Particles “Matter is made of atoms“ atom nucleus nucleon quark 10-10 m 10-14 m 10-15 m 10-18 m “Atoms are made of leptons and quarks“ νe u Leptons Quarks e d What Have We Learned? • Relativistic Quantum Mechanics is a good framework for descriBing nature • The universe is made of: Quarks: Leptons: Gauge Bosons: Anything else? Particles and Forces Leptons Strong Electromagnetic Electric Charge Gluons (8) Photon Tau -1 0 Tau Neutrino Muon -1 0 Muon Neutrino Quarks Atoms Electron -1 0 Electron Light Neutrino Mesons Chemistry Baryons Nuclei Electronics Quarks Gravitational Weak Electric Charge Graviton ? Bosons Bottom Top -1/3 2/3 (W+,W-,Z) Strange -1/3 2/3 Charm Neutron decay Down Solar system -1/3 2/3 Up Beta radioactivity Galaxies Neutrino interactions Black holes Burning of the sun each quark: R, B, G 3 colors Mass Spectrum Masses 1 TeV Quarks top quark as heavy as Tungsten Leptons 1 GeV 1 MeV Three light ν’s summed masses 1 eV 0.04-0.3 eV ν’s e μ τ u d s c b t 12 orders of magnitude diferences not explained; t quark as heavy as Tungsten M. Artuso, IF Meeting Argonne, 26 April, 2013! 5 • Why do the fermions have a mass spectrum which stretches over almost six orders of magnitudebetween the electron and the top quark? • Including neutrino masses the mass spectrum stretches over thirteen orders of magnitude. • We have no concrete understanding of the mass spectrum. Particle Masses These are all we “see” around us in everyday life but the others are crucial to defining what we are. Fundamental Forces Force Strengths: g2 Quantified By “coupling constants” α = 4π Strong: αs ~ 1 Electromagnetic: αem ~ 1/137 -6 Weak: αW ~ 10 -40 Gravity: αg ~ 10 EM force Weak force Strong force Electric charge (1) Weak charge (2) Colour charge (3) Massless photon Massive W±,Z 8 massless gluons Coupling g Coupling gW Coupling gs Only charged Only left handed Only quarks couple particles couple particles couple Weak Interaction Muon decay: -5 -2 Strength of weak force ~ GF ~ 10 GeV cf. strength of EM force ~ 0.01 _ νe W- e- µ νµ W Boson massive Factor involved in Boson exchange ~ 1/(E2+M2) (hence units) Strength of weak force = EM force if M~ 30 GeV (MW~80 GeV) _ Weak Interaction νe W couples to: W- Upper and lower memBers e- of a fermion generation. d u L- (R-) handed (anti)particles Z couples to: q Z e+ Matter and antimatter _ versions of a fermion. q e- Complicated mix of L-, R- particles. “vector, axial couplings”; Higgs mechanism Helicity of a Particle Definition of helicity (or handedness): λ = s • p / | p | = ± 1/2 It measures the sign of the component of the spin of the particle (jz = ± 1/2) along the direction of motion (z axis) s is a pseudo-vector: does not change for spatial inversion Hadrons Quarks only exist in “color neutral” comBinations blue - antiBlue green - antigreen red - antired red-green-blue Baryons (e.g. proton) Mesons (e.g. π ) u u u d u Hadrons There are hundreds of Baryons and mesons. See the online “Particle data Book” for the full list: http://pdg.lbl.gov Charmonium (charm-anticharm) Upsilon (Beauty-antiBeauty) c B c B Mesons • Many types • Many decay modes • Some are long lived, i.e., > 10–8 s • Massive ⇒ short life • Detection – Long lived • Interactions with detector matter – Short lived • Calculating comBined masses using detected particles The Charm Quark Discovered at Stanford in e+e- collisions and at Brookhaven, NY in p Be collisions, at exactly the same time, Nov. 1974 The charm-anticharm meson decays shortly after production c electron positron c The Beauty Quark Over the last decade, SLAC and KEK (a laB in Japan), produced aBout a Billion beauty-antiBeautyquarks in e+e- collisions, in the form of B and B mesons (hence the name of the SLAC detector, _ BaBar). Small differences Between B and B decays may help us understand why there is a matter-antimatter asymmetry in the universe today, although to date they mainly confirm the Standard Model explanation (KoBayashi+Maskawa, NoBel Prize 2008), which cannot produce a large enough asymmetry. d B B d _ B0 B0 The Top Quark Was postulated in 1973 By Makoto KoBayashi and Toshihide Maskawa to explain the oBserved CP violation in kaon decays. Discovered 1995 By the CDF and dØ experiments at FermilaB. Top quark antiquark (proton) (antiproton) Anti-top Antimatter The comBination of special relativity and Quantum Mechanics leads to a new entity - antimatter Einstein’s equation of motion: E 2 = p2c2 + m2c4 Two energy solutions for the same mass: • Matter • Antimatter - S=+1/2 + S=-1/2 electron Anti-electron “Positron” -1/3 S=+1/2 +1/3 S=-1/2 quark antiquark Every fermion has an antimatter version. Anti- electron/quark has opposite charge _ to electron/quark But + the same mass. _ Also: antiquark q, antimuon µ , antineutrino ν Antimatter Matter and antimatter is created/annihilated in pairs Photon We can collide matter with antimatter to make other matter/antimatter pairs Matter-Antimatter Collisions Can collide electrons and positrons in storage rings. Example of a collider experiment. Electron-positron annihilation: e+ + e- → γ + γ The Universe evolved from the Big Bang γ e+ e- Two Back-to-back γ each with γ 1/2 of the total availaBle energy Creating a packet of pure energy replicates the conditions at 10-9-10-12 s after creation (we are now at 1018 s). Understanding particle physics at these high energies helps understand how the universe evolved from early times. Matter-Antimatter Collisions It is possiBle to accelerate protons and antiprotons to much greater energies than electrons and positrons. This effectively makes a quark-antiquark collider. proton Anti-proton u u u u d d Proton-Antiproton Collisions FermilaB (Chicago) 980 GeV protons + 980 GeV antiprotons 4 miles circumference The CdF detector The Large Hadron Collider The LHC at CERN, Geneva. 27 km circumference, extends across France-Switzerland Border. Proton-proton collisions at 7000 GeV + 7000 GeV. World’s highest energy collider Proton-Proton Collisions 7 TeV 7 TeV The Standard Model also missing: dark matter (if it is an elementary particle) + anti quarks anti leptons not included: the graviton (spin 2) quantum theory à strings? spin 1/2 spin 1 The Standard Model • Very successful model which contains all known particles in particle physics today. • DescriBes the interaction Between spin 1/2 particles (quarks and leptons) mediated By spin 1 gauge bosons (gauge symmetry). • Standard Model unifies electromagnetic and weak forces and includes the strong force as well ● Based on SU(3) x SU(2) x U(1) symmetry group ● Does not say anything aBout gravity ● Gravitational force much too small, 35 orders of magnitude • Simple Lagrangian formalism descriBes this very well But only for massless particles – The equations only made sense if all the Bosons, and all the quarks and leptons, had no mass and moved at the speed of light! What is Mass • To Newton: F = ma, W = mg (measure of inertia) • To Einstein: E = mc2 Mass curves spacetime • All of this is correct. • But how do oBjects Become massive? • While developing the modern theory of fundamental forces and interactions, physicists hit a snag • Particles that carry forces had to Be massless But the data seemed to say otherwise! • Massless particles move at the speed of light – If particle has momentum p then E2=(mc2)2+(pc)2 – So, for a massless particle E=pc • Suppose there is a force field filling the universe that somehow slows particles down to Below the speed of light? – This would make them have mass! Higgs Field Interaction Massive Particle Part 2 素粒子論入門 ヒッグス粒子① ●●●● ●●● 宇宙のあらゆる場所，あなたの眼の前 にすら，「ヒッグス粒子」が満ちている 素粒子物理学の標準モデルでは，もう一つ未発見の素粒子 真空に満ちたヒッグス粒子 の存在が予言されています。それが「ヒッグス粒子」です。 標準モデルによると，宇宙空間のあらゆる場所，真空や物 ＊ 質の内部にさえ，ヒッグス粒子が満ちていると言います 。 ★ 電子 魚が周囲に満ちている水の存在に気づかないであろうよう ★ に，ヒッグス粒子はあらゆる場所に満ちているため，私たち ★ ★ はその存在に気づいていないのです。 ★ ウィークボソン（Ｗ粒子） ヒッグス粒子は，あらゆる素粒子の「重さ（質量）」を生 W ★ みだす源だと考えられています。標準モデルによると，本来， ★ ★ ★ あらゆる素粒子は質量がゼロだと考えられているのです。質 量とは，「物体の動かしにくさ」（より正確には「加速のしに ★ ★ くさ」）を意味します。質量の小さな（軽い）ピンポン球は， 光子 小さな力でも，いきおいよく動かすことができます。しかし γ 質量の大きな（重い）砲丸は，大きな力を加えないと，いき おいよく投げることはできません。 ヒッグス粒子が空間に満ちているため，素粒子が動こうと すると，ヒッグス粒子と衝突してしまうことがあります。こ れを素粒子の質量，すなわち，動かしにくさの起源だと考え るわけです。質量が大きい（重い）素粒子ほど，ヒッグス粒 ひんぱん 子と頻繁にぶつかることになります。 ヒッグス粒子がなかったら，私たちは存在できない 一方，光子のような質量ゼロの素粒子は，ヒッグス粒子と 衝突しません。光が自然界の最高速度（光速，秒速約 30 万 キロメートル）で進めるのは，このためです。 逆にいえば，光子は真空中を光速以下で進むことはできま せん。光子は，生まれた瞬間から光速で動きつづける運命な のだといえます。ヒッグス粒子がなければ，私たちの体をつ くっている電子などの素粒子も，光速で進んでしまい，その 場に留まっていられなくなります。物体の構造が保たれてい るのは，真空にヒッグス粒子が満ちているおかげなのです。 ＊： 真空に満ちているのは「ヒッグス場」で，加速器を使ってヒッグス場から たたき出される（次ページ参照）のが「ヒッグス粒子」と使い分ける方が， より正確ですが，この記事では「ヒッグス粒子」で統一することにします。 58 59 Higgs Field • The proBlem leading to the Higgs Boson was firstly aBout the masses of the quanta of the weak force. • Key postulate of the Higgs mechanism: – A new force field, the Higgs field, has an average value in the vacuum that Becomes non-zero as the early universe cooled. • Jargon: Spontaneous Broken symmetry • Non-zero average value of the Higgs field can also give masses to the fundamental fermions (quarks, electrons, muons, etc.) • Note: For composite oBjects such as proton, mass is m=E/c2, where E includes all the energies of the constituents. – Most of mass of proton comes from kinetic energies of its constituents not their masses. The Standard Model Quarks and leptons are classified according to their mass, electrical charge, and their quantum numBers, such as flavors and lepton numBer, and are divided into three groups, so-called generations. Standard Model Interactions The interaction of gauge bosons with fermions is described by the Standard Model Gluons Photon W+, W- Z0 massless massless very massive very massive.