Over The Top

Trying to pin down the most elusive member of the quark family is the perfect task for Melissa Franklin, a physicist with a flair for the eccentric and a love for the big machines.

By David H. Freedman|Wednesday, February 01, 1995
RELATED TAGS: SUBATOMIC PARTICLES
The most powerful particle smasher in the world is apparently about to blow up under Melissa Franklin’s feet, and she’s having a hard time hiding her irritation. Minutes earlier Franklin waved good-bye to a team of eager students who were about to make their way down on a minor repair mission into the pit, the part of the Fermilab Tevatron accelerator where protons and antiprotons smash into one another with enough ferocity to create weird forms of matter and energy. But something went wrong down there. Now every type of siren, Klaxon, and flashing light ever invented is operating with bone-shaking enthusiasm throughout the accelerator building. The message is clear: the students in the pit have already been reduced to fundamental particles by terrible forces, and the rest of us are about to die.

Or maybe not. Franklin rolls her eyes and strolls morosely along the cat-walk toward the exit. I bet it was a walkie-talkie that set it off, she grumbles when she’s far enough outside to be heard over the hellish tumult inside. It seems that the countless monitoring devices scattered throughout the accelerator are set to better-safe-than-sorry levels and don’t always effectively discriminate between meltdown death rays and radio messages like Wow, look at all these pipes. Such false alarms occur every three weeks or so, causing most of the people who work here to lose most of a day’s work. Everyone’s used to it. Jorge, one of the students who descended into the pit, comes strolling up, his grin still in place. Did you do that? asks Franklin accusingly, but only in a mock way. Probably, says Jorge, shrugging breezily.

Some 50 people are now standing around outside the accelerator building, joking, chatting with the newly arrived firefighters in neon green insulated suits. They are a sampling of the 850 scientists from various research institutes around the world who have dedicated a chunk of their lives to tracking down a particle known as the top quark. The search, being conducted by two relatively independent groups working in parallel, is in a sort of protracted limbo right now; the top quark hasn’t officially been discovered, but it’s not exactly missing anymore, either. One of the two groups has put together a pretty good case that the top quark has actually turned up a few times in the pit, but its case isn’t ironclad. Now it’s trying to gather the extra evidence it needs to claim unconditional discovery.

Franklin is one of the many key players in the effort, heading the small Harvard contingent that built and maintains two of the particle detectors in the pit. She has flown here to Batavia, outside Chicago, for a three-or-so-day visit to check on the experiment and her students, as she has done as frequently as every other week for the past ten years. But between the need for some minor repairs and the walkie-talkie incident, it’s clear that nothing much will be happening with the experiment this time. That’s often the case. We have this beautiful machine here, she explains, but we just don’t get to run it that often.

The quest for the last undiscovered particle of orthodox physics has an aura of glory and pure truth to it. Or at least it does to those of us who are outside looking in. To those who are in the thick of the search, however, the glory can be obscured by the mind-numbing routine and the frustrating glitches, the truth blurred by hand waving, negotiation, and politics. It’s been said that anyone who loves the law or sausages shouldn’t watch how either is made. You might want to add Big Physics discoveries to the list.

As almost anyone in the particle physics community will be happy to tell you, Franklin has a hyperactive, offbeat sense of humor. Tall and deadpan, a young-looking 38, she stalks the hallways of Harvard and Fermilab making faces at some colleagues, suddenly jumping out at others. In airports and restaurants and on city streets she regularly accosts strangers to comment on their clothing or food, and to enlist their support in making fun of any reporters who happen to be hanging around with her at the time. She bursts into a Groucho Marx strut in the middle of Harvard Yard; at a coffee shop she empties a small sack of tiny plastic pigs onto the table without explanation. It’s bizarre, but it’s usually pretty funny, except for the reporter part. She’s a jazz sax player, a high school dropout, and the first female full professor in the Harvard physics department.

But Franklin is defined far more by her specialty within physics than by her daffy, eccentric ways. She is no ivory-tower theorist lost in equations. She’s an experimentalist who routinely gets her hands dirty with enormous, temperamental machines. The sort of work she does takes place where the rubber of mathematically elegant hypotheses gets to meet the potholed, twisting road of reality laid by nature. Franklin is the first to point out that it’s not for everybody. You might have to spend five days doing nothing but getting voltage levels from the equipment, but somebody has to do it, she says. I happen to like doing it. There’s a tendency now at accelerators to build control rooms far away from the equipment. I want to be with the equipment. I need to stroke it.

It galls Franklin that there is an unstated but widely held notion among physicists that a career in experimentation is a fallback for those students who can’t cut it as theorists. Undergraduate physics programs are almost all theory, she charges, and it is taken for granted that those students who make top grades will continue their theoretical focus into graduate school, while the rest are left to consider experimentation. A better criterion for separating the budding theorists from the experimentalists, she jokes, would be strength of character. Theorists are wimps, she says. They might work hard, but they’re generally home for supper. If theorists had to commute across the country to experiments, physics wouldn’t get done.

Wanting to be an experimentalist from the beginning was just one factor that kept Franklin swimming against the stream in her career. The other, she claims, was being a woman in a male-dominated field. Expectations are so low for women in physics that it keeps most of them from doing well, she says. I had someone tell me to my face that he knew I’d make it even if I wasn’t the smartest person he’d ever met.

You couldn’t find a more fitting fundamental particle for Franklin than the top quark. Talk about offbeat, and swimming against the stream. The top is one of six quarks--the others being the up, down, strange, charm, and bottom--whose existence was predicted by the standard model, the tried-and-true scheme underlying our present understanding of matter and energy. (Triplets of up and down quarks make up the ordinary protons and neutrons that in turn make up an atomic nucleus. The others are the stuff of more exotic matter.) The up, down, strange, charm, and bottom quarks were all found by the late 1970s. In the decade and a half since, however, the top quark has thumbed its nose at a half-dozen different high- powered search teams. The problem, it seems, is that the top has turned out to be mind-bogglingly heavy--some 40 times heavier than the next heaviest quark, the bottom, and heavier than most atoms, which are made of entire communities of particles.

The heavier a particle is, the more energy it takes to create it- -odds are that since the Big Bang, the only places in the universe where enough energy exists to produce a top quark are supernovas. Also, the heavier the particle, the more ways it can quickly disintegrate into smaller, more stable particles. These patterns of decay are what give each species of heavy particle its unique signature. But with so many possible patterns, the top’s signature is extremely difficult to read with any confidence. A seemingly promising pattern could easily turn out to be the signature of something else.

Why is the top quark so heavy? Yeah, that’s the question--why? says Franklin. We don’t know. It’s weird. You’ve got six quarks; five of them are really light, and the sixth is unbelievably heavy. It’s as if you had Sleepy, Dopey, Grumpy, Bashful, Happy, and Kierkegaard.

In a sense, Franklin and the top quark have been on a slow-motion collision course for two decades. In the early 1970s, around the time theorists were polishing the standard model, Franklin was dropping out of high school to join other students in setting up an alternative school, then dropping out of that school too. But she managed to talk her way into the University of Toronto as a physics major a few years later, just as the charmed quark was being discovered.

By the time the first efforts of physicists to find the top quark were failing, Franklin was attending graduate school at Stanford. It was there that she started to become seriously immersed in particle physics experiments, working with the university’s electron-positron collider. She went on to do postgraduate work at the University of California at Berkeley, where she became involved in building a particle detector of the sort placed around the collision chambers in accelerators so that physicists can determine which particles are created in the collisions. By the time Fermilab was readying its powerful Tevatron, believed energetic enough to finally find the top quark, Franklin was installed at Harvard and fully committed to a particle search. By the time the Tevatron got the additional proton-smashing power it needed to really find the top quark, Franklin was an integral part of the team. I like protons, she explains. I like electrons too, but I had done those.

To fully appreciate the sort of sacrifices that Franklin and other experimentalists have made in the name of nailing down the top quark, you have to visit Harvard House, a tiny blue houselet on a drab but neat strip of similar houselets a mile from the accelerator. This is where Harvard students and researchers visiting Fermilab usually sleep. The decor is vintage Motel 6, and the three beds are often taken, meaning that people can sometimes be found sacking out on the couch or even the floor.

Not surprisingly, Harvard House is not a favorite hangout for those visiting Fermilab. Neither is the Fermilab village bar or its community library of used science fiction novels, much as both are appreciated in times of need. Even during late-night hours, most researchers can be found either at the accelerator or, more likely, in one of the nearby offices. Not the comfortable offices in the slickly contemporary, towering office building nearby, however; that building houses Fermilab’s theorists. More generally, top quark researchers are assigned to offices on the other side of the accelerator in a maze of interconnected trailers that smell of mildewed wood, white-board markers, and cigarettes. (Though few of the American physicists smoke, their international counterparts more than make up for their restraint.) The trailers were supposed to be temporary, but it’s pretty clear at this point that this is as good as it’s going to get.

The trailer offices are virtually half-time homes to many of the researchers carrying out the top quark search. Among them is Gary Houk, a slender, longhaired University of Pennsylvania physics graduate student who is trying to write his thesis on the top quark while he holds down the equivalent of a full-time job carrying out various tasks for the experiment. Part of his job involves fine-tuning and maintaining one of the devices that count electrons emerging from the Tevatron’s collision chamber. Another part is to reprogram software that is supposed to simulate one of the particle detectors; it seems the software doesn’t behave nearly as erratically as the detector does, so the software has to be changed. Houk says it’s easy to tell if a would-be physicist is destined for a career in experimentation, as opposed to theory: If you didn’t take apart a bike or a radio as a child and put it back together into working order, he says, then you’re probably stuck with theory.

Down the hall, Fermilab staff researchers Claudio Campagnari and Avi Yagil sit in a thick cigarette-smoke haze, mulling over computer data from the latest accelerator run. Campagnari, who is Italian, and Yagil, an Israeli, have different accents, but they look as if they could be related. They speak as though they share a mind too. This is the two discussing the challenge of getting good data:

Claudio: The detector wasn’t really designed for this job, because--

Avi: --nobody ever expected the top quark to be so heavy. But even though it was built for a different type of signal, it had the ability--

Claudio: --to go beyond.

Avi: If we don’t get any signal--

Claudio: --we’ll be in a very comfortable position because we won’t have anything to explain, but--

Avi: --if we get a signal, we’ll have to worry about what we might have done wrong. There won’t be any eureka for us with the top quark. It will be a gradual piecing together.

Some of the faces in the trailer park seem awfully young to be peering at computer simulations of protons smashing each other to bits. Many of these faces belong to students of Franklin’s; she makes a point of sponsoring undergraduates who have an interest in hands-on physics. Harvard senior Robin Coxe, for example, is sharing Franklin’s tiny trailer office for the summer. Like many researchers there, she spends much of her day hunched in front of a computer terminal. Her assignment is to ask what sort of unexpected particles the top quark might produce, on the very off chance that scientists have miscalculated what the top quark can and cannot do. After running a software simulation of bizarre patterns of particle disintegration, she will pore over pages and pages of experimental data to see if anything remotely similar has popped up in the accelerator. No one expects her to find any surprises; back at Harvard, Nobel Prize-winning theorist Sheldon Glashow has already gotten the message to Coxe that if she finds anything, she’s made a mistake.

Still, ruling out such things is considered moderately useful, if not particularly glamorous, work, and Coxe thinks she’s lucky to be here and to be contributing. I knew there was more to physics than sitting in classes, she says. Like many other young women at Harvard who cross Franklin’s path in a physics course, Coxe found herself gravitating to her for inspiration. Before Franklin became a full member of the Harvard physics department, only 10 percent of its graduate students were women; now nearly a third are. Oh, and by the way, Coxe reports that she took apart and flawlessly reassembled several of her mother’s small kitchen appliances when she was eight.

Another Franklin protégé is a wiry and exuberant graduate student named David Kestenbaum. Kestenbaum has been spending summers at Fermilab since he was in high school. He is now widely addressed by other researchers as the Kid, not so much because of the young age at which he started but rather because of his proclivity for Dennis-the-Menace-style misadventures. Once, for example, he accidentally epoxied his rear end to the floor while making repairs at the accelerator. Another time he found himself so captivated by the thousands of small blinking lights on the computer equipment during a late-night session alone in the darkened control room that he turned up his portable radio, climbed on a chair, and started dancing. When one of the older project directors walked in and became apoplectic at the sight, Kestenbaum blithely rejoined, Cool down, Dad. Now people employ the nickname with a certain respect.

But Kestenbaum is not there for comic relief. During the summers he sometimes puts in 80-hour weeks. He has spent countless nights on the Harvard House couch hoping his pager wouldn’t go off. And he was behind an important modification to one of the detectors that improved by 30 percent its ability to find muons--heavy electron-like particles that can be important signatures of a top quark. Helping researchers find more particles is a good way of getting their attention, he says.

When Franklin is not meeting with her students, she spends much of her time in the accelerator control room staring at the dozens of computer monitors that report on every aspect of the accelerator’s functioning. Sometimes she’s needed to fine-tune one of the three detectors she’s had a hand in building, and once in a while to direct repair missions in the pit. Most of the time, though, there is little to be done during a watch, and even the fine-tuning and repairs usually don’t really require her presence. But Franklin says she’s offended by the notion, held by many of the project’s senior members, that these tasks are grunge work. She wouldn’t dream of dumping the responsibility on someone else just to free up an extra weekend back in Cambridge: You know how you want to fix something, and you can’t tell someone else how to do it, and you just need to get your hands on it yourself? And sometimes you just have to be there because the important stuff comes from a comment someone makes after sitting around for 14 hours drinking coffee and eating doughnuts. The really useful people are the ones who have absorbed information by osmosis, so that even though they’re just sitting there bored, when something happens they remember exactly the right piece of knowledge to deal with the situation. You want to be there to rub elbows with these people.

Not all the personal interactions are quite so productive. The huge challenges and sheer size of the top quark hunt have engendered political bickering and contention in a number of forms. At the root of the problem is a physical constraint: the top quark, assuming it really does exist, is a highly unstable particle. Simply because it’s so massive (and therefore contains so much energy), it disintegrates into more mundane particles like electrons and muons within a trillionth of a trillionth of a second, far too short a time to observe it directly. To say that a top quark has been found, then, researchers must find the remains of the top quark’s brief appearance; that is, they must zero in on exactly the right combination of particles, each of which has the right energies to spell out a recognizable signature. Then these precise combinations must be analyzed to ensure that at least some of them are likely to be the detritus of the top quark rather than just the routine wake of a far more mundane event. Thus finding a top quark is not a cut-and-dried affair, but rather a Sherlock Holmesian exercise in inference in which a series of clues, each meaningless by itself, are carefully gathered, examined, then reexamined, over and over again until some glimmer of what may or may not be the truth starts to materialize from the haze, pointing an at least initially less- than-certain finger at the suspect.

If only Holmes were around to help. As it is, scientists of less legendary powers are left to wrestle with the problems of deciding which data to look for and then interpreting them, tasks that are highly subject to differences of opinion. The Tevatron produces 300,000 particles per second, but even the powerful minicomputers that fill a good-size room in the accelerator building aren’t capable of processing and recording that much information in such a short time. To whittle down the staggering rush of data to a manageable level, an array of electronic devices and software known as triggers sift through the products of each collision. Each trigger is designed to look for a particular characteristic in a particle-creating event--it might be, say, two highly energetic muons moving off in opposite directions. The trigger then selects that tiny fraction of events that meet its criterion and tosses out the rest. Thus the triggers make the initial cut through the raw data to pick out the events worthy of further perusal.

There are 180 triggers altogether, and they are arranged in three groups; to end up preserved in digital form for later analysis, a candidate event must be selected by at least one trigger in each of the three groups. (If one looks for muons, another might look for a certain combination of electrons, or total energy.) Of the initial 300,000 events per second, only about 5 typically make it through the gantlet of triggers to be recorded on tape.

Deciding how to set the triggers, then, is a subject of almost constant and occasionally acrimonious debate. Since the triggers determine which events are later analyzed and which ones are allowed to pass by unexamined, the criteria used to decide what stays and what goes are clearly critical. If the triggers aren’t set wisely, they could cause the experiment to appear top quark-less even if the particles were being produced at a prodigious rate. But different physicists often have very different thoughts about which patterns of particle decay are most likely to signal the top quark’s retroactive presence. Thus the biweekly meetings at which Franklin and other physicists discuss programming the triggers are sometimes testy affairs that leave some physicists feeling slighted. Franklin finds the arguments tiresome. No matter what we decide, she says with a shrug, we’ll probably look back ten years from now and think we were stupid.

The jostling among the project teams takes many other forms as well. For example, analyzing the events saved on tape requires loading the data onto a hard disk drive attached to Fermilab’s computer. But since there isn’t nearly enough disk space there--or in the entire world, for that matter--to handle all the data collected, researchers must settle for loading and looking at some tiny subset of the data. Needless to say, physicists don’t always agree on which tiny subsets should be analyzed first, or even which should be analyzed at all; they have to push for the subset of most interest to them. Some of the more well endowed universities can afford the $35,000 it takes to buy their own giant disk drives, giving them something of an edge and fostering envy and resentment among those that must make do with the project’s common disk space.

Another type of pecking order revolves around the placement of a group’s detector. Not surprisingly, the cleanest data come from detectors immediately surrounding the collision chamber, and most of those detectors happen to be the ones designed by Fermilab staff. Other detectors, like Harvard’s, are a little farther out, so Franklin and her similarly outplaced colleagues have to argue persuasively to have their results taken as seriously. For two years she and her students found that their data on electrons captured at their detector were widely ignored; finally they were able to prove that detector refinements actually made their electron count every bit as good as the counts taken closer to the collision chamber. But if two detectors are producing conflicting results, it’s not always clear which detector to believe. Franklin admits she indulges in placement politics herself. The University of Wisconsin’s detector is even farther away, she says. They keep pushing their data, but we tell them it’s crap.

Some of the infighting has more to do with personal issues than with physics, claims Franklin. Most of the people who are running groups are 45- to 55-year-old males who realize they’ve never done anything really important in their lives and think this is their last chance, so they have to try to take control, she says. Can you imagine 30 people like that in a meeting? I end up joining the struggle, too, just as a reaction to all their fighting.

The internal tensions reached a peak last April, when senior physicists from one of the two groups decided they had enough evidence of the top quark’s presence to warrant making a formal announcement about the suggestive data. But many of the rank and file felt the project should keep its mouth shut until it had clear, less ambiguous evidence of a discovery, as has always been the tradition among particle hunters. It wasn’t that they thought the results were wrong; they just didn’t see the point in risking potential embarrassment. But the objections were overruled--many physicists felt the project managers wanted to get out good news to ensure a continued flow of funding--and the announcement was made. Most journalistic accounts implied the top quark had been discovered, which led to further teeth gritting within the project. A lot of people felt angry and disempowered, says Franklin. But there was a strong push from above to get the paper out.

Still, nearly everyone on the project, including Franklin, seems to have little doubt that they really are seeing the top quark and that the recalcitrant particle is close to being officially discovered. Meanwhile, the Tevatron continues to gather the data needed to bolster last year’s halfhearted claim. Why spend all this time and money to do a slightly better job of discovering a particle that everyone knows is there? For one thing, notes Franklin, everyone might be wrong; perhaps the standard model isn’t the bastion of truth physicists have long held it to be and the top quark is nonexistent or takes some strange form physicists don’t know how to detect.

Besides, Franklin says, she’s in it more for the process of discovery than for the discovery itself, which, after all, will probably seem anticlimactic when it finally comes. And anyway, there’s more than finding the top quark: the groups are constantly making new and better measurements of a number of other particles and their complex interactions. As for the ambiguity, the chores, the equipment glitches--Franklin says she likes all that. What people don’t get about science is how great the craziness of it can be, she says. It’s about that feeling you get when you wake up in the morning and you really want to get going on this stuff.

For a long time Franklin wondered whether anyone could understand what it felt like for her when she was immersed in a really good experiment. Then, when she was building her first major detector, she saw a documentary on the late sculptor Alexander Calder and the construction of his Circus, an intricate, whimsical collection of small wire animals, acrobats, and other big-top performers. The film included footage of Calder engrossed in his work, sitting in his cluttered studio. From that time on, Franklin has felt a little less alone.

Everyone thinks the conceptual stuff is what’s important, she says. People don’t have a clue how hard it is and how rewarding to build something, to put something together with your hands. But that guy knew. He really knew.
Comment on this article
ADVERTISEMENT

Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

ADVERTISEMENT
ADVERTISEMENT
Collapse bottom bar
DSCNovCover
+

Log in to your account

X
Email address:
Password:
Remember me
Forgot your password?
No problem. Click here to have it emailed to you.

Not registered yet?

Register now for FREE. It takes only a few seconds to complete. Register now »