## Posts Tagged ‘Tevatron’

### Tweeting the Higgs

Wednesday, January 23rd, 2013

Back in July two seminars took place that discussed searches for the Higgs boson at the Tevatron and the LHC. After nearly 50 years of waiting an announcement of a $$5\sigma$$ signal, enough to claim discovery, was made and all of a sudden the twitter world went crazy. New Scientist presented an analysis of the tweets by Domenico et al. relating to the Higgs in their Short Sharp Scient article Twitter reveals how Higgs gossip reached fever pitch. I don’t want to repeat what is written in the article, so please take a few minutes to read it and watch the video featured in the article.

The distribution of tweets around the July 2nd and July 4th announcements (note the log scale)

Instead of focusing on the impressive number of tweets and how many people were interested in the news I think it’s more useful for me as a blogger to focus on how this gossip was shared with the world. The Higgs discovery was certainly not the only exciting physics news to come out of 2012, and the main reason for this is the jargon that was used. People were already familiar with acronyms such as CERN and LHC. The name “Higgs” was easy to remember (for some reason many struggled with “boson”, calling it “bosun”, or worse) and, much to physicists’ chagrin, “God particle” made quite a few appearances too. It seems that the public awareness was primed and ready to receive the message. There were many fellow bloggers who chose to write live blogs and live tweet the event (I like to think that I started bit of a trend there, with the OPERA faster than light neutrinos result, but that’s probably just wishful thinking!) Following the experiences of December 2011, when the webcast failed to broadcast properly for many users had twitter on standby, with tweets already composed, hungry for numbers. The hashtags were decided in advance and after a little jostling for the top spot it was clear which ones were going to be the most popular. Despite all the preparation we still saw huge numbers of #comicsans tweets. Ah well, we can’t win them all!

The point is that while the world learned about the Higgs results I think it’s just as important that we (the physicists) learn about the world and how to communicate effectively. This time we got it right, and I’m glad to see that it got out of our control as well. Our tweets went out, some questions were asked and points clarified and the news spread. I’m not particularly fond of the phrase “God particle” , but I’m very happy that it made a huge impact, carrying the message further and reaching more people than the less sensational phrase “Higgs boson”. Everyone knows who God is, but who is Higgs? I think that this was a triumph in public communication, something we should be building on. Social media technologies are changing more quickly each year, so we need to keep up.

A map of retweets on July 4th, showing the global spread.

I’m glad to see more physicists using Twitter and youtube and other sites to spread the word because that’s where we can build audiences faster. (Incidentally if you want to see why we should be creating new audiences rather than addressing existing ones then see this video by Vihart.) It takes more work and it’s more experimental, but it’s worth the effort. Why did I make an advent calendar? Why tell physics jokes on Twitter? Just to see what works and what doesn’t. I’m not the first person to do these things, and I’m certainly not going to be the last. All I can hope to do is try new ideas out and give other people ideas. I don’t know the people I inspire and those I am inspired by, but that’s also part of the experiment. A lot of my ideas come from people who leave comments or send E-mails or tweets. Occasionally it gets heated and controversial, but if it’s not worth fighting for then it’s not worth saying in the first place. Many comments come from other bloggers too, and we can learn from each other. When I first started to blog someone sent me a few paragraphs of advice and I forgot most of it except one part “Ignore other people’s expectations. Some people will want you to always write about physics, some people will hate that. Write what matters to you.” When I combine that with what Vihart says (essentially “If your content is worth attention then people will pay attention to it.”) then rest is easy. Well, not easy, but less stressful.

But moving back to the main point, the Higgs tweets went global and viral because they were well prepared and the names were simple. Other news included things like the search for the $$B_s$$ meson decaying to two muons and the limits that places on SUSY, but how does one make a hashtag for that? I would not want to put the hashtag #bs on my life’s work. It’s always more exciting to announce a discovery than an exclusion too. The measurement of $$\theta_{13}$$ was just as exciting in my opinion, but that also suffered the same problem. How is the general public supposed to interpret a Greek character and two numbers? I should probably point out that this is all to do with finding the right jargon for the public, and not about the public’s capacity to understand abstract concepts (a capacity which is frequently underestimated.) Understanding how $$\theta_{13}$$ fits in the PMNS mixing matrix is no more difficult than understanding the Higgs mechanism (in fact it’s easier!) It’s just that there’s no nice nomenclature to help spread the news, and that’s something that we need to fix as soon as possible.

As a side note, $$\theta_{13}$$ is important because it tells us about how the neutrinos mix. Neutrino mixing is beyond the Standard Model physics, so we should be getting more excited about it! If $$\theta_{13}$$ is non-zero then that means that we can put another term into the matrix and this fourth term is what gives us matter-antimatter asymmetry in the lepton sector, helping to explain why we still have matter hanging around in the universe, why we have solid things instead of just heat and light. Put like that is sounds more interesting and newsworthy, but that can’t be squeezed into a tweet, let alone a hashtag. It’s a shame that result didn’t get more attention.

It’s great fun and a fine challenge to be part of this whole process. We are co-creators, exploring the new media together. Nobody knows what will work in the near future, but we can look back what has already worked, and see how people passed on the news. Making news no longer stops once I hit “Publish”, it echoes around the world, through your tweets, and reblogs, and we can see its journey. If we’re lucky it gets passed on enough to go viral, and then it’s out of our control. It’s this kind of interactivity that it so rewarding and engaging.

You can read the New Scientist article or the original paper on the arXiV.

### What you need to know about the Higgs seminar

Tuesday, July 3rd, 2012

The upcoming Higgs seminar could be the biggest announcement in particle physics for nearly 30 years. There have been several excellent blog posts and videos explaining what the Higgs is and what it does, so I’ll link to those at the bottom of the page. What I want to do here is give you the overview of what you really need to know to get the best from the talk.

Of course you should follow along with the liveblog as well!

### What’s happening with the webcast?

CERN have put in a lot of resources for the webcast. General users can get to the webcast at http://cern.ch/webcast. If you have a CERN login you can use a second webcast at http://cern.ch/webcast/cern_users.

The webcast will start around 09:00 CST (that’s 00:00 US West Coast, 03:00 US East Coast, 08:00 UK, and 17:00 Melbourne.

### What is the Higgs boson? What does it do?

The Higgs boson is part of the Standard Model of particle physics. The Standard Model includes the quarks and leptons (which make up all the matter see around us) and the photon, gluons, and $$W$$ and $$Z$$ boson (which carry all the forces in nature, except for gravity.) Three of these particles, the $$W^+$$, $$W^-$$ and $$Z$$ bosons, have mass, but according to our framework of physics, they should not have mass, unless the Higgs boson exists. The Standard Model of physics predicts that the $$W$$, $$Z$$, photon and Higgs all come as a package and they are all related to each other. If we don’t see a Higgs boson, we don’t understand the world around us.

People say that the Higgs boson gives particles mass, but this isn’t quite what happens. The Higgs boson allows some particles to have mass. The Higgs boson does not explain the mass that comes from binding energies (for example, most of the mass of the proton) and it does not explain the mass associated with dark matter. If the Higgs boson is discovered it will complete the Standard Model of physics, but it will not complete our picture of the universe. There will still be many unanswered questions.

### What would a discovery look like?

In order to claim a discovery an experiment would need to see a 5 sigma excess over the expected background. A sigma is a measure of uncertainty, and the chance of seeing a 5 sigma excess due to statistical fluctuations is about 1 in 3 million. If both experiments see an excess of 5 sigma in the same region the chances that this is due to a fluctuation is 1 in 9 million million!

The experiments produce “Brazil plots”, which show what they expect to see if there is no Higgs, and compare it to what they actually see. The green band shows 1 sigma deviations, the yellow bands show 2 sigma deviations, and then you have to use your imagination to see the remaining bands, and colors. When the green and yellow bands pass below the SM=1 line, and the central black line does too, then the Higgs is excluded in that region to 95% confidence. If the black line stays above the SM=1 line then we haven’t excluded the Higgs boson in that region yet. So when the green and yellow bands fall far below the SM=1 line, but the black line stays above or at the SM=1 line then we accumulate evidence for a Higgs boson.

### How do we search for the Higgs boson?

The search for the Higgs boson depends on its mass. At high mass it can decay to heavy particles with clean signatures, so the high mass region was the first region to see an exclusion. At very high mass the width of the Higgs boson is large, so the events get spread out over a large range, so the searches take a little longer. At low mass the decays get very messy, so we have to pick our decay modes carefully. The cleanest modes are the two photon mode (often called gamma gamma), the ZZ* mode and the WW* mode. Of these three, the gamma gamma and ZZ* modes are the most sensitive, so we can expect to see these presented tomorrow.

The data are collected that the detectors and stored to disk, and the physicists spend their time analyzing the data. This is a slow process, full of potential pitfalls, so the internal review process is long and stringent. This is one of the reasons why we need two experiments, so that they can check each other’s findings. The experiments at Tevatron have already presented their results and they see an excess in the same region. This is vital because they are sensitive to different final states, so between the Tevatron and the LHC we have all the analyses covered.

For each analysis there are two kinds of background, the “reducible” backgrounds where particles fake the particles we are looking for (for example, a high energy electron can look just like a high energy photon) and the “irreducible” backgrounds where particles are the same kind as the ones we are looking for. So when you see plots showing the gamma gamma searches, you can expect to see four categories: gamma gamma (irreducible Standard Model background), jet gamma, jet jet, and “other”. As we make more and more stringent requirements to eliminate these backgrounds we also lose signal events, so we have trade off background rejection against signal acceptance.

On top of all these problems we also have to take reconstruction and acceptance into account. We cannot record every event, so we pick and choose events based on how interesting they look. Does an event have two high energy photon candidates? If so, record it. Does an event have four leptons in the signal state? If so, record it. These trigger decisions are affected by definitions of “high energy”, by the algorithms we use, and by the coverage of the detectors. We have to take all of these biases into account with systematic uncertainties, and these can dominate for some of the searches.

When we put all this together we end up asking some simple questions: “How many background events do we expect?” “How many events do we see in data?” “What is the total uncertainty on the background and signal?” “How many signal events do we think we see?” “How much larger is this than the uncertainty?” This then gives us the “n sigma” for that mode across the mass range. We combine these sigmas within a single experiment, taking correlated uncertainties into account, and that’s how we get our Brazil plots.

### How likely is a discovery?

In 2011 we had about $$5fb^{-1}$$ of luminosity and we saw about 3 sigma for each experiment. In 2012 we had about $$6.5fb^{-1}$$ of luminosity at slightly higher energy (giving a factor of 1.25). So we can work out what to expect for 2012 sensitivity- just take the 3 sigma and add it in quadrature to $$(\sqrt{1.25\times 6.5/5})\times 3$$ sigma and that comes out at 4.9 sigma. If we’re lucky one or more experiments might see more than 5 sigma, meaning we could have a discovery!

### What next for the Higgs?

If we make a discovery, either now or in the coming weeks, then we need to measure the properties of the new particle. We can’t claim to have discovered the Standard Model Higgs boson until we’ve measured its branching fractions and spin. Fortunately, if the Higgs boson is at 125GeV then we have a rich variety of decay modes, and this could give us insights into all kinds of interesting measurements, such as the quark masses.

Now go and enjoy the seminar!

What comes next? (Richard Ruiz)

How difficult is it find the Higgs? (Richard Ruiz)

(Video) What is a Higgs boson? (Dom Lincoln)

(Video) Higgs boson – Latest update (Dom Lincoln)

### Higgsdependence Day

Monday, July 2nd, 2012

On July 4th CERN will hold a seminar where ATLAS and CMS will present their latest findings on the search for the Higgs boson. There’s a reasonable chance that either or both experiments will see a 5 sigma excess, and this would be enough to claim a “discovery”. One of my US friends at CERN called this day Higgsdependence Day, and all over the USA people will be celebrating with fireworks and barbecues. (Okay, perhaps they will be celebrating something else. My boss tells me he might tar and feather me as the token British member of the group…)

CERN is not the only lab to be holding a seminar. Today at 09:00 CDT Fermilab will be announcing the latest results from CDF and D0. Rumors suggest a 3 sigma excess (technically an “observation”) in the interesting region. So if you can spare the time I’d recommend you listen in on the announcement. You can see the webcast information here.

In anticipation of the CERN seminar, when I came to my office this morning I found a bottle of champagne with a label hastily pasted to the back. It seems these might be placed alongside fire extinguishers in every office at CERN! (You can get your own label here.)

No Higgs seminar is complete without a bottle of Champagne, just in case!

For those of us who can’t get enough of the Higgs boson and want to brush up on the basics I would recommend the following show, put out by the BBC. This contains the latest results from the 2011 searches and it goes into quite a bit of depth about why we think the Higgs boson exists and what to expect from the 2012 searches.

Finally for those keeping score I still have $20 riding on a non-discovery. If a 5 sigma excess is seen on Wednesday there is a bit more work that needs to be done to show that it is the Standard Model Higgs, and that would probably take until the end of 2012 running. So my$20 is safe… for now.

### Auditioning for TED2013

Wednesday, June 13th, 2012

Editor’s note: Fermilab physicist Don Lincoln submitted an audition video to TED2013 on March 30. On May 22 he learned that he’d advanced to the next level of the audition process, and last Thursday, June 7, he gave his live audition in front of the TED leadership and insiders in New York City. He tells us how it went down.

Small. That was my first impression of the stage at Joe’s Pub in Greenwich Village in Manhattan. On the walls are photos of people who have performed here before, from Adele’s US debut in 2008, to Bono, to Dolly Parton, to Amy Winehouse. It was the kind of small and intimate nightclub that in another era would have had a jazz trio on the stage and been filled with stylishly dressed couples at small tables, with smoke languorously curling from their fashionable cigarettes. But, in 2012, the smoke was gone and the vibe was more bohemian, with casually dressed young twenty- and thirty-somethings assembled to watch a series of short and eclectic presentations. Following a global search for speakers, about 400 people have been invited to 14 locations around the world to audition for a coveted invitation to make a presentation at TED2013. The big TED conference has hosted newsmakers like Bill Gates and Richard Branson. This year, they have elected to build half of their program with “fresh faces.”

Well, I don’t know if my face really constitutes fresh, but here I am in New York City, one of 30 hopefuls, giving talks masterfully and wittily emceed by TED curator Chris Anderson, whose dry British humor adds a refining and cosmopolitan touch to each performer’s presentation. Each of us has between two and six minutes to make our pitch. Only about three or four of us will be going to Long Beach in February 2013. The subjects range widely, from the high school freshman who developed a test for pancreatic cancer while he was in the eighth grade to the young woman who battled depression by writing love letters to strangers and founded a movement of people who write letters to people they’ve never met to battle this increasingly lonely and isolated world. I’m the only one in the lot who does hard science. (I’m not sure the theoretical physicist and saxophonist who told how John Coltrane was his inspiration for an idea on quantum gravity counts. OK, I’m being catty. His science is good, but his talk was filled with lots of sax riffs. Come to think of it, his talk fit the venue very well.) I’ve elected to use my four minutes to tell the 200 or so people in the audience about how particle accelerators like the Tevatron and the LHC can recreate the conditions immediately after the Big Bang. I’m hoping that this will be a new idea for the audience and amaze them in the same way it amazed me when I first heard it. I don’t know. There are a lot of jaded New Yorkers in the audience, but they’re also ones who embrace new ideas. Are my ideas new enough for them?

The whole experience has been a little unsettling. While I’ve given many hundred public presentations in the past, this is the first where the organizers want to see the script and the multimedia before they’ll let me on the stage. It’s also the first where I needed to audition so I could audition. Each of us had to submit a video for evaluation before being invited to talk at the salon. While the TED people were cagey about the numbers, “many hundred” videos were submitted for the New York event and only thirty were invited. Not only did I have to audition to audition, I had to arrive a day early to rehearse in front of the organizers too. I didn’t have to jump through a hoop or juggle flaming chainsaws, but that could be next. In a way, the scrutiny is comforting, as TED performances have very high production quality, but it’s a lot to go through.

Now that the audition is over, the wait begins. In late June, videos of the 400 or so performances will be put online on the TED website and judged by the worldwide audience. The number of “likes” given to each video will be a factor in which 50 are selected to give an 18 minute-long presentation at TED2013. (In case that was too subtle, that is an invitation for you to tell all your friends, family, acquaintances, neighbors and random strangers to watch them and “like” mine. I’ll make another post when the links to the videos go live.)

Overall, it was a pretty cool experience. I got to meet some fascinating people, both the other speaker-candidates and the TED staff. It’s enjoyable talking with people who believe in the TED credo “Ideas worth spreading.”

Don Lincoln

Tuesday, March 6th, 2012

Each time news comes out about the Higgs boson I get questions from media, friends and family trying to grasp why this particle is so important. The following questions come up again and again. So with experimenters from using Fermilab’s  Tevatron announcing new Higgs results Wednesday at a conference in Italy, I thought it was time to share answers to the questions that might pop into your mind.

Why should the average person care if the Higgs is found?

Understanding more about the building blocks of matter and the forces that control their interactions helps scientists to learn how to manipulate those forces to humankind’s benefit. For example, the study of the electron led to the development of electricity, the study of quantum mechanics made possible the creation of GPS systems and the study of the weak force led to an understanding of radioactive decay and nuclear power.

Now what?

The Tevatron experiments will continue to further analyze the Higgs boson data to wring out more information. In addition, the Tevatron and LHC experiments are working to combine their data for a release at an unspecified date.

Even if both teams find evidence of a Higgs boson in the same location, physicists will need to do more analysis to make sure the Higgs boson isn’t a non-Standard Model Higgs masquerading as a resident of the Standard Model. That will require physicists to measure several properties in addition to mass.

What would finding the Higgs boson mean for the field of physics?

Finding evidence of the Higgs boson would expand the following three areas of study:

• Pin-pointing the mass range of the Higgs would help physicists condense the number of theories about the existence of undiscovered particles and the forces that interact on them. For example, a Standard Model Higgs boson would rule out classic QCD-like versions of technicolor theory. A Higgs boson with a mass larger than 125 GeV would rule out the simplest versions of supersymmetry, or SUSY, which predict that every known particle has an unknown sibling particle with a different mass. Other theories would gain more support. One such SUSY theory predicts that a Standard Model Higgs boson would appear as the lightest of a group of five or more Higgs bosons. Whether the Higgs boson exists or not does not affect theories about the existence of extra dimensions.

• Knowing the mass of the Higgs boson would give physicists more data to plug into other equations about how our universe formed and about some of the least understood particle interactions, such as magnetic muon anomaly.

• Finding evidence of a heavy mass Higgs boson (larger than 150 GeV) would require the existence of undiscovered particles and/or forces. Finding a light mass Higgs boson (less than 125 GeV) would not require the existence of new physics but doesn’t rule it out either.

What is the difference between the Higgs boson and the Higgs field?

The Higgs field exists like a giant vat of molasses spread throughout the universe. Particles that travel through it end up with globs of molasses sticking to them, slowing them down and making them heavier. You can think of the Higgs boson as the molasses globs, or a particle manifestation of this energy field akin to a ball of energy.

Physicists have different theories about how many Higgs bosons exist, akin to predicting whether the molasses would stick in one giant glob or several globlets.

How long have physicists been looking for the Higgs?

More than a decade. It started with the LEP experiment at CERN in the 1990s, continued with the Tevatron and now with the LHC.

How do physicists create a Higgs boson?

A high-energy particle accelerator such as the Tevatron or LHC can recreate the energy levels that permeated the universe shortly after the Big Bang. Colliding particles at this energy level can set free the right amount of energy to produce particles, including a Higgs boson. The collision energy is localized in a small space and transforms from energy into the mass of the Higgs boson.

How is the Higgs boson related to the Big Bang theory?

The Big Bang occurred 13.7 billion years ago sending massless particles and radiation energy zooming through the universe like cars at rush hour. Shortly afterward, the Higgs field appeared, as if a truck carrying molasses overturned and leaked all over the highway. Particles such as light, which went through the puddle super fast, avoided having any molasses stick to them, similar to the way hydroplaning cars skim the surface of water. Particles that went through the molasses puddle more slowly had molasses goblets cling to them, creating a drag that slowed them even more and made them more massive. How fast a particle made it through the puddle determined how much molasses clung to it, and thus how massive it became. When the universe began to cool, slow particles with mass began to bunch up like mini-traffic jams and form composite particles and then atoms.

How do we know this is where the Higgs is located?

Just as firemen sweep building floors to rule out the existence of trapped homeowners, physicists have used direct and indirect observations from experiments to rule out the existence of the Higgs boson in most energy ranges where the Standard Model predicts it could reside.

Does the mass of the Higgs compare to its weight?

Sort of. Non-physicists think of mass as how much something weighs. But scientists consider mass to take into account weight and other factors. Weight changes with gravity, so you would weigh less on the moon than on Earth. Mass remains constant throughout the universe. However, when talking about things on Earth, mass and weight are fairly interchangeable.

How did the Higgs boson get the nickname “the God particle”?

Nobel laureate Leon Lederman, a Fermilab physicist, wrote a book in the early 1990s about particle physics and the search for the Higgs boson. His publisher coined the name as a marketable title for the book. Scientists dislike the nickname.

What countries are involved in the CDF and DZero experiments?

• CDF: US, Canada, France, Germany, Greece, Italy, Japan, Korea, UK, Russia, Slovakia, Spain and Taiwan

• DZero; Brazil, China, Columbia, Czechoslovakia, Ecuador, France, Germany, India, Ireland, Korea, Mexico, Netherlands, UK, Ukraine, US, Russia, Spain and Sweden.

What is the competitive relationship between the Tevatron and LHC experiments?

It is closer to sibling rivalry than the traditional business competition you would find in something such as the auto industry.

Fermilab supports about 1,000 US CMS scientists and engineers by providing computing facilities, office and meeting space as well as the LHC Remote Operation Center. Fermilab helped design and build the CMS detector as well as equipment for the LHC accelerator, and Fermilab scientists are working on upgrades for both and analyzing data. About one third of the members of each of the Tevatron’s experiments, CDF and DZero, are also members of the LHC experiments.

– Tona Kunz

### A new year, a new outlook

Saturday, December 31st, 2011

2011 has been a year of change and excitement. We’ve had plenty of good news and bad news to deal with. The new year doesn’t mean just another calendar on the wall, it means a new way of looking at physics. There’s no better way to bring in the new year than watching the fireworks in central London, surrounded by friends. There’s usually a fantastic display, because London is not only one of the most important cities in the world, but it’s also home of universal time. With the Greenwich Meridian running through the capital, we’re reminded of the role that timekeeping has played in the development our history and our science. But this year was even more special, since London is literally inviting the world to its streets this year for the Olympics. So I got caught up in the excitement of it all my thoughts turned to what we’ve seen in the world of physics, and where we’re going next.

New year fireworks in London (New York Times)

2011 got off to a start with ATLAS announcing a startling asymmetry in the jet momenta in heavy ion collisions. However, the joy was tainted by a leaked abstract from an internal document. That document never made it through internal review and should never have been made public. We were faced with several issues of confidentiality, ethics and biases, and how having several thousand people, all armed with the internet and with friends on competing experiments makes the work tough for all of us. In the end we followed the right course, subjected all the analyses to the rigors of internal and external review, and presented some wonderful papers.

There was more gossip over the CDF dijet anomaly presented at Blois. CDF saw a bump, and D0 didn’t. Before jumping to any conclusions it’s important to remember why we have two experiments at Tevatron in the first place! These kinds of double checks are exactly what we need and they represent the high standard of scientific research that we expect and demand. The big news for Tevatron was, of course, the end of running. We’re all sad that the shutdown had to happen and grateful for such a long, productive run, but lets look to the future in the intensity frontier.

Meanwhile both ATLAS and CMS closed in on the Higgs boson, excluding the vast majority of the allowed regions. The combinations and results just got better and better, until eventually on December 13th we saw the result of 5fb-1 from each experiment. The world watched as the presentations were made and quite a few people were left feeling a little deflated. But that’s not the message we should take away. If the Higgs boson is there (and it probably is) then we’ll see by the end of the year. There’s no more of saying “Probably within a year, if we’re lucky”, or “Let’s not get ahead of ourselves”. This time we can be confident that this time next year we’ll have uncovered every reasonable stone. The strategies will change and we narrow the search. We may have new energies to explore, and we’ll tweak our analyses to get more discriminating power from the data. Now is the time to get excited! The game has changed and the end is definitely in sight.

Raise a glass as we say farewell to a great year of physics, and welcome another

It’s been a good year for heavy flavor physics as well. LHCb has gone from strength to strength, probing deeper and deeper into the data. We’ve seen the first new particle at the LHC, a state of bottomonium. Precision measurements of heavy flavor physics give some of the most sensitive tests of new physics models, and it’s easy to forget the vital role they play in discover.

ALICE has been busy exploring different questions about our origins, and they’ve studied the quark gluon plasma in great detail. The findings have told us that the plasma acts like a fluid, while showing unexpected suppression of excited bottomonium states. With even more data from 2011 being crunched we can expect even more from ALICE in 2012.

The result that came completely out of left field was the faster than light neutrinos from OPERA. After seeing neutrinos break the cosmic speed limit, OPERA repeated the measurements with finer proton bursts and got the same result. Something interesting is definitely happening with that result. Either it’s a subtle mistake that has eluded all the OPERA physicists and their colleagues across the world, or our worldview is about to be overturned. I don’t think we’ll get the answers in the immediate future, so let’s keep an eye out for results from MINOS and OPERA.

Finally it’s been an incredible year for public involvement. It’s been a pleasure to have such a responsive audience and to see how many people all across the world have been watching CERN and the LHC. A couple of years ago I would not have thought that the LHC and Higgs boson would get so much attention, and it’s been a of huge benefit to everyone. The discoveries we share with the world are not only captivating us all, they’re also inspiring the next generation of physicists. We need a constant supply of fresh ideas and new students to keep the cutting edge research going. If we can reach out to teenagers in schools and inspire some of them to choose careers in science then we’ll continue to answer the most fascinating, far reaching and beautiful questions about our origins.

So when you a raise a glass to the new year, don’t forget that we’ve had an incredible 2011 for physics, and that 2012 is going to deliver even more. We don’t even know what’s out there, but it’s going to be amazing. To physics!

### The Tevatron’s enduring computing legacy

Friday, December 30th, 2011

A night-time view of the Tevatron. Photo by Reidar Hahn.

This is the first part of a two-part series on the contribution Tevatron-related computing has made to the world of computing. This part begins in 1981, when the Tevatron was under construction, and brings us up to recent times. The second part will focus on the most recent years, and look ahead to future analysis.

Few laypeople think of computing innovation in connection with the Tevatron particle accelerator, which shut down earlier this year. Mention of the Tevatron inspires images of majestic machinery, or thoughts of immense energies and groundbreaking physics research, not circuit boards, hardware, networks, and software.

Yet over the course of more than three decades of planning and operation, a tremendous amount of computing innovation was necessary to keep the data flowing and physics results coming. In fact, computing continues to do its work. Although the proton and antiproton beams no longer brighten the Tevatron’s tunnel, physicists expect to be using computing to continue analyzing a vast quantity of collected data for several years to come.

When all that data is analyzed, when all the physics results are published, the Tevatron will leave behind an enduring legacy. Not just a physics legacy, but also a computing legacy.

### In the beginning: The fixed-target experiments

This image of an ACP system was taken in 1988. Photo by Reidar Hahn.

1981. The first Indiana Jones movie is released. Ronald Reagan is the U.S. President. Prince Charles makes Diana a Princess. And the first personal computers are introduced by IBM, setting the stage for a burst of computing innovation.

This image of an ACP system was taken in 1988. Photo by Reidar Hahn.Meanwhile, at the Fermi National Accelerator Laboratory in Batavia, Illinois, the Tevatron has been under development for two years. And in 1982, the Advanced Computer Program formed to confront key particle physics computing problems. ACP tried something new in high performance computing: building custom systems using commercial components, which were rapidly dropping in price thanks to the introduction of personal computers. For a fraction of the cost, the resulting 100-node system doubled the processing power of Fermilab’s contemporary mainframe-style supercomputers.

“The use of farms of parallel computers based upon commercially available processors is largely an invention of the ACP,” said Mark Fischler, a Fermilab researcher who was part of the ACP. “This is an innovation which laid the philosophical foundation for the rise of high throughput computing, which is an industry standard in our field.”

The Tevatron fixed-target program, in which protons were accelerated to record-setting speeds before striking a stationary target, launched in 1983 with five separate experiments. When ACP’s system went online in 1986, the experiments were able to rapidly work through an accumulated three years of data in a fraction of that time.

### Entering the collider era: Protons and antiprotons and run one

1985. NSFNET (National Science Foundation Network), one of the precursors to the modern Internet, is launched. And the Tevatron’s CDF detector sees its first proton-antiproton collisions, although the Tevatron’s official collider run one won’t begin until 1992.

The experiment’s central computing architecture filtered incoming data by running Fortran-77 algorithms on ACP’s 32-bit processors. But for run one, they needed more powerful computing systems.

By that time, commercial workstation prices had dropped so low that networking them together was simply more cost-effective than a new ACP system. ACP had one more major contribution to make, however: the Cooperative Processes Software.

CPS divided a computational task into a set of processes and distributed them across a processor farm – a collection of networked workstations. Although the term “high throughput computing” was not coined until 1996, CPS fits the HTC mold. As with modern HTC, farms using CPS are not supercomputer replacements. They are designed to be cost-effective platforms for solving specific compute-intensive problems in which each byte of data read requires 500-2000 machine instructions.

CPS went into production-level use at Fermilab in 1989; by 1992 it was being used by nine Fermilab experiments as well as a number of other groups worldwide.

1992 was also the year that the Tevatron’s second detector experiment, DZero, saw its first collisions. DZero launched with 50 traditional compute nodes running in parallel, connected to the detector electronics; the nodes executed filtering software written in Fortran, E-Pascal, and C.

### Gearing up for run two

"The Great Wall" of 8mm tape drives at the Tagged Photon Laboratory, circa 1990 - from the days before tape robots. Photo by Reidar Hahn.

1990. CERN’s Tim Berners-Lee launches the first publicly accessible World Wide Web server using his URL and HTML standards. One year later, Linus Torvalds releases Linux to several Usenet newsgroups. And both DZero and CDF begin planning for the Tevatron’s collider run two.

Between the end of collider run one in 1996 and the beginning of run two in 2001, the accelerator and detectors were scheduled for substantial upgrades. Physicists anticipated more particle collisions at higher energies, and multiple interactions that were difficult to analyze and untangle. That translated into managing and storing 20 times the data from run one, and a growing need for computing resources for data analysis.

Enter the Run Two Computing Project (R2CP), in which representatives from both experiments collaborated with Fermilab’s Computing Division to find common solutions in areas ranging from visualization and physics analysis software to data access and storage management.

R2CP officially launched in 1996. It was the early days of the dot com era. eBay had existed for a year, and Google was still under development. IBM’s Deep Blue defeated chess master Garry Kasparov. And Linux was well-established as a reliable open-source operating system. The stage is set for experiments to get wired and start transferring their irreplaceable data to storage via Ethernet.

The high-tech tape robot used today. Photo by Reidar Hahn.

“It was a big leap of faith that it could be done over the network rather than putting tapes in a car and driving them from one location to another on the site,” said Stephen Wolbers, head of the scientific computing facilities in Fermilab’s computing sector. He added ruefully, “It seems obvious now.”

The R2CP’s philosophy was to use commercial technologies wherever possible. In the realm of data storage and management, however, none of the existing commercial software met their needs. To fill the gap, teams within the R2CP created Enstore and the Sequential Access Model (SAM, which later stood for Sequential Access through Meta-data). Enstore interfaces with the data tapes stored in automated tape robots, while SAM provides distributed data access and flexible dataset history and management.

By the time the Tevatron’s run two began in 2001, DZero was using both Enstore and SAM, and by 2003, CDF was also up and running on both systems.

### Linux comes into play

The R2CP’s PC Farm Project targeted the issue of computing power for data analysis. Between 1997 and 1998, the project team successfully ported CPS and CDF’s analysis software to Linux. To take the next step and deploy the system more widely for CDF, however, they needed their own version of Red Hat Enterprise Linux. Fermi Linux was born, offering improved security and a customized installer; CDF migrated to the PC Farm model in 1998.

The early computer farms at Fermilab, when they ran a version of Red Hat Linux (circa 1999). Photo by Reidar Hahn.

Fermi Linux enjoyed limited adoption outside of Fermilab, until 2003, when Red Hat Enterprise Linux ceased to be free. The Fermi Linux team rebuilt Red Hat Enterprise Linux into the prototype of Scientific Linux, and formed partnerships with colleagues at CERN in Geneva, Switzerland, as well as a number of other institutions; Scientific Linux was designed for site customizations, so that in supporting it they also supported Scientific Linux Fermi and Scientific Linux CERN.

Today, Scientific Linux is ranked 16th among open source operating systems; the latest version was downloaded over 3.5 million times in the first month following its release. It is used at government laboratories, universities, and even corporations all over the world.

“When we started Scientific Linux, we didn’t anticipate such widespread success,” said Connie Sieh, a Fermilab researcher and one of the leads on the Scientific Linux project. “We’re proud, though, that our work allows researchers across so many fields of study to keep on doing their science.”

### Grid computing takes over

As both CDF and DZero datasets grew, so did the need for computing power. Dedicated computing farms reconstructed data, and users analyzed it using separate computing systems.

“As we moved into run two, people realized that we just couldn’t scale the system up to larger sizes,” Wolbers said. “We realized that there was really an opportunity here to use the same computer farms that we were using for reconstructing data, for user analysis.”

A wide-angle view of the modern Grid Computing Center at Fermilab. Today, the GCC provides computing to the Tevatron experiments as well as the Open Science Grid and the Worldwide Large Hadron Collider Computing Grid. Photo by Reidar Hahn.

Today, the concept of opportunistic computing is closely linked to grid computing. But in 1996 the term “grid computing” had yet to be coined. The Condor Project had been developing tools for opportunistic computing since 1988. In 1998, the first Globus Toolkit was released. Experimental grid infrastructures were popping up everywhere, and in 2003, Fermilab researchers, led by DZero, partnered with the US Particle Physics Data Grid, the UK’s GridPP, CDF, the Condor team, the Globus team, and others to create the Job and Information Management system, JIM. Combining JIM with SAM resulted in a grid-enabled version of SAM: SAMgrid.

“A pioneering idea of SAMGrid was to use the Condor Match-Making service as a decision making broker for routing of jobs, a concept that was later adopted by other grids,” said Fermilab-based DZero scientist Adam Lyon. “This is an example of the DZero experiment contributing to the development of the core Grid technologies.”

By April 2003, the SAMGrid prototype was running on six clusters across two continents, setting the stage for the transition to the Open Science Grid in 2006.

### From the Tevatron to the LHC – and beyond

Throughout run two, researchers continued to improve the computing infrastructure for both experiments. A number of computing innovations emerged before the run ended in September 2011. Among these was CDF’s GlideCAF, a system that used the Condor glide-in system and Generic Connection Brokering to provide an avenue through which CDF could submit jobs to the Open Science Grid. GlideCAF served as the starting point for the subsequent development of a more generic glidein Work Management System. Today glideinWMS is used by a wide variety of research projects across diverse research disciplines.

Another notable contribution was the Frontier system, which was originally designed by CDF to distribute data from central databases to numerous clients around the world. Frontier is optimized for applications where there are large numbers of widely distributed clients that read the same data at about the same time. Today, Frontier is used by CMS and ATLAS at the LHC.

“By the time the Tevatron shut down, DZero was processing collision events in near real-time and CDF was not far behind,” said Patricia McBride, the head of scientific programs in Fermilab’s computing sector. “We’ve come a long way; a few decades ago the fixed-target experiments would wait months before they could conduct the most basic data analysis.”

One of the key outcomes of computing at the Tevatron was the expertise developed at Fermilab over the years. Today, the Fermilab computing sector has become a worldwide leader in scientific computing for particle physics, astrophysics, and other related fields. Some of the field’s top experts worked on computing for the Tevatron. Some of those experts have moved on to work elsewhere, while others remain at Fermilab where work continues on Tevatron data analysis, a variety of Fermilab experiments, and of course the LHC.

The accomplishments of the many contributors to Tevatron-related computing are noteworthy. But there is a larger picture here.

“Whether in the form of concepts, or software, over the years the Tevatron has exerted an undeniable influence on the field of scientific computing,” said Ruth Pordes, Fermilab’s head of grids and outreach. “We’re very proud of the computing legacy we’ve left behind for the broader world of science.”

– Miriam Boon

### Fermilab hot on trail of Higgs boson with LHC, Tevatron

Tuesday, December 13th, 2011

Real CMS proton-proton collision events in which 4 high energy electrons (green lines and red towers) are observed. The event shows characteristics expected from the decay of a Higgs boson but is also consistent with background Standard Model physics processes. Courtesy: CMS

Today physicists at CERN on the CMS and ATLAS experiments at the Large Hadron Collider announced an update on their search for the Higgs boson. That may make you wonder ( I hope) what is Fermilab’s role in this. Well, glad you asked.

Fermilab supports the 1,000 US LHC scientists and engineers by providing office and meeting space as well as the Remote Operation Center. Fermilab helped design the CMS detector, a portion of the LHC accelerator and is working on upgrades for both. About one-third of the members of each of the Tevatron’s experiments, CDF and DZero, are also members of the LHC experiments.

That means that a good portion of the LHC researchers are also looking for the Higgs boson with the Tevatron.  Because the Tevatron and LHC accelerators collide different pairs of particles, the dominant way in which the experiments search for the Higgs at the two accelerators is different. Thus the two machines offer a complimentary search strategy.

If the Higgs exists and acts the way theorists expect, it is crucial to observe it in both types of decay patterns. Watch this video to learn how physicists search for the Higgs boson. These types of investigations might lead to the identification of new and unexpected physics.

Scientists from the CDF and DZero collaborations at Fermilab continue to analyze data collected before the September shutdown of the Tevatron in the search for the Higgs boson.

The two collaborations will announce their latest results for the Higgs boson search at an international particle physics conference in March 2012. This new updated analysis will have 20 to 40 percent more data than the July 2011 results as well as further improvements in analysis methods.

The Higgs particle is the last not-yet-observed piece of the theoretical framework known as the Standard Model of particles and forces. Watch this video to learn The nature of the Higgs boson and how it works. According to the Standard Model, the Higgs boson explains why some particles have mass and others do not. Higgs most likely has a mass between 114-137 GeV/c2, about 100 times the mass of a proton. This predicted mass range is based on stringent constraints established by earlier measurements made by Tevatron and other accelerators around the world, and confirmed by the searches of LHC experiments presented so far in 2011. This mass range is well within reach of the Tevatron Collider.

The Tevatron experiments already have demonstrated that they have the ability to ferret out the Higgs-decay pattern by applying well-established techniques used to search for the Higgs boson to observing extremely rare but firmly expected physics signature. This signature consists of pairs of heavy bosons (WW or WZ) that decay into a pair of b quarks, a process that closely mimics the main signature that the Tevatron experiments use to search for the Higgs particle, i.e. Higgs decaying to a pair of b quarks, which has by far the largest probability to happen in this mass range. Thus, if a Standard Model Higgs exists, the Tevatron experiments will see it.

If the Standard Model Higgs particle does not exist, Fermilab’s Tevatron experiments are on track to rule it out this winter. CDF and DZero experiments have excluded the existence of a Higgs particle in the 100-108 and the 156-177 GeV/c2 mass ranges and will have sufficient analysis sensitivity to rule out this winter the mass region between.

While today’s announcement shows the progress that the LHC experiments have made in the last few months, all eyes will be on the Tevatron and on the LHC in March 2012 to see what they have to say about the elusive Higgs Boson.

– Tona Kunz

### Tevatronic Rhapsody

Friday, September 30th, 2011

The big news today is that one of the biggest accelerators is shutting down after 28 years of excellent service. When SLAC closed down PEP-II, I wrote a tribute to the tune of American Pie (called “The Day the Mesons Died”) so it’s only fair that I do the same for Tevatron.

Although most of the time, Tevatron was an accelerator that always happened to be on the wrong side of the continent or the wrong side of the Atlantic, I did start my particle physics career with the help of CDF. I worked on Monte Carlo simulations, trying to find a strategy for measuring Bs oscillations. That’s where it all began, and for that I’m grateful.

So here we are, Tevatronic Rhapsody, (hastily written in the gaps between work) to the tune of Queen’s Bohemian Rhapsody. If you really want to annoy your office mates, you can sing along with this backing track.

### Tevatronic Rhapsody

Is this the data?
Is this Monte Carlo?
Caught in a meeting
No escape from the next slideshow
Look up to the slides and see
Is that the top quark?
Is it the final piece?
Because it’s rarely come
Quickly go
Mass is high
Any way it decays doesn’t really matter to me
(\ell b)

Bs just flipped it quarks
Put an s where there was b
Now it violates CP
Bs, you were too heavy
But not for D0 and CDF!
Bs, ooooh
And showed us how to violate CP
With a phase, complex phase
Because antimatter matters

Too late, our time has come
No funding for the beams
No more events to be seen
Goodbye antiprotons
We’ve got to go
Got to analyze the data for results

Bs, oooh (any way the fit goes)
You went to two muons
More often than in the Standard Model
[Celebratory guitar riff]

I see a little silhouette-o of a peak
Is it Higgs? Is it Higgs?!
Will we get a Nobel Prize?
ICHEP, Lepton-Photon,
Conferences they go on

Set the limits! (Set the limits!) Set the limits! (Set the limits!) Set the limits! Make a plot!

Here is a spectrum, with strange topology
It is a dijet, it’s an anomaly!
Technicolor, or a monstrosity?

Heavy top, lighter top, is it CPT?
CPT? No! It violates Lorentz!
CPT?
CPT? No! It violates Lorentz!
CPT?
CPT? No! It violates Lorentz!
Violates Lorentz!
(CPT?)
Violates Lorentz!
(CPT?)
Violates Lorentz-enz-enz-enz!

Oh bottom mesons, and charmed mesons, and baryons, we saw them!
The quark model had positions set aside for all, (except the X!)

So you think you can stop us and turn off our beams?
So you think we won’t be publishing reams?
Oh, data
We’ve still got loads of data!
Just gotta publish
Just gotta analyze data

[Time to rock out]

The universe, it matters, anyone can see
More than antimatters, to me

Have a great Friday! And congratulations to everyone who worked with Tevatron. Today is the end of a glorious era and A Job Well Done (as we Brits say).

### Tevatron past as LHC prologue

Wednesday, September 28th, 2011

This Friday, Fermilab will turn off the Tevatron for the last time after a 28-year run. It has been a constant in my life as a particle physicist, and indeed for a whole generation of particle physicists. I know some people who have managed to spend their entire careers involved with the Tevatron in some way. Not true for me; I was on hiatus at the Cornell Electron Storage Ring for five years as a graduate student. But the Tevatron was where I had my first experiences as an undergraduate researcher; as a college freshman, I was stunned to find myself with a Fermilab ID card in my pocket and suddenly in on the hunt for the top quark. (No dice; another six years, significant detector upgrades, and more than an order of magnitude more data had to come first.) And as a postdoctoral researcher, it was where I had my greatest triumphs (moderate as they may be) as a full-time researcher. (As a professor with many other things to juggle, it would be a stretch to call me a full-time researcher now.) I learned a tremendous amount along the way about physics and about how to be a physicist.

(But I will not be attending the shutdown ceremonies on September 30 — it’s Rosh Hashanah, the Jewish new year. What is it with the managers of particle physics laboratories who can’t read a calendar? So much for getting Fermilab Today to pick up this blog post….)

The Tevatron’s longevity surely puts it into a special category of scientific enterprises that have captured the public imagination because of their epic scope. The Voyager 1 satellite, for instance, has been chugging along since 1979, and barring unforeseen circumstances will continue to tell us about the nature of the universe. The Tevatron in its own way will keep chugging along too, as there is so much data yet to analyze that it will keep teaching us about the universe for some years to come.

I’m not going to tick off all of the accomplishments of the Tevatron and CDF and D0, its principal experiments; this has been done elsewhere, and also has been covered in excellent presentations at the DPF meeting by Steve Holmes and Paul Grannis, both of whom were there pretty much from the beginning. (Chris Quigg also provides a lovely summary of the physics achievements in the CERN Courier.) But what I would like to point out is that the Tevatron program of 2011 is not the program that was envisioned when the machine design was launched in the late 1970′s. The clear targets of the machine were the W and Z bosons and the top quark, and these are now understood in detail because of the Tevatron. But as far as I know, no one anticipated the program of bottom-quark physics that emerged, no one thought that precision measurements of masses could be done at a hadron collider, and even just a few years ago it would have been optimistic to suggest that the Tevatron experiments would have the capability to observe the Higgs boson. On the accelerator side, the final instantaneous luminosity was a factor of 400 better than design, meaning that there was an average 35% annual improvement over twenty years.

Since this is an LHC blog — what can we learn about the LHC from this? It is that we should not underestimate the potential that we have in front of us. The LHC will likely operate for as long as the Tevatron has, and we can realistically expect similar performance improvements along the way. We should also not underestimate how our experimental reach can be increased through advances in detector technology, and the just plain cleverness that physicists will bring to the table when given the chance to solve a challenging and important problem. In 2037, there will be new generation of particle physicists for whom the LHC is a constant of life, and I expect that we will be looking back on an LHC legacy that is just as memorable as that of the Tevatron.