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Posts Tagged ‘particle physics’

The Ties That Bind

Sunday, January 18th, 2015
Cleaning the ATLAS Experiment

Beneath the ATLAS detector – note the well-placed cable ties. IMAGE: Claudia Marcelloni, ATLAS Experiment © 2014 CERN.

A few weeks ago, I found myself in one of the most beautiful places on earth: wedged between a metallic cable tray and a row of dusty cooling pipes at the bottom of Sector 13 of the ATLAS Detector at CERN. My wrists were scratched from hard plastic cable ties, I had an industrial vacuum strapped to my back, and my only light came from a battery powered LED fastened to the front of my helmet. It was beautiful.

The ATLAS Detector is one of the largest, most complex scientific instruments ever constructed. It is 46 meters long, 26 meters high, and sits 80 metres underground, completely surrounding one of four points on the Large Hadron Collider (LHC), where proton beams are brought together to collide at high energies.  It is designed to capture remnants of the collisions, which appear in the form of particle tracks and energy deposits in its active components. Information from these remnants allows us to reconstruct properties of the collisions and, in doing so, to improve our understanding of the basic building blocks and forces of nature.

On that particular day, a few dozen of my colleagues and I were weaving our way through the detector, removing dirt and stray objects that had accumulated during the previous two years. The LHC had been shut down during that time, in order to upgrade the accelerator and prepare its detectors for proton collisions at higher energy. ATLAS is constructed around a set of very large, powerful magnets, designed to curve charged particles coming from the collisions, allowing us to precisely measure their momenta. Any metallic objects left in the detector risk turning into fast-moving projectiles when the magnets are powered up, so it was important for us to do a good job.

ATLAS Big Wheel

ATLAS is divided into 16 phi sectors with #13 at the bottom. IMAGE: Steven Goldfarb, ATLAS Experiment © 2014 CERN

The significance of the task, however, did not prevent my eyes from taking in the wonder of the beauty around me. ATLAS is shaped somewhat like a large barrel. For reference in construction, software, and physics analysis, we divide the angle around the beam axis, phi, into 16 sectors. Sector 13 is the lucky sector at the very bottom of the detector, which is where I found myself that morning. And I was right at ground zero, directly under the point of collision.

To get to that spot, I had to pass through a myriad of detector hardware, electronics, cables, and cooling pipes. One of the most striking aspects of the scenery is the ironic juxtaposition of construction-grade machinery, including built-in ladders and scaffolding, with delicate, highly sensitive detector components, some of which make positional measurements to micron (thousandth of a millimetre) precision. All of this is held in place by kilometres of cable trays, fixings, and what appear to be millions of plastic (sometimes sharp) cable ties.

Inside the ATLAS Detector

Scaffolding and ladder mounted inside the precision muon spectrometer. IMAGE: Steven Goldfarb, ATLAS Experiment © 2014 CERN.

The real beauty lies not in the parts themselves, but rather in the magnificent stories of international cooperation and collaboration that they tell. The cable tie that scratched my wrist secures a cable that was installed by an Iranian student from a Canadian university. Its purpose is to carry data from electronics designed in Germany, attached to a detector built in the USA and installed by a Russian technician.  On the other end, a Japanese readout system brings the data to a trigger designed in Australia, following the plans of a Moroccan scientist. The filtered data is processed by software written in Sweden following the plans of a French physicist at a Dutch laboratory, and then distributed by grid middleware designed by a Brazilian student at CERN. This allows the data to be analyzed by a Chinese physicist in Argentina working in a group chaired by an Israeli researcher and overseen by a British coordinator.  And what about the cable tie?  No idea, but that doesn’t take away from its beauty.

There are 178 institutions from 38 different countries participating in the ATLAS Experiment, which is only the beginning.  When one considers the international make-up of each of the institutions, it would be safe to claim that well over 100 countries from all corners of the globe are represented in the collaboration.  While this rich diversity is a wonderful story, the real beauty lies in the commonality.

All of the scientists, with their diverse social, cultural and linguistic backgrounds, share a common goal: a commitment to the success of the experiment. The plastic cable tie might scratch, but it is tight and well placed; its cable is held correctly and the data are delivered, as expected. This enormous, complex enterprise works because the researchers who built it are driven by the essential nature of the mission: to improve our understanding of the world we live in. We share a common dedication to the future, we know it depends on research like this, and we are thrilled to be a part of it.

ATLAS Collaboration Members

ATLAS Collaboration members in discussion. What discoveries are in store this year? IMAGE: Claudia Marcelloni, ATLAS Experiment © 2008 CERN.

This spring, the LHC will restart at an energy level higher than any accelerator has ever achieved before. This will allow the researchers from ATLAS, as well as the thousands of other physicists from partner experiments sharing the accelerator, to explore the fundamental components of our universe in more detail than ever before. These scientists share a common dream of discovery that will manifest itself in the excitement of the coming months. Whether or not that discovery comes this year or some time in the future, Sector 13 of the ATLAS detector reflects all the beauty of that dream.


New books for the physics fan

Saturday, December 13th, 2014

This article appeared in symmetry on Dec. 9, 2014.

These recently published popular science books will help you catch up on particle physics news, knowledge and history. Image: Artwork Sandbox Studio, Chicago, with Ana Kova

These recently published popular science books will help you catch up on particle physics news, knowledge and history. Image: Artwork Sandbox Studio, Chicago, with Ana Kova

Looking to stay current on your particle physics knowledge? Here are 10 recent popular science books you might want to check out.


1. Faraday, Maxwell and the Electromagnetic Field: How Two Men Revolutionized Physics

Nancy Forbes, Basil Mahon

Classical unified field theory came from the realization that electricity, magnetism and light all can be explained with a single electromagnetic field.

There is no modern physics without classical unified field theory—heck, there are no electronics without classical unified field theory—and there is no classical unified field theory without Michael Faraday (1791-1867) and James Clerk Maxwell (1831-1879).

The unlikely partners, born four decades apart, shared the achievement of upending a view of the world that had prevailed since Isaac Newton.

“The extraordinary idea put forward by Faraday and Maxwell was that space itself acted as a repository of energy and a transmitter of forces,” write Nancy Forbes and Basil Mahon in Faraday, Maxwell and the Electromagnetic Field: How Two Men Revolutionized Physics.

Faraday was largely self-taught and made important realizations without the benefit of a formal education in mathematics, while Maxwell was regarded as among the most brilliant mathematical physicists of his time. This double biography examines their differing lives and explains how their combined work paved the way for modern physics.


2. The Cosmic Cocktail: Three Parts Dark Matter

Katherine Freese

In The Cosmic Cocktail: Three Parts Dark Matter, physicist Katherine Freese explores the critical place dark matter occupies in our understanding of the cosmos.

It has yet to be observed directly. But, she tells us, dark matter’s day of reckoning might not be far off.

“Some new particles, unlike any from our daily experience, might be tearing through the galaxy,” she writes. “Scientists have already found hints of detection in their experiments… The nature of dark matter is one of the greatest puzzles of modern science, and it is a puzzle we are on the verge of solving.”

Freese, now the new director of the Nordic Institute for Theoretical Physics in Stockholm, admits to spending a disproportionate amount of time on the dance floor of nearby Studio 54 when she should have been focused on her doctoral studies at Columbia University. But she also tells a compelling history of the search for dark matter, from the cantankerous Fritz Zwicky’s early predictions in the 1930s to hopes for an appearance when the Large Hadron Collider fires up again in 2015.


3. The Large Hadron Collider: The Extraordinary Story of the Higgs Boson and Other Stuff that will Blow Your Mind

Don Lincoln

“My goal was to give readers an inside account of the hunt and discovery,” says Fermilab scientist Don Lincoln, a member of CERN’s CMS experiment, of his latest book, The Large Hadron Collider: The Extraordinary Story of the Higgs Boson and Other Stuff that will Blow Your Mind. “Almost all of the similar books have been written by non-physicists and theorists. I went to all the meetings, so I have a unique perspective.”

In the book, Lincoln describes the process of the discovery of the Higgs boson—and explains that it is not the end of the story.

Even though the widely celebrated appearance of the Higgs particle confirmed theorists’ predictions, Lincoln maintains that the relatively light mass of the Higgs raises enough questions to keep physicists awake at night.

“The measurement is quite inconsistent with the Standard Model and the quantum corrections,” he says. “This absolutely screams that there is something still to be found and this could be supersymmetry, extra dimensions, composite Higgs bosons or some other kind of new physics. In short, we know there is something big we’re missing.”


4. The Most Wanted Particle: The Inside Story of the Hunt for the Higgs, the Heart of the Future of Physics

Jon Butterworth

“I wanted it to give readers a sense of what it really feels like to work in a big experiment at such an amazing time and what it meant,” says University College London physicist Jon Butterworth of his book The Most Wanted Particle: The Inside Story of the Hunt for the Higgs, the Heart of the Future of Physics. “This meant occasionally the physics had to go a bit deeper than the common analogies, but also there is a lot of non-physics story which hopefully captures the real-time excitement.”

Butterworth, who works on the ATLAS experiment at CERN, uses a personalized approach to convey a sense of scene. In one chapter, he describes explaining the Higgs discovery to British TV reporter Tom Clarke while the two shoot pool.

He also uses his current hometown in England to describe his workplace at CERN, comparing the size of the Large Hadron Collider tunnel to the size of the London Underground.

The book, released in the UK in May under the title Smashing Physics: Inside the World’s Biggest Experiment, will be released in the US in January 2015.


5. The Perfect Wave: With Neutrinos at the Boundary of Space and Time

Heinrich Pas

Heinrich Pas, a theorist at the Technical University of Dortmund in Germany, studies neutrinos, particles that seem to defy the rules but may hold answers to the deepest questions of the universe.

In The Perfect Wave: With Neutrinos at the Boundary of Space and Time, Pas explains how powerful processes in the cosmos—from the fusion that lights the sun to the magnificent explosions of supernovae—are bound up in the workings of the mysterious particles.

“It is a story of an elementary particle that, just like the Silver Surfer in the superhero cartoons, surfs to the boundaries of knowledge, of the universe and of time itself,” Pas writes. “A story that captivates you as it sucks you into a maelstrom like an oversized wonderland. Jump on your board and hold tight.”


6. The Science of Interstellar

Kip Thorne

Kip S. Thorne, the Feynman Professor of Theoretical Physics Emeritus at Caltech, served as the executive producer for scientific credibility (and flexibility) on the space epic Interstellar. He explains that work in the book The Science of Interstellar.

In the film, astronaut Cooper (Matthew McConaughey) takes leaps and bounds over, under, around and through black holes and wormholes on his quest to find a refugee planet for the population of Earth, whose food supply is devastated by global blight.

Thorne writes that “[s]ome of the science is known to be true, some of it is an educated guess, and some is speculation.”

But he takes all of it seriously; Thorne and his colleagues even wrote a scientific paper based on their computer simulations of the movie’s black hole.


7. The Singular Universe and the Reality of Time

Roberto Mangabeira Unger, Lee Smolin

Physicist Lee Smolin of Canada’s Perimeter Institute for Theoretical Physics, author of the controversial book The Trouble With Physics, collaborated with philosopher and politician Roberto Mangabeira Unger on the new book The Singular Universe and the Reality of Time.

In it, Smolin and Unger argue against the idea of the multiverse and declare that it is time to view the cosmos as being governed by laws that are evolving rather than laws that are immutable. They contend that, “everything changes sooner or later, including change itself. The laws of nature are not exempt from this impermanence.”


8. Time in Powers of Ten: Natural Phenomena and their Timescales

Gerard ‘t Hooft, Stefan Vandoren

In Time in Powers of Ten: Natural Phenomena and their Timescales, Nobel Laureate Gerard ‘t Hooft and theorist Stefan Vandoren, both of Utrecht University in the Netherlands, step back and forth in time from the minutest fractions of a second to the age of the universe and beyond. Observations range from the orbits and rotations of planets and stars, down to the decay times of atoms and elementary particles and back to geological time scales.

“The smallest matter mankind has studied moves considerably faster than the quickest computing processes of the most expeditious machine; while on the other side of the timescale we see planets, stars and entire galaxies of unimaginably old age, some billions of years,” ‘t Hooft and Vandoren write. “Scientists believe they know almost exactly how old the universe is, but even its seemingly eternal lifetime does not constitute a limit for physicists’ research.”


9. Travelling to Infinity: The True Story Behind the Theory of Everything

Jane Hawking

In Travelling to Infinity: The True Story Behind the Theory of Everything, readers are introduced to a young, floppy-haired Stephen Hawking through the eyes of his first wife, Jane Hawking (née Wilde). Hawking published versions of this book in both 1999 and 2007, and the book was reissued this year to accompany the film adaptation, The Theory of Everything.

In the book, Jane describes an early impression of Stephen from a New Year’s party in 1963: “Clearly here was someone, like me, who tended to stumble through life and managed to see the funny side of situations. Someone who, like me, was fairly shy, yet not averse to sharing his opinions, someone who unlike me had developed a sense of his own worth and had the effrontery to convey it.”

Here is a love story in which love is not enough. Hawking leaves and marries one of the nurses who tended him. Jane marries an old family friend. The two have reconciled and are on amicable terms—a good thing when the person writing your life story is your former spouse.


10. What If? Serious Scientific Answers to Absurd Hypothetical Questions

Randall Munroe

Randall Munroe’s stick-figure web comic strip, xkcd, comes with a warning: “This comic occasionally contains strong language (which may be unsuitable for children), unusual humor (which may be unsuitable for adults), and advanced mathematics (which may be unsuitable for liberal-arts majors).”

There are no dumb questions, only humorous and provocative answers from Munroe, a former NASA roboticist, in his book What If? Serious Scientific Answers to Absurd Hypothetical Questions. For example:

“Q – What would happen if the Earth and all terrestrial objects stopped spinning, but the atmosphere retained its velocity?

“A – Nearly everyone would die. THEN things would get interesting…”

In “What If?” what seems like the end is often just the beginning.

Mike Perricone


Geometry and interactions

Tuesday, November 25th, 2014

Or, how do we mathematically describe the interaction of particles?

In my previous post, I addressed some questions concerning the nature of the wavefunction, the most truthful mathematical representation of a particle. Now let us make this simple idea more complete, getting closer to the deep mathematical structure of particle physics. This post is a bit more “mathematical” than the last, and will likely make the most sense to those who have taken a calculus course. But if you bear with me, you may also come to discover that this makes particle interactions even more attractive!

The field theory approach considers wavefunctions as fields. In the same way as the temperature field \(T(x,t)\) gives the value of the temperature in a room at space \(x\) and time \(t\), the wavefunction \(\phi (x,t)\) quantifies the probability of presence of a particle at space point \(x\) and time \(t\).
Cool! But if this sounds too abstract to you, then you should remember what Max Planck said concerning the rise of quantum physics: “The increasing distance between the image of the physical world and our common-sense perception of it simply indicates that we are gradually getting closer to reality”.

Almost all current studies in particle physics focus on interactions and decays of particles. How does the concept of interaction fit into the mathematical scheme?

The mother of all the properties of particles is called the Lagrangian function. Through this object a lot of properties of the theory can be computed. Here let’s consider the Lagrangian function for a complex scalar field without mass (one of the simplest available), representing particles with electric charge and no spin:

\(L(x) = \partial_\mu \phi(x)^* \partial^\mu \phi(x) \).

Mmm… Is it just a bunch of derivatives of fields? Not really. What do we mean when we read \(\phi(x)\)? Mathematically, we are considering \(\phi\) as a vector living in a vector space “attached” to the space-time point \(x\). For the nerds of geometry, we are dealing with fiber bundles, structures that can be represented pictorially in this way:


Click on image for larger version

The important consequence is that, if \(x\) and \(y\) are two different space-time points, a field \(\phi(x)\) lives in a different vector space (fiber) with respect to \(\phi(y)\)! For this reason, we are not allowed to perform operations with them, like taking their sum or difference (it’s like comparing a pear with an apple… either sum two apples or two pears, please). This feature is highly non-trivial, because it changes the way we need to think about derivatives.

In the \(L\) function we have terms containing derivatives of the field \(\phi(x)\). Doing this, we are actually taking the difference of the value of the field at two different space-time points. But … we just outlined that we are not allowed to do it! How can we solve this issue?

If we want to compare fields pertaining to the same vector space, we need to slightly modify the notion of derivative introducing the covariant derivative \(D\):

\( D_\mu = \partial_\mu + ig A_\mu(x) \).

Here, on top of the derivative \(\partial\), there is the action of the “connection” \(A(x)\), a structure which takes care of “moving” all the fields in the same vector space, and eventually allows us to compare apples with apples and pears with pears.
So, a better way to write down the Lagrangian function is:

\(L(x) = D_\mu \phi(x)^* D^\mu \phi(x) \).

If we expand \(D\) in terms of the derivative and the connection, \(L\) reads:

\(L(x) = \partial_\mu \phi(x)^* \partial^\mu \phi(x) +ig A_\mu (\partial^\mu \phi^* \phi – \phi^* \partial^\mu \phi) + g^2 A^2 \phi^* \phi \).

Do you recognize the role of these three terms? The first one represents the propagation of the field \(\phi\). The last two are responsible for the interactions between the fields \(\phi, \phi^*\) and the \(A\) field, referred to as the “photon” in this context.


Click on image for larger version

This slightly hand-waving argument involving fields and space-time is a simple handle to understand how the interactions among particles emerge as a geometric feature of the theory.

If we consider more sophisticated fields with spin and color charges, the argument doesn’t change. We need to consider a more refined “connection” \(A\), and we could see the physical interactions among quarks and gluons (namely QCD, Quantum Chromo Dynamics) emerging just from the mathematics.

 Probably the professor of geometry in my undergrad course would call this explanation “Spaghetti Mathematics”, but I think it can give you a flavor of the mathematical subtleties involved in the theory of particle physics.


I feel it mine

Tuesday, October 21st, 2014

On Saturday, 4 October, Nikhef – the Dutch National Institute for Subatomic Physics where I spend long days and efforts – opened its doors, labs and facilities to the public. In addition to Nikhef, all the other institutes located in the so-called “Science Park” – the scientific district located in the east part of Amsterdam – welcomed people all day long.

It’s the second “Open Day” that I’ve attended, both as a guest and as guide. Together with my fellow theoreticians we provided answers and explanations to people’s questions and curiosities, standing in the “Big Bang Theory Corner” of the main hall. Each department in Nikhef arranged its own stand and activities, and there were plenty of things to be amazed at to cover the entire day.

The research institutes in Science Park (and outside it) offer a good overview of the concept of research, looking for what is beyond the current status of knowledge. “Verder kijken”, or looking further, is the motto of Vrije Universiteit Amsterdam, my Dutch alma mater.

I deeply like this attitude of research, the willingness to investigating what’s around the corner. As they like to define themselves, Dutch people are “future oriented”: this is manifest in several things, from the way they read the clock (“half past seven” becomes “half before eight” in Dutch) to some peculiarities of the city itself, like the presence of a lot of cultural and research institutes.

This abundance of institutes, museums, exhibitions, public libraries, music festivals, art spaces, and independent cinemas makes me feel this city as cultural place. People interact with culture in its many manifestations and are connected to it in a more dynamic way than if they were only surrounded by historical and artistic.

Back to the Open Day and Nikhef, I was pleased to see lots of people, families with kids running here and there, checking out delicate instruments with their curious hands, and groups of guys and girls (also someone who looked like he had come straight from a skate-park) stopping by and looking around as if it were their own courtyard.

The following pictures give some examples of the ongoing activities:

We had a model of the ATLAS detector built with Legos: amazing!


Copyright Nikhef

And not only toy-models. We had also true detectors, like a cloud chamber that allowed visitors to see the traces of particles passing by!


Copyright Nikhef

Weak force and anti-matter are also cool, right?


Copyright Nikhef

The majority of people here (not me) are blond and/or tall, but not tall enough to see cosmic rays with just their eyes… So, please ask the experts!


Copyright Nikhef

I think I can summarize the huge impact and the benefit of such a cool day with the words of one man who stopped by one of the experimental setups. He listened to the careful (but a bit fuzzy) explanation provided by one of the students, and said “Thanks. Now I feel it mine too.”

Many more photos are available here: enjoy!


Why pure research?

Thursday, October 2nd, 2014

With my first post on Quantum Diaries I will not address a technical topic; instead, I would like to talk about the act (or art) of “studying” itself. In particular, why do we care about fundamental research, pure knowledge without any practical purpose or immediate application?

A. Flexner in 1939 authored a contribution to Harper’s Magazine (issue 179) named “The usefulness of useless knowledge”. He opens the discussion with an interesting question: “Is it not a curios fact that in a world steeped in irrational hatreds which threaten civilization itself, men and women – old and young – detach themselves wholly or partly from the angry current of daily life to devote themselves to the cultivation of beauty, to the extension of knowledge […] ?”

Nowadays this interrogative is still present, and probably the need for a satisfactory answer is even stronger.

From a pragmatic point of view, we can argue that there are many important applications and spin-offs of theoretical investigations into the deep structure of Nature that did not arise immediately after the scientific discoveries. This is, for example, the case of QED and antimatter, the theories for which date back to the 1920s and are nowadays exploited in hospitals for imaging purposes (like in PET, positron emission tomography). The most important discoveries affecting our everyday life, from electricity to the energy bounded in the atom, came from completely pure and theoretical studies: electricity and magnetism, summarized in Maxwell’s equations, and quantum mechanics are shining examples.

It may seem that it is just a matter of time: “Wait enough, and something useful will eventually pop out of these abstract studies!” True. But that would not be the most important answer. To me this is: “Pure research is important because it generates knowledge and education”. It is our own contribution to the understanding of Nature, a short but important step in a marvelous challenge set up by the human mind.

Personally, I find that research into the yet unknown aspects of Nature responds to some partly conscious and partly unconscious desires. Intellectual achievements provide a genuine ‘spiritual’ satisfaction, peculiar to the art of studying. For sake of truth I must say that there are also a lot of dark sides: frustration, stress, graduate-depression effects, geographical and economic instability and so on. But leaving for a while all these troubles aside, I think I am pretty lucky in doing this job.


Books, the source of my knowledge

During difficult times from the economic point of view, it is legitimate to ask also “Why spend a lot of money on expensive experiments like the Large Hadron Collider?” or “Why fund abstract research in labs and universities instead of investing in more socially useful studies?”

We could answer by stressing again the fact that many of the best innovations came from the fuzziest studies. But in my mind the ultimate answer, once for all, relies in the power of generating culture, and education through its diffusion. Everything occurs within our possibilities and limitations. A willingness to learn, a passion for teaching, blackboards, books and (super)computers: these are our tools.

Citing again Flexner’s paper: “The mere fact spiritual and intellectual freedoms bring satisfaction to an individual soul bent upon its own purification and elevation is all the justification that they need. […] A poem, a symphony, a painting, a mathematical truth, a new scientific fact, all bear in themselves all the justification that universities, colleges and institutes of research need or require.”

Last but not least, it is remarkable to think about how many people from different parts of the world may have met and collaborated while questing together after knowledge. This may seem a drop in the ocean, but research daily contributes in generating a culture of peace and cooperation among people with different cultural backgrounds. And that is for sure one of the more important practical spin-offs.


Watch Fermilab Deputy Director Joe Lykken in the latest entry in Huffington Post's "Talk Nerdy To Me" video series.

Watch Fermilab Deputy Director Joe Lykken in the latest entry in Huffington Post’s “Talk Nerdy To Me” video series.

What’s the smallest thing in the universe? Check out the latest entry in Huffington Post‘s Talk Nerdy to Me video series. Host Jacqueline Howard takes the viewer inside Fermilab and explains how scientists look for the smallest components that make up our world. Fermilab Deputy Director Joe Lykken talks about the new discoveries we hope to make in exploring the the subatomic realm.

View the 3-minute video at Huffington Post.


I know that the majority of the posts I’ve written have focused on physics issues and results, specifically those related to LHCb. I’d like to take this opportunity, however, to focus on the development of the field of High Energy Physics (HEP) and beyond.

As some of you know, in 2013, we witnessed an effectively year-long conversation about the state of our field, called Snowmass. This process is meant to collect scientists in the field, young and old alike, and ask them what the pressing issues for the development of our field are. In essence, it’s a “hey, stop working on your analysis for a second and let’s talk about the big issues” meeting. They came out with a comprehensive list of questions and also a bunch of working papers about the discussions. If you’re interested, go look at the website. The process was separated into “frontiers,” or groups that the US funding agencies put together to divide the field into the groups that they saw fit. I’ll keep my personal views on the “frontiers” language for a different day, and instead share a much more apt interpretation of the frontiers, which emerged from Jonathan Asaadi, of Snowmass Young and Quantum Diaries. He emphasizes that we are coming together to tackle the biggest problems as a team, as opposed to dividing into groups, illustrated as Voltron in his slide below.


Slide from presentation of Jonathan Asaadi at the USLUO (now USLUA) 2013 annual meeting in Madison, Wisconsin. The point here is collaboration between frontiers to solve the biggest problems, rather than division into separate groups.

And that’s just what happened. While I willingly admit that I had zero involvement in this process aside from taking the Snowmass Young survey, I still agree with the conclusions which were reached about what the future of our field should look like. Again, I highly encourage you to go look at the outcome.

Usually, this would be the end of the story, but this year, the recommendations from Snowmass were passed to a group called P5 (Particle Physics Project Prioritization Panel). The point of this panel was to review the findings of Snowmass and come up with a larger plan about how the future of HEP will proceed. The big ideas had effectively been gathered, now the hard questions about which projects can pursue these questions effectively are being asked. This specifically focuses on what the game plan will be for HEP over the next 10-20 years, and identifies the distinct physics reach in a variety of budget situations. Their recommendation will be passed to HEPAP (High Energy Physics Advisory Panel), which reviews the findings, then passes its recommendation to the US government and funding agencies. The P5 findings will be presented to HEPAP  on May 22nd, 2014 at 10 AM, EST. I invite you to listen to the presentation live here. The preliminary executive report and white paper can be found after 10 EST on the 22nd of May on the same site, as I understand.

This is a big deal.

There are two main points here. First, 10-20 years is a long time, and any sort of recommendation about the future of the field over such a long period will be a hard one. P5 has gone through the hard numbers under many different budget scenarios to maximize the science reach that the US is capable of. Looking at the larger political picture, in 2013, the US also entered the Sequester, which cut spending across the board and had wide implications for not only the US but worldwide. This is a testament to the tight budget constraints that we are working in now, and will most certainly face in the future. Even considering such a process as P5 shows that the HEP community recognizes this point, and understands that without well defined goals and tough considerations of how to achieve them, we will endanger the future funding of any project in the US or with US involvement.

Without this process, we will endanger future funding of US HEP.

We can take this one step further with a bit more concrete example. The majority of HEP workings are done through international collaboration, both experiment and theory alike. If any member of such a collaboration does not pull their weight, it puts the entire project into jeopardy. Take, for example, the US ATLAS and CMS programs, which have 23% and 33% involvement from the US, respectively, in both analysis and detector R&D. If these projects were cut drastically over the next years, there would have to be a massive rethinking about the strategies of their upgrades, not to mention possible lack of manpower. Not only would this delay one of the goals outlined by Snowmass, to use the Higgs as a discovery tool, but would also put into question the role of the US in the future of HEP. This is a simple example, but is not outside the realm of possibility.

The second point is how to make sure a situation like this does not happen.

I cannot say that communication of the importance of this process has been stellar. A quick google search yields no mainstream news articles about the process, nor the impact. In my opinion, this is a travesty and that’s the reason why I am writing this post. Symmetry Magazine also, just today, came out with an article about the process. Young members of our community who were not necessarily involved in Snowmass, but seem to know about Snowmass, do not really know about P5 or HEPAP. I may be wrong, but I draw this conclusion from a number of conversations I’ve had at CERN with US postdocs and students. Nonetheless, people are quite adamant about making sure that the US does continue to play a role in the future of HEP. This is true across HEP, the funding agencies and the members of Congress. (I can say this as I went on a trip with the USLUO, FNAL and SLAC representatives to lobby congress on behalf of HEP in March of this year, and this is the sentiment which I received.) So the first step is informing the public about what we’re doing and why.

The stuff we do is really cool! We’re all organized around how to solve the biggest issues facing physics! Getting the word out about this is key.

Go talk to your neighbor!

Go talk to your local physicist!

Go talk to your congressperson!

Just talk about physics! Talk about why it excites you and talk about why it’s interesting to explore! Maybe leave out the CLs plots, though. If you didn’t know, there’s also a whole mess of things that HEP is good for besides colliding particles! See this site for a few.

The final step is understanding the process. The biggest worry I have is what happens after HEPAP reviews the P5 recommendations. We, as a community, have to be willing to endure the pains of this process. Good science will be excluded. However, there are not infinite funds, nor was a guarantee of funding ever given. Recognition of this, while focusing on the big problems at hand and thinking about how to work within the means allowed is *the point* of the conversation. The better question is, will we emerge from the process unified or split? Will we get behind the Snowmass process and answer the questions posed to us, or fight about how to answer them? I certainly hope the answer is that we will unify, as we unified for Snowmass.

An allegorical example is from a slide from Nima Arkani-Hamed at Pheno2014, shown in the picture.

One slide from Nima Arkani-Hamed's presentation at Pheno2014

One slide from Nima Arkani-Hamed’s presentation at Pheno2014


The take home point is this: If we went through the exercise of Snowmass, and cannot pull our efforts together to the wishes of the community, are we going to survive? I would prefer to ask a different question: Will we not, as a community, take the opportunity to answer the biggest questions facing physics today?

We’ll see on the 22nd and beyond.



Update: May 27, 2014


As posted in the comments, the full report can be found here, the presentation given by Steve Ritz, chair of P5 can be found here, and the full P5 report can be found here.  Additionally, Symmetry Magazine has a very nice piece on the report itself. As they state in the update at the bottom of the page, HEPAP voted to accept the report.


Massive thoughts

Thursday, April 24th, 2014

This article appeared in symmetry on April 24, 2014.

The Higgs boson and the neutrino fascinate the general public and particle physicists alike. Why is that?

The Higgs boson and the neutrino fascinate the general public and particle physicists alike. Why is that?

If there are two particles that everyone has read about in the news lately, it’s the Higgs boson and the neutrino. Why do we continue to be fascinated by these two particles?

As just about everyone now knows, the Higgs boson is integrally connected to the field that gives particles their mass. But the excitement of this discovery isn’t over; now we need to figure out how this actually works and whether it explains everything about how particles get their mass. With time, this knowledge is likely to affect daily life.

One way it could possibly bridge the gap between fundamental research and the commercial market, I believe, is in batteries. The ultimate battery in nature is mass. The expression E=mc2 is a statement of that fact. During the early moments of the universe, all particles were massless and traveling at the speed of light. Once the Higgs mechanism turned on, particles suddenly began interacting with the field and, in this process, converted their energy into what we now refer to as mass. In a recent address to the Canadian Nuclear Society, I suggested that if engineers of the future could learn how to manipulate the Higgs field (to “turn it on and off”), then we would have developed the ultimate energy source and the best battery nature has created. This idea definitely belongs in the science-fiction category, but remember that progress in science is driven by thinking “outside the box!”

This sort of thinking comes from looking at the Higgs from another angle. According to the Standard Model, many particles come in left-handed and right-handed versions (in the former, the particle’s direction of spin matches its direction of motion, while in the latter, they are opposite).

Keeping this fact in mind, let’s look at the mass of the familiar electron as an example. When we say that the mass of the electron is created by interactions with the Higgs field, we can think of this as the Higgs field rapidly changing a left-handed electron into a right-handed electron, and vice versa. This switching back and forth is energy and, through E=mc2, energy is mass. A heavier particle like the top quark would experience this flipping at a much higher frequency than a lighter particle like the electron. As we learn more about how this process works, I encourage physicists to also seek applications of that knowledge.

And what about neutrinos? Do they get their mass from the Higgs field or in a completely different way? Once thought to be massless, neutrinos are now known to have a tiny mass. If the Higgs mechanism is responsible for that mass, there must exist both a left-handed and a right-handed neutrino. A good number of physicists think that both are out there, but we do not yet know. That knowledge may help us understand why the neutrino mass is tiny, as well as why there is more matter than antimatter in the universe—one of the most important questions facing our field of particle physics.

But since the neutrino is a neutral particle, the story gets more interesting. It may instead be possible that there is another type of mass. Referred to as a Majorana mass, it is not a mass described by the flipping of left- and right-handed neutrinos back and forth, but it is “intrinsic,” not derived from any kind of “motional energy.” I expect that the efforts by our field of particle physics, in the collective sense, will pursue the questions associated with both the Higgs boson and the neutrino with enthusiasm, and that the results will lead to advancements we can’t even imagine today.

Nigel Lockyer, Fermilab director


Data recall at the LHC?

Tuesday, April 1st, 2014

In a stunning turn of events, Large Hadron Collider (LHC) management announced a recall and review of thousands of results that came from its four main detectors, ATLAS, CMS, LHCb and ALICE, in the course of the past several years when it learned that the ignition switches used to start the LHC accelerator (see the enclosed image) might have been produced by GM. Image

GM’s CEO, A. Ibarra, who is better known in the scientific world for the famous Davidson-Ibarra bound in leptogenesis, will be testifying on the Capitol Hill today. This new revelation will definitely add new questions to the already long list of queries to be addressed by the embattled CEO. In particular, the infamous LHC disaster that happened almost six years ago on 10 September 2008 and cost taxpayers over 21Million dollars to fix, has long suspected been caused by a magnet quench. However, new data indicate that it might have been caused by too much paper accidentally placed on a switch by a graduate student, who was on duty that day.

“We want to know why it took LHC management more than five years to issue that recall”, an unidentified US Government official said in the interview, “We want to know what is being done to correct the problem. From our side, we do everything humanly possible to accommodate US high energy particle physics researchers and help them to avoid such problems in the future.  For example, we included a 6.6% cut in US HEP funding in the President’s 2015 budget request.” He added, “We suspected that something might be going on at the LHC after it was convincingly proven to us at our weekly seminar that the detected Higgs boson is ‘simply one Xenon atom of the 1 trillion 167 billion 20 million Xenon atoms which there are in the LHC!'”

This is not the first time accelerators cause physicists to rethink their results and designs. For example, last year Japanese scientists had to overcome the problem of unintended acceleration of positrons at their flagship facility KEK.

At this point, it is not clear how GM’s ignition switches problems would affect funding of operations at the National Ignition Facility in Livermore, CA.



A second chance at sight

Monday, February 17th, 2014

This article appeared in symmetry on February 4, 2014.

Silicon microstrip detectors, a staple in particle physics experiments, provide information that may be critical to restoring vision to some who lost it.

Silicon microstrip detectors, a staple in particle physics experiments, provide information that may be critical to restoring vision to some who lost it.

In 1995, physicist Alan Litke co-wrote a particularly prescient article for Scientific American about potential uses for an emerging technology called the silicon microstrip detector. With its unprecedented precision, this technology was already helping scientists search for the top quark and, Litke wrote, it could help discover the elusive Higgs boson. He further speculated that it could perhaps also begin to uncover some of the many mysteries of the brain.

As the article went to press, physicists at Fermilab announced the discovery of the top quark, using those very same silicon detectors. In 2012, the world celebrated the discovery of the Higgs boson, aided by silicon microstrip detectors at CERN. Now Litke’s third premonition is also coming true: His work with silicon microstrip detectors and slices of retinal tissue is leading to developments in neurobiology that are starting to help people with certain kinds of damage to their vision to see.

“The starting point and the motivation was fundamental physics,” says Litke, who splits his time between University of California, Santa Cruz, and CERN. “But once you have this wonderful technology, you can think about applying it to many other fields.”

Silicon microstrip detectors use a thin slab of silicon, implanted with an array of diode strips, to detect charged particles. As a particle passes through the silicon, a localized current is generated. This current can be detected on the nearby strips and measured with high spatial resolution and accuracy.

Litke and collaborators with expertise in, and inspiration from, the development of silicon microstrip detectors, fabricated two-dimensional arrays of microscopic electrodes to study the complex circuitry of the retina. In the experiments, a slice of retinal tissue is placed on top of one of the arrays. Then a movie—a variety of visual stimuli including flashing checkerboards and moving bars—is focused on the input neurons of the retina, and the electrical signals generated by hundreds of the retina’s output neurons are simultaneously recorded. This electrical activity is what would normally be sent as signals to the brain and translated into visual perceptions.

This process allowed Litke and his collaborators to help decipher the retina’s coded messages to the brain and to create a functional connectivity map of the retina, showing the strengths of connections between the input and output neurons. That in itself was important to neurobiology, but Litke wanted to take this research further, to not just record neural activity but also to stimulate it. Litke and his team designed a system in which they stimulate retinal and brain tissue with precise electrical signals and study the kinds of signals the tissue produces in response.

Such observations have led to an outpouring of new neurobiology and biomedical applications, including studies for the design of a retinal prosthesis, a device that can restore sight. In a disease like retinitis pigmentosa or age-related macular degeneration, the eye’s output system to the brain is fine, but the input system has degraded.

In one version of a retinal prosthesis, a patient could wear a small video camera—something similar to Google Glass. A small computer would process the collected images and generate a pattern of electrical signals that would, in turn, stimulate the retina’s output neurons. In this way, the pattern of electrical signals that a naturally functioning eye would create could be replicated. The studies with the stimulation/recording system are being carried out in collaboration with neurobiologist E. J. Chichilnisky (Salk Institute and Stanford University) and physicist Pawel Hottowy (AGH University of Science and Technology, Krakow). The interdisciplinary and international character of the research highlights its origins in high energy physics.

In another approach, the degraded input neurons—the neurons that convert light into electrical signals—are functionally replaced by a two-dimensional array of silicon photodiodes. Daniel Palanker, an associate professor at Stanford University, has been using Litke’s arrays, in collaboration with Alexander Sher, an assistant professor at UCSC, who completed his postdoctoral work with Litke, to study how a prosthesis of this type would interact with a retina. Palanker and Sher are also researching retinal plasticity and have discovered that, in patients whose eyes have been treated with lasers, which can cause scar tissue, healthy cells sometimes migrate into an area where cells have died.

“I’m not sure we would be able to get this kind of information without these arrays,” Palanker says. “We use them all the time. It’s absolutely brilliant technology.”

Litke’s physics-inspired technology is continuing to play a role in the development of neurobiology. In 2013, President Obama announced the BRAIN—Brain Research through Advancing Innovative Neurotechnologies—Initiative, with the aim of mapping the entire neural circuitry of the human brain. A Nature Methods paper laying out the initiative’s scientific priorities noted that “advances in the last decade have made it possible to measure neural activities in large ensembles of neurons,” citing Litke’s arrays.

“The technology has enabled initial studies that now have contributed to this BRAIN Initiative,” Litke says. “That comes from the Higgs boson. That’s an amazing chain.”