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Ed Hartouni
Trad climber
Livermore, CA
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Topic Author's Original Post - Apr 25, 2011 - 01:53pm PT
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What's all the buzz about?
commentary on recent results in particle physics
Jan makes the request:
"Hopefully Ed can comment on these."
By "these" she means the preceding post on the same page as Crodog's. The "rumor" is easy to comment on, I have none as the ATLAS collaboration has not yet released any information on the analysis that is alleged to contain the "discovery." In a collaboration as large as ATLAS, there are written rules, bylaws, on how research is conducted. This is to maintain a high level of scientific integrity in reported results, basically, the entire collaboration must examine the analysis in detail and all their questions must be answered before such an analysis is released. The analyses can be unbelievable complex, and it is easy to get it wrong. Most collaborations of that size (there are nearly 200 collaborating institutions) have multiple, independent analyses ongoing for the various physics topics, and their results must be reconciled internally. The bylaws prohibit the premature release of results before the entire collaboration's "blessing." So the rumor is a rumor, which may go away.
The Fermilab result is a bit further along, as there is an "ArXiv" paper posted on the web, which doesn't happen unless that collaboration, CDF (Colliding Detector at Fermilab), agreed to its release. This result is not related, physics wise, to the rumor from ATLAS.
In the CDF paper an analysis is reported of a subset of the data collected by CDF, the abstract says "4.3 fb^{-1}" read "four point three inverse femtobarns." A femtobarn is a measure of probability of interaction of the proton and anti-proton which are circulating in the Tevatron, and are brought to a collision point, where they may collide. The beams circulate for years now, and an inverse femtobarn or 10^{-15} barns is a sensitivity, that is, if the total cross section is 80 millibarns, the measure of probability of all possible reactions, a femtobarn sensitivity means that you could detect one event in 80x10^{-3}/4x10^{-15} = 2x10^{13} events in your detector, a true "needle in a haystack" search.
As an aside, the Tevatron is a machine that used some of the ideas of Frank Sacherer, the accelerator physicist. Frank was involved with the conceptual design and research of the properties of such machines. (See, also, the Wiki page for the Tevatron).
The subset of data that was the subject of this analysis contained "dijets" which are events with two "jets." A "jet" is a collection of particles coming out with essentially the same velocity, and close together in angle, and are thought to represent a single quark or gluon (components of all the hadronic particles we know, like protons and neutrons and pions, etc) "dressing" itself. This "dressing" is necessary to preserve a conservation rule governing a type of charge which we called "color," the rule being that none of the particles in our world can have color, they all must be "white" a combination of colors... so a color and anti-color charge (in a meson) is "white" and a combination of three colors (as in a baryon) can be "white" but a single color is not allowed. That is why we cannot see the individual components of these particles.
It is the interaction of these color charges that produces the Standard Model Theory, which includes Quantum Chromodynamics (QCD), that looks a bit like our quantum theory of electricity and magnetics... Quantum Electrodynamics (QED).
By combining the energy and momentum of these dijets we can calculate there equivalent mass through the Einstein equation E=mc˛, when we plot the frequency of a particular value on a graph we call a histogram we get the Figure 1. in the ArXiv release. (Note that releasing a pre-print is not the same as publishing in a peer review journal, though it often precedes such publication, it gets the word out on the street and allows other experiments and the theorists to think about the results.) These plots are complicated, but plotted in that figure (there are 4 panels) is the best analysis accounting for all of those events. In the region of the signal there are something like 600 to 700 events per mass bin...
...when the expected values are subtracted from the observed values, there appears a slight excess of events in one mass region, and that is what generates the buzz. We just follow Sherlock Homes in our logic here: "Eliminate all other factors, and the one which remains must be the truth.".
From what I can see, the integrated number of background events is in the range of 3600-4300 events, and their signal is on the order of 100 events, so the signal-to-background is like 1/40. For a quick statistical analysis date the square root of sqrt(3600) = 60 and that is the fluctuation in 6 bins you'd expect, they see twice that... an estimate of "2 sigma," their statistical analysis which is more sophisticated (and correct) indicates more than "3 sigma" which would have a probability of 0.3% of happening "randomly."
Our experience in particle physics leads us to a practical understanding of these statistics that require a "six sigma" signal to claim a discovery, but this would require the CDF collaboration to collect roughly 4 times the data, which is not going to happen because the Tevatron is shutting down this year, the LHC being the new "discovery" machine.
Even if they saw a "six sigma" signal we would expect confirmation from CDF's complementary experiment D0 running at Fermilab, with a different detector and a different collaboration, we'd expect a confirmatory observation. As far as I know, there is none. And also, we'd expect the LHC experiments ATLAS and CMS to see this particle state if it does exist.
So while this is an exciting "hint" at new physics, which the experimenters always like to find, everyone is cautious regarding what it means... it is not expected, so the theorists, at least some of them, are off trying to fit it into our current picture of what is going on in the universe.
The publication of the CDF collaboration comes because they know there is no future for their experiment after the end of Tevatron running, they want to identify all the loose ends for future experiments. Most likely all of the scientists have a place on one of the 4 large collaborations running at the LHC.
Closing the Tevatron is the right thing to do, it has had an amazing run over 30 years, and the LHC is the logical place to continue our exploration at the energy frontier of the universe. It is possible, however, that the USA will never have another machine at that frontier, though we pioneered the technologies and the physics for over 60 years. But more on that in some other thread.
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elcap-pics
Big Wall climber
Crestline CA
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Apr 25, 2011 - 01:59pm PT
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I couldn't agree more Ed!
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Ghost
climber
A long way from where I started
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Apr 25, 2011 - 02:07pm PT
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Ed, I think you and I should drink a bunch of English Ale and then write an article about this for the CAJ.
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Ed Hartouni
Trad climber
Livermore, CA
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Topic Author's Reply - Apr 25, 2011 - 02:14pm PT
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having a beer together: yes
writing the article: not a chance! (you know how authors feel about editors first hand...)
Aside from the Sacherer note, there isn't a whole lot tying this to climbing...
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Ed Hartouni
Trad climber
Livermore, CA
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Topic Author's Reply - Apr 25, 2011 - 02:20pm PT
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"What would climbing be without the Higgs?"
massless...
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stevep
Boulder climber
Salt Lake, UT
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Apr 25, 2011 - 03:37pm PT
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This post is exactly why this forum shouldn't just be limited to climbing topics.
Thanks Ed.
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Jan
Mountain climber
Okinawa, Japan
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Apr 25, 2011 - 04:07pm PT
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Thanks Ed for the explanation and the new rap song!
I downloaded the one from CERN a couple of years ago.
Interesting to read the statistics of probability where new particles are concerned and that no new particles have been found since 1985. No wonder there is impatience now to see new results.
Releasing snippets of potentially new discoveries to generate public buzz seems a bit risky unless they do come up with something new fairly soon. There's a fine line between public excitement and cynicism.
Also, there must be a lot of Americans applying for research grants and jobs at CERN now.
And finally, starting a separate thread for new discoveries is a good idea.
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rrrADAM
Trad climber
LBMF
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Apr 26, 2011 - 01:39pm PT
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Nice write up, Dr.
Closing the Tevatron is the right thing to do, it has had an amazing run over 30 years, and the LHC is the logical place to continue our exploration at the energy frontier of the universe. It is possible, however, that the USA will never have another machine at that frontier, though we pioneered the technologies and the physics for over 60 years. But more on that in some other thread. Too bad they never finished the SCSC, down in Texas (yea, Reagan), as it would have been ~3 times the energy (~40 TeV) of the LHC (17 TeV)... Bringing those highly technical jobs and research here.
I have a friend who got his PhD in TheoPhys, with a MS in Math, and was hoping to work there, but when he saw the writing on the wall, he pursued and recieved another PhD, in Political Science. And, another one of my collegues here at work, got his MS in High Energy Physics as well, hoping to work there. Instead, he works for a utility, and longs for what "could've been".
So, where is Texas now? Rewriting text books, moving us backwards. :/
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stevep
Boulder climber
Salt Lake, UT
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Apr 26, 2011 - 03:45pm PT
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Too bad they never finished the SCSC, down in Texas (yea, Reagan), as it would have been ~3 times the energy (~40 TeV) of the LHC (17 TeV)... Bringing those highly technical jobs and research here.
I have a friend who got his PhD in TheoPhys, with a MS in Math, and was hoping to work there, but when he saw the writing on the wall, he pursued and recieved another PhD, in Political Science. And, another one of my collegues here at work, got his MS in High Energy Physics as well, hoping to work there. Instead, he works for a utility, and longs for what "could've been".
So, where is Texas now? Rewriting text books, moving us backwards. :/
Agreed. That would have been a good thing to finish.
From what I understand these days, there's a fair number of physicists now working on Wall Street as quant analysts because of their math skills and the desire to earn more money.
Seems kind of unfortunate to me. To quote Bloom County "Research physicists need Porsches too!" Except for maybe Ed, who'd probably be satisfied with more large cams.
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Clint Cummins
Trad climber
SF Bay area, CA
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Apr 26, 2011 - 03:57pm PT
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Thanks, Ed, for a look into the world of particle physicists!
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cleo
Social climber
Berkeley, CA
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Apr 26, 2011 - 05:38pm PT
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Thanks, Ed! The collaboration and brainpower going into those physics experiments is... mind-blowing!
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Ghost
climber
A long way from where I started
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Apr 26, 2011 - 09:38pm PT
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If Supertopo was a navy ship, and we all had official ranks, then Dr. Ed would be...
The Boson's Mate.
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Ghost
climber
A long way from where I started
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Apr 26, 2011 - 09:41pm PT
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And on the subject of brilliant physicists, did you know that Stephen Hawking was... hmmm... no polite way to say this, so you better just watch this scene from The Superhero Movie
http://www.youtube.com/watch?v=On0q7x9yi3I
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healyje
Trad climber
Portland, Oregon
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Apr 26, 2011 - 10:24pm PT
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Not that he fought for it, but Clinton was right when he said:
"...abandoning the SSC at this point would signal that the United States is compromising its position of leadership in basic science"
We've been fighting an increasingly virulent anti-science faction in our society ever since Reagan was elected. Ironic that it was proposed on Reagan's watch and died under Clinton's - you would have expected the opposite. Then again, Reagan enacted the National Marine Sanctuary off Maui for the Humpbacks when Carter wouldn't...go figure.
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Ed Hartouni
Trad climber
Livermore, CA
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Topic Author's Reply - Apr 27, 2011 - 01:06am PT
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we're all bosons on this bus... squeak, squeak...
The Superconducting Super Collider, SSC, was to be built in Waxahachie, TX, and managed to dig a tunnel but did not survive the Congressional battle for funding. There was a lack of confidence in the management team's ability to bring the project in on time and on budget, the 1987 cost estimate was $4.4B and by 1993 the cost estimates were $12B.
It was a time of budget woes, not unlike today, the 1992 budget deficit was the largest up to that point, $290B. The projections had it growing to $455B by 2000. Of course, this is not what happened, there was a $230B budget surplus in 2000. But no one knew that that was going to happen, and the Congress chose to terminate the project.
An interesting passage from the book The Physicists, the history of a scientific community in modern America by Daniel Kevles:
"Johnston, like a number of analysts, blamed the execution on the House freshman, typically describing them as "the product of an angry electorate that wants to cut projects and cut perks." True enough, the 113 House freshman voted against the collider almost 3 to 1. And true enough, the House was in a budget-cutting mood, slashing out money for several smaller physics projects. Civilian research and development, which accounted for 11 percent of the domestic discretionary budget, was a natural fiscal target under the circumstances of the budget-cap rules.... the incumbent House voted against the collider by a margin of 200 to 111, almost 2 to 1... Besides, as Johnston pointed out several times, killing the SSC would not make much of a dent in the deficit, since the year's appropriation for it amounted to only a tiny fraction of the overall federal budget. The Congress of the United States is selective in its economizing, tending to be tolerant of expenditures for high national purpose, especially if they are reinforced by important local political and economic interests."
The machine would have been running in the early 2000's and would have made a number of wonderful discoveries by now, discoveries we are on the verge of making at the LHC, and some that are beyond the reach of that machine, and will have to wait for future machines.
The consequences of canceling the SSC was to cede US leadership in a field invented in the US, and one of magnificent intellectual scope and broad applicability. Physics will go on, we will make those discoveries, but it is unlikely that it will be done with US leadership, though it will be with US participation. I have mixed feelings about this as I believe that science is a truly international enterprise and it hardly matters which country is dominant. But from the point of view of the preeminence of the US it is clear that a broad support at the federal level for all basic research is necessary because we cannot predict what challenges will confront us in the future. The technologies required to produce an SSC, the intellect to conceive of it and of the science program to be executed by it, and the challenges to the commercial sector to build for it, all of these things strengthen a country.
The International Space Station, facing termination in the same Congress, did narrowly survive a vote. I would argue, strongly, that the technologies used to create the ISS are not very commercially relevant to us today, nor militarily relevant, and the science that has been produced by the ISS program is infinitesimal. I cannot argue that we should not have participated in the ISS, we should have and did. I would argue that we could easily have continued, at that time, to build the SSC without adverse affect to the national deficit, in the end its termination did not help turn the economy around.
Strong words were said on the floor of the House and the Senate for and against the SSC. Most of these words exaggerated its vices and virtues. In the end, it would have done amazing and wonderful science. The consequences of not doing it have been as people predicted, a diminished science program and a loss of science capability for the nation.
It is a lesson we should head in these times where action is demanded by an "angry electorate" and motion of any kind is easily mistaken for progress. One hopes for cooler heads to prevail.
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Ed Hartouni
Trad climber
Livermore, CA
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Topic Author's Reply - Apr 27, 2011 - 01:39am PT
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Talking about the SSC brings back all kinds of memories. Having us physicists there would have been an interesting cultural mix... I think Time magazine's headline was "there will be more colliding in Waxahachie then particles."
I had visited the site many times in preparations for doing science there. One time we were on a tour and I ended up signing the guest book at the Ellis County Courthouse. I was struck by the statue out in front, erected in 1912:
and I remember the inscription:
"IN HONOR OF
THE DEAD AND LIVING
OF ELLIS COUNTY,
WHO WORE THE GRAY.
BANNERS MAY BE FURLED,
BUT HEROISM LIVES
FOREVER.
ERECTED BY THE
DAUGHTERS OF THE
CONFEDERACY,
UNVEILED NOV. 2, 1912
1861-1865"
It was a different place than I had ever imagined could still exist.
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