The Higgs Boson as a Probe of New Physics Ian Lewis University of - PowerPoint PPT Presentation

The Higgs Boson as a Probe of New Physics Ian Lewis University of Kansas March 17, 2016 Ian Lewis (University of Kansas) 1

July 4, 2012 ● ATLAS and CMS announce discovery of a new particle. – Consistent with long sought-after Higgs boson. "We have reached a milestone in our understanding of Nature". --- CERN Director General Rolf Heuer March 17, 2016 Ian Lewis (University of Kansas) 2

Long Search ● 50+ years of work by theorists. ● 25+ years of work by thousands of experimentalists. March 17, 2016 Ian Lewis (University of Kansas) 3

● as March 17, 2016 Ian Lewis (University of Kansas) 4

Standard Model Complete Quarks: charge +2/3 (up type) and -1/3 (down type) Leptons: charge -1 and 0 March 17, 2016 Ian Lewis (University of Kansas) 5

Role of the Higgs ● Higgs is the source of fundamental mass in the Standard Model. – Important for understanding fundamental laws of nature. March 17, 2016 Ian Lewis (University of Kansas) 6

Masses ● Many massive particles in Standard Model ● Massive Gauge bosons. – W/Z. ● Photon and gluon are massless. ● What is the matter with mass? ● Natural units March 17, 2016 Ian Lewis (University of Kansas) 7

What's the matter with mass? ● Maxwell's equations: ● Invariant under the transformation: ● Add mass, break gauge invariance: ● Why photon is massless. March 17, 2016 Ian Lewis (University of Kansas) 8

The Need to Explain Masses ● Have masses for gauge bosons. ● What is source of gauge invariance breaking? ● Explicit breaking: – Equations of theory explicitly break an invariance. ● Spontaneous breaking: – Lowest lying energy state (vacuum) of theory breaks invariance. March 17, 2016 Ian Lewis (University of Kansas) 9

Ferromagnetism ● Before magnetization: ● After magnetization: ● Spontaneous symmetry breaking. March 17, 2016 Ian Lewis (University of Kansas) 10

Higgs Mechanism ● Introduce a Higgs. ● Write fundamental equations (with Higgs) invariant under all transformations. ● Vacuum breaks gauge invariance. – Higgs obtains a nonzero value throughout space. ● Vacuum expectation value, – Particles interact with Higgs vacuum, gaining mass. March 17, 2016 Ian Lewis (University of Kansas) 11

Standard Model Higgs Boson ● Introduce complex Higgs with four degrees of freedom. ● Three degrees of freedom absorbed into weak force carriers ( ) giving them masses. ● One degree of freedom left, the physical Higgs boson, h. March 17, 2016 Ian Lewis (University of Kansas) 12

Large Hadron Collider (LHC) Overview ● 17 mile ring outside Geneva, Switzerland. ● Colliding protons at a center of mass energy of 7-14 TeV. – ~10 mph less than speed of light. – ~1 GJ of energy stored at 14 TeV (Aircraft carrier traveling ~20 mph) ● Purpose is to discover new physics at the TeV scale . March 17, 2016 Ian Lewis (University of Kansas) 13

Hadron Collider ● Hadrons (like a proton) are made of quarks and gluons. ● LHC collides two protons at very high energy (7-14 TeV). ● Constituents of proton annihilate at a typical energy of ~ 1 TeV:

LHC March 17, 2016 Ian Lewis (University of Kansas) 15

Compact Muon Solenoid (CMS) March 17, 2016 Ian Lewis (University of Kansas) 16

Detecting Final State March 17, 2016 Ian Lewis (University of Kansas) 17

Amount of Data Produced ● Over 600 million collisions per second per experiment. – Amount of data produced is 1 petabyte per second – Could fill ~200,0000 DVDs per second – Comparable to total amount of digital data produced worldwide. ● Experiments store and analyze less. – Around 30 petabytes per year. – ~6,000,000 DVDs per year stored to be analyzed ● Very successful! March 17, 2016 Ian Lewis (University of Kansas) 18

Higgs Discovery! ● July 4, 2012 (mass of Tin atom) ● Created around 650,000 Higgs through 2015. March 17, 2016 Ian Lewis (University of Kansas) 19

Higgs production rate is small Higgs rate is small, need to dig signal out of all the other Standard Model processes. March 17, 2016 Ian Lewis (University of Kansas) 20

Higgs Production ● Masses in Standard Model come from Higgs mechanism. – Completely predictive. – Vacuum expectation value ● Protons made mostly of light quarks and gluons. March 17, 2016 Ian Lewis (University of Kansas) 21

Quantum Effects to the Rescue ● Top quark can mediate coupling to gluon. ● Dominant production mode at the LHC. March 17, 2016 Ian Lewis (University of Kansas) 22

Higgs Production Rates Other subdominant processes depend on W/Z and top quark couplings. What about decay? March 17, 2016 Ian Lewis (University of Kansas) 23

● WW and ZZ probes gauge boson mass generating mechanism. ● Decays to di-photon at 0.2% of the time March 17, 2016 Ian Lewis (University of Kansas) 24

Di-Photon ● Higgs discovered using quantum production and decay modes! March 17, 2016 Ian Lewis (University of Kansas) 25

Masses and Higgs Couplings ● Remarkably Standard Model like. ● Have measured Higgs rates to 20-40%. March 17, 2016 Ian Lewis (University of Kansas) 26

13 TeV LHC started in 2015 M. Lamont, Moriond 2015 ● 2023 : 10 times current data ● 2030s: 100 times current data March 17, 2016 Ian Lewis (University of Kansas) 27

Future Higgs Boson Measurements March 17, 2016 Ian Lewis (University of Kansas) 28

What do Higgs Measurements Tell Us? ● Consider very massive new physics. – Standard Model leading order in a power expansion of energies. – Precision measurements bound next order in expansion: ● Then measuring rates to ~5% give new physics scale at the TeV scale. March 17, 2016 Ian Lewis (University of Kansas) 29

Higgs is Central ● Production and decay modes quantum effects. – Sensitive to new physics ● Expect new physics to be related to Higgs boson properties. – Source of fundamental mass just starting to be probed. – Standard Model is simplest realization of mechanism ● Explains mass, but where does the Higgs vacuum expectation value come from? – Consider a simple harmonic oscillator. March 17, 2016 Ian Lewis (University of Kansas) 30

Harmonic Oscillator Example ● Stored Potential energy : – Invariant under ● Force equation : March 17, 2016 Ian Lewis (University of Kansas) 31

Deformed Harmonic Oscillator ● Stored Potential energy: – Invariant under ● Shift to a minimum: – Invariance not manifest at minimum: March 17, 2016 Ian Lewis (University of Kansas) 32

Higgs Potential ● Higgs potential: ● Have minimum: ● Expand about vacuum: March 17, 2016 Ian Lewis (University of Kansas) 33

Higgs Self-Interactions ● Higgs Potential: ● Potential has two parameters, everything determined: March 17, 2016 Ian Lewis (University of Kansas) 34

Measuring Higgs Potential ● Need to measure potential to test Standard Model ● Double Higgs production sensitive to trilinear coupling: ● Probing Higgs potential, source of mass. ● All couplings known in Standard Model. March 17, 2016 Ian Lewis (University of Kansas) 35

Future Measurements of Potential ● Measurement at LHC with 3000 ab -1 (2030s) – ATLAS: observe at 1.3 σ significance ATL-PHYS-PUB-2014-019 ● Bound – CMS: Observe at 1.9 σ significance CMS PAS FTR-15-002 ● Small rate, may be sensitive to new physics. ● Particularly new physics that alters Higgs potential. March 17, 2016 Ian Lewis (University of Kansas) 36

Extended Scalar Sector ● Standard Model Higgs source of all fundamental mass. – Can have multiple sources of gauge invariance breaking. – Two Higgses are possible, sometimes required. ● New source of new gauge invariance breaking contribute to W/Z masses. – Alter Higgs couplings to W/Z ● What about scalar bosons that don't contribute to gauge invariance breaking? – Can even probe new scalars unrelated to gauge invariance breaking. March 17, 2016 Ian Lewis (University of Kansas) 37

New Scalar ● Consider a new scalar with no Standard Model charges ● After gauge invariance breaking, the Higgs boson has no charge. ● The two can mix quantum mechanically. ● Changes Higgs couplings March 17, 2016 Ian Lewis (University of Kansas) 38

Higgs Couplings ● Write equations in gauge invariant way. ● Rotate into mass eigenstate basis ● Original particles are superpositions of mass eigenstates. ● Higgs precision measurements: ATLAS, JHEP11(2015)206 March 17, 2016 Ian Lewis (University of Kansas) 39

New Scalar Potential ● Any new scalar will alter potential – S has no couplings to anything else in Standard Model ● New potential – Interaction terms: – Expansion about vacuum – New Higgs Interactions. March 17, 2016 Ian Lewis (University of Kansas) 40

Higgs and Scalar Interactions ● Comes from: March 17, 2016 Ian Lewis (University of Kansas) 41

Double Higgs Resonance ● New Double Higgs production process. ● Resonant production and decay of scalar S. – Enhance rate. March 17, 2016 Ian Lewis (University of Kansas) 42