Posted on 07/09/2004 12:20:53 PM PDT by PatrickHenry
A team of nearly 100 physicists from around the world have achieved results verifying that the elementary particle known as the neutrino exhibits a distinctive pattern of oscillation. This discovery shows that it is likely that the Standard Model, proposed in the 1970s to describe the fundamental forces and particles that make up all matter, is incomplete. The findings provide the needed confirmation to their previous discovery of neutrino oscillation and give the most precise measurement yet of neutrino mass.
“These findings show that the Standard Model needs to be modified to better explain the fundamental forces that make up all matter,” says James Stone, a professor of physics at Boston University. “They clear the field of all other explanations for the earlier results.”
Stone and his collaborators are part of the Super-Kamiokande collaboration, a Japan-based project that involves researchers from more than 30 institutions worldwide. Stone serves as co-principal investigator for the “Super-K” experiment as well as being a member of the experiment’s Executive Committee and co-spokesperson for the participating U.S. researchers. The results of the collaboration’s efforts will be published next month in Physical Review Letters.
The Super-K collaboration’s new analysis focused on atmospheric neutrino data. Atmospheric neutrinos are produced by high-energy collisions of cosmic rays with Earth’s upper atmosphere. The neutrinos come in two types, or “flavors,” called electron-type and muon-type.
The Super-K group first reported that neutrinos oscillated in 1998. This discovery grew from their observation that the number of upward-going muon-neutrinos (those traveling the full distance through Earth) was considerably fewer than the number of downward-going muon-neutrinos (those that traveled only the “short” distance from the upper atmosphere to the underground Super-K detector). In their report, the researchers show that the size of the measured difference depends on the distance traveled in a way that is consistent with the theory of neutrino oscillation. Their full analysis of the data shows the muon-neutrino most likely changes into a third flavor of neutrino, the tau-neutrino, which is not produced in cosmic-ray collisions.
According to the neutrino mixing theory of the Standard Model, the probability that a neutrino of one flavor changes to another can be determined by dividing the distance a neutrino travels (L) by its energy (E). The distinctive, sinusoidal pattern described by the theory says that the probability of a flavor change dips toward zero and then recovers as the L/E ratio increases.
The Super-K physicists invented a new method for this analysis of atmospheric neutrino data, one that used only those neutrino “events” that had very good measurements of travel distance and neutrino energy. This is an improvement over the 1998 analysis. In that analysis, the distinctive oscillatory pattern had been washed out because many of the events had poor travel distance and neutrino energy measurements. In this newly reported analysis, each selected event was assigned a well-defined L and E value, and the number of neutrino events was studied as a function of the ratio L/E. Analysis of data gathered using this improved technique shows a prominent dip at a value of L/E that is consistent with the theory of neutrino mixing.
Theoretically, neutrinos can change from one flavor to another only if they have mass. The Standard Model, however, assumes neutrinos are without mass. Thus, the 1998 discovery of neutrino oscillation was also the first evidence that neutrinos have mass. A few unusual theories, however, had offered explanations for the “loss” of upward-going muon neutrinos that differed from the 1998 conclusion of the Super-K group. Instead of determining that the deficit indicated that muon-neutrinos changed to a new flavor, these theories noted that the deficit was likely the result of neutrino decay to other particles.
The new analysis by the Super-K collaboration rejects these theories on the basis that they fail to predict the oscillatory pattern found in the 1998 analysis. In addition, the recent analysis finds that the location of the dip in the oscillatory pattern shows the mass difference between the neutrinos. It is the most precise measurement yet of that difference in mass.
The Super-Kamiokande collaboration, which includes scientists from institutions in Japan, the United States, and Korea, is funded by the Japanese Ministry of Education, Science, Sports, and Culture; the United States Department of Energy; and the National Science Foundation.
The Physics Department at Boston University provides opportunities for research in experimental high-energy physics and astrophysics, experimental medium-energy physics, experimental condensed-matter physics and polymer physics, molecular biophysics, theoretical high-energy particle physics and cosmology, and theoretical condensed-matter physics, polymer physics, and statistical mechanics.
Note to editors: A copy of the Physical Review Letters paper describing these findings can be found HERE.
The square root of the unladen airspeed of a swallow (expressed in furlongs/fortnight).
Excellent!!
Say, Jack looks a bit pensive in that picture.
Yes, but don't forget to factor in drag for each coconut carried.
Sniff..... Ol RA is left out in the cold once again!
Pirated neutrino's must walk the planck! Harrr!
Note that the swallow is unladen.
But you do have to factor in whether it's English or African...
And religion doesn't?
Haha - that's funny. But seriously, with physics these days, everything is counter-intuitive. The correct answer is the Economy Model.
Indeed! :-)
Then you see pictures of them on the sides of milk cartons.
Shouldn't that be "on the sides of Milky Way cartons"?
(ducking)
"Better to have studied a century ago. In 1904, before relativity, QM, nuclear physics and the big bang, at least you felt that you had a good grasp of things."
I was planning on sitting in on Weinberg's class in the fall, but maybe I should wait a few years.
I think of you in the context of larger particles. Much larger. Like planets. You're my "big picture" guy.
By fudging industry standard definitions (in the Phys Biz) light does have mass if you mean that mass is something that moves something else that it slams into. In fact, if you twist the polarization of a wave train, your twister will even recoil in the opposite direction.
But standard definitions require that we use the term "rest mass"-- that light only acts like it has mass when it's moving at light speed, and that if a neutrino has a finite 'rest mass' then it can never attain light speed because then its mass would have to be infinite.
Well, gee, I never would have guessed that.
Hmmph. How would you feel if I went around discussing the mass of a jennyp?
Or, for that matter, the flavor of a jennyp?
I'm not missing. I just oscillated around the local area for a few hours.
I believe they're legally dead after 7 light years.
Bite your tongue!
I saw an Arabic swallow which had been laden.
Does it make for better beer or cure ED?
<;P
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