## Posts Tagged ‘particle physics’

### 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!

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!

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

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!

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.

### Latest video in Huffington Post’s Talk Nerdy to Me video series

Monday, August 11th, 2014

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.

### Snowmass, P5, HEPAP, HEP and what it all means to you

Tuesday, May 20th, 2014

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 local physicist!

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

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

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.

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

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.”

### How particle physics can save your life

Monday, November 11th, 2013

A version of this article appeared in symmetry on Nov. 5, 2013.

From new medicines to cancer treatment, the tools of particle physics play an important role in hospitals around the world. Image: Sandbox Studio

The same particle-physics technology used to understand the universe is also used to improve health and medicine. Accelerators and detectors play an important role in diagnosing disease, shrinking tumors and sterilizing medical equipment. Large-scale computing makes it possible to determine which potential new drugs are most likely to work before starting large-scale human trials. And particle-physics-trained scientists serve as medical physicists, making sure it all works as planned.

#### Sterilizing instruments and supplies

Particle physics technology can be used to disinfect syringes, bandages, scalpels, stethoscopes and other tools without damaging them. Medical equipment is sent through a series of small particle accelerators and bombarded with beams of electrons or X-rays. In a matter of seconds, the beams eradicate any surface microbes.

#### Distributed and grid computing

The World Wide Web is not the only computing advancement to come out of particle physics. In order to cope with the huge amount of data produced by experiments, particle physicists developed a network of grids allowing multiple users to share computing power and storage capacity. The grid concept has a number of uses in the medical field, including screening drug candidates to determine which ones are most likely to fight disease.

#### Simulation

Practice makes perfect, and when it comes to our health, the closer to perfect, the better. So some doctors and medical physicists are designing treatment plans using modeling tools developed for particle physics to predetermine the electromagnetic and nuclear interactions of particles with tissue. In radiation therapy, this software can help doctors understand what will happen when a beam of particles passes through a patient’s body.

#### Semiconductors

In the heart of particle physics detectors around the world, hundreds of detectors made with silicon semiconductors splay out around particle collision points, tracking charged particles to create pictures of their paths. Physicians make use of this semiconductor technology in many medical devices, including semiconductor lasers. These discrete beams of high-intensity light are perfect for delicate operations like eye surgery.

#### Particle-physics-trained staff

Many particle physicists can be found inside hospitals and clinics. Particle physicists who cross over into the medical field often come with extensive training in the operation and maintenance of accelerators. With their thorough understanding of particle beams, these scientists are highly valued as specialists who manage the medical imaging systems that detect tumors and who operate the accelerator beams that kill cancer cells.

#### PET

PET scanners are common tools that let medical professionals examine organs and tissues inside the body. The PET scanner’s genealogy traces back to detector technologies developed in the 1980s to identify individual photons in particle physics experiments. It may sound strange, but PET scanners use antimatter produced inside the body. When a special tracer is injected into a patient, a type of radioactive decay occurs, emitting positrons—the antimatter counterparts to electrons. These positrons annihilate with nearby electrons, releasing bursts of photons. The photons are detected and compiled into three-dimensional images.

#### MRI

Magnetic resonance imaging, the basic principles of which emerged from early research in physics, is more discerning than traditional screening, which sometimes can’t make out tumors hidden within dense tissue. When a patient is subjected to the powerful magnetic field inside an MRI machine, atoms inside his body line up in the direction of the field. A radio frequency current is temporarily switched on, causing the protons inside those atoms to flip around until the radio frequency is removed. At that point, the protons pivot back into place—each at a different rate. The varying rates are measured, allowing scientists to determine what’s happening inside the living tissue.

#### Cancer treatment

One of the most effective techniques to fight cancer uses the same technology particle physicists employ to accelerate particle beams to nearly the speed of light. There are more than 17,000 particle accelerators worldwide used for the diagnosis and treatment of disease. Doctors exchange a scalpel for a beam of charged particles, which they aim at cancerous tissue, killing malignant cells by destroying DNA strands in the nuclei while sparing the surrounding healthy tissue.

Kelly Izlar

### Answers to big questions could lie in small particles

Thursday, November 7th, 2013

Scientists planning the next decade in US particle physics consider what we can learn from fundamental particles called neutrinos.

We live in a galaxy permeated with tiny particles called neutrinos. Trillions of them stream through each of us each second. They are everywhere, but much remains a mystery about these particles, which could be key to understanding our universe.

During the first weekend of November, a couple of hundred scientists gathered at Fermilab to discuss ways to unravel the mystery of neutrinos.

The meeting was part of the process of planning the next decade of particle physics research for the United States. A group of 25 scientists on the Particle Physics Project Prioritization Panel, or P5, is studying an abundance of research opportunities in particle physics. In spring they will make recommendations about which of these opportunities should take priority in the United States.

In their first town-hall meeting, the group dedicated a full day to discussing neutrino research.

“Neutrinos have already revealed many properties of the universe, some of them unexpected,” says Antonio Masiero, the vice president of Italy’s National Institute of Nuclear Physics, who provided an international perspective at the meeting. “They still keep secrets which could reveal aspects which are new and answer questions which are still open.”

Neutrinos might help scientists understand what caused the imbalance between matter and antimatter that allowed our universe to form. They could give insight into why particles seem naturally to be organized into three generations. They could help reveal undiscovered principles of nature.

“The neutrino is still a mysterious particle,” says Fermilab physicist Vaia Papadimitriou, pictured above giving a presentation at the meeting. “When I was a graduate student, we didn’t even know neutrinos had masses.”

The next generations of neutrino experiments could reveal other surprises. For example, says Northwestern physicist Andre de Gouvea, neutrinos could turn out to be identical to antineutrinos. They could give scientists clues to the existence of undiscovered types of neutrinos, such as massive ones theorists think might have had a great influence early in the formation of the universe. Neutrinos could turn out to be the only fundamental particles that gain their mass from a source other than the just-discovered Higgs field.