Posted on 06/10/2004 4:00:48 PM PDT by PatrickHenry
Researchers from the University of Rochester have helped measure the elusive top quark with unparalleled precision, and the surprising results affect everything from the Higgs boson, nicknamed the “God particle,” to the makeup of the dark matter that comprises 90 percent of the universe. The scientists developed a new method to analyze data from particle accelerator collisions at Fermilab National Accelerator Laboratory, which is far more accurate than previous methods and has the potential to change the dynamics of the Standard Model of particle physics. Details of the research are in today’s issue of the journal Nature.
“This is a remarkable achievement in the measurement of the top quark,” says Thomas Ferbel, professor of physics and astronomy at the University of Rochester, and a principal author of the paper. “The improvement has caused quite a stir because it has changed the accepted mass of the top quark in such a way that the Higgs boson is now in an energy range we have yet to explore. It’s as if we’ve been digging a hole for the Higgs, and suddenly we realize we read the map wrong and it’s really somewhere else.” The masses of the top quark and Higgs boson are critical to understanding how the quantum world works, including answering one of science’s great conundrums—what gives mass, mass?
The revision of the top quark mass started as a thesis project for one of Ferbel’s doctoral students, Juan Estrada. He decided to see if there were a better way to calculate the mass of the top quark from the measurements already collected at Fermilab’s particle accelerator. Ferbel was initially skeptical since scientists figured they’d wrung every bit of information from the data collected since the top quark’s discovery in 1995. But Estrada, along with Fermilab scientist Gaston Gutierrez, developed a method based on probabilities that seemed to give a dramatic increase in precision. Ferbel brought in a third student, Florencia Canelli, to help extend the method to calculate the top quark’s spin properties as well as its mass.
When the real-world data was parsed, the method yielded a nearly 40 percent increase in precision; less than predicted, but still a tremendous boon to physicists. The improved method allows researchers to glean as much information from the available data as would have been possible from a sample two and a half times as large, which is invaluable when collecting data from each collision is such an delicate and arduous task.
The second major fallout from the new measurements is that the Higgs boson—the particle that is theorized to give rise to mass itself—apparently exists at higher energy levels than where scientists have been searching. Since all subatomic particles are related to each other, changes in the characteristics of one ripples through other particles, and since the top quark is especially massive, changes to it result in the largest changes in other particles—especially the Higgs. Based on the old accepted value of the top quark mass, physicists expected to find the Higgs boson at around 96 GeV/c2 (gigaelectron-volts), but have been able to rule out that it actually exists there. That threw the whole Standard Model into a quandary. The new measurement for the top quark mass, however, now places the Higgs at about 117 GeV/c2, which is a range accelerators haven’t yet searched, putting the elusive Higgs back into play.
“No matter how hard we try to break the Standard Model, it always seems to flex and still work,” says Ferbel. “It’s puzzling because we know in the long run the model isn’t quite right, but it won’t be beaten down. Every time we put stress on it, it shows it’s still alive and breathing.”
The new technique took a probabilistic approach to the measurements gleaned from the Fermilab collider. When the accelerator smashes a quark and an anti-quark together, a top quark and an anti-top quark are occasionally created. These quickly decay into other particle types, which themselves decay into yet more particles before the Fermilab detectors can begin to study them. This means the researchers have to work backward, looking at the third generation particles and inferring how they were made back in time, much like looking at a scattering of pool balls and deducing where they were three moves ago. Traditionally, researchers would assign a mass to the initial top and anti-top quarks and figure out what the decayed results should look like, then compare those results with what the detectors actually saw. The new technique works similarly, but assigns probabilities to a range of initial masses, giving more importance to the most accurate readings. The result, when played out over many collisions, is a measurement that’s much more precise.
“Effectively increasing the data by two and a half times makes an impossible cause possible, if you’re on the edge of discovering something like the Higgs,” says Ferbel.
Fermilab is a national laboratory in Ill., funded by the Office of Science of the U.S. Department of Energy, operated by Universities Research Association, Inc.
Science list ping (a subset of the evolution list). FReepmail me to be added or dropped.
Hag Hogs Higgs
President Hillary Clinton claimed personal credit today for the discovery of the Higgs boson ...
It was at my house eating chicken and dumplings last weekend.
Everyone definitely ended up more massive, so we're sure it was Higgs.
So9
A yet-to-be-discovered particle that I shall dub RosieOdonnelium.
There's no Top Quark really. Quarks belong to an autonomous hadronic commune.
LOL!
She will share the Nobel Prize for Physics with Al Gore the inventor of Atom Smasher.
Haha, VR wins the day! Brilliant.
You must hace cheated, that's too funny. Hrmph.
Yee-Hah Patrick! Bookmarked.
The article is slightly misleading here; the Universe is not 90% dark matter. What they mean to say is that of the matter that exists in the Universe, 90% of THAT is dark matter.
The latest figures for composition of the Universe are something like 4% ordinary matter, 21% dark matter, and about 75% dark energy. Matter of all types accounts for only about a quarter of the total composition.
</ nit-picking mode>
Points, lines, angles, surfaces, and completing curves....causal units, portal units, form units, and structure units....aerogen, pyrogen, geogen, and fluogen....on-ness, in-ness, through-ness, and presence....and other stuff, including fuddle.
...the Universe is not 90% dark matter. What they mean to say is that of the matter that exists in the Universe, 90% of THAT is dark matter.Hmmm... but 21%/25% is 84%. So I guess you're both wrong.The latest figures for composition of the Universe are something like 4% ordinary matter, 21% dark matter, and about 75% dark energy.
President Hillary Clinton claimed personal credit today for the discovery of the Higgs boson ...
LOL!
Hmmm. I'm a bit confused by this journalist's description of the Fermilab collisions. The article says that "When the accelerator smashes a quark and an anti-quark together, a top quark and an anti-top quark are occasionally created..." It was my understanding that free-standing quarks could not be created or observed; the amount of energy necessary to drag a quark out of another particle (due to the Strong force) would be enough to create another quark, so efforts to "liberate" quarks simply result in another composite particle. Did I miss something major, and do they actually have a collider that will accelerate and smash quarks? This has got to be journalist error...
The top and antitop quarks do not form hadrons, not through any mechanism that prevents their confinement, but by virtue of the fact that they decay so quickly. They decay in a time that is very short compared to the time it takes to form the hadrons.
I'm delighted that Physicist responded to your question to which you pinged him and me; however, let the record be clear: I had no clue as to how to answer your question.
Admit it; you think "hadrons" come from an ancient wall in England....
;-)
Actually, I thought that's what they call the tormented inhabitants of the underworld.
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