Kiwi Particle Physicist

June 28, 2006

Group Meeting Presentation

Every Tuesday morning our lab gets together for a weekly meeting, and then afterwards someone has to give a presentation. Normally we take it in turns each week, but I’ve been away a bit and skipped my last few chances, and it finally caught up with me yesterday. Usually the person giving the presentation explains what they’re working on, or they introduce a recent physics paper, and we all go through it and tear it to shreds together. I decided to go a different route, however, and give a summary of what I learnt at the ILC school last month.

I spent most of the night before going through and copy/pasting the slides from the lectures notes. In the end I had to condense so much out of it, and then make up for the gaps with other slides of my own, that it wasn’t as time effective as I thought it would be. I ended up with way too many slides, and I only got through a rough intro, and an explanation of the electron and positron sources and capture section. It’s my turn again four or five weeks from now, and I’ll try and finish off the rest of the machine then.

Overall the reception from our professor and the second year masters students and doctors students was pretty good, but the new students were fairly quiet throughout the whole ordeal. I’ll have to try a bit harder for the next talk. On the bright side, one of the kouhais sounded interested, and is thinking of attending the ILC school the next time it is held.

Suprisingly accurate comic courtesy of PhD.

June 25, 2006

B-Lab and Open Access to Data

JoAnne over at Cosmic Variance has an interesting post on whether our data should be made public. Apparently at SUSY06 Tao Han proposed that “the LHC data should be made available to the community.” Currently most particle physics experiments refuse to release some or all of their raw or processed data publicly.

At Belle we make 1/nb of data available on request (Japanese only) for public outreach. Seeing as this corresponds to less than 1/600,000,000 of the total data, it is unlikely that anything will be found that hasn’t already been seen by the collaboration in the full data set, and we don’t really have to worry about other people going off and writing papers on our data.

As far as I’m aware the data consists of the same quantities we use to do physics analyses: 4-vectors of the charged tracks, neutral pions and photons. I assume it also includes PID information on the charged tracks, so you can see the probability of a given track being an electron, muon, pion, kaon or proton.

The data is mainly used by high school students to search for new resonances. For example, they might combine two proton tracks to search for a doubly charged six-quark state. One small problem is that somebody actually found one. Apparently claims for the discovery of violation of conservation of energy or electric charge are quite common as well. Of course, when you consider the possibility of particle misidentification and the limited acceptance of the detector these are easy enough to explain. I think it’s possible for someone to find just about anything they want to look for if they misinterpret the data correctly enough, which would obviously mean that there would be credibility issues with results published by anyone not on the collaboration.

Openly releasing data like this is great for physics outreach, and for getting students interested and involved in the experiment. I don’t think this is what Tao had in mind when he asked for the 4-vectors from the LHC experiments though. I assume he is asking for all the processed data, so that particle physics theorists and others could do their own analyses.

Given the massive amounts of data involved with Belle or LHC though I can’t see how this could possibly work. Surely the only way would be to cut down the number of events by releasing only selected signal events after an analysis has been performed by the collaboration, which would sort of defeat the point. Having the data out there might improve everyone’s confidence in the experiment, but in practice I just can’t see how anyone could possibly sift through all of it on their own and pick up something missed by the rest of the collaboration.

June 12, 2006

ILC School Update

More news from the ILC school. There is a nice article about it on the net, with quotes from the organizers and some of the students who took part (I’m not in there though.) It seems like all the students were fairly unanimous on the homework situation, and I think the organizers got the message. Otherwise it sounds like the reception from the students was fairly good. As an aside, we got our homework results back. I made the top half, which I’m pretty happy with. Not bad for my first crack at accelerator physics, but next time a bit more preparation and study might be a good idea.

In other news, between all of us taking part in the school we managed to eat too much at the buffet, and the hotel had to ask us to pay extra for breakfast and dinner each day. How did this happen? This is the first time I’ve heard of anyone eating too much at an all you can eat buffet and being asked to pay extra (although I remember having to pay extra for drinking too much at an all you can drink pub a few years back, but that’s slightly different.) On that note, I thought I’d start an informal poll to get everyone’s opinion:

Q. Why did we eat too much at the buffet?
a) Because we were mainly foreigners.
b) Because we were mainly students.
c) Because we were mainly physicists.
d) All of the above.
e) Other?

I feel a little bad about the stereotypes, but I’m drawing a blank on any other possible reasons. Suggestions welcome.

June 07, 2006

600/fb Celebration

Just had the 600/fb party tonight. At a particle collider like KEKB, which produces the B mesons detected by the Belle experiment, the efficiency with which collisions occur is measured by “luminosity,” and depends on how many particles we can smash into a tiny area each second. The total amount of data recorded is called “integrated luminosity,” and is calculated by adding up the luminosity over the lifetime of the experiment.

This integrated luminosity is a direct measure of the number of collisions that have occurred, and is measured in units of /fb (inverse femto barns). For us, 1/fb of integrated luminosity will produce approximately one million B meson pairs, and takes about one day to accumulate. The more integrated luminosity we record, the more rare matter/antimatter decays we can see, and the better we can understand the difference between the behavior of matter and antimatter.

The original goal of KEKB was to produce 100/fb in 3 years, although due to a lot of improvements to the accelerator we’ve ended up taking six times that amount in just twice the time. Good work accelerator team.

(Above photo was taken from the KEKB page)

June 02, 2006

Couldn't Resist

I'm trying to stear clear of commenting about Japanese news here, but there are a few stories today that I couldn't resist.

Firstly, the mayor of Bonn has ordered Japanese soccer fans not to jump into the Rhine during the World Cup. After the Hanshin Tigers baseball team won the central division title in 2003, over 5000 fans jumped into the Dotonbori river in Osaka, and one person drowned. When I was in Sydney for New Year's Eve 2000 we were watching the fireworks just after midnight and a handful of Japanese tourists jumped into Sydney Harbour naked and started swimming around as well. The police eventually had to come to get them out. Why do they do this? These Japanese fans are normally well behaved and good about following the rules, what causes them to snap and jump naked into a polluted river?

Secondly, Japan's fertility rate set another record low in 2005. In addition, Japan's population decreased for the first time since World War II. Commentators predictably lashed out at Japan's poor childcare facilities and the cost of having children here, while politicians pretended to be deeply concerned. "We have to take this figure very seriously," Prime Minister Junichiro Koizumi told reporters. The only news here though is the inability of the government to predicit long term population trends. The 1.25 fertility rate is significantly lower than the the long-term forecast of 1.31 predicted just three years earlier. Otherwise, the general trend towards lower fertility rates has been obvious for decades now, not just in Japan but in many other developed countries as well, as shown in the map below.

The article mentions rates of 1.16 in South Korea, and 1.24 in Singapore, but doesn't point out that the rates are 1.79 in New Zealand, 1.47 in the EU, or 2.09 in the US, all of which are below replacement rate, and all of which are commonly used in Japan as examples of countries with more child-friendly societies. Policies supposed to help improve the fertility rate in certain European countries have produced only moderate increases. It seems that this trend towards lower fertility rates and population decline is inevitable. I don't see why it has to be a problem though. The planet is overpopulated already, can't we just raise the retirement age to offset the economic effects and forget about it? Why is this option almost never brought up?