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Archive for November, 2009

Visiting DAMTP, Cambridge.

Monday, November 30th, 2009

画像-0020It’s been long since I have visited Cambridge before, probably it was already 4 years ago. I lived in Cambridge for half a year, as a visiting researcher then at DAMTP (Department of Applied Math and Theoretical Physics), universtiy of Cambridge. I have good memories on my days at Cambridge.

Last time when I was here at Cambridge, I couldn’t imagine that I would be working on nuclear physics. The talk I gave here 4 years ago was on ADHM construction of instantons and its D-brane realization, and the motivation was purely mathematical physics. But this time, again in my talk I told about ADHM construction, but now applied to nucleon nucleon interaction realized and computed in string theory. It is interesting that, although the mathematical tools are quite similar to each other (and almost the same), the motivations were totally different.

Discussions with my friends at DAMTP were joyful, and are always insightful. And, one more thing — winter in Cambridge, it is beautiful.

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Via Twitter, CERN reports:

A new record. Both beams in LHC reach 1.18 TeV at 00:42 on 30 November.

That makes the Large Hadron Collider the highest-energy accelerator in the world! It will be the world’s highest energy collider once it brings the beams together at that energy. I’m not quite sure when that will be — the LHC team is making such fast progress that it’s hard for the experiments even to keep up with what their plans are — but I bet it will be soon enough.

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Beam … beams in the LHC Tunnel

Sunday, November 29th, 2009

The past 10 days have been extremely exciting for every one at CERN or working for the CERN experiments. The accelerator injected first one beam, then two beams in the tunnel; a bunch of proton was spinning in each directions and made to collide in the centres of the different experiments. During these first tests, the energy of the beam in the LHC is the same as at the injection (450 GeV), nevertheless it proved to be a very successful performance of the machine and of the experiments. Because of the low energy, no new particles can be produced, but the data collected are crucial for understanding the detector timing. The electronics sitting in the detector reads the signal produced by the particles flying through. When should the readout start? The accelerator propagates a signal (the “clock”) to indicate when collisions are likely to happen. However, if the detector is not properly timed, the electronics won’t read any signal out of the different sensors. Roughly 10 days ago, so called “splash events” were provided by the accelerator. In this case. The beam collimators at the door of the experiments are closed; one beam hits them producing a splash of  particles shining the detector.  The understanding of these type of events is challenging, because they are geometrically different from what the experiments is designed to record. The particles fly from the side of the detector, and not radially from the centre. The electronics and the software needed to be adjusted to use these events as “calibration” tools.

0911189_51-A4-at-144-dpi

atlas2009-vp1-140370-2666-web

The appearance of signal in the detector caused quite some excitement in the ATLAS Control room! Even if it is the second time I see an experiment starting (after my CDF experience), I was extremely happy to feel the same empathy and the same joy. People in operations devoted their life for years (decades?) to see the apparatus working. Being in the same room with experts staring at their system taking data was extraordinary.

0911189_01-A5-at-72-dpi

0911189_14-A4-at-144-dpi

atlas2009-collision-vp1-140541-171897-new

The tests and fast processing of the splash events were successful. ATLAS was finally ready for the first LHC Collisions of 2009! LHC and the 4 experiments joined into a celebration on Thursday: during a very crowded seminar held in the CERN auditorium knowledge about the status of the machine and of the experiments, lessons learnt with the first events was shared … and above all the excitement for the new beginning.

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Shanzhai Reactor

Sunday, November 29th, 2009

Shan Zhai Reactor

“Shan Zhai” is a popular word in Chinese. Invented in 2008 from “shan zhai cell phone”, it means copycat, fast, and popularization. A MediaTek Inc. chip makes “shan zhai cell phone” possible. It integrates almost all common advanced functions of a cell phone, and can be customized simply by software. A lot of tiny companies, many of them are underground or in gray zone, started to produce cell phone with this chip and models copying from large company products. This word extends to other area soon, e.g. shan zhai star in a TV show, means that a player is widely supported because she looks very like a famous actress.

Last weekend IHEP had a 2-day strategic workshop to discuss the future plans. Accelerator Driven Sub-critical System (ADS) is one of them. IHEP director Prof. Hesheng Chen mentioned a new scheme ADTR by Prof. Rubia, i.e. Accelerator Driven Thorium Reactor. IHEP is the leader of accelerator technology in China, has completed a R&D project on ADS, but has no experience on building reactor. Prof. Chen said, “we should not try to build Shan Zhai reactor ourselves”.

山寨反应堆

“山寨”一词大约2008年起源于山寨手机,其主要特点为仿造性、快速化、平民化,并迅速成为一个在中国广为流行的语汇。
上周末高能所开了一次为期两天的战略研讨会,讨论高能所未来的发展规划。加速器驱动的清洁核能源是其中一个很有吸引力的发展方向。陈和生所长介绍了Rubia最近提出的一个新方案ADTR,即加速器驱动的钍反应堆。高能所在加速器方面无疑是国内的领导者,并且进行了ADS(加速器驱动的次临界洁净核能系统)的预研究,但是在反应堆方面没有经验。陈和生说“我们不会去搞山寨反应堆”。

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Writing and publishing a scientific paper in a high energy physics experiment and a large collaboration is usually a long road: The data analysis is complex, often many people from different institutions on different continents are involved, and the end result has to make everybody happy.

I’ve just made it through this process again in the collaboration that was my home for my PhD and post-doc times, the STAR collaboration. 10 days ago I’ve finally submitted a paper I’ve been working on with others for quite a while.

It is titled “Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV”

You can check it out here.

So, what is that about? One of the physics goal of the experiments at the Relativistic Heavy Ion Collider (STAR is one of the two remaining experiments there) is to study the spin structure of the proton. We are trying to answer the question of how the proton gets its spin of 1/2. A good question to ask, after all, the proton is not an elementary particle, but consists of many constituents, quarks, anti-quarks and gluons. And protons make up a good part of us, so understanding how a proton works is definitely a worthy goal.

Now, the proton has exactly the same spin as an electron, which is quite important for the structure of matter. But how do all the pieces of the proton come together to make the spin exactly right? An obvious solution would be that the three valence quarks, two ups and one down, each with a spin of 1/2, combine in such a way that two cancel out and 1/2 is left over for the proton. However, experiments in the late 80’s have found that the quarks only make up approximately 25% of the total spin of the proton. So other contributions have to come in. This leaves essentially the gluons, and orbital motion of the constituents within the proton.

Several experiments, among them the RHIC experiments, are now investigating the gluon contribution. At STAR, we collide polarized protons, and look for differences in particle production depending on the spin orientation of the protons. Since we know the effects from the quarks from the previous measurements, we can extract the gluon contributions to the proton spins by measuring spin asymmetries in the particle production (That is where the title of the paper comes from). There are several processes that can be used for these measurements. The one with the highest statistical power is inclusive jet production, since the cross section (i.e. production probability) is high, and a jet is relatively easy to measure in our detector. An alternative is to look at neutral pions, particles we can identify in our electromagnetic calorimeter. A neutral pion decays almost instantaneously into two photons, which we can identify in the calorimeter. From those two photons, we can reconstruct the properties of the original pion. The spin measurements with pions measure essentially the same thing as the jets, in the situation where a neutral pion is the leading particle of the jet. This extra requirement obviously reduces the available statistics, making the measurement less accurate. However, the systematic uncertainties (coming in from detector understanding, the trigger system and the like) are quite different than those for the jet measurements. Using pions as well as jets gives us thus an independent cross check for our results.

The main plot: The spin asymmetry we measured for neutral pions (the black dots), compared to calculations based on different assumed gluon contributions to the proton spin. The red curve, a scenario with very large gluon contributions, is excluded by the data. The others, which have negative, small or vanishing gluon contributions are still in. The proton spin remains a puzzle...

The main plot: The spin asymmetry we measured for neutral pions (the black dots), compared to calculations based on different assumed gluon contributions to the proton spin. The red curve, a scenario with very large gluon contributions, is excluded by the data. The others, which have negative, small or vanishing gluon contributions are still in. The proton spin remains a puzzle...

Since jets play such an important role in proton-proton collisions (trust me, you’ll hear a lot about jets once LHC results come flooding in), we’ve also looked at the relationship of the neutral pions to jets, by looking at the energy fraction the pions we have in our analysis typically carry from the jet they “live” in. To verify that the theoretical calculations we are using to interpret the results match our data, we have also measured the production cross section for neutral pions in proton-proton collisions at the RHIC energy. This measurement is also important as a reference for heavy ion collisions, the other corner stone of RHIC physics. To ensure consistency of analysis techniques across the spin physics and the heavy ion physics communities within STAR, I was working together with heavy ion guys for this paper.

So, what did we learn? Of course you can get the full story from the paper, but the short version is: The spin contribution of gluons to the overall spin of the proton is not terribly big, at least in the range that is accessible to the RHIC experiments. This was also shown by other measurements, both with jets at STAR and neutral pions from our competitors, the PHENIX experiment. We have now completed our first neutral pion analysis, but more data is available and is currently being analyzed (not by me, though), promising more precise results in the future.

I’m glad the paper is done, now I’m waiting for the referee reports, and then further down the road the publication… A happy ending for a large piece of work.

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Local news

Friday, November 27th, 2009

Admittedly, it is a little harder to follow all the LHC excitement if you are here in the US rather than at CERN.  The announcement of first collisions on Monday came while I was teaching my class, and I’ve been trying to piece together the whole story by talking to our people over there and reading the slides from various meetings.  Of note was a public meeting at CERN yesterday (yes, Thanksgiving Day, another impediment if you are in the US) with presentations from Steve Meyers, CERN’s director for accelerators, and the four LHC experiments.  See the slides and video here.  As everyone else has been saying, the past week has been a thrill (or at least a vicarious one!) for the LHC, the four experiments on the ring, and really all of HEP.  Check out Meyers’s slides in particular, where he documents just how far we have come in the past fourteen months.  The experiments have turned around information from these first few collisions very quickly; some detectors are already able to reconstruct decays of the neutral pion, for instance.  We have huge expectations for the next set of collisions and then for the increases in collision energy that will follow.

My particular contribution to CMS has been in computing, and I’m happy to say that all of that has gone quite smoothly so far.  The prompt reconstruction of events went off without a hitch, and data was flowing very quickly out of CERN to the Tier-1 and Tier-2 sites.  We soon lost track of how many sites had copies of the collision data, and now we’re seeing plenty of people use the distributed computing system to analyze it.  When the next round of collisions comes, we’ll be ready to do it all again.

So while it’s hard to follow the news up to the minute, I’m still connected to the start of a great particle physics adventure.  I’m trying to drag the rest of Nebraska along with me — we managed to get a release placed in the local paper, and if you read this post soon enough, you can hear me at 8:30 AM Central time on Saturday 11/28 on KZUM, Lincoln’s community radio station.  I’ve already taped the interview; let’s hope I didn’t sound incoherent!  (At least when I type the blog posts, there is a backspace key….).

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Thanksgiving Feynman Turkey

Thursday, November 26th, 2009

Yesterday I was tidying up my office and I found something cute on my chalkboard:

DSC05531

Do you see it? Amidst the remnants of a discussion with one of my colleagues, it appears that I now have a Feynman diagram of a Thanksgiving turkey:

DSC05529

Actually, I’m not sure if it’s a turkey, but it’s certainly some kind of poultry. The diagram was drawn by another theory grad student, Yuhsin Tsai. The irony is that we were discussing whether this process should be considered to be a penguin diagram. There are also diagrams called seagull diagrams. I guess physicists have a thing for birds in their diagrams. (By the way, this isn’t the first time I’ve found funny-looking diagrams.)

Hopefully in the near future I’ll be able to write up a few posts explaining how Feynman diagrams work. In the meanwhile, happy Thanksgiving everyone!

Flip

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Supporting science at home and abroad

Wednesday, November 25th, 2009

This Thanksgiving particle physicists have a lot to be thankful for, not the least of which have been the exciting progress with collisions at the LHC.

Happy ATLAS Scientists

Happy ATLAS Scientists, Image from the ATLAS press release.

While images of happy LHC-ers made a big splash in the media, somewhat understated in the news was President Obama’s reaffirmation of his commitment to science and science education through the a new “Educate to Innovate” campaign whose goal is to make American science and mathematics education second to none. Here’s the video of the announcement (and the transcript):

[youtube 33_nZaOUWYw]

If I may interject some personal opinion, a concerted effort to elevate “STEM” (“science, technology, engineering, and math”) education in the US is as important (if not more so) to the sustained well-being of American science as the LHC. The president also made the key point that this is important not just for the sake of science itself, but also for the country as a whole:

The key to meeting these challenges — to improving our health and well-being, to harnessing clean energy, to protecting our security, and succeeding in the global economy — will be reaffirming and strengthening America’s role as the world’s engine of scientific discovery and technological innovation.  And that leadership tomorrow depends on how we educate our students today, especially in those fields that hold the promise of producing future innovations and innovators.  And that’s why education in math and science is so important.

The Educate to Innovate Campaign draws from the private and public sectors to find ways to promote science to kids. As someone who grew up watching Bill Nye the Science Guy, I was very pleased to see that many of these plans involve tying in science programming on television shows. Further, it was good to hear the president reaffirm the goal that we need to transform the culture of education in this country. He remarked that during his recent trip to Asia, he was impressed by the “hunger for knowledge” and “insistence on excellence” that formed the foundation of each students’ education.

Speaking of Asia, I would be remiss if I didn’t share another understated physics news item from this past week: the Institute for Physics and Mathematics of the Universe (IPMU) is in danger of funding cuts from the newly elected Japanese government. For those that are not familiar, the IPMU was recently established to be a high-profile international center for research on the interface of physics and mathematics. It has great potential to act as a focus for theoretical physics in Japan that can connect physicists and mathematicians from all over the world. As reported by Sean at Cosmic Variance, funding cuts are looming ominously for IPMU and the Japanese Ministry of Education and Science is looking for input from scientists around the world. More information is available in an IPMU press release.

Earlier this year the Science and Technology Facilities Council of the United Kingdom provided a renewed funding grant to the Institute for Particle Physics Phenomenology (IPPP) at Durham University, where I was fortunate to have been able to spend a year as a student. Hopefully IPMU will also be able to continue onwards even during tight economic times.

I know this is the US LHC blog, but the fact of the matter is that particle physics is very much an international effort. CERN itself was, in some sense, a precursor to the European Union and today scientists from around the world contribute to the forefront of particle physics research. Researchers at American universities hail from all over the world and academia flourishes in this environment of diverse backgrounds. And you know what? That’s part of what makes this line of work so much fun. Happy Thanksgiving everyone!

Flip

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dishwasher

With all the encouragement I give others to learn French before they, you know, move to France, I’ve forgotten to mention that you’ll often encounter appliances with German on them. I don’t know what they’re doing here in France, maybe they’re cheap.

All I know is, we just set the dishwasher to “Universal Plus” and let it do its thing.  I’ll have to see if WordReference can tell me what KALT VORSPÜLEN is…

–Mike

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As has been communicated quite well by many of my colleagues here on Quantum Diaries we are officially in a VERY exciting time in particle physics. The Large Hadron Collider has had its first collisions marking a very significant milestone in what has been a long and hard journey of a new accelerator and the many experiments that will be receiving data for many years to come.

While I am not currently at CERN and I continue to spend most of my days slugging it out with the data here at Fermilab, I can’t help but be caught up in the amazing images of the first collisions and while I am sure many people have already seen these I wanted to make sure I had them up on my blog as well.

Display of first collisons at CMS

Display of first collisons at CMS

These images and data that are first coming off of the CMS detector are really captivating and profound. They are but a snapshot of the work of thousands tirelessly giving to the cause of building what is sure to become a triumph of modern science and engineering. All with the hopes that these experiments will allow us to unlock the deep mysteries of the universe.

However, it is with some ironic nostalgia that I received the news of the first collisions at the LHC and saw pictures of the scientists toasting in the control room and producing these high quality images of the first events. I say ironic nostalgia because I was given cause to pause and ponder…”what was the first collisions like at the Tevatron and CDF?” So after some chatting with the people here at Fermilab and my adviser I unearthed some old images of what it was like here.

CDF Logbook (that is right they used to acutally write in a book) the night of first collisions...how large do you suppose CMS's book would be?

CDF Logbook (that is right they used to acutally write in a book) the night of first collisions...how large do you suppose CMS's book would be?

Please remember that 24 years, 1 month, and 10 days ago when CDF saw their first collisions I was 4.5 years old. I barely knew the difference between a dog and a cat…little alone a proton and a anti-proton. But when I was looking through these images what I found was many of the same people that I’ve gotten to know and love here at Fermilab and in the particle physics community at large were not only here for the first collisions, but are also involved at CERN as well. So in the span of my lifetime while I’ve been figuring out what animal goes “woof” and what animal goes “meow” These people have seen two energy frontiers and have been at the forefront of both! I am humbled and excited to see what will happen during the next 24 years and where I’ll show up in the old photo logs! Many of these images can be found here and you can keep up with the latest and greatest stuff from CMS and the LHC here

Steve and Dee Hahn at CDF first collisions...and still here keeping the ship afloat

Steve and Dee Hahn at CDF first collisions...and still here keeping the ship afloat

First Collision at CDF...not quite as beautiful graphics rendering as they have nowadays

First Collision at CDF...not quite as beautiful graphics rendering as they have nowadays

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