What Is a Higgs Boson?, What Did CERN See?, and Why It's a Big Deal!

This is my disclaimer - I AM NOT A PARTICLE PHYSICIST!  Therefore, this subject does not fall into my realm of expertise.  However, I do have a very basic training in the physics behind all of this so I would like to share with you a little bit about why all of us physicists have been so excited of late...


WHAT IS A HIGGS BOSON?

The Higgs boson (regular Wikipedia entry, Simple English Wikipedia entry) is the elementary particle that gives matter mass.  Many of us have probably heard about Einstein's famous equation:

This image is taken from Wikipedia.

While this equation is famous, the true meaning behind what it means is often not fully appreciated (I used to see it and simply think "Einstein!").  It means that mass can be converted to energy and energy can be converted to mass, also known as the mass-energy equivalence.  The energy, E, from an amount of mass, m, is equal to the mass multiplied by the speed of light, c, squared (c² = c*c, c is about 670,616,629 miles/hour).  If you were to convert 1 oz of matter into energy, you would have about 2,500,000,000,000,000 Joules of energy and this would keep a 100 W light bulb lit for over 807,389 years!  So, a little bit of matter can be converted into an immense amount of energy!  It is this conversion of mass to energy that makes nuclear weapons so destructive.

But, if we convert energy into mass, where does this mass come from?  The Standard Model, which is the working description of how the fundamental particles interact (I talked about this in my post discussing gravitons), says it comes from the Higgs field.  This is a field similar to the electric field and the magnetic field (more on fields in general here).  At the instant after the Big Bang, all particles moved at the speed of light (c from above) since none of them had mass because there was no Higgs field.  In the next instant (about a trillionth of a second later), the Higgs field came into existence and produced a resistance to particles based on what they were made of.  This resistance manifests itself as mass: the slower a particle moves through the Higgs field, the more massive it is.  The Standard Model also allows fields to manifest themselves as particles (the photon is the particle associated with the electric and magnetic fields).  Therefore, this Higgs field should also manifest itself as a particle and we call it the Higgs boson.

The only particle from the Standard Model that has not been detected is this Higgs boson.  (Note that gravity is not described by the Standard Model.)  This is because the Higgs boson is very massive for a fundamental particle at about 133 times the mass of a proton.  The amount of energy conversion needed to produce this mass is much larger than we have been able to create in the past.  That is, until CERN built the Large Hadron Collider (LHC)...


WHAT DID CERN SEE?

View of the CMS experiment [note the person near the center] (© CERN)

CERN is the home to several experiments including CMS and ATLAS.  Both of these experiments smash together protons with very large energies.  The protons and their energy can change into a Higgs boson (if there is enough energy).  The Higgs boson decays (changes into something else) almost immediately, so the LHC experiments look for the Higgs boson's signature in the resulting particles.  There are 5 pairs of particles that result from the decay of a Higgs boson, including 2 photons.

Both CMS and ATLAS saw the Higgs signature in 2 of the 5 different resulting decay pairs.  Only CMS had sufficient data to look for all 5 kinds of decay pairs and saw with high certainty signatures in 4 of the pairs.  More research is needed for the signature CMS didn't see.

Diagram of the ATLAS experiment [note the people on the bottom left] (© CERN)

WHY IT'S A BIG DEAL!

The official conclusion is that CERN has indeed observed a Higgs-like particle.  "Higgs-like" does not mean that they are unsure if they found what they were looking for.  Instead, it appears that the Higgs boson they observed has more properties to it than the Standard Model predicted.  The LHC has found what it is looking for as well as hints that there is new physics to be discovered.

So this is the big deal: the population of the Standard Model is complete but the model itself doesn't appear to describe everything.  That is something we knew before, but now we are seeing it with the apparent complication in what was and wasn't observed in the discovery of the Higgs boson.

I am a physicist because every time you discover something new, not only do you understand the Universe better, but you have even more exciting questions to answer!  Soon enough, it is going to be gravitational waves stirring up excitement like this and I am going to be in the midst of it all!


Side Note:
IT'S NOT THE 'GOD PARTICLE'

The Higgs boson is sometimes referred to as the "God particle," especially by the media.  However, it has nothing more to do with God than any other particle in the Universe.  The origin of this misnomer is a book by Nobel Laureate Leon Lederman titled The God Particle: If the Universe Is the Answer, What Is the Question?.  Likening the Higgs boson as a God particle refers to it being the origin of all matter's mass.  Physicists (like me as well as Lederman himself) generally dislike this nickname since it places much more import on this particle than it deserves.  But above that, it is offensive to people of faith and makes us look like we are trying to replace God.  We aren't. 


Want More? ...
Watch the announcement seminar
Read the official CERN press release

No "Faster Than Light" Neutrinos

SCIENCE AS A PROCESS

Most people see science as purporting itself to be infallible and they can twist this perception for many reasons (e.g. "See, they didn't see what they thought they saw so science cannot be trusted.").  The truth is that science is a process.  It must be reproducible by others.  Sometimes, an experiment comes around that seems to defy the current understanding of science and people are quick to jump and accuse science of being unreliable.  Really, when results like this come to light, it is the duty of other scientists to scrutinize the results: to try to reproduce them and, if they cannot, try to find where the errors in the original experiment occurred.  Most of the time, radical findings are disproved.  When they are not, this is an exciting time for science to learn more about the world around us!  We scientists often spend as much time trying to disprove things as we spend trying to prove them.  Truly revolutionary results often exploit a subtlety in a theory (which in science means a highly tested and verified description of how something works and NOT a hypothesis or guess as it is sometimes used in everyday language) or law that opens the way to a deeper understanding.  Science is not created or invented by scientists - the Universe has its properties and we simply pursue the discovery of them so we can understand better how it works.

THE "FASTER THAN LIGHT" NEUTRINOS

While at the APS April Meeting this past week, there was a lot of excitement (see the talk abstracts in this session) about the "faster than the speed of light" neutrinos that the OPERA collaboration claimed to have observed.  There was extra excitement since there was a final resolution at the beginning of the meeting along with a little drama.  There were even talks on how to use this new coverage as a great outreach opportunity to illustrate science as a process (don't think of the scientific method that you were taught in school - science almost never follows that prescription but it is a good starting point).  I've had many people bring this up to me when I talk about how gravitational waves are expected to travel at the speed of light but could travel slower - never faster.  Then there is usually someone who asks about the new neutrino results and this is when I get to talk about how science is a process.  So, I've decided that I would dedicate today's blog post to the subject matter.  Spoiler alert: there are NO "faster than light" neutrinos!  If you are interested in a very good discussion of these results, disproof, and aftermath, read more about it here.

***  What is a neutrino?  ***

A neutrino is a virtually massless particle that interacts so weakly with matter that it can travel right through any matter with only a few (of billions and billions) interacting with matter.  The neutrino has never been directly detected but we know when one interacts with matter because it produces other subatomic particles or radiation.  Every second, about 10,000,000,000,000 (that's 10 trillion) neutrinos from our Sun pass through every square foot when the Sun is directly overhead.  Those neutrinos pass right through you and, since they so rarely interact with anything, you don't notice a thing. 

Because neutrinos are virtually massless (I say virtually because there is evidence they they do indeed have mass, but it is so small that it hasn't been accurately measured) they can travel at or so near the speed of light that we haven't measured evidence of them traveling slower.  This agrees with special relativity: only massless particles can travel the speed of light and massive particles can only travel slower (there are theoretical particles called tachyons that can only travel as slow as the speed of light and travel faster otherwise - these have never been observed).

***  What is the OPERA experiment?  ***

The OPERA experiment used a beam of neutrinos created at CERN on the Franco-Swiss border to send to the OPERA detector in Gran Sasso, Italy.  That's right, the beam of neutrinos was shot right through the intervening earth between these 2 sites.  Since the distance is known to high precision, the time it takes the neutrinos to arrive at OPERA is directly related to their speed.  It appeared that they were measuring their arrival about 60 nanoseconds (0.00000006 seconds) before they should have if they traveled at the speed of light. 

***  What did we know about the speed of neutrinos before OPERA?  ***

There have been many experiments that have observed neutrinos traveling at the speed of light.  These experiments have been both Earth-sourced (where we create and then detect the resulting neutrinos) and Universe-sourced.  A spectacular example of using neutrinos from space was the detection of neutrinos that preceded the supernova 1987a.  They arrived 3 hours before the light from the stellar explosion did.  This is what is expected because neutrinos are created when the matter in the star collapses before the supernova explosion.  If neutrinos traveled as fast as the OPERA collaboration claimed to have observed them traveling, then after traveling the more than 160,000 light years to Earth they would have arrived 4 years before the accompanying light we observed.

***  Should OPERA have published their result?  ***

So, was the OPERA collaboration wrong to publish their observations?  Absolutely not (in my opinion at least)!  Nowhere in their paper did they claim that they have found a fault with the current understanding of the physics - they simply couldn't disprove their own observations so they opened their experiment up to the scrutiny of the scientific community.  They even recognize the controversial results and their desire for scrutiny of their experiment in their paper (which can be read in full here):

"Despite the large significance of the measurement reported here and the stability of the analysis, the potentially great impact of the result motivates the continuation of our studies in order to investigate possible still unknown systematic effects that could explain the observed anomaly. We deliberately do not attempt any theoretical or phenomenological interpretation of the results. "

THE RESOLUTION TO THE CONTROVERSY AND THE FALLOUT

In the end, it was found that a loose fiber optic cable and an error in their timing produced the superluminal (fancy way of saying 'faster than the speed of light') observations.  THERE IS NO EVIDENCE TO SUPPORT THAT NEUTRINOS CAN TRAVEL FASTER THAN THE SPEED OF LIGHT.  Also, the ICARUS experiment (located in Gran Sasso with OPERA) independently reproduced the experiment and found no faster than light neutrinos.

The heads of the collaboration resigned their post on March 30 (just a few days ago) after a vote of no confidence.  There were scientists in the collaboration who felt the publication of the results was premature, and that not everything that was done was good experimental procedure.  It seems that the resignations were the result of their rush to publish the paper, more than what they published.