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Searching for Dark Matter Ron-Chou Hsieh CYCU 4703819

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LHC Physics

Introduction

For the LHC Focus Group (FG), there are currently six executive committee members, including Prof. Chuan-Hung Chen (NCKU), Prof. Chuan-Ren Chen (NTNU), Prof. Kingman Cheung (NTHU), Prof. Cheng-Wei Chiang (NCU), Prof. Kwei-Chou Yang (CYCU), and Prof. Tzu-Chiang Yuan (AS). The current chief coordinator is Kwei-Chou Yang. Besides, from various universities and institutes, there are about 20 other faculty and 10 postdoc members actively participating the activities held by FG. As stated in our original proposal, we mainly focus on LHC-related physics, more specifically in the following directions:
*Physics of electroweak symmetry breaking and Higgs mechanism
*Physics beyond the standard model
*Probing the nature of dark matter
*Flavor physics and CP violation
Outcome

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Searching for Dark Matter Ron-Chou Hsieh CYCU 4703819

  1. 1. Searching for Dark Matter Ron-Chou Hsieh CYCU
  2. 2. • It seems to have something there! • What are they? • Link with physics beyond the SM. • DM searches. • Constructing a DM model • Summary
  3. 3. • Galactic rotation curves: – In 1932, Dutch astronomer Jan Oort – In 1933, Swiss astrophysicist Fritz Zwicky – In 1936, Sinclair Smith – In 1970, American astronomer Vera Rubin The stars move faster than expected!!! For 3
  4. 4. • Gravitational lensing Spacetime around a massive object (such as a galaxy cluster or a black hole) is curved, and as a result light rays from a background source (such as a galaxy) propagating through spacetime are bent. Strong gravitational lensing as observed by the Hubble Space Telescope in Abell 1689 indicates the presence of dark matter Bending light around a massive object from a distant source. The orange arrows show the apparent position of the background source. The white arrows show the path of the light from the true position of the source
  5. 5. Collision of two clusters of galaxies (Bullet Cluster, 1E 0657-56) http://chandra.harvard.edu/photo/2006/1e0657/
  6. 6. Collision of two clusters of galaxies (Bullet Cluster, 1E 0657-56) http://chandra.harvard.edu/photo/2006/1e0657/
  7. 7. • Massive compact halo object (MACHOs) • A MACHO is a body composed of normal baryonic matter, which emits little or no radiation and drifts through interstellar space unassociated with any planetary system. • MACHOs may sometimes be black holes or neutron stars as well as brown dwarfs or unassociated planets. White dwarfs and very faint red dwarfs have also been proposed as candidate MACHOs.
  8. 8. • Wilkinson Microwave Anisotropy Probe (WMAP) The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA Explorer mission that launched June 2001 to make fundamental measurements of cosmology -- the study of the properties of our universe as a whole. Content of the Universe WMAP Three year data reveals that its contents include an estimate of 4% atoms, the building blocks of stars and planets. Dark matter comprises 22% of the universe. This matter, different from atoms, does not emit or absorb light. It has only been detected indirectly by its gravity. 74% of the universe, is composed of "dark energy", that acts as a sort of an anti- gravity. This energy, distinct from dark matter, is responsible for the present- day acceleration of the universal expansion.
  9. 9. • Abundances of the Helium
  10. 10. • Basic requirements of DM  Stability  Charge neutrality  Non negligible mass to avoid EM interactions and prevent DM to shine at least on timescales comparable to the age of the universe a lower limit on the mass of weakly interacting DM candidates to explain the formation of the smallest objects observed in the Universe, which is of a few keV
  11. 11. • Mechanisms to produce the DM relic density  Free out-----DM particles which have been in thermal equilibrium with radiation at some stage of the cosmic evolution should subsequently decouple in two ways: decay and pair annihilation processes.  Free in-----DM particles are created through annihilation into DM particles, A A→DM DM, or through a decay process A→DM B. The observed DM relic density implies that: 1) The annihilation cross-section of DM particles should be comparable to the weak interaction cross section. 2) Fermionic DM particles should be heavier than a few GeV(Hut-Lee-Weinberg limit). WIMP!
  12. 12. • The non-baryonic candidate zoo  Weakly interacting massive particles (WIMPs) Axions SUSY particles Extra Dimensions
  13. 13. • WIMPs Interaction only through the weak nuclear force and gravity, or at least with interaction cross-sections no higher than the weak scale; Large mass compared to standard particles (WIMPs with sub-GeV masses may be considered to be light dark matter). o q o q~ q _ o q, l o q, l _ Z , _ 0 2 o o  + W+ 
  14. 14. DM searches
  15. 15. • Direct detection : elastic WIMP-atom scattering Three physical consequences of nuclear recoils are used to search for evidence of WIMP scattering. a) Ionization of target atoms b) Fluorescent radiation given off by electrons of target atoms c) Phonon excitations generated in crystals by the nuclear recoils
  16. 16. • Indirect detection Indirect detection experiments search for the products of WIMP annihilation. If WIMPs are Majorana particles (the particle and antiparticle are the same) then two WIMPs colliding could annihilate to produce gamma rays or particle-antiparticle pairs. This could produce a significant number of gamma rays, antiprotons or positrons in the galactic halo. o q o q~ q _ o q, l o q, l _ Z , _ 0 2 o o  + W+ 
  17. 17. • The EGRET gamma ray telescope observed more gamma rays than expected from the Milky Way, but scientists concluded that this was most likely due to an error in estimates of the telescope's sensitivity. The Fermi Gamma-ray Space Telescope, launched June 11, 2008, is searching for gamma ray events from dark matter annihilation. At higher energies, ground-based gamma-ray telescopes have set limits on the annihilation of dark matter in dwarf spherical galaxies and in clusters of galaxies. • The PAMELA experiment (launched 2006) has detected a larger number of positrons than expected. These extra positrons could be produced by dark matter annihilation, but may also come from pulsars. No excess of anti-protons has been observed. • A few of the WIMPs passing through the Sun or Earth may scatter off atoms and lose energy. This way a large population of WIMPs may accumulate at the center of these bodies, increasing the chance that two will collide and annihilate. This could produce a distinctive signal in the form of high energy neutrinos originating from the center of the Sun or Earth. It is generally considered that the detection of such a signal would be the strongest indirect proof of WIMP dark matter. High energy neutrino telescopes such as AMANDA, IceCube and ANTARES are searching for this signal. • WIMP annihilation from the Milky Way Galaxy as a whole may also be detected in the form of various annihilation products. The Galactic center is a particularly good place to look because the density of dark matter may be very high there.
  18. 18. Energy spectrum as detected by EGRET Diffuse gamma-ray spectrum as calculated with the GALPROP model. Main sources of background are: - Decay of o mesons Inelastic pp or p-He collisions - Inverse Compton scattering - Bremsstrahlung from electrons - Extra galactic background
  19. 19. • Basic requirements of DM  Stability  Charge neutrality  Non negligible mass to avoid EM interactions and prevent DM to shine at least on time scales comparable to the age of the universe a lower limit on the mass of weakly interacting DM candidates to explain the formation of the smallest objects observed in the Universe, which is of a few keV The observed DM relic density implies that (in WIMP scenario): 1) Interaction only through the weak force and gravity, or at least with interaction cross-sections no higher than the weak scale. 2) Fermionic DM particles should be heavier than a few GeV (Hut-Lee-Weinberg limit). 25
  20. 20. • Minimal DM model with •Weakly interactive •Charge neutrality (Q=0) 26
  21. 21. Elastic scattering of DM with nucleus We obtain Here c = 1 for fermionic DM and c = 4 for scalar DM 27 Exceed observed data limit!
  22. 22. Must have 28 However, for case , following contributions
  23. 23. 29 We obtain Also exceed observed data limit! Must consider : Weak isospin singlet DM
  24. 24. 30 Interacting with SM fermion through exotic vector boson Ansatz: •Annihilating into SM fermion pair •Renormalizable interaction •Fermionic DM SM SingletSM Singlet DM
  25. 25. Minimally coupled exotic vector boson The Lagrangian describing the model is With For simplification, we only consider the vector interaction such that with 31
  26. 26. •Thermal relic abundance 32 The thermal relic abundance in WIMP scenario can be calculated by solving Boltzmann equation through following annihilation process Interaction rate per particle Numbers of particle Boltzmann equation: with
  27. 27. 33 We assume
  28. 28. 34 •Elastic scattering with nucleus Xenon100 2012 DAMA LI 2008 CDMS CDMSII 2011 CoGent 2011 CRESSII 2011 EdelweissII 2011 KIMS 2011 SIMPLE 2011 Xenon10 2011 ZEPLINIII 2011 Contact Interaction Extrapolated RegionThis Work 10 20 50 100 200 500 1000 2000 10 45 10 44 10 43 10 42 10 41 10 40 m GeV N Z cm2 Spin Independentcross section
  29. 29. 35 •Annihilation to muon pair
  30. 30. Summary • Astronomical observations and measurements indicate the existence of Dark Matter • Models in particle physics offer candidates for Dark Matter • We are searching for Dark Matter by  producing new particles at colliders  indirect detection of the products of WIMP annihilation  direct detection through elastic WIMP-nucleus scattering

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