draft of my new papers which are at my hand after my collaborators’ revisions. Hopefully we can put the draft out to the archive in coming weeks.

The seminar speaker today at my group was prof. Furusaki who leads condensed matter theory group in Riken. His introduction of topological insulators was insightful, and I was again amazed by how topological concepts and K-theory have been applied to classify insulators and superconductors. I thought that the K-theory is highly mathematical tool which, even in string theory, doesn’t appear so often, and today I saw that it really is related to real materials, that is fantastic. After the seminar which is for three hours (as usual), we trap the seminar speaker at our common room and enjoyed (asking) questions. Almost all of my confusions were resolved there. Furusaki-san also pointed out some reference, eventually that is the one written by one of my aquaintance at Yukawa institute, so I need to look at that paper. In any case, it is very nice to have discussions with Furusaki-san — I happened to know him for long years but haven’t actually had serious discussions before. Now his office is at a floor below our floor in the same building in Riken, so I can just walk to him and ask him questions — I hope he may not feel bothered by my stupid basic questions on condensed matter physics!

Next week, I will visit Nagoya university to give a talk on cosmic strings. I look forward to interact with poeple there in high energy physics, gravity and cosmology, and hadron physics.

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“Science News Cycle”

Wednesday, May 20th, 2009

PhD Comics were started by a Stanford Student and (humorously) chronicles the graduate experience. I started reading them while an undergraduate at MIT, and now I find them even closer to home as a grad at Stanford.

PhD Comics

PhD Comics

This week the topic strayed a bit from the normal topic of “grad school” but still certainly hit its mark: The Science News Cycle.

The comic certainly brings to mind the news “coverage” of the LHC, and how it mostly focused on one guy thinking the LHC might destroy the world. Even my family – who have spent years listening to me talk about the LHC – kept asking if it was going to destroy the world. I worry that Angels and Demons will have a similar effect. Scientists may give public lectures to clarify the fact and fiction in the movie/book, but the media thrives off scandal and fear.

While some science news coverage can be accurate, insightful, and (most importantly) correct, that sort of coverage usually is confined to science-specific publications. This isn’t always true! My father has continued subscriptions to Discover and Scientific American magazines that I received in high school. He was once telling me about an article describing “what I do” as leading to transporter technology in the next decade or so. I couldn’t imagine how anyone would say that, and thought he was misreading the article. The next time I visited he showed me the article, which said current particle physics research will provide transporter (a la Star Trek) technology very soon. I have no idea how the author had come to that conclusion, because I certainly haven’t seen any transporters in the work.

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Cosmic Tennis, anyone?

Tuesday, May 19th, 2009

I had a fascinating thought (to me anyway) today, which is more in the realms of science fiction than real science, but nevertheless entertaining.

It concerns the possibility of advanced, intelligent life, elsewhere in the Universe. Back in the early days of radio astronomy, and later with the SETI program, the consensus was that any alien civilization worth their salt would use radio signals to attempt to communicate with some unknown other civilization like ourselves, out there in the void. After all, radio signals are relatively easy to generate, albeit requiring some reasonably advanced technology to generate signals powerful enough to reach far off places with enough detectability for our perhaps primitive instruments.

With some excitement concerning periodic cosmic radio signals leading to the discovery of exotic stellar objects like pulsars, rather than the ‘Hello World’ of some advanced Galactic neighbor, the fascination with the search for extraterrestial intelligence using radio waves seems to have diminished a little.

My thought was as follows. Let’s suppose that a civilization much more advanced than ourselves has resolved to start trying to make contact with other civilizations. But let us suppose also that with this advancement comes a certain amount of inherit wisdom and the benefit of hindsight as to how other civilizations, perhaps less advanced than themselves, might be developing. Perhaps they know then, first of all, that such a civilization might still be embroiled in a culture fractured by religious schisms, war and instability, in which case they would be reluctant to assume contact should their sudden appearance cause shock and upheaval, potentially leading to the destruction of that civilization or at least causing one great religious war – maybe because they themselves almost reached that level of self-destruction at one stage in their development due to religious conflict. So, then, not to contact us too early, but how to know?

Maybe they also know, that the detection of radio waves is not necessarily the best sign of technological advancement. After all, radio waves were already discovered, studied, adapted and in use well before the age of computers, atomic weapons, the understanding of particle and nuclear physics. They might also know that at some point after the discovery and manipulation of radio waves our civilization would develop atomic then thermonuclear weapons, arriving at the stage where we have the ability to completely destroy the inhabitability of our own planet (having been there themselves), and would necessarily go through a century or so of equilibrating until the world had finally reached a peaceful and balanced enough stage to cope with signals from extraterrestial life.

Again, pure speculation, but they might also predict that we would have environmental problems due to the onset of the petrochemical age, the successor of an industrial revolution, that would go hand-in-hand with some of the developments needed for a nuclear age (assuming of course that these neighbors were also inhabitants of a class M planet once abundant in carbon-based fossil fuels). 

Detecting our ability in advanced space travel could be one criterion for contact, such as the buried monolith on the Moon in Arthur C Clarke’s 2001 A Space Odyssey was meant to signal to the aliens who placed it there. But the aliens would have of course, have had to have been here. 

So they scratch their heads (if they have them) and say ‘what signals could this civilization not detect and interpret until they are past the nuclear age, and at the stage where they have built up a physics-based model of the universe which is globally accepted by their population, such that they would be funded to build large enough projects to detect them?’

What about a beam of neutrinos, notoriously difficult to detect, requiring advanced knowledge of nuclear and particle physics, flavor-changing, industrial know-how for the huge-scale detectors? This is an option, however just like they would know that we knew about the existence of pulsars and AGN things that produce localized and periodic radio bursts, maybe they also know that we know about supernovae and other events that produce neutrinos. The same could be said of gamma rays, as we live in a constant swarm of them, bursts also coming from ‘natural’ events that we’re just discovering.

The one type of thing that might work, are ultra high-energy cosmic rays, such as those recently discovered (well, 1962) and now being studied by the Pierre Auger Observatory in Argentina, some of them seemingly from a localized source (as far as I have read). They would know that we know about the GZK cut-off. They would know that we would know the immense power required to accelerate these charged particles. Assuming that they themselves could build something powerful enough to accelerate particles to the 5 x 1010 GeV needed to exceed the GZK cutoff (but essentially giving them a ‘sphere of influence’), then these signals might be a great choice. This is pure science fiction of course, but it is interesting to entertain these suggestions. Building an accelerator some 7 million times more powerful than the LHC is no mean feat! (although the first accelerated beam nuclear physics experiment was performed on an accelerator some 8 million times less energetic than the LHC). However, if one day we actually harness some form of abundant energy, and eventually gain that capability, maybe a future Earth SETI program might involve firing ultra high-energy cosmic rays at class M planets and seeing if our ‘service is returned’!

Of course, the conventional hypotheses for the sources of these UHECRs include objects such as hypernovae, active galactic nuclei with supermassive black holes, or gamma ray bursts. However the alien explanation would make for a great sequel to Sagan’s Contact…..

 

 

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Size of electron

Tuesday, May 19th, 2009

This is continuation of the previous blog. Electron has various nature. PDG is reporting the following values;
1) Electron mass:0.510998910 +/- 0.000000013 MeV/C2.
2) Mass difference between electron(e) and positro(e+) : (Me+–Me)/(Me++Me) < 8×10–9.
3) Charge difference between e+ and e : (qe+–qe)/e < 4×10–8.
4) Electron magnetic moment(g) anomaly: (g-2)/2=(1159.65218111 +/- 0.00000074)x10–6.
5) g anomaly difference between e+ and e: (g_e+-g_e/g(average) = (-0.5 +/- 2.1)x10–12.
6) Electron dipole moment(d): d = (0.069 +/- 0.074)x 10–26 ecm
7) Electron mean life from e to electron neutrino and photon : > 4.6×1026 yr .

You see electron is so stable more than 1024 years from 7) .

How about the size of electron? As a matter of fact, there is no direct report on it. Alternatively, there is a measurement on the compositeness of electron. In the framework of the standard theory, electron and positron are assumed as point-like particle, which means they have no spread and no structure in space, and they can be scattered just via photon.

But one can consider that we just can’t see the size of electron because we have poor accelerators. If electron has a structure, we must observe the reaction of direct scattering of electron and positron using enough magnification by the more powerful accelerator.

This effect can be introduced to put assumed compositeness scale into the equation of electron of which dimension should be the energy. Experiments have measured the angular distribution of electron or positron through the reaction: e+ e going to e+ e, so called Bhabha scattering, and have seen the difference from the distribution predicted by the standard theory. Up to now, the distribution is consistent well with the theory, then the statistical treatment tells us the lower limit of the compositeness.

In PDG, it is reported in “Other searches (SUSY, Compositeness, …)” after “Particle Listing”, the scale of contact interactions should be more than 8 TeV. Because the corresponding length is inverse of energy scale, it means that electron has no structure more than in 1/1018 m.

この話は前回からの続きです。電子はいろいろな性質を持っており、PDGサイトでは次のような測定値が報告されています。

1) 電子の質量:0.510998910 +/- 0.000000013 MeV/C2.
2) 電子と陽電子の質量の差
:(Me+–Me)/(Me++Me) < 8×10–9.(つまり差は観測されていなし)
3) 電子と陽電子の電荷の差:(qe+–qe)/e < 4×10–8(やはり差は観測されていない)
4) 電子の異常磁気モーメント(2からのずれ): (g-2)/2=(1159.65218111 +/- 0.00000074)x10–6. (非常に精度よく測定されています。)
5) 電子と陽電子の異常磁気モーメントの差: (g_e+-g_e/g(average) = (-0.5 +/- 2.1)x10–12.(これも差はないということ)
6) 電子の2重極モーメント(d):d = (0.069 +/- 0.074)x 10–26 ecm
7) 電子がニュートリノと光子に崩壊する平均寿命: 4.6×1026 年以上(つまり崩壊は観測されていない)

7)から電子は1024年以上安定して、崩壊しないことが測定されてることがわかります。

では、電子の大きさは測られていないのでしょうか?実は、直接電子の大きさを測ってはいないのですが、その代わり電子を複合粒子と仮定した測定が報告されています。標準理論の枠組みでは、電子や陽電子は点状の粒子で空間的に広がりをもたないものと仮定されています。また、電子と陽電子が反応するときも光子を通してのみ散乱するとしています。

しかし実験的には、まだまだエネルギーの低い加速器を使って実験しているから、電子のサイズを測ることができないのだろうと、考えることもできます。電子に何らかの構造があって、よりエネルギーの高い加速器、言い換えればより倍率の高い顕微鏡があれば電子や陽電子が光子を媒介せずに、直接内部の要素を交換して反応を起こす現象を観測できはしないか、と考えるのです。

電子の方程式に電子の複合性が見えてくるエネルギースケールを導入することで、そのような効果を取り入れることができます。実験的には、電子と陽電子が衝突して、電子と陽電子に散乱される反応「バーバー散乱」を使います。散乱して測定器を通った電子や陽電子の軌跡の角度分布を観測することで分かります。もしその分布が標準理論の予測する分布と異なっていたら、電子の構造を示すエネルギースケールが見えることになります。しかし、現在までのところどの実験でも散乱の分布は標準理論の予測とよく合っていますので、統計的扱いにより、電子の複合性を示すエネルギースケールの下限値しか得られていません。

PDGでは、”Particle Listing”で、”Other searches (SUSY, Compositeness, …)”をクリックすると実験結果が報告されており、それによると、そのエネルギースケールの下限値は8000GeVであることがわかります。このエネルギースケールの逆数が”長さ”に対応するので、結局電子の大きさは1/1018 m以下であると測定されていると言えるのです。

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