Imaginary Potential

According to my Librarian, The National Geographic Channel will be re-airing a show on man made marvels tomorrow and next Thursday on antarctic construction, with a partial highlight of the IceCube Experiment.  IceCube is a cubic kilometer of arctic ice laden with photomultipliers, and a surface array to detect air showers.   The PMT’s pick up Cherenkov light from fast moving charged particles (mostly muons), which come from cosmic rays and neutrino collisions with the water molecules.  Once completed, you can think of IceCube as being, among other things, a giant cubic telescope that views the universe with neutrinos instead of light.  It also contains an earlier detector called AMANDA, which is shown here as the yellow cylinder.  Photo comes from  gallery.icecube.wisc.edu.

If you speak German, and like science history, you can download Weyl’s 1919 Zeit, Raum, Materie book in PDF for free from The Internet Archive. I wanted a sort of journalistic, “this is how it went down” kind of book, but that doesn’t seem to be the case. There’s some nice first person stuff in the forward, and some nice philisophical musing at the end, but mostly is seems textbook stylie. I just skimmed it a bit, so maybe the gems are buried deeper.

If anyone can find anything on his early attempt at gauge invariant therory of unified electronmagnetism and gravity, I’d be grateful to hear from you.

You can also check out a collection of original papers on Relativity from before 1920, too. These are all translated into english.

I’m part of a collaboration that built and operated a particle detector at a collider which finished taking data in July of last year. I wasn’t here to build it by a long shot, but I did run and repair part of it during last two years of data taking. Now I’m only analysing data for my thesis, not doing any hardware work anymore, and I’m finding its a mixed blessing. (more…)

Today I’m writing conference proceedings, which are boring me to write, so they will probably be inhumanely boring to read, and lethally boring to publish. I may try to write them so the first letters spell out a hidden message, just to stay focused.

Part of the way I’m constructively procrastinating is skimming a review paper on Generalized Parton Distributions. They’re a pretty cool idea. So QCD can’t be perturbatively calculated at arbitrarily soft scales, so nobody knows how to directly calculate from first principles whats happening inside of hadrons. The lattice folk are making progress here, but that technique takes a lot of power, so those calculations can’t easily get incorporated into general calculations.   You can parametrize what’s happening in a hadron, measure it, and the factorization theorem tells you your resulting functions are universal, modulo an evolution of the factorization scale. So we can measure parton distributions functions here at HERA, and then you can roll them up to the LHC/TeVatron scales or down to a fixed target, and everyone agrees on what these functions are and do. If you are operating at first order, the vanilla type of PDFs naively tell you what the probability of finding a quark or gluon of a certain type and certain longitudinal momentum is. At higher orders the interpretation isn’t so clear, but they still return a real scalar. There’s no interference, no helicity, no transverse momentum. You can tack on spin or other stuff, but its always a bit of a blunt object.  How the proton gets its spin out of the quark-gluon shimmy is still a big mystery, so theorists have been experimenting with difference ways to combine PDFs and form factors, to include interference terms, and understand all components of nulceon spin. The situation is stabilizing a bit, and this paper seems to imply that the parameterization they describe is widely used.

I got a bit shocked by the following couple of lines:

…according to an extension of the equivalence principle of general relativity to describe the interaction of the nucleon with the external gravitational field one arrives to the interpretation of B(0) as an anomalous gravitomagnetic moment being the analog of the anomalous magnetic moment [47]. There is also evidence supporting the conjecture that the equivalence principle is valid separately for quarks and gluons resulting in exact equipartition of momenta and angular momenta in the nucleon. The most precise numerical support comes from lattice calculations [48].

AH!  What!!?!?!  Who said anything about gravity!?!?!  But it’s not really what it looked like at first glance.  B(0) is zero, btw, so whatever you want to call it is moot, but the cool thing is that [47] paper, where the author sees a relationship similar to the equivalence principle, and this cancels out that B(0) thing at all orders.  I can’t do GR, so I can’t comment on the validity of the approach, but its a cool idea…..

I read a post by a biologist philosopher about how supposedly physicists are undertaking “stamp collecting.” And I’m fairly annoyed that they missed the entire point. They read this article on attempted classification of string vaccua, and likens this attempt to taxonomy in biology, in their eyes lowering physics to a descriptive science. This whole flame war started with Rutherford claiming “In science there is only physics. All the rest is stamp collecting.” Let me liberally translate to clarify: “In science the only quantitatively predictive field is Physics, and everything else is descriptive.” This certainly was true in Rutherford’s time, but discovery of atomic structure elevated Chemistry to predictive, and the discovery of DNA elevated biology. Now we’re all buddy-buddy. In real science, 99% of the time you first gather data, then classify, then build models, and then you have a quantitative principle to make predictions. This went faster with physics because we deal with much more homogeneous systems. An old friend and ex-ZEUS student I know is now writing Monte Carlo simulations for Neuro Bio. That aint taxonomy. Heck, even economists have real models these days, and their particles have agency.

The big missed point is the following: String Theory isn’t predictive, or descriptive, yet. It has never made better than tenuous qualitative connection with reality, and I wouldn’t bet any money that it will improve soon. Why? Because its history is all bass-ackwards. It may have started from meson spectroscopy and QCD flux tubes in the late 60’s, but then everyone thought they smelled gravity and got the great idea to start from a unprobeable scale and grope their way back down to experimentally plausible energies. In string theory you first assume an underlying principle, then build a phenomenological model, then gather data. This isn’t to say its totally unmotivated, but it does incur a large investment risk.

The authors whole point is that stamp-collecting is a type of science, and shouldn’t be looked down on. This is half true. It is necessary for developing falsifiable theories, but should not be considered a form of science in itself. People can gather data, and arrange it in clever ways, but without predictions and basic principles, There’s very little objectivity, or application.

So biology in Rutherford’s time was like stamp collecting, but all those stamps they collected were issued from a genuine authority. Woit claims the String Vaccua Project “…is stamp-collecting done by people who don’t have any stamps, just some very speculative ideas about what stamps might look like.” He breakdown of the string vaccua project on his blog, if you want to read more. He also comments on the original biologist’s philosopher’s post.

Edit: Dr. John S. Wilkins, the author of said blog, is a postdoctoral research fellow of philosophy, not biology, as originally stated.

You know, I love my work, but there are days I wish I did physics with cooler demo-potential.

Awesome. I love it when people do good old-fashioned straight-up QCD Pheno. RHIC sees tons of cool effects where the theory just can’t cut the muster, so I get really excited when someone hits QCD head-on, instead of doing something easier, or unfalsifiable.

So I just read this paper this morning, which basically extends DGLAP parton showering to include iteractions with Quark Gluon Plasma. This is pretty cool, as that it seems to qualitatively reproduce some of R_AA supressions. Sad thing is they neglect the reaction of the medium, so I doubt this will describe the mach cone, which is one of my favorite things out of RHIC. Can’t have it all, I guess.

In case you’re wondering, RHIC is a versatile collider on Long Island, which collides combinations of protons, deuterons, copper ions, and gold ions. The goal is to study lots of processes, but most significantly to create really hot, dense conditions where we may be able to observe a phase transition in QCD to something called the quark-gluon plasma. Maybe we already have seen it, but the theory is wicked hard, and no one is certain whether there’s really a phase transition or not. Whatever they are making, the “medium” is hot, dense, and is pretty much in thermal equilibrium as its expanding. They also know that it smears hadronic information, but electromagnetic stuff passes through unscattered. The hadronic smearing I’m talking about seen in the R_AA plots, which are ratios of stuff from gold-gold and proton-proton collisions. The basic idea is, there’s a hard scatter in pp or AuAu which are essentially the same, the energy has to pass through the medium in AuAu, and the distributions are really different. You can read more here from the STAR collaboration. The mach cone thing I mentioned is a hunch that people are seeing something analogous to a sonic boom as partons traverse the medium. This is fantastic, because if you can measure a mach cone, you can measure a speed of “sound.” If you can find a place where the speed of “sound” suddenly changes, thats pretty good evidence for a phase transition, which is the name of the game. Heres some slides of a talk I saw at DIS last year. Its a good introduction and overview to RHIC.

For those of you interested in pattern classification, machine learning, etc, there’s a really nice package called TMVA, which contains a ton of multivariate techniques which are fairly easy to integrate into High Energy Analyses, as they are a ROOT extension. Even if you don’t do HEP, they’re nice because all the methods have comparable inputs, so you can test tons of different ones without a big development hit. I’ve only futzed with the Multi-Layer Perception package, but that was pretty quick and painless to implement. A buddy of mine at H1 used it for electron tagging, and tested like seven different methods before settling on a Boosted Decision Tree. I mention this now, because Anselm Vossen just released a couple of lecture notes (I think they’re from the CERN Computing School) on the principles of some of the implemented techniques specifically Support Vector Machines and one which has a nice discussion of data preprocessing for MVA. If your shopping for selection criteria, check em out.

That reminds me, a reader “A. Game Coder” commented before that they’d like to see more posts on computing in Physics. While I’m thinking about it, check out the slides from the CERN summer school in 2006 and 2005. Lots of fun stuff like genetic algortihms and management of large data sets.

Today, the Department of Energy announced that it will award $13.7 Million for 11 university projects that develop Photo Voltaic Devices. They write :

These projects have the potential to significantly reduce the cost of electricity produced by PV from current levels of $0.18-$0.23 per Kilowatt hour (kWh) to $0.05 - $0.10 per kWh by 2015 – a price that is competitive in markets nationwide.

Don’t start writing applications. They’re announcing the winners. Hey Bonna, MIT is on there. Is that your stuff?

For those of you interested in HEP in general and Higgs searches in specific, you may have already heard of the Combined CDF/D0 top mass preliminary release. They’ve changed from last year to which is a total uncertainty of 0.8%. Tommaso Dorigo has a really nice post on the individual measurements and combined uncertainties that went in to the result. There’s also a bit of general discussion on how to combine measurements and an interesting point on how top mass measurements may-or-may-not be effected by jet multiplicities in the final state. He suggests that the full luminoisty this might improve to 0.5% .

For those of you who don’t get all giggly at slightly lower error bars for their own sake, the top quark is the heaviest of the six flavors of quarks, and was first measured with certainty around 1994-5. The mass of the top is an important parameter in estimating properties of the yet-to-be-seen Higgs Boson, as well as an important input to describing the plethora of other physics processes at the LHC. If you want to know where to look for the Higgs, and you want to know what backround stuff isn’t new physics, then you want to know the top mass really really well.