Fundamental particles.pptx

The presentation is meant for senior secondary or A Level physics students

1. Fundamental particles Topic for senior secondary or A-level physics students ~ Lalit Kishore

2. Historical perspective Till 19 th centaury atom was considered to the fundamental particle (ultimate: not formed by any other particles or sub-atomic prticles ) In 20 th centaury, Chadwick discovered independent neutrons and protons...protons were found in solar flares...some stars behaved as if they were neutron stars. Studies of cosmic rays led to discovery of new fundamental particles Nuclear force was – the strongest force that can could bind like charges – studied With high power / energy particle accelerators, very many new particles and their anti-particles were discovered and are still being discovered Families / classifications/ series have created to find the missing particles including the God particle

3. Hadrons particles Hadrons as new fundamental particles Quark model of hadrons with six flavours and their charge value and strangeness With discovery of new particles using particle accelerators (collision experiments) to be classified in categories of those affected by strong forces and those not affected 2 conclusions from collision experiments / nuclear reactions Total charge always remains constant Total number of nucleons at times but rarely changed The particles with properties different from neutrons and protons discovered which were called hadrons From the collision studies lead to quark model of hadrons It was proposed that hadrons was further made of fundamental particles called quarks which led to discovery more particles Many types or ‘flavours’ (six)of quarks were discovered and proposed

4. Hadrons’ classification as baryons and mesons With discovery of anti-quarks and various combination with quarks led to new classification of hadrons called baryons and mesons Baryon family : protons, Neutrons and their anti-particles, they consist of 3 quarks Meson family (consisting of quarks / anti-quarks): Pions and kappas

5. Leptons Definition and neutron decay Quark model reaction The fundamental particles not affected by strong forces – no more composed of smaller particles Examples: Electron; positron, neutrino, anti-neutrino In the decay of a neutron; proton, electron and antineutrino are emitted

6. Beta decay explanation in terms of quarks and leptons Weak force presence Proton decay quark model reaction Beta decay is not due strong force and, therefore, must be due to another force called ‘weak force’ or ‘weak interaction’ In beta decay, the lepton number before and after decay remains the same During the decay of a proton in the nucleus, a neutron is formed and a neutrino is emitted

7. Quark model facts Quark model attributes Some quark compositions Quark model has 6 flavours of quark Up Down Strange Charm Bottom Top Quarks have fractional charges A meson contains a quark and an antiquark Baryons contain three either 3 quarks or 3 antiquarks Protons are composed of quarks up, up, and down Neutrons are composed of quarks up, up and down During minus beta decay, a down quark quark changes to an up quark During plus beta decay, an up quark changes to a down quark