The Large Hadron Collider and Beyond Steve King, University of Southampton, Masterclass, 24th March, 2010
L L e.g. bats use high frequency sonar with wavelength less than or about same the size of an insect. So, like bats, to see small things we need light with small wavelength and high frequency – hence high energy photons since Why “High Energy”? There are three reasons: • The resolving power of a microscope is limited by the wavelength of the light.
The basic unit of energy is the “electron Volt” which is the energy that a single electron receives when it passes from the negative terminal to the positive terminal of a 1 Volt battery. 2. Einstein taught us that So high energy is equivalent to large mass. With high energies we are able to produce very heavy particles.
3. Boltzmann taught us that so high energy means high temperature where is Boltzmann’s constant. In the early Universe, just after the big bang, the universe was very small and very hot.So high energy physics teaches us about the early Universe.
Answer: only 84 times! A single atom A nucleus with orbiting electrons nanometre What have we learned from High Energy Physics? - Matter is made of particles (“particle physics”) To understand this, take an apple and a knife, and cut the apple in half once. Then cut one half in half again. Then continue the process. After some number of cuts you will arrive at a single atom. Question: how many cuts are required?
Matter Antimatter Matter The electrical attraction is caused by photon exchange -
The quarks are stuck together by gluons The nucleus of the atom is positively charged It is made of protons (p) and neutrons (n) The protons and neutrons are made of charged quarks The quarks also carry a new “colour charge”
This decay process is very weak (15 minutes is an eternity!) Without such weak interactions the Sun would shut down! Nothing lasts for ever The (free) neutron is radioactive and beta decays after 15 minutes into proton, electron and “neutrino” (electron-like neutral particle)
Photo of Sun taken underground using neutrinos Neutrinos from the Sun Question: How many neutrinos from the Sun are passing through your fingernail in one second? Answer: 40 billion! – day and night since neutrinos can pass right through the Earth without interacting
The mystery of spin All observed elementary particles have spin i.e. spinning angular momentum like a spinning top In quantum mechanics the basic unit of angular momentum is Planck’s constant h divided by 2 Photons and gluons have one unit of spin e.g. polarization of light is due to the photon spin Quarks and leptons have half a unit of spin e.g. In chemistry each s-orbital can only be occupied by at most two electrons, spin-up and spin-down. N.B. Without spin any number of electrons could pile into the lowest energy s-orbital and Chemistry AS level would not exist – unfortunately you not exist either!
Mass t u d c e s b What is the origin of the particle masses?
The Higgs Boson In the“Standard Model”the origin of mass is addressed using a mechanism named after the British physicistPeter Higgs.This predicts a spinless particle:Higgs boson According to Higgs, space is filled with a new type of field analagous to magnetic or electric fields…
The CERN Large Hadron Collider (LHC) Atlas particle_event_full_ns.mov
Pictorial History of the LHC 10th September 2008 - LHC switched on – BBC devote a whole day of coverage to “Big Bang day” -Soothsayers predict the end of the World - Scientists at CERN celebrate Too many late nights?
Pictorial History of the LHC 19th September 2008 – LHC explosion due to bad soldering joint between two magnets – repairs took 14 months
Pictorial History of the LHC 20th November 2009 – LHC switched on again 23rd November 2009 – first LHC proton- proton collisions
Pictorial History of the LHC 16th December 2009 – LHC routine shut down for Christmas 28th February 2010 – LHC switched on again 19th March 2010 (last Friday) – LHC proton beams at 3.5 TeV E=3.5 TeV mc2=0.938 GeV World land speed record for protons
1 TeV The CERN Large Hadron Collider (LHC) will next Tuesday collide protons on protons at energy of 3.5 TeV +3.5 TeV = 7 TeV LHC plans to run at 7 TeV for 18-24 months to acquire as many collision events as possible
Fermions have half units of spin, and tend to shy away from each other, like people who always stay in single rooms at the fermion motel. Bosons have zero or integer units of spin, and like to be with each other, like people who stay in shared dormitories at the boson inn. Supersymmetry says that for every fermion in Nature there must be a boson and vice-versa. Supersymmetric particles have not been observed (yet) so they must be heavier - SUSY must be broken by some mechanism Supersymmetry ? All particles in nature are either fermions or bosons.
SPIN ½ FERMIONS SPIN 0 BOSONS Squarks Quarks Sleptons SUSY Leptons The Generations of Smatter The Generations of Matter
BOSONS SUSY Photino FERMIONS Gluino Gravitino
Could dark matter observed in the collisions of galaxy clusters be the photino? – LHC will “see” it
Standard Model SUSY Strong Weak Electromagnetic SUSY permits a unification of forces
string1.avi Strings live in 11 dimensions
What if no Higgs or SUSY is discovered? My personal best bet for the first discovery at the LHC is a heavier version of the Z boson called a Z-primed Other possibilities include a fourth family, composite quarks and leptons, extra dimensions, technicolour, black holes (environmentally friendly), extra exotic particles with weird charges and colours, etc.. Nightmare scenario: one Higgs boson and nothing else! I DON’T BELIEVE THIS WILL HAPPEN More likely LHC will discover something no-one has thought of – let us hope that whatever is found will be of great benefit humanity – I think there is every chance
What has the LHC done for us? • Many technological and medical spin-offs: • Medical imaging chips developed at CERN • Software developed at CERN used in medical physics • World Wide Web developed at CERN • Many top engineers and scientists trained at CERN • Oxford positron systems founded by CERN physicst • - Young people attracted into science by CERN physics