Physics 457 Particle Physics and Cosmology Part - 3 Mysteries that cannot be explained by SM 1) Neutrino Oscillations 2) Dark Matter … Bing Zhou Fall 2018 1 Big Questions - not explained by the Standard Model- What is the origin of neutrino masses? What is the nature of Dark Matter in the universe? Can the fundamental interactions be unified? Galaxies are spinning too fast to be Do we understand the large corrections to the Higgs held together by gravity of the stars boson mass from quantum corrections (“fine-tuning problem”) ? What is dark energy ? (Not only is the universe expanding, it is accelerating!) ….. 2 Neutrino and Oscillation Discoveries mν > 0! 3 Introduction to Neutrino Physics • Brief history • How do we detect neutrino? • How the neutrino types are determined? • Neutrino oscillation and how to measure them? • Neutrino mass and how to measure them? 4 Brief History of Neutrino 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 Mystery of continuous beta-ray spectrum “I have created a particle that can never be 1930 ● Pauli postulate neutrino detected…” W. Pauli 1933-34 ● Fermi theory 1956 ● Discovery of neutrino(Reines&Cowan)Another struggle Time of struggle & inspiration 1957 ● Discovery of parity violation(Wu) 1957 ● Helicity of neutrino (Goldhaver/Grodzins/Sunyar) Discovery race1962 ● Discovery of νµ (Lederman/Schwartz/Steinberger) 1973 ● Prediction of W,Z(GWS) st 1 golden age 1974 ● Discovery of neutral current (Gargamelle@CERN) 1984 ● Discovery of W,Z(CERN UA1 C.Rubbia) 1969 Solar neutrino problem 1986 Atm nu anomaly • Massless Neutrinos in the SM(‘60s) 1987 ● Kamiokande SN1987 • Evidence for neutrino mass from SuperK Discovery of nu osc.=mass● 1998 (1998) and SNO (2002). First evidence 1989~ Nν=3 at LEP (CERN) that the SM is incomplete Discovery of tau nu ● 2001 nd • 2002 Nobel prize to pioneers: Davis and Sol nu prob. solved by osc.(SK/SNO) ● 2002 2 golden age Koshiba nu ocs confirmed by K2K ● 2004 First geo-nu detection (KamLAND) ● 2005 T2K started ● 2009 • Mysteries of neutrino has been fascinating for all the time. • Continue to fascinate particle physicists for many decades. 5 Puzzle with β Spectrum – Neutrino Hypnoses • Three-types of radioactivity: α, β, γ. • Both α, γ have discrete spectrum because E α, γ = Ei – Ef • 1914, J. Chadwick first demonstrated that β spectrum is continuous breakdown of energy conservation, or a particle is missing F. A. Scott, Phys. Rev. 48, 391 (1935) 6 Sources of Neutrinos Super Nova Sun Nuclear reactor Galaxy νe νµ ντ Super Nova Accelerato r 7 ~ The Discovery of νe (1956) In the early 1950s, + + − F. Reines and C.L. Cowan Jr. set up ̅ → an experiment at the Savannah River nuclear reactor in South Carolina, unambiguously proved the existence of the neutrino. Signature: 2 back to back γ followed by a delayed (a few µs) 3rd γ signal. 8 The Nobel Prize in Physics 1995 Martin L. Perl Frederick Reines “For pioneering experimental contributions to lepton physics" jointly with one half to Martin L. Perl "for the discovery of the tau lepton" and with one half to Frederick Reines "for the detection of the neutrino". 9 Discovery of Muon Neutrinos at BNL Nobel Prize 1988 (Lederman, Schwartz, Steinberg) 1 0 Solar Neutrino (νe) Thermonuclear fusion reactions in the solar core produce energy and neutrinos Sun pp chain: 2 + ν p + p H + e + e : 4 + CNO cycle _ 3 4p H + 2e + 2ν 3 4 7 γ, 7 -7 ν ρ ∼ 146 g/cm e e He+ He Be+ _ Be+e Li+ e : 7 8 γ, 8Β8 + ν Τ ∼ 15x106 K (core) Energy released Be+p B+ Be+e + e • ~26.73 MeV for each complete • Energy release <1% ν reach earth in cycle • Dominate only in stars of much about 8 min. • > 99% of the Sun large mass 11 Binding Energy, Fusion and Fission 12 Protons and neutrons can be combined into stable systems called Nuclei. Examples 6C = “Carbon 12” 14 it contains 6 proton and 6 neutron. 6C = “Carbon 14”, it contains 6 proton and 8 neutron. Nuclei having same Z, but different A are called Isotopes. To form stable systems, proton and neutrons must be attracted to one another. Binding Energy Per Nucleon = EB/A vs mass number A The total energy of such a “bound” state must be lower than the total energy of the neutrons and protons when they are unbounded or far apart. The difference between the bound and unbound configuration is called “Binding EB/A decreases with A for large A. This energy”. means that energy can be released by splitinga heavy nucleus into lighter When protons and neutrons combine, the fragments. This process of resulting binding energy is released in the fragmentation is called “FISSION” form of radiation. This process of combination is called “FUSION”. 12 Energetics of Fusion Process • If you want to ram two positive charges together to within a distance = r, you have to supply the 2 following amount of energy to overcome the electrostatic repulsion: ECoulomb = kq /r. • In the Sun, this energy is supplied by the kinetic energy associated with the thermal motion at high -23 temperature. This energy is approximately Ethermal = KT (K = 1.38x10 J/degree) For fusion, you have to get within RANGE of nuclear force, -13 or rNucl ~ 10 m. So required 2 ECoulomb = kq /r = 8.99x109 (1.6x10-19)2/10-15 = 2.3x10-13 Joules In the Sun core, T ~ 15x106 K, So -23 6 -16 Ethermal = KT = 1.38x10 (15x10 ) = 2.1x10 Joules We have an apparent paradox: Ecoulomb>> Ethermal . How do the particles ever get close enough to fuse? Answer: It's The Power Of Quantum Mechanics That “Quantum tunneling” Allows The Sun To Shine! 13 Protons and Neutrinos From Sun • The fusion process produces photons (γ) and neutrinos (νe) with energies of around 1 MeV. • The photons interact intensely with all the charged particles (p, e, and ions) in the Sun. This process both degrades the photon energy and produces lets of new (low energy) photons. • So, the Sun emits large numbers of low energy photons from its surface. Typical energy: Eγ = hf = hc/λ =6.63x10-34 (3x108)/5.55x10-7 = 3.6x10-19 Joules = 2.3 eV • The neutrinos, on the other hand, have essentially no interaction in the Sun, and Eν ~ 1 MeV. • Solar neutrinos have been observed in the huge underground water-filled detectors used for search for proton decay. 14 Discovery of Solar Neutrino Homestake Solar Neutrino Observatory (1967-2001) 615 ton of tetrachloroethylene led by Raymond Davis Jr. (Shared the 2002 Nobel 30 Prize in Physics with M. Koshiba and R. Giacconi) ~ 2x10 chlorine atoms ν + 37Cl 37Ar + e- The first results appeared (1968): observed flux much lower than the theoretical expectation. Theoretical prediction 8.5 ± 0.9 SNU The final results (1998) Confirmed by other radiochemical Experiments 2.56 ± 0.16 (stat) ± 0.16 (sys) SNU GALLEX/GNO/SAGE, Kamioka Observatory. All ~30% of the predicted ones observed solar rate in this energy range was at about 50% of the SSM prediction, a discrepancy at the 5σ level. Missing solar neutrinos!!! 15 The Nobel Prize in Physics 2002 Raymond Davis Jr. Masatoshi Koshiba Riccardo Giacconi To Raymond Davis Jr. and Masatoshi Koshiba "for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos" and to Riccardo Giacconi "for pioneering contributions to astrophysics, which have led to the discovery of cosmic X-ray sources". 16 Calculate Solar Neutrino Induced Event Rate Homework An experiment in a gold mine in South Dakoda has been carried out to detect solar neutrinos, using 37 37 - the reaction ν + Cl Ar +e . The detector contained 615 ton of tetrachloroethylene (C2Cl4 ) ~ 2x1030 chlorine atoms. Estimate how many atoms of 37Ar per day would be produced, making the following assumptions: (a) solar constant = 8.8x1011 MeV cm-2 s-1; (b) 10% of thermonuclear energy of Sun appears in neutrinos, of mean energy 1 MeV; (c) 1% of all neutrinos are energetic enough to induce the above; (d) cross-section per 37Cl nucleus for “active” neutrinos is 10-45 cm2; (e) 37Cl isotopic abundance is 25%; -1 (f) density of C2Cl4 is 1.5 g ml . (Hint, the event rate here can be calculated by R =σ φ N, where σ is the cross section per nucleus for neutrino absorption, φ is the neutrino flux and N is the total number of nuclei in the detector. You can take 8 164 as the molecular weight of C2Cl4, and the total mass of liquid as 6x10 g to obtain the total number of 37CL nuclei.) 17 Neutrino Oscillations In the SM • Lepton numbers are conserved • Neutrinos are massless • Neutrino flavors do not oscillate Neutrino oscillation means that neutrinos have zero masses; or finite mass of neutrinos imply that the neutrinos can oscillate SM is incomplete! There should be new physics that beyond the SM. 18 The Sudbury Neutrino Observatory (SNO) Neutrino flux from Sun ~6x1010 cm-2 s-1 1000 ton Ultra pure heavy water D2O 9500 photon multiplier tube (PMT), φ=20 cm Charge current: only sensitive to νe - νe + d p + p + e Neutral current: sensitive to all νi νi + d p + n + νi (i=e, µ, τ) Elastic scattering: cross section about 12 m 6 times smaller for νµ and ντ - - νi + e νi + e Measure the total neutrino flux, φ(νe) + φ(νμ) + φ(ντ) 19 Results from SNO First results from 2001-2002: providing evidence for neutrino flavor conversion and showing that the total flux of 8B neutrinos was in agreement with the SSM. Final results from 2013 Theoretically expected 5.94 (1 ± 0.11) [SSM BPS08], or 5.58(1 ± 0.14) [SSM SHP11] The flux of νµ and ντ deduced deviating significantly from zero.