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

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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,

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)

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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

Tags: @bravelittlemuon, data, December, fb, fb-1, inverse femtobarn, LHC, schedule
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Why The Higgs Boson Should Not Exist and Why This Is a Good Thing

Thursday, September 13th, 2012

Theoretically, the Higgs boson solves a lot of problems. Theoretically, this Higgs boson is a problem.

Greetings from the good ol’ U.S. of A.

Now that Fall is here, classes are going, holidays are wrapping up, and research programs are in full steam. Unfortunately, all is not well in the Wonderful World of Physics. To refresh, back on 4th of July, the LHC experiments announced the outstanding and historical discovery of a new particle with properties consistent with the Standard Model Higgs boson. No doubt, this is a fantastic feat by the experiments, a triumph and culmination of a decades-long endeavor. However, there is deep concern about the existence of a 125 GeV Higgs boson. Being roughly 130 times the proton’s mass, this Higgs boson is too light. A full and formal calculation of the Higgs boson’s mass, according to the theory that predicts it, places the Higgs mass pretty close to infinity. Obviously, the Higgs boson’s mass is less than infinite. So let’s talk mass and why this is still a very good thing for particle physics.

For an introduction to the Higgs boson, click here, here, or here (This last one is pretty good).

The Standard Higgs

The Standard Model of Particle Physics (SM) is the theory that describes, well, everything with the exception of gravity (Yes, this is admittedly a pretty big exception). It may sound pompous and arrogant, but the SM really does a good job at explaining how things work: things like the lights in your kitchen, or smoke detectors, or the sun.

Though if this “theory of almost-everything” can do all this, then when written out explicitly, it must be pretty big, right? Yes. The answer is yes. Undeniably, yes. When written out fully and explicitly, the “Lagrangian of the Standard Model” looks like this (click to enlarge):

Figure 1: The Standard Model Lagrangian in the Feynman Gauge. Credit: T.D. Gutierrez

This rather infamous and impressive piece of work is by Prof. Thomas Gutierrez of Cal Poly SLO. Today, however, we only care about two terms (look for the red circles):

Figure 2: The Standard Model Lagrangian in the Feynman Gauge with the Higgs boson tree-level mass and 4-Higgs vertex interactions terms circles. Original Credit: T.D. Gutierrez

The first term is pretty straightforward. It expresses the fact that the Higgs boson has a mass, and this can represented by the Feynman diagram in Fig 3. (below). As simple and uneventful as this line may appear, its existence has a profound impact on the properties of the Higgs boson. For example, because of its mass, the Higgs boson can never travel at the speed of light; this is the complete opposite for the massless photon, which can only travel at the speed of light. The existence of the diagram if Fig. 3 also tells us exactly how a Higgs boson (denoted by h) travels from one place in the Universe, let’s call is x, to another place in the Universe, let’s call it y. Armed with this information, and a few other details, we can calculate the probability that a Higgs boson will travel from point x to point y, or if it will decay at some point in between.

Figure 3: The tree-level Feynman diagram the represents a SM Higgs boson (h) propagating from a point x in the Universe to a point y somewhere else in the Universe. Credit: Mine

The second term is an interesting little fella. It expresses the way the Higgs boson can interact with other Higgs bosons, or even itself. The Feynman diagram associated with this second term is in Fig. 4. It implies that there is a probability a Higgs boson (at position w) and a second Higgs boson (at position x) can collide into each other at some point in the Universe, annihilate, and then produce two Higgs bosons (at point z and y). To recap: two Higgses go in, two Higgses go out.

Figure 4: The tree-level Feynman diagram the represents two SM Higgs bosons (h) at points w and x in the Universe annihilating and producing two new SM Higgs bosons at points z and y somewhere else in the Universe. Credit: Mine

This next step may seem a little out-of-the-blue and unmotivated, but let’s suppose that one of the incoming Higgs bosons was also one of the outgoing Higgs bosons. This is equivalent to supposing that w was equal to z. The Feynman diagram would look like Fig. 5 (below).

Figure 5: By making an incoming Higgs boson (h) the same as an outgoing Higgs boson in the 4-Higgs interaction term, we can transform the tree-level 4-Higgs interaction term into the 1-loop level correction to the Fig. 1, the diagram the represents the propagation of a Higgs boson in the Universe. Credit: Mine

In words, this “new” diagram states that as a Higgs boson (h) at position x travels to position y, it will emit and absorb a second Higgs boson somewhere in between x and y. Yes, the Higgs boson can and will emit and absorb a second Higgs boson.

If you look carefully, this new diagram has the same starting point and ending point at our first diagram in Fig. 3, the one that described the a Higgs boson traveling from position x to position y. According to the well-tested rules of quantum mechanics, if two diagrams have the same starting and ending conditions, then both diagrams contribute to all the same processes and both must be included in any calculation that has the same stating and ending points. In terms of Feynman diagrams, if we want to talk about a Higgs boson traveling from point x to point y, then we need to look no further than Fig. 6.

Figure 6: The tree-level (L) and 1-loop level (R) contributions to a Higgs boson (h) traveling from point x to point y. Credit: Mine

What Does This All Mean?

Now that I am done building things up, let me quickly get to the point. The second diagram can be considered a “correction” to the first diagram. The first diagram is present because the Higgs boson is allowed to have mass (mH). In a very real sense, the second diagram is a correction to the Higgs boson’s mass. In a single equation, the two diagrams in Fig. 6 imply

Equation 1: The theoretical prediction for the SM Higgs boson's observed mass, which includes the "tree-level" contribution ("free parameter"), and 1-loop level contribution ("cutoff"). Credit: Mine

In Eq. (1), term on the far left is the Higgs boson’s mass that has been experimentally measured, i.e., 125 GeV. Hence the label, “what we measure.” The term just right of that (the “free parameter”) is the mass of the Higgs boson associated with the first term in the SM Lagrangian (Fig. 2 and 3). When physicists talk about the Standard Model not predicting the mass of the Higgs boson, it is this term (the free parameter) that we talk about. The SM makes no mention as to what it should be. We have to get down, dirty, and actually conduct an experiment get the thing. The term on the far right can be ignored. The term “Λ” (the “cutoff scale“), on the other hand, terrifies and mystifies particle physicists.

Λ is called the “cutoff scale” of the SM. Physically, it represents the energy at which the SM stops working. I mean it: we stop calculating things when we get to energies equal to Λ. Experimentally, Λ is at least a few hundred times the mass of the proton. If Λ is very LARGE, like several times larger than the LHC’s energy range, then the observed Higgs mass gets an equally LARGE bump. For example, if the SM were 100% correct for all energies, then Λ would be infinity. If this were true, then

(the Higgs boson’s mass) = (something not infinity) + (something infinity) ,

which comes out inevitably to be infinity. In other words, if the Standard Model of Physics were 100% correct, then the Higgs boson’s mass is predicted to be infinity. The Higgs boson is not infinity, obviously, and therefore the Standard Model is not 100%. Therefore, the existence of the Higgs boson is proof that there must be new physics somewhere. “Where and at what energy?,” is a whole different question and rightfully deserves its own post.

Happy Colliding

- Richard (@bravelittlemuon)

Tags: @bravelittlemuon, Feynman Diagrams, Higgs, Loop Corrections, new physics
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What Comes Next?

Tuesday, July 3rd, 2012

Suppose for a moment the LHC experiments announce the discovery of a new object Wednesday. What comes next?

Figure 1: The list of all known elementary particles in Standard Model. The existence of the Higgs boson has yet to be confirmed. Credit: AAAS

Hi All,

In fewer than 20 hours, on Wednesday, July 4th, now dubbed Higgsdependence Day, something very important will happen. In a physics laboratory just outside of Geneva, Switzerland, in a pretty spacious auditorium, the spokespeople for two rival experiments will unveil their independent searches for a microscopic object predicted to exist almost over 40 years ago. Not impressed?

Well, I will put it another way. In fewer than 20 hours, the world will learn just how a near hundred-billion dollar industry, the same industry that invented both the World Wide Web and new cancer treatments, will spend the next 10 to 20 years after finally learning if the Higgs boson really is responsible for the origin of mass in the visible Universe!

Figure 2: 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. Credit: Me.

The who, what, where, why, whom, regarding the Higgs boson has been covered quite extensively and so I will not dwell on it. What I am talking about today is the BIG question on every physicist’s mind. At this point, us physicists have stopped asking whether or not the LHC experiments will announce the definitive discovery of a new particle. We are now more focused on answering,

What do we need to do after Wednesday?

Quite frankly, there just has to be at least one new particle lurking in the data. It does not have to be THE Higgs boson as predicted by the Standard Model by any means. So long as this object fulfills the role of the Higgs boson, physics works. How am I so sure of this? Well, taking the Higgs Boson out of the Standard Model causes a rather ludicrous prediction:

The probability of WW scattering (Fig. 2) at the LHC becomes infinity.

That result, my dear friends, I promise you is total rubbish. This is the famous “Unitarity Problem” and is heroically solved by assuming that the Higgs boson is a real particle and has a mass less than 1400 times the mass of the proton.

Figure 3: The combined limits on the expected number of SM Higgs bosons decaying into bottom quark-anti-bottom quark pairs from the Tevatron experiments (CDF+DZero) July 2012, using almost 10 fb-1 of data. Data indicates a excess of events compared to the no-Higgs hypothesis, and thus consistent with the existence of a higgs-like object. Credit: FNAL.

Furthermore, if the LHC experiments confirm the existence of a Higgless Standard Model, then we have to explain why, as of Monday, the Tevatron has seen: an excess in the number of bottom-anti-bottom quark pairs (Fig. 3) and 2-photons events, but a deficit of the number of expected W+W- pairs.

Announcing the discovery of a higgs-like object on Wednesday will literally dictate the (non-neutrino) high energy physics programme until well-after the end of the decade. This will take a lot of data, and hence time & effort, to accurately tabulate all the quantum numbers of a new particle.

For starters, we need to immediately confirm what we have is a particle without any intrinsic angular momentum! In physics talk, this is called “spin.” One way to determine the spin of a particle capable of decaying into into a bottom-anti-bottom quark pair is to look at the angle between the two quarks as the object decays. This angle has a very unique shape if the new particle has no intrinsic angular momentum (spin-0), a single unit of angular momentum (spin-1), two units of angular momentum (spin-2), and so on. They should look something like the three plots below (L is spin-0; C is spin-1; R is spin-2). For more information, see the original QD post. The point I am trying to make is that it is very straightforward to confirm the “spin” of any new Higgs-like particle.

: Figure 4 (a): The angular distribution of a spin-0 object decaying to a bottom and anti-bottom quark pair. Credit: Me.

: Figure 4 (b): The angular distribution of a spin-1 object decaying to a bottom and anti-bottom quark pair. Credit: Me.

: Figure 4 (c): The angular distribution of a spin-2 object decaying to a bottom and anti-bottom quark pair. Credit: Me.

Another quintessential piece of information: determining into what particles this new particle can decay. If this mystery object is our beloved Standard Model Higgs boson, then the probability it will decay into quarks and leptons is proportional to how heavy individual quarks and leptons are. Therefore, the rate at which this potential Higgs-like object decays into lighter particles must be carefully measured to confirm that it decays into bottoms quarks (mass = 4 GeV) more often than it does to muons (mass = 0.1 GeV). New theories, like Supersymmetry (SUSY), can alter such rates slightly. Consequentially, precisely measuring the decay rates of any Higgs-like object is automatically a test SUSY.

Figure 5: In SUSY, the correction to Higgs mass by the top quark (L) is inherently cancelled by the contribution from the top quark's supersymmetric partner, the stop (R). Credit: Chuan-Ren Chen.

Science is all about explaining how nature works by carefully and methodically testing hypotheses. The Higgs boson may be the final piece of the Standard Model puzzle but our work hardly stops on Wednesday. If we have truly found the Higgs boson at roughly 125 times the mass of the proton, then there is a very troublesome issue:

The Higgs boson mass is too heavy!

Recovering a 125 GeV Higgs boson requires a few contrived cancellations that are pretty unsatisfactory. It is significantly more rigorous if terms cancel based on physical principles. Remember, since this is real life and not a chalkboard, there are hardline, concrete principles for the way nature works the way it does. To suggest otherwise is silly. Oddly enough, such cancellations do occur inherently in Supersymmetry (Fig. 5). Understanding the precise value of the Higgs mass is another item on our ever-growing Higgs Boson Properties checklist.

At the end of the day, discovering a Higgs boson means, experimentally and theoretically, pushing the bounds of our knowledge of the Universe that much further. Yes, it is likely that after tomorrow many physics textbooks will be outdated. This is a very good thing. However, confirming ALL the spin, decay, mass, mixing, etc. properties of this new particle, if there is indeed a new particle, will require many years, and you can count on hearing all about it from us!

Happy Colliding

- richard (@bravelittlemuon)

Tags: @bravelittlemuon, Higgs, LHC
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Neutrino 2012: Day 5 Part 1: The Return of the FTL Neutrino

Friday, June 8th, 2012

What has no thumbs and travels at the speed of light, to within experimental uncertainty?

Hi All,

I will just say this right away, the Borexino, ICARUS, LVD, OPERA, and MINOS Experiments have all independently found, within experimental uncertainty, that neutrinos travel at the speed of light. To enlighten, last September the OPERA Experiment at the Gran Sasso Laboratory, in Gran Sasso, Italy, observed what appeared to indicate that neutrinos travel faster than the speed of light. (More information available from veteran QDers Aiden and Seth).

The reported quantity is time it took neutrinos to travel from CERN to Gran Sasso minus the time it would have taken light. I should also mention that the statistical (stat.) and systematic (sys.) uncertainties are incredibly important.

δt = (Time it took neutrinos to reach GS from CERN) – (Distance between GS and CERN)/(Speed of Light)

Figure 1: Results from four Gran Sasso Laboratory experiments indicating neutrinos travel at the speed of light, to within exerpeimental uncertainty. Reported quantity is time it took neutrinos to travel from CERN to Gran Sasso minus the time it would have taken light. Credit: BERTOLUCCI, Sergio

Figure 2: Results from the MINOS Experiment indicating neutrinos travel at the speed of light, to within exerpeimental uncertainty. Reported quantity is time it took neutrinos to travel from Fermilab to MINOS minus the time it would have taken light. Credit: ADAMSON, Phil

To clarify the situation, this result was not a typical “Hey! We discovered new physics!” result. Had OPERA correctly observed a massive particle traveling faster than light, then we would truly be in the midst of a physic revolution. That is not a hyperbole either. As a result, everyone, theorists and experimentalists alike, put on their scientists hats and scrutinized the result to no end. Much drama ensued and at long last the problem has been resolved. The issue at hand were actually two very subtle effects that worked against each other. The first was that a 5.2 mi (8.3 km) cable was accidentally stretched back in 2008 and systematically introduced a 74 nanosecond delay in the system that recorded the time the neutrinos arrived at the detector. The second issue involved the highly precise master clock system for the entire experiment; it was slow by about 15 nanoseconds. 74 – 15 = 59 nanoseconds was exactly how much sooner the neutrinos were arriving than they were expected.

Figure 3: Two previously unaccounted issues regarding the OPERA Experiment. Credit: DRACOS, Marcos

In conclusion, neutrinos may still travel faster than the speed of light. It is unlikely, but still possible. Officially as of today, though, we know that all measurements of neutrinos’ speed show are consistent with the speed of light.

Tags: #Neutrino12, @bravelittlemuon, Day 5, neutrino, Neutrino 2012, Neutrino2012
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Neutrino 2012: Day 3+4

Friday, June 8th, 2012

How many types of neutrinos are there? That was Day 3+4′s Big Question.

Hi All,

Your Day 3+4 breakdown is finally here. A lack of internet access is always an issue. At any rate, things were a very great mix of experimental results and theoretical discussions that all pointed to one question: How many types of neutrinos are there in the Universe? According to the Standard Model, which itself is founded on very rich experimental results, there are 3 flavors: electron-neutrino, muon-neutrino, and tau-neutrino. However, it is very possible there are more neutrinos that do not have any charges under the Standard Model. Such neutrinos are called sterile neutrino or singlet neutrinos.

Without further ado: MiniBooNE, Neutrino Anomalies, KamLAND-Zen, EXO-200, and Day 4.

MiniBooNE

A quick breakdown of what the Miniature Booster Neutrino Experiment, or MiniBooNE for short, is all about can be given in the following two slides. Fermilab accelerates protons into a fixed target to produce pions and kaons. The pions and kaons are then directed toward the ground and squeezed together by a system of magnetic fields called “the horn.” The pions then fly for a period of time, decaying into muons, electrons, and neutrinos. The muons further decay into more neutrinos and electrons. When the electron and neutrino beam hits the ground, the electrons are absorbed and the neutrinos pass through the planet. Finally, after popping out in a deep underground Minnesota mine, the neutrino beam flies through the MiniBooNE detector and physics is born.

One of MiniBooNE’s chief scientific goals is to confirm or refute the result of a previous experiment, LSND, which observed an excess of neutrinos. The excess was best described by introducing a single sterile neutrino and we still do not know if the result was a statistical fluke or something more serious.

Figure 1: Summary of the MiniBooNE Experiment at Fermilab with motivation for its science programme. Credit: POLLY, Chris

Figure 2: Breakdown of the MiniBooNE Experiment at Fermilab. Credit: POLLY, Chris

The experiment has announced for the first time with its full dataset, that it has observed an excess number of anti-muon-neutrinos converting to anti-electron-neutrinos. This excess is almost entirely in the lower energy range, i.e., smaller energy transfer between neutrinos and detector, and the experiment is trying vigorously to determine if this has been caused by a previously unknown background.

Figure 3: Results showing an excess in the number of low energy anti-electron neutrinos observed. Credit: POLLY, Chris

When combing the anti-neutrino and neutrino excesses, the overall excess in number of events grows in significance. The two results are consistent with each other, so there is no measurable difference between matter and anti-matter has been observed. If it is there, it is beyond the detector’s capabilities. There are a few ideas to explain the more-than-expected number of neutrinos and they are individually being studied as we speak. A VERY preliminary result (so preliminary I am choosing not the put up the plot here) is that the data is somewhat well-described by assuming the existence of two sterile neutrinos. This actually is more preferred than a single sterile neutrino, so theorists are a bit happy at the moment.

Figure 4: Results showing an excess in the number of low energy electron-neutrinos and anti-electron neutrinos observed. Credit: POLLY, Chris

Neutrino Anomalies

The prospect of adding a new neutrino to the Standard Model is a tricky issue, let alone adding two. Theoretically it is not terribly difficult but such a step would have very obvious and quickly testable predictions. The first of several theory talks (I am skipping my synopsis of all other theory talks) had a summary of known anomalies from neutrino experiments. LSND and MiniBooNE has already been discussed and the largest. A rather recently discovered discrepancy is the number of neutrinos predicted to be produced by nuclear reactors. The calculation is very well known but had not been updated in years. After recalculating the expected neutrino production rate, the predicted rate was found to be larger than the observed rate. Strictly speaking, all results ARE consistent with the Standard Model and we cannot make any definitive statements based solely on what is listed here.

Figure 5: . Credit: LASSERRE, Thierry

KamLAND-Zen

On to KamLAND-Zen, which stands for Kamioka Liquid Scintillator Anti-neutrino Detector – Zero Neutrino Double β-Decay (pronounced: beta-decay). This experiment has got to be the best example of when an experiment collaboration just stops trying to write its experiment name as a logical acronym. It is still a wicked-cool name. Nuclear β-decay is one of the most well-studied examples of radioactivity where a nucleus in an atom will disintegrate into a lighter nucleus, plus an electron (or a positron), and an anti-electron-neutrino (or a regular electron-neutrino). Some radioactive elements can also undergo the super rare double β-decay where two β-decays occur simultaneously. In the case that a sterile neutrino does indeed exist, then the even more rare neutrino-less double β-decay should be possible. In this situation, two nuclei in an element will disintegrate into two lighter nuclei and only two electrons (or positrons!). KamLAND-Zen is looking for such a decay in the gas xenon but has had no such luck. It has, however, been able to measure the rate of the still-very-rare 2-neutrino-double β-decay in xenon, an impressive feat in and of itself. The experiment was also able to disprove a previous measurement of this rate from a different experiment called DAMA. Here are the results.

Figure 6: KamLAND-Zen's measurement of the half-life of double β-decay in xenon gas. Credit: INOUE, kunio

Figure 7: Summary of KamLAND-Zen's experimental results. Credit: INOUE, kunio

EXO-200

The Enriched Xenon Observatory Experiment, or EXO-200 for short (the 200 is explained on wiki), is KamLAND-Zen’s biggest competitor in the race for finding neutrino-less double-β-decay. The first slide shows how much more data they have since the last time their results were announced. The second slide shows their background and the fact that they have observed almost 22,000 2-neutrino double β-decay events! I cannot describe how cool that is other than say just that: it is really cool that they have so many events. Consequentially, their results are in good agreement with KamLAND-Zen’s results. So sadly, no neutrino-less events.

Figure 8: Details of the EXO-200 Experiment, its analysis, and differences from its previous analysis. Credit: FARINE, Jacques

Figure 9: Results from EXO-200 Experiment. Credit: FARINE, Jacques

Figure 10: Results from EXO-200 Experiment with comparison to other experiments.. Credit: FARINE, Jacques

Day 4

Day 4 was a much needed rest for conference goers. Like most other attendees, I spent the day exploring Kyoto and then working with my adviser on a paper we are hoping to finish soon. In the evening, however, we were treated to a dance performance by real-life geisha dancers. I was unable to get too many photos but below is a good one. The two dancers are both geiko-sans (fully-fledged geisha dancers) but there were also three maikos (apprentice geisha dancers).

: Figure 11: Something. Credit: Mine

After the short entertainment, the main event began: a public lecture on the importance of neutrinos and their influence on how the Universe evolved, given by Prof. Hitoshi Murayama, Director of the University of Tokyo’s Institute for Physics and Mathematics of the Universe. Sadly, I was unable to find his slides online, which is especially unfortunate considering his talk was entitled, “Neutrinos May Be Our Mother.” I was able to snap this photo of Prof. Murayama discussing his recent meeting with the Prime Minister of Japan and philanthropist Fred Kavli, of the famed Kavli Foundation. Mr. Kavli’s generous contributions to physics and astronomy have led to the construction of dozens of institutes around the world to focus and have allowed us to concentrate on the most important mysteries of this universe we call home.

Figure 12: Prof. Hitoshi Murayama (Far Left), sharing a picture of his meeting with Mr. Fred Kavli (Second from Right), and Prime Minister Yoshihiko Noda (Far Right). Credit: Mine.

Tags: #Neutrino12, @bravelittlemuon, Day 3, neutrino, Neutrino 2012, Neutrino2012
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Neutrino 2012: Day 2

Tuesday, June 5th, 2012

When it comes to neutrino experiments, they were all there Day 2: T2K, MINOS, OPERA, ICARUS, and NOνA, and LBNE!

Hi All,

Here is a run down of what happened Tuesday. I will try to post Day 3 things this afternoon, which should be Wednesday morning for the US. An update on the LBNE is at the bottom of the post.

Happy Colliding

- richard (@bravelittlemuon)

T2K

Figure 1: Update of T2K experiment after March 11, 2011 earthquake that struct Japan. Credit: NAKAYA, Tsuyoshi.

The Tokai to Kamoika Experiment, or T2K for short, is a one impressive behemoth of an experiment. Much like MINOS Experiment at Fermilab, you shoot protons into a target to make pions. The pions then decay into neutrinos, and the neutrinos travel 183 mi (295 km) through the Earth to the (Super-, Hyper-) Kamiokande detector in Kamioka, Japan.

When the March 2011 earthquake struck Japan, the proton accelerator at the J-PARC physics lab was heavily damaged, and power throughout the country was effectively shut off. Due to immense leadership of J-PARC’s director, Shoji Nagamiya, the accelerator was back online December 9, 2011, and by December 24, 2011, neutrinos were being observed in Kamioka. It is baffling that despite all this, the experiment still marched on and announced the herculean result it had observed 10 events where a muon-neutrino had converted into electron-neutrino. The predicted results were 9.07±0.93 event assuming sin²2θ₁₃=0.1, and 2.73±0.37 events assuming sin²2θ₁₃=0.0. Consequently, the experiment was able to measure θ₁₃ itself and found sin²2θ₁₃=0.104 ^+0.060_-0.045

: Figure 2: Schematic of T2K (Tokai To Kamioka) Experiment. Image: http://www2.warwick.ac.uk/newsandevents/news/t2k

MINOS

The MINOS Experiment at Fermilab is most simply described at the US version of T2K. It is unfair and a disservice to both MINOS and T2K to make that comparison because of the unique features of the experiments, but I have a lot to write. In 2010, MINOS caused a bit of a stir when it measured the mass difference between two of the three anti-neutrinos. The measurement itself was not at all controversial. The issue was that this result differed from the well measured mass difference for regular neutrinos. Here the Fermilab presser that can tell you all about it. On Day 2, MINOS announced that the discrepancy between neutrinos and anti-neutrinos has completely disappeared and that the previous disagreement is believed to have been a statistical fluctuation. It appears that Fermilab has released a new press release this morning explaining things in more detail. Below are the main plots. Oh, and MINOS data also slightly favors inverted hierarchy for anyone interested in that. Fun fact: In its seven years of running, MINOS has used over 1.5 sextillion protons to produce all of its neutrinos.

Figure 3: Preliminary results from the MINOS detector showing best fit value for neutrino mass splitting and mixing angle. Credit: NICHOL, Ryan

Figure 4: Preliminary results from the MINOS detector showing best fit value for anti-neutrino mass splitting and mixing angle. Credit: NICHOL, Ryan

Figure 5: Preliminary results from the MINOS detector showing best fit value for neutrino and anti-neutrino mass splitting and mixing angle. Credit: NICHOL, Ryan

OPERA

The OPERA Experiment, or Oscillation Project with Emulsion-tRacking Apparatus, is a fine and mighty experiment capable of one of the most time-consuming tasks in neutrino physics that even tests the patience of sleeping mountains: observing the conversion of tau-neutrinos into muon-neutrinos. Like T2K and MINOS, OPERA gets its neutrinos from pions, which are produced when protons strike a fixed target. Specifically, the experiment uses CERN protons in its first four years of running has used about 14.2 x 1019 protons!

Figure 6: A breakdown, by year, of how many protons the OPERA experiment has observed. Credit: NAKAMURA, Mitsuhiro

OPERA’s defining characteristic is how well it is able to extract out a signal from everything else. Below is an example of a real event in which a neutrino has collided with a nucleus, producing a charge lepton and nucleus somewhat fragments.

Figure 7: An example of a real neutrino event being extracted from the data. Credit: NAKAMURA, Mitsuhiro

The big news from OPERA on Day 2 was the second observation of a muon-neutrino converting into a tau-neutrino! 2 events in over four years; I told you this thing required patience. Here is how the event works.

Figure 8: The OPERA Experiment's second candidate event of a muon-neutrino converting into a tau-neutrino. Credit: NAKAMURA, Mitsuhiro

Here is an explanation of the event.

Figure 9: A breakdown of OPERA's second tau-neutrino candidate. Credit: NAKAMURA, Mitsuhiro

Finally, here is a summary of the status of OPERA’s search tau-neutrinos. It is worth mentioning that the experiment also announced it has observed 19 instances where a muon-neutrino has converted into an electron-neutrino!

Figure 10: A summary of the current status of the OPERA Experiment's search for appearances of tau-neutrinos. Credit: NAKAMURA, Mitsuhiro

A Few Words on ICARUS and NOνA

Due to the lack of time, I will simply say that one can expect big things from ICARUS and NOνA when they both have results. ICARUS has already started running and the gigantic, LHC-Detector-sized NOνA will start running next year when Fermilab flips on its proton beam again. NOνA will be capable of determining whether neutrinos have normal mass hierarchy or inverted mass hierarchy.

LBNE

Interesting things happen at conferences, like an impromptu talk added the morning of the second day of events. Long Baseline Neutrino Experiment co-spokesperson Robert Svoboda surprisingly gave an update of the LBNE, the first since its budget was gravely slashed. Much is still being kept internally for another few weeks when the final proposal will be submitted, so I will limit what I say. In summary, there are three options being considered for the experiment for phase 1 construction. Beyond that, it is up to the Funding Lords.

Figure 11: Update of the Long Baseline Neutrino Experiment. Credit: SVOBODA, Robert

Figure 12: Update of the Long Baseline Neutrino Experiment. Credit: SVOBODA, Robert

Tags: #Neutrino12, @bravelittlemuon, Day 2, neutrino, Neutrino 2012, Neutrino2012
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Neutrino 2012: Day 1

Sunday, June 3rd, 2012

Updated: Tuesday June 5, 2012 13:23 local (Kyoto) time.

Day 1 Events

Hi All,

Sorry for the delay. The conference’s schedule is jammed packed, and not basking in a wireless cloud limits my access to the site. At any rate, Monday was a very productive day. For the first time under a single roof, all the nuclear reactor-based experiments showed their measurement of θ₁₃, the physical quantity that stipulates the probability of two specific neutrinos turning into each other. θ₁₃ (pronounced: theta-one-three) has been extensively covered here if you are interested in reading more about it. Herein lies the purpose of conferences: to allow experimentalists and theorists the opportunity to compare and contrast highly important results from similar experiments. Checking that everyone’s results agree also shows the importance of redundant experiments.

As I mentioned, the conference open with Laureate Jack Steinberger giving a quite overview of the history of neutrinos. He paid quite a homage to his hero Bruno Pontecorvo for his everlasting contributions to physics. Pontecorvo is the definition of a man born ahead of his time. Not only did he first postulate that neutrinos could oscillate back in 1957 (first confirmed in 1998), he also recognized that the rate of detecting cosmic muons was comparable to the rate of radioactive (beta) decay. According to Steinberger, Pontecorvo’s result was largely ignored. Fermi himself “did not think there could be a relationship between the muon… and the electron. It was too much an intellectual jump.”

Fig. 1: Me with Nobel Laurate Jack Steinberger at the first poster session of the Neutrino 2012 Confereince in Kyoto, Japan.

However, it was CERN’s historic Gargamelle Experiment that made Steinberger’s just beam with excitement. The experiment was the first to demonstrate evidence for the existence of the Z boson, the most unique prediction of the Electroweak Theory (Standard Model). He thinks of it as “the most important experiment ever done at CERN” and confirmation of the Electroweak Theory is the “most glorious result at cern.”

A rather interesting talk was a talk entitled “Application of Reactor Anti-Neutrinos.” Nuclear reactors are incredibly useful for physics because they are a controlled source of neutrinos. Unfortunately, plutonium is an inherent byproduct of nuclear reactors. However, we can look at this another way: plutonium-producing reactor is a generous producer of neutrinos. This clever rearrangement of words is the premise of one potential breakthrough in nuclear non-proliferation: uncovering the mass production of Pu via neutrinos. I have to run, but in short “the anti-nutrino has a possibility to monitor reactor operation and Pu contents in operation core.” It reminds me a bit of Laureate Luis Alvarez’s clever use of cosmic rays to image the internal structure of Egyptian pyramids.

Happy Colliding

- richard (@bravelittlemuon)

Greetings from Kyoto! The sun is high and the solar neutrino rate is brimming.

Conference Poster for Neutrino 2012 in Kyoto, Japan (http://neu2012.kek.jp/)

It is Day 1 of Neutrino 2012, an annual conference dedicated to all things neutrino, and today’s talks about about to begin shortly with a welcome from, count them: two Nobel laureates. The first is by Jack Steinberger, co-discoverer of the muon neutrino along with science education advocate Leon Lederman, on the present state of neutrinos, what we know about them, and what we definitely do not know. It is a highly appropriate talk to kick off such an important conference. The second talk is by Makoto Kobayashi, “K” of the famed CKM matrix, and is on the existence of neutrino masses and how that discovery has defined a generation of on-going research.

Okay, time for the bad news. There is no internet in the main lecture hall and, as a consequence, I cannot physically live-blog this week. This is a bit of a disappointment but check back here often for regular updates through the week. After an interesting conversation on the flight over here, I am expecting to hear some very interesting and very new results.

Happy Colliding

- richard (@bravelittlemuon)

Tags: #Neutrino12, Day 1, neutrino, Neutrino 2012, Neutrino2012
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… and it is summer travel season, too!

Friday, June 1st, 2012

Summer is a productive time for us and tends to involve lots of traveling.

Fig. 1: My 2010 PDG booklet and my Japan Rail pass. I am not sure which is more important.

Hi All,

As fellow QDer Aidan posted this morning, it is conference season, again! Lots and lots of conferences for all the different sub-sub-fields in physics. Two big ones on my plate are Neutrino 2012, which is about ALL things that begin with the letters n-e-u-t-r-i-n-o and end in the letter -s; and ICHEP 2012, which is the mother-of-all high energy physics conferences. (Much more on ICHEP in a few weeks seeing that I have been invited to be a panelist on the “Social Media in Science Communication” session. Trust me, it will be good.)

Neutrinos are all the rage these days: from #FTLneutrinos to θ13, we are determined to know precisely how neutrinos work. Fortunate for us, there is a huge international conference, imaginatively called “Neutrino,” next week in the gorgeous, ancient city of Kyoto, Japan, and you can definitely count on there be a Quantum Diaries presence. QDer Zeynep Isvan will be around, and, with the suggestion from my chief editor, Daisy, I will be live-blogging the plenary sessions when I can. The programme is also already online, so feel free to check out the topics.

After the conference, however, is when things get kicked into high gear for me. A few months ago I won a NSF summer fellowship to research dark matter in Japan. It is now summer, so for the next three months I will be a visitor at University of Tokyo’s prestigious Institute for the Physics and Mathematics of the Universe, or IPMU for short. I still have plots to make for a meeting today and my first flight is (literally) 24 hours from now. At least I have my trusty messenger bag already packed with two of the more important things: a Japan Rail pass and my 2010 PDG booklet!

See you in Kyoto!

Happy Colliding

- richard (@bravelittlemuon)

PS While adding links and sources to the post, I found my IPMU host on Twitter.

PPS More than 3.6 fb-1 worth of data has already been collected by the collider experiments.

Fig. 2: Conference Poster for Neutrino 2012 in Kyoto, Japan (http://neu2012.kek.jp/)

Tags: @bravelittlemuon, IPMU, japan, neutrino, Neutrino2012, Summer, travel
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And So It Begins: Pheno 2012

Monday, May 7th, 2012

Hi All! Today marks the beginning of the Phenomenology 2012 Symposium, Pheno for short, or #Pheno2012 if you are into hashtags, here at the University of Pittsburgh.

Phenomenology 2012 Symposium Poster (Click for Full Size)

It will definitely be an exciting three days because this conference is dedicated solely to promoting the partnership and collaboration between experimentalists and theorists. For experimentalists, this is a grand opportunity to learn about new theories that may actually be testable at the Large Hadron Collider; it is also a chance to learn about new ways to test well-known ideas. Similarly, for theorists, this is an opportunity to learn about the fine details of a particular study for new physics. It is one thing to rule out the existence of certain particles (like squarks!); it is an entirely separate situation if there were special caveats were assumed (like most every search for squarks!).

From Tokyo, to Hawaii, to Heidelberg, hundreds of particle physicists from around the world are assembling for what will be a great melding of minds. Even a couple fellow QDers, including Flip Tanedo and Corrinne Mills, will be in attendance. In fact, Corinne has the star-studded honor of being first talk and will be presenting the latest Standard Model results from the ATLAS and CMS experiments. (Good luck!)

Updates from ATLAS, CMS, and LHCb will definitely be available via #Pheno2012, and, as always, Happy Colliding.

- richard (@bravelittlemuon)

PS, The detector experiments have already received 1 fb-1 worth of proton-proton collisions.

Tags: #Pheno2012, ATLAS, CMS, LHC, LHCb, Pheno, Pheno 2012, Phenomenology, Pittsburgh, University of Pittsburgh
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Richard Ruiz | Univ. of Pittsburgh | U.S.A.

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