From FNAL: “Poles and masses”

Origin Story

The Origin Story for the Blog

I am telling the reader this story in the hope of impelling him or her to find their own story and start a wordpress blog. We all have a story. Find yours.

The oldest post I can find for this blog is From FermiLab Today: Tevatron is Done at the End of 2011 (but I am not sure if that is the first post, just the oldest I could find.)

But the origin goes back to 1985, Timothy Ferris Creation of the Universe PBS, November 20, 1985, available in different videos on YouTube; The Atom Smashers, PBS Frontline November 25, 2008, centered at Fermilab, not available on YouTube; and The Big Bang Machine, with Sir Brian Cox of U Manchester and the ATLAS project at the LHC at CERN.

In 1993, our idiot Congress pulled the plug on The Superconducting Super Collider, a particle accelerator complex under construction in the vicinity of Waxahachie, Texas. Its planned ring circumference was 87.1 kilometers (54.1 mi) with an energy of 20 Tev per proton and was set to be the world’s largest and most energetic. It would have greatly surpassed the current record held by the Large Hadron Collider, which has ring circumference 27 km (17 mi) and energy of 13 TeV per proton.

If this project had been built, most probably the Higgs Boson would have been found there, not in Europe, to which the USA had ceded High Energy Physics.

(We have not really left High Energy Physics. Most of the magnets used in The LHC are built in three U.S. DOE labs: Lawrence Berkeley National Laboratory; Fermi National Accelerator Laboratory; and Brookhaven National Laboratory. Also, see below. the LHC based U.S. scientists at Fermilab and Brookhaven Lab.)

I have recently been told that the loss of support in Congress was caused by California pulling out followed by several other states because California wanted the collider built there.

The project’s director was Roy Schwitters, a physicist at the University of Texas at Austin. Dr. Louis Ianniello served as its first Project Director for 15 months. The project was cancelled in 1993 due to budget problems, cited as having no immediate economic value.

Some where I learned that fully 30% of the scientists working at CERN were U.S. citizens. The ATLAS project had 600 people at Brookhaven Lab. The CMS project had 1,000 people at Fermilab. There were many scientists which had “gigs” at both sites.

I started digging around in CERN web sites and found Quantum Diaries, a “blog” from before there were blogs, where different scientists could post articles. I commented on a few and my dismay about the lack of U.S recognition in the press.

Those guys at Quantum Diaries, gave me access to the Greybook, the list of every institution in the world in several tiers processing data for CERN. I collected all of their social media and was off to the races for CERN and other great basic and applied science.

Since then I have expanded the list of sites that I cover from all over the world. I build .html templates for each institution I cover and plop their articles, complete with all attributions and graphics into the template and post it to the blog. I am not a scientist and I am not qualified to write anything or answer scientific questions. The only thing I might add is graphics where the origin graphics are weak. I have a monster graphics library. Any science questions are referred back to the writer who is told to seek his answer from the real scientists in the project.

The blog has to date 900 followers on the blog, its Facebook Fan page and Twitter. I get my material from email lists and RSS feeds. I do not use Facebook or Twitter, which are both loaded with garbage in the physical sciences.

That is my Origin Story

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richardmitnick 7:31 am on June 5, 2016 Permalink Reply
Tags: Basic Research ( 16,546 ), FNAL ( 706 ), HEP ( 1,467 ), Particle Accelerators ( 1,322 ), Particle detectors ( 17 ), Particle Physics ( 2,492 ), Poles and masses at the Tevatron
From FNAL: “Poles and masses”

FNAL Art Image by Angela Gonzales

Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

June 2, 2016
Leo Bellantoni

From top left to bottom right: Andreas Jung (Fermilab, now at Purdue University), Jiri Franc (Czech Technical University, Prague, Czech Republic), Slava Shary and Frederic Deloit (CEA Irfu SPP, Saclay, France), Yegor Aushev and Mykola Savitskyi (Taras Shevchenko National University, Kiev, Ukraine) and Michal Stepanek (Czech Technical University, Prague, Czech Republic) are the primary analysts for this measurement.

This is the Feynman diagram for a quark-antiquark pair on the left combining to form a gluon (marked g), which breaks into a top and antitop that decay on the right. As described in the text, it is possible from the diagram to calculate the rate at which this type of event occurs.

The figure [above], called a Feynman diagram, shows a quark and an antiquark on the left merging to form a gluon; then the gluon turns into a top quark and a top antiquark, each of which decays into some other particles on the right. In a very simple and intuitive way, this depicts a certain type of event that was measured in the Tevatron.

Tevatron map; Tevatron tunnel; DZero; CDF

But the diagram also is a symbol for a number. You see, this whole process is quantum mechanical; one can only give a probability for that type of event to happen. The really nifty thing about the diagram is that it is a shorthand code for how to compute that probability. From the diagram, using a table for decoding it, you can write down the mathematical expression that gives you the probability.

In this particular case, for the gluon you write down igαβ/ (p2 + ie) or some such thing; I won’t go into the definitions of g and p and such, but the point is that this is in the end some specific number. And you will multiply this by some other numbers for the initial quarks and for the antiquark, and for the top quark and so on. The resulting product will tell you how frequently this type of event occurs.

The number that you write for the top quark depends on the mass of the top quark. You might think then, “Oh, go measure the mass, and then you know that number.”

Unfortunately, subatomic particle physics isn’t that simple. Top quarks, or indeed, any quarks, exist only in a sea of other particles that wink in and out of existence. They aren’t part of the top quark, but they can’t be separated from it, either. Should they be counted as contributing to the mass of the top? The mass that is usually measured in collider experiments is different still, since it comes from measuring what the top quark decays into. It’s called the MC mass, and it isn’t necessarily the same as what we want for the number that goes with the diagram. After all, the number that goes with the diagram (called the pole mass) is involved in how often the event occurs, not what comes out of it.

So there is this long-standing theoretical question: How does the MC mass relate to, say, the pole mass? Y’know, clearly they are related, but how, exactly?

Here comes the trick: Measure the pole mass directly. We can do this by measuring how often the event occurs and knowing all the other numbers that you read off the diagram. Then you know the number for the top quark and therefore you know the pole mass. The result isn’t as precise as measuring what the top quark decays into and figuring the MC mass, but at least you know the number that goes with the diagram.

Recently, DZero measured the rate at which top-antitop pairs were created in the Tevatron; specifically, we measured the production cross section with a refined strategy to improve the accuracy of the measurement. The result is picobarns. From that, we then went and obtained the pole mass of the top quark. The result, GeV, is the most precise determination of the top quark’s pole mass at the Tevatron. Despite the lower precision than the MC mass taken from the decay products, it is a more powerful measure of the top quark’s role in the world.

See the full article here .

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Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
collaborate at Fermilab on experiments at the frontiers of discovery.
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