Hybrid cars… Hybrid accelerators November 3, 2009
Posted by gordonwatts in History, accelerator, physics.5 comments
By now I think most people know how the Prius and other hybrid cards operate. Most cars’ breaks are just like a bycycle break: a clamp that generates a large amount of friction and slows the car down. This is a terrible waste of energy: the car’s motion is converted into heat and damage (to the brake pads) and can never be reclaimed. Think of it as wasted gas, excess pollution, etc.
![Bicycle-Brakes[1]](http://gordonwatts.files.wordpress.com/2009/11/bicyclebrakes1.jpg?w=212&h=244 "Bicycle-Brakes[1]")
Hybrids are much more clever. They attach an electric motor/generator directly to the wheel and when you want to break then use the wheel’s motion to run the generator. This requires work – which slows down the car. Instead of the energy being lost, however, it is poured into a battery. The energy can then be reused to get the car started again. Huge savings in gas! This is also why hybrids tend to amazing at city driving, but not long distance driving (where this doesn’t help much because you aren’t stop/start).
Before we got sophisticated with generators and batteries we did something much more mechanical. At least for public transportation: the gyrobus:
![Gyrobus_G3-1[1]](http://gordonwatts.files.wordpress.com/2009/11/gyrobus_g311.jpg "Gyrobus_G3-1[1]")
Instead of a battery, however, a giant flywheel was used to store the energy. These things were built back in the 1950’s.
Guess what… the same technology has been used for particle accelerators – specifically the Bevatron!
![Bevatron[1]](http://gordonwatts.files.wordpress.com/2009/11/bevatron1.jpg "Bevatron[1]")
Blah
![96602956.lowres[1]](http://gordonwatts.files.wordpress.com/2009/11/96602956-lowres1.jpg "96602956.lowres[1]")
These are 65 ton flywheels, and there are two of them. Here is an abstract from a paper that describes the control system that ran these puppies:
The Bevatron/Bevalac main guide field power supply stores 680 MJ in the flywheel-shaft systems of two independent motor-generator sets. During the normal acceleration cycle of various heavy-ion beams, the energies of the rotating shafts are converted to energy stored in the main magnet guide field. At the end of the acceleration cycle, the magnet energy is inverted back to the shafts. Generally, this takes place from 10 to 15 times per minute. The rapid switching of ions, energy, and beam lines at the Bevalac has required various control techniques for fast switching between all operational Bevalac fields within 1 min. The power supply control systems and operating parameters are described.
The principle is same as with the hybrid car, or the gyrobus, but all the sizes and power are extreme (as usual for the field of particle physics). Imagine spinning up and down those flywheels at a rate of once every 10 seconds or so! Of course, that system would never have fit in a car!
While I don’t know the answer to this, I suspect that flywheels are still one of the best ways to store energy that has to be quickly extracted over the timescale of seconds. Batteries probably can’t do it without costing a huge amount, and capacitors probably have a much lower energy density – though they are ideal for other stored energy applications that require much faster discharge times!
Dark Matter Discovered – Loosing Control Of Your Data October 26, 2009
Posted by gordonwatts in GLAST, physics, physics life, science.2 comments
Ok, so it is a sensationalist title. But it was triggered by archive submission with the following title: Possible Evidence For Dark Matter Annihilation In The Inner Milky Way From The Fermi Gamma Ray Space Telescope. Wow! That is quite a title!
First, a bit of background on this paper. This is authored by two theorists who analyzed publically released FermiLAT/GLAST data. Fermi is a NASA funded project and one of its stipulations is that all data it collects must be made publically available 6 months after it has been collected. The authors of the paper downloaded the data, used a simple background model, added in their dark matter theory, and did a fit. And pow:
The red points are the data from Fermi, the dash-dot line and the dotted line are backgrounds (galactic diffuse, and a single TeV source), and the dashed line is their model. Nice fit, eh? Yep – looking at this my first reaction is “Wow – is this right? This is big – how did Fermi miss this?” and then I run across the hall to find someone that actually knows this data well.
It turns out the basic problem with this analysis is that not all sources of background are included. This is the galactic center, and, as one would imagine, there are lots of sources there. Not just one TeV source modeled above. My impression from hallway conversations is that when you take into account all of these sources there is much less (if any) room left for the dark matter model. I don’t think that Fermi has published a paper on this yet, but I suspect they will try a some point soon.
Ok, so all’s well. Fermi will publish the paper and everyone will know the right way to do this non-trivial analysis. Except that things got away from them. Nature news has picked it up and wrote a short update. This is pretty widely read. Now Fermi has a PR problem on its hands – people are running around talking about their data and they’ve not really had a voice yet (the science coordinator for Fermi was interviewed for this bit, but her comments were relegated to the end of the post). Fermi is a big collaboration (yes, not the size of the LHC), even if their paper is close to publication it would probably be at least a month or more before the collaboration could agree on a response. So what to do?
There are a lot of issues surrounding making data public. To first order, it is the tax payers that are paying for these experiments, so the data should be public. On the other hand, you can already see that besides the work and infrastructure of making the data public (which costs real $$ – especially for a big experiment like Fermi or one of the LHC experiments), you have to respond to other folks that analyze your data – basically pointing out their mistakes and trying to help them along, even when they might be in competition with some of your internal analyses. In NASA’s case all the data has to be made public – it is written into every grant submission and NASA even provides money for it. This is not currently the case for particle physics. In many of these advanced experiments the data is quite complex – and someone that can’t depend on the large infrastructure of the experiment to help interpret it is bound to have some difficulties.
One only wishes that the authors had gotten in contact with some Fermi folks before submitting their note to the archive…
Units, Units, Units October 23, 2009
Posted by gordonwatts in physics, physics life.4 comments
Undergraduates know that Physics Professors get all wound up about units. We can’t help ourselves.
But in reading a nytimes article this morning I couldn’t help myself:
In addition, Mr. Holder said, the authorities have seized more than $32 million in American currency, 2,700 pounds of methamphetamine, 4,400 pounds of cocaine, 16,000 pounds of marijuana and 29 pounds of heroin. More arrests are expected.
Well… this is what happens when you wait until the evening to write a blog post you spotted in the morning – they change the article. That 2700 pounds? It was 2700 kilograms (which is significantly more). In short – they had mixed kilograms and pounds. I was going to get on my high horse and… well, seems someone at the times is as sensitive about this as us physicists are.
But it also occured to me that the notion of units is rather flexible. For example, when we do particle physics calculations we often set the speed of light to 1. Normally it is 300000000 meters/second (really fast!). Seriously. We just set it to 1. We are so annoyed by having to carry around that number in our calculations that we just up and set it to one. We do that with an other constant as well (called h-bar). Your unit system ends up being very weird when you do that:
Normal Every Day Units Units in h-bar = c = 1 Energy Energy Time 1/Energy Mass Energy Length 1/Energy
I know this seems weird – but you see it all the time. This is just like making the following unit conversion in the list of drugs: instead of telling us the number of pounds or kilograms, tell us how much pot they got in terms of its street value. And to tell the truth, that would have been a very useful number to have in that article.
Heck, in the old days, the unit of measure in the market was the length of the king’s forearm. When the king changed, the whole country would change its unit system…
Un physics professors getting wound up with units is ironic – we don’t really use them that heavily when we get to more advanced calculations. On the other hand, we can only drop them because we have already learned how to use them. At least, that is what we tell ourselves and everyone else! 
DPF & Lepton-Photon August 20, 2009
Posted by gordonwatts in Conference, DeepTalk, physics.add a comment
It is conference season! Whee!
A few weeks ago the main American particle physics conference, DPF occurred. This is a big conference with lots of plenary and parallel sessions:
At the time I was a short distance away from Detroit, in Ann Arbor, being a Dad. It was a bummer not to be able to attend. I made sure the conference was rendered on my DeepTalk site (picture grab from above). I spent a few lunches the other day browsing it – there are some excellent talks – I definitely recommend checking it out!
This week it is the big Lepton-Photon conference here in Europe. They are simul-casting it as well, so I’m doing my best to watch and record bits of it (more on that in another post). I see someone already submitted that to DeepTalk, so it is partly rendered already. Unfortunately, DeepTalk can’t yet tell that the conference is still ongoing, so it doesn’t automatically update itself. I’ll make sure that happens over the weekend.
Physics on the Mind July 28, 2009
Posted by gordonwatts in computers, physics.2 comments
It is conference season again. The big one coming up now is Lepton/Photon ‘09 (and yes, I will deeptalk it when it is done!). The run-up to a conference like this is a huge amount of work. The analyzers who are trying to submit analysis are all furiously putting finishing touches on the experiment. And everyone else in the collaboration is busy reviewing these analyses to make sure they don’t have mistakes!
I’m on one of the review boards. It is a lot of work – we regularly get analysis notes that are more than 100 pages in length. As you can imagine, going over them with a fine-tooth comb is a lot of work. And Tevatron analyses are now getting extremely sophisticated. They have to in order to extract every last bit of value from the data rolling out of Fermilab.
I’m used to reading these by now. But I’m always impressed when I listen to other fellow reviewers at how often I miss things. So this time around I’m trying something new to organize my thoughts, comments, etc. A mind map. I’ve used this stuff in the past and found it most useful for organizing a brain-storming session. I’ve never tried to do something this detailed or careful with it before.
It turns out getting a mind map up with questions for the review the first time isn’t that hard:
The real test will come when I incorporate people’s answers back into this. Anyone else tried to do something like this before?
As far as the software I’m actually using. I once tried out MindManager from MindJet. I loved it because it was well integrated with my tablet (i.e. I could use my pen to think, which seems to be how my mind works). It does way more than I ever needed – and I didn’t like the price tag so much, either. So I’ve been using FreeMind – free and java based and not really well integrated with Windows, but it works.
Watch Feynman July 16, 2009
Posted by gordonwatts in physics.5 comments
Microsoft Research just posted the Cornell Messenger Series of lectures by Feynman. He is excellent. I’d never seen him speak before this – his wry wit – many of the jokes he uses to teach seem rather too fitting given today’s world. I’ve not finished watching them yet – but they are just too good to pass up. The first lecture seems to be fairly general – he is talking about what a physical law is and what it means – so I suspect anyone interested in science would be able to get something out of these.
The site is called Project Tuva. It will require some time. 
And for the places that the audio isn’t totally clear they have a transcript that runs underneath the video. Spotted on the science feed of the Register.
Long Lived Particles Break HEP May 13, 2009
Posted by gordonwatts in Conference, physics.2 comments
In my last post I mentioned that long lived particles break some basic assumptions that we make in the way we design our software and hardware in HEP. One fascinating example of this that was brought into clear relief for me at this workshop is the interaction between Monte Carlo generation and detector simulation. Look again at the picture I had up last time:
While what I’ve shown above is real data, lets imagine it was a simulation for sake of discussion. Simulation is crucial – it allows us to compare what we think we know against nature. You might imagine that the code that generates everything that happens at the very center of that picture on the left is different from the code that propagates the particles out through the detector (the green, yellow, and blue lines). In fact, this is exactly how we structure our code in HEP – as a two step process.
The first step is to generate the actual physics interaction. Say a top quark production, or Higgs production and decay, or Hidden Valley decay. As output the generator produces a list of particles and what directions they are heading. Most of them will then stream through the detector leaving tracks and data similar to the right side of that above picture. At this point we’ve got the starting point for all those “lines” or particle trajectories on the left.
Then the detector simulator program takes over. Its job is to simulate the detector. It takes each one of the particles and steps it, a millimeter at a time, through the detector. As it moves through the detector it decides if it should loose some energy interacting with the material, or leave a signal in a detector, etc. Once the simulation is done what we have is something that looks like the experiment was actually run – we can feed it through the same software that we use for real data to find electrons, tracks, etc.
But some of these long lived particle models have particles that interact as they move through the detector. The Quirk model is the poster-boy for this (odd, a model without a web page! At least that I could find). As pairs of these move through the detector they interact with each other and with the material they are traveling through. In short – the detector simulation has to act a bit like the generator – we are mixing these two things.
The main detector simulation program (GEANT4) – written in C++ and carefully planned out – does not look anything like an event generator – written in FORTRAN (common blocks!? ‘nuff said – wait, that was flame bait, wasn’t it?). My guess is it will take a year or so to get GEANT4 updated to accommodate models like Quirks. While it isn’t a complete rewrite of the package – it was quite generally designed – the GEANT4 folks probably didn’t think of a modification to allow interactions like this as a possibility.
Which makes me wonder if in the future generators will really just be subroutines (methods, sub-classed objects, etc.) in detector simulations? We all know that detectors are the most important things out there, after all!
Hidden Valley Workshop May 11, 2009
Posted by gordonwatts in Conference, Hidden Valley, physics.3 comments
I spent a very enjoyable week attending a workshop here at UW – Workshop on Signatures of Long-Lived Exotic Particles at the LHC. These workshops are funded by the DOE – and allow us to fly in a small list of experts to discuss a particular topic for a week. As you might imagine, things can get pretty intense (in a good way!).
The point about long lived particles is they are long lived! And not much else in the standard model is long lived the way these guys can be. Sure, a bottom quark might travel a few millimeters – and most of us tend to call that long-lived. But the things considered at this workshop can go much furthers – meters even. All sorts of models can generate these particles – like SUSY or Hidden Valley.
Nothing in a particle physics experiment is really designed for these things – not the hardware and not the software, certainly. Not clear our brains are thinking about them too well either! This is part of what makes them so fascinating!
Take the hardware, for example. Just about everything in the Standard Model decays very quickly after it is created in a collider. Millimeters:
That is an exploded schematic view of what happens in our detector (this is a CDF event, I’ve stolen, from Fermilab). The inner circle on the left is about 2 inches in diameter. You see the exploded view on the right? The distance between the vertex and the secondary vertex is about a millimeter or so. That is normal long lived particle for particle physics. All of our code and the design of our detectors are built to discover exactly those kinds of long lived particles.
That picture is from the small conference dinner we set up at Anthony’s, a local nice fish place here in Seattle. I’ve got more pictures from the dinner posted on my flickr account.
Observed! March 5, 2009
Posted by gordonwatts in physics.add a comment
Abstract: We report first observation of the electroweak production of single top quarks in ppbar collisions at sqrt(s) = 1.96 TeV based on 2.3 fb^-1 of data collected by the D0 detector at the Fermilab Tevatron Collider. Using events containing an isolated electron or muon and missing transverse energy, together with jets originating from the fragmentation of b quarks, we measure a cross section of sigma(ppbar -> tb + X, tqb + X) = 3.94 +- 0.88 pb. The probability to measure a cross section at this value or higher in the absence of signal is 2.5 x 10^-7, corresponding to a 5.0 standard deviation significance for the observation.
I don’t think it was 5 years in the making – but close to that. Congratulations to everyone involved, and there were a lot of people.
I and my students and post-doc were intimately involved in the evidence paper, but this one I was mostly looking in the from the outside. But getting to 5 sigma was definitely harder than our earlier 3 sigma result. I can’t tell you how happy I am that this result has been submitted to the journals! Excellent!
Update: And CDF got it too – a joint discovery!
We report observation of single top quark production using 3.2 fb1 of pp collision data with ps = 1:96 TeV collected by the Collider Detector at Fermilab. The signicance of the observed data is 5.0 standard deviations, and the expected sensitivity is in excess of 5.9 standard deviations. We measure a cross section of 2:3+0:6-0:5(stat + syst) pb, extract the CKM matrix element value|Vtb|= 0:91+0:11-0:11(stat + syst) 0:07(theory), and set the limit |Vtb|> 0:71 at the 95% C.L.
English Language Summaries December 19, 2008
Posted by gordonwatts in D0, physics, physics life.add a comment
This is pretty neat. The RNA Biology journal is now requiring a Wikipedia article along with every submitted paper. The guidance from the journal is as follows:
At least one stub article (essentially an extended abstract) for the paper should be added to either an author’s userspace at Wikipedia (preferred route) or added directly to the main Wikipedia space (be sure to add literature references to avoid speedy deletion). This article will be reviewed alongside the manuscript and may require revision before acceptance. Upon acceptance the former articles can easily be exported to the main Wikipedia space.
Keep in mind that Wikipedia articles are to be targeted at a level that an undergraduate could comprehend. Try to avoid jargon and do provide links to other Wikipedia articles at the first use of specific terms, e.g. [[RNA]]. Also the title of the page should appear in bold at the first use of the text of the article, e.g. "eRNA."
This is fantastic. For a long time here at DZERO we were trying to write English Language Summaries (or Plain English Summaries) of all of our papers. For example, here is one for an old Z+b analysis. These were aimed at people who weren’t particle physicists, but had some real interest in the science – the general interested public. We have mostly given up on this, however (I haven’t followed why). Currently the best summaries of this nature I know about are on a blog – Tomasso’s, specifically (e.g. here and here for recent examples).
But Wikipedia is a great idea! It is an increasingly popular search destination. And it is, supposedly, better organized than a blog. And more permanent. Writing the results up there I think would be a great idea. The only thing thing that this doesn’t address is a central pillar of the power of Wikipedia: inter linking. For these articles to really fit in they have to be linked. And if similar results (for example, measurements by both CDF and DZERO of the same thing) are presented then pages would have to be combined or correctly linked. Perhaps a page a paper and then other pages that discuss the specific pages? The experiments could appoint topical editors (i.e. service work) that maintains all the W/Z results, all the Higgs results, etc. Ok, now this is starting to sound like lots of work!
A neat idea, however!
