A Spin on the Higgs Boson

St. Columba's College

7pm Monday 12th November 2012

Nigel Buttimore

Trinity College Dublin

Universe is made of Fermions & Bosons

Fermions relate to matter particles (Enrico Fermi)

• First particle was discovered in 1897, electron (e⁻, a lepton)
• Other leptons were found in 20c, neutrinos, muons and taus
• Lepton masses range from a millionth to 7000 times that of e⁻
• Centres of atoms found to be composed of quarks and gluons
• The heaviest quark is about 70,000 times that of the lightest
• Why is the top quark mass a trillion times the neutrino mass?

Bosons relate to forces between particles (S N Bose)

• The electromagnetic field is carried by a boson called a photon
• The weak interaction (radioactivity) relates to bosons W and Z
• Peter Higgs, and five others, introduced a scalar field in 1964
• This field would give a mass to W and Z, but not to a photon
• Higgs alone said there should be a Boson to generate masses
• A Higgs-like Boson was found at CERN's LHC on 4th July 2012
• It seems that electromagnetic & weak interactions are unified

Higgs Boson and Electroweak Interaction Tests

• Does the Higgs Boson have zero spin so that it is a scalar?
• Such a scalar would decay without any preferred direction
• Does it decay to leptons or quarks such as a tau lepton pair?
• Decays to photons, Ws and Zs have been checked so far
• A leptophobic Higgs Boson would not be expected, but . . .
• A Kyoto conference this Science Week will have information

The strong interaction (gluon field) and Gravity

• The strong force is carried by a vector boson called a gluon
• The gluon interacts only with quarks, antiquarks and itself
• The photon interacts with charged bosons, leptons and quarks
• Gravity is mediated by the graviton causing masses to attract
• Photons, gluons and gravitons are all neutral massless bosons
• The Standard Model of Particle Physics may be summarised

A history of the Radiation dominated Universe

• The universe initially consisted of massless quarks, leptons, bosons, and antiparticles all travelling at the speed of light
• As the universe expanded it cooled; at the temperature 3 P°K a Higgs field appeared everywhere giving mass to many particles
• At temperature 2 T°K, quarks condensed to protons & neutrons
• At 1 G°K, protons & neutrons form deuterons & helium nuclei; also electrons and positrons react to produce many photons

A history of the Matter dominated Universe

• At 4 k°K, the few left-over electrons combined with protons, deuterons and helium nuclei to form hydrogen & helium atoms
• After 200 Myr, atoms coalesced under gravity to form stars which then created heavier elements by burning and exploding
• Heavy elements condensed to form the solar system at 9 Gyr; Life on earth began at 10 Gyr; animals appeared at 13.6 Gyr
• Humans evolved and try to understand life and the universe

 


       100 YRS AGO       50 YRS         CONSTITUENTS AND INTERACTIONS
  
        Hydrogen        Fermions                   .-----.               
                                                  /       \
                                                  \       /
                                                   'gluon'         
                                                      |
                           up                         |
         proton            up                .----- quark -----.     
           (              down              /         |         \    
            )                              /          |          ?   
           (             Bosons         gamma ----- vector ---- Higgs 
            )                              \          |          ?   
           (                                \         |         /    
        electron        neutrino             '----- lepton ----'     
         




       ATOM (1911)                      PARTICLES (1932-83)  (2012 ?)