Stefania Ricciardi RAL, March 2009 A short journey to the infinitely small Fundamentals of Particle Physics Building blocks: particles and forces Current areas of research Stefania Ricciardi RAL, March 2009

Warning Stay awake and keep an open mind! This journey may change your vision of the Universe. What you will hear may alter your perception of reality. Stay awake and keep an open mind! We are entering a Quantum World..

We and all things around us are made of atoms Human Hair ~ 50 mm = 50 10-6 m = 0.000050 m Atom ~ 10-10 m = 0.0000000001 m Magritte

Atoms Atoms are all similarly made of: - protons and neutrons in the nucleus - electrons orbiting around proton The electron was the first elementary particle to be discovered (JJ Thomson 1897) Protons, neutrons are made up of quarks electron neutron

From the atom to the quark How small are the smallest constituents of matter? <10-18 m <10-1 8 m ~ 10-14 m ~ 10-10 m ~ 10-15 m Atoms and sub-atomic particles are much smaller than visible light wave-length Therefore, we cannot really “see” them (all graphics are artist’s impressions) To learn about the sub-atomic structure we need particle accelerators

Quarks detected within protons Freeway 280 End Station A experimental area 2 miles long accelerator Stanford (SLAC), California, late 1960s Fire electrons at proton: big deflections seen!

Is the whole Universe made only of quarks and electrons? No! There are also neutrinos! Electron, proton and neutrons are rarities! For each of them in the Universe there is 1 billion neutrinos Neutrinos are the most abundant matter-particles in the Universe! n n n n n nnnnnnnn nn n n nn n nnnnnnn n nn nn nn n n n n n nn n n nn n nnnnnn n nn nn nn nnnnnnn nn nn n nnn nnnnnnn Within each cm3 of space: ~300 neutrinos from Big Bang 1 cm 1 cm Neutrinos are everywhere! in the outer space, on Earth, in our bodies..

Neutrinos get under your skin! per second from Sun are zipping through you n Every cm2 of Earth surface is crossed every second by more than 10 billion (1010) neutrinos produced in the Sun Within your body at any instant: roughly 30 million neutrinos from the Big Bang No worries! Neutrinos do not harm us. Our bodies are transparent to neutrinos

Protons and neutrons in the quark model Quarks have fractional electric charge! u electric charge + 2/3 d electric charge -1/3 proton (charge +1) neutron (charge 0) u u u d So we know now that protons and neutrons are made of quarks. d d

The particles of ordinary matter ne e- u d -1/3 +2/3 charge Leptons: n = neutrino e = electron Quarks: u = up d = down -1 All stable matter around us can be described using electrons, neutrinos, u and d “quarks”

3 Families (or Generations) 1st generation 2nd generation 3rd generation ne e- u d -1/3 +2/3 +2/3 +2/3 nm m- c s nt t- t b -1 -1 -1/3 -1 -1/3 Ordinary matter Cosmic rays Accelerators 3 generations in everything similar but the mass We believe these to be the fundamental building blocks of matter

Quark masses 175 GeV Top (discovered 1995) E= mc2 1 proton mass ~ 1GeV (10-27 Kg) 0.003 0.006 4.5 0.095 1.2 The mass grows larger in each successive family

Anti-matter For every fundamental particle of matter there is an anti-particle with same mass and properties but opposite charge Matter Anti-Matter ne e- u d -1/3 +2/3 e+ +1/3 -2/3 +1 -1 Bar on top to indicate anti-particle positron Correspondent anti-particles exist for all three families Anti-matter can be produced using accelerators

Matter-antimatter pair creation Electron-positron pair created out of photons hitting the bubble-chamber liquid Example of conversion of photon energy into matter and anti-matter Matter and anti-matter spiral in opposite directions in the magnetic field due to the opposite charge Energy and momentum is conserved

Building more particles B mesons (bq) c c J/y b b Y Many more mesons and baryons…

Quark confinement There are no free quarks, quarks and antiquarks are “confined” in colourless doublet (mesons) or triplets (baryons) by the exchange of gluons Decay Z0 Gluon hold quarks together as they move further apart until the gluon connection snaps, and other quark-antiquark pairs are created out of the energy released The new quarks bound to the old quarks and form new mesons ® S.Ward

Quarks and colour All quark flavours come in 3 versions, called “colours” u d +2/3 -1/3 up down Quarks combine together to form colourless particles Baryons (three quarks: red+ green + blue = white) Mesons (quark-antiquark pair) such as red u+anti-red ubar state Strong forces “glue” quarks together in bound states proton p u pion u p

Confinement Color confinement, often simply called confinement, is the phenomenon that color charged particles (such as quarks) cannot be isolated singularly, and therefore cannot be directly observed.[1] Quarks, by default, clump together to form groups, or hadrons. The two types of hadrons are the mesons (one quark, one antiquark) and the baryons (three quarks).

Confinement The constituent quarks in a group cannot be separated from their parent hadron, and this is why quarks currently cannot be studied or observed in any more direct way than at a hadron level

Confinement The force responsible for holding quarks together is the strong nuclear force, which is notable as the only fundamental force that does Not decrease with distance (a property known technically as color confinement).

Confinement For these reasons, as more and more energy is pumped into a system in an attempt to separate the quarks, we find that eventually it takes so much energy that we end up producing a new quark pair (quark and antiquark) before getting the quarks separated beyond the strong force range.

The Particle Physicist’s Bible: Particle Data Book https://pdg.lbl.gov "Young man, if I could remember the names of these particles, I would have been a botanist!“ E.Fermi to his student L. Lederman (both Nobel laureates) The Particle Physicist’s Bible: Particle Data Book https://pdg.lbl.gov Most particles are not stable and can decay to lighter particles..

The 4 forces of Nature Weak Electromagnetic weak charge Electric Beta-decay pp fusion Electromagnetic TV, PCs Magnets e- e+ creation weak charge Electric charge Strong Quark binding Gravity Responsible of Keeping us well-planted on earth strong charge mass

THE WEAK FORCE Beta Decay n p Antineutrino Electron

A (free) neutron decays after 15 min Neutron b-decay At quark level: d→ u e- ne u d p u d n 15 min e- ne A (free) neutron decays after 15 min Long life time (15min is an eternity in particle physics!)  “weak” without such weak interactions the Sun would shut down!

Electromagnetic force The repulsive force that two approaching electrons “feel” e- e- Photon is the particle associated to the electromagnetic force “smallest bundle” of force Photon

Photon exchange Feynman Diagram

Weak force: W-,W+,Z0 b-decay n→pene W- Electric charge conserved at each vertex

Strong force: gluons Gluons interact with quarks Gluons interact with other gluons

Feynman diagrams Reference the Feynman videos!

Force Particles (summary) Particles interact and/or decay thanks to forces Forces are also responsible of binding particles together Strong: gluons Only quarks (because of their colour charge) Weak: W+, W-, Z0 Leptons and quarks (only force for neutrinos) Electromagnetic:g Quarks and charged leptons (no neutrinos) Gravity: graviton? Still to be discovered Negligible effects on particles

The Standard Model Framework which includes: Not gravity! No quantum Matter 6 quarks 6 leptons Grouped in three generations Forces Electroweak: g (photon) Z0, W± Strong g (gluon) Not gravity! No quantum field theory of gravity yet.. H= the missing ingredient: the Higgs Boson Very successful to describe all observed phenomena in the subatomic world so far. But there ought to be more..

Beyond the Standard Model:Unification of forces ELECTRO- MAGNETIC UNIFIED FORCE? GRAVITY STRONG WEAK Looking for a simple elegant unified theory

Recap Leptons: electrons, (tau) 𝜏 or (mu) μ and associated neutrinos Hadrons: either mesons or baryons Mesons are made from an antimatter-matter pair Baryons are made from 3 quarks with colour confinement rules

Conservation Laws Lepton number, strangeness, baryon number and charge are all conserved in particle physics interactions (strong force). All quarks have a strangeness of 0, except the strange particle (naturally) with a strangeness of -1. All leptons have a lepton number of 1 and anti-leptons have a lepton number of -1. All quarks have a baryon number of 1/3.So all baryons have a baryon # = 1. Mesons have a baryon # = 0.

Conservation Laws Example: Determine the quark content of a meson with charge +1 and strangeness 0 and that of a baryon with charge –1 and strangeness –3. Meson: Baryon:

Conservation Laws Example: Determine the quark content of a meson with charge +1 and strangeness 0 and that of a baryon with charge –1 and strangeness –3. Meson: made of matter-antimatter. 𝑢 𝑑 Baryon: made of 3 quarks but strange particle only one with strangeness of -1: so it must be sss

Kaons A Kaon is a meson made with strange quarks. It’s a K-meson. K+ is 𝑢 𝑠 K0 is d 𝑠 or s 𝑑 K- is 𝑠 𝑢

Conservation Laws Example 2: The following particle interaction is proposed. p + π– → K– + π+ In this interaction, charge is conserved. State, in terms of baryon and strangeness conservation, whether the interaction is possible.