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. 𝑒𝑒 Cowan Jr. set up 𝜈𝜈̅ 𝑝𝑝 → 𝑛𝑛 𝑒𝑒 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, 8Β8 + 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. A comparison with the total 8B flux clearly demonstrates that about two thirds of the solar νe changed flavor, arriving at Earth as νµ and ντ.

20 Atmospheric Neutrino

• Neutrino energy: 100 MeV – GeV • Flavor ratio predicted

R = νµ / νe = 2 ( E < 1 GeV) • Distance in flight ~20km (down) to 12700 km (up) • Flux at the surface of the Earth is expected to be isotropic, independent of the zenith angle.

21 Super-Kamiokande Experiment 50000 T water: 11000 PMT(p=50cm)

Elastic scattering

22 Detection PrincipleCherenkov Light

５０ｃｍＰＭＴ

23 Neutrinos Observed in Super-Kamiokande electron neutrino muon neutrino

The sizes of the circles show the observed light intensity. The color of the circles shows the timing information of the observed light.

24 Results of SK: Zenith Angle Distribution

< 1.3 GeV No oscillation

νµ-ντ oscillation

> 1.3 GeV

Up going Down going 25 Confirmed By Many Experiments

Super-K’s oscillation results were confirmed by • MACRO and Soudan • Long-baseline accelerator experiments K2K , MINOS and T2K • Large neutrino telescopes ANTARES and IceCube • OPERA experiment in Gran Sasso, with a neutrino beam from CERN  Appearance of tau-neutrinos in a muon- neutrino beam.

26 The Nobel Prize in Physics 2015

Takaaki Kajita Arthur B. McDonald Prize share: 1/2 Prize share: 1/2 "for the discovery of neutrino oscillations, which shows that neutrinos have mass" 27 Neutrino Oscillations  Mixing of Neutrinos

Question: Is neutrino oscillations indicate the lepton number violation in weak interaction ? Answer: NO. The oscillation is due to mixing of neutrinos – see theoretical model next page

28 Two Neutrino Oscillations Model

ν1 and ν2 are mass eigenstates ν ν θ is the missing angle e and µ are weak-interaction eigenstates

E1 and E2 are energies of ν1 and ν2 | ( ) = cos , = [ ] −𝑖𝑖𝑖𝑖1𝑡𝑡 −𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑒𝑒 −𝑖𝑖𝑖𝑖2𝑡𝑡 −𝐸𝐸1𝑡𝑡 𝜈𝜈𝑒𝑒 𝜈𝜈𝜇𝜇 𝑡𝑡 θ 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 −𝑖𝑖𝑖𝑖2𝑡𝑡 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑒𝑒 − 𝑒𝑒 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 𝑒𝑒

29 Neutrino Oscillations Occur if Neutrino Massive

∆E∆t~ ∆p∆x~ ℏ 1 ℏ using = 1 2 2E 182 -1 1 km = 10𝑠𝑠𝑠𝑠𝑠𝑠 x𝐴𝐴 5.068 GeV− 𝑐𝑐𝑐𝑐𝑐𝑐푐𝑐𝑐 ∆m2 in (eV)2, L in Km, E in GeV

30 Neutrino Oscillations Ref. book: Introduction to Elementary Particle Physics, by Alessandro Bettini

• Appearance experiment 2 2 2 P(νµ-ντ, t) = sin 2θsin [1.27∆m (L(km)/E(GeV)]

• Disappearance experiment 2 2 2 P(νµ-νµ, t) = 1- sin 2θsin [1.27∆m (L(km)/E(GeV)]

31 Mixing of Three Neutrinos ν  ν   e   1  Mass ν µ  = UPMNSν 2      eigenstates ντ  ν 3  U is Pontecorvo-Maki-Nakagawa-Sakata Matrix (CKM matrix in lepton sector) Atm/Acc If neutrinos are Acc/Reactor Sol/Reactor Dirac particles

cij = cos(θij ), sij = sin(θij )

0 0 0 θ23 =45°±6.0 θ13 =9.1°±0.6 θ12=33.6°±1.0 δ CP= CP violation

2 2 2 • Independent parameters govern oscillation: θ12, θ23, θ13, δ, ∆m12 , ∆m23 , ∆m13 , 2 2 2 where ∆mij =mi -mj . • Phase factor δ , induces novel CP violation effect, which have not yet been observed.

32 The neutrino oscillation picture

33 Present Knowledge of Neutrino Mixging

Normal Inverse Sol/Reactor hierarchy hierarchy

Atm/Acc OR

0.0250 +- 1.1E-4 Reactor Which? δ unkown Big diff from KM matrix

34 Measurements of Neutrino Mass

3 Supernova: Cosmology: ∑ m j • LSS, CMB, … j=1 • ToF measurement SN 1987A • model dependent • status: mν < 5.7 eV (PDG 2006) • status: Σmν < 0.4 eV (0.3 – 2.0 eV) • future sensitivity: sub-eV ? • future sensitivity: 0.1 – 0.6 eV

S. Hannestad et al., JCAP 08 (2010) 001

neutrino mass measurements

3 3 2 α 2 0νββ-decay: U ⋅ei j ⋅m U ⋅m • eff. Majorana mass ∑ ej j β ∑ ej j j=1 -decay: j=1 • model dependent (NME) • eff. neutrino mass • cancellation ? (Majorana phase α) • model independent (kinematics) • status: mββ = 0.32 eV ? (K.-K.) • status: mβ < 2 eV (Mainz, Troitsk) • future sensitivity: 0.02 – 0.05 eV • future sensitivity: 0.2 eV

35 Double Beta Decay Models

36 The path to the neutrino CP violation

37 Questions BSM on Neutrinos  What are the masses of the neutrinos?

 What is the pattern of neutrino mixing?

 Are neutrinos their own antiparticles?

 Do neutrinos violate the matter-antimatter CP symmetry?

 Are there sterile neutrinos — neutrinos that do not experience any of the known forces of nature except gravity?

 What can neutrinos, acting as messengers, reveal about astrophysical phenomena?

38 Dark Matter Observations in Space Search for Dark Matter particles

39 Dark Matter (DM)

Introduction • Constitute of the universe • Evidence of DM • Candidates of DM Searches • Method, technology and challenge • Indirect searches: AMS, PAMELA, Fermi-LAT, IceCube • Direct searches: XNEON 100/1T, JUX, PandaX, DAMA, CEDEX, LHC

40 From Astrophysics experimental observations, the constitute of the Universe are ~70% Dark Energy ~25% Dark Matter ~5% Ordinary matter

Non of the known SM particles can be counted as dark matter particle!

Search for DM particle is a hot topic in particle physics research

41 Early History of Dark Matter

42 Big Astronomical Objects: the big picture

Average distance between stars is about 4 light-years ~ 250,000 x distance from Earth to Sun

The Milky Way

1 pc = 3.26 light year

light year = 3x108 m/s x 31536000s = 94608 x108 km ~9.5x1012 km

Kpc = 1000 pc Mpc = 1000,000 pc

43 Our Galaxy The Milky Way

Our Galaxy – 30 Kpc 44 Clusters of galaxies (size ~ 10 Mpc)

45 Rotation Curves of Spiral Galaxies

46 Evidence for Dark Matter

Vera Rubin (1928 – 2016) was an American astronomer who pioneered work on galaxy rotation rates. She uncovered the discrepancy between the predicted angular motion of galaxies and the observed motion, by studying galactic rotation curves

47 Dark Matter Halo

• Solar system moves in the galaxy (DM halo) with a speed of 220 km/s. Everyday we are in the dark matter shower, with 108? hitting our body every second.

48 Gravitation Lensing Basics

49 Gravitational Lensing

• Recall that a ray of light that grazes the Sun is bent gravitationally by q = 1.75 Arc Seconds. A light source placed at a large distance directly behind the Sun would appear as a “ring” of light.

Source Sun Observer

Image 𝜃𝜃

• Actually, the Sun is so bright, it would be essentially impossible to observe the faint image ring. However, bright distance source (quasars) that are gravitationally focused by intervening Galaxy clusters comprised primarily of dark matter are easily observed as multiple images, arcs, or rings… depending on the alignment of source, focusing system, and observer.

50 Gravitational Lensing

51 Gravitational Lensing Distance source

A lens of DM

Focal point: Earth

52 Map of the Temperature Differences Across the Whole Sky from WMAP

Wilkinson Microwave Anisotropy Probe

. The darker region are colder and the clearer region are hotter. . The temperature non-uniformities, at the level of 1 part. of 105, are tell- tales of density non-uniformities  lumps in the early universe matter distribution. . The lumps are responsible for forming galaxies and stars through the subsequent gravitational aggregation.

53 WMAP

54 Power Spectrum - Evidence for Dark Matter

• Analyze data of map of temperature in term of its spherical harmonics

n: unit vector indicating a direction in space • Power spectrum

Continuous line shows the best fit to a model that assumes DM to be cold.

55 Planck Measured Power Spectrum

56 Dark Matter Particles – not in SM • Hot dark matter – non baryonic particles that move ultra relativistically, e.g. neutrino-like. • Warm dark matter – non baryonic particles that move relativistically, typified by sterile neutrinos that does not interact via any of the fundamental interactions of the SM except gravity. • Cold dark matter – non baryonic particles that move non- relativistically. • Analyses of structure formation in the Universe indicate that most DM should be “cold” or “cool”, i.e., should have been non-relativistic at the onset of galaxy formation.

57 Candidates for Cold DM Candidates for non-baryonic DM must • be stable on cosmological time scales (otherwise they would have decayed by now). • interact very weakly with electromagnetic radiation (otherwise they wouldn’t qualify as dark matter). • have the right relic density. Candidates include • primordial black holes • axions • sterile neutrinos • weakly interacting massive particles(WIMPs) Density of cold, non-baryonic matter from measurement: 2 ± Ωnbmh = 0.112 0.006 58 Weakly Interacting Massive Particle

WIMP • Stable, massive particle produce thermally in the early universe χχ ↔ ff • Weak-scale cross section gives observed relic density WIMPs 2 WMAP data: 0.095 < Ωch < 0.129 -37 2 σχ ~ 10 cm -38 2 σν ~ 10 cm (at 1 GeV)

The WIMP “miracle”

59 How to Test the WIMP Hypothesis?

In space

Colliding beams

Underground

60 WIMP Direct Detection Underground

61 Expected WIMP Event Rate

62 Experimental Background

63 Status of Direct Search DM

64 What is Needed for Discovery Underground

65 Search for Dark Matter with LHC

Initial state gluon radiation Invisible DM particle

Invisible DM particle

66 Searches With Mono-X (X=Jet, γ, W, Z) With Large Missing Energy (at LHC)

Related to dark matter, large extra dimension, SUSY and Higgs to invisible particles

Mono-jet Mono-photon Mono-Z

G Mono-Z

q, g Jet, γ q, g

67 LHC Results Compared to Direct Search • Search for dark matter particles at LHC with a single Z recoil • Unique sensitivity if dark matter couples predominantly to EWK bosons ArXiv: 1404.0051

• Strong limits in spin-dependent processes. • Large sensitivity in case of spin-independent. 68 Invisible Higgs Search With ZHll+Emiss

PRL 112, 201802

Pure Higgs portal interpretation

The strongest available limits for low-mass dark matter candidates DM Particle Annihilate in Space

70 DM Indirect Detection In Space

• In the early universe, DM kept in equilibrium with SM particles by annihilation (σ). • Today, DM expected to annihilate with the same σ, in places where its density is enhanced.

71 Indirect Detection Experiments

72 AMS2: Observed Flux of Positron Excess

DM signal or other Astrophysics signature?

73 Questions

• Why the SM cannot describe the neutrino mass? • What we observed neutrinos in experiments are from the weak interaction Eigen states or from their mass Eigen states? • If neutrino oscillation indicates lepton number violations – why or why not? • What are the evidence from observations that dark-matter exist? • Why non of the SM particles are possible candidates of DM particles? Please briefly describe. • If neutrino masses are measured in experiments? If not, what do we know so far? • If PMNS matrix parameters are all measured?

74 Two Neutrino Oscillations

75 Microlensing is a form of gravitational lensing in which the light from a background source is bent by the gravitational field of a foreground lens to create distorted, multiple and/or brightened images.

76 Neutrino Massmeasurements

β-decay 0νββ

m(νe) mββ Overall information by comparing the results of

• Direct measurement from β- decay energy spectrum

• 0νββ experiment

• Cosmological studies – Σ mi cosmology measure total neutrino mass