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Richard Ruiz | Univ. of Pittsburgh | U.S.A.

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Photon Colliders: Making Matter from Light Since 1994

Tuesday, June 17th, 2014

Protons are the brave casualties in the search for new physics, but sometimes everybody lives.

Hi Folks,

The CERN Large Hadron Collider (LHC), history’s largest and most energetic proton collider, is currently being tuned up for another round of new discoveries. A Higgs boson, incredibly rare B meson decays, and evidence for vector boson fusion have already been identified, so there is great anticipation on what we may find during Run II.

Our discoveries, however, come at the cost of protons. During 2012, the ATLAS, CMS, and LHCb experiments collected a combined 48 fb-1 (48 “inverse femtobarns“), and another 12 fb-1 in 2011. To translate, an “inverse femtobarn” is a measure of proton collisions and  is the equivalent of 70 trillion proton-proton collisions. Hence, 60 fb-1 is equivalent to about 4,200 trillion proton-proton collisions, or 8,400 trillion protons. We hope to generate almost twice as much data per year when everything starts back up winter/spring 2015. You know, suddenly, @LHCproton‘s many fears of its day job make sense:

With so many protons spent in the name of science, one can reasonably ask

Is it possible to find new physics at the LHC without destroying a proton?

The answer is


Sometimes, just sometimes, if we are very lucky, two protons can pass each other, interact and make new particles, but remain intact and unbroken. It sounds mind-boggling, but it has been one of the best tests of quantum electrodynamics (QED), the theory of light and matter at small distances and large energies.

From Maxwell to Photon Beams at the LHC

The idea is simple, the consequences are huge, and goes like this: Protons, like electrons, muons and W bosons, are electrically charged, so they can absorb and emit light. Protons, like electrons, do not just radiate light at random. Light is emitted following very specific rules and travel/propagate in very specific directions, dictated by Maxwell’s equations of electrodynamics. However, the rules of quantum mechanics state that at large enough energies and small enough distances, in other words an environment like we have at the LHC, particles of light (called photons) will interact with each other, with a predicted probability. Yes, you read that correctly, quantum mechanics states that light interacts with itself at small enough distances. The more protons we accelerate in the LHC, the more photons are radiated from protons that remain intact, and the more likely two photons will interact with each other, producing matter we can observe with detectors! An example of such a process that has already by observed is the pair production of muons from photons:

Muon pair production from photon scattering via elastic photon emission from protons. Credit: CMS, JHEP 1201 (2012) 052

To understand this more, lets take a look at Maxwell’s Equations, named after Scottish physicist J. C. Maxwell but really represent seminal contributions of several people. Do not worry about the calculus, we will not be working out any equations here, only discussing their physical interpretation. Without further ado, here are the four laws of electrodynamics:


The very first law, Gauss’ law, tells us that since the proton has an electric charge, it also it the source of an electric field (E). The bottom equation, Ampere’s Law, tells us that if we have a moving electric charge (a proton circling the LHC ring for example), then both the moving electric field (E) and the electric current (J) will generate a magnetic field (B). In the LHC, however, we do not just have a moving beam of protons, but an accelerating beam of protons. This means that the magnetic field is changing with time as the proton circles around the collider. The third equation, Faraday’s law, tells us that when a magnetic field (B) changes with time, an electric field (E) is generated. But since we already have an electric field, the two fields add together into something that also changes with time, and we end up back at Ampere’s law (the bottom equation). This is when something special happens. Whenever a charged particle is accelerated, the electric and magnetic fields that are generated feed into each other and create a sort of perpetual feedback. We call it electromagnetic radiation, or light. Accelerating charged particles emit light.


Schematic representation of the strength of the electric (blue) and magnetic (red) fields as light propagates through space. Credit: Wikipedia

Maxwell’s equations  in fact tell us a bit more. They also tell us the direction in which light is emitted. The crosses and dots tell us whether things are perpendicular (at right angles) or parallel to each other. Specifically, they tell us that the generated magnetic field is always at right angles to both the electric field and direction the proton is travelling, and that light travels perpendicular to both the electric and magnetic field.  Since protons are travelling in a circle at the LHC, their tangential velocity, which always points forward, and their radial acceleration, which always points toward the center of the LHC ring, are always at right angles to each other. This crucial bit fixes the direction of the emitted light. As the protons travel in a circle, the generated electric field points in the direction of acceleration (the center); the generated magnetic is perpendicular to both of these, so it points upward if the proton is travelling in a counter-clockwise direction, or downward if the proton is travelling in a clockwise direction. The light must then always travel parallel to the proton! Along side the LHC proton beam is a hyper focused light beam! Technically speaking, this is called synchrotron radiation.


(a) Relative orientation of an electrically charged particle travelling in a circle and its electromagnetic field likes. (b) Synchrotron radiation emitted tangent to a circular path traversed by an electrically charged particle. Credit: Wikipedia

The last but still important step is to remember that all of this is happening at distances the size of a proton and smaller. In other words, at distances where quantum mechanics is important. At these small distances, it is appropriate to talk about individual pieces (quanta) of light, called photons. That beam of synchrotron radiation travelling parallel to the proton beam can appropriately be identified as a beam of photons.  In summary, along side the LHC proton beam is the LHC photon beam! This photon beam is radiated from the protons in the proton beam, but the protons remain intact and do not rupture as long as the momentum transfer to the photon beam is not too large. A very important note I want to make is that the photon beams do not travel in a circle; they travel in straight lines and are constantly leaving the proton beam. Synchrotron radiation continuously drains the LHC beams of energy, which is why the LHC beam must be continuously fed with more energy.

Making Matter from Light Since 1994

Synchrotron radiation has been around for quite sometime. Despite recent claims, the first evidence for direct production of matter from photon beams came in 1994  from the DELPHI experiment at the Large Electron Positron (LEP) Collider, the LHC’s predecessor at CERN. There are earlier reports of photon-photon scattering at colliders but I have been unable to track down the appropriate citations. Since 1994, evidence for photon-photon scattering has been observed by the Fermilab’s CDF experiment at the Tevatron, as reported by the CERN Courier, and there is even evidence for the pair production of muons and W bosons at the CMS Experiment. Excitingly, there has also been so research to a potential Higgs factory using a dedicated photon collider. This image shows a few photon-photon scattering processes that result in final-state bottom quark and anti-bottom quark pairs.

Various photon-photon scattering processes that result in final-state bottom quark and anti-bottom quark pairs. Credit: Phys.Rev. D79 (2009) 033002


We can expect to see much more from the LHC on this matter because photon beams offer a good handle on understanding the stability of proton beam themselves and are a potential avenue for new physics.

Until next time, happy colliding.

- Richard (@BraveLittleMuon)


And So Summer (Conferences) Begin

Friday, May 2nd, 2014

The summer conference season starts Monday and QD will be there at every turn.

Hi Folks,

On Monday, the University of Pittsburgh in the US has honor of kicking off the 2014 summer conference season with the Phenomenology 2014 Symposium, and on its tail will be the Americas Workshop on Linear Collider at Fermilab also in the US, and beyond that are more results from around the world. Notably, the International Conference on High Energy Physics (ICHEP 2014) will be held in Valencia, Spain, and Supersymmetry 2014: The International Conference on Supersymmetry and Unification of Fundamental Interactions will be at the University of Manchester in England. Both ICHEP and SUSY are biannual conferences, and the last time ICHEP was held the Higgs discovery was announced. Whatever great result is announced this summer, QD will be there…. and possibly even giving the talk. :) So check out the list below and start planning your summer getaway. (Note: For a great list of conferences/schools/and workshops that is regularly maintained, see Heather Logan ‘s (Carleton) conference page).

Happy Colliding

- richard (@BraveLittleMuon)

Phenomenology 2014 Symposium (#Pheno14)

Dates: 5-7 May. Host: University of Pittsburgh. Homepage


Americas Workshop on Linear Colliders 2014 (#AWLC14)

Dates: 12-16 May. Host: Fermilab.  Homepage

International Conference From the Planck Scale to the Electroweak Scale (#Planck14)

Dates: 26-30 May. Host: Institut des Cordeliers. Homepage

Muon Accelerator Program 2014 Spring Workshop (#Muon14)

Dates: 27-31 May. Host: Fermilab. Homepage

Large Hadron Collider Physics (LHCP) Conference (#LHCP14)

Dates:  2-7 June. Host: Brookhaven National Laboratory and Columbia University. Location: Columbia University. Homepage.

International Conference on Neutrino Physics and Astrophysics (#Neutrino14)

Dates:  2-7 June. Host: Boston University, Harvard University, Massachusetts Institute of Technology, and Tufts University. Location: Boston University. Homepage

LoopFest XIII (#Loop13)

Dates: 18-20 June. Host: New York City College of Technology. Homepage


7th Future Circular Collider / Tri- Large Electron Positron Physics Workshop (#TLEP)

Dates: 19-21 June. Host: CERN. Homepage

International Conference on High Energy Physics 2014 (#ICHEP14)

Dates: 2-9 July. Location: Valencia, Spain. Homepage

Coordinated Theoretical-Experimental Project on QCD Summer School (#CTEQ)

Dates: 8 – 18 July. Host: Peking University (PKU), Beijing. Homepage

Pre-SUSY 14 Summer School (#SUSY14)

Dates: 15-19 July. Host: University of Manchester. Homepage

Supersymmetry 2014 (#SUSY14)

Dates: 21-26 July. Host: University of Manchester. Homepage

SLAC Summer Institute (#SSI14)

Dates: 4-15 August. Host: SLAC. Homepage


Top Quarks… So Many Top Quarks

Wednesday, April 30th, 2014

Thousands of paper on top quarks exist. Why?

There are literally thousands of papers, collaboration notes, and conference notes with the words “Top” and “Quark” in the title. As of this post, there are 3,477 since 1979 listed on inSpires. There are many, many more that omit the word “quark”. And sure, this is meager compared to the 5,114 papers with the words “Higgs Boson” written since ’74, but that is over 50,000 pages of top quarks (estimating 15 pages/paper). To be fair, there are also many, many more that omit the word “boson”. But for further comparison, there are only 395 papers with a title including the words “Bottom Quark“, 211 with “Bottomonium“, and 125 with “Bottom Hadron“. So why are there so many papers written about the top quark? The answer is that the top quark is weird special.


A single top quark candidate event at the Collider Detector experiment at Fermilab. Credit: CDF Collaboration

The top quark is very heavy, about 185 times heavier than the proton and ranks as the heaviest known elementary particle in all the particle kingdom. The second heaviest quark, the bottom quark, is only 4 or 5 times heavier than the proton. If you or I were a proton, then a medium-to-large school bus (without any people) would be a top quark. In fact, the top quark is so heavy it can decay into a real (on-shell) W boson, which is roughly half its mass. The only other particle that can do this is the Higgs. Though it is rare, exceedingly rare, the top quark can decay into real Z  and Higgs bosons as well. Not even the Higgs can top that last feat.

Top quark decaying into real, on-shell W boson and bottom quark. Credit: DZero Collaboration

However, the top quark is still a quark. It has an electric charge that is 2/3 as large as the proton. It has an intrinsic angular momentum (spin) equal to the proton’s or electron’s spin. The top quark is also colored, meaning that is interacts with gluons and is influenced by the strong nuclear force (QCD). When colored objects (quarks and gluons) are produced at collider and fixed target experiments, they undergo a process called hadronization. Hadronization is when two colored objects are far away from one another and the strong nuclear attraction between the two becomes so strong that a pair of colored objects will spontaneously be produced in the space between them. These new colored particles will then form bound states with the old colored states. However, the process hadronization means that we only observe the bound states of colored objects and not the colored objects themselves. Physicists have to infer their properties from the physics of bound states…. or do we?


Colored objects before (L), during (Center L and Center R), and after (R) hadronization.

The onset of hadronization is typically occurs about 10-24 seconds after the creation of a colored object. Yes, that is 0.000000000000000000000001 seconds. That is incredibly fast and well beyond anything that can be done at an experiment. The mean lifetime of the top quark on the other hand is about 10-25 seconds. In other words, the top quark is much more likely to decay in to a W boson, its principle decay mode, than hadronize. By looking at the decays of the W boson, for example to an electron and an electron-neutrino, their angular distributions, and other kinematic properties, we can measure directly the top quark’s quantum numbers. The top quark is special because it is the only quark whose spin and charge quantum numbers we can measure directly.


Top quark decaying into real, on-shell W boson and bottom quark. The W boson can subsequently decay into a charged lepton and a neutrino or into a quark and anti-quark. Credit: DZero Collaboration

The top quark tells us much about the Standard Model of particle physics, but it also may be a window to new physics. Presently, no one has any idea why the top quark is so much heavier than the bottom quark, or why both are orders of magnitude heavier than the electron and muon. This is called the “Mass Hierarchy Problem” of the Standard Model and stems from the fact that the quark and lepton masses in the theory are not predicted but are taken as input parameters. This does not mean that the Standard Model is “wrong”. On the contrary, the model works very, very well; it is simply incomplete. Of course there are new models and hypotheses that offer explanations, but none have been verified by data.

However, thanks to the 2012 discovery of the Higgs boson, there is a new avenue that may shed light upon the mass hierarchy problem. We now know that quarks and leptons interact with the Higgs boson proportionally to their masses. Since the top quark is ~40 times more massive than the bottom quark, it will interact with Higgs boson 40 times more strongly. There is suspicion that since the Higgs boson is sensitive to the different quark and lepton masses, it may somehow play a role in how masses are assigned.

Happy Colliding

- richard (@BraveLittleMuon)


Getting to the Bottom of the Higgs

Thursday, January 30th, 2014

Updated Friday, January 31, 2014: Candidate event of Higgs boson decaying to bottom quarks has been added at the bottom.

CMS has announced direct evidence of the Higgs coupling to bottom quarks. This is special.

Last week, the Compact Muon Solenoid Experiment, one of the two general purpose experiments at the CERN Large Hadron Collider (LHC), submitted two papers to the arXiv. The first claims the first evidence for the Higgs boson decaying directly to tau lepton pairs and the second summarizes the evidence for the Higgs boson decaying directly to bottom quarks and tau leptons. (As an aside: The summary paper is targeted for Nature Physics, so it is shorter and more broadly accessible than other ATLAS and CMS publications.) These results are special, and why they are important is the topic of today’s post. For more information about the evidence was obtained, CERN posted a nice QD post last month.

Event display of a candidate Higgs boson decaying into a tau lepton and anti-tau lepton in the CMS detector.

Fig 1. Event display of a candidate Higgs boson decaying into a tau lepton and anti-tau lepton in the ATLAS detector.

There is a litany of results from ATLAS and CMS regarding the measured properties of the Higgs boson. However, these previous observations rely on the Higgs decaying to photons, Z bosons, or W bosons, as well as the Higgs being produced from annihilating gluons or being radiated off a W or Z. Though the top quark does contribute to the Higgs-photon and Higgs-gluon interactions, none of these previous measurements directly probe how fermions (i.e., quarks and leptons) interact with the Higgs boson. Until now, suggestions that the Higgs boson couples to fermions (i) proportionally to their masses and (ii) that the couplings possess no other scaling factor were untested hypotheses. In fact, this second hypothesis remains untested.


Fig. 2: Event display of a candidate Higgs boson decaying into a tau lepton and anti-tau lepton in the CMS detector.

As it stands, CMS claims “strong evidence for the direct coupling of the 125 GeV Higgs boson” to bottom quarks and tau leptons. ATLAS has comparable evidence but only for tau leptons. The CMS experiment’s statistical significance of the signal versus the “no Higgs-to-fermion couplings” hypothesis is 3.8 standard deviations, so no rigorous discovery yet (5 standard deviations is required). For ATLAS, it is 4.1 standard deviations. The collaborations still need to collect more data to satisfactorily validate such an incredible claim. However, this should not detract from that fact that we are witnessing phenomena never before seen in nature. This is new physics as far as I am concerned, and both ATLAS and CMS should be congratulated on discovering it.

Event display of a candidate Higgs boson decaying into a tau lepton and anti-tau lepton in the CMS detector.

Fig. 3: Event display of a candidate Higgs boson decaying into a bottom quark and anti-bottom quark in the ATLAS detector. HT to Jon Butterworth for the link.

The Next Step

Once enough data has been collected to firmly and undoubtedly demonstrate that quarks and leptons directly interact with the Higgs, the real tests of the Standard Model of particle physics start up. In the Standard Model, the strength at which a fermion interacts with the Higgs is proportional to the fermion mass and inversely proportional to the ground state energy of the Higgs field. There is no other factor involved. This is definitively not the case for a plethora of new physics models, including scenarios with multiple Higgs bosons, like supersymmetry, as well as scenarios with new, heavy fermions (heavy bottom quark and tau lepton partners). This is definitely a case of using newly discovered physics to find more new physics.

Happy Colliding.

- Richard (@bravelittlemuon)

PS I was unable to find an event display of a Higgs boson candidate decaying into a pair of bottom quarks. If anyone knows where I can find one, I would be very grateful.

PSS Much gratitude toward Jon Butterworth for providing a link to Higgs-bbar candidate events.


Questions I Wish I Asked When Applying for Graduate School

Monday, October 21st, 2013

Grad School in the sciences is a life-changing endeavour, so do not be afraid to ask questions.

Hi Folks,

Quantum Diaries is not just a place to learn the latest news in particle physics; it is also a resource. It is a forum for sharing ideas and experiences.

In science, it is almost always necessary to have a PhD, but what is a PhD? It is a certification that the holder has demonstrated unambiguously her or his ability to thoroughly carry out an independent investigation addressing a well-defined question. Unsurprisingly, the journey to earning a PhD is never light work, but nor should it be. Scientists undertake painstaking work to learn about nature, its underpinnings, and all the wonderful phenomena that occur in everyday life. This journey, however, is also filled with unexpected consequences, disappointment, and sometimes even heartbreak.

It is also that time of year again when people start compiling their CVs, resumes, research statements, and personal statements, that time of year when people begin applying for graduate programs. For this post, I have asked a number of good friends and colleagues, from current graduate students to current post docs, what questions they wished they had asked when apply for graduate school, selecting a school, and selecting a research group.

However, if you are interested in applying to for PhD programs, you should always first yourself,  “Why do I want a research degree like a PhD?”

If you have an experience, question, or thought that you would like to share, comment below! A longer list only provides more information for applicants.

As Always, Happy Colliding

- Richard (@bravelittlemuon)

PS I would like to thank Adam, Amy, John, Josh, Lauren, Mike, Riti, and Sam for their contributions.

Applying to Graduate School:

“When scouting for grad schools, I investigated the top 40 schools in my program of interest.  For chemistry, research primarily occurs in one or two research labs, so for each school, I investigated the faculty list and group research pages.  I eliminated any school where there werre fewer than two faculty members whose fields I could see myself pursuing.  This narrowed down my list to about a dozen schools.  I then filtered based on location: I enjoy being near a big city, so I removed any school in a non-ideal location.  This let me with half a dozen schools, to which I applied.” - Adam Weingarten, Chemistry, Northwestern

“If there is faculty member you are interested in working for, ask both the professor and especially the students separately about the average length of time it takes students to graduate, and how long financial support might be available.” – Lauren Jarocha, Chemistry, UNC

“My university has a pretty small physics program that, presently, only specializes in a few areas. A great deal of the research from my lab happens in conjunction with other local institutes (such as NIST and NIH) or with members of the chemistry or biology departments. If you are interested in a smaller department, ask professors about Institutes and interdisciplinary studies that they might have some connection to, be it within academia or industry.” – Marguerite Brown, Physics, Georgetown

“If you can afford the application fees and the time, apply as broadly as you can.  It’s good to have options when it comes time to make final decisions about where to go. That said, don’t aim too high (you want to make sure you have realistic schools on your list, whatever “realistic” means given your grades and experience), and don’t aim too low (don’t waste time and money applying to a school that you wouldn’t go to even if it was the only school that accepted you, whether because of academics, location, or anything else).  Be as honest as possible with yourself on that front and get input from trusted older students and professors.  On the flip side, if you don’t get rejected from at least one or two schools, you didn’t aim high enough.  You want a blend of reach schools and realistic schools.” – Amy Lowitz, Physics, Wisconsin

Choosing a School

“One of the most common mistakes I see prospective graduate students make is choosing their institution based on wanting to work with a specific professor without getting a clear enough idea of the funding situation in that lab.  Don’t just ask the professor about funding.  Also ask their graduate students when the professor isn’t present.  Even then, you may have to read between the lines; funding can be a delicate subject, especially when it is lacking.” – Amy Lowitz, Physics, Wisconsin

“If you have a particular subfield/group you *know* you are interested in, check how many profs/postdocs/grads are in these groups, check if there are likely to be open slots, and if there are only 1 or 2 open slots make sure you know how to secure one. If they tell you there are currently no open slots, take this to mean that this group is probably closed for everything but the most exceptional circumstances, and do not take into account that group when making your decision.” – Samuel Ducatman, Physics, Wisconsin

“When choosing a school, I based my decision on how happy the grad students seemed, how energetic/curious the faculty appeared, and if the location would allow me to have extracurricular pursuits (such as writing, improv, playing games with people, going to the movies…basically a location where I could live in for 4-6 years).” – Adam Weingarten, Chemistry, Northwestern

“At the visitor weekend, pay attention to how happy the [current] grads seem. Remember they are likely to be primarily 1st years, who generally are the most happy, but still check. Pay attention to the other students visiting, some of them will be in your incoming class. Make sure there is a good social vibe.” – Samuel Ducatman, Physics, Wisconsin

“When I was visiting a prospective grad student, there was a professor at a university I was visiting whose research I was really interested in, but the university would only allow tuition support for 5 years. When I asked his students about graduation rates and times, however, the answer I got was, ‘Anyone who graduates in 5 years hasn’t actually learned anything, it takes at least 7 or 8 years before people should really graduate anyway. Seven years is average for our group.’ In some fields, there is a stigma associated with longer graduation times and a financial burden that you may have to plan for in advance.” – Lauren Jarocha, Chemistry, UNC

Choosing a Group

“When considering a sub-field, look for what interests you of course, but bear in mind that many people change their focus, many don’t know exactly what they want to do immediately upon entering grad school, and your picture of the different areas of research may change over time. Ask around among your contemporaries and older students, especially when it comes to particular advisers.” – Joshua Sayre, PhD, Physics, Pittsburgh
“If you know that you’re interested in an academic career that is more teaching oriented or research oriented, ask about teaching or grant writing opportunities, respectively. I know plenty of fellow students who didn’t start asking about teaching opportunities their 4th or 5th year of their program, and often by then it was too late. If you know that finding funding will be a big part of your future, joining a group where the students take an active part in writing grants and grant renewals is invaluable experience.” -  Lauren Jarocha, Chemistry, UNC
“For choosing groups, I attended group and subgroup meetings, met with faculty to discuss research and ideas, and read several recent publications from each group of interest.  What I did not do (and wish I had) was talk with the graduate students, see how they and the group operated.  For example, I am very motivated and curious to try new ideas, so in my current research group my PI plays a minimal role in my life.  The most important aspect is how well one’s working style fits with the group mentality, followed by research interest.  There’s a ton of cool, exciting research going on, but finding a group with fun, happy, motivated people will make or break the PhD experience.” – Adam Weingarten, Chemistry, Northwestern
“I went into [Condensed Matter Theory] and not [X] because (1) In the summer of my first year I had no research, and I came close to having no income because of this. I realized I needed someone who could promise me research/funding and real advising. The [X] group was pretty filled up (and there were some politics), so it was impossible to get more than this. (2) I thought the professors in CMT treated me with more respect then the [X] profs I talked to.” - John Doe, Physics
“I believe that choosing which grad schools to apply to should primarily be about the research, so this question is more for after you’ve (hopefully) been accepted to a couple schools.  If you are going into theoretical physics, and if you don’t have some sort of fellowship from them or an outside agency, ask them how much their theory students [teach].  Do they have to TA every semester for their funding?  Do they at least get summers off?  Or do they only have to TA for the first one or two years?  This shouldn’t be the primary factor in deciding where to go – research always is – but it’s not something that should be ignored completely.  Teaching is usually somewhat rewarding in my experience, but it adds absolutely no benefit to your career if you are focused on a professorship at a research university.  Every hour you spend steaching is an hour someone else is researching and you aren’t.  And 10-20 hours a week of teaching adds up.” – Michael Saelim, Physics, Cornell

The International Linear Collider: More than Just a Higgs Factory

Friday, August 23rd, 2013

The ILC site has been chosen. What does this mean for Japan?

Credit: linearcollider.org

The two ILC candidate sites: Sefuri in the South and Kitakami in the North. Credit: linearcollider.org

Hi Folks,

It is official [Japanese1,Japanese2]: the Linear Collider Collaboration and the Japanese physics community have selected the Kitakami mountain range in northern Japan as the site for the proposed International Linear Collider. Kitakami is a located in the Iwate Prefecture and is just north of the Miyagi prefecture, the epicenter of the 2011 Tohoku Earthquake. Having visited the site in June, I cannot aptly express how gorgeous the area is, but more importantly, how well-prepared Iwate City is for this responsibility.

Science is cumulative: new discoveries are used to make more discoveries about how nature works, and physics is no different. The discovery of the Higgs boson at the Large Hadron Collider was a momentous event. With its discovery, physicists proved how some particles have mass and why others have no mass at all. The Higgs boson plays a special role in this process, and after finally finding it, we are determined to learn more about the Higgs. The International Linear Collider (ILC) is a proposed Higgs boson factory that would allow us to intimately understand the Higgs. Spanning 19 miles (31 km) [310 football pitches/soccer fields], if constructed, the ILC will smash together electrons and their antimatter partners, positrons, to produce a Higgs boson (along with a Z boson). In such a clean environment (compared to proton colliders), ultra-precise measurements of the Higgs boson’s properties can be made, and thereby elucidate the nature of this shiny new particle.

credit: li

The general overview schematic of the International Linear Collider. Credit: linearcollider.org

However, the ILC is more than just a experiment. Designing, constructing, and operating the machine for 20 years will be a huge undertaking with lasting effects. For staters, the collider’s Technical Design Report (TDR), which contains every imaginable detail minus the actual blueprints, estimates the cost of the new accelerator to be 7.8 billion USD (2012 dollars). This is not a bad thing. Supposing 50% of the support came from Asia, 25% from the Americas, and 25% from Europe, that would be nearly 2 billion USD invested in new radio frequency technology in England, Germany, and Italy. In the US, it would be nearly 2 billion USD invested in coastal and Midwestern laboratories developing new cryogenic and superconducting technology. In Asia, this would be nearly 4 billion USD invested in these technologies as well as pure labor and construction. Just as the LHC was a boon on the European economy, a Japanese-based ILC will be a boon for an economy temporarily devastated  by an historic earthquake and tsunami. These are just hypothetical numbers; the real economic impact will be  larger.

I had the opportunity to visit Kitakami this past June as a part of a Higgs workshop hosted by Tohoku University. Many things are worth noting. The first is just how gorgeous the site is. Despite its lush appearance, the site offers several geological advantages, including stability against earthquakes of any size. Despite its proximity to the 2011 earthquake and the subsequent tsunami, this area was naturally protected by the mountains. Below is a photo of the Kitakami mountains that I took while visiting the site. Interestingly, I took the photo from the UNESCO World Heritage site Hiraizumi. The ILC is designed to sit between the two mountains in the picture.


The Kitamaki Mountain Range as seen from the UNESCO World Heritage Site in Hiraizumi, Japan. Credit: Mine

What I want to point out in the picture below is the futuristic-looking set of tracks running across the photo. That is the rail line for the JR East bullet train, aka the Tohoku Shinkansen. In other words, the ILC site neighbours a very major transportation line connecting the Japanese capital Tokyo to the northern coast. It takes the train just over 2 hours to traverse the 250 miles (406.3 km) from Tokyo station to the Ichinoseki station in Iwate. The nearest major city is Sendai, capital of Miyagi, home to the renown Tohoku University, and is only a 10 minute shinkansen ride from Ichinoseki station.


The Kitamaki Mountain Range as seen from the UNESCO World Heritage Site in Hiraizumi, Japan. Credit: Mine

What surprised me is how excited the local community is about the collider. After exiting the Ichinoseki station I discovered this subtle sign of support:

There is much community support for the ILC: The Ichinoseki Shinkansen Station in Iwate Prefecture, Japan. Credit: Mine

The residents of Iwate and Miyagi, independent of any official lobbying organization, have formed their own “ILC Support Committee.” They even have their own facebook page. Over the past year, the residents have invited local university physicists to give public lectures on what the ILC is; they have requested that more English, Chinese, Korean, and Tagalog language classes be offered at local community centers; that more Japanese language classes for foreigners are offered in these same facilities; and have even discussed with city officials how to prepare Iwate for the prospect of a rapid increase in population over the next 20 years.

Despite all this, the real surprises were the pamphlets. Iwate has seriously thought this through.


Pamphlets showcasing the Kitakami Mountain Range in Iwate, Japan. Credit: Mine

The level of detail in the pamphlets is impressive. My favourite pamphlet has the phrase, “Ray of Hope: Tohoku Is Ready to Welcome the ILC” on the front cover. Inside is a list of ways to reach the ILC site and the time it takes. For example: it takes 12 hours 50 minutes to reach Tokyo from Rome and 9 hours 40 minutes from Sydney. The brochure elaborates that the Kitakami mountains maintain roughly the same temperature as Switzerland (except in August-September) but collects much more precipitation through the year. Considering that CERN is located in Geneva, Switzerland, and that many LHC experimentalists will likely become ILC experimentalists, the comparison is very helpful. The at-a-glance annual festival schedule is just icing on the cake.


“Ray of Hope” pamphlet describing how to each different ILC campuses by train.  Credit: Mine

Now that the ILC site has been selected, surveys of the land can be conducted so that blue prints and a finalized cost estimate can be established. From my discussions with people involved in the site selection process, the decision was very difficult. I have not visited the Fukuoka site, though I am told it is a comparably impressive location. It will be a while still before any decision to break ground is made. And until that happens, there is plenty of work to do.

Happy Colliding

- Richard (@bravelittlemuon)



The Take Away Message of Snowmass on the Mississippi

Friday, August 9th, 2013

Snowmass Came and Passed. What have we learned from it?


Skyline of Minneapolis, home of the University of Minnesota and host city of the Community Summer Study 2013: Snowmass on the Mississippi.

Hi All,

Science is big. It is the systematic study of nature, so it has to be big. In another way, science is about asking questions, questions that expands our knowledge of nature just a bit more. Innocuous questions like, “Why do apples fall to the ground?”, “How do magnets work?”, or “How does an electron get its mass?” have lead to understanding much more about the universe than expected. Our jobs as scientists come down to three duties: inventing questions, proposing answers (called hypotheses), and testing these proposals.

As particle physicists, we ask “What is the universe made of?” and “What holds the universe together?”  Finding out that planets and stars only make up 5% of the universe really makes one pause and wonder, well, what about everything else?

From neutrino masses, to the Higgs boson, to the cosmic microwave background, we have learned  much about the origin of mass in the Universe as well as the origin of the Universe itself in the past 10 years. Building on recent discoveries, particle physicists from around the world have been working together for over a year to push our questions further. Progress in science is incremental, and after 10 days at the Community Summer Study 2013: Snowmass on the Mississippi Conference, hosted by the University of Minnesota, we have a collection of questions that will drive and define particle physic for the next 20 years. Each question is an incremental step, but each answer will allow us to expand our knowledge of nature.

I had a chance to speak with SLAC‘s Michael Peskin, a convener for the Snowmass Energy Frontier study group and author of the definitive textbook on Quantum Field Theory, on how he sees the high energy physics community proceeding after Snowmass. “The community did a lot of listening at Snowmass. High energy physics is pursuing a very broad array of questions.  I think that we now appreciate better how important all of these questions are, and that there are real strategies for answering them.”  An important theme of Snowmass, Peskin said, was “the need for long-term, global planning”.  He pointed to the continuing success of the Large Hadron Collider, which is the result of the efforts of thousands of scientists around the world.  This success would not have happened without such a large-scale, global  effort.  ”This is how high energy physics will have to be, in all of its subfields, to answer our big questions.”

Summary presentations of all the work done for Snowmass are linked below in pdf form and are divided into two categories: how to approach questions (Frontiers) and what will enable us to answer these questions. These two categories represent the mission of the US Department of Energy’s Office of Science. A summary of the summaries is at the bottom.

What is the absolute neutrino mass scale? What is the neutrino mass ordering? Is CP violated in the neutrino sector? What new knowledge will neutrinos from astrophysical sources bring?

What is dark matter? What is dark energy? Why more matter than anti-matter? What is the physics of the Universe at the highest energies?

Where are the new particles that modify the Higgs, t, W couplings? What particles comprise the dark matter? Why is the Higgs boson so light?

The growth in data drives need for continued R&D investment in data management, data access methods, networking. Challenging resource needs require efficient and flexible use of all resources HEP needs both Distributed High-Throughput computing (experiment program) and High-Performance computing (mostly theory/simulation/modeling)

Encourage and enable physicists to be involved in and support local, national and world-wide efforts that offer long–term professional development and training opportunities for educators (including pre-service educators), using best practice and approaches supported by physics education research. and Create learning opportunities for students of all ages, including classroom, out-of-school and online activities that allow students to explore particle physics

Our vision is for the US to have an instrumentation program for particle physics that enables the US to maintain a scientific leadership position in a broad, global, experimental program; and develops new detection capabilities that provides for cutting edge contributions to a world program

Is dark energy a cosmological constant? Is it a vacuum energy? From where do ultra high energy cosmic rays originate? From where do ultra high energy neutrinos originate?

How would one build a 100 TeV scale hadron collider? How would one build a lepton collider at >1 TeV? Can multi-MW targets survive? If so, for how long?

To provide a conduit for untenured (young) particle physicists to participate in the Community Summer Study. To facilitate and encourage young people to get involved.
Become a long term asset to the field and a place where young peoples voices can be heard

Several great posts from QD (Family, Young, Frontierland), Symmetry Magazine (Push, Q&A, IceSlam, Decade), and even real-time updates from QD’s Ken Bloom (@kenbloomunl) and myself (@bravelittlemuon) via #Snowmass are available. All presentations can be found at the Snowmass Indico page.

Until next time, happy colliding.

- Richard (@bravelittlemuon)

Community Summer Study: Snowmass 2013 Poster

Community Summer Study: Snowmass 2013 Poster


The Definite Article Problem

Tuesday, June 4th, 2013

A Little Bit of the Higgs Boson for Everyone

Hi All,

This post is long overdue but nonetheless I am thrilled to finally write it. We have discovered the a some  ??? Higgs boson, and it is precisely my trouble writing this very sentence that inspires a new post. CERN‘s press office has keenly presented a new question in particle physics known as the Definite Article Problem:

Have we discovered “a” Higgs boson or “the” Higgs boson?

We can express the Article problem in another way:

Are there more Higgs bosons?

Before I touch upon that problem, I want to explain about why the Higgs boson is important. In particular, I want to talk about the Sun! Yes, the Sun.


The Higgs Boson and Electroweak Symmetry Breaking is Important because the Sun Shines.

Okay, there is no way to avoid this: I really like the sun.

Slide Credit: Mine. Image Credit: GOES Collaboration

It shines. It keeps the planet warm. There is liquid water on Earth, and some very tasty plants too.

Slide Credit: Mine. Image Credit: NobelPrize.org

At the heart of the Sun is a ranging nuclear furnace and involves two types of processes: (1) those that involve the Strong nuclear force and (2) those that involve the Weak nuclear force (look for the neutrinos!). The two types of processes work together in a solar relay race to complete a circuit, only to do it over and over again for billions of years. And just like a real relay race, the speed at which the circuit is finished is set by the slowest member. In this case, the Weak force is the limiting factor and considerably slows down the rate at which the sun could theoretically operate. If we make the Weak force stronger, then the Sun would shine more brightly. Conversely, if we make the Weak force even weaker, the Sun would be dimmer.

Slide Credit: Mine. Image Credit: NobelPrize.org

From studying the decays of radioactive substances, we have learned that the rate of Weak nuclear processes is set by a physical constant called Fermi’s Constant. Fermi’s Constant is represented by symbol GF. From study the Higgs boson and the Higgs Mechanism, we have learned that Fermi’s Constant is literally just another constant, v, in disguise. This second physical constant (v) is called the Higgs “vacuum expectation value” , or “vev” for short, and is the amount of energy the Higgs field has at all times relative to the vacuum.

The point I want to make is this: If we increase the Higgs vev, Fermi’s Constant gets smaller, which reduces the rate of Weak nuclear interactions. In other words, a larger Higgs vev would make the sun shine less brightly. Going the other way, a smaller Higgs vev would make the sun shine more brightly. (This is really cool!)

Slide Credit: Mine. Image Credit: Jacky-Boi

The Higgs vev is responsible for some other things, too. It is a source of energy from which all elementary particles can draw. Through the Higgs Mechanism, the Higgs field provides mass to all elementary particles and massive bosons. One would think that for such an important particle we would have a firm theoretical understanding it, but we do not.

Credit: Mine

We have a very poor theoretical understanding of the Higgs boson. Among other things, according to our current understanding of the Higgs boson, the particle should be much heavier than what we have measured.

Credit: Mine

The Definite Article Problem

There are lots of possible solutions to the problems and theoretical inconsistencies we have discovered relating to the Standard Model Higgs boson. Many of these ideas hypothesize the existence of other Higgs bosons or particles that would interact like the Higgs boson. There are also scenarios where Higgses have identity crises: the Higgs boson we have observed could be a quantum mechanical combination (superposition) of several Higgs bosons.

I do not know if there are additional Higgses. Truthfully, there are many attractive proposals that require upping the number Higgs bosons. What I do know is that our Higgs boson is interesting and merits much further studying.


Credit: Mine

Happy Colliding

- richard (@bravelittlemuon)

PS In case anyone is wondering, yes, I did take screen shots from previous talks and turn them into a DQ post.


Using Physics to Find More Physics

Thursday, February 14th, 2013

The best kind of physics is the new kind. How do you find new physics? By using physics of course!

Hi All,

A maxim in particle physics says to

use physics to find more physics!

I forget from where or whom I first heard this saying but the idea goes something like this: When a new particle is discovered, in principle, our knowledge of the particle only consists of what we have directly measured and what the theory that lead us to its discovery tells us. The theory, of course, is most likely incorrect but that is the point. As far as we know, any newly discovered particle might have some hereto unknown quantum number. But if this is the case, then by scrutinizing a new particle we might get lucky, very luck and discover something completely unexpected. One perfect example comes from neutrino physics. After finally discovering them, physicists learned eventually how to make beams of neutrinos only to find out (1) that there are several types of neutrinos and (2) they have mass. Another example involves the W boson and brief history of modern particle colliders.

The purpose of particle colliders like the Super Proton Synchrotron (SPS), the Large Electron-Positron collider (LEP), the Tevatron, or the Large Hadron Collider (LHC) is to test physical theories in order to ultimately figure out what works and doesn’t work. Sometimes all the time we get disappointing results (technicolor, extra dimensions, additional vector bosons), and sometimes rarely we score big (top quark, Higgs boson). It’s all a part of the business. The utility of colliders is that, with them, there are multiple ways hypotheses can be tested. One particularly powerful method to test models like the Standard Model of Particle Physics (SM) is to look for processes that are both (a) relatively rare and (b) relatively unique. For example: in the theory that governs how light and matter interact, also known as Quantum Electrodynamics (QED), we can take an electron (e-) and its antiparticle, a positron, (e+), and use them to produce two photons, the particles of light (γ). Figure 1 below shows how this can happen diagrammatically. In short, either the electron or the positron first radiate a photon (γ), and then the electron and positron annihilate forming the second photon (γ).

Figure 1. A Feynman diagram representing the production of two photons from electron (e-) and positron (e+) annihilation.

In the 1990s, back when the Large Hadron Collider (LHC) was just a dream on paper, another accelerator called the Large Electron-Positron collider (LEP) existed in the same tunnel the LHC currently occupies. The goal of LEP was to study the very fine details (“precision work”) of the theory we now call the Standard Model of Particle Physics (SM). At the time, this was particularly concerning because the W and Z bosons had only been discovered ten years prior at the Super Proton Synchrotron collider (SPS), and establishing the SM hinged on knowing their properties. LEP, along with the Tevatron, did just this. In fact, some of the most precisely measured results of the SM bosons still come from LEP.

At LEP, physicists decided to pursue an idea that made many of the same people who discovered the W and Z bosons pause for just a moment. LEP experimentalists set out to produce two W bosons and two Z bosons at the same time. Just like the diagram for producing two photons in QED (Fig. 1), there is diagram depicting how two W bosons can be produced from an electron (e-) and positron (e+). See Figure 2 below. The diagram for producing two Z bosons is identical to Fig. 1, just replace “γ” with “Z“. In the case of W+W- production, either an electron or a positron first radiates a W boson; an e- will radiate a negatively charged W boson, W-, and an e+ will radiate an positively charge W boson, W+. After radiating the boson, the electron (or positron!) is converted into a neutrino (or anti-neutrino!), and annihilates with the positron (or electron!) to produce the second W boson.

Figure 2: A Feynman digram representing how the neutrino contributes to W+W- pair production from electron (e-) and positron (e+) annihilation.

However, unlike producing two photons, there is another process that can contribute to producing two W bosons. Figure 3 below shows that an electron (e-) and positron (e+) can also annihilate into a photon (or a Z boson), and then the photon (or Z boson) can split into a W+ and W- boson.

Figure 3: A Feynman digram representing how the photon and Z boson contribute to W+W- pair production from electron (e-) and positron (e+) annihilation.

In the 2000s, physicists at the Tevatron took this a step further. It starts by recognizing that since electrons and positrons can produce two W bosons, and since physics going forward in time behaves identical to physics operating backward in time (time-reversal symmetry), then two W bosons can be used to produce an electron and positron. Figure 4 below shows how this can happen diagrammatically.

Figure 4: A Feynman diagram representing how to produce an electron (e-) and positron (e+) pair from a W+ and W- boson pair.

Here is physicists got clever. The diagram in Figure 3 and the left diagram in Figure 4 have the same intermediate particle: a photon or Z boson. The rules of quantum field theory allow us to then take the second half of Fig. 3 and the first half of the left diagram in Fig. 4, and attach them! As a result, two bosons can be used to produce two more bosons! A few examples: a W+ boson and a W- boson can annihilate or exchange a photon (or Z boson) and produce another two W bosons (Figure 5 below); two W bosons can also go in and produce two photons, two Z bosons, or a photon and Z boson; in fact, two photons can go in and even produce two W bosons! This sort of phenomena is generically called “Weak Boson Scattering,” “Vector Boson Scattering,” or “Vector Boson Fusion,” and in 2006, the Tevatron‘s DZero detector experiment provided the proof of this process when it measured the rate of two Z bosons being produced simultaneously (press release).

Figure 5: A Feynman diagram representing how the photon and Z boson contribute to W+W- scattering.

Warning: Technical Detail. Abandon hope all ye who… I mean, Weak Boson Scattering at the Tevatron differs from producing two bosons at LEP in a subtle way. At LEP, both the electron (e-) and positron (e+) ultimately annihilated and ceased to exist. At the Tevatron, each initial W and Z boson came from a quark (or antiquark) that radiated the boson but did not ultimately annihilate (Figure 6 below.). The analogous process that occurred at LEP did occur at the Tevatron (and vice versa), but the two processes can be to some extent distinguished from each other.

Figure 6: Diagram depicting the process known as WW Scattering, where two quarks from two protons each radiate a W boson that then elastically interact with one another.

However, we have to be careful here. Much like how we needed to include an additional diagram when progressing from producing two photons to W+W- production with electrons and positrons, we need to include additional diagrams for W+W- production when starting with two W bosons. A hugely important process that warranted the Higgs boson’s existence long before it was found is when we replace the intermediate photon and Z in Fig. 5 (above)  with a Higgs boson. See Figure 7 below. By measuring the rate of weak boson scattering, one can in principle infer the mass of the Higgs boson. This is precisely how physicists at the Tevatron and the LHC were able to rule out the existence of a very massive Higgs boson.

Figure 7: A Feynman diagram representing how the Higgs boson contributes to W+W- scattering.

In fewer than 30 years, physicists have gone from discovering the W and Z bosons (SPS),  to producing two of them simultaneously (LEP), to creating a proof-of-principle vector boson collider (Tevatron), to using a new vector boson collider as a probe for new physics (LHC)! We have already discovered the Higgs boson using this method and we are definitely hoping to find something more. If there are more vector bosons in the universe, then it is certainly possible that they may contribute to vector boson scattering by replacing any of the lines in Fig. 5; see Figure 8 below.

Figure 8: A Feynman diagram representing how a new vector boson (?) can contribute to W+W- scattering.

It is also certainly possible that there are additional Higgs bosons. Those can contribute to vector boson scattering by replacing the Higgs boson in Fig. 7; see Figure 9 below.

Figure 9: A Feynman diagram representing how a new scalar (?) can contribute to W+W- scattering.

This is how research in high energy physics progresses: discover something new, turning it around, and throwing it back at itself. You can be certain that there is already research into scattering Higgs bosons and how this next iteration of collisions could be excellent tests of theories like technicolor, extra dimensions, or the existence of additional vector bosons. Until next time!


Happy Colliding

- richard (@bravelittlemuon)



Read-Set-Go: The LHC 2012 Schedule

Thursday, September 20th, 2012

From Now Until Mid-December, Expect One Thing from the LHC: More Collisions.

Figure 1: Integrated luminosity for LHC Experiments versus time. 8 TeV proton-proton collisions began in April 2012. Credit: CERN


Hi All,

Quick post today. That plot above represents the amount of 8 TeV data collected by the LHC experiments. As of this month, the ATLAS and CMS detector experiments have each collected 15 fb-1 of data. A single fb-1 (pronounced: inverse femto-barn) is equivalent to 70 trillion proton-proton collisions. In other words, ATLAS and CMS have each observed 1,050,000,000,000,000 proton-proton collisions. That is 1.05 thousand-trillion, or 1.05×1015.

To understand how gargantuan a number this is, consider that it took the LHC’s predecessor, the Tevatron, 24 years to deliver 12 fb-1 of proton-antiproton collisions*. The LHC has collected this much data in five months. Furthermore,  proton-proton collisions will officially continue until at least December 16th, at which time CERN will shut off the collider for the holiday season. Near the beginning of the calendar year, we can expect the LHC to collide lead ions for a while before the long, two-year shut down. During this time, the LHC magnets will be upgraded in order to allow protons to run at 13 or 14 TeV, and the detector experiments will get some much-needed tender loving care maintenance and upgrades.

To estimate how much more data we might get before the New Year, let’s assume that the LHC will deliver 0.150 fb-1 per day from now until December 16th. I consider this to be a conservative estimation, but I refer you to the LHC’s Performance and Statistics page. I also assume that the experiments operate at 100% efficiency (not so conservative but good enough). Running 7 days a week puts us at a little over 1 fb-1 per week. According to the LHC schedule, there about about 10 more weeks of running (12 weeks until Dec. 16 minus 2 weeks for “machine development”).

By this estimation, both ATLAS and CMS will have at least 25 fb-1 of data each before shut down!

25 fb-1 translates to 1.75 thousand-trillion proton-proton collisions, more than four times as much 8 TeV data used to discover the Higgs boson in July**.

Fellow QDer Ken Bloom has a terrific breakdown of what all this extra data means for studying physics. Up-to-the-minute updates about the LHC’s performance are available via the LHC Programme Coordinate Page, @LHCstatus, and @LHCmode. There are no on-going collisions at the moment because the LHC is currently under a technical stop/beam recommissioning/machine development/scrubbing, but things will be back to normal next week.


Happy Colliding

- richard (@bravelittlemuon)


* 10 fb-1 were recorded each by CDF and DZero, but to be fair, it also took Fermilab about 100 million protons to make 20 or so antiprotons.

** The Higgs boson discovery used 5 fb-1 of 7 TeV data and 5.5 fb-1 of 8 TeV data