Dark Side of the Universe

Transcription

1 Dark Side of the Universe Bhaskar Dutta Department of Physics & Astronomy Texas A&M University Dark Side of the Universe 1

2 Content of the Universe 4% The 23% is still unobserved in the laboratory.. (This new matter can not be seen visually!) We call this Dark Matter.. Dark Dark Side Side of the of Universe the Universe 2

3 Message from the Universe How do we measure the content of the Universe? We look at the the oldest light which set out on its journey long before the Earth or even our galaxy existed. This light forms the background of the Universe: Cosmic Microwave Background (CMB) Measurement of this light tells us the story of the Universe. Dark Side of the Universe 3

4 The Most Distant Light CMB was emitted when the Universe was only 380,000 years old. Dark Side of the Universe 4

5 The Universe Pie Today, we discuss DM. Dark Side Side of of the the Universe 5

6 Existence of Dark Matter Examples of observations: We know that dark matter exist. Collisions of the galaxies Rotation curves of the galaxies March 24, 2007 Dark Side of the Universe 6

7 time Cosmic Collision of 2 Galaxy Clusters splitting normal matter and dark matter 1 apart Ordinary Matter (NASA s Chandra X Observatory) Another Clear Evidence of Dark Matter Dark Matter (Gravitational Lensing) Approximately the same size as the Milky Way Dark Side Side of of the the Universe 7

8 What is Dark Matter? Neutral and long-lived object Can it be one of the known particles? Dark Side of of the Universe 8

9 Building Blocks of Matter What are the elementary particles? Dark Side of the Universe 9

10 Zoo: 12 Particle Animals The elementary particles are fundamental building blocks of matter. All masses in MeV. ANIMAL MASSES SCALE WITH PARTICLE MASSES Dark Side of the Universe 10

11 Fundamental Forces Gluons (g) for strong force Quarks experience them. Protons & neutrons form. Photons (g) for electromagnetic force Quarks, leptons (other than neutrinos) experience this force. W s for weak forces Quarks, leptons experience this force. NOTE : Graviton (G) ( not found) carries gravitational force. Dark Side of the Universe 11

12 The Standard Model The Standard Model is a model which describes all these particles and 3 of 4 forces: We have confirmed the existence of SM in the laboratory experiments. Dark Side of the Universe 12

13 Higgs? One major particle is still missing in the experiment: Higgs There is a strong indication of its existence from the Large Hadron Collider (LHC) data Higgs generates mass for all particles in the Standard Model (other than neutrinos) So, can the Standard Model explain our Universe? Dark Side of the Universe 13

14 Dark Matter Particle? x x x x x x x x x x x x x x x x Quarks, electron, muon, tau particles, and force carriers can not be the dark matter, since their interactions are stronger than what we expect. Neutrinos can, but they have other problems. We need a new model, called Supersymmetric Standard Model or SUSY. This model has a new charge-less (neutral) particle: Neutral-ino 1) What is the new model? 2) Can the neutralino be observed and consistent with the dark matter content of the Universe? Dark Side of the Universe 14

15 Dream of Unification Physicists always dream about unification of all the forces. The grand unification of the forces occur in the SUSY model. Dark Side of the Universe 15

16 Boselab Mirror Reflection Fermilab Dark Side of the Universe 16

17 Supersymmetric Reflection g e e But, one of them is neutralino. This is a leading candidate for dark matter particle. 0 ~ 1 Dark Side of the Universe 17

18 When Were the Dark Matter Particles Created? Now ~ seconds Dark Side of the Universe 18

19 Thinking of Dark Matter Detection My Universe Dark Side Side of of the the Universe 19

20 How Can We See Them in the Lab? One type of experiment: in deep underground µ detector Dark Matter particle Dark Side of the Universe 20

21 Collider One promising way: In collisions Dark Side of the Universe 21

22 Particle Collider One promising way: In particle collisions Electron-Positron Collider Dark Side of the Universe 22

23 Large Hadron Collider (LHC) Proton Proton collider The LHC lies in a tunnel 27 kilometres (17 mi) in circumference, as deep as 175 metres (574 ft) beneath the France-Swiss border near Geneva, Switzerland. It is designed to collide protons CERN, Geneva Dark Side of the Universe 23

24 Collisions Dark Side Side of of the the Universe 24

25 Pattern Recognition How do we produce the neutralinos at the LHC? We have to extract this reaction out of many trillion pp collisions. neutralinos (dark matter particles) Dark Side of the Universe 25

26 How do you know that the neutralinos (we will observe) at the collider are responsible for the dark matter content? We measure the masses (m) of the particles at the LHC. We calculate the dark matter content (W) in the new model of the Universe. W = x(m) x y / z + g x h (m) - p (m) / q + r (m) x 45 / x u r (m) x t y + d x s (m) + j (m) x p (m) = 0.23 Dark Side of the Universe 26

27 Anatomy of dark matter content W cdm 2 annv ~ ~ 1pb 2 M W CDM -1 DM particle +. 2 DM particle Dark Side of the Universe 27

28 Goal at the LHC Establish the dark matter signal Measure SUSY masses Determine Model parameters Calculate W CDM and compare it with 23% obtained from the WMAP data Dark Side of the Universe 28

29 Determining the dark matter content Using various complicated measurements We have shown that the supersymmetry masses can be measured at the LHC and using those masses Dark matter can be measured 50 fb -1 L 10 fb -1 Phys. Rev. Lett. 100, (2008) Phys.Rev. D82 (2010) Phys.Rev. D79 (2009) W h / W 2 ~ 0 ~ h 2 6.2%(30 fb 4.1%(70 fb -1-1 ) ) Phys.Lett. B703 (2011)

30 Conclusion So far in the laboratories we have seen the particles responsible for 4% of the universe. The ongoing experiments are trying to probe the nature of 23 % of the universe: dark matter. Challenge: 73% of the universe is still a major puzzle. Not yet understood theoretically! Dark Side of the Universe 30

31 Conclusion So far in the laboratories we have seen the particles responsible for 4% of the universe. The ongoing experiments are trying to probe the nature of 23 % of the universe: dark matter. Challenge: 73% of the universe is still a major puzzle. Not yet understood TO SOLVE theoretically! THE PUZZLE OF THE UNIVERSE. Dark Side Side of of the the Universe 31

32 Any Question? Dark Side of the Universe 32