Knocking on the Heaven’s Door

Author: Lisa Randall
Publisher: Harper Collins 2011

Higgs boson is extremely unstable.  When experimenters were looking for Higgs, they were actually looking for particles Higgs decays into.  The particles into which Higgs decays have to have a sufficiently large interaction with Higgs for such a process to occur.  Bottom quark is less than half of the measured mass of the Higgs (125 GeV) .  Therefore, a Higgs can decay into a bottom quark and an anti-bottom quark without violating any known conservation laws.  Even though this is the dominant Higgs decay mode, when the Higgs discovery was announced it was detected via two weaker decay modes; decay into photons and decay through weak gauge bosons.

Quantum mechanics allows a Higgs to decay into two photons because it allows for virtual particles.  They are particles that briefly come into existence, can have further interactions, and then disappear.  The Higgs decays into photons a 0.05% of the time.  Weak gauge bosons also get produced as virtual particles.  Experimenters using ATLAS and CMC—two general-purpose detectors at the Large Hadron Collider—observed that a particle was decaying into two photons at a rate that exceeded expected rate in the absence of a Higgs boson.  The same particle was decaying into two gauge bosons confirming the finding.  

The weak force—one of the four fundamental forces—affects only matter that is within extremely close range.  Two particles must be within one ten thousand trillionth of a centimeter to influence each other via weak force.  According to the quantum field theory, the short range of the weak force could mean only one thing: the weak gauge bosons communicating the force had to have nonzero mass.  However, according to the original theory of forces, gauge bosons such as photon must have zero mass.  Further, according to the naive version of the standard model, neither the gauge bosons, nor the elementary particles such as quarks and leptons should have non-zero masses.  But the measurements show that these particles have non-zero masses.  So, the original theory was clearly wrong.  The solution is to propose a Higgs mechanism.

Higgs mechanism involves a field call the Higgs field.  One way to think about the Higgs mechanism and the origin of the masses is that it lets the vacuum behave like a viscous fluid—a Higgs field that permeates a vacuum—that carries weak charge.  Particles that carry weak charge such as quarks, leptons and weak gauge bosons can interact with this fluid, and these interactions slow them down.  Particles with zero mass move at a speed of light.  The slowing down then corresponds to the particles acquiring mass.

Each type of field generates its own particular type of particle.  An electron field is the source of electrons and Higgs field is the source of Higgs particles.  

If you feel that you have no clue of what I am talking about after reading thus far, then join the club.  I am still looking for a book or an expository article on Higgs mechanism that goes beyond this type of popular science explanations but falls short of a textbook explanation.