Dr. Kenneth Bloom is a postdoctoral researcher in experimental high-energy particle physics at the University of Michigan.
More photos from Ken Bloom
If you haven't figured it out already, when you have 500 co-workers, you go to a lot of meetings. (You also read a lot of e-mail, but that story would require its own daylong "Diary.") I can't say that attending meetings is fun, but at least we try to make them efficient. Thursday is our biggest meeting day; many collaborators who don't live at Fermilab arrange their schedules so that they can visit the lab on that day.
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The focal point of Thursday is the weekly meeting for the entire experiment, where we discuss news and issues that are of interest to all of us. About 80 people packed into our largest conference room for today's meeting, putting a severe load on the air conditioning. We typically hear reports on the state of our operations—how many collisions the accelerator has delivered, and how many we have managed to record for future analysis. This week, we got interesting news from lab management: They do not plan to stop running the collider for any extended period between now and the end of the year. That's good news for us; we think that if the accelerator and detector remain stable for the next four months, we should accumulate enough data to start studying top quarks.
We also had a meeting of the top-physics group, where the main topic of the day was what we have to do to establish for a fact that we are seeing top quarks, and how to do it in time for the major conferences that occur in the late winter. If we have enough data, then it's just a question of getting the work done. We heard presentations from groups of people working on different parts of the problem—reconstructing and identifying the top-decay products, using complementary data samples to estimate backgrounds, and using simulations to determine how many top quarks we might miss because of imperfections in the experiment. It sounds as if we will do just fine, as long as we coordinate our work and plan carefully. After six years of building our detector and a year of taking data, we're going to hit the payoff—the physics that motivated us to begin with.
That isn't all the planning we are doing—while keeping our experiment running and analyzing the data that come out of it, we also look toward the future. Accelerators are such large and complicated devices that they take a very long time to build. It can take 20 years for a machine to make it from the first glimmerings of an idea to regular operations, with about half of that time spent actually building the thing. Right now, many particle physicists are looking toward the Large Hadron Collider at CERN, which will collide protons with other protons on the outskirts of Geneva, Switzerland, starting in 2007. LHC collisions will have seven times the energy of Tevatron collisions, which we believe is enough energy to create a new class of massive particles that should help us explain the origins of mass. Meanwhile, the particle-physics community has been involved in an active debate over what kind of machine should be next on our drawing boards. We have settled on a very different idea, a linear accelerator (it's a line, rather than a circle) that will collide electrons and anti-electrons at energies similar to Tevatron energies. This kind of machine will allow us to make precision measurements of any particles that we discover at the Tevatron or LHC.
Building a linear collider will be a worldwide effort, with several nations sharing in the construction, management, operation, and cost. We worry a lot about the cost—we figure it's about $7.5 billion to build the thing, spread over 10 years and several international partners. In the grand scheme of things, however, I'm not sure that it costs all that much, at least in comparison with, for instance, the $6.35 billion that Americans spent buying video games last year. (The annual budget for particle physics in the United States is $0.8 billion, with $0.3 billion going to Fermilab.) Still, we understand that to get support for this project, we need to convince the world that research in particle physics is interesting and important.
By now you probably understand why particle physics is interesting and important to me, but why should it be the same to you? There are some good arguments about how research in the physical sciences underpins the remarkable progress that has been made in the biological sciences over the past decade, and about how spinoffs from basic research turn into technological applications that help drive the economy, and how students trained in basic research become leaders in applied and industrial research. It's all true, but I prefer to focus on the bigger picture. Particle physics is a science of origins and essence; it is about what we are made of, and how we got to be here. If the properties of elementary particles, even those we only encounter in accelerator experiments, were any different, then the properties of atoms would be different, and the world around us would be different; life itself may not be possible. We ourselves are, ultimately, extremely large aggregates of subatomic particles, and to understand them is to understand ourselves. Such self-understanding (in this scientific sense and in other senses, too) has been a goal of societies throughout history, and it should be a goal of ours, too. This may not shine through in my day-to-day activities, but that's what the work is really about.
During congressional hearings on the establishment of Fermilab, Director Robert Wilson was asked whether the lab's research would contribute anything to the nation's defense. "It has nothing to do directly with defending our country, except to make it worth defending," Wilson said. I hope you agree.
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Notes From The Fray Editor:
Discussions of people doing remarkably complex things tend to move in two directions: toward the people and toward the remarkably complex things. In this case, Air Vent began a discussion of physicists that sounds like almost every group-of-physicists-yukking-it-up I have ever been around while andy finished off (more or less) a discussion of the relationship between the complicated math and the reality of the reality it speaks to (previous posts in that thread are less daunting).
Remarks From The Fray:
I recommend against counting 'Daves' at Fermi, as the statement 'Dave is a common name in particle physics' is an unsupported statement. Fermilab is I think unrepresentative of particle physic generally. I think CERN must be sampled too and two universities also. I think Cal Tech and the U. of Michigan must be sampled as well. At CERN there may be some Dave's who go by Pierre for example to fit in and at Fermilab there may be some Pierre's who go by Dave to fit in at Fermilab. I suggest checking birth certificates. So just in conversation you may have picked up both some false negatives and some false positives on this score. Hope this is helpful to further research.
--Air Vent
(To reply, click here.)
the retrospective realism comment is perceptive.
we talk about the various flavors of quarks as if they're real (also the leptons and gauge bosons); to the extent that we can measure quantities that appear to correspond to each of the particles, we should consider to be real. but there are ambiguities.
first, even field theorists generally do not focus on the elementary particles as the fundamental concepts of reality. rather, the main concept in particle physics is the so called SU(3) X SU(2) X U(1) local gauge symmetry. it's the symmetry principle that takes precedence; the particles are looked on as the quantum excitations of the vacuum induced by the field operators present in the theory. i suspect that many theorists would say that what's real is the symmetry principle, and the observations of the various particles and the manner in which they interact with each other confirm the prediction of the symmetry-based gauge theory.
second, field theory may not be "fundamental". quantum field theories are often referred to by theorists as "effective field theories" these days. the reason is that most people doing theory nowadays believe that QED/flavordynamics and QCD are only approximations of an underlying level of complexity at higher energies (corresponding to shorter distances.)
one of the many reasons for the prevalence of this belief is the existence of infinities in various calculations. theorists tend to think that such infinities indicate the theories are incomplete; this explains the interests that theorists have in strings, M-theory etc. this brings us to a third ambiguity in the concept of the top quark:
one of the field theory calculations that give infinite result concerns the mass of the quarks. obviously, the infinity present in the calculation is not observed, so we try to "sweep" it under the rug by replacing it with some arbitrary parameter which is determined by measurements made at a specific energy scale [this trick is generally known as 'renormalization' and one of the most popular schemes for doing so is called 'modified minimal subtraction']. however, from QCD theoretical calculations, it turns out that the mass of a quark varies depending upon the energy scale at which we perform the renormalization. thus the "mass" of the top quark is a somewhat ambiguous concept.
Finally, as you already know, we can't observe free quarks even at the energies that will be reached by the future LHC collider at CERN. this is due to the nature of QCD which dictates that the strong force increases in strength at lower energies (larger distances); the concept of six quarks organized into three 'families' is postulated from the fact that such an arrangement would consistently describe other particles as quark composites...otherwise there'd be hundreds of known "elementary particles". so to a certain extent, a quark is a convenient construct.
-- andy
(To reply, click here.)
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