Physicist tapes together particle data
Magnetic tape, the transformative medium that made it possible for 1990s teenagers to commit carefully curated pop songs to cassettes and present them like audio billets-doux to their crushes, has long been superannuated by hard drives. Getting a mix from Pandora just isn’t the same.
The difference in sensibility is just as true for physics experiments.
As homage to tape and physics, MIT postdoctoral associate Teppei Katori, who works at Fermilab, created the art piece Selex. Named for a fixed-target charmed baryon experiment that ran in Fermilab’s Tevatron from 1996-97, Selex is part of the exhibit Tape: A Celebration currently showing at the Chicago Art Department in the city’s Pilsen neighborhood.
“It’s the only digital tape piece in the exhibit,” Katori says, noting that the exhibit’s other dozen or so pieces are related to analog tape. “There are no analog tapes in particle physics. I’m a bit biracial.”
In Selex, Katori’s intent is to capture the sharpness and precision needed in science data, creating clean lines and stark contrast using 400 actual data storage tapes from the Selex experiment.
These black, 8-millimeter digital tape cassettes, affixed at their short sides to a white paper background, spell out the word ‘SELEX’. The background is photocopied pages of the 2005 Physical Review Letters paper on Selex’s most highly cited discovery. Suspended from the ceiling by chains, the piece also comprises more tapes lying flat on the floor beneath it, forming a rectangular carpet of cassettes.
In physics experiments today, data tapes are stored in and accessed at remote computing farms. Out of experimenters’ sight, they are also almost always out of mind. But in the bygone era recalled by Selex, tapes were at scientists’ fingertips. Katori’s piece is a nostalgic recollection of that immediacy.
It’s also a nod to early digitization, Katori says. Because the word SELEX is formed from discrete cassettes rather than, say, a continuous unreeled strip, it calls to mind the formation of lettering such as that from a dot matrix. And because these cassettes are jumbo-sized dots, it also recalls the style of a pastime that has come a long way over the decades:
“It’s like the classic video games where the graphics are made of huge dots, like Super Mario Bros.,” Katori says. “It’s like it’s made from a low number of bits.”
The Selex tapes, though, are anything but low-bit. Each small cassette contains 5 gigabytes of data, not too shabby considering how big your average 5-gig drive would have been in 1997. The Selex experiment required 3,000 of them to store its data.
Selex scientists were on the hunt for charmed baryons, particles made of three quarks and including at least one charm quark.
“These things are hard to make and hard to see – they’re heavier than two-quark mesons and you don’t get as many,” says Fermilab’s Peter Cooper, deputy spokesperson for Selex. With more than 120 scientists from 20 institutions in 10 different countries working on Selex, researchers gathered enough information over the two-year lifetime of Selex to describe the mass, lifetime, decay modes and other basic properties of charmed baryons such as ΛC and ΞC.
“There’s a whole list of physics questions associated with the heavy family of the proton and neutron,” Cooper says. Protons and neutrons, themselves baryons, are available in nature. Other baryons have to be made in the laboratory. The Selex finding that made the cover of Physical Review Letters was the discovery of the double-charmed baryon Ξcc+.
“No one had ever seen it before,” he says.
And without tape, particles wouldn’t be seen at all.
With Selex, Katori celebrates an important experiment in particle physics history and the medium that made it and many other science discoveries possible.
As for any concern for the fate of data now enshrined in Selex, it all lives in a more permanent place. For older physics experiments such as Selex, once the data on outmoded storage materials is transferred to modern hardware, the usual life cycle of these materials concludes either at a recycling plant or in a neglected box. For the lives of Selex tapes, it was the latter. The particular tapes for Katori's work were those that contained backup data, and were in Cooper's possession when Katori set out to create Selex. As the tapes were the sole property of Selex, it was decided that they be recycled in an artistic matter rather than undergoing the unseemly and less artistic fate of a shredder.