مبانی فیزیک ذرات

مبانی فیزیک ذرات

اسلاید 1: A short journey to the infinitely small Fundamentals of Particle Physics Stefania RicciardiRAL, March 2009 Building blocks: particles and forces Current areas of research

اسلاید 2: WarningThis journey may change your vision of the Universe. What you will hear may alter your perception of reality. We are entering a Quantum World.. Stay awake and keep an open mind!

اسلاید 3: We and all things around us are made of atomsHuman Hair ~ 50 mm = 50 10-6 m = 0.000050 m Atom ~ 10-10 m = 0.0000000001 m Magritte

اسلاید 4: AtomsAtoms are all similarly made of:- protons and neutrons in the nucleus- electrons orbiting aroundelectronprotonneutronProtons, neutrons are made up of quarksThe electron was thefirst elementaryparticle to be discovered(JJ Thomson 1897)

اسلاید 5: From the atom to the quarkAtoms 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 How small are the smallest constituents of matter?~ 10-10 m~ 10-14 m~ 10-15 m<10-18 m<10-1 8 m

اسلاید 6: Wave-particle duality of NatureCentral concept of quantum mechanics:all particles present wave-like propertiesDe Broglie showed that moving particles have anequivalent wavelength l So high momentum gives us short wavelengths so we can make out small detailsExample: electron microscope Not only light has a dual naturelElectron Microscope ImageGold atoms(0.2 nm apart)Copyright © FEI

اسلاید 7: 1911Rutherford found a nucleus in the atom by firing alpha particles at gold and observing them bounce backRutherford: atoms are not elementary particles!Precursor of modern scattering experiments at accelerator

اسلاید 8: Quarks detected within protonsStanford (SLAC), California, late 1960s Fire electrons at proton: big deflections seen!2 miles long acceleratorEnd Station Aexperimental areaFreeway 280

اسلاید 9: Protons and neutrons in the quark modelproton (charge +1)neutron (charge 0)udduudQuarks have fractional electric charge!u electric charge + 2/3d electric charge -1/3

اسلاید 10: 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 n nnnnnnnn nn n n nn n nnnnnnnn nn nn nn n n n n n nn n n nn n nnnnnnn nn nn nn nnnnnnnnn nn n nnn nnnnnnnnn nn n nnn nnnnnnn1 cm Within each cm3 of space: ~300 neutrinos from Big BangNeutrinos are everywhere!in the outer space, on Earth, in our bodies..1 cm

اسلاید 11: Neutrinos get under your skin!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 neutrinos1014 neutrinos per second from Sunare zipping through you nEvery cm2 of Earth surface is crossed every second by more than 10 billion (1010) neutrinos produced in the Sun

اسلاید 12: The particles of ordinary matternee-ud-1/3+2/30-1chargeAll stable matter around uscan be described using electrons, neutrinos, u and d “quarks”Quarks:u = upd = downLeptons:n = neutrinoe = electron

اسلاید 13: 3 Families (or Generations)nmm-csntt-tbOrdinary matterCosmic raysAccelerators1st generation2nd generation3rd generation3 generations in everything similar but the mass -1/3-1/3+2/3+2/3nee-ud-1/3+2/3We believe these to be the fundamental building blocks of matter-1-1-1000

اسلاید 14: Quark masses0.0030.0060.0951.24.5Top(discovered 1995)175 GeVE= mc21 proton mass ~ 1GeV (10-27 Kg)The mass grows larger in each successive family

اسلاید 15: Anti-matterFor every fundamental particle of matter there is an anti-particle with same mass and properties but opposite chargenee-ud-1/3+2/3nee+ud+1/3-2/3+10-10positron Correspondent anti-particles exist for all three families Anti-matter can be produced using accelerators MatterAnti-MatterBar on top to indicateanti-particle

اسلاید 16: Matter-antimatter pair creationElectron-positron pair created out of photons hitting the bubble-chamber liquidExample 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

اسلاید 17: Quarks and colourAll quark flavours come in 3 versions, called “colours”ud+2/3-1/3uuddupdownQuarks combine together to form colourless particlesBaryons (three quarks: red+ green + blue = white) Mesons (quark-antiquark pair) such as red+anti-red u-ubar stateprotonuupionppStrong forces “glue” quarks together in bound states

اسلاید 18: Building more particlesbbJ/yccYbuB-ubB+bdB0dbB0B mesons (bq)Many more mesons and baryons…

اسلاید 19: The Particle Physicist’s Bible: Particle Data Book https://pdg.lbl.govYoung 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) Most particles are not stable and can decay to lighter particles..

اسلاید 20: THE WEAK FORCE Beta DecaynpAntineutrinoElectron

اسلاید 21: Neutron b-decayA (free) neutron decays after 15 min uddnuudpe-d→ u e- nene15 minAt quark level:Long life time (15min is an eternity in particle physics!)  “weak” without such weak interactions the Sun would shut down!

اسلاید 22: The 4 forces of NatureWeak Beta-decay pp fusionStrong Quark bindingElectromagneticTV, PCs Magnets e- e+ creationGravityResponsible ofKeeping us well-planted on earthElectric chargemassweak chargestrongcharge

اسلاید 23: Electromagnetic forcee-e-PhotonThe repulsive force that two approaching electrons “feel” Photon is the particle associated to the electromagnetic force“smallest bundle” of force

اسلاید 24: Photon exchange Feynman Diagrame-e-e-e-g

اسلاید 25: Weak force: W-,W+,Z0b-decayn→peneElectric chargeconserved at eachvertexW-

اسلاید 26: Strong force: gluonsGluons interact with quarksGluons interact with other gluons

اسلاید 27: Quark confinement There are no free quarks, quarks and antiquarks are “confined” in colourless doublet (mesons) or triplets (baryons) by the exchange of gluonsThe new quarks boundto the old quarks and form new mesonsuntil the gluon connection snaps, and other quark-antiquark pairs are created out of the energy releasedGluon hold quarks together as they move further apartZ0Decay® S.Ward

اسلاید 28: Force Particles (summary)Particles interact and/or decay thanks to forcesForces are also responsible of binding particles together

اسلاید 29: The Standard ModelMatter6 quarks6 leptonsGrouped in three generationsForcesElectroweak:g (photon) Z0, W± Strong g (gluon) Very successful to describe all observed phenomena in the subatomic world so far. But there ought to be more..Framework which includes:Not gravity! No quantum field theory of gravity yet..H= the missing ingredient: the Higgs Boson

اسلاید 30: Beyond the Standard Model:Unification of forcesWEAKSTRONG GRAVITYELECTRO-MAGNETICUNIFIEDFORCE?Looking for a simple elegant unified theory

اسلاید 31: Open question: Why is the Universe made of matter and not equally of anti-matter?We have seen that for every fundamental particle there is a corresponding antiparticle.Where are these anti-particles? Large amount of matter but no evidence of large amount of antimatter in the Universe..

اسلاید 32: Why has all the anti-matter gone?Anti-matterThe development of the Universe containing matter and no antimatter requires that matter and antimatter behave differentlyThis phenomenon is due to CP violation..matterPuffGood thing for us that there is no antimatter around!

اسلاید 33: CP ViolationCP = Charge Conjugation (reverse charge) x Parity (reverse spatial coordinates as in a mirror)CPbeautyanti-beautyB0B0“Nobody is perfect”CP-Violation: B0 and B0 do not behave exactly in the same way (their decay pattern as a function of time is different)

اسلاید 34: Discovery of CP violation in the B-meson system at Babar (SLAC, 2001)A visible difference is detected, but tiny, not enough to explain the matter-antimatter asymmetry in the Universe

اسلاید 35: The CPV quest will go on at LHCCMSALICECERNLHCb experiment:700 physicists50 institutes 15 countriesLHCb cavernLHCbATLAS

اسلاید 36: Recent view of the LHCb cavernIt’s complete!RICH-1The experiment is fully installed and ready for first collisionsRICH2RICH1Muon detectorCalorimetersOTMagnetVELO

اسلاید 37: Another open question: What is the Dark Matter?Astronomical observations have shown that “observable” mass represent less than 4% of the Universe!What is dark matter? We don’t really know …Perhaps partially composed of neutrinos, or possibly neutralinos particles predicted by super-symmetric theories beyond the Standard Model? Dark MatterVisible MatterFalse-color imagesThe brightness of clumps corresponds to the density of mass.

اسلاید 38: Looking for Dark Matter at the Boulby Underground Laboratory

اسلاید 39: Neutrinos do matter to us: If there were no neutrinos the sun would not shine! Almost no interactions (only weak) Can cross light-years of material without being affected Can travel from the most remote corners of the Universe bringing information from the origin of space and timePuzzling neutrinos

اسلاید 40: R. Davis: measuring the solar neutrino flux in a gold mine in South Dakota for 30 years (1969-1999)…and observing only 1/3 of the expected flux!! Why?R. DavisSolar neutrinos pioneer

اسلاید 41: Neutrino oscillationsIf you let the neutrino travel enough, it can change its flavour! mtnenmnta huge neutrino detectorin the right place exists!A detector here does not see any nmKamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyoa huge neutrino detector exists!A detector here sees all nm

اسلاید 42: in the Kamioka mine in Japan SuperKamiokande is measuring neutrinos born in the atmosphereabove the detector..nm flux from below only ½ of flux from above!..and below the detector (on the other side of the Earth!!)Total neutrino flux from below = total flux from above _

اسلاید 43: Discovery of neutrino oscillation Super-Kamiokande (1998)Half of the nm are lost! Oscillated to undetected nt 2002 Nobel PrizeKoshiba (superK Spokesman)shared with DavisUp-goingDown-going

اسلاید 44: What have we learnt? A number of surprising things:A limited number of forces and matter particles describe all the Universe we know about;A theory of the interactions of matter with forces called the Standard Model describes successfully the phenomena of the subatomic world; There are evidences that there is lot more that we do not know about and our research should find: such as the missing anti-matter, dark matter, puzzling neutrino properties, but also the Standard Model key-vault ..the Higgs!

اسلاید 45: Looking into the futureThe Higgs should be found at the LHC…please be patient for a few more hours….and you will learn about the Higgs, the LHC, and much more! NOT