Electroweak and Higgs Physics

Transcription

1 Electroweak and Higgs Physics Lecture 2 : Higgs Mechanism in the Standard and Supersymmetric Models Alexei Raspereza DESY Summer Student Program Hamburg August 2017

2 Standard Model (Summary) Building blocks of Standard Model fermions : matter fields gauge bosons : force carriers Aesthetics of model : classification of fields U(1) SU(2) symmetry gauge interactions simple Lagrange formalism describes this very well but only for massless particles fermion and gauge boson terms break SU(2) symmetry model is fairly consistent with experimental data assuming massive fermion and weak boson fields one needs gauge invariant mechanism of mass generation 2

3 Higgs Mechanism Consider SU(2) doublet of scalar complex fields 3

4 Spontaneous Symmetry Breaking Higgs Potential 4-Dimensional sphere of minima Ground state ( vacuum ) 4

5 Higgs Mechanism Higgs Lagrangian Radial excitations of vacuum: physical state with mass 5

6 Higgs mechanism Impose local gauge invariance Consider ground state ( vacuum ) 6

7 Generation of Gauge Boson Masses The kinetic term in the Higgs Lagrangian Recall : 7

8 Generation of Weak Boson Masses These are W and Z boson mass terms! field remains massless W and Z bosons acquire masses through interaction with the Higgs ground state (vacuum)! 8

9 Yukawa Interactions Yukawa interactions interactions between fermions and Higgs doublet corresponding gauge invariant Lagrangian (lepton sector) : 9

10 Generation of Fermion Masses Consider Yukawa interactions between ground Higgs state (vacuum) and leptons Mass terms generated! Masses of charged leptons are given by 10

11 Generation of Fermion Masses Yukawa coupling of lepton to Higgs field Masses of down-type quarks are generated in similar way Masses of up-type quarks are generated via Yukawa interactions with charge conjugate Higgs doublet 11

12 Destiny of Physical State (Higgs boson) And what happens to physical state (Higgs boson)? Let's take look at kinetic term of 12

13 Higgs boson Interactions with W and Z This generates additional terms : Tri-linear Higgs gauge boson interactions Quartic Higgs gauge boson interactions 13

14 Higgs boson Interactions with Fermions Gauge invariant Yukawa interactions generate not only fermion masses but also interactions between Higgs boson and fermions same relations hold for quarks! 14

15 Prominent Feature of Higgs Mechanism Let us inspect couplings of Higgs boson to SM particles Higgs boson couples stronger to heavier particles decays more often into heavier accessible particles 15

16 Higgs Boson Decay Branching Ratios 16

17 Higgs Sector in Minimal Supersymmetric Standard Model (MSSM) 17

18 Supersymmetry fermions bosons stabilizes radiative corrections to Higgs self-energy points towards unification of gauge constants provides a candidate for dark matter lightest supersymmetric particle, e.g. in R-parity conserving SUSY models 18

19 Higgs Sector in MSSM Higgs Sector in MSSM Two Higgs Doublet Model (2HDM) Type II 2HDM Ф1 couples to down-type quarks and charged leptons Ф2 couples to up-type quarks Modified couplings to gauge and fermion fields 19

20 MSSM Higgs Phenomenology Higgs phenomenology in MSSM is very rich new physical states many new production and decay modes possible hard task for experimentalists Supersymmetric bosons are also searched for at LHC 21