Tony Liss Saturday Physics for Everyone November 9, 2013 (With debts to Chris Quigg, Leonard Susskind, Hitoshi Murayama) Mass is stuff Mass is the stuff that gravity acts on FG ravity G M blue M red r r 2 Mass is stuff that resists you when you push it F Ma Mass is rest energy E0 M c 2 Ordinary Matter A proton is made of u u d Add an electron to make a hydrogen atom A neutron is made of d d u Now you have all the building blocks of the periodic table. ~173000 Mev/c2 ~4.8 Mev/c2 ~2.3 Mev/c2 .511 MeV/c2 According to theory, the Higgs boson gives these particles their mass. Helium: Iron: Hydrogen: 26 Two protons, protons, One 30 proton, neutrons, two one neutrons, electron 26 electrons two electrons 2 = 938.890124 MFeM c2He=M c252,019 =3,728.398128 MeV MeV MeV Hc MFe/(26M MHeP+30M /M(2M +2M )=0.9909 = 0.999999986 H/(M NP+26M P+MeN)e+2M e) = 0.9927 ~173000 Mev/c2 No! Proton: Two up quarks and a down quark (2Mu+Md)c2< 10 MeV MPc2 = 938 MeV ! Neutron: Two down quarks and an up quark (2Md+Mu)c2 ~12 MeV MNc2 = 940 MeV ! ~4.8 Mev/c2 ~2.3 Mev/c2 The mass of neutrons and protons is2 due (mostly) to .511 MeV/c the strong force (QCD) that holds them together: M E c 2 • The mass of atoms is the sum of the mass of their parts (with very small corrections) – protons+neutrons+electrons • The mass of protons and neutrons is not the sum of the mass of their parts (quarks) • It is mostly from the energy in the strong force (QCD) binding the quarks together. • Therefore, the mass of periodic table and the visible universe comes not from the masses of the fundamental particles, but from QCD! Consider the proton & neutron masses The proton is electrically charged & therefore surrounded by its own electric field. The neutron is electrically neutral. E ( field ) M c 2 You would guess that the proton is heavier than the neutron. But M N M P 1.29 M eV c 2 Mdown > Mup Mneutron > Mproton e e The heavier neutron “beta decays” in about 15 minutes into a proton plus an electron and a neutrino If the quarks had no mass, then MP > MN The proton would beta decay into a neutron No hydrogen atom If the electron had no mass… No atoms at all No me No you The Higgs ‘potential’ Electroweak force Force carriers Interactions Atoms Beta decay d u d d u u – W e– e e e http://www.philica.com/display_article.php?article_id=126 In the 1960s, the electromagnetic & weak interactions were unified into a single framework based on electroweak symmetry. The symmetry principle requires the carriers of the electromagnetic and weak forces to have zero mass. Quarks and leptons also have no mass. But this isn’t true. Only the photon has no mass. Weak interactions are very short-ranged, implying that the carriers, W & Z bosons, are very massive. Electroweak symmetry must be hidden. I first saw this demo in a talk by Chris Quigg ? Energy of field All other fields 0 Strength of field The Higgs field The minimum energy has a non-zero Higgs field! http://commons.wikimedia.org/wiki/File:Mexican_hat_potential_polar_with_details.svg + p Water molecules: Electrically neutral, but with a ‘dipole moment’ - H H O O H H H + - O O E H H H (Thanks to Leonard Susskind) It is certainly A Higgs boson Therefore we know It is responsible for at least some of the W and Z mass (strong evidence). It is probably responsible for at least some of the fermion masses (evidence getting stronger). We don’t yet know: If it is the ONLY Higgs boson. Why it is so light. The energy in the electric field adds to the electron mass 2 mec ~ Electric field lines around an electron 1 re We know the mass of the electron: 2 m e c 0.511 M eV This observed mass is an unobservable bare mass plus a correction due to the field energy 0.511 M eV m e c We know re 10 17 cm 2 bare mec 2 , then mec2 ~ 10 GeV and 0.511 MeV = (-9999.489 + 10000.000) MeV This is fine tuning Hitoshi Murayama http://arxiv.org/abs/hep-ph/0002232 + + + + + - + + + Electron-positron pairs ‘pop’ out of the vacuum and shield the bare charge of the electron e e 2 Mh obs h 2 Mh 0 bare t h 2 M h 0 t The problem is, M h2 is very very large (~1038 GeV) if there is nothing else going on. This requires M h and give 2 to be equally large in magnitude to cancel it bare M h obs 125 G eV c 2 SUSY includes a partner to the top quark, the ‘stop quark’ or ‘top squark’ that nearly cancels the top quark loop h t 0 h 0 t 2 M h top 2 M h stop 2 2 ~ m top m stop But we haven’t found the stop quark yet. The more we don’t find it, the heavier it must be – if it exists at all… Nature could be fine tuned. There is no law that forbids 125 G eV = 100000000000000000000000000000000000000 - 99999999999999999999999999999999999987 5 It’s just not very pleasing. Since we are here, the fundamental constants must have values in the narrow range compatible with conscious life. Is there more than one Higgs boson? • Supersymmetry, and many other ideas, include a family. Does the Higgs boson give dark matter it’s mass? Does the Higgs boson have anything to do with neutrino mass? Is the anthropic principle correct? What in the Universe is dark energy?