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Junpei Fujimoto | KEK | Japan

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Quantification 3 —the case of mine —

Friday, April 10th, 2009
from edge of KEK territory

from the edge of KEK territory

Why don’t you visit KEK now? You can appreciate full cherry blossoms here. I have, however, never counted the number of them. What do I usually quantify in my physics research? As written, the accelerator experiments supply us the particle reactions and physicists count the number of events etc.. In order to compare with results from experiments, I make quantification of the formulas from the theory, which are usually presented in symbolic expressions. As we, human-beings, don’t have enough mathematics, yet, quantification just can be achieved step by step.

First, we get a rough number from the formulas with some approximation. Please remember the number from experiments also has an error in measurement. If you count the number of events as 100, then you have an error in 10% to conclude something from this observation. In this case, it is not hard to get numbers by means of the first approximation.

But if you have 10,000 events from experiments, you can talk about this phenomenon in 1% level. So we have to step further to the second approximation against this precision, which means the number of formulas to evaluate becomes increased and complicated. Traditionally this step is called ‘radiative corrections’. Because it is beyond the calculation by hand, we need the power of computers.

In the LEP experiments of electron and positron collision held at CERN in 90’s, the experiments accumulated more than 1,000,000 events in each process of particle reactions, of which accuracy reached to 0.1%!  Physicists needed predictions from the theory accurate enough . After a lot of efforts were paid by the physicists in the world, the weak-force part of the standard model was established precisely, at last.






Quantification 2 — the case of particle physics —

Sunday, April 5th, 2009

As in previous my blog, the quantification is the first step of physics. What do modern particle physicists quantify? I put two pictures. I think you see these kinds of ones often. Those show the tracks of particles produced by the accelerator, so called ‘events’. Elementary particles are so tiny, then we can’t see them directly but we have technology to observe where they passed through.

Japan's first bubble chamber, built by KEK, tracked production of two pairs of electron-positron.Image credit : KEK

Japan's first bubble chamber, built by KEK, tracked production of two pairs of electron-positron.Image credit : KEK

The first picture was taken early in 70’s at KEK with the bubble chamber. The bubble chamber was designed as follows; when particles pass through the low pressured liquid hydrogen, particles initiate to create foams. Connecting foams, we can recognize tracks of particles by eyes. One often called this kind of pictures ‘cosmic dances’.

The second picture is an event figure taken by Belle from KEK, which shows the reaction after the collision of electron and positron of KEKB. Contrary of using the bubble chamber, this event was not observed by eyes, but was taken as the digital signal and was reconstructed using the computer.

Particle physicists accumulated this kind of events as much as possible like Tycho. Essentially they count not only the number of events but also get distributions of the direction, momentum and energy of scattered particles, which can be predicted with the theory. The theory contains the knowledge of all nature of particles and strength of forces between particles. If observed numbers and distributions are consistent with the prediction of the theory, then we can judge the theory is right or not.

Example of a fully reconstructd evrnt in the Belle detector.Image credit : KEK

Example of a fully reconstructd evrnt in the Belle detector.Image credit : KEK







Monday, March 30th, 2009

Hi, Tony. Thank you very much for your comment for ‘Japan on the globe’. Yes, surely we should remember the effects from ancient Greeks and ancient Egypt, so on. Here I would like to say physics consists of two steps;

  1. Quantify the phenomena and book numbers.
  2. Analyze the structure behind numbers.
Ticho Brahe's notebook

Tycho Brahe's notebook

In the 16th cent., Tycho Brahe accumulated the data on movement of Mars for 16 years!! Then with this data, Johannes Kepler got ‘Kepler’s Three Laws of Planetary Motion’.

Kepler’s insight from data to the laws was marvelous which led the theory of gravity of Newton. But I am also quite interested in quantification of Tycho. The accuracy of his data were within 1 arc-minute if referred by fixed stars, within 2 arc-minute in usual and within 4 arc-minute on the location of planets. It was so accurate when compared with the case of Copernicus, who was satisfied if his theory agreed with data in 10 arc-minute.

European seems to have tradition to respect to accumulate piles of numbers since those days. In the case of Japanese, we might prefer composing a poem for admiring its beautyof Mars or holding the tea ceremony under the sky. There is still tendency for Japanese to feel quantification to be less humanity, though it is a key step to do Physics.


1) 数量化(データベース化)
2) 抽象化(法則化)






Japan on the globe

Friday, March 27th, 2009

Welcome to my page!!

I hope you will enjoy reading the life of a Japanese physicist.
map4I put the map of the world. Can you find Japan? I think people from Euope and from the U.S.A.  have strange feeling with this map, because the view is so different from them. The Pacific Ocean is drawn in the center of the map! This is an ordinary map to be used in Japan. As you see, Japan is located in the so called far-east region on the globe.

Japan is one of the first countries to get morning in the world. In the 7th century, we already recognized Japan was the country rising of the sun and the big country China beyond the western sea was one of sunset. The emperor in China disliked much this expression, of cource. We call our country ‘Nihon’ in Japanese, of which literal meaning is ‘rising of the sun’. I think Japan has originated with ‘Nihon’ (-> ‘Nippon’ -> ‘Jippon’ ->Jepang’ ->’Japan’).

Anyway, Japan has such a long history because we are located at the edge and also enough isolated from the continent by the sea.  Various culture were introduced through Korea and China, for example, Chinese characters and Buddhism, so on. Simultaneously, thanks to this location, we could easily close our country to block the effect out from other countries and to grow up our own culture. The last opening of our country was the end of ‘Shougun(Edo)’ era in 19th century after 260 years closing. Japanese liked to follow the culture of Europe as soon as possible. Physics was also introduced at that time.

In Shougun era, Japanese already had skill of astronomical observation and made a map of Japan in very precise accuracy. But such a concept of the motion of equation was introduced just 150 years ago. Our Japanese is still very young on physics, when we compare with the introduction of Buddhism in the 6th century. On the other hand, if Galileo Galilei is considered as one of fathers of the modern physics, Europe has more than 300-year-old history. I am very interested in why physics was born in Europe.